Tolerance of normal tissue to therapeutic irradiation

First-In-Human Results on the Biodistribution, Pharmacokinetics, and Dosimetry of [177Lu]Lu-DOTA.SA.FAPi and [177Lu]Lu-DOTAGA.(SA.FAPi)2

Recently, great interest has been gained regarding fibroblast activation protein (FAP) as an excellent target for theranostics. Several FAP inhibitor molecules such as [68Ga]Ga-labelled FAPI-02, 04, 46, and DOTA.SA.FAPi have been introduced and are highly promising molecular targets from the imaging point of view. FAP inhibitors introduced via bifunctional DOTA and DOTAGA chelators offer the possibility to complex Lutetium-177 due to an additional coordination site, and are suitable for theranostic applications owing to the increased tumor accumulation and prolonged tumor retention time. However, for therapeutic applications, very little has been accomplished, mainly due to residence times of the compounds. In an attempt to develop a promising therapeutic radiopharmaceutical, the present study aimed to evaluate and compare the biodistribution, pharmacokinetics, and dosimetry of [177Lu]Lu-DOTA.SA.FAPi, and [177Lu]Lu-DOTAGA.(SA.FAPi)2 in patients with various cancers. The FAPi agents, [177Lu]Lu-DOTA.SA.FAPi and [177Lu]Lu-DOTAGA.(SA.FAPi)2, were administered in two different groups of patients. Three patients (mean age-50 years) were treated with a median cumulative activity of 2.96 GBq (IQR: 2.2-3 GBq) [177Lu]Lu-DOTA.SA.FAPi and seven (mean age-51 years) were treated with 1.48 GBq (IQR: 0.6-1.5) of [177Lu]Lu-DOTAGA.(SA.FAPi)2. Patients in both the groups underwent serial imaging whole-body planar and SPECT/CT scans that were acquired between 1 h and 168 h post-injection (p.i.). The residence time and absorbed dose estimate in the source organs and tumor were calculated using OLINDA/EXM 2.2 software. Time versus activity graphs were plotted to determine the effective half-life (Te) in the whole body and lesions for both the radiotracers. Physiological uptake of [177Lu]Lu-DOTA.SA.FAPi was observed in the kidneys, colon, pancreas, liver, gall bladder, oral mucosa, lacrimal glands, and urinary bladder contents. Physiological biodistribution of [177Lu]Lu-DOTAGA.(SA.FAPi)2 involved liver, gall bladder, colon, pancreas, kidneys, and urinary bladder contents, lacrimal glands, oral mucosa, and salivary glands. In the [177Lu]Lu-DOTA.SA.FAPi group, the highest absorbed doses were noted in the kidneys (0.618 ± 0.015 Gy/GBq), followed by the colon (right colon: 0.472 Gy/GBq and left colon: 0.430 Gy/GBq). In the [177Lu]Lu-DOTAGA.(SA.FAPi)2 group, the colon received the highest absorbed dose (right colon: 1.160 Gy/GBq and left colon: 2.870 Gy/GBq), and demonstrated a significantly higher mean absorbed dose than [177Lu]Lu-DOTA.SA.FAPi (p < 0.011). [177Lu]Lu-DOTAGA.(SA.FAPi)2 had significantly longer median whole-body Te compared to that of [177Lu]Lu-DOTA.SA.FAPi [46.2 h (IQR: 38.5-70.1) vs. 23.1 h (IQR: 17.8-31.5); p-0.0167]. The Te of tumor lesions was significantly higher for [177Lu]Lu-DOTAGA.(SA.FAPi)2 compared to [177Lu]Lu-DOTA.SA.FAPi [86.6 h (IQR: 34.3-94.6) vs. 14 h (IQR: 12.8-15.5); p-0.0004]. The median absorbed doses to the lesions were 0.603 (IQR: 0.230-1.810) Gy/GBq and 6.70 (IQR: 3.40-49) Gy/GBq dose per cycle in the [177Lu]Lu-DOTA.SA.FAPi, and [177Lu]Lu-DOTAGA.(SA.FAPi)2 groups, respectively. The first clinical dosimetry study demonstrated significantly higher tumor absorbed doses with [177Lu]Lu-DOTAGA.(SA.FAPi)2 compared to [177Lu]Lu-DOTA.SA.FAPi. [177Lu]Lu-DOTAGA.(SA.FAPi)2 is safe and unveiled new frontiers to treat various end-stage cancer patients with a theranostic approach.

Narrative review: prostate-specific membrane antigen-radioligand therapy in metastatic castration-resistant prostate cancer

Radioactive-labelled ligands targeting the prostate-specific membrane antigen (PSMA), a transmembrane protein overexpressed in prostate cancer (PC), have shown promising activity in treatment of metastatic castration-resistant prostate cancer (mCRPC). PSMA-617 and PSMA-I&T (imaging and therapy), both labeled to the beta-emitter lutetium-177 (Lu177), are most frequently used in clinical routine and have shown a favorable side-effect profile. Common side effects are transient xerostomia. Severe side effects, e.g., treatment-associated myelosuppression, are rare. Currently treatment with Lu177-PSMA outside clinical trials is available for compassionate use for patients who exhausted conventional therapies. Previous retro- and prospective studies reported promising results with ≥50% PSA declines observed in at least one third of patients. Retrospective data suggests worse biochemical response in patients with visceral metastases. Preliminary data from the randomized phase II (TheraP) trial showed an improved biochemical response rate of Lu177-PSMA as compared to cabazitaxel in patients progressing after docetaxel. Following these promising data, the results of the randomized, prospective phase III VISION study are eagerly anticipated. A major challenge remains resistance to radioligand therapy with Lu177-PSMA. As an alternative, a PSMA-ligand labeled to the alpha-emitter Actinium-225 (Ac-225) may be offered to patients, which shows promising activity in patients developing progression under Lu177-PSMA at the cost of higher toxicity. Mostly permanent xerostomia is a relevant side effect resulting in treatment discontinuation in up to a quarter of patients. This review summarizes the literature on activity and toxicity of PSMA-targeted radioligand therapy in mCRPC.

Normal tissue complication probability models for prospectively scored late rectal and urinary morbidity after proton therapy of prostate cancer

Background and purpose

Photons and protons have fundamentally different properties, i.e. protons have a reduced dose bath but a higher relative biological effectiveness. Photon-based normal tissue complication probability (NTCP) models may therefore not immediately be applicable to proton therapy (PT). The aim was to derive parameters of the Lyman-Kutcher-Burman (LKB) NTCP model using prospectively recorded late morbidity data from PT, focusing on rectal morbidity and prostate cancer.

Materials and methods

Prospectively collected data were available for 1151 prostate cancer patients treated with passive scattering PT and prescribed target doses of 78–82 Gy (RBE = 1.1) in 2 Gy fractions. Morbidity data (CTCAE v3.0) consisted of two alternative late grade 2 rectal bleeding endpoints: Medical Grade2A (GR2A) and procedural Grade2B (GR2B), as well as late grade 3 + urinary morbidity. GR2A + 2B were observed in 156/1047 patients (15%), GR2B in 45/1047 patients (4%), and urinary grade 3 + in 51/1151 patients (4%). LKB NTCP model parameters (D50, m, and n) were derived by maximum likelihood estimation.

Results

For the rectum/rectal wall the volume parameter n was low (0.07–0.14) for both GR2A + 2B and GR2B, as was the m parameter (range: 0.16–0.20). For the bladder/bladder wall both parameters were high (n-range: 0.20–0.36; m-range: 0.32–0.36). D50 parameters were higher for GR2B of the rectum/rectal wall (95.9–98.0 Gy) and bladder/bladder wall (118.1–119.9 Gy), but lower for GR2A2B (71.7–73.6 Gy).

Conclusion

PT specific LKB NTCP model parameters were derived from a population of more than 1000 patients. The D50 parameter differed for all structures and endpoints and deviated from typical photon-based LKB model values.

Hypofractionated preoperative radiotherapy for high risk soft tissue sarcomas in a geriatric patient population

Background

Standard therapy for localised, resectable high risk soft tissue sarcomas consists of wide excision and radiotherapy over several weeks. This treatment schedule is hardly feasible in geriatric and frail patients. In order not to withhold radiotherapy from these patients, hypofractionated radiotherapy with 25 Gy in 5 fractions was evaluated in a geriatric patient population.

Patients and methods

A retrospective analysis was performed of 18 geriatric patients with resectable high risk soft tissue sarcomas of extremities and thoracic wall. Wound healing and short term oncologic outcome were analysed. In addition, dose constraints for radiotherapy of the extremities were transferred from normofractionated to hypofractionated radiotherapy regimens.

Results

Feasibility was good with 17/18 patients completing treatment as planned. Wound healing complication rate was in the range of published data. Two patients developed local and distant recurrence, two patients isolated distant recurrences. No isolated local recurrences were observed. Keeping the constraints was possible in all cases without compromising the coverage of the target volume.

Conclusions

Hypofractionated radiotherapy and surgery was well tolerated even in this specific patient population. With feasibility concerning early wound healing problems and adapted constraints, which allow for the treatment of most resectable extremity tumours, the concept warrants further evaluation in patients unfit for standard radiotherapy.

Normal tissue complication probability modeling to guide individual treatment planning in pediatric cranial proton and photon radiotherapy

PURPOSE

Proton therapy (PT) is broadly accepted as the gold standard of care for pediatric patients with cranial cancer. The superior dose distribution of PT compared to photon radiotherapy reduces normal tissue complication probability (NTCP) for organs at risk. As NTCPs for pediatric organs are not well understood, clinics generally base radiation response on adult data. However, there is evidence that radiation response strongly depends on the age and even sex of a patient. Furthermore, questions surround the influence of individual intrinsic radiosensitivity (α/β ratio) on pediatric NTCP. While the clinical pediatric NTCP data is scarce, radiobiological modeling and sensitivity analyses can be used to investigate the NTCP trends and its dependence on individual modeling parameters. The purpose of this study was to perform sensitivity analyses of NTCP models to ascertain the dependence of radiosensitivity, sex, and age of a child and predict cranial side-effects following intensity-modulated proton therapy (IMPT) and intensity-modulated radiotherapy (IMRT).

