Respiratory gated irradiation system for heavy-ion radiotherapy

Real-time delivered dose assessment in carbon ion therapy of moving targets

Objective. Real-time adaptive particle therapy is being investigated as a means to maximize the treatment delivery accuracy. To react to dosimetric errors, a system for fast and reliable verification of the agreement between planned and delivered doses is essential. This study presents a clinically feasible, real-time 4D-dose reconstruction system, synchronized with the treatment delivery and motion of the patient, which can provide the necessary feedback on the quality of the delivery.Approach. A GPU-based analytical dose engine capable of millisecond dose calculation for carbon ion therapy has been developed and interfaced with the next generation of the dose delivery system (DDS) in use at Centro Nazionale di Adroterapia Oncologica (CNAO). The system receives the spot parameters and the motion information of the patient during the treatment and performs the reconstruction of the planned and delivered 4D-doses. After each iso-energy layer, the results are displayed on a graphical user interface by the end of the spill pause of the synchrotron, permitting verification against the reference dose. The framework has been verified experimentally at CNAO for a lung cancer case based on a virtual phantom 4DCT. The patient's motion was mimicked by a moving Ionization Chamber (IC) 2D-array.Mainresults. For the investigated static and 4D-optimized treatment delivery cases, real-time dose reconstruction was achieved with an average pencil beam dose calculation speed up to more than one order of magnitude smaller than the spot delivery. The reconstructed doses have been benchmarked against offline log-file based dose reconstruction with the TRiP98 treatment planning system, as well as QA measurements with the IC 2D-array, where an average gamma-index passing rate (3%/3 mm) of 99.8% and 98.3%, respectively, were achieved.Significance. This work provides the first real-time 4D-dose reconstruction engine for carbon ion therapy. The framework integration with the CNAO DDS paves the way for a swift transition to the clinics.

Modeling of the resensitization effect on carbon-ion radiotherapy for stage I non-small cell lung cancer

Objective. To investigate the effect of redistribution and reoxygenation on the 3-year tumor control probability (TCP) of patients with stage I non-small cell lung cancer (NSCLC) treated with carbon-ion radiotherapy.Approach. A meta-analysis of published clinical data of 233 NSCLC patients treated by carbon-ion radiotherapy under 18-, 9-, 4-, and single-fraction schedules was conducted. The linear-quadratic (LQ)-based cell-survival model incorporating the radiobiological 5Rs, radiosensitivity, repopulation, repair, redistribution, and reoxygenation, was developed to reproduce the clinical TCP data. Redistribution and reoxygenation were regarded together as a single phenomenon and termed 'resensitization' in the model. The optimum interval time between fractions was investigated for each fraction schedule using the determined model parameters.Main results.The clinical TCP data for 18-, 9-, and 4-fraction schedules were reasonably reproduced by the model without the resensitization effect, whereas its incorporation was essential to reproduce the TCP data for all fraction schedules including the single fraction. The curative dose for the single-fraction schedule was estimated to be 49.0 Gy (RBE), which corresponds to the clinically adopted dose prescription of 50.0 Gy (RBE). For 18-, 9-, and 4-fraction schedules, a 2-to-3-day interval is required to maximize the resensitization effect during the time interval. In contrast, the single-fraction schedule cannot benefit from the resensitization effect, and the shorter treatment time is preferable to reduce the effect of sub-lethal damage repair during the treatment.Significance.The LQ-based cell-survival model incorporating the radiobiological 5Rs was developed and used to evaluate the effect of the resensitization on clinical results of NSCLC patients treated with hypo-fractionated carbon-ion radiotherapy. The incorporation of the resensitization into the cell-survival model improves the reproducibility to the clinical TCP data. A shorter treatment time is preferable in the single-fraction schedule, while a 2-to-3-day interval between fractions is preferable in the multi-fraction schedules for effective treatments.

Analysis of respiratory-induced motion trajectories of individual liver segments in patients with hepatocellular carcinoma

PURPOSE

To analyze the respiratory-induced motion trajectories of each liver segment for hepatocellular carcinoma (HCC) to derive a more accurate internal margin and optimize treatment protocol selection.

MATERIALS AND METHODS

Ten-phase-gated four-dimensional computed tomography (4DCT) scans of 14 patients with HCC were analyzed. For each patient, eight representative regions of interest (ROI) were delineated on each liver segment in all 10 phases. The coordinates of the center of gravity of each ROI were obtained for each phase, and then the respiratory motion in the left-right (LR), anteroposterior (AP), and craniocaudal (CC) directions was analyzed. Two sets of motion in each direction were also compared in terms of only two extreme phases and all 10 phases.

RESULTS

Motion of less than 5 mm was detected in 12 (86%) and 10 patients (71%) in the LR and AP directions, respectively, while none in the CC direction. Motion was largest in the CC direction with a maximal value of 19.5 mm, with significant differences between liver segment 7 (S7) and other segments: S1 (p < 0.036), S2 (p < 0.041), S3 (p < 0.016), S4 (p < 0.041), and S5 (p < 0.027). Of the 112 segments, hysteresis >1 mm was observed in 4 (4%), 2 (2%), and 15 (13%) in the LR, AP, and CC directions, respectively, with a maximal value of 5.0 mm in the CC direction.

CONCLUSION

A significant amount of respiratory motion was detected in the CC direction, especially in S7, and S8. Despite the small effect of hysteresis, it can be observed specifically in the right lobe. Therefore, caution is required when using 4DCT to determine IM using only end-inspiration and end-expiration. Understanding the respiratory motion in individual liver segments can be helpful when selecting an appropriate treatment protocol.

Carbon-ion radiotherapy for hepatocellular carcinoma with major vascular invasion: a retrospective cohort study

BACKGROUND

Macroscopic vascular invasion (MVI) significantly impacts survival in patients with hepatocellular carcinoma (HCC), warranting systemic therapy over locoregional therapy. Despite novel approaches, HCC with MVI has a poor prognosis compared to early-to intermediate-stage HCC. This study aimed to evaluate the safety and efficacy of carbon-ion radiotherapy (C-ion RT) for HCC characterized by MVI.

METHODS

This retrospective cohort study evaluated HCC patients with MVI treated using C-ion RT with a dose of 45.0-48.0 Gy/2 fractions or 52.8-60.0 Gy/4 fractions between 1995 and 2020 at our institution in Japan. We analyzed the prognostic factors and rates of local recurrence, survival, and adverse events. The local recurrence rate was determined using the cumulative incidence function, with death as a competing event. Survival rates were determined using the Kaplan-Meier method. The log-rank test for univariate analysis and the Cox proportional hazards model for multivariate analysis were used to compare subgroups.

RESULTS

In total, 76 patients with a median age of 71 years (range, 45-86 years) were evaluated. Among them, 68 had Child-Pugh grade A while eight had grade B disease. In 17 patients, the vascular tumor thrombus reached the inferior vena cava or main trunk of the portal vein. Over a median follow-up period of 27.9 months (range, 1.5-180.4 months), the 2-year overall survival, progression-free survival, and local recurrence rates were 70.0% (95% confidence interval [CI]: 57.7-79.4%), 32.7% (95% CI: 22.0-43.8%), and 8.9% (95% CI: 1.7-23.5%), respectively. A naïve tumor and a single lesion were significant prognostic factors for overall survival in the univariate analysis. Albumin-bilirubin grade 1 and a single lesion were independent prognostic factors in the multivariate analysis. Overall, four patients (5%) experienced grade 3 late adverse events, with no observed grade 4 or 5 acute or late adverse events.

CONCLUSIONS

C-ion RT for HCC with MVI showed favorable local control and survival benefits with minimal toxicity.

Long-Term Outcomes of Ablative Carbon-Ion Radiotherapy for Central Non-Small Cell Lung Cancer: A Single-Center, Retrospective Study

The aim of this study is to assess the efficacy and safety of ablative carbon ion radiotherapy (CIRT) for early stage central non-small cell lung cancer (NSCLC). We retrospectively reviewed 30 patients who had received CIRT at 68.4 Gy in 12 fractions for central NSCLC in 2006-2019. The median age was 75 years, and the median Karnofsky Performance Scale score was 90%. All patients had concomitant chronic obstructive pulmonary disease, and 20 patients (67%) were considered inoperable. In DVH analysis, the median lung V5 and V20 were 15.5% and 10.4%, and the median Dmax, D0.5cc, D2cc of proximal bronchial tree was 65.6 Gy, 52.8 Gy, and 10.0 Gy, respectively. At a median follow-up of 43 months, the 3-year overall survival, disease-specific survival, and local control rates were 72.4, 75.8, and 88.7%, respectively. Two patients experienced grade 3 pneumonitis, but no grade ≥3 adverse events involving the mediastinal organs occurred. Ablative CIRT is feasible and effective for central NSCLC and could be considered as a treatment option, especially for patients who are intolerant of other curative treatments.

