The potential benefit of radiotherapy with protons in head and neck cancer with respect to normal tissue sparing: a systematic review of literature

Long-term outcomes and prognostic factors of eye-preserving treatment with particle beam radiotherapy for orbital malignancies

BACKGROUND

This retrospective study report the clinical experience of eye-preserving treatment follow by particle beam radiotherapy (IMPT or CIRT) for orbital malignancies. And to evaluate prognostic factors for orbital and lacrimal gland tumors.

METHODS

Sixty-two patients with orbital malignancies were identified in the records of a single center between 2015 and 2021. Sixty-one patients met inclusion criteria. All of the patients received eye-preserving treatment before PBRT. Majority of the patients (91.8%) were treatment with CIRT. Clinical data, treatment modality, local control, metastases and survivals and visual outcomes, as well as associated prognostic indicators were were assessed.

RESULTS

Sixty-one patients were followed with a median of 40.7 months (44.3 months for surviving patients). The 3- and 5-year DSS and LC rates were 88.1% and 69.9%, and the 3- and 5-year DMC rates were 77.5% and 74.2% for entire orbital malignancies. For lacrimal gland carcinoma, the 5-year DSS, LC, DMC, and PFS rates were 83.3%, 64.8%, 66.8%, and 53.4%. Tumor size, T stage, extraorbital invasion, and bone invasion influenced survivals. No grade 3 or higher acute toxicities were observed. A total of 8 patients experienced grade 3-4 visual impairment.

CONCLUSIONS

Particle radiotherapy following eye-preserving treatment provided a favorable local control and survivals with moderate acute and late toxicities, even in patients with unresectable disease. Particle radiotherapy was a promising strategy for management of orbital tumors.

Critical review of patient outcome study in head and neck cancer radiotherapy

Rapid technological advances in radiation therapy have significantly improved dose delivery and tumor control for head and neck cancers. However, treatment-related toxicities caused by high-dose exposure to critical structures remain a significant clinical challenge, underscoring the need for accurate prediction of clinical outcomes-encompassing both tumor control and adverse events (AEs). This review critically evaluates the evolution of data-driven approaches in predicting patient outcomes in head and neck cancer patients treated with radiation therapy, from traditional dose-volume constraints to cutting-edge artificial intelligence (AI) and causal inference framework. The integration of linear energy transfer in patient outcomes study, which has uncovered critical mechanisms behind unexpected toxicity, was also introduced for proton therapy. Three transformative methodological advances are reviewed: radiomics, AI-based algorithms, and causal inference frameworks. While radiomics has enabled quantitative characterization of medical images, AI models have demonstrated superior capability than traditional models. However, the field faces significant challenges in translating statistical correlations from real-world data into interventional clinical insights. We highlight that how causal inference methods can bridge this gap by providing a rigorous framework for identifying treatment effects. Looking ahead, we envision that combining these complementary approaches, especially the interventional prediction models, will enable more personalized treatment strategies, ultimately improving both tumor control and quality of life for head and neck cancer patients treated with radiation therapy.

Online Adaptive Proton Therapy Facilitated by Artificial Intelligence-Based Autosegmentation in Pencil Beam Scanning Proton Therapy

PURPOSE

Online adaptive proton therapy (oAPT) is essential to address interfractional anatomical changes in patients receiving pencil beam scanning proton therapy. Artificial intelligence (AI)-based autosegmentation can increase the efficiency and accuracy. Linear energy transfer (LET)-based biological effect evaluation can potentially mitigate possible adverse events caused by high LET. New spot arrangement based on the verification computed tomography (vCT) can further improve the replan quality. We propose an oAPT workflow that incorporates all these functionalities and validate its clinical implementation feasibility with patients with prostate cancer.

METHODS AND MATERIALS

AI-based autosegmentation tool AccuContour (Manteia) was seamlessly integrated into oAPT. Initial spot arrangement tool on the vCT for reoptimization was implemented using raytracing. An LET-based biological effect evaluation tool was developed to assess the overlap region of high dose and high LET in selected organs at risk. Eleven patients with prostate cancer were retrospectively selected to verify the efficacy and efficiency of the proposed oAPT workflow. The time cost of each component in the workflow was recorded for analysis.

RESULTS

The verification plan showed significant degradation of the clinical target volume coverage and rectum and bladder sparing due to the interfractional anatomical changes. Reoptimization on the vCT resulted in great improvement of the plan quality. No overlap regions of high dose and high LET distributions were observed in bladder or rectum in replans. Three-dimensional γ analyses in patient-specific quality assurance confirmed the accuracy of the replan doses before delivery (γ passing rate, 99.57% ± 0.46%) and after delivery (98.59% ± 1.29%). The robustness of the replans passed all clinical requirements. The average time for the complete execution of the workflow was 9.12 ± 0.85 minutes, excluding manual intervention time.

CONCLUSIONS

The AI-facilitated oAPT workflow demonstrated to be both efficient and effective by generating a replan that significantly improved the plan quality in prostate cancer treated with pencil beam scanning proton therapy.

Enabling clinical use of linear energy transfer in proton therapy for head and neck cancer - A review of implications for treatment planning and adverse events study

Proton therapy offers significant advantages due to its unique physical and biological properties, particularly the Bragg peak, enabling precise dose delivery to tumors while sparing healthy tissues. However, the clinical implementation is challenged by the oversimplification of the relative biological effectiveness (RBE) as a fixed value of 1.1, which does not account for the complex interplay between dose, linear energy transfer (LET), and biological endpoints. Lack of heterogeneity control or the understanding of the complex interplay may result in unexpected adverse events and suboptimal patient outcomes. On the other hand, expanding our knowledge of variable tumor RBE and LET optimization may provide a better management strategy for radioresistant tumors. This review examines recent advancements in LET calculation methods, including analytical models and Monte Carlo simulations. The integration of LET into plan evaluation is assessed to enhance plan quality control. LET-guided robust optimization demonstrates promise in minimizing high-LET exposure to organs at risk, thereby reducing the risk of adverse events. Dosimetric seed spot analysis is discussed to show its importance in revealing the true LET-related effect upon the adverse event initialization by finding the lesion origins and eliminating the confounding factors from the biological processes. Dose-LET volume histograms (DLVH) are discussed as effective tools for correlating physical dose and LET with clinical outcomes, enabling the derivation of clinically relevant dose-LET volume constraints without reliance on uncertain RBE models. Based on DLVH, the dose-LET volume constraints (DLVC)-guided robust optimization is introduced to upgrade conventional dose-volume constraints-based robust optimization, which optimizes the joint distribution of dose and LET simultaneously. In conclusion, translating the advances in LET-related research into clinical practice necessitates a better understanding of the LET-related biological mechanisms and the development of clinically relevant LET-related volume constraints directly derived from the clinical outcomes. Future research is needed to refine these models and conduct prospective trials to assess the clinical benefits of LET-guided optimization on patient outcomes.

Dual-energy CT in head and neck applications

Dual-energy CT (DECT), also known as spectral CT, has advanced diagnostic capabilities in head and neck pathologies beyond those of conventional single-energy CT (SECT). By having images at two distinct energy levels, DECT generates virtual monoenergetic images (VMIs), iodine maps, and quantitative features such as iodine concentration (IC) and spectral Hounsfield unit attenuation curves (SHUAC), which leads to enhancing tissue characterization, reducing artifacts, and differentiating head and neck pathologies. This review highlights DECT's applications in evaluating head and neck squamous cell carcinoma (SCC), thyroid cartilage invasion, cervical lymph node metastasis, radiation therapy planning, post-treatment assessment, and role in other head and neck conditions, such as infection and sialolithiasis. Additionally, it explores emerging applications of DECT in radiomics and artificial intelligence. The review also discusses about integrating DECT into clinical practice requires overcoming workflow challenges and ensuring radiologist proficiency with its diverse image reconstructions. As DECT technology evolves, its integration promises to further enhance the efficacy of managing head and neck pathologies.

A probabilistic evaluation of the Dutch robustness and model-based selection protocols for Head-and-Neck IMPT: A multi-institutional study

BACKGROUND AND PURPOSE

In the Netherlands, 2 protocols have been standardized for PT among the 3 proton centers: a robustness evaluation (RE) to ensure adequate CTV dose and a model-based selection (MBS) approach for IMPT patient-selection. This multi-institutional study investigates (i) inter-patient and inter-center variation of target dose from the RE protocol and (ii) the robustness of the MBS protocol against treatment errors for a cohort of head-and-neck cancer (HNC) patients treated in the 3 Dutch proton centers.

MATERIALS AND METHODS

Clinical treatment plans of 100 HNC patients were evaluated. Polynomial Chaos Expansion (PCE) was used to perform a comprehensive robustness evaluation per plan, enabling the probabilistic evaluation of 100,000 complete fractionated treatments. PCE allowed to derive scenario distributions of clinically relevant dosimetric parameters to assess CTV dose (D99.8%/D0.2%, based on a prior photon plan calibration) and tumour control probabilities (TCP) as well as the evaluation of the dose to OARs and normal tissue complication probabilities (NTCP) per center.

RESULTS

For the CTV70.00, doses from the RE protocol were consistent with the clinical plan evaluation metrics used in the 3 centers. For the CTV54.25, D99.8% were consistent with the clinical plan evaluation metrics at center 1 and 2 while, for center 3, a reduction of 1 GyRBE was found on average. This difference did not impact modelled TCP at center 3. Differences between expected and nominal NTCP were below 0.3 percentage point for most patients.

CONCLUSION

The standardization of the RE and MBS protocol lead to comparable results in terms of TCP and the NTCPs. Still, significant inter-patient and inter-center variation in dosimetric parameters remained due to clinical practice differences at each institution. The MBS approach is a robust protocol to qualify patients for PT.

Acute toxicities in proton therapy for head and neck cancer - A matched analysis of the DAHANCA 35 feasibility study

Background and purpose

As preparation for a national randomized study comparing proton radiotherapy to photon radiotherapy, DAHANCA 35, we performed a non-randomized pilot study to investigate patient selection, logistics, planning, and treatment delivery. With the present study, as a comprehensive safety analysis, we want to compare toxicity during and up to two months after therapy to a historically matched group of patients treated with photon radiotherapy.

Materials and methods

62 patients treated with protons were matched to 124 patients who received photon treatment outside a protocol. Available data were retrieved from the DAHANCA database. Patients were matched on treatment centre, concurrent chemotherapy, tumour site, stage, p16 status for oropharynx cancers. Selection of patients for proton therapy was based on comparative treatment plans with a NTCP reduction for dysphagia and xerostomia at six months.