METHODS

Previously, six sex-matched pediatric cranial datasets (5, 9, and 13 years old) were planned in Varian Eclipse treatment planning system (13.7). Up to 108 scanning beam IMPT plans and 108 IMRT plans were retrospectively optimized for a range of simulated target volumes and locations. In this work, dose-volume histograms were extracted and imported into BioSuite Software for radiobiological modeling. Relative-Seriality and Lyman-Kutcher-Burman models were used to calculate NTCP values for toxicity endpoints, where TD50, (based on reported adult clinical data) was varied to simulate sex dependence of NTCP. Plausible parameter ranges, based on published literature for adults, were used in modeling. In addition to sensitivity analyses, a 20% difference in TD50 was used to represent the radiosensitivity between the sexes (with females considered more radiosensitive) for ease of data comparison as a function of parameters such as α/β ratio.

RESULTS

IMPT plans resulted in lower NTCP compared to IMRT across all models (p < 0.0001). For medulloblastoma treatment, the risk of brainstem necrosis (> 10%) and cochlea tinnitus (> 20%) among females could potentially be underestimated considering a lower TD50 value for females. Sensitivity analyses show that the difference in NTCP between sexes was significant (p < 0.0001). Similarly, both brainstem necrosis and cochlea tinnitus NTCP varied significantly (p < 0.0001) across tested α/β as a function of TD50 values (assumption being that TD50 values are 20% lower in females). If the true α/β of these pediatric tissues is higher than expected (α/β ∼ 3), the risk of tinnitus for IMRT can significantly increase (p < 0.0001).

CONCLUSION

Due to the scarcity of pediatric NTCP data available, sensitivity analyses were performed using plausible ranges based on published adult data. In the clinical scenario where, if female pediatric patients were 20% more radiosensitive (lower TD50 value), they could be up to twice as likely to experience side-effects of brainstem necrosis and cochlea tinnitus compared to males, highlighting the need for considering the sex in NTCP models. Based on our sensitivity analyses, age and sex of a pediatric patient could significantly affect the resultant NTCP from cranial radiotherapy, especially at higher α/β values.

Practical kidney dosimetry in peptide receptor radionuclide therapy using [177Lu]Lu-DOTATOC and [177Lu]Lu-DOTATATE with focus on uncertainty estimates

Background

Kidney dosimetry after peptide receptor radionuclide therapy using ¹⁷⁷Lu-labelled somatostatin analogues is a procedure with multiple steps. We present the SPECT/CT-based implementation at Aarhus University Hospital and evaluate the uncertainty of the various steps in order to estimate the total uncertainty and to identify the major sources of uncertainty. Absorbed dose data from 115 treatment fractions are reported.

Results

The total absorbed dose with uncertainty is presented for 59 treatments with [¹⁷⁷Lu]Lu-DOTATOC and 56 treatments with [¹⁷⁷Lu]Lu-DOTATATE. For [¹⁷⁷Lu]Lu-DOTATOC the mean and median specific absorbed dose (dose per injected activity) is 0.37 Gy/GBq and 0.38 Gy/GBq, respectively, while for [¹⁷⁷Lu]Lu-DOTATATE the median and mean are 0.47 Gy/GBq and 0.46 Gy/GBq, respectively. The uncertainty of the procedure is estimated to be about 13% for a single treatment fraction, where the absorbed dose calculation is based on three SPECT/CT scans 1, 4 and 7 days post-injection, while it increases to about 19% if only a single SPECT/CT scan is performed 1 day post-injection.

Conclusions

The specific absorbed dose values obtained with the described procedure are comparable to those from other treatment sites for both [¹⁷⁷Lu]Lu-DOTATOC and [¹⁷⁷Lu]Lu-DOTATATE, but towards the lower end of the range of reported values. The estimated uncertainty is also comparable to that from other reports and judged acceptable for clinical and research use, thus proving the kidney dosimetry procedure a useful tool. The greatest reduction in uncertainty can be obtained by improved activity determination, partial volume correction and additional SPECT/CT scans.

Gel spacer to protect carotid artery and reconstructed jejunum in image-guided interstitial brachytherapy for recurrent hypopharyngeal cancer: a technical report

In this technical report, patient with total pharyngolaryngectomy and jejunum interposition experienced lymph node metastasis in the reconstructed mesenteric lymph nodes. Because this patient received 45 Gy of whole neck radiation therapy 24 years ago and small bowel's tolerance dose of the reconstructed jejunum was considered to be low, spacer gel injection was applied during image-guided interstitial brachytherapy to decrease doses to the reconstructed jejunum and previously irradiated carotid artery.

New curative approach using embolization followed by moderate-dose radiotherapy after surgical failure for large right heart metastasis

•

Rapid improvement observed in a patient with a large cardiac metastasis.

•

There is today no curative therapeutic option when the tumor is inoperable.

•

Transcoronary tumor embolization plus moderate targeted radiotherapy should be a new option for tumor control.

Purpose

Cardiac metastasis is a rare fatal event. An intracavitary right tumor mainly in the ventricle is difficult to manage. Literature reports suggest that cardiac surgery in oligometastatic patients could offer median survival of 1 year. We investigated salvage treatment comprising transcoronary tumor embolization followed 15 days later by cardiac radiotherapy (40.5 Gy/15 fractions).

Cases

We report two cases of severe right cardiac metastasis with a history of abdominal cancer managed by this salvage treatment following residual cardiac mass after previous cardiac surgery.

Conclusion

Both symptomatic patients improved progressively and were locally controlled for at least 1 year without toxicity.

Tolerance of Normal Rabbit Facial Bones and Teeth to Synchrotron X-Ray Microbeam Irradiation

Microbeam radiation therapy, an alternative radiosurgical treatment under preclinical investigation, aims to safely treat muzzle tumors in pet animals. This will require data on the largely unknown radiation toxicity of microbeam arrays for bones and teeth. To this end, the muzzle of six young adult New Zealand rabbits was irradiated by a lateral array of microplanar beamlets with peak entrance doses of 200, 330 or 500 Gy. The muzzles were examined 431 days postirradiation by computed microtomographic imaging (micro-CT) ex vivo, and extensive histopathology. The boundaries of the radiation field were identified histologically by microbeam tracks in cartilage and other tissues. There was no radionecrosis of facial bones in any rabbit. Conversely, normal incisor teeth exposed to peak entrance doses of 330 Gy or 500 Gy developed marked caries-like damage, whereas the incisors of the two rabbits exposed to 200 Gy remained unscathed. A single, unidirectional array of microbeams with a peak entrance dose ≤200 Gy (valley dose14 Gy) did not damage normal bone, teeth and soft tissues of the muzzle of normal rabbits longer than one year after irradiation. Because of that, Microbeam radiation therapy of muzzle tumors in pet animals is unlikely to cause sizeable damage to normal teeth, bone and soft tissues, if a single array as used here delivers a limited entrance dose of 200 Gy and a valley dose of ≤14 Gy.

A Review of the Role of Hypoxia in Radioresistance in Cancer Therapy

Hypoxia involves neoplastic cells. Unlike normal tissue, solid tumors are composed of aberrant vasculature, leading to a hypoxic microenvironment. Hypoxia is also known to be involved in both metastasis initiation and therapy resistance. Radiotherapy is the appropriate treatment in about half of all cancers, but loco-regional control failure and a disease recurrence often occur due to clinical radioresistance. Hypoxia induces radioresistance through a number of molecular pathways, and numerous strategies have been developed to overcome this. Nevertheless, these strategies have resulted in disappointing results, including adverse effects and limited efficacy. Additional clinical studies are needed to achieve a better understanding of the complex hypoxia pathways. This review presents an update on the mechanisms of hypoxia in radioresistance in solid tumors and the potential therapeutic solutions.

DMSA-SPECT: A Novel Approach to Nephron Sparing SBRT for Renal Cell Carcinoma

PURPOSE

Stereotactic body radiation therapy (SBRT) treatment planning for renal cell carcinoma requires accurate delineation of tumor from normal tissue due to the radiosensitivity of normal renal cortical tissue. Tc-99m dimercapto succinic acid (DMSA) renal imaging is a functional imaging technique that precisely differentiates normal renal cortical tissue from tumor. There are no prior publications reporting using this imaging modality for SBRT treatment planning.

METHODS AND MATERIALS

A 59-year-old female with stage IV renal cell carcinoma progressed on systemic therapy and was dispositioned to primary cytoreduction with SBRT. She had baseline renal dysfunction and her tumor was 9 cm without clear delineation from normal tissue on conventional imaging. DMSA-single-photon emission computerized tomography (SPECT)/computed tomography (CT) was used for treatment planning.

RESULTS

DMSA-SPECT/CT precisely delineated normal renal cortical tissue from tumor. Three months after treatment, labs were stable and DMSA-SPECT/CT was unchanged. The treated lesion had markedly decreased positron emission tomography avidity.

CONCLUSIONS

DMSA-SPECT or SPECT/CT can be incorporated into radiation therapy planning for renal lesions to improve target delineation and better preserve renal function.

The impact of nutritional counseling on thyroid disorders in head and neck cancer patients after (chemo)radiotherapy: results from a prospective interventional trial

Objective

To analyze the impact of nutritional counseling on the development of hypothyroidism after (chemo)radiotherapy in head and neck cancer patients to propose a new normal tissue complication probability (NTCP) model.

Materials and methods

At baseline, at the end of (chemo)radiotherapy, and during follow-up, thyroid-stimulating hormone (TSH) with free thyroxin (fT3 and fT4), nutritional status, and nutrient intake were prospectively analyzed in 46 out of 220 screened patients. Patients received (chemo)radiotherapy within an intervention (individual nutritional counseling every 2 weeks during therapy) and a control group (no nutritional counseling).

