Comparison of risk of radiogenic second cancer following photon and proton craniospinal irradiation for a pediatric medulloblastoma patient

Case report: successful treatment of primary intradural extramedullary extraskeletal Ewing sarcoma in adult patient with intralesional surgery, chemotherapy, and proton beam therapy of the cerebrospinal axis

Ewing sarcoma is a rare malignant neoplasm that primarily affects bone in children. Extraskeletal location is less common, while intradural extramedullary Ewing sarcoma (IEES) in adults is a casuistic phenomenon. Due to its rarity, a standardized treatment strategy for IEES has not been established. The clinical use of proton beam therapy (PBT) for craniospinal irradiation (CSI) in the treatment of IEES has not been reported in the literature. A 41-year-old previously healthy man presented with disabling gluteal and lower extremity pain, decreased sensation, and progressive paraparesis without sphincter dysfunction. Imaging showed intradural extramedullary spinal lesions. The patient underwent urgent surgery. Histology and immunohistochemistry suggested a poorly differentiated neuroendocrine tumor. Negative chromogranin staining and a high Ki67 index prompted further investigation. Next-generation sequencing later confirmed an EWSR1/FLI1 translocation, leading to the diagnosis of extraskeletal Ewing sarcoma. The patient received standardized chemotherapy with marked clinical improvement. PBT CSI was initiated but was interrupted due to COVID-19 and other complications. At 20 months follow-up, no recurrence was observed, and the patient reported an active life. Despite intra-spinal spread and multiple complications, intensive chemotherapy combined with PBT CSI led to a favorable outcome. CSI rather than focal radiotherapy should be considered for patients with IEES limited to the cerebrospinal axis. PBT may be used as an alternative to photon radiotherapy to better spare organs at risk.

Secondary cancer risk assessment in healthy organs following craniospinal irradiation

INTRODUCTION

Medulloblastoma is a central nerves tumor that often occurs in pediatrics. The main radiotherapy technique for this tumor type is craniospinal irradiation (CSI), through which the whole brain and spinal cord are exposed to radiation. Due to the immaturity of healthy organs in pediatrics, radiogenic side effects such as second cancer are more severe. Accordingly, the current study aimed to evaluate the risk of secondary cancer development in healthy organs following CSI.

MATERIALS AND METHODS

Seven organs at risk (OARs) including skin, eye lens, thyroid, lung, liver, stomach, bladder, colon, and gonads were considered and the dose received by each OAR during CSI was measured inside an anthropomorphic RANDO phantom by TLDs. Then, the mean obtained dose for each organ was used to estimate the probability of secondary malignancy development according to the recommended cancer risk coefficients for specific organs.

RESULTS

The results demonstrated that the stomach and colon are at high risk of secondary malignancy occurrence, while the skin has the lowest probability of secondary cancer development. The total received dose after the treatment course by all considered organs was lower than the corresponding tolerable dose levels.

CONCLUSIONS

From the results, it can be concluded that some OARs during CSI are highly at risk of secondary cancer development. This issue may be of concern due to organ immaturity in pediatrics which can intensify the radiogenic effects of radiation exposure. Accordingly, strict shielding the OARs during craniospinal radiotherapy and/or sparing them from the radiation field through modern techniques such as hadron therapy is highly recommended.

Modelling the influence of radiosensitivity on development of second primary cancer in out-of-field organs following proton therapy for paediatric cranial cancer

OBJECTIVE

Radiobiological modelling the risks of second primary cancer (SPC) after proton therapy (PT) for childhood cranial cancer remains largely unknown. Organ-specific dose-response risk factors such as radiosensitivity require exploration. This study compared the influence of radiosensitivity data (slope of βEAR) on children's lifetime attributable risks (LAR) of SPC development in out-of-field organs following cranial scattering and scanning PT.

METHODS

Out-of-field radiosensitivity parameter estimates for organs (α/β and βEAR) were sourced from literature. Physical distances for 13 out-of-field organs were measured and input into Schneider's SPC model. Sensitivity analyses were performed as a function of radiosensitivity (α/β of 1-10 Gy) and initial slope (βEAR) from Japanese/UK data to estimate the influence on the risk of radiation-induced SPC following scattering and scanning PT.

RESULTS

Models showed similar LAR of SPC estimates for age and sex-matched paediatric phantoms, however, for breast there was a significant increase using Japanese βEAR data. For most organs, scattering PT demonstrated a larger risk of LAR for SPC which increased with α/β.

CONCLUSION

Breast tissue exhibited the highest susceptibility in calculated LAR risk, demonstrating the importance for accurate data input when estimating LAR of SPC.

ADVANCES IN KNOWLEDGE

The findings of this study demonstrated younger female patients undergoing cranial proton therapy have a higher risk of developing second primary cancer of the breast tissue. Long-term multicenter registries are important to improve predictive radiobiological modelling studies of side effects.

Comparison of out-of-field normal tissue dose estimates for pencil beam scanning proton therapy: MCNP6, PHITS, and TOPAS

Monte Carlo (MC) methods are considered the gold-standard approach to dose estimation for normal tissues outside the treatment field (out-of-field) in proton therapy. However, the physics of secondary particle production from high-energy protons are uncertain, particularly for secondary neutrons, due to challenges in performing accurate measurements. Instead, various physics models have been developed over the years to reenact these high-energy interactions based on theory. It should thus be acknowledged that MC users must currently accept some unknown uncertainties in out-of-field dose estimates. In the present study, we compared three MC codes (MCNP6, PHITS, and TOPAS) and their available physics models to investigate the variation in out-of-field normal tissue dosimetry for pencil beam scanning proton therapy patients. Total yield and double-differential (energy and angle) production of two major secondary particles, neutrons and gammas, were determined through irradiation of a water phantom at six proton energies (80, 90, 100, 110, 150, and 200 MeV). Out-of-field normal tissue doses were estimated for intracranial irradiations of 1-, 5-, and 15-year-old patients using whole-body computational phantoms. Notably, the total dose estimates for each out-of-field organ varied by approximately 25% across the three codes, independent of its distance from the treatment volume. Dose discrepancies amongst the codes were linked to the utilized physics model, which impacts the characteristics of the secondary radiation field. Using developer-recommended physics, TOPAS produced both the highest neutron and gamma doses to all out-of-field organs from all examined conditions; this was linked to its highest yields of secondary particles and second hardest energy spectra. Subsequent results when using other physics models found reduced yields and energies, resulting in lower dose estimates. Neutron dose estimates were the most impacted by physics model choice, and thus the variation in out-of-field dose estimates may be even larger than 25% when considering biological effectiveness.

Risk of secondary malignant neoplasms in children following proton therapy vs. photon therapy for primary CNS tumors: A systematic review and meta-analysis

Background

Central nervous system tumors are now the most common primary neoplasms seen in children, and radiation therapy is a key component in management. Secondary malignant neoplasms (SMNs) are rare, but dreaded complications. Proton beam therapy (PBT) can potentially minimize the risk of SMNs compared to conventional photon radiation therapy (RT), and multiple recent studies with mature data have reported the risk of SMNs after PBT. We performed this systematic review and meta-analysis to characterize and compare the incidence of SMNs after proton and photon-based radiation for pediatric CNS tumors.

Methods

A systematic search of literature on electronic (PubMed, Cochrane Central, and Embase) databases was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) method. We included studies reporting the incidence and nature of SMNs in pediatric patients with primary CNS tumors. The crude incidence of SMNs and all secondary neoplasms were separately extracted, and the random-effects model was used for pooled analysis and subgroup comparison was performed between studies using photons vs. protons.