Results

Baseline characteristics between groups were well balanced, except for the type of drug used concurrently; more photon patients received Carboplatin (21.2 % vs 5.8 %, p = 0.01). Proton therapy was associated with significantly less weight loss at the end of treatment, mean weight loss of 3 % for protons and 5 % for photons (p < 0.001). There were more grade 3 skin reactions and grade 3 mucositis after proton treatment compared with photons at the end of treatment, Risk Ratio (RR) 1.9 (95 % CI: 1.01-3.5, p = 0.04) and RR 1.5 (95 % CI: 1.3-1.7, p < 0.001), respectively. All differences resolved at follow up two months after treatment. There were no significant differences between groups on opioid use, use of feeding tubes, or hospitalization during the observation period.

Conclusion

Proton treatment resulted in excess objective mucositis and dermatitis, which was transient and did not seem to negatively influence weight or treatment compliance and intensity. Selection bias was likely especially since NTCP models were used for selection of proton treatment and photon treated patients were matched manually. We are currently including patients in a randomized controlled trial.

Validation of Fully Automated Robust Multicriterial Treatment Planning for Head and Neck Cancer IMPT

PURPOSE

Our purpose was to compare robust intensity modulated proton therapy (IMPT) plans, automatically generated with wish-list-based multicriterial optimization as implemented in Erasmus-iCycle, with manually created robust clinical IMPT plans for patients with head and neck cancer.

METHODS AND MATERIALS

Thirty-three patients with head and neck cancer were retrospectively included. All patients were previously treated with a manually created IMPT plan with 7000 cGy dose prescription to the primary tumor (clinical target volume [CTV]7000) and 5425 cGy dose prescription to the bilateral elective volumes (CTV5425). Plans had a 4-beam field configuration and were generated with scenario-based robust optimization (21 scenarios, 3-mm setup error, and ±3% density uncertainty for the CTVs). Three clinical plans were used to configure the Erasmus-iCycle wish-list for automated generation of robust IMPT plans for the other 30 included patients, in line with clinical planning requirements. Automatically and manually generated IMPT plans were compared for (robust) target coverage, organ-at-risk (OAR) doses, and normal tissue complication probabilities (NTCP). No manual fine-tuning of automatically generated plans was performed.

RESULTS

For all automatically generated plans, voxel-wise minimum D98% values for the CTVs were within clinical constraints and similar to manual plans. All investigated OAR parameters were favorable in the automatically generated plans (all P < .001). Median reductions in mean dose to OARs went up to 667 cGy for the inferior pharyngeal constrictor muscle, and median reductions in D0.03cm3 in serial OARs ranged up to 1795 cGy for the spinal cord surface. The observed lower mean dose in parallel OARs resulted in statistically significant lower NTCP for xerostomia (grade ≥2: 34.4% vs 38.0%; grade ≥3: 9.0% vs 10.2%) and dysphagia (grade ≥2: 11.8% vs 15.0%; grade ≥3: 1.8% vs 2.8%).

CONCLUSIONS

Erasmus-iCycle was able to produce IMPT dose distributions fully automatically with similar (robust) target coverage and improved OAR doses and NTCPs compared with clinical manual planning, with negligible hands-on planning workload.

Proton beam therapy in paediatric cancer: Anticipating the opening of the Australian Bragg Centre for Proton Therapy and Research

Proton Beam Therapy (PBT) has the potential to improve paediatric cancer care by reducing radiation exposure and thus long-term toxicities. Ethical concerns and debates surrounding the treatment, such as eligibility and accessibility, are ongoing in Australia. The Australian Bragg Centre for Proton Therapy and Research (ABCPTR) (named after Sir William Henry Bragg who described the Bragg peak in his laboratory at the University of Adelaide in 1903) aims to increase access to PBT in Australasia and offer a patient-centred care approach. Research is underway to assess PBT's safety and cost-effectiveness, using tools including Normal Tissue Complication Probability (NTCP) models. Collaborative efforts are focused on developing tailored survivorship clinics to enhance patient follow-up and quality of life. With the anticipated opening of the ABCPTR, Australia is preparing to take a significant step in radiation oncology, offering new research opportunities and creating a publicly funded treatment centre. The initiative aims to balance treatment efficacy with patient care, setting the stage for a future in which radiation therapy will reduce long-term side effects compared to the current standard of care. The implementation of PBT in Australia represents a complex and promising approach to paediatric oncology. This article provides an overview of the current landscape, highlighting the potential benefits and challenges of a treatment that could redefine the quality of survivorship and contribute to global research and best clinical practice.

Deep-learning based fast and accurate 3D CT deformable image registration in lung cancer

BACKGROUND

Deformable Image Registration (DIR) is an essential technique required in many applications of radiation oncology. However, conventional DIR approaches typically take several minutes to register one pair of 3D CT images and the resulting deformable vector fields (DVFs) are only specific to the pair of images used, making it less appealing for clinical application.

PURPOSE

A deep-learning-based DIR method using CT images is proposed for lung cancer patients to address the common drawbacks of the conventional DIR approaches and in turn can accelerate the speed of related applications, such as contour propagation, dose deformation, adaptive radiotherapy (ART), etc. METHODS: A deep neural network based on VoxelMorph was developed to generate DVFs using CT images collected from 114 lung cancer patients. Two models were trained with the weighted mean absolute error (wMAE) loss and structural similarity index matrix (SSIM) loss (optional) (i.e., the MAE model and the M+S model). In total, 192 pairs of initial CT (iCT) and verification CT (vCT) were included as a training dataset and the other independent 10 pairs of CTs were included as a testing dataset. The vCTs usually were taken 2 weeks after the iCTs. The synthetic CTs (sCTs) were generated by warping the vCTs according to the DVFs generated by the pre-trained model. The image quality of the synthetic CTs was evaluated by measuring the similarity between the iCTs and the sCTs generated by the proposed methods and the conventional DIR approaches, respectively. Per-voxel absolute CT-number-difference volume histogram (CDVH) and MAE were used as the evaluation metrics. The time to generate the sCTs was also recorded and compared quantitatively. Contours were propagated using the derived DVFs and evaluated with SSIM. Forward dose calculations were done on the sCTs and the corresponding iCTs. Dose volume histograms (DVHs) were generated based on dose distributions on both iCTs and sCTs generated by two models, respectively. The clinically relevant DVH indices were derived for comparison. The resulted dose distributions were also compared using 3D Gamma analysis with thresholds of 3 mm/3%/10% and 2 mm/2%/10%, respectively.

RESULTS

The two models (wMAE and M+S) achieved a speed of 263.7±163 / 265.8±190 ms and a MAE of 13.15±3.8 / 17.52±5.8 HU for the testing dataset, respectively. The average SSIM scores of 0.987±0.006 and 0.988±0.004 were achieved by the two proposed models, respectively. For both models, CDVH of a typical patient showed that less than 5% of the voxels had a per-voxel absolute CT-number-difference larger than 55 HU. The dose distribution calculated based on a typical sCT showed differences of ≤2cGy[RBE] for clinical target volume (CTV) D95 and D5 , within ±0.06% for total lung V5 , ≤1.5cGy[RBE] for heart and esophagus Dmean , and ≤6cGy[RBE] for cord Dmax compared to the dose distribution calculated based on the iCT. The good average 3D Gamma passing rates (> 96% for 3 mm/3%/10% and > 94% for 2 mm/2%/10%, respectively) were also observed.

CONCLUSION

A deep neural network-based DIR approach was proposed and has been shown to be reasonably accurate and efficient to register the initial CTs and verification CTs in lung cancer.

Current management of xerostomia in head and neck cancer patients

Radiotherapy (RT) continues to play a key role in the management of head and neck cancer (HNC). Xerostomia remains a principal detriment to the quality of life (QoL) for 80 % of surviving patients receiving head and neck radiation. Radiation-induced injury to the salivary glands is dose-dependent, and thus efforts have been focused on decreasing radiation to the salivary glands. Decreased saliva production reduces both short-term and long-term quality of life in head and neck survivors by impacting on taste and contributing to dysphagia. Several radioprotective agents to the salivary gland have been investigated. Although not widely practiced, surgical transfer of the submandibular gland prior to RT is the mainstay of surgical options in preventing xerostomia. This review focuses on the strategies to improve xerostomia following radiation therapy in head and neck cancers.

Deep-Learning-based Fast and Accurate 3D CT Deformable Image Registration in Lung Cancer

PURPOSE

In some proton therapy facilities, patient alignment relies on two 2D orthogonal kV images, taken at fixed, oblique angles, as no 3D on-the-bed imaging is available. The visibility of the tumor in kV images is limited since the patient's 3D anatomy is projected onto a 2D plane, especially when the tumor is behind high-density structures such as bones. This can lead to large patient setup errors. A solution is to reconstruct the 3D CT image from the kV images obtained at the treatment isocenter in the treatment position.

METHODS

An asymmetric autoencoder-like network built with vision-transformer blocks was developed. The data was collected from 1 head and neck patient: 2 orthogonal kV images (1024x1024 voxels), 1 3D CT with padding (512x512x512) acquired from the in-room CT-on-rails before kVs were taken and 2 digitally-reconstructed-radiograph (DRR) images (512x512) based on the CT. We resampled kV images every 8 voxels and DRR and CT every 4 voxels, thus formed a dataset consisting of 262,144 samples, in which the images have a dimension of 128 for each direction. In training, both kV and DRR images were utilized, and the encoder was encouraged to learn the jointed feature map from both kV and DRR images. In testing, only independent kV images were used. The full-size synthetic CT (sCT) was achieved by concatenating the sCTs generated by the model according to their spatial information. The image quality of the synthetic CT (sCT) was evaluated using mean absolute error (MAE) and per-voxel-absolute-CT-number-difference volume histogram (CDVH).

RESULTS

The model achieved a speed of 2.1s and a MAE of <40HU. The CDVH showed that <5% of the voxels had a per-voxel-absolute-CT-number-difference larger than 185 HU.

CONCLUSION

A patient-specific vision-transformer-based network was developed and shown to be accurate and efficient to reconstruct 3D CT images from kV images.

Spot scanning proton arc therapy reduces toxicity in oropharyngeal cancer patients

BACKGROUND

Proton arc technology has recently shown dosimetric gains for various treatment indications. The increased number of beams and energy layers (ELs) in proton arc plans, increases the degrees of freedom in plan optimization and thereby flexibility to spare dose in organs at risk (OARs). A relationship exists between dosimetric plan quality, delivery efficiency, the number of ELs -and beams in a proton arc plan.

PURPOSE

This work aims to investigate the effect of the number of beams and ELs in a proton arc plan, on toxicity and delivery time for oropharyngeal cancer patients (OPC) selected for intensity modulated proton therapy (IMPT) based on the Dutch model-based approach.