Results

Overall median follow-up was 16.5 [IQR: 12; 22] months. Fourteen patients (30.4%) presented with hypothyroidism after 13.5 [8.8; 17] months. During (chemo)radiotherapy, nutritional status worsened in the entire cohort: body mass index (p < 0.001) and fat-free mass index (p < 0.001) decreased, calorie deficit (p = 0.02) increased, and the baseline protein intake dropped (p = 0.028). The baseline selenium intake (p = 0.002) increased until the end of therapy. Application of the NTCP models by Rønjom, Cella, and Boomsma et al. resulted in good performance of all three models, with an AUC ranging from 0.76 to 0.78. Our newly developed NTCP model was based on baseline TSH and baseline ferritin. Model performance was good, receiving an AUC of 0.76 (95% CI: 0.61–0.87), with a sensitivity of 57.1% and specificity of 96.9% calculated for a Youden index of 0.73 (p = 0.004; area = 0.5).

Conclusion

Baseline TSH and ferritin act as independent predictors for radiotherapy-associated hypothyroidism. The exclusion of such laboratory chemistry parameters in future NTCP models may result in poor model performance.

Current emerging MRI tools for radionecrosis and pseudoprogression diagnosis

PURPOSE OF REVIEW

This review aims to cover current MRI techniques for assessing treatment response in brain tumors, with a focus on radio-induced lesions.

RECENT FINDINGS

Pseudoprogression and radionecrosis are common radiological entities after brain tumor irradiation and are difficult to distinguish from real progression, with major consequences on daily patient care. To date, shortcomings of conventional MRI have been largely recognized but morphological sequences are still used in official response assessment criteria. Several complementary advanced techniques have been proposed but none of them have been validated, hampering their clinical use. Among advanced MRI, brain perfusion measures increase diagnostic accuracy, especially when added with spectroscopy and susceptibility-weighted imaging. However, lack of reproducibility, because of several hard-to-control variables, is still a major limitation for their standardization in routine protocols. Amide Proton Transfer is an emerging molecular imaging technique that promises to offer new metrics by indirectly quantifying intracellular mobile proteins and peptide concentration. Preliminary studies suggest that this noncontrast sequence may add key biomarkers in tumor evaluation, especially in posttherapeutic settings.

SUMMARY

Benefits and pitfalls of conventional and advanced imaging on posttreatment assessment are discussed and the potential added value of APT in this clinicoradiological evolving scenario is introduced.

Can volumetric modulated arc radiation therapy reduce organ at risk dose in stage 4 sinonasal tumors in dogs treated with boost irradiation?

Intensity modulated radiation therapy (IMRT) introduced marked changes to cancer treatment in animals by reducing dose to organs at risk (OAR). As the next technological step, volumetric modulated arc therapy (VMAT) has advantages (increased degrees-of-freedom, faster delivery) compared to fixed-field IMRT. Our objective was to investigate a possible advantage of VMAT over IMRT in terms of lower OAR doses in advanced-disease sinonasal tumors in dogs treated with simultaneously-integrated boost radiotherapy. A retrospective, analytical, observational study design was applied using 10 pre-existing computed tomography datasets on dogs with stage 4 sinonasal tumors. Each dataset was planned with both, 5-field IMRT and 2 arc VMAT with 10x4.83 Gy to the gross tumor volume and 10x4.2 Gy to the planning target volume. Adequate target dose coverage and normal tissue complication probability of brain ≤5% was required. Dose constraints aspired to were D60 <15 Gy for eyes, D2 <35.4 Gy for corneae, and Dmean <20 Gy for lacrimal glands. OAR dose was statistically significantly higher in IMRT plans than in VMAT plans. Median eye D60% was 18.5 Gy (interquartile range (IQR) 17.5) versus 16.1 Gy (IQR 7.4) (p = 0.007), median lacrimal gland dose 21.8 Gy (IQR 20.5) versus 18.6 Gy (IQR 7.0) (p = 0.013), and median cornea D2% 45.5 Gy (IQR 6.8) versus 39.9 Gy (IQR 10.0) (p<0.005) for IMRT versus VMAT plans, respectively. Constraints were met in 21/40 eyes, 7/40 corneae, and 24/40 lacrimal glands. Median delivery time was significantly longer for IMRT plans than for VMAT plans (p<0.01). Based on these results, VMAT plans were found to be superior in sparing doses to eyes, lacrimal glands, corneae. However, not all ocular OAR constraints could be met while ensuring adequate dose coverage and restricting brain toxicity risk for both planning techniques.

Sox9+ cells are required for salivary gland regeneration after radiation damage via the Wnt/β-catenin pathway

Radiotherapy for head and neck cancer can cause serious side effects, including severe damage to the salivary glands, resulting in symptoms such as xerostomia, dental caries, and oral infection. Due to the lack of long-term treatment for the symptoms of xerostomia, current research has focused on finding endogenous stem cells that can differentiate into various cell lineages to replace lost tissue and restore functions. Here, we report that Sox9⁺ cells can differentiate into various salivary epithelial cell lineages under homeostatic conditions. After ablating Sox9⁺ cells, the salivary glands of irradiated mice showed more severe phenotypes and the reduced proliferative capacity. Analysis of online single-cell RNA-sequencing data reveals the enrichment of the Wnt/β-catenin pathway in the Sox9⁺ cell population. Furthermore, treatment with a Wnt/β-catenin inhibitor in irradiated mice inhibits the regenerative capability of Sox9⁺ cells. Finally, we show that Sox9⁺ cells are capable of forming organoids in vitro and that transplanting these organoids into salivary glands after radiation partially restored salivary gland functions. These results suggest that regenerative therapy targeting Sox9⁺ cells is a promising approach to treat radiation-induced salivary gland injury.

PSMA targeting in metastatic castration-resistant prostate cancer: where are we and where are we going?

Prostate-specific membrane antigen (PSMA) is highly expressed on the membrane of most prostate cancer cells and to a lesser extent in normal tissues. Many vectors targeting this protein have been created over the past decade and numerous clinical studies have positively demonstrated the tolerance and efficacy of radiolabeled prostate-specific membrane antigen ligands for PSMA radioligand therapy (PRLT). Preliminary results are encouraging that PRLT will become an important addition to the current therapeutic options in a number of settings. Improvement in radiopharmaceutical targeting and combination with other oncological agents are under investigation to further improve its therapeutic efficacy. These encouraging results have led to the development of other therapies using PSMA as a target, such as PSMA-targeted chimeric antigen receptor T-cells, PSMA-targeted antibody drug conjugates, and PSMA-targeted bi-specific T-cell-directed therapy. This narrative review details the current state and advancements in prostate-specific membrane antigen targeting in prostate cancer treatment.

The Impact of Pelvic Nodal Radiotherapy on Hematologic Toxicity: A Systematic Review with Focus on Leukopenia, Lymphopenia and Future Perspectives in Prostate Cancer Treatment

INTRODUCTION

Hematologic toxicity (HT), particularly leukopenia, is a common side-effect of oncologic treatments for pelvic malignancies. Pelvic nodal radiotherapy (PNRT) has been associated with HT development mainly through incidental bone marrow (BM) irradiation; however, several questions remain about the clinical impact of radiotherapy-related HT. Herein, we perform a systematic review of the available evidence on PNRT and HT.

MATERIALS AND METHODS

A comprehensive systematic literature search was performed through EMBASE. Hand searching and clinicaltrials.gov were also used.

RESULTS

While BM-related dose-volume parameters and BM-sparing techniques have been more thoroughly investigated in pelvic malignancies such as cervical, anal, and rectal cancers, the importance of BM as an organ-at-risk has received less attention in prostate cancer treatment.

CONCLUSIONS

We examined the available evidence regarding the impact of PNRT on HT, with a focus on prostate cancer treatment. We suggest that BM should be regarded as an organ-at-risk for patients undergoing PNRT.

Multi-institutional Comparison of Intensity Modulated Photon Versus Proton Radiation Therapy in the Management of Squamous Cell Carcinoma of the Anus

Purpose

Concurrent chemoradiation therapy is a curative treatment for squamous cell carcinoma of the anus, but patients can suffer from significant treatment-related toxicities. This study was undertaken to determine whether intensity modulated proton therapy (IMPT) is associated with less acute toxicity than intensity modulated radiation therapy (IMRT) using photons.

Materials and Methods

We performed a multi-institutional retrospective study comparing toxicity and oncologic outcomes of IMRT versus IMPT. Patients with stage I-IV (for positive infrarenal para-aortic or common iliac nodes only) squamous cell carcinoma of the anus, as defined by the American Joint Committee on Cancer's AJCC Staging Manual, eighth edition, were included. Patients with nonsquamous histology or mixed IMPT and IMRT treatment courses were excluded. Acute nonhematologic toxicities, per the National Cancer Institute's Common Terminology Criteria for Adverse Events (CTCAE), version 4, were recorded prospectively at all sites. Acute and late toxicities, dose metrics, and oncologic outcomes were compared between IMRT and IMPT using univariable and multivariable statistical methods. To improve the robustness of our analysis, we also analyzed the data using propensity score weighting methods.

Results

A total of 208 patients were treated with either IMPT (58 patients) or IMRT (150 patients). Of the 208 total patients, 13% had stage I disease, 36% stage II, 50% stage III, and 1% stage IV. IMPT reduced the volume of normal tissue receiving low-dose radiation but not high-dose radiation to bladder and bowel. There was no significant difference between treatment groups in overall grade 3 or greater acute toxicity (IMRT, 68%; IMPT, 67%; P = .96) or 2-year overall grade 3 or greater late toxicity (IMRT, 3.5%; IMPT, 1.8%; P = .88). There was no significant difference in 2-year progression-free survival (hazard ratio, 0.8; 95% CI, 0.3-2.0).