Results

Twenty-four studies were included for analysis. A total of 418 SMNs were seen in 38,163 patients. The most common SMN were gliomas (40.6%) followed by meningiomas (38.7%), sarcomas (4.8%), and thyroid cancers (4.2%). The median follow-up was 8.8 years [3.3–23.2].The median latency to SMN for photons and protons were 11.9 years [5-23] and 5.9 years [5-6.7], respectively. The pooled incidence of SMNs was 1.8% (95% CI: 1.1%–2.6%, I² = 94%) with photons and 1.5% (95% CI: 0%–4.5%, I² = 81%) with protons. The pooled incidence of all SNs was not different [photons: 3.6% (95% CI: 2.5%–4.8%, I² = 96%) vs. protons: 1.5% (95% CI: 0–4.5%, I² = 80%); p = 0.21].

Conclusion

We observed similar rates of SMN with PBT at 1.5% compared to 1.8% with photon-based RT for pediatric CNS tumors. We observed a shorter latency to SMN with PBT compared to RT. With increasing use of pencil beam scanning PBT and VMAT, further studies are warranted to evaluate the risk of secondary cancers in patients treated with these newer modalities.

Adult Medulloblastoma: Updates on Current Management and Future Perspectives

Medulloblastoma (MB) is a malignant embryonal tumor of the posterior fossa belonging to the family of primitive neuro-ectodermic tumors (PNET). MB generally occurs in pediatric age, but in 14–30% of cases, it affects the adults, mostly below the age of 40, with an incidence of 0.6 per million per year, representing about 0.4–1% of tumors of the nervous system in adults. Unlike pediatric MB, robust prospective trials are scarce for the post-puberal population, due to the low incidence of MB in adolescent and young adults. Thus, current MB treatments for older patients are largely extrapolated from the pediatric experience, but the transferability and applicability of these paradigms to adults remain an open question. Adult MB is distinct from MB in children from a molecular and clinical perspective. Here, we review the management of adult MB, reporting the recent published literature focusing on the effectiveness of upfront chemotherapy, the development of targeted therapies, and the potential role of a reduced dose of radiotherapy in treating this disease.

The Current State of Radiotherapy for Pediatric Brain Tumors: An Overview of Post-Radiotherapy Neurocognitive Decline and Outcomes

Tumors of the central nervous system are the most common solid malignancies diagnosed in children. While common, they are also found to have some of the lowest survival rates of all malignancies. Treatment of childhood brain tumors often consists of operative gross total resection with adjuvant chemotherapy or radiotherapy. The current body of literature is largely inconclusive regarding the overall benefit of adjuvant chemo- or radiotherapy. However, it is known that both are associated with conditions that lower the quality of life in children who undergo those treatments. Chemotherapy is often associated with nausea, emesis, significant fatigue, immunosuppression, and alopecia. While radiotherapy can be effective for achieving local control, it is associated with late effects such as endocrine dysfunction, secondary malignancy, and neurocognitive decline. Advancements in radiotherapy grant both an increase in lifetime survival and an increased lifetime for survivors to contend with these late effects. In this review, the authors examined all the published literature, analyzing the results of clinical trials, case series, and technical notes on patients undergoing radiotherapy for the treatment of tumors of the central nervous system with a focus on neurocognitive decline and survival outcomes.

Determining Out-of-Field Doses and Second Cancer Risk From Proton Therapy in Young Patients—An Overview

Proton therapy has the potential to provide survival and tumor control outcomes comparable and frequently superior to photon therapy. This has led to a significant concern in the medical physics community on the risk for the induction of second cancers in all patients and especially in younger patients, as they are considered more radiosensitive than adults and have an even longer expected lifetime after treatment. Thus, our purpose is to present an overview of the research carried out on the evaluation of out-of-field doses linked to second cancer induction and the prediction of this risk. Most investigations consisted of Monte Carlo simulations in passive beam facilities for clinical scenarios. These works established that equivalent doses in organs could be up to 200 mSv or 900 mSv for a brain or a craniospinal treatment, respectively. The major contribution to this dose comes from the secondary neutrons produced in the beam line elements. Few works focused on scanned-beam facilities, but available data show that, for these facilities, equivalent doses could be between 2 and 50 times lower. Patient age is a relevant factor in the dose level, especially for younger patients (by means of the size of the body) and, in addition, in the predicted risk by models (due to the age dependence of the radiosensitivity). For risks, the sex of the patient also plays an important role, as female patients show higher sensitivity to radiation. Thus, predicted risks of craniospinal irradiation can range from 8% for a 15-year-old male patient to 58% for a 2-year-old female patient, using a risk model from a radiological protection field. These values must be taken with caution due to uncertainties in risk models, and then dosimetric evaluation of stray radiation becomes mandatory in order to complement epidemiological studies and be able to model appropriate dose–response functions for this dose range. In this sense, analytical models represent a useful tool and some models have been implemented to be used for young patients. Research carried out so far confirmed that proton beam therapy reduces the out-of-field doses and second cancer risk. However, further investigations may be required in scanned-beam delivery systems.

Volumetric de-escalation and improved acute toxicity with proton craniospinal irradiation using a vertebral body-sparing technique

PURPOSE

In growing children, craniospinal irradiation (CSI) has historically treated the entire vertebral body (VB) to avoid potential long-term spinal abnormalities. Vertebral body-sparing proton craniospinal irradiation (VBSpCSI) is a technique that spares the majority of the VB from significant irradiation, and long-term safety outcomes have been reported previously. This retrospective study reviews the acute toxicity profile of children treated with VBSpCSI in a cohort comparison with photon-based craniospinal radiotherapy (3DCRT).

METHODS

Thirty-eight pediatric CSI patients treated between 2008 and 2018 were retrospectively evaluated for treatment-related toxicity. Acute toxicity outcomes and acute hematologic profiles were compared according to treatment modality, either VBSpCSI or 3DCRT. Statistical analysis was performed using Fisher's exact test for toxicity.

RESULTS

Twenty-five patients received VBSpCSI and 13 patients received photon CSI. Mean patient age at treatment was 7.5 years (range 2-16). The cohorts were well matched with respect to gender, age, and CSI dose. Patients receiving VBSpCSI had lower rates of grade 2+ gastrointestinal (GI) toxicity (24% vs. 76.5%, p = .005), grade 2+ nausea (24% vs. 61.5%, p = .035), and any-grade esophagitis (0% vs. 38%, p = .0026). Patients treated with VBSpCSI had lower red blood cell transfusion rates (21.7% vs. 60%, p = .049) and grade 4+ lymphopenia (33.3% vs. 77.8%, p = .046).

CONCLUSIONS

VBSpCSI in children is a volumetric de-escalation from traditional volumes, which irradiate the entire VB to full or intermediate doses. In our study, VBSpCSI was associated with lower rates of acute GI and hematologic toxicities. Long-term growth outcomes and disease control outcomes are needed for this technique.

Out-of-field doses in pediatric craniospinal irradiations with 3D-CRT, VMAT and scanning proton radiotherapy - a phantom study

PURPOSE

Craniospinal irradiation (CSI) has greatly increased survival rates for patients with a diagnosis of medulloblastoma and other primitive neuroectodermal tumors. However, as it includes exposure of a large volume of healthy tissue to unwanted doses, there is a strong concern about the complications of the treatment, especially for the children. To estimate the risk of second cancers and other unwanted effects, out-of-field dose assessment is necessary. The purpose of this study is to evaluate and compare out-of-field doses in pediatric CSI treatment using conventional and advanced photon radiotherapy (RT) and advanced proton therapy. To our knowledge, it is the first such comparison based on in-phantom measurements. Additionally, for out-of-field doses during photon RT in this and other studies, comparisons were made using analytical modeling.