METHODS

The EL reduction algorithm iteratively selects ELs from beams equidistantly spaced over a 360° arc. The beams in the final plan may contain multiple ELs, making them suited for static delivery on the studied treatment machine. The produced plans can therefore be called "step and shoot" proton arc plans. The number of beams and ELs were varied to determine the relationship with the planning cost function value, normal tissue complication probability (NTCP) and delivery time. Proton arc plans with robust target coverage and optimal energy layer reduction (ELR) settings to reduce NTCP, were generated for 10 OPC patients. Proton arc plans were compared to clinical volumetric modulated arc therapy (VMAT) and IMPT plans in terms of integral dose, OAR dose, NTCP for xerostomia and dysphagia and delivery time. Furthermore, dose-weighted average linear energy transfer (LET_d ) distributions were compared between the IMPT and proton arc plans. A dry run delivery of a plan containing 20 beams and 360 ELs was performed to evaluate delivery time and accuracy.

RESULTS

We found 360 ELs distributed over 30 beams generated proton arc plans with near minimal expected plan toxicity. Relative to corresponding IMPT and VMAT plans, an average reduction of 21 ± 3% and 58 ± 10% in integral dose was observed. D m e a n $_{mean}$ was reduced most in the pharyngeal constrictor muscle (PCM) medius structure, with on average 9.0 ± 4.2 Gy(RBE) (p = 0.0002) compared to the clinical IMPT plans. The average NTCP for grade≥2 and grade≥3 xerostomia at 6 months after treatment significantly decreased with 4.7 ± 1.8% (p = 0.002) and 1.7 ± 0.8% (p = 0.002), respectively, while the average NTCP for grade≥2 and grade≥3 dysphagia decreased with 4.4 ± 2.9% (p = 0.002) and 0.9 ± 0.4% (p = 0.002), respectively, increasing the benefit of protons relative to VMAT. For a "step and shoot" proton arc delivery with auto beam sequencing the estimated delivery time is 11 min, similar to the delivery time of a 6-field IMPT treatment. Gamma analysis between the planned and delivered dose distribution resulted in a 99.99% pass rate using 1mm/1% dose difference/distance to agreement criteria.

CONCLUSIONS

"Step and shoot" proton arc demonstrates potential to further reduce toxicity compared to IMPT and VMAT in OPC treatment. By employing 360 ELs and 30 beams in the proposed ELR method, delivery time can reach clinically acceptable levels without compromising plan toxicity when automatic beam sequencing is available.

Dosimetric impact of adaptive proton therapy in head and neck cancer - A review

Background

Intensity Modulated Proton Therapy (IMPT) in head and neck cancer (HNC) is susceptible to anatomical changes and patient set-up inaccuracies during the radiotherapy course, which can cause discrepancies between planned and delivered dose. The discrepancies can be counteracted by adaptive replanning strategies. This article reviews the observed dosimetric impact of adaptive proton therapy (APT) and the timing to perform a plan adaptation in IMPT in HNC.

Methods

A literature search of articles published in PubMed/MEDLINE, EMBASE and Web of Science from January 2010 to March 2022 was performed. Among a total of 59 records assessed for possible eligibility, ten articles were included in this review.

Results

Included studies reported on target coverage deterioration in IMPT plans during the RT course, which was recovered with the application of an APT approach. All APT plans showed an average improved target coverage for the high- and low-dose targets as compared to the accumulated dose on the planned plans. Dose improvements up to 2.5 Gy (3.5 %) and up to 4.0 Gy (7.1 %) in the D98 of the high- and low dose targets were observed with APT. Doses to the organs at risk (OARs) remained equal or decreased slightly after APT was applied. In the included studies, APT was largely performed once, which resulted in the largest target coverage improvement, but eventual additional APT improved the target coverage further. There is no data showing what is the most appropriate timing for APT.

Conclusion

APT during IMPT for HNC patients improves target coverage. The largest improvement in target coverage was found with a single adaptive intervention, and an eventual second or more frequent APT application improved the target coverage further. Doses to the OARs remained equal or decreased slightly after applying APT. The most optimal timing for APT is yet to be determined.

Pre-treatment analysis of non-rigid variations can assist robust intensity-modulated proton therapy plan selection for head and neck patients

PURPOSE

To incorporate small non-rigid variations of head and neck patients into the robust evaluation of intensity-modulated proton therapy (IMPT) for the selection of robust treatment plans.

METHODS

A cohort of 20 nasopharynx cancer patients with weekly kilovoltage CT (kVCT) and 15 oropharynx cancer patients with weekly cone-beam CT (CBCT) were retrospectively included. Anatomical variations between week 0/week 1 of treatment were acquired using deformable image registration (DIR) for all 35 patients and then applied to the planning CT of four patients who have kVCT scanned each week to simulate potential small non-rigid variations (sNRVs). The robust evaluations were conducted on IMPT plans with: (1) different number of beam fields from 3-field to 5-field; (2) different beam angles. The robust evaluation before treatment, including the sNRVs and setup uncertainty, referred to as sNRV+R evaluation was compared with the conventional evaluation (without sNRVs) in terms of robustness consistency with the gold standard evaluation based on weekly CT.

RESULTS

Among four patients (490 scenarios), we observed a maximum difference in the sNRV+R evaluation to the nominal dose of: 9.37% dose degradation on D₉₅ of clinical target volumes (CTVs), increase in mean dose (D mean $_{\text{mean}}$ ) of parotid 11.87 Gy, increase in max dose (D max $_{\text{max}}$ ) of brainstem 20.82 Gy. In contrast, in conventional evaluation, we observed a maximum difference to the nominal dose of: 7.58% dose degradation on D₉₅ of the CTVs, increase in parotid D mean $_{\text{mean}}$ by 4.88 Gy, increase in brainstem D max $_{\text{max}}$ by 13.5 Gy. In the measurement of the robustness ranking consistency with the gold standard evaluation, the sNRV+R evaluation was better or equal to the conventional evaluation in 77% of cases, particularly, better on spinal cord, parotid glands, and low-risk CTV.

CONCLUSION

This study demonstrated the additional dose discrepancy that sNRVs can make. The inclusion of sNRVs can be beneficial to robust evaluation, providing information on clinical uncertainties additional to the conventional rigid isocenter shift.

"I don't want to hear statistics, I want real life stories": Systematic review and thematic synthesis of patient and caregiver experiences of Proton Beam Therapy

PROBLEM IDENTIFICATION

Proton Beam Therapy (PBT) is an advanced form of radiotherapy, yet little evidence exists on patient experience to inform decision making and improve future care. We thematically synthesized the qualitative evidence of patient and caregivers' perceptions and experiences of PBT.

LITERATURE SEARCH

Five electronic databases were systematically searched, using Medical Subject Headings (MeSH) terms and keywords. Two reviewers independently screened search results for qualitative studies relating to patients' and caregivers' experiences of PBT. The search generated 4,020 records, of which nine were eligible. Study quality (assessed by CASP checklist) varied.

DATA SYNTHESIS

Qualitative results were analyzed using thematic synthesis. Three main themes were generated: decision making and perceptions, living in the PBT "bubble," and coping with the cancer treatment journey.

CONCLUSIONS

PBT is not yet widely accessible worldwide, which uniquely influences the patient experience. Our review uncovers areas PBT providers could target to improve patient-centered care; however, additional primary qualitative research is recommended.

Virtual particle Monte Carlo: A new concept to avoid simulating secondary particles in proton therapy dose calculation

BACKGROUND

In proton therapy dose calculation, Monte Carlo (MC) simulations are superior in accuracy but more time consuming, compared to analytical calculations. Graphic processing units (GPUs) are effective in accelerating MC simulations but may suffer thread divergence and racing condition in GPU threads that degrades the computing performance due to the generation of secondary particles during nuclear reactions.

PURPOSE

A novel concept of virtual particle (VP) MC (VPMC) is proposed to avoid simulating secondary particles in GPU-accelerated proton MC dose calculation and take full advantage of the computing power of GPU.

METHODS

Neutrons and gamma rays were ignored as escaping from the human body; doses of electrons, heavy ions, and nuclear fragments were locally deposited; the tracks of deuterons were converted into tracks of protons. These particles, together with primary and secondary protons, are considered to be the realistic particles. Histories of primary and secondary protons were replaced by histories of multiple VPs. Each VP corresponded to one proton (either primary or secondary). A continuous-slowing-down-approximation model, an ionization model, and a large angle scattering event model corresponding to nuclear interactions were developed for VPs by generating probability distribution functions (PDFs) based on simulation results of realistic particles using MCsquare. For efficient calculations, these PDFs were stored in the Compute Unified Device Architecture textures. VPMC was benchmarked with TOPAS and MCsquare in phantoms and with MCsquare in 13 representative patient geometries. Comparisons between the VPMC calculated dose and dose measured in water during patient-specific quality assurance (PSQA) of the selected 13 patients were also carried out. Gamma analysis was used to compare the doses derived from different methods and calculation efficiencies were also compared.

RESULTS

Integrated depth dose and lateral dose profiles in both homogeneous and inhomogeneous phantoms all matched well among VPMC, TOPAS, and MCsquare calculations. The 3D-3D gamma passing rates with a criterion of 2%/2 mm and a threshold of 10% was 98.49% between MCsquare and TOPAS and 98.31% between VPMC and TOPAS in homogeneous phantoms, and 99.18% between MCsquare and TOPAS and 98.49% between VPMC and TOPAS in inhomogeneous phantoms, respectively. In patient geometries, the 3D-3D gamma passing rates with 2%/2 mm/10% between dose distributions from VPMC and MCsquare were 98.56 ± 1.09% in patient geometries. The 2D-3D gamma analysis with 3%/2 mm/10% between the VPMC calculated dose distributions and the 2D measured planar dose distributions during PSQA was 98.91 ± 0.88%. VPMC calculation was highly efficient and took 2.84 ± 2.44 s to finish for the selected 13 patients running on four NVIDIA Ampere GPUs in patient geometries.

CONCLUSION

VPMC was found to achieve high accuracy and efficiency in proton therapy dose calculation.

Exploratory study of seed spots analysis to characterize dose and linear energy transfer effect in adverse event initialization of pencil beam scanning proton therapy

BACKGROUND

Both dose and linear-energy-transfer (LET) could play a substantial role in adverse event (AE) initialization of cancer patients treated with pencil-beam-scanning proton therapy (PBS). However, not all the voxels within the AE regions are directly induced from the dose and LET effect. It is important to study the synergistic effect of dose and LET in AE initialization by only including a subset of voxels that are dosimetrically important.

PURPOSE

To perform exploratory investigation of the dose and LET effects upon AE initialization in PBS using seed spots analysis.