Conclusions

Despite reducing the volume of normal tissue receiving low-dose radiation, IMPT was not associated with decreased grade 3 or greater acute toxicity as measured by CTCAE. Additional follow-up is needed to assess whether important differences arise in late toxicities and if further prospective evaluation is warranted.

ACTIVITY CONCENTRATION ESTIMATION IN AUTOMATED KIDNEY SEGMENTATION BASED ON CONVOLUTION NEURAL NETWORK METHOD FOR 177LU-SPECT/CT KIDNEY DOSIMETRY

For 177Lu-DOTATATE treatments, dosimetry based on manual kidney segmentation from computed tomography (CT) is accurate but time consuming and might be affected by misregistration between CT and SPECT images. This study develops a convolution neural network (CNN) for automated kidney segmentation that accurately aligns CT segmented volume of interest (VOI) to the kidneys in SPECT images. The CNN was trained with SPECT/CT images performed over the abdominal area of 137 patients treated with 177Lu-DOTATATE. Activity concentrations in automated and manual segmentations were strongly correlated for both kidneys (r > 0.96, p < 0.01) in the testing cohort (n = 20). The Bland-Altman analyses demonstrated higher accuracy for the CNN segmentation compared to the manual segmented kidneys without VOI adjustment. The CNN demonstrated a potential for accurate kidney segmentation. The CNN was a fast and robust approach for assessment of activity concentrations in SPECT images, and performed equally well as the manual segmentation method.

Lobar Radioembolization for Intermediate and Advanced Hepatocellular Carcinoma: Retrospective and Prospective Data

Historically, outcomes reporting for radioembolization with yttrium-90 ( ⁹⁰ Y) of hepatocellular carcinoma has included patients across the range of Barcelona Clinic Liver Cancer (BCLC) stages. With the potential for curative radiation segmentectomy for BCLC 0/A patients and evolution of systemic therapy for BCLC C patients, focused review by group is of increasing interest. In this review, we report on efficacy of ⁹⁰ Y in patients with intermediate (BCLC B) and advanced (BCLC C) hepatocellular carcinoma as well as expected toxicities. Additionally, we review existing trials comparing ⁹⁰ Y to transarterial chemoembolization and systemic treatments in these patient groups and outline future studies.

Radioimmunotherapy for solid tumors: spotlight on Glypican-1 as a radioimmunotherapy target

Radioimmunotherapy (i.e., the use of radiolabeled tumor targeting antibodies) is an emerging approach for the diagnosis, therapy, and monitoring of solid tumors. Often using paired agents, each targeting the same tumor molecule, but labelled with an imaging or therapeutic isotope, radioimmunotherapy has achieved promising clinical results in relatively radio-resistant solid tumors such as prostate. Several approaches to optimize therapeutic efficacy, such as dose fractionation and personalized dosimetry, have seen clinical success. The clinical use and optimization of a radioimmunotherapy approach is, in part, influenced by the targeted tumor antigen, several of which have been proposed for different solid tumors. Glypican-1 (GPC-1) is a heparan sulfate proteoglycan that is expressed in a variety of solid tumors, but whose expression is restricted in normal adult tissue. Here, we discuss the preclinical and clinical evidence for the potential of GPC-1 as a radioimmunotherapy target. We describe the current treatment paradigm for several solid tumors expressing GPC-1 and suggest the potential clinical utility of a GPC-1 directed radioimmunotherapy for these tumors.

Comparison of dose volumetric parameters of oesophagus in the radiation treatment of carcinoma breast with and without oesophagus delineation

Aim:

There are only limited studies available in literature that discuss methods to reduce the oesophageal dose and acute oesophagitis during breast cancer radiotherapy. The aim of this study is to compare dose volumetric parameters of oesophagus in radiation treatment of breast with and without oesophagus delineation.

Methods:

Treatment plans of 44 patients, who underwent chest wall and supraclavicular fossa irradiation, were selected for the study. Oesophagus was later delineated and treatment replanned using three-dimensional conformal radiotherapy (3DCRT) considering oesophagus as an organ at risk (OAR). The dose prescribed was 40 Gy/15 fractions to the planning target volume (PTV). Dose volumetric parameters of oesophagus such as maximum dose (Dmax), mean dose (Dmean), the percentage of oesophagus volume receiving ≥15Gy (V15), ≥25Gy(V25), ≥33Gy(V33) and ipsilateral lung volume parameters V4, V8 and V16 were compared with already executed plans in which oesophagus was not delineated.

Results:

Contouring the oesophagus as an OAR as a part of the radiotherapy treatment for Carcinoma Breast resulted in statistically significant reduction in dose to the oesophagus. No statistically significant change was found in the ipsilateral lung volume parameters. No compromise in plan quality was required as evident from the statistically non-significant differences in Homogeneity index and Conformity index.

Findings:

3DCRT planning with oesophagus delineation can be considered as a method to reduce oesophageal dose and the acute oesophageal toxicity during radiotherapy for carcinoma breast.

Pediatric Craniospinal Irradiation - The implementation and Use of Normal Tissue Complication Probability in Comparing Photon versus Proton Planning

Purpose:

The preferred radiotherapy treatment for medulloblastoma is craniospinal irradiation (CSI). With the aim of developing the potential to reduce normal tissue dose and associated post-treatment complications with photon and proton radiotherapy techniques for CSI. This report aims to carefully compare and rank treatment planning and dosimetric outcomes for pediatric medulloblastoma patients using normal tissue complication probability (NTCP) formalism between photon (three-dimensional conformal radiotherapy, intensity-modulated radiotherapy [IMRT], volumetric-modulated arc therapy [VMAT], and HT) and proton CSI.

Methods and Materials:

The treatment data of eight pediatric patients who typically received CSI treatment were used in this study. The patients were 7 years of age on average, with ages ranging from 3 to 11 years. A prescription dose of 3600 cGy was delivered in 20 fractions by the established planning methods. The Niemierko's and Lyman–Kutcher–Burman models were followed to carefully estimate NTCP and compare different treatment plans.

Results:

The NTCP of VMAT plans in upper and middle thoracic volumes was relatively high compared to helical tomotherapy (HT) and pencil beam scanning (PBS) (all P < 0.05). PBS rather than IMRT and VMAT in the middle thoracic region (P < 0.06) could significantly reduce the NTCP of the heart. PBS significantly reduced NTCP of the lungs and liver (all P < 0.05).

Conclusion:

The NTCP and tumor control probability (TCP) model-based plan ranking along with dosimetric indices will help the clinical practitioner or medical physicists to choose the best treatment plan for each patient based on their anatomical or clinical challenges.

Prospective evaluation of organ-specific dose and lesional doses following therapeutic [177Lu]Lu-EDTMP administration in patients with multiple skeletal metastases and its correlation with clinical hematological toxicity

AIM

In patients with multiple skeletal metastases, accurate estimation of absorbed doses to radiosensitive bone marrow in bone-directed systemic radionuclide therapies (RNT) is critically important from clinical dose determination standpoint. The primary aim of the present study was to estimate the radiation absorbed doses of therapeutic [177Lu]Lu-EDTMP to bone marrow by two methods viz. Medical Internal Radiation Dose (MIRD) schema and using OLINDA software and correlate with hematological toxicity.

METHODS

A total of 15 patients diagnosed to have multiple painful skeletal metastases being treated with [177Lu]Lu-EDTMP for palliation of pain, were enrolled for this prospective study. For all patients, urine was collected immediately after infusion of [177Lu]Lu-EDTMP up to 24 h post-administration and cumulative activity excreted from body via urine was calculated. For dosimetry, patients underwent post-administration whole-body scintigraphy at five-time points: 0.5 (pre-void), 2, 24, 48 and 120 h (post-void). From the time-activity curves generated by drawing regions of interest (ROIs) on the images, number of disintegrations was determined. Absorbed doses for organs and bone lesions were calculated using OLINDA 2.2.0 software. For bone marrow dose estimates, in addition to OLINDA 2.2.0 software, MIRD schema was also adopted. Hematological profile was monitored in all patients during the treatment and post-treatment follow-up (estimating complete blood counts, every 15 d for 3 months after therapy).

RESULTS

The mean ± standard deviation activity of [177Lu]Lu-EDTMP administered per patient per cycle was 2.08 ± 0.45 GBq. The results demonstrated higher uptake of [177Lu]Lu-EDTMP in bone metastases compared to normal bones. Within 2 and 24 h of administration of [177Lu]Lu-EDTMP, [177Lu]Lu activity excreted from the body was 24 ± 9% and 39 ± 14%, respectively. The mean absorbed organ doses (mean ± SD) in Gy/GBq were as follows: osteogenic cells 3.15 ± 1.85, bone marrow 0.57 ± 0.31, kidneys 0.08 ± 0.05, urinary bladder 0.32 ± 0.04, and bone lesions 2.91 ± 1.88. Strong correlation was found between (a) MIRD schema and OLINDA 2.2.0 software method for estimation of bone marrow doses (r = 0.96; P = <0.0001) and (b) Bone marrow absorbed dose and hematological toxicity (r = 0.81, P = 0.0027).

CONCLUSION

Radiation absorbed doses to the bone marrow and skeletal metastatic lesions, following therapeutic [177Lu]Lu-EDTMP were estimated using a convenient and non-invasive quantitative imaging method. The estimated bone marrow absorbed dose, either by MIRD schema or the OLINDA 2.2.0 software method, demonstrated strong correlation. Strong correlation was also observed between bone marrow absorbed dose and hematological toxicity.