METHODS

In order to describe the out-of-field doses absorbed in a pediatric patient during actual clinical treatment, an anthropomorphic phantom which mimics the 10-year-old child was used. Photon 3D-conformal radiotherapy (3D-CRT) and two advanced, highly conformal techniques: photon volumetric modulated arc therapy (VMAT) and active pencil beam scanning (PBS) proton radiotherapy were used for CSI treatment. Radiophotoluminescent (RPL) and poly-allyl-diglycol-carbonate (PADC) nuclear track detectors were used for photon and neutron dosimetry in the phantom, respectively. Out-of-field doses from neutrons were expressed in terms of dose equivalent. A two-Gaussian model was implemented for out-of-field doses during photon RT.

RESULTS

The mean VMAT photon doses per target dose to all organs in this study were under 50% of the target dose (i.e., <500 mGy/Gy), while the mean 3D-CRT photon dose to oesophagus, gall bladder and thyroid, exceeded that value. However, for 3D-CRT, better sparing was achieved for eyes and lungs. The mean PBS photon doses for all organs were up to 3 orders of magnitude lower compared to VMAT and 3D-CRT and exceeded 10 mGy/Gy only for the oesophagus, intestine and lungs. The mean neutron dose equivalent during PBS for 8 organs of interest (thyroid, breasts, lungs, liver, stomach, gall bladder, bladder, prostate) ranged from 1.2 mSv/Gy for bladder to 23.1 mSv/Gy for breasts. Comparison of out-of-field doses in this and other phantom studies found in the literature showed that a simple and fast two-Gaussian model for out-of-field doses as a function of distance from the field edge can be applied in a CSI using photon RT techniques.

CONCLUSIONS

PBS is the most promising technique for out-of-field dose reduction in comparison to photon techniques. Among photon techniques, VMAT is a preferred choice for most of out-of-field organs and especially for the thyroid, while doses for eyes, breasts and lungs, are lower for 3D-CRT. For organs outside the field edge, a simple analytical model can be helpful for clinicians involved in treatment planning using photon RT but also for retrospective data analysis for cancer risk estimates and epidemiology in general. This article is protected by copyright. All rights reserved.

A patient-specific hybrid phantom for calculating radiation dose and equivalent dose to the whole body

OBJECTIVE

As cancer survivorship increases, there is growing interest in minimizing the late effects of radiation therapy such as radiogenic second cancer, which may occur anywhere in the body. Assessing the risk of late effects requires knowledge of the dose distribution throughout the whole body, including regions far from the treatment field, beyond the typical anatomical extent of clinical CT scans.

APPROACH

A hybrid phantom was developed which consists of in-field patient CT images extracted from ground truth whole-body CT (WBCT) scans, out-of-field mesh phantoms scaled to basic patient measurements, and a blended transition region. Four of these hybrid phantoms were created, representing male and female patients receiving proton therapy treatment in pelvic and cranial sites. To assess the performance of the hybrid approach, we simulated treatments using the hybrid phantoms, the scaled and unscaled mesh phantoms, and the ground truth whole-body CTs. We calculated absorbed dose and equivalent dose in and outside of the treatment field, with a focus on neutrons induced in the patient by proton therapy. Proton and neutron dose was calculated using a general purpose Monte Carlo code.

MAIN RESULTS

The hybrid phantom provided equal or superior accuracy in calculated organ dose and equivalent dose values relative to those obtained using the mesh phantoms in 78% in all selected organs and calculated dose quantities. Comparatively the default mesh and scaled mesh were equal or superior to the other phantoms in 21% and 28% of cases respectively.

SIGNIFICANCE

The proposed methodology for hybrid synthesis provides a tool for whole-body organ dose estimation for individual patients without requiring CT scans of their entire body. Such a capability would be useful for personalized assessment of late effects and risk-optimization of treatment plans.

Radiotherapy in Medulloblastoma-Evolution of Treatment, Current Concepts and Future Perspectives

Simple Summary

Craniospinal irradiation (CSI) is the backbone of medulloblastoma treatment and the first treatment to achieve a cure in many patients. Within the last decades, significant efforts have been made to enhance efficacy in combination with chemotherapy. With this approach, a majority of low- and standard-risk patients can be cured. In parallel, many clinical trials have dealt with CSI-dose reduction and reduction of boost volume in order to decrease long-term toxicity, particularly neurotoxicity. Within these trials, standardized quality assurance has helped to increase the accuracy of treatment and improve prognosis. More recently, advances of radiotherapy techniques such as proton treatment allowed for better sparing of healthy tissue in order to further diminish detrimental long-term effects. Major future challenges are the adaption of radiotherapy regimens to different molecularly defined disease groups alone or together with new targeted agents. Moreover, and even more importantly, innovative combinatorial treatments are needed in high- and very-high risk situations.

Abstract

Medulloblastoma is the most frequent malignant brain tumor in children. During the last decades, the therapeutic landscape has changed significantly with craniospinal irradiation as the backbone of treatment. Survival times have increased and treatments were stratified according to clinical and later molecular risk factors. In this review, current evidence regarding the efficacy and toxicity of radiotherapy in medulloblastoma is summarized and discussed mainly based on data of controlled trials. Current concepts and future perspectives based on current risk classification are outlined. With the introduction of CSI, medulloblastoma has become a curable disease. Due to combination with chemotherapy, survival rates have increased significantly, allowing for a reduction in radiation dose and a decrease of toxicity in low- and standard-risk patients. Furthermore, modern radiotherapy techniques are able to avoid side effects in a fragile patient population. However, high-risk patients remain with relevant mortality and many patients still suffer from treatment related toxicity. Treatment needs to be continually refined with regard to more efficacious combinatorial treatment in the future.

Cost-effectiveness analysis using lifetime attributable risk of proton beam therapy for pediatric medulloblastoma in Japan

Compared to conventional X-ray therapy, proton beam therapy (PBT) has more clinical and physical advantages such as irradiation dose reduction to normal tissues for pediatric medulloblastoma. However, PBT is expensive. We aimed to compare the cost-effectiveness of PBT for pediatric medulloblastoma with that of conventional X-ray therapy, while focusing on radiation-induced secondary cancers, which are rare, serious and negatively affect a patient's quality of life (QOL). Based on a systematic review, a decision tree model was used for the cost-effectiveness analysis. This analysis was performed from the perspective of health care payers; the cost was estimated from medical fees. The target population was pediatric patients with medulloblastoma below 14 years old. The time horizon was set at 7.7 years after medulloblastoma treatment. The primary outcome was the incremental cost-effectiveness ratio (ICER), which was defined as the ratio of the difference in cost and lifetime attributable risk (LAR) between conventional X-ray therapy and PBT. The discount rate was set at 2% annually. Sensitivity analyses were performed to model uncertainty. Cost and LAR in conventional X-ray therapy and PBT were Japanese yen (JPY) 1 067 608 and JPY 2436061 and 42% and 7%, respectively. The ICER was JPY 3856398/LAR. In conclusion, PBT is more cost-effective than conventional X-ray therapy in reducing the risk of radiation-induced secondary cancers in pediatric medulloblastoma. Thus, our constructed ICER using LAR is one of the valid indicators for cost-effectiveness analysis in radiation-induced secondary cancer.

Reduce Patient Treatment wait time in a Proton Beam Facility - A Gatekeeper Approach

Patient wait time can negatively impact treatment quality in a proton therapy center, where multiple treatment rooms share one proton beam. Wait time increases patient discomfort that can lead to patient motion, dissatisfaction, and longer treatment delay. This study was to develop a patient call-back model that reduced patient wait while efficiently utilizing the proton beam. A "Gatekeeper" logic allowing therapists to adjust the time of a patient's call-back to the treatment room was developed. It uses a two-pronged approach to minimize overlap of long treatment and the possibility of excessive wait in the queue to receive the proton beam. The goal was to reduce the maximum wait time to less than eight minutes per field for a four-room facility. The effectiveness of this logic was evaluated through simulation, and five scenarios were compared. Four scenarios implementing various levels of gatekeeper logic were compared with the original scenario without the logic. The best performing model provided a reduction of the maximum field wait by 26% and met the predefined goal. Adjusting call-back extended the treatment day length by an average of 6 min and a maximum of 12 min in total. The use of this gatekeeper logic significantly reduces patient field wait with minimal impact on treatment day length for a four-room proton facility. A sample interface that adopts this logic for therapists to make informed decision on patient call-back time is demonstrated.