METHODS

113 head and neck (H&N) cancer patients receiving curative PBS were included. Among them, 20 patients experienced unanticipated CTCAEv4.0 grade≥3 AEs (AE group) and 93 patients did not (control group). Within the AE group, 13 AE patients were included in the seed spot analysis to derive the descriptive features of AE initialization and the remaining 7 mandible osteoradionecrosis patients and 93 control patients were used to derive the feature-based volume constraint of mandible osteoradionecrosis. The AE regions were contoured and the corresponding dose-LET volume histograms (DLVHs) of AE regions were generated for all patients in the AE group. We selected high LET voxels (the highest 5% of each dose bin) with a range of moderate to high dose (≥∼40 Gy[RBE]) as critical voxels. Critical voxels which were contiguous with each other were grouped into clusters. Each cluster was considered as a potential independent seed spot for AE initialization. Seed spots were displayed in a 2D dose-LET plane based on their mean dose and LET to derive the descriptive features of AE initialization. A volume constraint of mandible osteoradionecrosis was then established based on the extracted features using a receiver operating characteristic curve.

RESULTS

The product of dose and LET (xBD) was found to be a descriptive feature of seed spots leading to AE initialization in this preliminary study. The derived xBD volume constraint for mandible osteoradionecrosis showed good performance with an area-under-curve of 0.87 (sensitivity of 0.714 and specificity of 0.807 in the leave-one-out cross validation) for the very limited patient data included in this study.

CONCLUSION

Our exploratory study showed that both dose and LET were observed to be important in AE initializations. The derived xBD volume constraint could predict mandible osteoradionecrosis reasonably well in the very limited H&N cancer patient data treated with PBS included in this study. This article is protected by copyright. All rights reserved.

Dose and robustness comparison of nominal, daily and accumulated doses for photon and proton treatment of sinonasal cancer

INTRODUCTION

The aim was to evaluate and compare the dosimetric effect and robustness towards day-to-day anatomical and setup variations in the delivered dose for photon and proton treatments of sinonasal cancer (SNC) patients.

MATERIALS AND METHODS

Photon (VMAT) and proton (IMPT) plans were optimized retrospectively for 24 SNC patients. Synthetic CTs (synCT) were obtained by deforming the planning CT (pCT) to the anatomy of every daily cone-beam CT. Both VMAT and IMPT plans were recalculated on the synCTs. The recalculated daily dose was accumulated over the whole treatment on the pCT. Target coverage and dose to organs and risk (OARs) were evaluated for all patients for the nominal, daily and accumulated dose distribution.

RESULTS

In general, dose to OARs farther away from the target, including brain, chiasm and contralateral optic nerve, was lower for proton plans than photon plans. Whereas, OARs in proximity of the target received a lower dose for photon plans. For proton plans, the target coverage (volume of CTV receiving 95% of prescribed dose), V95%, fell below 99% for 9/24 patients in one or more fractions. For photon plans, 4/24 patients had one or more fractions where V95% fell below 99%. For accumulated doses, V95% was below 99% only in two cases, but above 98% for all patients.

CONCLUSION

Photon and proton treatment have different strengths regarding OAR sparing. The robustness was high for both treatment modalities. Patient selection for either proton or photon radiation therapy of SNC patients should be based on a case-by-case comparison.

Proton Therapy for Squamous Cell Carcinoma of the Head and Neck: Early Clinical Experience and Current Challenges

Simple Summary

Proton therapy is a promising type of radiation therapy used to destroy tumor cells. It has the potential to further improve the outcomes for patients with head and neck cancer since it allows to minimize the radiation dose to vital structures around the tumor, leading to less toxicity. This paper describes the current experience worldwide with proton therapy in head and neck cancer.

Abstract

Proton therapy (PT) is a promising development in radiation oncology, with the potential to further improve outcomes for patients with squamous cell carcinoma of the head and neck (HNSCC). By utilizing the finite range of protons, healthy tissue can be spared from beam exit doses that would otherwise be irradiated with photon-based treatments. Current evidence on PT for HNSCC is limited to comparative dosimetric analyses and retrospective single-institution series. As a consequence, the recognized indications for the reimbursement of PT remain scarce in most countries. Nevertheless, approximately 100 PT centers are in operation worldwide, and initial experiences for HNSCC are being reported. This review aims to summarize the results of the early clinical experience with PT for HNSCC and the challenges that are currently faced.

Radiosensitization to γ-Ray by Functional Inhibition of APOBEC3G

The radiosensitization of tumor cells is one of the promising approaches for enhancing radiation damage to cancer cells and limiting radiation effects on normal tissue. In this study, we performed a comprehensive screening of radiosensitization targets in human lung cancer cell line A549 using an shRNA library and identified apolipoprotein B mRNA editing enzyme catalytic subunit 3G (APOBEC3G: A3G) as a candidate target. APOBEC3G is an innate restriction factor that inhibits HIV-1 infection as a cytidine deaminase. APOBEC3G knockdown with siRNA showed an increased radiosensitivity in several cancer cell lines, including pancreatic cancer MIAPaCa2 cells and lung cancer A549 cells. Cell cycle analysis revealed that APOBEC3G knockdown increased S-phase arrest in MIAPaCa2 and G2/M arrest in A549 cells after γ-irradiation. DNA double-strand break marker γH2AX level was increased in APOBEC3G-knocked-down MIAPaCa2 cells after γ-irradiation. Using a xenograft model of A549 in mice, enhanced radiosensitivity by a combination of X-ray irradiation and APOBEC3G knockdown was observed. These results suggest that the functional inhibition of APOBEC3G sensitizes cancer cells to radiation by attenuating the activation of the DNA repair pathway, suggesting that APOBEC3G could be useful as a target for the radiosensitization of cancer therapy.

GPU-accelerated Monte Carlo-based online adaptive proton therapy - a feasibility study

PURPOSE

To develop an online Graphic-Processing-Unit (GPU)-accelerated Monte-Carlo-based adaptive radiation therapy (ART) workflow for pencil beam scanning (PBS) proton therapy to address inter-fraction anatomical changes in patients treated with PBS.

METHODS AND MATERIALS

A four-step workflow was developed using our in-house developed GPU-accelerated Monte-Carlo-based treatment planning system to implement online Monte-Carlo-based ART for PBS. The first step conducts diffeomorphic demon-based deformable image registration (DIR) to propagate contours on the initial planning CT (pCT) to the verification CT (vCT) to form a new structure set. The second step performs forward dose calculation of the initial plan on the vCT with the propagated contours after manual approval (possible modifications involved). The third step triggers a re-optimization of the plan depending on whether the verification dose meets the clinical requirements or not. A robust evaluation will be done for both the verification plan in the second step and the re-opotimized plan in the third step. The fourth step involves a two-stage (before and after delivery) patient specific quality assurance (PSQA) of the re-optimized plan. The before-delivery PSQA is to compare the plan dose to the dose calculated using an independent fast open-source Monte Carlo code, MCsquare. The after-delivery PSQA is to compare the plan dose to the dose re-calculated using the log file (spot MU, spot position, and spot energy) collected during the delivery. Jaccard index (JI), Dice similarity coefficients (DSCs), and Hausdorff distance (HD) were used to assess the quality of the propagated contours in the first step. A commercial plan evaluation software, ClearCheck™, was integrated into the workflow to carry out efficient plan evaluation. 3D Gamma analysis was used during the fourth step to ensure the accuracy of the plan dose from re-optimization. Three patients with three different disease sites were chosen to evaluate the feasibility of the online ART workflow for PBS.

RESULTS

For all three patients, the propagated contours were found to have good volume conformance [JI (lowest-highest: 0.833-0.983) and DSC (0.909-0.992)] but sub-optimal boundary coincidence [HD (2.37-20.76 mm)] for organs at risk (OARs). The verification dose evaluated by ClearCheck™ showed significant degradation of the target coverage due to the inter-fractional anatomical changes. Re-optimization on the vCT resulted in great improvement of the plan quality to a clinically acceptable level. 3D Gamma analyses of PSQA confirmed the accuracy of the plan dose before delivery (mean Gamma index = 98.74% with a threshold of 2%/2 mm/10%), and after delivery based on the log files (mean Gamma index = 99.05% with a threshold of 2%/2 mm/10%). The average time cost for the complete execution of the workflow was around 858 seconds, excluding the time for manual intervention.

CONCLUSION

The proposed online ART workflow for PBS was demonstrated to be efficient and effective by generating a re-optimized plan that significantly improved the plan quality. This article is protected by copyright. All rights reserved.

A Decision Support Tool to Optimize Selection of Head and Neck Cancer Patients for Proton Therapy

Simple Summary

A decision support tool was developed to select head and neck cancer patients for proton therapy. The tool uses delineation data to predict expected toxicity risk reduction with proton therapy and can be used before a treatment plan is created. The positive predictive value of the tool is >90%. This tool significantly reduces delays in commencing treatment and avoid redundant photon vs. proton treatment plan comparison.

Abstract

Selection of head and neck cancer (HNC) patients for proton therapy (PT) using plan comparison (VMAT vs. IMPT) for each patient is labor-intensive. Our aim was to develop a decision support tool to identify patients with high probability to qualify for PT, at a very early stage (immediately after delineation) to avoid delay in treatment initiation. A total of 151 HNC patients were included, of which 106 (70%) patients qualified for PT. Linear regression models for individual OARs were created to predict the D_mean to the OARs for VMAT and IMPT plans. The predictors were OAR volume percentages overlapping with target volumes. Then, actual and predicted plan comparison decisions were compared. Actual and predicted OAR D_mean (VMAT R² = 0.953, IMPT R² = 0.975) and NTCP values (VMAT R² = 0.986, IMPT R² = 0.992) were highly correlated. The sensitivity, specificity, PPV and NPV of the decision support tool were 64%, 87%, 92% and 51%, respectively. The expected toxicity reduction with IMPT can be predicted using only the delineation data. The probability of qualifying for PT is >90% when the tool indicates a positive outcome for PT. This tool will contribute significantly to a more effective selection of HNC patients for PT at a much earlier stage, reducing treatment delay.

Proton Image-guided Radiation Assignment for Therapeutic Escalation via Selection of locally advanced head and neck cancer patients [PIRATES]: A Phase I safety and feasibility trial of MRI-guided adaptive particle radiotherapy

INTRODUCTION

Radiation dose-escalation for head and neck cancer (HNC) patients aiming to improve cure rates is challenging due to the increased risk of unacceptable treatment-induced toxicities. With "Proton Image-guided Radiation Assignment for Therapeutic Escalation via Selection of locally advanced head and neck cancer patients" (PIRATES), we present a novel treatment approach that is designed to facilitate dose-escalation while minimizing the risk of dose-limiting toxicities for locally advanced HPV-negative HNC patients. The aim of this Phase I trial is to assess the safety & feasibility of PIRATES approach.