Reassessment of the lung dose limits for radioembolization

Radioembolization, also known as selective internal radiation therapy (SIRT), is an established treatment for the management of patients with unresectable liver tumors. Advances in liver dosimetry and new knowledge about tumor dose-response relationships have helped promote the well-tolerated use of higher prescribed doses, consequently transitioning radioembolization from palliative to curative therapy. Lung dosimetry, unfortunately, has not seen the same advances in dose calculation methodology and renewed consensus in dose limits as normal liver and tumor dosimetry. Therefore, the efficacy of curative radioembolization may be compromised in patients where the current lung dose calculations unnecessarily limit the administered activity. The field is thus at a stage where a systematic review and update of lung dose limits is necessary to advance the clinical practice of radioembolization. This work summarizes the historical context and literature for origins of the current lung dose limits following radioembolization, that is, the 25-year-old, single institution, small patient cohort series that helped establish the lung shunt fraction and dose limits. Newer clinical evidence based on larger patient cohorts that challenges the historical data on lung dose limits are then discussed. We conclude by revisiting the rationale for current lung dose limits and by proposing a staged approach to advance the field of lung dosimetry and thus the practice of radioembolization as a whole.

Safety of PSMA-Targeted Molecular Radioligand Therapy with 177Lu-PSMA-617: Results from the Prospective Multicenter Phase 2 Trial RESIST-PC (NCT03042312)

The purpose of this analysis was to report the safety evaluation of 177Lu-PSMA-617 derived from the cohort of 64 patients exposed to 177Lu-PSMA-617 in the RESIST-PC trial NCT03042312 Methods: RESIST-PC was a prospective multicenter phase 2 trial. Patients with progressive metastatic castration-resistant prostate cancer after ≥ 1 novel androgen-axis drug, either chemotherapy naïve or postchemotherapy, with sufficient bone marrow reserve, normal kidney function, sufficient PSMA expression by PSMA PET, and no PSMA-negative soft-tissue lesions were eligible. Patients were randomized (1:1) into 2 activity groups (6.0 or 7.4 GBq per cycle) and received up to 4 cycles every 8 wk. The primary safety endpoint was assessed by collecting and grading adverse events using the Common Terminology Criteria for Adverse Events. Patients were followed until disease progression, death, serious or intolerable adverse events, study termination by sponsor, patient withdrawal, lost to follow-up, or 24 mo after the first cycle. Results: The study was closed at enrollment of 71 of 200 planned patients because of sponsorship transfer. A total of 64 (90.1%) patients received at least 1 cycle of 177Lu-PSMA-617: 28 (36%) in arm 1 (6.0 GBq) and 41 (64%) in arm 2 (7.4 GBq). There were 10 (43.5%), 19 (46.5%), and 29 (45.3%) patients who completed 4 cycles of 177Lu-PSMA-617 in the 6.0-GBq arm, 7.4-GBq arm, and overall, respectively. The most common treatment-emergent adverse events (TEAEs) of any grade in the 6.0-GBq arm, the 7.4-GBq arm and overall, were dry mouth (47.8%; 63.4%; 57.8%, respectively), fatigue (56.5%; 51.2%; 53.1%, respectively), nausea (52.2%; 43.9%; 46.9%, respectively), and diarrhea (13.0%; 31.7%; 25.0%, respectively). Frequencies of all other TEAEs were comparable among the 2 groups (within 10% difference). Serious possibly drug-related TEAEs were reported for 5 (7.8%) patients overall (none were considered as probably or definitely related to treatment): 1 subdural hematoma grade 4, 1 anemia grade 3, 1 thrombocytopenia grade 4, 1 gastrointestinal hemorrhage grade 3, and 1 acute kidney injury grade 3. There were no clinically significant changes in vital signs in electrocardiograms in the 2 treatment groups. No trend to creatinine increase or increasing frequency of shifts from normal to abnormal over time for any hematologic parameter was noted. Conclusion:177Lu-PSMA-617 was safe and well-tolerated at 6.0 and 7.4 GBq per cycle given at 8-wk intervals with side effects easily managed with standard medical support. With established safety, further clinical trials applying individualized dosimetry and testing different 177Lu-PSMA-617 administration schemes (activity levels, time intervals) are needed to optimize tumor dose delivery and treatment efficacy.

Radiotherapy for a rare phosphaturic mesenchymal tumor in the middle ear presenting with oncogenic osteomalacia: A case report

RATIONALE

Phosphaturic mesenchymal tumor (PMT) is a rare neoplasm causing oncogenic osteomalacia. Surgery remains the definitive treatment for PMT, and radiotherapy is seldom employed. However, surgery for PMT involving the head and neck is often difficult due to the local invasion and complicated anatomy. We report the first case of PMT, which was successfully treated with the combination of radiotherapy and supplementation of activated vitamin D.

PATIENT CONCERNS

A 55-year-old woman suffered from pain in the hip and bilateral femur. Serum phosphate and calcium decreased to abnormal levels. Serum alkaline phosphatase and fibroblast growth factor 23 increased to abnormal levels. The hearing loss of the right ear had continued and a middle ear tumor was revealed.

DIAGNOSES

Subsequent biopsy provided the diagnosis of PMT that caused oncogenic osteomalacia. These clinical and pathological characteristics were consistent with and provided the final diagnosis of benign PMT.

INTERVENTIONS

Surgery of the PMT was difficult and the patient underwent radiotherapy. The prescribed dose was 36 Gy in 10 fractions. Simultaneously, the patient started supplementation of 1,25-dihydroxyvitamin D3 (1-2 μg/day) and continued for 2 years.

OUTCOMES

Near-complete resolution of the symptoms was achieved and abnormal laboratory values recovered. At 5 years of follow-up, the irradiated tumor showed no regrowth. Severe hearing loss of the right ear was not observed.

LESSONS

Radiotherapy was effective for the PMT and could be an important treatment option for inoperable cases.

Mean heart dose-based normal tissue complication probability model for pericardial effusion: a study in oesophageal cancer patients

We investigated the normal tissue complication probability (NTCP) of the incidence of pericardial effusion (PCE) based on the mean heart dose (MHD) in patients with oesophageal cancer treated with definitive chemoradiotherapy. The incidences of PCE in any grade (A-PCE) and symptomatic PCE (S-PCE) were evaluated separately. To identify predictors for PCE, several clinical and dose-volume parameters were analysed using a receiver operating characteristic (ROC) curve and multivariate regression analysis. To validate its clinical applicability, the generated NTCP model was compared to the Lyman–Kutcher–Burman (LKB) model. Among 229 eligible patients, A-PCE and S-PCE were observed in 100 (43.7%) and 18 (7.9%) patients, respectively. MHD showed a preferable area under the curve (AUC) value for S-PCE (AUC = 0.821) and A-PCE (AUC = 0.734). MHD was the only significant predictor for A-PCE; MHD and hypertension were selected as significant factors for S-PCE. The estimated NTCP, using the MHD-based model, showed excellent correspondence to the LKB model in A-PCE and S-PCE. The NTCP curve of A-PCE was gentler than that of S-PCE and had no threshold. The MHD-based NTCP model was simple but comparable to the LKB model for both A-PCE and S-PCE. Therefore, the estimated NTCP may provide clinically useful parameters for predicting PCE.

The Impact of Monosodium Glutamate on 68Ga-PSMA-11 Biodistribution in Men with Prostate Cancer: A Prospective Randomized, Controlled Imaging Study

The prostate-specific membrane antigen (PSMA) has been targeted for PET imaging and radioligand therapy (RLT) in patients with prostate cancer. Xerostomia is a common side effect of RLT because of the high salivary gland uptake of PSMA radioligands. Here, we aimed to determine the impact of monosodium glutamate (MSG) administration on PSMA-radioligand biodistribution within healthy organs and tumor lesions by using 68Ga-PSMA-11 PET imaging. Methods: Sixteen men with prostate cancer were randomized (1:1) into oral ingestion and oral topical application ("swishing") arms. Each subject underwent 2 68Ga-PSMA-11 PET/CT scans within 14 d under baseline and MSG conditions. The salivary glands and whole-body tumor lesions were segmented using qPSMA software. We quantified tracer uptake via SUVmean and SUVmax and compared parameters within each patient. Results: For the oral ingestion arm, salivary gland SUVmean and SUVmax decreased on average from the control scan to the MSG scan by 45% ± 15% (P = 0.004) and 53% ± 11% (P < 0.001), respectively. Tumor lesion SUVmean and SUVmax also decreased by 38% (interquartile range, -67% to -33%) and -52% (interquartile range, -70% to -49%), respectively (P = 0.018). Swishing had no significant effect on 68Ga-PSMA-11 accumulation in normal organs or tumor lesions. Conclusion: Oral ingestion but not topical application of MSG reduced 68Ga-PSMA-11 uptake in salivary glands. Tumor uptake also declined; therefore, the clinical application of MSG is unlikely to be useful in the framework of RLT.

Radiation therapy-associated toxicity: Etiology, management, and prevention

Radiation therapy (RT) is a curative treatment for many malignancies and provides effective palliation in patients with tumor-related symptoms. However, the biophysical effects of RT are not specific to tumor cells and may produce toxicity due to exposure of surrounding organs and tissues. In this article, the authors review the clinical context, pathophysiology, risk factors, presentation, and management of RT side effects in each human organ system. Ionizing radiation works by producing DNA damage leading to tumor death, but effects on normal tissue may result in acute and/or late toxicity. The manifestation of toxicity depends on both cellular characteristics and affected organs' anatomy and physiology. There is usually a direct relationship between the radiation dose and volume to normal tissues and the risk of toxicity, which has led to guidelines and recommended dose limits for most tissues. Side effects are multifactorial, with contributions from baseline patient characteristics and other oncologic treatments. Technological advances in recent decades have decreased RT toxicity by dramatically improving the ability to deliver RT that maximizes tumor dose and minimizes organ dose. Thus the study of RT-associated toxicity is a complex, core component of radiation oncology training that continues to evolve alongside advances in cancer management. Because RT is used in up to one-half of all patients with cancer, an understanding of its acute and late effects in different organ systems is clinically pertinent to both oncologists and nononcologists.