Out-of-field dose in stereotactic radiotherapy for paediatric patients

Background and purpose

Stereotactic radiotherapy combines image guidance and high precision delivery with small fields to deliver high doses per fraction in short treatment courses. In preparation for extension of these treatment techniques to paediatric patients we characterised and compared doses out-of-field in a paediatric anthropomorphic phantom for small flattened and flattening filter free (FFF) photon beams.

Method and materials

Dose measurements were taken in several organs and structures outside the primary field in an anthropomorphic phantom of a 5 year old child (CIRS) using thermoluminescence dosimetry (LiF:Mg,Cu,P). Out-of-field doses from a medical linear accelerator were assessed for 6 MV flattened and FFF beams of field sizes between 2 × 2 and 10 × 10 cm².

Results

FFF beams resulted in reduced out-of-field doses for all field sizes when compared to flattened beams. Doses for FFF and flattened beams converged for all field sizes at larger distances (>40 cm) from the central axis as leakage becomes the primary source of out-of-field dose. Rotating the collimator to place the MLC bank in the longitudinal axis of the patient was shown to reduce the peripheral doses measured by up to 50% in Varian linear accelerators.

Conclusion

Minimising out-of-field doses by using FFF beams and aligning the couch and collimator to provide tertiary shielding demonstrated advantages of small field, FFF treatments in a paediatric setting.

Outcomes following limited-volume proton therapy for multifocal spinal myxopapillary ependymoma

PURPOSE

Spinal myxopapillary ependymoma (MPE) often presents with a multifocal distribution, complicating attempts at resection. There remains no standard approach to irradiating these patients. We report disease control and toxicity in pediatric patients with multifocal spinal MPE treated with limited-volume proton therapy.

MATERIALS/METHODS

Twelve patients (≤21 years old) with multifocal spinal MPE were treated between 2009 and 2018 with limited-volume brain-sparing proton therapy. Median age was 13.5 years (range, 7-21). Radiotherapy was given as adjuvant therapy after primary surgery in five patients (42%) and for recurrence in seven (58%). No patient received prior radiation. Eleven patients (92%) had evidence of gross disease at radiotherapy. Eleven patients received 54 GyRBE; one received 50.4 GyRBE. Treatment toxicity was graded per the CTCAEv4.0. We estimated disease control and survival using the Kaplan-Meier product-limit method.

RESULTS

The median follow-up was 3.6 years (range, 1.8-10.6). The five-year actuarial rates of local control, progression-free survival, and overall survival were 100%, 92%, and 100%, respectively. One patient experienced an out-of-field recurrence in the spine superior to the irradiated region. No patients developed in-field recurrences. Following surgery and irradiation, one patient developed grade three spinal kyphosis and one patient developed grade 2 unilateral L5 neuropathy.

CONCLUSION

54 GyRBE to a limited volume appears effective for disseminated spinal MPE in both the primary and salvage settings, sparing children the toxicity of full craniospinal irradiation. Compared with historical reports, this approach using proton therapy improves the therapeutic ratio, resulting in minimal side effects and high rates of disease control.

Craniospinal irradiation as part of re-irradiation for children with recurrent intracranial ependymoma

BACKGROUND

The goal of this study was to evaluate outcomes in children with relapsed, molecularly characterized intracranial ependymoma treated with or without craniospinal irradiation (CSI) as part of a course of repeat radiation therapy (re-RT).

METHODS

This was a retrospective cohort study of 31 children. Patients with distant relapse received CSI as part of re-RT. For patients with locally recurrent ependymoma, those treated before 2012 were re-irradiated with focal re-RT. In 2012, institutional practice changed to offer CSI, followed by boost re-RT to the site of resected or gross disease.

RESULTS

Median follow-up was 5.5 years. Of 9 patients with distant relapse after initial RT, 2-year freedom from progression (FFP) and overall survival (OS) were 12.5% and 62.5%, respectively. There were 22 patients with local failure after initial RT. In these patients, use of CSI during re-RT was associated with improvement in 5-year FFP (83.3% with CSI vs 15.2% with focal re-RT only, P = 0.030). In the subgroup of patients with infratentorial primary disease, CSI during re-RT also improved 5-year FFP (100% with CSI, 10.0% with focal re-RT only, P = 0.036). Twenty-three patients had known molecular status; all had posterior fossa group A tumors (n = 17) or tumors with a RELA (v-rel avian reticuloendotheliosis viral oncogene homolog A) fusion (n = 6). No patient developed radiation necrosis after fractionated re-RT, though almost all survivors required assistance throughout formal schooling. Five out of 10 long-term survivors have not developed neuroendocrine deficits.

CONCLUSIONS

Re-irradiation with CSI is a safe and effective treatment for children with locally recurrent ependymoma and improves disease control compared with focal re-irradiation, with the benefit most apparent for those with infratentorial primary tumors.

A Monte Carlo model for organ dose reconstruction of patients in pencil beam scanning (PBS) proton therapy for epidemiologic studies of late effects

Significant efforts such as the Pediatric Proton/Photon Consortium Registry (PPCR) involving multiple proton therapy centers have been made to conduct collaborative studies evaluating outcomes following proton therapy. As a groundwork dosimetry effort for the late effect investigation, we developed a Monte Carlo (MC) model of proton pencil beam scanning (PBS) to estimate organ/tissue doses of pediatric patients at the Maryland Proton Treatment Center (MPTC), one of the proton centers involved in the PPCR. The MC beam modeling was performed using the TOPAS (TOol for PArticle Simulation) MC code and commissioned to match measurement data within 1% for range, and 0.3 mm for spot sizes. The established MC model was then tested by calculating organ/tissue doses for sample intracranial and craniospinal irradiations on whole-body pediatric computational human phantoms. The simulated dose distributions were compared with the treatment planning system dose distributions, showing the 3 mm/3% gamma index passing rates of 94%-99%, validating our simulations with the MC model. The calculated organ/tissue doses per prescribed doses for the craniospinal irradiations (1 mGy Gy^-1 to 1 Gy Gy^-1) were generally much higher than those for the intracranial irradiations (2.1 μGy Gy^-1 to 0.1 Gy Gy^-1), which is due to the larger field coverage of the craniospinal irradiations. The largest difference was observed at the adrenal dose, i.e. ∼3000 times. In addition, the calculated organ/tissue doses were compared with those calculated with a simplified MC model, showing that the beam properties (i.e. spot size, spot divergence, mean energy, and energy spread) do not significantly influence dose calculations despite the limited irradiation cases. This implies that the use of the MC model commissioned to the MPTC measurement data might be dosimetrically acceptable for patient dose reconstructions at other proton centers particularly when their measurement data are unavailable. The developed MC model will be used to reconstruct organ/tissue doses for MPTC pediatric patients collected in the PPCR.

The Risk of Radiogenic Second Cancer Based on Differential DVH: Central Nervous System Malignant Tumor in Children

OBJECTIVES

To quantify the risk of radiogenic second cancer in pediatric patients receiving hippocampal-sparing craniospinal irradiation either with intensity-modulated radiation therapy or tomotherapy due to the development of a solid second cancer after radiotherapy using the concept of excess absolute risk.