METHODS

The PIRATES protocol employs a multi-faceted dose-escalation approach to minimize the risk of dose-limiting toxicities (DLTs): 1) sparing surrounding normal tissue from extraneous dose with intensity-modulated proton therapy, 2) mid-treatment hybrid hyper-fractionation for radiobiologic normal tissue sparing; 3) Magnetic Resonance Imaging (MRI) guided mid-treatment boost volume adaptation, and 4) iso-effective restricted organ-at-risk dosing to mucosa and bone tissues.The time-to-event Bayesian optimal interval (TITE-BOIN) design is employed to address the challenge of the long DLT window of 6 months and find the maximum tolerated dose. The primary endpoint is unacceptable radiation-induced toxicities (Grade 4, mucositis, dermatitis, or Grade 3 myelopathy, osteoradionecrosis) occurring within 6 months following radiotherapy. The second endpoint is any grade 3 toxicity occurring in 3-6 months after radiation.

DISCUSSION

The PIRATES dose-escalation approach is designed to provide a safe avenue to intensify local treatment for HNC patients for whom therapy with conventional radiation dose levels is likely to fail. PIRATES aims to minimize the radiation damage to the tissue surrounding the tumor volume with the combination of proton therapy and adaptive radiotherapy and within the high dose tumor volume with hybrid hyper-fractionation and not boosting mucosal and bone tissues. Ultimately, if successful, PIRATES has the potential to safety increase local control rates in HNC patients with high loco-regional failure risk.Trial registration: ClinicalTrials.gov ID: NCT04870840; Registration date: May 4, 2021.Netherlands Trial Register ID: NL9603; Registration date: July 15, 2021.

Per-voxel constraints to minimize hot spots in linear energy transfer-guided robust optimization for base of skull head and neck cancer patients in IMPT

PURPOSE

Due to the employment of quadratic programming using soft constraints to implement dose volume constraints and the "trial-and-error" procedure needed to achieve a clinically acceptable plan, conventional dose volume constraints (upper limit) are not adequately effective in controlling small and isolated hot spots in the dose/linear energy transfer (LET) distribution. Such hot spots can lead to adverse events. In order to mitigate the risk of brain necrosis, one of the most clinically significant adverse events in patients receiving intensity-modulated proton therapy (IMPT) for base of skull (BOS) cancer, we propose per-voxel constraints to minimize hot spots in LET-guided robust optimization.

METHODS AND MATERIALS

Ten BOS cancer patients treated with IMPT were carefully selected by meeting one of the following conditions: (1) diagnosis of brain necrosis during follow-up; and (2) considered high risk for brain necrosis by not meeting dose constraints to the brain. An optimizing structure (BrainOPT) and an evaluating structure (BrainROI) that both contained the aforementioned hot dose regions in the brain were generated for optimization and evaluation, respectively. Two plans were generated for every patient: one using conventional dose-only robust optimization, the other using LET-guided robust optimization. The impact of LET was integrated into the optimization via a term of extra biological dose (xBD). A novel optimization tool of per-voxel constraints to control small and isolated hot spots in either the dose, LET, or combined (dose/LET) distribution was developed and used to minimize dose/LET hot spots of the selected structures. Indices from dose-volume histogram (DVH) and xBD dose-volume histogram (xBDVH) were used in the plan evaluation. A newly developed tool of the dose-LET-volume histogram (DLVH) was also adopted to illustrate the underlying mechanism. Wilcoxon signed-rank test was used for statistical comparison of the DVH and xBDVH indices between the conventional dose-only and the LET-guided robustly optimized plans.

RESULTS

Per-voxel constraints effectively and efficiently minimized dose hot spots in both dose-only and LET-guided robust optimization and LET hot spots in LET-guided robust optimization. Compared to the conventional dose-only robust optimization, the LET-guided robust optimization could generate plans with statistically lower xBD hot spots in BrainROI (VxBD,50 Gy[RBE], p = 0.009; VxBD,60 Gy[RBE], p = 0.025; xBD1cc, p = 0.017; xBD2cc, p = 0.022) with comparable dose coverage, dose hot spots in the target, and dose hot spots in BrainROI. DLVH analysis indicated that LET-guided robust optimization could either reduce LET at the same dose level or redistribute high LET from high dose regions to low dose regions.

CONCLUSION

Per-voxel constraint is a powerful tool to minimize dose/LET hot spots in IMPT. The LET-guided robustly optimized plans outperformed the conventional dose-only robustly optimized plans in terms of xBD hot spots control.

Adaptive proton therapy

Radiation therapy treatments are typically planned based on a single image set, assuming that the patient's anatomy and its position relative to the delivery system remains constant during the course of treatment. Similarly, the prescription dose assumes constant biological dose-response over the treatment course. However, variations can and do occur on multiple time scales. For treatment sites with significant intra-fractional motion, geometric changes happen over seconds or minutes, while biological considerations change over days or weeks. At an intermediate timescale, geometric changes occur between daily treatment fractions. Adaptive radiation therapy is applied to consider changes in patient anatomy during the course of fractionated treatment delivery. While traditionally adaptation has been done off-line with replanning based on new CT images, online treatment adaptation based on on-board imaging has gained momentum in recent years due to advanced imaging techniques combined with treatment delivery systems. Adaptation is particularly important in proton therapy where small changes in patient anatomy can lead to significant dose perturbations due to the dose conformality and finite range of proton beams. This review summarizes the current state-of-the-art of on-line adaptive proton therapy and identifies areas requiring further research.

Optimal Allocation of Proton Therapy Slots in Combined Proton-Photon Radiation Therapy

PURPOSE

Proton therapy is a limited resource that is not available to all patients who may benefit from it. We investigated combined proton-photon treatments, in which some fractions are delivered with protons and the remaining fractions with photons, as an approach to maximize the benefit of limited proton therapy resources at a population level.

METHODS AND MATERIALS

To quantify differences in normal-tissue complication probability (NTCP) between protons and photons, we considered a cohort of 45 patients with head and neck cancer for whom intensity modulated radiation therapy and intensity modulated proton therapy plans were previously created, in combination with NTCP models for xerostomia and dysphagia considered in the Netherlands for proton patient selection. Assuming limited availability of proton slots, we developed methods to optimally assign proton fractions in combined proton-photon treatments to minimize the average NTCP on a population level. The combined treatments were compared with patient selection strategies in which patients are assigned to single-modality proton or photon treatments.

RESULTS

There is a benefit of combined proton-photon treatments compared with patient selection, owing to the nonlinearity of NTCP functions; that is, the initial proton fractions are the most beneficial, whereas additional proton fractions have a decreasing benefit when a flatter part of the NTCP curve is reached. This effect was small for the patient cohort and NTCP models considered, but it may be larger if dose-response relationships are better known. In addition, when proton slots are limited, patient selection methods face a trade-off between leaving slots unused and blocking slots for future patients who may have a larger benefit. Combined proton-photon treatments with flexible proton slot assignment provide a method to make optimal use of all available resources.

CONCLUSIONS

Combined proton-photon treatments allow for better use of limited proton therapy resources. The benefit over patient selection schemes depends on the NTCP models and the dose differences between protons and photons.

Oncologic Outcomes for Head and Neck Skin Malignancies Treated with Protons

Purpose

Radiation therapy (RT) is the standard treatment for patients with inoperable skin malignancies of the head and neck region (H&N), and as adjuvant treatment post surgery in patients at high risk for local or regional recurrence. This study reports clinical outcomes of intensity-modulated proton therapy (IMPT) for these malignancies.

Materials and Methods

We retrospectively reviewed cases involving 47 patients with H&N malignancies of the skin (squamous cell, basal cell, melanoma, Merkel cell, angiosarcoma, other) who underwent IMPT for curative intent between July 2016 and July 2019. Overall survival was estimated via Kaplan-Meier analysis, and oncologic outcomes were reported as cumulative incidence with death as a competing risk.

Results

The 2-year estimated local recurrence rate, regional recurrence rate, local regional recurrence rate, distant metastasis rate, and overall survival were 11.1% (95% confidence interval [CI], 4.1%-30.3%), 4.4% (95% CI, 1.1%-17.4%), 15.5% (95% CI, 7%-34.3%), 23.4% (95% CI, 5.8%-95.5%), and 87.2% (95% CI, 75.7%-100%), respectively. No patient was reported to have a grade 3 or higher adverse event during the last week of treatment or at the 3-month follow-up visit.

Conclusion

IMPT is safe and effective in the treatment of skin malignancies of the H&N.

A Systematic Review of Proton Therapy for the Management of Nasopharyngeal Cancer

Purpose

With improved technology, more patients with nasopharyngeal cancer (NPC) are receiving definitive treatment with proton therapy, which allows greater sparing of dose to normal tissues without compromising efficacy. As there is no randomized data, the purpose of this study was to systematically review the available literature on proton therapy in this setting, focusing on the toxicity endpoints.

Materials and Methods

A systematic search using PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines was conducted in 5 databases: PubMed, Embase, SCOPUS, Web of Science, and the Cochrane Central Register of Controlled Trials. A total of 491 studies were found on the topic of NPC and proton therapy. Following independent study selection by 2 investigators, 9 studies were found to have sufficient focus and relevance to be incorporated into the systematic review.

Results

All 9 studies were retrospective and examined only NPC patients except for one that also included paranasal sinus cancer. One study was a reirradiation study. Four studies used 3D or double scatter technique, while all others used intensity-modulated proton therapy. Oncologic outcomes were similar to intensity-modulated radiation therapy (IMRT) rates, with 2-year local and regional progression-free survival (LRFS) ranging from 84% to 100%, 2-year progression-free survival (PFS) ranging from 75% to 88.9%, and 2-year overall survival (OS) ranging from 88% to 95% in the up-front setting. Four comparison studies with IMRT found significantly lower feeding tube rates (20% versus 65%, P = .015; and 14% versus 85%, P < .001) with proton therapy as well as lower mucositis (G2 46% versus 70%, P = .019; and G3 11% versus 76%, P = .0002). All other acute and late effects were largely improved with proton therapy but not statistically significant.

Conclusions

NPC patients receiving proton therapy maintain good outcomes with improved toxicity profile, likely due to sparing of dose to normal structures. Prospective studies are ongoing to better quantify the magnitude.

Technical Note: 4D robust optimization in small spot intensity-modulated proton therapy (IMPT) for distal esophageal carcinoma

PURPOSE

To compare the dosimetric performances of small-spot three-dimensional (3D) and four-dimensional (4D) robustly optimized intensity-modulated proton (IMPT) plans in the presence of uncertainties and interplay effect simultaneously for distal esophageal carcinoma.