Automated robust SBPT planning using EUD-based prediction of SBRT plan for patients with lung cancer

PURPOSE

To evaluate the quality of robust stereotactic body proton therapy (RSBPT) plans generated by one-clicking scripting method for patients with lung cancer.

MATERIALS AND METHODS

Retrospective analysis was performed on fifty lung cancer patients whose plan with robustly stereotactic body radiation therapy (SBRT). Thirty out of fifty patients were used for training to build a regression model, based on robust SBRT reference doses, to predict EUD values of ROIs for robust SBPT planning. Thereafter, robust SBPT plans with both automated EUD-Based mimicking (Automated Robust Proton ARP) and manual (Manual Robust Proton MRP) methods were evaluated in the remaining 20 patients. Plans were compared in terms of dosimetric parameters and planning time.

RESULTS

A statistically significantly improvement in target dose fall off was observed for ARP plans compare to MRP plans (Dose fall off: 135 for MRP and 88 for ARP, p < 0.01), while no differences in target coverage and conformity. A statistically significantly reduce in normal lung tissue were observed for ARP plans compare to MRP plans (Lung [D_mean cGy (RBE)]: MRP: 478 vs. ARP: 351, p < 0.01; Lung [V_{5Gy (RBE)} (%)]: MRP: 16.1 vs. ARP: 12.1, p < 0.01; Lung [V_{20Gy (RBE)} (%)]: MRP: 8.5 vs. ARP: 6.8, p < 0.01). Planning time was reduced for ARP plans compare to MRP plans (optimization time: 12 min for MRP vs. 8 min for ARP; total plan time: 23 min for MRP vs. 18 min for ARP).

CONCLUSION

The automated robust SBPT plans using EUD-Based mimicking of SBRT reference dose improve target dose fall off, reduced the radiation doses to the lungs, reduce planning time, which might be beneficial for patient with lung cancer in clinical.

Differences in radiotherapy application according to regional disease characteristics of hepatocellular carcinoma

There are differences in opinion regarding the application of external beam radiotherapy in the treatment of hepatocellular carcinoma. Some major guidelines state that external beam radiotherapy is yet to attain a sufficient level of evidence. However, caution should be exercised when attempting to understand the clinical need for external beam radiotherapy solely based on the level of evidence. Previously, external beam radiotherapy had low applicability in the treatment of hepatocellular carcinoma before computed tomography-based planning was popularized. Modern external beam radiotherapy can selectively target tumor cells while sparing normal liver tissues. Recent technologies such as stereotactic body radiotherapy have enabled more precise treatment. The characteristics of hepatocellular carcinoma differ significantly according to the regional etiology. The main cause of hepatocellular carcinoma is the hepatitis B virus. It is commonly diagnosed as a locally advanced tumor but with relatively preserved hepatic function. The majority of these hepatocellular carcinoma cases are found in the East Asian population. Hepatocellular carcinoma caused by hepatitis C virus or other benign hepatitis tends to be diagnosed as a less locally aggressive tumor but with deteriorated liver function. The western world and Japan tend to have patients with such causes. External beam radiotherapy has been more commonly performed for the former, although the use of external beam radiotherapy in the latter might have more concerns with regard to hepatic toxicity. This review discusses the above subjects along with perspectives regarding external beam radiotherapy in recent guidelines.

Neuro-ophthalmologic outcomes of standard versus hypo-fractionated stereotactic radiotherapy of AVPM

BACKGROUND

Most anterior visual pathway meningiomas (AVPM) are benign and slow-growing, but these tumors may affect visual functions, including visual acuity (VA) and visual field (VF). Due to location, most are treated non-surgically by fractionated stereotactic radiotherapy (FSRT), aiming to prevent tumor progression and visual functions deterioration. Unfortunately, FSRT in itself may affect visual functions. The current preferred treatment regimen (in terms of safety and effectiveness) is undetermined. While most cases are treated with conventional fractionation (cFSRT)-50.4-54 Gy in 28-30 fractions of 1.8-2 Gy, advances in technology have allowed shortening of total treatment length to hypofractionation (hSRT)-25-27 Gy in 3-5 fractions of 5-9 Gy. Our aim was to evaluate the association of radiotherapy regimen for treating AVPM (cFSRT vs. hSRT) with visual function outcomes (VA, VF) at the last neuro-ophthalmologic evaluation.

METHODS

We conducted a retrospective cohort study of AVPM cases treated at Sheba Medical Center during 2004-2015. We compared cFSRT and hSRT regimens regarding visual function (VA, VF) outcomes at the last neuro-ophthalmologic evaluation. VA was determined by the logarithm of the minimum angle of resolution (LogMAR). VF was determined by the mean deviation (MD). A clinically relevant change in VA was defined as 0.2 LogMAR.

RESULTS

48 patients (13 receiving hSRT, 35 receiving cFSRT) were included, with a median follow-up of 55 months. No significant difference was evident regarding LogMAR or MD of involved eyes at the last evaluation. Six (17%) patients in the cFSRT group experienced clinically relevant VA deterioration in the involved eye, compared with six (46%) in hSRT (p = 0.06).

CONCLUSION

Our findings, using comprehensive and meticulous investigation of visual outcomes, suggest that hSRT may be associated with higher risk for VA and VF deterioration in AVPM especially in ONSM. We recommend the use of cFSRT for ONSM.

Study of relationship between dose, LET and the risk of brain necrosis after proton therapy for skull base tumors

PURPOSE

We investigated the relationship between RBE-weighted dose (DRBE) calculated with constant (cRBE) and variable RBE (vRBE), dose-averaged linear energy transfer (LETd) and the risk of radiographic changes in skull base patients treated with protons.

METHODS

Clinical treatment plans of 45 patients were recalculated with Monte Carlo tool FRED. Radiographic changes (i.e. edema and/or necrosis) were identified by MRI. Dosimetric parameters for cRBE and vRBE were computed. Biological margin extension and voxel-based analysis were employed looking for association of DRBE(vRBE) and LETd with brain edema and/or necrosis.

RESULTS

When using vRBE, Dmax in the brain was above the highest dose limits for 38% of patients, while such limit was never exceeded assuming cRBE. Similar values of Dmax were observed in necrotic regions, brain and temporal lobes. Most of the brain necrosis was in proximity to the PTV. The voxel-based analysis did not show evidence of an association with high LETd values.

CONCLUSIONS

When looking at standard dosimetric parameters, the higher dose associated with vRBE seems to be responsible for an enhanced risk of radiographic changes. However, as revealed by a voxel-based analysis, the large inter-patient variability hinders the identification of a clear effect for high LETd.

Simple model for estimation of absorbed dose by organs and tumors after PRRT from a single SPECT/CT study

Background

Following each cycle of peptide receptor radionuclide therapy (PRRT), absorbed doses by tumors and normal organs are typically calculated from three quantitative single-photon emission computed tomography (SPECT)/computed tomography (CT) studies acquired at t₁ = 24 h, t₂ = 96 h, t₃ = 168 h after the first cycle of treatment and from a single study at t₁ after the subsequent cycles. In the present study, we have assessed the feasibility of a single SPECT/CT study after each PRRT cycle using a trained multiple linear regression (MLR) model for absorbed dose calculation and have evaluated its impact on patient management. Quantitative [¹⁷⁷Lu]-DOTA-TATE SPECT/CT data after PRRT of seventy-two consecutive metastatic neuroendocrine tumors patients were retrospectively evaluated. A set of 40 consecutive studies was used to train the MLR model. The two independent variables of the model included the time of imaging after administration of the treatment and the radiopharmaceutical activity concentration in a given  organ/tumor. The dependent variable was the dose absorbed by the organ/tumor obtained with the standard protocol. For bone marrow dosimetry, the independent variables included the time of imaging, and the blood and remainder of the body activity concentration. The model was evaluated in 32 consecutive patients. Absorbed doses were assessed for kidneys, bone marrow, liver, spleen and tumor sites.

Results

There was no difference in management decisions, whether PRRT can be safely continued or not because unsafe absorbed dose to risk organs between the standard and the MLR model-based protocol using a single SPECT/CT study performed at t₃ = 168 h after the first cycle and at t₁ = 24 h after the subsequent cycles. Cumulative absorbed doses were obtained with mean relative differences of − 0.5% ± 5.4%, 1.6% ± 15.1%, − 6.2% ± 7.3%, − 5.5% ± 5.8% and 2.9% ± 12.7% for kidneys, bone marrow, liver, spleen and tumors, respectively (Pearson’s r correlation coefficient 0.99, 0.91, 0.99, 0.99 and 0.97, respectively).

Conclusion

Dosimetry calculations using a MLR model with a single SPECT/CT study are in good agreement with the standard protocol, while avoiding the use of dosimetry software and enabling improved patient comfort and reduced scanner and staff time.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-021-00409-z.

Symptoms Related to Brachial Plexus Neuropathy After Supraclavicular Irradiation and Boost in Breast Cancer

PURPOSE

To evaluate the incidence of symptoms related to brachial plexus neuropathy (BPN) and the dose distribution to the brachial plexus (BP) in patients with breast cancertreated with supraclavicular (SCV) irradiation and boost.

METHODS AND MATERIALS

In this study, 117 patients with initial ipsilateral supraclavicular lymph node (SLN) metastasis and 39 with recurrent SLN metastasis between 2008 and 2018 in our cancer center were retrospectively analyzed. All patients were treated with 50 Gy of SCV irradiation in 25 fractions and a boost (median dose, 10 Gy; range, 10-16 Gy) to involved nodes in the SCV area. Symptoms related to BPN (including ipsilateral arm numbness, pain, and weakness) were recorded and graded according to the Common Terminology Criteria for Adverse Events, version 5.0. The BP was delineated on simulation computed tomography, and the dose distributions to the BP were evaluated. Meanwhile, 297 patients treated with SCV irradiation without boost during the same period were identified as a control group to compare the incidences of BPN-related symptoms and dosimetric data with patients who received an SCV boost.