Biomedical advances and future prospects of high-precision three-dimensional radiotherapy and four-dimensional radiotherapy

Biomedical advances of external-beam radiotherapy (EBRT) with improvements in physical accuracy are reviewed. High-precision (±1 mm) three-dimensional radiotherapy (3DRT) can utilize respective therapeutic open doors in the tumor control probability curve and in the normal tissue complication probability curve instead of the one single therapeutic window in two-dimensional EBRT. High-precision 3DRT achieved higher tumor control and probable survival rates for patients with small peripheral lung and liver cancers. Four-dimensional radiotherapy (4DRT), which can reduce uncertainties in 3DRT due to organ motion by real-time (every 0.1-1 s) tumor-tracking and immediate (0.1-1 s) irradiation, have achieved reduced adverse effects for prostate and pancreatic tumors near the digestive tract and with similar or better tumor control. Particle beam therapy improved tumor control and probable survival for patients with large liver tumors. The clinical outcomes of locally advanced or multiple tumors located near serial-type organs can theoretically be improved further by integrating the 4DRT concept with particle beams.

Clinical impact of spacer placement surgery with expanded polytetrafluoroethylene sheet for particle therapy

BACKGROUND

Spacer placement surgery is useful in particle therapy (PT) for patients with abdominopelvic malignant tumors located adjacent to the gastrointestinal tract. This study aimed to assess the safety, efficacy, and long-term outcomes of spacer placement surgery using an expanded polytetrafluoroethylene (ePTFE) spacer.

METHODS

This study included 131 patients who underwent ePTFE spacer placement surgery and subsequent PT between September 2006 and June 2019. The overall survival (OS) and local control (LC) rates were calculated using Kaplan-Meier method. Spacer-related complications were classified according to the National Cancer Institute Common Terminology Criteria for Adverse Events (version 5.0).

RESULTS

The median follow-up period after spacer placement surgery was 36.8 months. The 3-year estimated OS and LC rates were 60.5% and 76.5%, respectively. A total of 130 patients (99.2%) were able to complete PT. Spacer-related complications of ≥ grade 3 were observed in four patients (3.1%) in the acute phase and 13 patients (9.9%) in the late phase. Ten patients (7.6%) required removal of the ePTFE spacer.

CONCLUSIONS

Spacer placement surgery using an ePTFE spacer for abdominopelvic malignant tumors is technically feasible and acceptable for subsequent PT. However, severe spacer-related late complications were observed in some patients. Since long-term placement of a non-absorbable ePTFE spacer is associated with risks for morbidity and infection, careful long-term follow-up and prompt therapeutic intervention are essential when complications associated with the ePTFE spacer occur.

TRIAL REGISTRATION

retrospectively registered.

Multi-parametric MRI for radiotherapy simulation

Magnetic resonance imaging (MRI) has become an important imaging modality in the field of radiotherapy (RT) in the past decade, especially with the development of various novel MRI and image-guidance techniques. In this review article, we will describe recent developments and discuss the applications of multi-parametric MRI (mpMRI) in RT simulation. In this review, mpMRI refers to a general and loose definition which includes various multi-contrast MRI techniques. Specifically, we will focus on the implementation, challenges, and future directions of mpMRI techniques for RT simulation.

Clinical results of carbon ion radiotherapy for inoperable stage I non-small cell lung cancer: a Japanese national registry study (J-CROS-LUNG)

BACKGROUND AND PURPOSE

Radiotherapy is a standard treatment for inoperable stage I non-small cell lung cancer (NSCLC), and carbon-ion radiation therapy (CIRT) may be used for such treatment. Although CIRT for stage I NSCLC has demonstrated favorable outcomes in previous reports, the reports covered only single-institution studies. We conducted a prospective nationwide registry study including all CIRT institutions in Japan.

MATERIALS AND METHODS

Ninety-five patients with inoperable stage I NSCLC were treated by CIRT between May 2016 and June 2018. The dose fractionations for CIRT were selected from several options approved by the Japanese Society for Radiation Oncology.

RESULTS

The median patient age was 77 years. Comorbidity rates for chronic obstructive pulmonary disease and interstitial pneumonia were 43% and 26%, respectively. The most common schedule for CIRT was 60 Gy (relative biological effectiveness (RBE)) in four fractions, and the second most common was 50 Gy (RBE) in one fraction. The 3-year overall survival, cause-specific survival, and local control rates were 59.3%, 77.1%, and 87.3%, respectively. Female sex and ECOG performance status of 0-1 were favorable prognostic factors for overall survival in a multivariate analysis. No grade 4 or higher adverse event was observed. The 3-year cumulative incidence of grade 2 or higher radiation pneumonitis was 3.2%. The risk factors for radiation pneumonitis were a forced expiratory volume in 1 second (FEV1) of <0.9L and a total dose[[EQUATION]]67 Gy (RBE).

CONCLUSION

This study provides real-world treatment outcomes of CIRT for inoperable stage I NSCLC in Japan.

Long-Term Results of Proton Therapy for Hepatocellular Carcinoma Using Four-Dimensional Computed Tomography Planning without Fiducial Markers

We report here the long-term results of marker-less respiratory-gated proton therapy (PT), without fiducial markers for hepatocellular carcinoma (HCC), which was planned using a four-dimensional computed tomography technique. Local tumor control (LTC) and overall survival (OS) were estimated using the Kaplan-Meier method. Toxicity was graded per CTCAE v5.0. Patients (n = 105; median age 73 years, range 38-90 years) with 128 lesions were treated. The median radiation dose was 66 gray relative biological effectiveness (GyRBE) (range, 52.8-82.5 GyRBE) delivered in 2.0 to 6.6 GyRBE fractions, depending on lesion volume, the involved liver, and the patient's condition. The median follow-up of surviving patients was 63 months (range, 1-126 months), and the 5-year LTC and OS rates were 93.2% and 40.4%, respectively. Univariate and multivariate analyses identified tumors near the gastrointestinal tract as an independent risk factor for local recurrence and revealed that hepatic reserve, tumor stage, performance status, operability, sex, and portal vein thrombosis were independent risk factors for OS. Acute and late treatment-related grade 3 toxicities were experienced by eight patients (7.6%). Adverse events ≥ grade 4 were not evident. Marker-less respiratory-gated PT for HCC is a safe and effective treatment without severe complications.

The Influence of Motion on the Delivery Accuracy When Comparing Actively Scanned Carbon Ions versus Protons at a Synchrotron-Based Radiotherapy Facility

Simple Summary

The interplay of breathing and beam motion reduces the efficacy of particle irradiation in moving tumours. The effect of motion on protons and carbon ion treatments was investigated dosimetrically and the results were benchmarked against each other by employing an anthropomorphic thorax phantom that was able to simulate tumour, rib, and lung motion. The critical question was whether target coverage and organ-at-risk sparing could be maintained when the application of simple motion mitigation was addressed. Special focus was put on unique synchrotron characteristics, such as pulsed beam delivery and beam intensity variations. It could be demonstrated that the effect of motion was greater for carbon ions than for protons. These findings demonstrated the need for applying motion mitigation techniques depending on the motion amplitude, particle type, and treatment prescription considering complex time correlations.

Abstract

Motion amplitudes, in need of mitigation for moving targets irradiated with pulsed carbon ions and protons, were identified to guide the decision on treatment and motion mitigation strategy. Measurements with PinPoint ionisation chambers positioned in an anthropomorphic breathing phantom were acquired to investigate different tumour motion scenarios, including rib and lung movements. The effect of beam delivery dynamics and spot characteristics was considered. The dose in the tumour centre was deteriorated up to 10% for carbon ions but only up to 5% for protons. Dose deviations in the penumbra increased by a factor of two when comparing carbon ions to protons, ranging from 2 to 30% for an increasing motion amplitude that was strongly dependent on the beam intensity. Layer rescanning was able to diminish the dose distortion caused by tumour motion, but an increase in spot size could reduce it even further to 5% within the target and 10% at the penumbra. An increased need for motion mitigation of carbon ions compared to protons was identified to assure target coverage and sparing of adjacent organs at risk in the penumbra region and outside the target. For the clinical implementation of moving target treatments at a synchrotron-based particle facility complex, time dependencies needed to be considered.