METHOD AND MATERIALS

Thirteen (13) patients were selected and re-planned with small-spot ( σ  ~ 2-6 mm) 3D and 4D robust optimization in IMPT, respectively. The internal clinical target volumes (CTV_high3d , CTV_low3d ) were used in 3D robust optimization. Different CTVs (CTV_high4d , CTV_low4d ) were generated by subtracting an inner margin of the motion amplitudes in three cardinal directions from the internal CTVs and used in 4D robust optimization. All patients were prescribed the same dose to CTVs (50 Gy[RBE] for CTV_high3d /CTV_high4d and 45 Gy[RBE] for CTV_low3d /CTV_low4d ). Dose-volume histogram (DVH) indices were calculated to assess plan quality. Comprehensive plan robustness evaluations that consisted of 300 perturbed scenarios (10 different motion patterns to consider irregular motion (sampled from a Gaussian distribution) and 30 different uncertainties scenarios (sampled from a 4D uniform distribution) combined), were performed to quantify robustness to uncertainties and interplay effect simultaneously. Wilcoxon signed-rank test was used for statistical analysis.

RESULTS

Compared to 3D robustly optimized plans, 4D robustly optimized plans had statistically improved target coverage and better sparing of lungs and heart (heart D_mean , P = 0.001; heart V_30Gy[RBE] , P = 0.001) in the nominal scenario. 4D robustly optimized plans had better robustness in target dose coverage (CTV_high4d V_100% , P = 0.002) and the protection of lungs and heart (heart D_mean , P = 0.001; heart V_30Gy[RBE] , P = 0.001) when uncertainties and interplay effect were considered simultaneously.

CONCLUSIONS

Even with small spots in IMPT, 4D robust optimization outperformed 3D robust optimization in terms of normal tissue protection and robustness to uncertainties and interplay effect simultaneously. Our findings support the use of 4D robust optimization to treat distal esophageal carcinoma with small spots in IMPT.

Multimodal Treatment With Orbital Organ Preservation in Adult Patients With Locally Advanced Small-Round-Cell Malignancy of the Nasal Cavity and Paranasal Sinus

Background

To investigate the efficacy of induction chemotherapy followed by concurrent chemotherapy and helical tomotherapy in adult patients with locally advanced small-round-cell malignancy of the nasal cavity and paranasal sinus in regard to orbital organ preservation and quality of life.

Methods

The clinical data of 49 patients with orbital involvement of locally advanced small-round-cell malignancy of the nasal cavity and paranasal sinus who received multimodal treatment for orbital organ preservation between December 2009 and January 2019 were retrospectively analyzed. Treatment efficacy and side effects were assessed. The study included three different pathological types. All patients were treated with induction chemotherapy followed by concurrent chemoradiotherapy. Helical tomotherapy was applied as radiotherapy. Adverse reactions to the chemotherapy were assessed according to Common Terminology Criteria for Adverse Events, Version 3. The overall survival (OS) rate, progression-free survival (PFS) rate, and orbital preservation rate were calculated using the Kaplan-Meier method.

Results

After multimodal treatment, the 3- and 5-year OS rates of the 49 patients were 63.8% and 54.5%, respectively, and the 3- and 5-year total PFS rates were 66.8% and 63.1%, respectively.

Conclusions

Multimodal treatment can preserve the orbital organs of adult patients with small-round-cell malignancy of the nasal cavity and paranasal sinus, achieve relatively ideal organ protection and survival rates, and improve quality of life, thus providing a new treatment option for these patients.

Analysis of acute-phase toxicities of intensity-modulated proton therapy using a model-based approach in pharyngeal cancer patients

Pharyngeal cancer patients treated with intensity-modulated proton therapy (IMPT) using a model-based approach were retrospectively reviewed, and acute toxicities were analyzed. From June 2016 to March 2019, 15 pharyngeal (7 naso-, 5 oro- and 3 hypo-pharyngeal) cancer patients received IMPT with robust optimization. Simulation plans for IMPT and intensity-modulated X-ray therapy (IMXT) were generated before treatment. We also reviewed 127 pharyngeal cancer patients with IMXT in the same treatment period. In the simulation planning comparison, all of the normal-tissue complication probability values for dysphagia, dysgeusia, tube-feeding dependence and xerostomia were lower for IMPT than for IMXT in the 15 patients. After completing IMPT, 13 patients completed the evaluation, and 12 of these patients had a complete response. The proportions of patients who experienced grade 2 or worse acute toxicities in the IMPT and IMXT cohorts were 21.4 and 56.5% for dysphagia (P < 0.05), 46.7 and 76.3% for dysgeusia (P < 0.05), 73.3 and 62.8% for xerostomia (P = 0.43), 73.3 and 90.6% for mucositis (P = 0.08) and 66.7 and 76.4% for dermatitis (P = 0.42), respectively. Multivariate analysis revealed that IMPT was independently associated with a lower rate of grade 2 or worse dysphagia and dysgeusia. After propensity score matching, 12 pairs of IMPT and IMXT patients were selected. Dysphagia was also statistically lower in IMPT than in IMXT (P < 0.05). IMPT using a model-based approach may have clinical benefits for acute dysphagia.

Model-based comparison of organ at risk protection between VMAT and robustly optimised IMPT plans

The comparison between intensity-modulated proton therapy (IMPT) and volume-modulated arc therapy (VMAT) plans, based on models of normal tissue complication probabilities (NTCP), can support the choice of radiation modality. IMPT irradiation plans for 50 patients with head and neck tumours originally treated with photon therapy have been robustly optimised against density and setup uncertainties. The dose distribution has been calculated with a Monte Carlo (MC) algorithm. The comparison of the plans was based on dose-volume parameters in organs at risk (OARs) and NTCP-calculations for xerostomia, sticky saliva, dysphagia and tube feeding using Langendijk's model-based approach. While the dose distribution in the target volumes is similar, the IMPT plans show better protection of OARs. Therefore, it is not the high dose confirmation that constitutes the advantage of protons, but it is the reduction of the mid-to-low dose levels compared to photons. This work investigates to what extent the advantages of proton radiation are beneficial for the patient's post-therapeutic quality of life (QoL). As a result, approximately one third of the patients examined benefit significantly from proton therapy with regard to possible late side effects. Clinical data is needed to confirm the model-based calculations.

Beam angle comparison for distal esophageal carcinoma patients treated with intensity-modulated proton therapy

Purpose

To compare the dosimetric performances of intensity‐modulated proton therapy (IMPT) plans generated with two different beam angle configurations (the Right–Left oblique posterior beams and the Superior–Inferior oblique posterior beams) for the treatment of distal esophageal carcinoma in the presence of uncertainties and interplay effect.

Methods and Materials

Twenty patients’ IMPT plans were retrospectively selected, with 10 patients treated with the R‐L oblique posterior beams (Group R‐L) and the other 10 patients treated with the S‐I oblique posterior beams (Group S‐I). Patients in both groups were matched by their clinical target volumes (CTVs—high and low dose levels) and respiratory motion amplitudes. Dose‐volume‐histogram (DVH) indices were used to assess plan quality. DVH bandwidth was calculated to evaluate plan robustness. Interplay effect was quantified using four‐dimensional (4D) dynamic dose calculation with random respiratory starting phase of each fraction. Normal tissue complication probability (NTCP) for heart, liver, and lung was calculated, respectively, to estimate the clinical outcomes. Wilcoxon signed‐rank test was used for statistical comparison between the two groups.

Results

Compared with plans in Group R‐L, plans in Group S‐I resulted in significantly lower liver D_mean and lung V_30Gy[RBE] with slightly higher but clinically acceptable spinal cord D_max. Similar plan robustness was observed between the two groups. When interplay effect was considered, plans in Group S‐I performed statistically better for heart D_mean and V_30Gy[RBE], lung Dmean and V_5Gy[RBE], and liver D_mean, with slightly increased but clinically acceptable spinal cord D_max. NTCP for liver was significantly better in Group S‐I.

Conclusions

IMPT plans in Group S‐I have better sparing of liver, heart, and lungs at the slight cost of spinal cord maximum dose protection, and are more interplay‐effect resilient compared to IMPT plans in Group R‐L. Our study supports the routine use of the S‐I oblique posterior beams for the treatments of distal esophageal carcinoma.

Particle beam radiation therapy for sinonasal malignancies: Single institutional experience at the Shanghai Proton and Heavy Ion Center

Background

Sinonasal malignancies (SNM) include malignant neoplasms of various histologies that originate from the paranasal sinuses or nasal cavity. This study reported the safety and efficacy of particle‐beam radiation therapy (PBRT) for the treatment of sinonasal malignancies.

Methods and materials

One‐hundred‐and‐eleven patients with nonmetastatic sinonasal malignancies received definitive (82.9%) or salvage (31.5%) PBRT. The majority (85.6%) of patients presented with T3/4 disease, and only 19 (17.1%) had R0 or R1 resection. Seventy (63.1%) patients received carbon‐ion radiotherapy (CIRT), 37 received proton radiotherapy (PRT) followed by CIRT boost, and 4 received PRT alone. Prognostic factors were analyzed using Cox regression for univariate and multiple regression. Toxicities were reported using the Common Terminology Criteria for Adverse Events (version 4.03).

Results

The median follow‐up was 20.2 months for the entire cohort. The 2‐year local progression‐free survival (LPFS), regional progression‐free survival (RPFS), distant metastasis‐free survival (DMFS), progression‐free survival (PFS), and overall survival (OS) rates were 83%, 97.2%, 85.9%, 66%, and 82%, respectively. Re‐irradiation and large GTV were the significant factors for OS. Melanoma and sarcoma patients had significantly higher distant metastatic rate, and poorer OS and PFS. Late toxicity occurred in 22 (19.8%) patients, but only 4 (3.6%) patients experienced grades 3‐4 late toxicity.

Conclusions

Particle‐beam radiation therapy results in excellent local‐regional control with extremely low serve toxicities for patients with SNM. Sarcoma and melanoma were featured with a greater risk of death from distant dissemination. Patients who underwent re‐irradiation had significantly worse OS. PBRT is feasible and safe in the management of SNM.

Intensity-modulated particle beam radiation therapy in the management of olfactory neuroblastoma

Background

To report the clinical experience and short-term efficacy in the management of olfactory neuroblastoma (ONB).

Methods

We performed a retrospective analysis of 12 ONB patients treated with particle beam radiation therapy (PBRT) between 12/2015 and 5/2019 at the Shanghai Proton and Heavy Ion Center. Four (33.3%) patients presented with Kadish B ONB, and 8 (66.7%) presented with Kadish C or D disease. Eleven patients received proton radiotherapy (PRT) followed by a carbon ion radiotherapy (CIRT) boost, one patient received CIRT only. The 2-year survival rates were calculated using the Kaplan-Meier method. Acute and late adverse events were summarized and scored according to the CTCAE (version 4.03).