METHODS

Computed tomography images of 15 pediatric patients who received craniospinal irradiation treatment were selected for this study. For each case, intensity-modulated radiation therapy and tomotherapy plans were computed. Then, the dosimetry parameters were analyzed. Differential dose-volume histograms were generated, and the excess absolute risks were calculated for each plan of each patient.

RESULTS

The tomotherapy group was superior to the intensity-modulated radiation therapy group in target area homogeneity index (P < .001). Tomotherapy offered greater hippocampal sparing than intensity-modulated radiation therapy in terms of D _2% (15.66 vs 23.05 Gy, P < .001) and D_mean (9.79 vs 20.29 Gy, P < .001). Tomotherapy craniospinal irradiation induced a much higher risk than intensity-modulated radiation therapy craniospinal irradiation to the thyroid and lungs (excess absolute risk: thyroid 28.7 vs 26.9 per 10 000 PY, P = .010; lung 20.5 vs 18.9 per 10 000 PY, P = .003). Both techniques conferred a higher risk to the stomach, but there was little difference. In addition, the 2 plans induced less carcinogenic risk to the liver (excess absolute risk 4.2 vs 4.0 per 10 000 PY, P = .020).

CONCLUSIONS

The tomotherapy plan has obvious advantages in the protection of the hippocampus for children undergoing craniospinal irradiation treatment. Tomotherapy increased the risk of radiogenic second cancer in organ at risk, and therefore, it is imperative to take the risk factor into consideration in the formulation of treatment protocols.

Paediatric proton therapy

Proton beam therapy is a highly conformal form of radiation therapy, which currently represents an important therapeutic component in multidisciplinary management in paediatric oncology. The precise adjustability of protons results in a reduction of radiation-related long-term side-effects and secondary malignancy induction, which is of particular importance for the quality of life. Proton irradiation has been shown to offer significant advantages over conventional photon-based radiotherapy, although the biological effectiveness of both irradiation modalities is comparable. This review evaluates current data from clinical and dosimetric studies on the treatment of tumours of the central nervous system, soft tissue and bone sarcomas of the head and neck region, paraspinal or pelvic region, and retinoblastoma. To date, the clinical results of irradiating childhood tumours with high-precision proton therapy are promising both with regard to tumour cure and the reduction of adverse events. Modern proton therapy techniques such as pencil beam scanning and intensity modulation are increasingly established modern facilities. However, further investigations with larger patient cohorts and longer follow-up periods are required, in order to be able to have clear evidence on clinical benefits.

Estimation of radiation-induced second cancer risk associated with the institutional field matching craniospinal irradiation technique: A comparative treatment planning study

Aim

To estimate and compare the lifetime attributable risk (LAR) of radiation-induced second cancer (SC) in pediatric medulloblastoma patients planned with institutional 3D conformal field matching method, gap junction method and Intensity Modulated Radiotherapy (IMRT).

Background

The epidemiological studies on childhood cancer survivors reported that long-term cancer survivors who received radiotherapy are at a significantly increased risk for the development of SC. Hence, the increased concern to predict the SC risk for long-term survivors.

Materials and methods

In addition to institutional field matching planning method, IMRT and gap junction methods were created for ten pediatric medulloblastoma patients. The risk estimates were made based on the site-specific cancer risk coefficient provided by the BEIR VII committee according to the organ equivalent dose for various critical organs. Also, plans were compared for target volume dose distribution and dose received by critical organs.

Results

When compared to the gap junction method, the IMRT and institutional field matching method were superior in normal tissue sparing and dose conformity. However, highly significant volume of low dose associated with IMRT was the main concern for the SC risk. The accumulated LAR for all the critical organs with 3D conformal gap junction and IMRT method was 23-25% while for the 3D conformal field matching method it was 21%.

Conclusion

The LAR associated with the institutional field matching technique was substantially lower. As this method is highly robust and easy to set up, it can be a better choice of a craniospinal irradiation technique where 3DCRT is the only choice of treatment.

The risk of secondary cancer in pediatric medulloblastoma patients due to three-dimensional conformal radiotherapy and intensity-modulated radiotherapy

BACKGROUND

Craniospinal irradiation (CSI) is the standard radiation therapy treatment for medulloblastoma. The aim of this study was to estimate and compare the lifetime risk of radiation-induced secondary cancer in pediatric medulloblastoma patients using three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT).

MATERIALS AND METHODS

3D-CRT and IMRT plans were performed for 10 CSI pediatric patients. The average absorbed doses for organs at risk (OARs) was calculated from dose-volume histograms on the treatment planning system. The average lifetime risk of radiation-induced secondary cancer was then calculated.

RESULTS

Lifetime risk of secondary cancer for CSI pediatric patients treated using IMRT decreases in some OARs compared with those treated using 3D-CRT. This is attributable to the decrease in the average absorbed dose in some OARs when using IMRT technique.

CONCLUSION

Follow-up of medulloblastoma pediatric patients should be performed after ending the treatment course in order to diagnose early secondary tumors. IMRT technique is substantially better than 3D-CRT in terms of lifetime risk of radiation-induced secondary cancer, probably due to reduced dose to OARs especially to the thyroid, which is the most sensitive organ to radiation.

Independent application of an analytical model for secondary neutron equivalent dose produced in a passive-scattering proton therapy treatment unit

The purpose of this study was to independently apply an analytical model for equivalent dose from neutrons produced in a passive-scattering proton therapy treatment unit, H. To accomplish this objective, we applied the previously-published model to treatment plans of two pediatric patients. Their model accounted for neutrons generated by mono-energetic proton beams stopping in a closed aperture. To implement their model to a clinical setting, we adjusted it to account for the area of a collimating aperture, energy modulation, air gap between the treatment unit and patient, and radiation weighting factor. We used the adjusted model to estimate H per prescribed proton absorbed dose, D _Rx , for the passive-scattering proton therapy beams of two children, a 9-year-old girl and 10-year-old boy, who each received intracranial boost fields as part of their treatment. In organs and tissues at risk for radiation-induced subsequent malignant neoplasms, T, we calculated the mass-averaged H, H _T , per D _Rx . Finally, we compared H _T /D _Rx values to those of previously-published Monte Carlo (MC) simulations of these patients' fields. H _T /D _Rx values of the adjusted model deviated from the MC result for each organ on average by 20.8  ±  10.0% and 44.2  ±  17.6% for the girl and boy, respectively. The adjusted model underestimated the MC result in all T of each patient, with the exception of the girl's bladder, for which the adjusted model overestimated H _T /D _Rx by 3.1%. The adjusted model provided a better estimate of H _T /D _Rx than the unadjusted model. That is, between the two models, the adjusted model reduced the deviation from the MC result by approximately 37.0% and 46.7% for the girl and boy, respectively. We found that the previously-published analytical model, combined with adjustment factors to enhance its clinical applicability, predicted H _T /D _Rx in out-of-field organs and tissues at risk for subsequent malignant neoplasms with acceptable accuracy. This independent application demonstrated that the analytical model may be useful broadly for clinicians and researchers to calculate equivalent dose from neutrons produced externally to the patient in passive-scattering proton therapy.