Impact of Different Synchrotron Flattop Operation Modes on 4D Dosimetric Uncertainties for Scanned Carbon-Ion Beam Delivery

Purpose

The characteristic of pulsed beam delivery for synchrotron-based carbon-ion radiotherapy has led to the emergence of many scanning scenarios in order to improve the treatment efficiency and accuracy of moving target volume. Here, we aim to evaluate a novel breathing guidance motion mitigation performance under different synchrotron flattop operation modes in carbon-ion radiotherapy.

Methods

With the use of twelve 4DCT datasets of lung cancer patients who had been treated with respiratory-gated carbon-ion pencil beam therapy, range-adapted internal target volume (raITV) plans were optimized. Under the fixed flattop with single-energy and extended flattop with multi-energy synchrotron operation modes, the 4D treatments with breathing guidance and free breathing-based gated phase-controlled rescanning (PCR) beam delivery were simulated. Dose metrics (D95 and D5–D95 in clinical target volume (CTV)) and treatment time of the resulting 4D plans were compared.

Results

The two synchrotron operation modes provided different scanning dynamics. For the free breathing-based PCR method delivered in the extended flattop operation mode, the averaged CTV-D95 values were 90.4% ± 3.7%, 95.4% ± 1.7%, 96.9% ± 1.5%, 97.2% ± 1.5%, and 97.3% ± 1.5% for the 1-scanning, 2-PCR, 4-PCR, 6-PCR, and 8-PCR, respectively. For the breathing guidance-based PCR method delivered in the extended flattop mode, these values were 89.1% ± 4.0%, 97.0% ± 1.4%, 98.2% ± 0.7%, 98.6% ± 0.7%, and 98.9% ± 0.7%, respectively. However, CTV-D95 significantly increased to 98.5% ± 1.0% even with just 1-scanning breathing guidance-based fixed flattop operation mode (p < 0.01). Moreover, there was no significant difference in treatment time among the three technical combinations (p > 0.15).

Conclusions

The combination of the breathing guidance and PCR methods should be an alternative way for motion mitigation for the fixed flattop synchrotron operation mode. The target dose coverage and homogeneity could be further improved by the combination of the breathing guidance and PCR methods than the traditional PCR-only technology for the extended flattop synchrotron operation mode.

Commissioning and quality assurance of a novel solution for respiratory-gated PBS proton therapy based on optical tracking of surface markers

We present the commissioning and quality assurance of our clinical protocol for respiratory gating in pencil beam scanning proton therapy for cancer patients with moving targets. In a novel approach, optical tracking has been integrated in the therapy workflow and used to monitor respiratory motion from multiple surrogates, applied on the patients' chest. The gating system was tested under a variety of experimental conditions, specific to proton therapy, to evaluate reaction time and reproducibility of dose delivery control. The system proved to be precise in the application of beam gating and allowed the mitigation of dose distortions even for large (1.4cm) motion amplitudes, provided that adequate treatment windows were selected. The total delivered dose was not affected by the use of gating, with measured integral error within 0.15cGy. Analysing high-resolution images of proton transmission, we observed negligible discrepancies in the geometric location of the dose as a function of the treatment window, with gamma pass rate greater than 95% (2%/2mm) compared to stationary conditions. Similarly, pass rate for the latter metric at the 3%/3mm level was observed above 97% for clinical treatment fields, limiting residual movement to 3mm at end-exhale. These results were confirmed in realistic clinical conditions using an anthropomorphic breathing phantom, reporting a similarly high 3%/3mm pass rate, above 98% and 94%, for regular and irregular breathing, respectively. Finally, early results from periodic QA tests of the optical tracker have shown a reliable system, with small variance observed in static and dynamic measurements.

Report of AAPM Task Group 290: Respiratory motion management for particle therapy

Dose uncertainty induced by respiratory motion remains a major concern for treating thoracic and abdominal lesions using particle beams. This Task Group report reviews the impact of tumor motion and dosimetric considerations in particle radiotherapy, current motion‐management techniques, and limitations for different particle‐beam delivery modes (i.e., passive scattering, uniform scanning, and pencil‐beam scanning). Furthermore, the report provides guidance and risk analysis for quality assurance of the motion‐management procedures to ensure consistency and accuracy, and discusses future development and emerging motion‐management strategies. This report supplements previously published AAPM report TG76, and considers aspects of motion management that are crucial to the accurate and safe delivery of particle‐beam therapy. To that end, this report produces general recommendations for commissioning and facility‐specific dosimetric characterization, motion assessment, treatment planning, active and passive motion‐management techniques, image guidance and related decision‐making, monitoring throughout therapy, and recommendations for vendors. Key among these recommendations are that: (1) facilities should perform thorough planning studies (using retrospective data) and develop standard operating procedures that address all aspects of therapy for any treatment site involving respiratory motion; (2) a risk‐based methodology should be adopted for quality management and ongoing process improvement.

Target motion management in breast cancer radiation therapy

Background

Over the last two decades, breast cancer remains the main cause of cancer deaths in women. To treat this type of cancer, radiation therapy (RT) has proved to be efficient. RT for breast cancer is, however, challenged by intrafractional motion caused by respiration. The problem is more severe for the left-sided breast cancer due to the proximity to the heart as an organ-at-risk. While particle therapy results in superior dose characteristics than conventional RT, due to the physics of particle interactions in the body, particle therapy is more sensitive to target motion.

Conclusions

This review highlights current and emerging strategies for the management of intrafractional target motion in breast cancer treatment with an emphasis on particle therapy, as a modern RT technique. There are major challenges associated with transferring real-time motion monitoring technologies from photon to particles beams. Surface imaging would be the dominant imaging modality for real-time intrafractional motion monitoring for breast cancer. The magnetic resonance imaging (MRI) guidance and ultra high dose rate (FLASH)-RT seem to be state-of-the-art approaches to deal with 4D RT for breast cancer.

Real-time CT image generation based on voxel-by-voxel modeling of internal deformation by utilizing the displacement of fiducial markers

PURPOSE

To show the feasibility of real-time CT image generation technique utilizing internal fiducial markers that facilitate the evaluation of internal deformation.

METHODS

In the proposed method, a linear regression model that can derive internal deformation from the displacement of fiducial markers is built for each voxel in the training process before the treatment session. Marker displacement and internal deformation are derived from the four-dimensional computed tomography (4DCT) dataset. In the treatment session, the three-dimensional deformation vector field is derived according to the marker displacement, which is monitored by the real-time imaging system. The whole CT image can be synthesized by deforming the reference CT image with a deformation vector field in real-time. To show the feasibility of the technique, image synthesis accuracy and tumor localization accuracy were evaluated using the dataset generated by extended NURBS-Based Cardiac-Torso (XCAT) phantom and clinical 4DCT datasets from six patients, containing 10 CT datasets each. In the validation with XCAT phantom, motion range of the tumor in training data and validation data were about 10 and 15 mm, respectively, so as to simulate motion variation between 4DCT acquisition and treatment session. In the validation with patient 4DCT dataset, eight CT datasets from the 4DCT dataset were used in the training process. Two excluded inhale CT datasets can be regarded as the datasets with large deformations more than training dataset. CT images were generated for each respiratory phase using the corresponding marker displacement. Root mean squared error (RMSE), normalized RMSE (NRMSE), and structural similarity index measure (SSIM) between the original CT images and the synthesized CT images were evaluated as the quantitative indices of the accuracy of image synthesis. The accuracy of tumor localization was also evaluated.

RESULTS

In the validation with XCAT phantom, the mean NRMSE, SSIM, and three-dimensional tumor localization error were 7.5 ± 1.1%, 0.95 ± 0.02, and 0.4 ± 0.3 mm, respectively. In the validation with patient 4DCT dataset, the mean RMSE, NRMSE, SSIM, and three-dimensional tumor localization error in six patients were 73.7 ± 19.6 HU, 9.2 ± 2.6%, 0.88 ± 0.04, and 0.8 ± 0.6 mm, respectively. These results suggest that the accuracy of the proposed technique is adequate when the respiratory motion is within the range of the training dataset. In the evaluation with a marker displacement larger than that of the training dataset, the mean RMSE, NRMSE, and tumor localization error were about 100 HU, 13%, and <2.0 mm, respectively, except for one case having large motion variation. The performance of the proposed method was similar to those of previous studies. Processing time to generate the volumetric image was <100 ms.

CONCLUSION

We have shown the feasibility of the real-time CT image generation technique for volumetric imaging.