Results

With a median follow-up of 17.5 (range, 2.53–49.9) months, all patients but 1 were alive. Eight patients were alive without evidence of disease, and 2 additional patients achieved partial response and remained alive with residual disease. One patient died of toxicity associated with salvage chemotherapy for distant metastasis and local failure. Another patient developed distant metastasis only and was alive at the time of the last follow-up. The 2-year OS, PFS, LRPFS, and DMFS rates were 83.3%, 75.8%, 87.5%, and 79.5%, respectively. No acute or late toxicities of ≥ grade 3 was observed.

Conclusions

Intensity modulated PBRT of ONB is well tolerated. While longer follow-up is needed, early outcomes suggested that PBRT is safe and effective for the treatment of ONB with minimal adverse events.

Maxillo-mandibular osteoradionecrosis following C-ion radiotherapy: Clinical notes and review of literature

Osteoradionecrosis (ORN) is one of the most feared complications after head and neck radiotherapy. Among head and neck sites, the mandible is the most commonly involved bone. Heavy ion radiotherapy delivers high-dose distribution focused to the target while simultaneously sparing of the adjacent organs but there are anyway some reported cases of ORN. Cases in literature reported well-known risk factors for its developing (e.g. tobacco and alcohol abuse, diabetes), but other are still debated (e.g. teeth extraction during radiotherapy). Prevention is mandatory but multimodal care may be required, tailoring all treatments on the patient needs. This study, after a brief revision of the literature, reports and a case of maxillo-mandibular ORN following carbon-ion (C-ion) radiotherapy and its treatment.

Salivary Gland Hypofunction and Xerostomia in Head and Neck Radiation Patients

BACKGROUND

The most manifest long-term consequences of radiation therapy in the head and neck cancer patient are salivary gland hypofunction and a sensation of oral dryness (xerostomia).

METHODS

This critical review addresses the consequences of radiation injury to salivary gland tissue, the clinical management of salivary gland hypofunction and xerostomia, and current and potential strategies to prevent or reduce radiation injury to salivary gland tissue or restore the function of radiation-injured salivary gland tissue.

RESULTS

Salivary gland hypofunction and xerostomia have severe implications for oral functioning, maintenance of oral and general health, and quality of life. Significant progress has been made to spare salivary gland function chiefly due to advances in radiation techniques. Other strategies have also been developed, e.g., radioprotectors, identification and preservation/expansion of salivary stem cells by stimulation with cholinergic muscarinic agonists, and application of new lubricating or stimulatory agents, surgical transfer of submandibular glands, and acupuncture.

CONCLUSION

Many advances to manage salivary gland hypofunction and xerostomia induced by radiation therapy still only offer partial protection since they are often of short duration, lack the protective effects of saliva, or potentially have significant adverse effects. Intensity-modulated radiation therapy (IMRT), and its next step, proton therapy, have the greatest potential as a management strategy for permanently preserving salivary gland function in head and neck cancer patients.Presently, gene transfer to supplement fluid formation and stem cell transfer to increase the regenerative potential in radiation-damaged salivary glands are promising approaches for regaining function and/or regeneration of radiation-damaged salivary gland tissue.

A multidimensional cohort study of late toxicity after intensity modulated radiotherapy for sinonasal cancer

PURPOSE

To evaluate the occurrence of late toxicity after curatively intended intensity modulated radiotherapy (IMRT) for sinonasal cancer and assess dose-response associations.

METHODS

Patients treated with IMRT in 2008-2016 were included. Cross sectional examinations of toxicity from the optic pathway, the brain, the pituitary gland and the nose were performed along with quality of life - (QoL) and dose-response analyses.

RESULTS

Twenty-seven patients were enrolled; median age was 67 years (range 47-83). Five patients (19%) had radiation-related ocular toxicity. The risk of visual acuity impairment increased with increasing dose (grade 2 odds ration (OR) 1.12, p = 0.01; grade 3 OR 1.14, p = 0.02) and dose constraint violations (grade 2, OR = 21, p < 0.01; grade 3, OR = 41, p < 0.01). Six patients (22%) exhibited evidence of radiation-related hypopituitarism, but no dose-response association was detected. Seventeen patients (63%) had impaired olfactory function. The risk of olfactory impairment increased with higher stage (OR = 3.32, p = 0.03). Three patients (11%) had structural abnormalities in irradiated areas of the brain, and impaired cognitive function was present in 17 patients (63%). Cognitive, physical, role functioning as well as fatigue and insomnia were affected the most in QOL analyses. Fifteen patients (56%) had grade 2 radiation-related impairment in at least one organ. Grade 3 toxicity was only present in patients with toxicities in >3 organs and in patients initially treated for T4 tumours. Three patients (11%) had radiation-related impaired function in all examined OARs.

CONCLUSION

Late toxicity after radiotherapy was substantial in all examined organs, with dose-response associations between visual acuity impairment and the optic nerve. The results have led to changed praxis for follow-up examinations in Denmark.

Commissioning and beam characterization of the first gantry-mounted accelerator pencil beam scanning proton system

PURPOSE

To present and discuss beam characteristics and commissioning process of the first gantry-mounted accelerator single room pencil beam scanning (PBS) proton system.

METHODS

The Mevion HYPERSCAN employs a design configuration with a synchrocyclotron mounted on the gantry to eliminate the traditional beamline and a nozzle that contains the dosimetry monitoring chambers, the energy modulator (Energy Selector (ES)), and an Adaptive Aperture (AA). To characterize the beam, we measured the integrated depth dose (IDDs) for 12 energies, from highest energy of 227 MeV down to 28 MeV with a range difference ~ 2 cm between the adjacent energies, using a large radius Bragg peak chamber; single-spot profiles in air at five locations along the beam central axis using radiochromic EBT3 film and cross compared with a scintillation detector; and determined the output using a densely packed spot map. To access the performance of AA, we measured interleaf leakage and the penumbra reduction effect. Monte Carlo simulation using TOPAS was performed to study spot size variation along the beam path, beam divergence, and energy spectrum.

RESULTS

This proton system is calibrated to deliver 1 Gy dose at 5 cm depth in water using the highest beam energy by delivering 1 MU/spot to a 10 × 10 cm² map with a 2.5 mm spot spacing. The spot size in air varies from 4 mm to 26 mm from 227 MeV to 28 MeV at the isocenter plane with the nozzle retracted 23.6 cm from isocenter. The beam divergence of 28 MeV beam is ~ 52.7 mrad, which is nearly 22 times that of 227 MeV proton beam. The binary design of the ES has resulted in shifts of the effective SSD toward the isocenter as the energy is modulated lower. The peaks of IDD curves have a constant 80%-80% width of 8.4 mm at all energies. The interleaf leakage of the AA is less than 1.5% at the highest energy; and the AA can reduce the penumbra by 2 mm to 13 mm for the 227 and 28 MeV energies at isocenter plane in air.

CONCLUSIONS

The unique design of the HYPERSCAN proton system has yielded beam characteristics significantly different from that of other proton systems in terms of the Bragg peak shapes, spot sizes, and the penumbra sharpening effect of the AA. The combination of the ES and AA has made PBS implementation possible without using beam transport line and range shifter devices. Different considerations may be required in treatment planning optimization to account for different design and beam characteristics.

Temporal Lobe Necrosis in Head and Neck Cancer Patients after Proton Therapy to the Skull Base

PURPOSE

To demonstrate temporal lobe necrosis (TLN) rate and clinical/dose-volume factors associated with TLN in radiation-naïve patients with head and neck cancer treated with proton therapy where the field of radiation involved the skull base.

MATERIALS AND METHODS

Medical records and dosimetric data for radiation-naïve patients with head and neck cancer receiving proton therapy to the skull base were retrospectively reviewed. Patients with <3 months of follow-up, receiving <45 GyRBE or nonconventional fractionation, and/or no follow-up magnetic resonance imaging (MRI) were excluded. TLN was determined using MRI and graded using Common Terminology Criteria for Adverse Events (CTCAE) v5.0. Clinical (gender, age, comorbidities, concurrent chemotherapy, smoking, radiation techniques) and dose-volume parameters were analyzed for TLN correlation. The receiver operating characteristic curve and area under the curve (AUC) were performed to determine the cutoff points of significant dose-volume parameters.

RESULTS

Between 2013 and 2019, 234 patients were included. The median follow-up time was 22.5 months (range = 3.2-69.3). Overall TLN rates of any grade, ≥ grade 2, and ≥ grade 3 were 5.6% (N = 13), 2.1%, and 0.9%, respectively. The estimated 2-year TLN rate was 4.6%, and the 2-year rate of any brain necrosis was 6.8%. The median time to TLN was 20.9 months from proton completion. Absolute volume receiving 40, 50, 60, and 70 GyRBE (absolute volume [aV]); mean and maximum dose received by the temporal lobe; and dose to the 0.5, 1, and 2 cm3 volume receiving the maximum dose (D0.5cm3, D1cm3, and D2cm3, respectively) of the temporal lobe were associated with greater TLN risk while clinical parameters showed no correlation. Among volume parameters, aV50 gave maximum AUC (0.921), and D2cm3 gave the highest AUC (0.935) among dose parameters. The 11-cm3 cutoff value for aV50 and 62 GyRBE for D2cm3 showed maximum specificity and sensitivity.

CONCLUSION

The estimated 2-year TLN rate was 4.6% with a low rate of toxicities ≥grade 3; aV50 ≤11 cm3, D2cm3 ≤62 GyRBE and other cutoff values are suggested as constraints in proton therapy planning to minimize the risk of any grade TLN. Patients whose temporal lobe(s) unavoidably receive higher doses than these thresholds should be carefully followed with MRI after proton therapy.

Particle therapy tumour outcomes: An updated systematic review

Particle therapy (PT) offers the potential for reduced normal tissue damage as well as escalation of target dose, thereby enhancing the therapeutic ratio in radiation therapy. Reflecting the building momentum of PT use worldwide, construction has recently commenced for The Australian Bragg Centre for Proton Therapy and Research in Adelaide - the first PT centre in Australia. This systematic review aims to update the clinical evidence base for PT, both proton beam and carbon ion therapy. The purpose is to inform clinical decision-making for referral of patients to PT centres in Australia as they become operational and overseas in the interim. Three major databases were searched by two independent researchers, and evidence quality was classified according to the National Health and Medical Research Council evidence hierarchy. One hundred and thirty-six studies were included, two-thirds related to proton beam therapy alone. PT at the very least provides equivalent tumour outcomes compared to photon controls with the possibility of improved control in the case of carbon ion therapy. There is suggestion of reduced morbidities in a range of tumour sites, supporting the predictions from dosimetric modelling and the wide international acceptance of PT for specific indications based on this. Though promising, this needs to be counterbalanced by the overall low quality of evidence found, with 90% of studies of level IV (case series) evidence. Prospective comparative clinical trials, supplemented by database-derived outcome information, preferably conducted within international and national networks, are strongly recommended as PT is introduced into Australasia.