Evaluation of surface and shallow depth dose reductions using a Superflab bolus during conventional and advanced external beam radiotherapy

The purpose of this study was to evaluate a methodology to reduce scatter and leakage radiations to patients’ surface and shallow depths during conventional and advanced external beam radiotherapy. Superflab boluses of different thicknesses were placed on top of a stack of solid water phantoms, and the bolus effect on surface and shallow depth doses for both open and intensity‐modulated radiotherapy (IMRT) beams was evaluated using thermoluminescent dosimeters and ion chamber measurements. Contralateral breast dose reduction caused by the bolus was evaluated by delivering clinical postmastectomy radiotherapy (PMRT) plans to an anthropomorphic phantom. For the solid water phantom measurements, surface dose reduction caused by the Superflab bolus was achieved only in out‐of‐field area and on the incident side of the beam, and the dose reduction increased with bolus thickness. The dose reduction caused by the bolus was more significant at closer distances from the beam. Most of the dose reductions occurred in the first 2‐cm depth and stopped at 4‐cm depth. For clinical PMRT treatment plans, surface dose reductions using a 1‐cm Superflab bolus were up to 31% and 62% for volumetric‐modulated arc therapy and 4‐field IMRT, respectively, but there was no dose reduction for Tomotherapy. A Superflab bolus can be used to reduce surface and shallow depth doses during external beam radiotherapy when it is placed out of the beam and on the incident side of the beam. Although we only validated this dose reduction strategy for PMRT treatments, it is applicable to any external beam radiotherapy and can potentially reduce patients’ risk of developing radiation‐induced side effects.

Low- and middle-income countries can reduce risks of subsequent neoplasms by referring pediatric craniospinal cases to centralized proton treatment centers

Few children with cancer in low- and middle-income countries (LMICs) have access to proton therapy. Evidence exists to support replacing photon therapy with proton therapy to reduce the incidence of secondary malignant neoplasms (SMNs) in childhood cancer survivors. The purpose of this study was to estimate the potential reduction in SMN incidence and in SMN mortality for pediatric medulloblastoma patients in LMICs if proton therapy were made available to them. For nine children of ages 2 to 14 years, we calculated the equivalent dose in organs or tissues at risk for radiogenic SMNs from therapeutic and stray radiation for photon craniospinal irradiation (CSI) in a LMIC and proton CSI in a high-income country. We projected the lifetime risks of SMN incidence and SMN mortality for every SMN site with a widely-used model from the literature. We found that the average total lifetime attributable risks of incidence and mortality were very high for both photon CSI (168% and 41%, respectively) and proton CSI (88% and 26%, respectively). SMNs having the highest risk of mortality were lung cancer (16%), non-site-specific solid tumors (16%), colon cancer (5.9%), leukemia (5.4%), and for girls breast cancer (5.0%) after photon CSI and non-site-specific solid tumors (12%), lung cancer (11%), and leukemia (4.8%) after proton CSI. The risks were higher for younger children than for older children and higher for girls than for boys. The ratios of proton CSI to photon CSI of total risks of SMN incidence and mortality were 0.56 (95% CI, 0.37 to 0.75) and 0.64 (95% CI, 0.45 to 0.82), respectively, averaged over this sample group. In conclusion, proton therapy has the potential to lessen markedly subsequent SMNs and SMN fatalities in survivors of childhood medulloblastoma in LMICs, for example, through regional centralized care. Additional methods should be explored urgently to reduce therapeutic-field doses in organs and tissues at risk for SMN, especially in the lungs, colon, and breast tissues.

Clinical Implementation of Robust Optimization for Craniospinal Irradiation

With robust optimization for spot scanning proton therapy now commercially available, the ability exists to account for setup, range, and interfield uncertainties during optimization. Robust optimization is particularly beneficial for craniospinal irradiation (CSI) where the large target volume lends itself to larger setup uncertainties and the need for robust match lines can all be handled with the uncertainty parameters found inside the optimizer. Suggested robust optimization settings, parameters, and image guidance for CSI patients using proton therapy spot scanning are provided. Useful structures are defined and described. Suggestions are given for perturbations to be entered into the optimizer in order to achieve a plan that provides robust target volume coverage and critical structure sparing as well as a robust match line. Interfield offset effects, a concern when using multifield optimization, can also be addressed within the robust optimizer. A robust optimizer can successfully be employed to produce robust match lines, target volume coverage, and critical structure sparing under specified uncertainties. The robust optimizer can also be used to reduce effects arising from interfield uncertainties. Using robust optimization, a plan robust against setup, range, and interfield uncertainties for craniospinal treatments can be created. Utilizing robust optimization allows one to ensure critical structures are spared and target volumes are covered under the desired uncertainty parameters.

Craniospinal irradiation prior to stem cell transplant for hematologic malignancies with CNS involvement: Effectiveness and toxicity after photon or proton treatment

PURPOSE/OBJECTIVE(S)

Craniospinal irradiation (CSI) improves local control of leukemia/lymphoma with central nervous system (CNS) involvement; however, for adult patients anticipating stem cell transplant (SCT), cumulative treatment toxicity is a major concern. We evaluated toxicities and outcomes for patients receiving proton or photon CSI before SCT.

METHODS AND MATERIALS

We identified 37 consecutive leukemia/lymphoma patients with CNS involvement who received CSI before SCT at our institution. Photon versus proton toxicities during CSI, transplant, and through 100 days posttransplant were compared using Fisher exact and Wilcoxon rank sum tests. Long-term neurotoxicity, disease response, and overall survival were analyzed.

RESULTS

Thirty-seven patients (23 photon, 14 proton) underwent CSI for CNS involvement of acute lymphoblastic leukemia (49%), acute myeloblastic leukemia (22%), chronic lymphocytic leukemia (3%), chronic myelocytic leukemia (14%), lymphoma (11%), and myeloma (3%). CSI was used for consolidation (30 patients, 81%) and gross disease treatment (7 patients, 19%). Median radiation dose (interquartile range) was 24 Gy (23.4-24) for photons and 21.8 Gy (21.3-23.6) for protons (P = .03). Proton CSI was associated with lower rates of Radiation Therapy Oncology Group grade 1-3 mucositis during CSI (7% vs 44%, P = .03): 1 grade 3 with protons versus 5 grade 1, 3 grade 2, and 2 grade 3 with photons. During CSI, other toxicities (infection, gastrointestinal symptoms) did not differ. Allogeneic stem cell transplant (SCT) was used in 95% of patients, with 53% of patients in remission before SCT. Myeloablative conditioning was used for 76%. During SCT admission and 100 days post-SCT, toxicities did not differ by CSI technique. Successful engraftment occurred in 95% of patients (P = .67). Progression or death occurred for 47% of patients, with only 1 CNS relapse.

CONCLUSION

In our cohort, CSI offered excellent local control for CNS-involved hematologic malignancies in the pre-SCT setting. Acute mucositis occurred less frequently with proton CSI with comparable peritransplant/long-term toxicity profile, suggesting the need to further explore the benefit/toxicity profile of this technique.

Comparative study of the effects of different radiation qualities on normal human breast cells

BACKGROUND

As there is a growing number of long-term cancer survivors, the incidence of carcinogenesis as a late effect of radiotherapy is getting more and more into the focus. The risk for the development of secondary malignant neoplasms might be significantly increased due to exposure of healthy tissue outside of the target field to secondary neutrons, in particular in proton therapy. Thus far, the radiobiological effects of these neutrons and a comparison with photons on normal breast cells have not been sufficiently characterised.

METHODS

MCF10A cells were irradiated with doses of up to 2 Gy with neutrons of different energy spectra and X-rays for comparison. The biological effects of neutrons with a broad energy distribution ( = 5.8 MeV), monoenergetic neutrons (1.2 MeV, 0.56 MeV) and of the mixed field of gamma's and secondary neutrons ( = 70.5 MeV) produced by 190 MeV protons impinging on a water phantom, were analysed. The clonogenic survival and the DNA repair capacity were determined and values of relative biological effectiveness were compared. Furthermore, the influence of radiation on the sphere formation was observed to examine the radiation response of the potential fraction of stem like cells within the MCF10A cell population.