Validation of dose distribution for liver tumors treated with real-time-image gated spot-scanning proton therapy by log data based dose reconstruction

In spot scanning proton therapy (SSPT), the spot position relative to the target may fluctuate through tumor motion even when gating the radiation by utilizing a fiducial marker. We have established a procedure that evaluates the delivered dose distribution by utilizing log data on tumor motion and spot information. The purpose of this study is to show the reliability of the dose distributions for liver tumors treated with real-time-image gated SSPT (RGPT). In the evaluation procedure, the delivered spot information and the marker position are synchronized on the basis of log data on the timing of the spot irradiation and fluoroscopic X-ray irradiation. Then a treatment planning system reconstructs the delivered dose distribution. Dose distributions accumulated for all fractions were reconstructed for eight liver cases. The log data were acquired in all 168 fractions for all eight cases. The evaluation was performed for the values of maximum dose, minimum dose, D99, and D5-D95 for the clinical target volumes (CTVs) and mean liver dose (MLD) scaled by the prescribed dose. These dosimetric parameters were statistically compared between the planned dose distribution and the reconstructed dose distribution. The mean difference of the maximum dose was 1.3% (95% confidence interval [CI]: 0.6%-2.1%). Regarding the minimum dose, the mean difference was 0.1% (95% CI: -0.5%-0.7%). The mean differences of D99, D5-D95 and MLD were below 1%. The reliability of dose distributions for liver tumors treated with RGPT-SSPT was shown by the evaluation of the accumulated dose distributions.

Visualized Analysis of Heavy Ion Radiotherapy: Development, Barriers and Future Directions

Background

Heavy ion radiotherapy (HIRT) has great advantages as tumor radiotherapy.

Methods

Based on 1,558 literatures from core collections of Web of Science from 1980 to 2020, this study visually analyzes the evolution of HIRT research, and sorts out the hotspots and trends of HIRT research using CiteSpace software.

Results

Research on HIRT has received more extensive attention over the last 40 years. The development of HIRT is not only closely related to radiation and oncology, but also closely related to the development of human society. In terms of citation frequency, "International Journal of Radiation Oncology*Biology*Physics" was the top journal. In terms of influence, "Radiotherapy and Oncology" was the top journal. "Radiation therapy" and "carbon ion radiotherapy" were the two most frequently used keywords in this field.

Conclusion

The evolution of the HIRT research has occurred in approximately three stages, including technological exploration, safety and effectiveness research and technological breakthroughs. Finally, some suggestions for future research are put forward.

Motion management with variable cycle-based respiratory guidance method for carbon-ion pencil beam scanning treatment

PURPOSE

A novel variable cycle-based respiratory guidance method was proposed to synchronize the patterns between patients' breathing and the magnetic excitation of synchrotron under the mode of full-energy depth scanning beam delivery, in order to improve the treatment precision and efficiency for carbon ion therapy.

METHODS

Audio-visual biofeedback system with variable cycle-based respiratory guidance method was developed. We enrolled 6 healthy volunteers and a simulation study of the fixed cycle-based and variable cycle-based respiratory guidance with three treatment fractions was performed. A total of 72 breathing curves were collected for 4D dose calculations with three 4DCT datasets of lung tumor cases. Target dose coverage (D95: the percent dose covering 95% of the target), dose homogeneity (D5-D95), and treatment time were analyzed. The Wilcoxon signed-rank test was used for statistical difference analysis, and p < 0.05 was considered significant.

RESULTS

With the variable cycle-based respiratory guidance method, the breath hold phase of breathing curve could be synchronized with the synchrotron flat-top phase over time. The dose homogeneity was improved by factors of 1.94-2.92 compared to the fixed cycle-based respiratory guidance maneuvers alone or in combination with gating technique. Moreover, the treatment efficiency increased by 11-23%, depending on the duty cycle settings of the gating window.

CONCLUSIONS

The proposed variable cycle-based respiratory guidance method could improve both the treatment efficiency and precision under the mode of the full-energy depth scanning beam delivery for synchrotron-based carbon ion therapy.

Gated Radiotherapy Development and its Expansion

One of the most important challenges in treatment of patients with cancerous tumors of chest and abdominal areas is organ movement. The delivery of treatment radiation doses to tumor tissue is a challenging matter while protecting healthy and radio sensitive tissues. Since the movement of organs due to respiration causes a discrepancy in the middle of planned and delivered dose distributions. The moderation in the fatalistic effect of intra-fractional target travel on the radiation therapy correctness is necessary for cutting-edge methods of motion remote monitoring and cancerous growth irradiancy. Tracking respiratory milling and implementation of breath-hold techniques by respiratory gating systems have been used for compensation of respiratory motion negative effects. Therefore, these systems help us to deliver precise treatments and also protect healthy and critical organs. It seems aspiration should be kept under observation all over treatment period employing tracking seed markers (e.g. fiducials), skin surface scanners (e.g. camera and laser monitoring systems) and aspiration detectors (e.g. spirometers). However, these systems are not readily available for most radiotherapy centers around the word. It is believed that providing and expanding the required equipment, gated radiotherapy will be a routine technique for treatment of chest and abdominal tumors in all clinical radiotherapy centers in the world by considering benefits of respiratory gating techniques in increasing efficiency of patient treatment in the near future. This review explains the different technologies and systems as well as some strategies available for motion management in radiotherapy centers.

Physics of Particle Beam and Hypofractionated Beam Delivery in NSCLC

The dosimetric advantages of particle therapy lead to significantly reduced integral dose to normal tissues, making it an attractive treatment option for body sites such as the thorax. With reduced normal tissue dose comes the potential for dose escalation, toxicity reduction, or hypofractionation. While proton and heavy ion therapy have been used extensively for NSCLC, there are challenges in planning and delivery compared with X-ray-based radiation therapy. Particularly, range uncertainties compounded by breathing motion have to be considered. This article summarizes the current state of particle therapy for NSCLC with a specific focus on the impact of dosimetric uncertainties in planning and delivery.

Robustness of daily dose for each beam angle and accumulated dose for inter-fractional anatomical changes in passive carbon-ion radiotherapy for pancreatic cancer: Bone matching versus tumor matching

PURPOSE

We aimed to assess the robustness of accumulated dose distributions for inter-fractional changes in passive carbon-ion radiotherapy for pancreatic cancer.

METHODS

Ninety-five daily CT image sets acquired after the treatment of eight patients with pancreatic cancer were used in this prospective study. Dose distributions with treatment beam fields were recalculated for bone matching (BM) and tumor matching (TM) positions on all daily CT images, the accumulated doses being calculated using deformable image registration methods. The prescribed dose was 55.2 Gy (relative biological effectiveness [RBE]) in 12 fractions. Dose volume parameters of V95 (%) for CTV and GTV, and D2cc (Gy(RBE)) for the stomach and duodenum were evaluated.

RESULTS

The medians (range) of CTV V95 (%) were 91.9 (86.1-100.0), 80.5 (56.1-90.6), and 86.4 (72.5-96.5) for the Plan, accumulated with BM and TM, respectively; GTV values (%) were 98.0 (85.7-100.0), 93.3 (65.7-99.9), and 96.2 (84.8-100.0), respectively. There were significant differences between all combinations apart from the Plan and TM for both targets. The values of stomach D2cc (Gy(RBE)) were 36.0 (16.9-43.4), 36.7 (17.9-45.0), and 35.2 (16.8-43.5), respectively; duodenum values (Gy(RBE)) were 25.2 (21.3-40.3), 30.1 (23.3-48.6), and 28.3 (20.4-50.6), respectively. There was a significant difference between the Plan and BM for duodenum only.

CONCLUSIONS

TM is recommended over BM because it can achieve higher target dose coverage than BM. Nevertheless, it is not enough in some cases. Further technical improvements are necessary to improve the target dose coverage.

Biomedical Research Programs at Present and Future High-Energy Particle Accelerators

Biomedical applications at high-energy particle accelerators have always been an important section of the applied nuclear physics research. Several new facilities are now under constructions or undergoing major upgrades. While the main goal of these facilities is often basic research in nuclear physics, they acknowledge the importance of including biomedical research programs and of interacting with other medical accelerator facilities providing patient treatments. To harmonize the programs, avoid duplications, and foster collaboration and synergism, the International Biophysics Collaboration is providing a platform to several accelerator centers with interest in biomedical research. In this paper, we summarize the programs of various facilities in the running, upgrade, or construction phase.

Organ motion quantification and margins evaluation in carbon ion therapy of abdominal lesions

PURPOSE

In image-guided particle radiotherapy of abdominal lesions, respiratory motion hinders treatment accuracy. In this study, 2D cineMRI data were used to quantify the tumor (GTV) motion and to evaluate the clinical approach based on deriving an internal target volume (ITV) from a planning 4DCT for gating treatments.