Clinical implementation in proton therapy of multi-field optimization by a hybrid method combining conventional PTV with robust optimization

To implement a robust multi-field optimization (MFO) technique compatible with the application of a Monte Carlo (MC) algorithm and to evaluate its robustness. Nine patients (three brain, five head-and-neck, one spine) underwent proton treatment generated by a novel robust MFO technique. A hybrid (hMFO) approach was implemented, planning dose coverage on isotropic PTV compensating for setup errors, whereas range calibration uncertainties are incorporated into PTV robust optimization process. hMFO was compared with single-field optimization (SFO) and full robust multi-field optimization (fMFO), both on the nominal plan and the worst-case scenarios assessed by robustness analysis. The SFO and the fMFO plans were normalized to hMFO on CTV to obtain iso-D95 coverage, and then the organs at risk (OARs) doses were compared. On the same OARs, in the normalized nominal plans the potential impact of variable relative biological effectiveness (RBE) was investigated. hMFO reduces the number of scenarios computed for robust optimization (from twenty-one in fMFO to three), making it practicable with the application of a MC algorithm. After normalizing on D95 CTV coverage, nominal hMFO plans were superior compared to SFO in terms of OARs sparing (p   <  0.01), without significant differences compared to fMFO. The improvement in OAR sparing with hMFO with respect to SFO was preserved in worst-case scenarios (p   <  0.01), confirming that hMFO is as robust as SFO to physical uncertainties, with no significant differences when compared to the worst case scenarios obtained by fMFO. The dose increase on OARs due to variable RBE was comparable to the increase due to physical uncertainties (i.e. 4-5 Gy(RBE)), but without significant differences between these techniques. hMFO allows improving plan quality with respect to SFO, with no significant differences with fMFO and without affecting robustness to setup, range and RBE uncertainties, making clinically feasible the application of MC-based robust optimization.

A comparison study between single- and dual-energy CT density extraction methods for neurological proton monte carlo treatment planning

Monte Carlo proton dose calculations requires mass densities calculated from the patient CT image. This work investigates the impact of different single-energy CT (SECT) and dual-energy CT (DECT) to density conversion methods in proton dose distributions for brain tumours.Material and methods: Head CT scans for four patients were acquired in SECT and DECT acquisition modes. Commercial software was used to reconstruct DirectDensity^™ images in Relative Electron Densities (RED, [Formula: see text]) and to obtain DECT-based pseudo-monoenergetic images (PMI). PMI and SECT images were converted to RED using piecewise linear interpolations calibrated on a head-sized phantom, these fits were referred to as "PMI2RED" and "CT2RED". Two DECT-based calibration methods ("Hünemohr-15it" and "Saito-15it") were also investigated. [Formula: see text] images were converted to mass-densities ([Formula: see text]) to investigate [Formula: see text]differences and one representative patient case was used to make a proton treatment plan. Using CT2RED as reference method, dose distribution differences in the target and in five organs-at-risk (OARs) were quantified.Results: In the phantom study, Saito-15it and Hünemohr-15it produced the lowest [Formula: see text]root-mean-square error (0.7%) and DirectDensity^™ the highest error (2.7%). The proton plan evaluated in the Saito-15it and Hünemohr-15it datasets showed the largest relative differences compared to initial CT2RED plan down to -6% of the prescribed dose. Compared to CT2RED, average range differences were calculated: -0.1 ± 0.3 mm for PMI2RED; -0.8 ± 0.4 mm for Hünemohr-15it, and -1.2 ± 0.4 mm for Saito-15it.Conclusion: Given the wide choice of available conversion methods, studies investigating the density accuracy for proton dose calculations are necessary. However, there is still a gap between performing accuracy studies in reference [Formula: see text]phantoms and applying these methods in human CT images. For this treatment case, the PMI2RED method was equivalent to the conventional CT2RED method in terms of dose distribution, CTV coverage and OAR sparing, whereas Hünemohr-15it and Saito-15it presented the largest differences.

Improve the dosimetric outcome in bilateral head and neck cancer (HNC) treatment using spot-scanning proton arc (SPArc) therapy: a feasibility study

BACKGROUND

To explore the dosimetric improvement, delivery efficiency, and plan robustness for bilateral head and neck cancer (HNC) treatment utilizing a novel proton therapy technique - the spot-scanning proton arc (SPArc) therapy.

METHODS

We evaluated fourteen bilateral HNC patients retrospectively. Both SPArc and 3-field Intensity Modulated Proton Therapy (IMPT) plans were generated for each patient using the same robust optimization parameters. The prescription doses were 70Gy (relative biological effectiveness (RBE) for CTV_high and 60Gy[RBE] for CTV_low. Clinically significant dosimetric parameters were extracted and compared. Root-mean-square deviation dose (RMSDs) Volume Histogram(RVH) was used to evaluate the plan robustness. Total treatment delivery time was estimated based on the machine parameters.

RESULTS

The SPArc plan was able to provide equivalent or better robust target coverage while showed significant dosimetric improvements over IMPT in most of the organs at risk (OARs). More specifically, it reduced the mean dose of the ipsilateral parotid, contralateral parotid, and oral cavity by 25.8%(p = 0.001), 20.8%(p = 0.001) and 20.3%(p = 0.001) respectively compared to IMPT. This technique reduced D1 (the maximum dose covering 1% volume of a structure) of cord and brain stem by 20.8% (p = 0.009) and 10.7% (p = 0.048), respectively. SPArc also reduced the average integral dose by 17.2%(p = 0.001) and external V3Gy (the volume received 3Gy[RBE]) by 8.3%(p = 0.008) as well. RVH analysis showed that the SPArc plans reduced the dose uncertainties in most OARs compared to IMPT, such as cord: 1.1 ± 0.4Gy[RBE] vs 0.7 ± 0.3Gy[RBE](p = 0.001), brain stem: 0.9 ± 0.7Gy[RBE] vs 0.7 ± 0.7Gy[RBE](p = 0.019), contralateral parotid: 2.5 ± 0.5Gy[RBE] vs 2.2 ± 0.6Gy[RBE](p = 0.022) and ipsilateral parotid: 3.1 ± 0.7Gy[RBE] vs 2.8 ± 0.6Gy[RBE](p = 0.004) respectively. The average total estimated treatment delivery time were 283.4 ± 56.2 s, 469.2 ± 62.0 s and 1294.9 ± 106.7 s based on energy-layer-switching-time (ELST) of 0.1 s, 1 s, and 5 s respectively for SPArc plans, compared to the respective values of 328.0 ± 47.6 s(p = 0.002), 434.1 ± 52.0 s(p = 0.002), and 901.7 ± 74.8 s(p = 0.001) for 3-field IMPT plans. The potential clinical benefit of utilizing SPArc will lead to a decrease in the mean probability of salivary flow dysfunction by 31.3%(p = 0.001) compared with IMPT.

CONCLUSIONS

SPArc could significantly spare OARs while providing a similar or better robust target coverage compared with IMPT in the treatment of bilateral HNC. In the modern proton system with ELST less than 0.5 s, SPArc could potentially be implemented in the routine clinic with a practical, achievable treatment delivery efficiency.

Reduced radiation-induced toxicity by using proton therapy for the treatment of oropharyngeal cancer

Patients with squamous cell carcinoma of the oropharynx are generally treated with (chemo) radiation. Patients with oropharyngeal cancer have better survival than patients with squamous cell carcinoma of other head and neck subsites, especially when related to human papillomavirus. However, radiotherapy results in a substantial percentage of survivors suffering from significant treatment-related side-effects. Late radiation-induced side-effects are mostly irreversible and may even be progressive, and particularly xerostomia and dysphagia affect health-related quality of life. As the risk of radiation-induced side-effects highly depends on dose to healthy normal tissues, prevention of radiation-induced xerostomia and dysphagia and subsequent improvement of health-relatedquality of life can be obtained by applying proton therapy, which offers the opportunity to reduce the dose to both the salivary glands and anatomic structures involved in swallowing.This review describes the results of the first cohort studies demonstrating that proton therapy results in lower dose levels in multiple organs at risk, which translates into reduced acute toxicity (i.e. up to 3 months after radiotherapy), while preserving tumour control. Next to reducing mucositis, tube feeding, xerostomia and distortion of the sense of taste, protons can improve general well-being by decreasing fatigue and nausea. Proton therapy results in decreased rates of tube feeding dependency and severe weight loss up to 1 year after radiotherapy, and may decrease the risk of radionecrosis of the mandible. Also, the model-based approach for selecting patients for proton therapy in the Netherlands is described in this review and future perspectives are discussed.

Multimodal Therapy for Sinonasal Malignancies: Updates and Review of Current Treatment

OPINION STATEMENT

Sinonasal malignancies pose a significant challenge in management due to their low incidence, biologic diversity, and significant symptom burden. Even though surgery remains the primary therapeutic modality, a multi-modality approach has been shown to benefit a significant proportion of patients and its success depends largely on stage and histologic type. Non-surgical approaches such as novel radiation approaches as well as intensification with systemic therapy hold promise in altering the organ preservation rate as well as overall survival for patients. Practice changing randomized trials to test these novel modalities are overdue and desperately needed.

Combined proton-photon treatments - A new approach to proton therapy without a gantry

PURPOSE

Although the number of proton therapy centres is growing worldwide, proton therapy is still a limited resource. The primary reasons are gantry size and cost. Therefore, we investigate the potential of a new design for proton therapy, which may facilitate proton treatments in conventional bunkers and allow the widespread use of protons.

MATERIALS AND METHODS

The treatment room consists of a standard Linac for IMRT, a motorized couch for treatments in lying position, and a horizontal proton beamline equipped with pencil beam scanning. As proton beams are limited to a coronal plane, treatment plans may be suboptimal for many tumour sites. However, high-quality plans may be realized by combining protons and photons. Treatment planning is performed by simultaneously optimizing IMRT and IMPT plans based on their cumulative physical dose. We demonstrate this concept for three head&neck cancer cases.

RESULTS

Optimal combinations use photons to improve dose conformity while protons reduce the integral dose to normal tissues. In fact, combined treatments improve on single-modality IMRT and fixed beamline IMPT plans for quality-of-life-limiting OARs and retain most of the integral dose reduction in the healthy tissues of the pure IMPT plans. The lower doses that can be obtained with multi-modality treatments reduce the risk for side effects compared to single-modality IMRT plans.

CONCLUSION

Combined proton-photon treatments may play a role in developing a new solution for proton therapy without a gantry. Optimal combinations improve on IMRT plans and reduce the risk of side effects while making protons available to more patients.