RESULTS

The 5-year overall survival rate was 80.3% for patients with initial SLN metastasis and 51.0% for patients with recurrent SLN metastasis. For patients who received an SCV boost, incidence rates of ipsilateral arm numbness, pain, and weakness were 23.9%, 18.3%, and 34.3%, respectively. Four patients (5.6%) developed grade 2 numbness and 3 (4.3%) developed grade 2 arm weakness. In the control group, incidence rates of arm numbness, pain, and weakness were 31.6%, 21.9%, and 36.0%, respectively. The incidence of BPN-related symptoms was not significantly different between the 2 groups. Symptoms of grade 3 were not observed in either cohort. The mean doses to the BP in patients who received boost and who did not were 56.8 and 46.8 Gy, respectively (P < .001). The maximum doses to the BP in patients who received boost and who did not were 64.5 and 53.5 Gy, respectively (P < .001). The BP volumes receiving at least 50 Gy, 60 Gy, 61 Gy, and 62 Gy were also significantly higher in the boosted group compared with the control group (P < .001).

CONCLUSIONS

This study found that an SCV boost of 10 Gy did not increase the incidence of BPN-related symptoms and that the toxicity to the BP was acceptable. Comprehensive treatment including SCV irradiation and boost led to satisfactory survival outcomes in patients with breast cancer who had SLN metastasis.

Unrecognized digestive toxicities of radiation therapy

The aim of this article is to review unrecognized toxicities resulting from radiation therapy of digestive neoplasms. Due to their precocious occurrence, acute toxicities are well-known by radiation oncologist, and their treatment well-established. Thus, acute toxicities will not be described in this review. We will focus on incidence, diagnosis, and management of late and uncommon toxicities occurring in the digestive tract and digestive organs. Prevention, by respecting healthy tissues constraints, is the main tool to reduce incidence of those rare complications. Nonetheless, once installed, late toxicities remain a major burden in terms of quality of life and can even be life threatening. Hence, information and education about their diagnosis and management is important.

Kidney Protection with the Radical Scavenger α1-Microglobulin (A1M) during Peptide Receptor Radionuclide and Radioligand Therapy

α₁-Microglobulin (A1M) is an antioxidant found in all vertebrates, including humans. It has enzymatic reductase activity and can scavenge radicals and bind free heme groups. Infused recombinant A1M accumulates in the kidneys and has therefore been successful in protecting kidney injuries in different animal models. In this review, we focus on A1M as a radioprotector of the kidneys during peptide receptor radionuclide/radioligand therapy (PRRT/RLT). Patients with, e.g., neuroendocrine tumors or castration resistant prostate cancer can be treated by administration of radiolabeled small molecules which target and therefore enable the irradiation and killing of cancer cells through specific receptor interaction. The treatment is not curative, and kidney toxicity has been reported as a side effect since the small, radiolabeled substances are retained and excreted through the kidneys. In recent studies, A1M was shown to have radioprotective effects on cell cultures as well as having a similar biodistribution as the somatostatin analogue peptide ¹⁷⁷Lu-DOTATATE after intravenous infusion in mice. Therefore, several animal studies were conducted to investigate the in vivo radioprotective potential of A1M towards kidneys. The results of these studies demonstrated that A1M co-infusion yielded protection against kidney toxicity and improved overall survival in mouse models. Moreover, two different mouse studies reported that A1M did not interfere with tumor treatment itself. Here, we give an overview of radionuclide therapy, the A1M physiology and the results from the radioprotector studies of the protein.

Evaluation of Safety and Dosimetry of 177Lu-DOTA-ZOL for Therapy of Bone Metastases

Palliative treatment of bone metastasis using radiolabeled bisphosphonates is a well-known concept proven to be safe and effective. A new therapeutic radiopharmaceutical for bone metastasis is 177Lu-DOTA-zoledronic acid (177Lu-DOTA-ZOL). In this study, the safety and dosimetry of a single therapeutic dose of 177Lu-DOTA-ZOL were evaluated on the basis of a series of SPECT/CT images and blood samples. Methods: Nine patients with exclusive bone metastases from metastatic castration-resistant prostate cancer (mCRPC) (70.8 ± 8.4 y) and progression under conventional therapies participated in this prospective study. After receiving 5,780 ± 329 MBq 177Lu-DOTA-ZOL, patients underwent 3-dimensional whole-body SPECT/CT imaging and venous blood sampling over 7 d. Dosimetric evaluation was performed for main organs and tumor lesions. Safety was assessed by blood biomarkers. Results:177Lu-DOTA-ZOL showed fast uptake and high retention in bone lesions and fast clearance from the bloodstream in all patients. The average retention in tumor lesions was 0.02% injected activity per gram at 6 h after injection and approximately 0.01% at 170 h after injection. In this cohort, the average absorbed doses in bone tumor lesions, kidneys, red bone marrow, and bone surfaces were 4.21, 0.17, 0.36, and 1.19 Gy/GBq, respectively. The red marrow was found to be the dose-limiting organ for all patients. A median maximum tolerated injected activity of 6.0 GBq may exceed the defined threshold of 2 Gy for the red bone marrow in individual patients (4/8). Conclusion:177Lu-DOTA-ZOL is safe and has a favorable therapeutic index compared with other radiopharmaceuticals used in the treatment of osteoblastic bone metastases. Personalized dosimetry, however, should be considered to avoid severe hematotoxicity for individual patients.

Hepatocellular carcinoma patients with portal vein thrombosis treated with robotic radiosurgery: Interim results of a prospective study

BACKGROUND

This is a prospective study evaluating the role of stereotactic body radiotherapy (SBRT) with CyberKnife (CK) in Indian patients suffering from hepatocellular carcinoma with portal vein thrombosis (HCC-PVT).

METHODS

Patients with inoperable HCC-PVT, good performance score (PS), and liver function are accrued for treatment on CK (version M6) and planned with Multiplan (iDMS V2.0). Triple-phase contrast computed tomography (CT) scan was done for contouring, and the gross tumor volume (GTV) included contrast-enhancing mass within main portal vein and adjacent parenchymal disease. Dose prescription was as per-risk stratification protocol (22-50 Gy in 5 fractions) while achieving the constraints of mean liver dose <15 Gy, 800 cc liver <8 Gy, and the duodenum max of ≤24 Gy).

RESULTS

Seventy-two HCC-PVT accrued till date (mean age 63 years [38-76 years], 96% male; Child-Pugh [CP] A 84%, B 9%; Barcelona-Clinic Liver Cancer [BCLC] C 96%; PS0-1: 80%, Karnofsky performance score [KPS]>70: 88%; co-morbidities 42%; infective 12%, alcohol intake 31%, adjuvant sorafenib 39%). CP scores 5, 6, 7, and 8 were in 35%, 32%, 8%, and 18%, respectively. Focal disease with portal vein thrombus (PVT) in 21%, liver involvement >50% and <50% in 46% and 32%. Liver cancer study group of Japan staging-based portal vein invasion VP2, VP3, and VP4 in 22%, 29%, and 40%. Cancer of the Liver Italian Programm (CLIP) scores 1, 2, 3, 4, and 5 were in 8%, 26%, 31%, 26%, and 7%, respectively. Mean follow-up was 7.3 months (median 6 months, standard deviation [SD] 6; range 3-30 months). Mean actuarial overall survival (OS) was 11.4 months (SE 1.587; 95% CI: 8-14.2 months). Six months and 12 months actuarial OS 55% and 38%, respectively. At last follow-up, 25/69 (36%) were alive and 44/69 (64%) were dead. Among 54 patients evaluated for response assessment, 23 (30%) had radiological confirmed PVT response, 1 (3%) had response of IVC thrombus, and 30 (42%) had no or minimal response to SBRT. Actuarial OS in responders and non-responders were 14.4 months (95% CI 9.4-19.2) and 7.4 months (95% CI 4.9-9.7), p-value: 0.022. Six and 12 months survival in responders and non-responders were 65.7% and 37% and 49% and 24.6%, respectively. Post-SBRT, 4 (12%) patients underwent transarterial chemoembolization (TACE) 3 patients (8%) and 1 patient (4%) transarterial radioembolization (TARE). Post-CK, (<4 weeks) 2 patients (4%) had decompensation.

CONCLUSIONS

PVT response or recanalization after SBRT is a statistically significant prognostic factor for survival function in HCC-PVT.

Impact of daily plan adaptation on organ-at-risk normal tissue complication probability for adrenal lesions undergoing stereotactic ablative radiation therapy

INTRODUCTION

Stereotactic ablative radiotherapy (SABR) can achieve good local control for metastatic adrenal lesions. Magnetic resonance (MR)-guidance with daily on-table plan adaptation can augment the delivery of SABR with greater dose certainty. The goal of this study was to quantify the potential clinical benefit MR-guided daily-adaptive adrenal SABR using the normal tissue complication probability (NTCP) framework.

METHODS

Patients treated with adrenal MR-guided SABR at a single institution were retrospectively reviewed. Lyman-Kutcher-Burman NTCP models were used to calculate the NTCP of upper abdominal organs-at-risk (OARs) at simulation and both before and after daily on-table plan adaptation. Differences in OAR NTCPs were assessed using signed-rank tests. Potential predictors of the benefits of adaptation were assessed by linear regression.

RESULTS

Fifty-two adrenal MR-guided SABR courses were analyzed. The baseline simulation plan underestimated the absolute stomach NTCP by 10.0% on average (95% confidence interval: 4.7-15.2%, p < 0.001). Daily on-table adaptation lowered absolute NTCP by 8.7% (4.2-13.2%, p < 0.001). The most significant predictor of the benefits of adaptation was lesion laterality (p = 0.018), with left-sided lesions benefitting more (13.3% [6.3-20.4%], p < 0.001) than right-sided lesions (2.1% [-1.6-5.7%], p = 0.25). Sensitivity analyses did not change the statistical significance of the findings.