METHODS

Seven patients with abdominal lesions were treated with carbon-ion therapy at the National Centre of Oncological Hadron-therapy (Italy). The MR scan was performed on the same day of the 4DCT acquisition. For four patients, an additional MR was acquired approximately after 1 week. The cineMRI combined with deformable image registration algorithm was used to quantify tumor motion. Afterwards, two ITVs were defined considering (1) all phases (ITVFB) and (2) only phases within the gating window (ITVG), and then compared with the clinical (4DCT-derived) ITVs (ITVCG and ITVCFB).

RESULTS

Tumor residual motion estimated by cineMRI data in the two MRI sessions resulted not significantly different from 4DCT, although cineMRI accounted for cycle-to-cycle variations. The ITV normalized for the GTV median values were higher for ITVFB with respect to ITVG, ITVCFB and ITVCG. The Hausdorff distances with respect to the GTV were up to 10.55 mm, 3.13 mm, 5.56 mm and 2.51 mm, for ITVFB, ITVG, ITVCFB and ITVCG, respectively. According to both metrics, ITVCG and ITVG were not found significantly different.

CONCLUSIONS

CineMRI acquisitions allowed to quantify organ motion without delivering additional dose to the patient and to verify treatment margins in gated carbon-ion therapy of abdominal lesions.

Perturbation analysis of 4D dose distribution for scanned carbon-ion beam radiotherapy

PURPOSE

To evaluate the patients' set-up error-induced perturbation effects on 4D dose distributions (4DDD) of range-adapted internal target volume-based (raITV) treatment plan using lung and liver 4DCT data sets.

METHODS

We enrolled 20 patients with lung and liver cancer treated with respiratory-gated carbon-ion beam scanning therapy. PTVs were generated by adding a 2 mm range-adapted set-up margin on the raITVs. Set-up errors were simulated by shifting the beam isocenter in three translational directions of ±2 mm, ±4 mm, and ±6 mm. 4DDDs were calculated for both nominal and isocenter-shifted situations. Dose metrics of CTV dose coverage (D95) and normal tissue sparing were evaluated. Statistical significance with p < 0.01 was considered by Wilcoxon signed rank test.

RESULTS

The CTV dose coverage was more sensitive to set-up errors for lung cases than for liver cases, and more serious in superior-inferior direction. The sufficient CTV-D95 > 98% could be achieved with set-up errors less than ±2 mm in all shift directions both for lung and liver cases. With the increase of set-up error, the CTV dose coverage decreased gradually. The clinical criterial of CTV-D95 > 95% could not be fulfilled with set-up error reached to ±4 mm for lung cases, and ±6 mm for liver cases. OAR doses did not have a significant difference with each set-up error for both lung and liver cases.

CONCLUSIONS

The range-adapted set-up margin successfully prevented dose degradation of 4DDDs in the presence of the same magnitude of set-up error for raITV-based carbon-ion beam scanning therapy.

Dynamic gating window technique for the reduction of dosimetric error in respiratory-gated spot-scanning particle therapy: An initial phantom study using patient tumor trajectory data

Spot-scanning particle therapy possesses advantages, such as high conformity to the target and efficient energy utilization compared with those of the passive scattering irradiation technique. However, this irradiation technique is sensitive to target motion. In the current clinical situation, some motion management techniques, such as respiratory-gated irradiation, which uses an external or internal surrogate, have been clinically applied. In surrogate-based gating, the size of the gating window is fixed during the treatment in the current treatment system. In this study, we propose a dynamic gating window technique, which optimizes the size of gating window for each spot by considering a possible dosimetric error. The effectiveness of the dynamic gating window technique was evaluated by simulating irradiation using a moving target in a water phantom. In dosimetric characteristics comparison, the dynamic gating window technique exhibited better performance in all evaluation volumes with different effective depths compared with that of the fixed gate approach. The variation of dosimetric characteristics according to the target depth was small in dynamic gate compared to fixed gate. These results suggest that the dynamic gating window technique can maintain an acceptable dose distribution regardless of the target depth. The overall gating efficiency of the dynamic gate was approximately equal or greater than that of the fixed gating window. In dynamic gate, as the target depth becomes shallower, the gating efficiency will be reduced, although dosimetric characteristics will be maintained regardless of the target depth. The results of this study suggest that the proposed gating technique may potentially improve the dose distribution. However, additional evaluations should be undertaken in the future to determine clinical applicability by assuming the specifications of the treatment system and clinical situation.

Managing treatment-related uncertainties in proton beam radiotherapy for gastrointestinal cancers

In recent years, there has been rapid adaption of proton beam radiotherapy (RT) for treatment of various malignancies in the gastrointestinal (GI) tract, with increasing number of institutions implementing intensity modulated proton therapy (IMPT). We review the progress and existing literature regarding the technical aspects of RT planning for IMPT, and the existing tools that can help with the management of uncertainties which may impact the daily delivery of proton therapy. We provide an in-depth discussion regarding range uncertainties, dose calculations, image guidance requirements, organ and body cavity filling consideration, implanted devices and hardware, use of fiducials, breathing motion evaluations and both active and passive motion management methods, interplay effect, general IMPT treatment planning considerations including robustness plan evaluation and optimization, and finally plan monitoring and adaptation. These advances have improved confidence in delivery of IMPT for patients with GI malignancies under various scenarios.

A novel design of proton computed tomography detected by multiple-layer ionization chamber with strip chambers: A feasibility study with Monte Carlo simulation

PURPOSE

Uncertainty in proton range can be reduced by proton computed tomography (CT). A novel design of proton CT using a multiple-layer ionization chamber with two strip ionization chambers on the surface is proposed to simplify the imaging acquisition and reconstruction.

METHODS

Two strip ionization chambers facing the proton source were coupled into a multiple-layer ionization chamber (MLIC). The strip chambers measured locations and lateral profiles of incident proton beamlets after exiting the imaging object, while the integral of depth dose measured in the MLIC was translated into the residual energy of the beamlet. The simulation was performed at five levels of imaging dose to demonstrate the feasibility and performance expectations of our design. The energy of the proton beamlet was set to 150 ± 0.6 MeV. A collimator with a round slit of 1 cm in diameter was placed in the central beam axis upstream from steering magnets. Proton stopping power ratio (SPR) was reconstructed through inverse radon transform on sinograms generated with proton beamlets scanning through an imaging phantom from a half-circle gantry rotation. The imaging phantom was 10 cm in diameter. The base was made of water-equivalent material holding 13-tissue equivalent inserts constructed according to ICRP 1975 (Task Group on Reference Man. "Report of the Task Group on Reference Man: A Report", Pergamon Press 23, 1975). All inserts were 1 cm in diameter with materials ranging from lung to cortical bone. Percentage discrepancies were reported by comparing to the ground truths. The imaging dose and quality were also evaluated.

RESULTS

The maximum deviation in reconstructed proton SPR from the ground truths was reported to be 1.02% in one of the 13 inserts when the number of protons per beamlet passing through the slit dropped to 10³ . Imaging dose was correlated linearly to incident protons and was determined to be 0.54 cGy if 5 × 10² protons per beamlet were used. Imaging quality was acceptable for planning purpose and held consistently through all levels of imaging dose. Spatial resolution was measured as five line pairs per cm consistently in all simulations varying in imaging dose.

CONCLUSIONS

Proton CT using a multiple-layer ionization chamber with two strip ionization chambers on the surface simplifies data acquisition while achieving excellent accuracy in proton SPR and acceptable spatial resolution. The imaging dose is lower compared to kV CBCT, making it potentially a great tool for localization and plan adaption in proton therapy.

Long-Term Results of High-Dose 2-Fraction Carbon Ion Radiation Therapy for Hepatocellular Carcinoma

Purpose

Carbon ion beams have several physical and biological advantages compared with conventional radiation for cancer therapy. The objective of this study is to evaluate the safety and effectiveness of 2-fraction carbon ion radiation therapy (CIRT) in patients with hepatocellular carcinoma (HCC).

Methods and Materials

Between December 2008 and March 2013, 57 patients with localized HCC were treated with CIRT at a total dose of 45 Gy (relative biological effectiveness) in 2 fractions and retrospectively analyzed after long-term observation. The main endpoints of this study were treatment-related toxicity and local tumor control. Toxicity was assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events, version 4.0. Changes in the Child-Pugh score from before to after CIRT were also examined to evaluate hepatic toxicity. Local control was defined as no progression of the irradiated lesion according to the modified Response Evaluation Criteria in Solid Tumors.