RESULTS

X-rays and neutrons caused dose-dependent decreases of survival fractions after irradiations with up to 2 Gy. Monoenergetic neutrons with an energy of 0.56 MeV had a higher effectiveness on the survival fraction with respect to neutrons with higher energies and to the mixed gamma - secondary neutron field induced by proton interactions in water. Similar effects were observed for the DNA repair capacity after exposure to ionising radiation (IR). Both experimental endpoints provided comparable values of the relative biological effectiveness. Significant changes in the sphere formation were notable following the various radiation qualities.

CONCLUSION

The present study compared the radiation response of MCF10A cells after IR with neutrons and photons. For the first time it was shown that monoenergetic neutrons with energies around 1 MeV have stronger radiobiological effects on normal human breast cells with respect to X rays, to neutrons with a broad energy distribution ( = 5.8 MeV), and to the mixed gamma - secondary neutron field given by interactions of 190 MeV protons in water. The results of the present study are highly relevant for further investigations of radiation-induced carcinogenesis and are very important in perspective for a better risk assessment after secondary neutron exposure in the field of conventional and proton radiotherapy.

A review of dosimetric and toxicity modeling of proton versus photon craniospinal irradiation for pediatrics medulloblastoma

BACKGROUND

Craniospinal irradiation (CSI) is the standard radiation therapy treatment for medulloblastoma. Conventional CSI photon therapy (Photon-CSI) delivers significant dose to surrounding normal tissue (NT). Research into pediatric CSI with proton therapy (Proton-CSI) has increased, with the aim of exploiting the potential to reduce NT dose and associated post-treatment complications. This review aims to compare treatment outcomes of pediatric medulloblastoma patients between Proton- and Photon-CSI treatments.

MATERIAL AND METHODS

A search and review of studies published between 1990 and 2016 comparing pediatric (2-18 years) medulloblastoma Proton- and Photon-CSI in three aspects - normal organ sparing and target coverage; normal organ dysfunction and second malignancy risks - was completed.

RESULTS

Fifteen studies were selected for review and the results were directly compared. Proton-CSI reported improved out-of-field organ sparing while target coverage improvements were inconsistent. Normal organ dysfunction risks were predicted to be lower following Proton-CSI. Secondary malignancy risks (SMRs) were generally lower with Proton-CSI based on several different risk models.

CONCLUSIONS

Proton-CSI conferred better treatment outcomes than Photon-CSI for pediatric medulloblastoma patients. This review serves to compare the current literature in the absence of long-term data from prospective studies.

Proton Beam Therapy for Pediatric Brain Tumor

Cancer is a major cause of childhood death, with central nervous system (CNS) neoplasms being the second most common pediatric malignancy, following hematological cancer. Treatment of pediatric CNS malignancies requires multimodal treatment using a combination of surgery, chemotherapy, and radiotherapy, and advances in these treatments have given favorable results and longer survival. However, treatment-related toxicities have also occurred, particularly for radiotherapy, after which secondary cancer, reduced function of irradiated organs, and retarded growth are significant problems. Proton beam therapy (PBT) is a particle radiotherapy with excellent dose localization that permits treatment of liver and lung cancer by administration of a high dose to the tumor while minimizing damage to surrounding normal tissues. Thus, PBT has the potential advantages for pediatric cancer. In this context, we review the current knowledge on PBT for treatment of pediatric CNS malignancies.

Out-of-field doses from pediatric craniospinal irradiations using 3D-CRT, IMRT, helical tomotherapy and electron-based therapy

Medulloblastoma treatment involves irradiation of the entire central nervous system, i.e. craniospinal irradiation (CSI). This is associated with the significant exposure of large volumes of healthy tissue and there is growing concern regarding treatment-associated side effects. The current study compares out-of-field organ doses in children receiving CSI through 3D-conformal radiotherapy (3D-CRT), intensity modulated radiotherapy (IMRT), helical tomotherapy (HT) and an electron-based technique, and includes radiation doses resulting from imaging performed during treatment. An extensive phantom study is performed, using an anthropomorphic phantom corresponding to a five year old child, in which organ absorbed doses are measured using thermoluminescent detectors. Additionally, the study evaluates and explores tools for calculating out-of-field patient doses using the treatment planning system (TPS) and analytical models. In our study, 3D-CRT resulted in very high doses to a limited number of organs, while it was able to spare organs such as the lungs and breast when compared to IMRT and HT. Both IMRT and HT spread the dose over more organs and were able to spare the heart, thyroid, bladder, uterus and testes when compared to 3D-CRT. The electron-based technique considerably decreased the out-of-field doses in deep-seated organs but could not avoid nearby out-of-field organs such as the lungs, ribs, adrenals, kidneys and uterus. The daily imaging dose is small compared to the treatment dose burden. The TPS error for out-of-field doses was most pronounced for organs further away from the target; nevertheless, no systematic underestimation was observed for any of the studied TPS systems. Finally, analytical modeling was most optimal for 3D-CRT although the number of organs that could be modeled was limited. To conclude, none of the techniques studied was capable of sparing all organs from out-of-field doses. Nevertheless, the electron-based technique showed the most promise for out-of-field organ dose reduction during CSI when compared to photon techniques.

A review of uncertainties in radiotherapy dose reconstruction and their impacts on dose-response relationships

Proper understanding of the risk of radiation-induced late effects for patients receiving external photon beam radiotherapy requires the determination of reliable dose-response relationships. Although significant efforts have been devoted to improving dose estimates for the study of late effects, the most often questioned explanatory variable is still the dose. In this work, based on a literature review, we provide an in-depth description of the radiotherapy dose reconstruction process for the study of late effects. In particular, we focus on the identification of the main sources of dose uncertainty involved in this process and summarise their impacts on the dose-response relationship for radiotherapy late effects. We provide a number of recommendations for making progress in estimating the uncertainties in current studies of radiotherapy late effects and reducing these uncertainties in future studies.

Proton therapy in craniospinal irradiation: a systematic review

Aim

Craniospinal irradiation is a technique indicated when a patient has a malignancy that has either disseminated, or is at risk of disseminating, throughout the subarachnoid space. While the craniospinal axis is treatable with conventional radiotherapy, the high doses to organs at risk carry an increased risk of acute and late side effects. Proton craniospinal irradiation is an expensive technique that shows great theoretical promise arising from reduced exit doses. The purpose of this systematic review is to determine the potential role of proton therapy as a standard modality for craniospinal irradiation.

Materials and methods

A literature review was performed to determine the efficacy and cost of proton craniospinal irradiation. The Cochrane Library and the Inspec, Medline (via Pubmed) and Scopus databases were searched. After exclusion criteria were applied, the remaining papers were systematically appraised utilising the Scottish Intercollegiate Guidelines Network critical appraisal checklists.

Results

A total of 14 articles remained following the application of the screening and critical appraisal processes. In total, five of the articles concluded that the risk of secondary malignancy was lower with proton therapy, while ten of the articles included data showing that toxicity rates and organs at risk doses were lower with proton therapy. Doses to most thoracic and abdominal organs at risk analysed in the literature were reduced when proton therapy was used, with the sole exception of the oesophagus, the dose to which depended on whether or not the entire vertebral body was treated. Proton therapy also delivered optimal doses to organs at risk in the head and neck compared with conformal radiation therapy. However, in one study that compared tomotherapy to proton therapy, tomotherapy outperformed proton therapy by delivering lower doses to organs at risk in the head and neck, as well as the kidneys. The two cost-effectiveness studies did not indicate proton therapy as an optimal modality for all treatment sites; however, one of the studies found that for medulloblastoma, protons were more cost effective than conventional radiation therapy.

Findings

Proton therapy is a superior treatment option for craniospinal irradiation. The reduction in risk of toxicity and radiocarcinogenesis offered by proton craniospinal irradiation appear to outweigh the increased costs.