CONCLUSION

NTCP analysis revealed that patients with left adrenal tumors were more likely to benefit from MR-guided daily on-table adaptive SABR using current dose/fractionation regimens due to reductions in predicted gastric toxicity. Right-sided adrenal lesions may be considered for dose escalation due to low predicted NTCP.

Reducing the renal retention of low- to moderate-molecular-weight radiopharmaceuticals

The field of nuclear imaging and therapy is rapidly progressing with the development of targeted radiopharmaceuticals that show rapid targeting and rapid clearance with minimal background. Unfortunately, they are often reabsorbed in the kidneys, leading to possible nephrotoxicity, limiting the therapeutic dose, and/or reducing imaging quality. The blocking of endocytic receptors has been extensively used as a strategy to reduce kidney radiation. Alternatively, the physicochemical properties of radiotracers can be modulated to either prevent their reuptake or promote the excretion of radiometabolites. Other interesting strategies focus on the insertion of a cleavable linker between the radiolabel and the targeting moiety or pretargeting approaches in which the targeting moiety and radiolabel are administered separately. In the context of this review, we will discuss the latest advances and insights on strategies used to reduce renal retention of low- to moderate-molecular-weight radiopharmaceuticals.

Mixed Photon and Carbon-Ion Beam Radiotherapy in the Management of Non-Metastatic Nasopharyngeal Carcinoma

Background

Carbon-ion radiotherapy (CIRT) may further increase the therapeutic ratio for patients with newly diagnosed nasopharyngeal carcinoma (NPC). The purpose of the current study is to examine the effectiveness and toxicity profile of photon-based intensity-modulated radiotherapy (IMRT) plus CIRT boost in a relatively large cohort of NPC patients.

Methods

In the current study, non-metastatic NPC patients treated with IMRT plus CIRT boost at Shanghai Proton and Heavy Ion Center between June, 2015 and June, 2018 were included. Overall survival (OS), progression-free survival (PFS), local control, regional control, and distant control were calculated with Kaplan–Meier method. Acute and late toxicities were graded using CTCAE 4.03.

Results

A total of 69 patients were included in the analysis. Among those, 74% of the patients had locoregionally advanced (stage III/IV) disease, and 92.8% had cervical lymphadenopathy. With a median follow-up of 31.9 months, the 3-year OS, PFS, local control, regional control, and distant control rates were 94.9, 85.2, 96.9, 98.4, and 89.7%, respectively. Mixed treatment of IMRT with CIRT boost was well tolerated. Severe acute toxicities induced by radiation therapy were observed in only two patients (dermatitis). No severe radiation-induced late toxicity was observed at the time of analysis. Univariable analysis showed N2/3 disease was correlated with an inferior distant control (p = 0.040).

Conclusion

Mixed treatment of IMRT plus CIRT boost provides an excellent disease control and a favorable toxicity profile for patients with non-metastatic NPC. Further follow-up is necessary to evaluate the long-term survivals and toxicities more accurately.

Remote control of neural function by X-ray-induced scintillation

Scintillators emit visible luminescence when irradiated with X-rays. Given the unlimited tissue penetration of X-rays, the employment of scintillators could enable remote optogenetic control of neural functions at any depth of the brain. Here we show that a yellow-emitting inorganic scintillator, Ce-doped Gd₃(Al,Ga)₅O₁₂ (Ce:GAGG), can effectively activate red-shifted excitatory and inhibitory opsins, ChRmine and GtACR1, respectively. Using injectable Ce:GAGG microparticles, we successfully activated and inhibited midbrain dopamine neurons in freely moving mice by X-ray irradiation, producing bidirectional modulation of place preference behavior. Ce:GAGG microparticles are non-cytotoxic and biocompatible, allowing for chronic implantation. Pulsed X-ray irradiation at a clinical dose level is sufficient to elicit behavioral changes without reducing the number of radiosensitive cells in the brain and bone marrow. Thus, scintillator-mediated optogenetics enables minimally invasive, wireless control of cellular functions at any tissue depth in living animals, expanding X-ray applications to functional studies of biology and medicine.

Impact of nodal boost irradiation and MR-based brachytherapy on oncologic outcomes in node-positive cervical cancer

This study aimed to prospectively evaluate the impact of dose-escalated irradiation of nodal metastases on clinical outcomes compared to no boost in patients with node-positive, bulky, locally advanced cervical cancer (LACC) undergoing standard chemoradiation and MRI-based brachytherapy.

METHODS

This comparative study included 161 patients with node-positive LACC treated with definitive chemoradiation and MRI-based brachytherapy. The prospective Boost arm accrued 71 patients to receive nodal boost either sequentially or simultaneously to an equivalent dose of 60 Gy. The control arm comprised 90 patients treated before this protocol period with no additional nodal boost.

RESULT

Baseline patient and tumor characteristics were similar in both groups. All patients had at least one tumor dimension >5 cm at presentation, and 31% had para-aortic node involvement. With a median follow-up of 36 months (IQR:19-50.5), the overall 3-year Local control rate was 88.8%. The 3-year Regional control (93% vs. 80%, p = 0.035) was statistically better in the Boost arm. No nodal failure was observed in nodes <3 cc and < 2 cm, even in the No-boost arm. There was no significant difference in Disease-free survival (67.6% vs. 58.9%,p = 0.454) and Overall Survival (78.9% vs. 74.4%,p = 0.87) between the two arms. Incidence of acute or late toxicities did not differ significantly with nodal boost or the boost delivery technique.

CONCLUSION

The addition of external radiation nodal boost to standard treatment of high-volume cervical cancer has improved pelvic control with an acceptable rate of toxicities. However, high systemic failures continue to pose a challenge in improving survival outcomes.

Exploratory Investigation of Dose-Linear Energy Transfer (LET) Volume Histogram (DLVH) for Adverse Events Study in Intensity Modulated Proton Therapy (IMPT)

PURPOSE

We proposed a novel tool-a dose linear energy transfer (LET)-volume histogram (DLVH)-and performed an exploratory study to investigate rectal bleeding in prostate cancer treated with intensity modulated proton therapy.

METHODS AND MATERIALS

The DLVH was constructed with dose and LET as 2 axes, and the normalized volume of the structure was contoured in the dose-LET plane as isovolume lines. We defined the DLVH index, DLv%(d,l) (ie, v% of the structure) to have a dose of ≥d Gy and an LET of ≥l keV/μm, similar to the dose-volume histogram index Dv%. Nine patients with prostate cancer with rectal bleeding (Common Terminology Criteria for Adverse Events grade ≥2) were included as the adverse event group, and 48 patients with no complications were considered the control group. A P value map was constructed by comparison of the DLVH indices of all patients between the 2 groups using the Mann-Whitney U test. Dose-LET volume constraints (DLVCs) were derived based on the P value map with a manual selection procedure facilitated by Spearman's correlation tests. The obtained DLVCs were further cross-validated using a multivariate support vector machine (SVM)-based normal tissue complication probability (NTCP) model with an independent testing data set composed of 8 adverse event and 13 control patients.

RESULTS

We extracted 2 DLVC constraints. One DLVC was obtained, Vdose/LETboundary:2.5keVμmat 75 Gy to 3.2keVμmat8.65Gy <1.27% (DLVC1), revealing a high LET volume effect. The second DLVC, V(72.2Gy,0keVμm) < 2.23% (DVLC2), revealed a high dose volume effect. The SVM-based NTCP model with 2 DLVCs provided slightly superior performance than using dose only, with an area under the curve of 0.798 versus 0.779 for the testing data set.

CONCLUSIONS

Our results demonstrated the importance of rectal "hot spots" in both high LET (DLVC1) and high dose (DLVC2) in inducing rectal bleeding. The SVM-based NTCP model confirmed the derived DLVCs as good predictors for rectal bleeding when intensity modulated proton therapy is used to treat prostate cancer.

Prediction of the minimum spacer thickness required for definitive radiotherapy with carbon ions and photons for pelvic tumors: an in silico planning study using virtual spacers

We aimed to predict the minimum distance between a tumor and the gastrointestinal (GI) tract that can satisfy the dose constraint by creating simulation plans with carbon-ion (C-ion) radiotherapy (RT) and photon RT for each case assuming insertion of virtual spacers of various thicknesses. We enrolled 55 patients with a pelvic tumor adjacent to the GI tract. Virtual spacers were defined as the overlap volume between the GI tract and the volume expanded 7-17 mm from the gross tumor volume (GTV). Simulation plans (70 Gy in 35 fractions for at least 95% of the planning target volume [PTV]) were created with the lowest possible dose to the GI tract under conditions that meet the dose constraints of the PTV. We defined the minimum thickness of virtual spacers meeting D2 cc of the GI tract <50 Gy as 'MTS'. Multiple regression was used with explanatory variables to develop a model to predict MTS. We discovered that MTSs were at most 9 mm and 13 mm for C-ion RT and photon RT plans, respectively. The volume of overlap between the GI tract and a virtual spacer of 14 mm in thickness (OV14)-PTV was found to be the most important explanatory variable in the MTS prediction equation for both C-ion and photon RT plans. Multiple R2 values for the regression model were 0.571 and 0.347 for C-ion RT and photon RT plans, respectively. In conclusion, regression equations were developed to predict MTS in C-ion RT and photon RT.

Contemporary radiotherapy: present and future

Oncology care is increasingly a multidisciplinary endeavour, and radiation therapy continues to have a key role across the disease spectrum in nearly every cancer. However, the field of radiation oncology is still one of the most poorly understood of the cancer disciplines. In this Review, we attempt to summarise and contextualise developments within the field of radiation oncology for the non-radiation oncologist. We discuss advancements in treatment technologies and imaging, followed by an overview of the interplay with advancements in systemic therapy and surgical techniques. Finally, we review new frontiers in radiation oncology, including advances within the metastatic disease continuum, reirradiation, and emerging types of radiation therapy.