Results

The median age of the patients was 75 years (range, 49-89 years). Of these patients, 41 had a newly diagnosed lesion, and 16 had residual or recurrent lesions after previous treatments. The median follow-up duration was 54 months (range, 7-103 months). All surviving patients were followed for more than 51 months. Two patients experienced grade 3 acute skin reactions, but no other grade 3 or higher toxicities were observed in any organ. No patient exhibited an increase in the Child-Pugh score of 2 or more points after CIRT. The local tumor control rates at 1, 3, and 5 years were 98%, 91%, and 91% after CIRT, respectively. All lesions that failed to respond to previous treatments were successfully controlled by CIRT. The 1-, 3-, and 5-year overall survival rates were 97%, 67%, and 45%, respectively.

Conclusions

Two-fraction CIRT was a well-tolerated and effective treatment for patients with HCC.

Sparse proportional re-scanning with hadron beams

Spot Scanning is a well-established technique to deliver the dose with hadron therapy systems. For many years re-scanning (called also re-painting) has been used to achieve uniform dose distribution in particular for moving organs, although it leads to an increase of the treatment time. Reducing this time is a major focus of present research. In this paper, after reviewing the current re-scanning techniques, sparse proportional re-scanning is defined and applied to 29 proton patient cases for a total of 54 fields. In this technique, only the highest weighted spot in the whole target is visited a number of times that is equal to the number N of re-scans. The number of visits of the beam spot to all remaining spots is scaled down proportionally to their weight. Sparse proportional re-scanning is advantageous especially in volumetric re-scanning. In order to quantify the potential advantages of this technique in terms of treatment time, a reduction factor of the number of scanned spots has been introduced, evaluated and analysed for 54 proton fields. The conclusion is that the reduction factor is a function of N (having values equal to 2.8 ± 0.3 and 3.6 ± 0.4 for N = 5 and N = 12 respectively) and does not depend either on the shape and volume of the target or on the distance between the scanned layers and the spot grid. The same values are approximately valid also for carbon ion treatments.

Real-time intrafraction motion monitoring in external beam radiotherapy

Radiotherapy (RT) aims to deliver a spatially conformal dose of radiation to tumours while maximizing the dose sparing to healthy tissues. However, the internal patient anatomy is constantly moving due to respiratory, cardiac, gastrointestinal and urinary activity. The long term goal of the RT community to 'see what we treat, as we treat' and to act on this information instantaneously has resulted in rapid technological innovation. Specialized treatment machines, such as robotic or gimbal-steered linear accelerators (linac) with in-room imaging suites, have been developed specifically for real-time treatment adaptation. Additional equipment, such as stereoscopic kilovoltage (kV) imaging, ultrasound transducers and electromagnetic transponders, has been developed for intrafraction motion monitoring on conventional linacs. Magnetic resonance imaging (MRI) has been integrated with cobalt treatment units and more recently with linacs. In addition to hardware innovation, software development has played a substantial role in the development of motion monitoring methods based on respiratory motion surrogates and planar kV or Megavoltage (MV) imaging that is available on standard equipped linacs. In this paper, we review and compare the different intrafraction motion monitoring methods proposed in the literature and demonstrated in real-time on clinical data as well as their possible future developments. We then discuss general considerations on validation and quality assurance for clinical implementation. Besides photon RT, particle therapy is increasingly used to treat moving targets. However, transferring motion monitoring technologies from linacs to particle beam lines presents substantial challenges. Lessons learned from the implementation of real-time intrafraction monitoring for photon RT will be used as a basis to discuss the implementation of these methods for particle RT.

Carbon-ion radiotherapy for cholangiocarcinoma: a multi-institutional study by and the Japan carbon-ion radiation oncology study group (J-CROS)

To evaluate the safety and efficacy of carbon-ion radiotherapy (CIRT) for cholangiocarcinoma via a multicenter retrospective study. Clinical data were collected from patients with cholangiocarcinoma who had received CIRT at one of four treating institutions in Japan. Of 56 eligible patients, none received surgery for cholangiocarcinoma before or after CIRT. The primary endpoint was overall survival (OS). Based on the tumor site, the 56 cases were categorized as intrahepatic cholangiocarcinoma (IHC) (n=27) or perihilar cholangiocarcinoma (PHC) (n=29). In all patients, the median tumor size was 37 (range, 15‒110) mm, and the most commonly prescribed dose was 76 Gy (relative biological effectiveness) in 20 fractions. The median survival was 14.8 (range, 2.1-129.2) months, and the 1- and 2-year OS rates were 69.7% and 40.9%, respectively. The median survival times of the patients with IHC and those with PHC were 23.8 and 12.6 months, respectively. Both univariate and multivariate analyses revealed that cholangitis pre-CIRT and Child‒Pugh class B were significant prognostic factors for an unfavorable OS. Of four patients who died of liver failure, one with IHC was suspected to have radiation-induced liver disease because of newly developed ascites, and died at 4.3 months post-CIRT. Grade 3 CIRT-related bile duct stenosis was observed in one IHC case. No other CIRT-related severe adverse events, including gastrointestinal events, were observed. These results suggest that CIRT yields relatively favorable treatment outcomes, especially for patients with IHC, and acceptable toxicities were observed in patients with cholangiocarcinoma who did not receive surgery.

Numerical simulation of novel concept 4D cardiac microtomography for small rodents based on all-optical Thomson scattering X-ray sources

Accurate dynamic three-dimensional (4D) imaging of the heart of small rodents is required for the preclinical study of cardiac biomechanics and their modification under pathological conditions, but technological challenges are met in laboratory practice due to the very small size and high pulse rate of the heart of mice and rats as compared to humans. In 4D X-ray microtomography (4D μCT), the achievable spatio-temporal resolution is hampered by limitations in conventional X-ray sources and detectors. Here, we propose a proof-of-principle 4D μCT platform, exploiting the unique spatial and temporal features of novel concept, all-optical X-ray sources based on Thomson scattering (TS). The main spatial and spectral properties of the photon source are investigated using a TS simulation code. The entire data acquisition workflow has been also simulated, using a novel 4D numerical phantom of a mouse chest with realistic intra- and inter-cycle motion. The image quality of a typical single 3D time frame has been studied using Monte Carlo simulations, taking into account the effects of the typical structure of the TS X-ray beam. Finally, we discuss the perspectives and shortcomings of the proposed platform.

Tumor localization accuracy for high-precision radiotherapy during active breath-hold

BACKGROUND

Conventionally fractionated and stereotactic body radiation therapy (SBRT) for thoracoabdominal tumors may utilize breath-hold techniques. However, there are concerns that differential amounts of inspired airflow may result in unplanned tumor dislocation and underdosing. Thus, we investigated tumor localization accuracy associated with lung volume variations during breath-hold treatment via an automated-gating interface.

METHODS

Twelve patients received breath-hold treatment with the active breathing coordinator (ABC) through an automated-gating interface. All breath-hold volumes were recorded at CT simulation, setup imaging, and during treatment, and analyzed as a function of airflow rate into the ABC. The variation of breath-hold volumes was calculated for each fraction over entire course. Intrafraction target motion related to the breathing variation was investigated based on daily imaging acquired before the breath-hold treatment. Correlation between target location and breath-hold variation was statistically analyzed.

RESULTS

The air volume held by the ABC increased as the airflow rate increased on inhalation and decreased on exhalation. The mean range of airflow rate was 0.77 L/s and 0.29 L/s in the conventionally fractionated and SBRT patients, respectively. The maximum air volume difference with respect to the reference volume at the CT simulation was 1.0 L for conventional fractionation and 0.16 L for SBRT. The target dislocation caused by 0.25 L of air volume difference was 6 mm for SBRT. Three patients showed significant correlation between the target location and breath-hold variations.

CONCLUSIONS

This investigation shows that because variations in the breath-hold volume may cause target dislocation, patient-specific breath-hold setting is required to improve tumor localization accuracy.

First-In-Human Phase 1 Study of a Nonwoven Fabric Bioabsorbable Spacer for Particle Therapy: Space-Making Particle Therapy (SMPT)

Purpose

Surgical spacer placement (SSP) is useful in particle therapy (PT) for patients with abdominal or pelvic tumors located adjacent to normal organs. We developed a nonwoven fabric bioabsorbable spacer made of polyglycolic acid (PGA) sutures that degrades via hydrolysis. We then conducted this first-in-human phase 1 study of the combination of SSP and PT using the PGA spacer, which we termed space-making PT (SMPT). This study aimed to evaluate the safety and efficacy of SMPT in patients with unresectable malignant tumor located adjacent to normal organs.

Methods and Materials

The eligibility criteria included histologically proven malignant abdominal or pelvic tumor adjacent to the intestines, no metastasis, and no previous radiation therapy. Periodic computed tomography (CT) images were obtained before SSP and before, during, and after PT until the spacer disappeared. Treatment planning was performed for each CT image set until the end of PT, and doses for the planning target volume and organs at risk were analyzed. The thickness and volume of the PGA spacer were measured in each CT image set. Adverse events were evaluated according to the Common Terminology Criteria for Adverse Events version 4.0.

Results

Five patients were enrolled in this study. All patients received 70.4 Gy (relative biological effectiveness) of irradiation. V_95% of the planning target volume before SSP, at the beginning of PT, and at the end of PT was 82.1% ± 11.3%, 98.1% ± 1.1%, and 97.1% ± 0.8%, respectively. The PGA spacers maintained enough thickness (≥1 cm) until the end of PT and disappeared within 8 months after SSP in all patients. No grade ≥3 acute adverse events were observed.

Conclusions

The SMPT is feasible and useful for abdominal or pelvic tumors adjacent to the intestines. This method may be applicable to unresectable tumors located adjacent to normal organs and may expand the indications of PT.

RIDOS: A new system for online computation of the delivered dose distributions in scanning ion beam therapy

PURPOSE

To describe a new system for scanned ion beam therapy, named RIDOS (Real-time Ion DOse planning and delivery System), which performs real time delivered dose verification integrating the information from a clinical beam monitoring system with a Graphic Processing Unit (GPU) based dose calculation in patient Computed Tomography.

METHODS

A benchmarked dose computation algorithm for scanned ion beams has been parallelized and adapted to run on a GPU architecture. A workstation equipped with a NVIDIA GPU has been interfaced through a National Instruments PXI-crate with the dose delivery system of the Italian National Center of Oncological Hadrontherapy (CNAO) to receive in real-time the measured beam parameters. Data from a patient monitoring system are also collected to associate the respiratory phases with each spot during the delivery of the dose. Using both measured and planned spot properties, RIDOS evaluates during the few seconds of inter-spill time the cumulative delivered and prescribed dose distributions and compares them through a fast γ-index algorithm.

RESULTS

The accuracy of the GPU-based algorithms was assessed against the CPU-based ones and the differences were found below 1‰. The cumulative planned and delivered doses are computed at the end of each spill in about 300 ms, while the dose comparison takes approximatively 400 ms. The whole operation provides the results before the next spill starts.

CONCLUSIONS

RIDOS system is able to provide a fast computation of the delivered dose in the inter-spill time of the CNAO facility and allows to monitor online the dose deposition accuracy all along the treatment.

Comparing the effectiveness and efficiency of various gating approaches for PBS proton therapy of pancreatic cancer using 4D-MRI datasets

Abdominal organ motion may lead to considerable uncertainties in pencil-beam scanning (PBS) proton therapy of pancreatic cancer. Beam gating, where irradiation only occurs in certain breathing phases in which the gating conditions are fulfilled, may be an option to reduce the interplay effect between tumor motion and the scanning beam. This study aims to, first, determine suitable gating windows with respect to effectiveness (low interplay effect) and efficiency (high duty cycles). Second, it investigates whether beam gating allows for a better mitigation of the interplay effect along the treatment course than free-breathing irradiations. Based on synthetic 4D-CTs, generated by warping 3D-CTs with vector fields extracted from time-resolved magnetic resonance imaging (4D-MRI) for 8 pancreatic cancer patients, 4D dose calculations (4DDC) were performed to analyze the duty cycle and homogeneity index HI  =  d5/d95 for four different gating scenarios. These were based on either fixed threshold values of CTV (clinical target volume) mean or maximum motion amplitudes (5 mm), relative CTV motion amplitudes (30%) or CTV overlap criteria (95%), respectively. 4DDC for 28-fractions treatment courses were performed with fixed and variable initial breathing phases to investigate the fractionation-induced mitigation of the interplay effect. Gating criteria, based on patient-specific relative 30% CTV motion amplitudes, showed the significantly best HI values with sufficient duty cycles, in contrast to inferior results by either fixed gating thresholds or overlap criteria. For gated treatments with 28 fractions, less fractionation-induced mitigation of the interplay effect was observed for gating criteria with gating windows  ⩾30%, compared to free-breathing treatments. The gating effectiveness for multiple fractions was improved by allowing a variable initial breathing phase. Gating with relative amplitude thresholds are effective for proton therapy of pancreatic cancer. By combining beam gating with variable initial breathing phases, a pronounced mitigation of the interplay effect by fractionation can be achieved.

Investigation of thoracic four-dimensional CT-based dimension reduction technique for extracting the robust radiomic features

Robust feature selection in radiomic analysis is often implemented using the RIDER test-retest datasets. However, the CT Protocol between the facility and test-retest datasets are different. Therefore, we investigated possibility to select robust features using thoracic four-dimensional CT (4D-CT) scans that are available from patients receiving radiation therapy. In 4D-CT datasets of 14 lung cancer patients who underwent stereotactic body radiotherapy (SBRT) and 14 test-retest datasets of non-small cell lung cancer (NSCLC), 1170 radiomic features (shape: n = 16, statistics: n = 32, texture: n = 1122) were extracted. A concordance correlation coefficient (CCC) > 0.85 was used to select robust features. We compared the robust features in various 4D-CT group with those in test-retest. The total number of robust features was a range between 846/1170 (72%) and 970/1170 (83%) in all 4D-CT groups with three breathing phases (40%-60%); however, that was a range between 44/1170 (4%) and 476/1170 (41%) in all 4D-CT groups with 10 breathing phases. In test-retest, the total number of robust features was 967/1170 (83%); thus, the number of robust features in 4D-CT was almost equal to that in test-retest by using 40-60% breathing phases. In 4D-CT, respiratory motion is a factor that greatly affects the robustness of features, thus by using only 40-60% breathing phases, excessive dimension reduction will be able to be prevented in any 4D-CT datasets, and select robust features suitable for CT protocol of your own facility.

A quality assurance for respiratory gated proton irradiation with range modulation wheel

The purpose of this study was to provide periodic quality assurance (QA) methods for respiratory-gated proton beam with a range modulation wheel (RMW) and to clarify the characteristics and long-term stability of the respiratory-gated proton beam. A two-dimensional detector array and a solid water phantom were used to measure absolute dose, spread-out Bragg peak (SOBP) width and proton range for monthly QA. SOBP width and proton range were measured using an oblique incidence beam to the lateral side of a solid water phantom and compared between with and without a gating proton beam. To measure the delay time of beam-on/off for annual QA, we collected the beam-on/off signals and the dose monitor-detected pulse. We analyzed the results of monthly QA over a 15-month period and investigated the delay time by machine signal analysis. The dose deviations at proximal, SOBP center and distal points were -0.083 ± 0.25%, 0.026 ± 0.20%, and -0.083 ± 0.35%, respectively. The maximum dose deviation between with and without respiratory gating was -0.95% at the distal point and other deviations were within ±0.5%. Proximal and SOBP center doses showed the same trend over a 15-month period. Delay times of beam-on/off for 200 MeV/SOBP 16 cm were 140.5 ± 0.8 ms and 22.3 ± 13.0 ms, respectively. Delay times for 160 MeV/SOBP 10 cm were 167.5 ± 15.1 ms and 19.1 ± 9.8 ms. Our beam delivery system with the RMW showed sufficient stability for respiratory-gated proton therapy and the system did not show dependency on the energy and the respiratory wave form. The delay times of beam-on/off were within expectations. The proposed QA methods will be useful for managing the quality of respiratory-gated proton beams and other beam delivery systems.

Prospective clinical trial of 12-fraction carbon-ion radiotherapy for primary renal cell carcinoma

The aims of this study were to clarify the safety and efficacy of 12-fraction carbon-ion radiotherapy (CIRT) for primary renal cell carcinoma (RCC) and to confirm the recommended dose in a prospective clinical trial.

This clinical trial was planned as a non-randomized, open-label, single-center phase I/II study of CIRT monotherapy. The incidence of acute adverse events was the primary endpoint. Dose-limiting toxicities (DLTs) were defined as grade ≥3 skin, gastrointestinal tract, or urologic adverse events.

Based on the eligibility criteria, 8 patients with primary RCC, including 3 medically inoperable patients and 5 patients with tumors >4 cm, were enrolled. Of the 8 patients, 5 were treated with 66 Gy (relative biological effectiveness [RBE]), and subsequently, the dose was escalated to 72 Gy (RBE) for the remaining 3 patients. The median follow-up time was 43.1 months. No DLTs were observed at any dose level though the end of follow-up. Although 1 patient died of pneumonia 3 months after CIRT, which was determined to be unrelated to CIRT, no grade 3 or higher adverse events were observed, and both local control and cancer-specific survival rates were 100%.

In conclusion, the safety and efficacy of CIRT hypofractionation using 12-fractions for the treatment of eligible RCC patients, including those with inoperable or tumor size >4 cm, were confirmed in this prospective trial, and a recommended dose of 72 Gy (RBE) was established.

Commissioning of a respiratory gating system involving a pressure sensor in carbon-ion scanning radiotherapy

This study reports the commissioning methodology and results of a respiratory gating system [AZ - 733 V/733 VI (Anzai Medical Co., Japan)] using a pressure sensor in carbon-ion scanning radiotherapy. Commissioning includes choosing a location and method for pressure sensor installation, delay time measurement of the system, and the final flow test. Additionally, we proposed a methodology for the determination of a threshold level of generating an on/off gate for the beam to the respiratory waveform, which is important for clinical application. Regarding the location and method for installation of the pressure sensor, the actual person's abdomen, back of the body position, and supine/prone positioning were checked. By comparing the motion between the pressure sensor output and the reference LED sensor motion, the chest rear surface was shown to be unsuitable for the sensor installation, due to noise in the signal caused by the cardiac beat. Regarding delay time measurement of the system, measurements were performed for the following four steps: (a). Actual motion to wave signal generation; (b). Wave signal to gate signal generation; (c). Gate signal to beam on/off signal generation; (d). Beam on/off signal to the beam irradiation. The total delay time measured was 46 ms (beam on)/33 ms (beam off); these were within the prescribed tolerance time (<100 ms). Regarding the final flow test, an end-to-end test was performed with a patient verification system using an actual carbon-ion beam; the respiratory gating irradiation was successfully performed, in accordance with the intended timing. Finally, regarding the method for determining the threshold level of the gate generation of the respiration waveform, the target motion obtained from 4D-CT was assumed to be correlated with the waveform obtained from the pressure sensor; it was used to determine the threshold value in amplitude direction.

Tracking, gating, free-breathing, which technique to use for lung stereotactic treatments? A dosimetric comparison

BACKGROUND

The management of breath-induced tumor motion is a major challenge for lung stereotactic body radiation therapy (SBRT). Three techniques are currently available for these treatments: tracking (T), gating (G) and free-breathing (FB).

AIM

To evaluate the dosimetric differences between these three treatment techniques for lung SBRT.

MATERIALS AND METHODS

Pretreatment 4DCT data were acquired for 10 patients and sorted into 10 phases of a breathing cycle, such as 0% and 50% phases defined respectively as the inhalation and exhalation maximum. GTVph, PTVph (=GTVph + 3 mm) and the ipsilateral lung were contoured on each phase.For the tracking technique, 9 fixed fields were adjusted to each PTVph for the 10 phases. The gating technique was studied with 3 exhalation phases (40%, 50% and 60%). For the free-breathing technique, ITVFB was created from a sum of all GTVph and a 3 mm margin was added to define a PTVFB. Fields were adjusted to PTVFB and dose distributions were calculated on the average intensity projection (AIP) CT. Then, the beam arrangement with the same monitor units was planned on each CT phase.The 3 modalities were evaluated using DVHs of each GTVph, the homogeneity index and the volume of the ipsilateral lung receiving 20 Gy (V 20Gy).

RESULTS

The FB system improved the target coverage by increasing D mean (75.87(T)-76.08(G)-77.49(FB)Gy). Target coverage was slightly more homogeneous, too (HI: 0.17(T and G)-0.15(FB)). But the lung was better protected with the tracking system (V 20Gy: 3.82(T)-4.96(G)-6.34(FB)%).

CONCLUSIONS

Every technique provides plans with a good target coverage and lung protection. While irradiation with free-breathing increases doses to GTV, irradiation with the tracking technique spares better the lung but can dramatically increase the treatment complexity.

Single fraction carbon ion radiotherapy for colorectal cancer liver metastasis: A dose escalation study

Prognosis is usually grim for those with liver metastasis from colorectal cancer (CRC) who cannot receive resection. Radiation therapy can be an option for those unsuitable for resection, with carbon ion radiotherapy (CIRT) being more effective and less toxic than X-ray due to its physio-biological characteristics. The objective of this study is to identify the optimal dose of single fraction CIRT for colorectal cancer liver metastasis. Thirty-one patients with liver metastasis from CRC were enrolled in the present study. Twenty-nine patients received a single-fraction CIRT, escalating the dose from 36 Gy (RBE) in 5% to 10% increments until unacceptable incidence of dose-limiting toxicity was observed. Dose-limiting toxicity was defined as grade ≥3 acute toxicity attributed to radiotherapy. The prescribed doses were as follows: 36 Gy (RBE) (3 cases), 40 Gy (2 cases), 44 Gy (4 cases), 46 Gy (6 cases), 48 Gy (3 cases), 53 Gy (8 cases) and 58 Gy (3 cases). Dose-limiting toxicity was not observed, but late grade 3 liver toxicity due to biliary obstruction was observed in 2 patients at 53 Gy (RBE). Both cases had lesions close to the hepatic portal region, and, therefore, the dose was escalated to 58 Gy (RBE), limited to peripheral lesions. The 3-year actuarial overall survival rate of all 29 patients was 78%, and the median survival time was 65 months. Local control improved significantly at ≥53 Gy (RBE), with a 3-year actuarial local control rate of 82%, compared to 28% in lower doses. Treatment for CRC liver metastasis with single-fraction CIRT appeared to be safe up to 58 Gy (RBE) as long as the central hepatic portal region was avoided.

Radiobiological issues in prospective carbon ion therapy trials

Carbon ion radiotherapy (CIRT) is developing toward a versatile tool in radiotherapy; however, the increased relative biological effectiveness (RBE) of carbon ions in tumors and normal tissues with respect to photon irradiation has to be considered by mathematical models in treatment planning. As a consequence, dose prescription and definition of dose constraints are performed in terms of RBE weighted rather than absorbed dose. The RBE is a complex quantity, which depends on physical variables, such as dose and beam quality as well as on normal tissue- or tumor-specific factors. At present, three RBE models are employed in CIRT: (a) the mixed-beam model, (b) the Microdosimetric Kinetic Model (MKM), and (c) the local effect model. While the LEM is used in Europe, the other two models are employed in Japan, and unfortunately, the concepts of how the nominal RBE-weighted dose is determined and prescribed differ significantly between the European and Japanese centers complicating the comparison, transfer, and reproduction of clinical results. This has severe impact on the way treatments should be prescribed, recorded, and reported. This contribution reviews the concept of the clinical application of the different RBE models and the ongoing clinical CIRT trials in Japan and Europe. Limitations of the RBE models and the resulting radiobiological issues in clinical CIRT trials are discussed in the context of current clinical evidence and future challenges.

Short-course carbon-ion radiotherapy for hepatocellular carcinoma: A multi-institutional retrospective study

BACKGROUND & AIMS

Carbon-ion radiation therapy has shown encouraging results in hepatocellular carcinoma patients in single-centre studies. We evaluated the effectiveness and safety of short-course carbon-ion radiation therapy for hepatocellular carcinoma in a multicentre study conducted by the Japan Carbon Ion Radiation Oncology Study Group.

METHODS

Consecutive hepatocellular carcinoma patients who were treated with carbon-ion radiation therapy in four or fewer fractions at four Japanese institutions between April 2005 and November 2014 were analysed retrospectively. The primary outcome was overall survival; secondary outcomes were local control rate, treatment-related toxicity and radiation-induced liver disease.

RESULTS

A total of 174 patients were included in this study. Prescribed carbon-ion radiation therapy doses were (relative biological effectiveness): 48.0 Gy in two fractions (n = 46), and 52.8 Gy (n = 108) and 60.0 Gy (n = 20) in four fractions. The median follow-up period was 20.3 (range, 2.9-103.5) months. The overall survival and local control rates at 1, 2 and 3 years were 95.4%, 82.5% and 73.3%; and 94.6%, 87.7% and 81.0% respectively. Multivariate analysis revealed that Eastern Cooperative Oncology Group performance status 1-2, Child-Pugh class B, maximum tumour diameter ≥3 cm, multiple tumours and serum alpha foetoprotein level >50 ng/mL were significant prognostic factors of overall survival. No treatment-related death occurred during the follow-up period. Grades 3 or 4 treatment-related toxicities were observed in 10 patients (5.7%); radiation-induced liver disease was observed in three patients (1.7%).

CONCLUSIONS

Short-course carbon-ion radiation therapy is a safe, effective and potentially curative therapy for hepatocellular carcinoma.