Pediatric craniospinal irradiation with conventional technique or helical tomotherapy: impact of age and body volume on integral dose

PURPOSE

The use of helical tomotherapy (HT) for craniospinal irradiation (CSI) in pediatric patients remains an issue of discussion. In this study, we evaluated the integral dose (ID) to organs at risk (OARs) and to the whole body delivered with conventional 3-dimensional conformal radiotherapy (3D-CRT) and HT for pediatric patients and made a comparison according to different whole body volumes.

METHODS

We selected 10 pediatric patients with different body volumes and of different ages undergoing CSI. Plans for 3D-CRT and HT were developed for each patient. The ID to OARs and to the whole body were compared and statistical analyses were performed to determine differences.

RESULTS

We noticed that variations of ID depend on the different anatomical location of the organs relatively to the target, with lower ID to OARs opposed to the target and increased ID to lateral organs: ID tomotherapy/3D-CRT ratio was higher in lungs, kidneys, and mammary region, while it was lower in heart, liver, thyroid, and esophagus. The ID of the body increased with large volumes both in HT and in 3D-CRT plans, but in tomotherapy plans ID increased significantly more with large volumes than with small ones.

CONCLUSIONS

While there are no differences in using tomotherapy or 3D-CRT with small body volumes, we found a difference with large volumes (≥20,000 mL vs ≤20,000 mL). Therefore, for very small patients, the use of intensity-modulated radiotherapy provided with tomotherapy to reduce the dose to OARs can be reconsidered.

A Review of Radiotherapy-Induced Late Effects Research after Advanced Technology Treatments

The number of incident cancers and long-term cancer survivors is expected to increase substantially for at least a decade. Advanced technology radiotherapies, e.g., using beams of protons and photons, offer dosimetric advantages that theoretically yield better outcomes. In general, evidence from controlled clinical trials and epidemiology studies are lacking. To conduct these studies, new research methods and infrastructure will be needed. In the paper, we review several key research methods of relevance to late effects after advanced technology proton-beam and photon-beam radiotherapies. In particular, we focus on the determination of exposures to therapeutic and stray radiation and related uncertainties, with discussion of recent advances in exposure calculation methods, uncertainties, in silico studies, computing infrastructure, electronic medical records, and risk visualization. We identify six key areas of methodology and infrastructure that will be needed to conduct future outcome studies of radiation late effects.

[Glioblastoma metastases: a literature review and a description of six clinical observations]

INTRODUCTION

since the 1990s, the literature has described cases of glioblastoma metastases with the development of foci located at a distance from the primary tumor. However, the pathogenesis of this process remains unclear until the end. This focus is believed to result, on the one hand, from tumor metastasis from the primary site and, on the other hand, from multifocal growth. This article presents a literature review and a description of clinical observations of patients with glioblastoma metastases.

MATERIAL AND METHODS

The study included 6 patients (1 female and 5 males) with brain glioblastomas who received treatment at the Burdenko Neurosurgical Institute (5 patients) and the Department of Neurosurgery of the Research Center of Neurology (1 patient) in the period from 2010 to 2014. Neurophysiological control was used if the tumor was localized near the eloquent cortical areas and pathways; 4 of 6 patients were operated on using the methods of intraoperative fluorescence diagnosis (5-ALA agent--Alasens).

RESULTS

Four patients had metastases within one hemisphere, two had metastases in the contralateral hemisphere in the period of 5 to 18 months after the first operation. The primary tumor site was located near the ventricular system in two patients. In one patient, the lateral ventricle was opened during the first operation. In another patient, the prepontine cistern was opened during the first operation. In two patients, the primary tumor site was located at a distance from the lateral ventricles, however, the tumor was located near them during recurrence. Based on metabolic navigation, fluorescence of the tumor was observed in the four patients during both the first and repeated operations.

CONCLUSIONS

The close relationship between primary glioblastomas and metastases and the cerebrospinal fluid circulation pathways may confirm the fact of dissemination of tumor cells with cerebrospinal fluid flow. In our opinion, there should be an increased suspicion of the possibility for metastases of glioblastomas that are closely associated with the cerebrospinal fluid circulation pathways. Metabolic navigation with 5-ALA is effective both during primary surgery in patients with glioblastomas and during resection of glioblastoma metastases.

A Comparative Planning Analysis and Integral Dose of Volumetric Modulated Arc Therapy, Helical Tomotherapy, and Three-dimensional Conformal Craniospinal Irradiation for Pediatric Medulloblastoma

INTRODUCTION

The purpose of this study was to compare volumetric modulated arc therapy (VMAT) with helical tomotherapy (HT) and three-dimensional conformal radiation therapy (3D-CRT) for craniospinal irradiation (CSI) in children with medulloblastoma.

METHODS

Five children treated with 3D-CRT were retrospectively replanned with HT and VMAT. Tomotherapy plans used a single helical arc, thereby eliminating field junctions. VMAT plans used two arcs rotating alternatively clockwise and counterclockwise, respectively. Conformity and homogeneity indices, dose-volume histograms, integral doses, monitor units delivered, and beam-on times were compared.

RESULTS

VMAT showed an improved mean conformity index of 1.05 in comparison with 3D-CRT (1.58, P = .04) and HT (1.34, P = .04). The mean homogeneity index of VMAT (1.13) was not significantly different from 3D-CRT (1.16) but higher than HT (1.08, P = .04). For normal tissues, VMAT resulted in a lower mean dose to the skin, eyes, lenses, optic nerves, cochlea, esophagus, heart, peritoneal cavity, bladder, and rectum compared with 3D-CRT (all P = .04). There were few significant differences in dose-volume statistics for normal tissues between VMAT and HT. The mean nontarget tissue integral dose for VMAT of 80.8 J was significantly lower than for 3D-CRT (91.5 J, P = .04) and HT (95.6 J, P = .04). Body and nontarget tissue integral doses were lowest with VMAT in every patient.

CONCLUSIONS

For CSI, VMAT provides comparable normal tissue sparing with tomotherapy and may reduce the integral dose. Compared with 3D-CRT, VMAT improved normal tissue sparing at higher doses despite larger volumes receiving lower doses. These findings have potential implications in the risk of the development of late adverse effects and radiation-related second malignancies in children with curable primary disease.

An analytical model of leakage neutron equivalent dose for passively-scattered proton radiotherapy and validation with measurements

Exposure to stray neutrons increases the risk of second cancer development after proton therapy. Previously reported analytical models of this exposure were difficult to configure and had not been investigated below 100 MeV proton energy. The purposes of this study were to test an analytical model of neutron equivalent dose per therapeutic absorbed dose (H/D) at 75 MeV and to improve the model by reducing the number of configuration parameters and making it continuous in proton energy from 100 to 250 MeV. To develop the analytical model, we used previously published H/D values in water from Monte Carlo simulations of a general-purpose beamline for proton energies from 100 to 250 MeV. We also configured and tested the model on in-air neutron equivalent doses measured for a 75 MeV ocular beamline. Predicted H/D values from the analytical model and Monte Carlo agreed well from 100 to 250 MeV (10% average difference). Predicted H/D values from the analytical model also agreed well with measurements at 75 MeV (15% average difference). The results indicate that analytical models can give fast, reliable calculations of neutron exposure after proton therapy. This ability is absent in treatment planning systems but vital to second cancer risk estimation.

Visualization of risk of radiogenic second cancer in the organs and tissues of the human body

BACKGROUND

Radiogenic second cancer is a common late effect in long term cancer survivors. Currently there are few methods or tools available to visually evaluate the spatial distribution of risks of radiogenic late effects in the human body. We developed a risk visualization method and demonstrated it for radiogenic second cancers in tissues and organs of one patient treated with photon volumetric modulated arc therapy and one patient treated with proton craniospinal irradiation.

METHODS

Treatment plans were generated using radiotherapy treatment planning systems (TPS) and dose information was obtained from TPS. Linear non-threshold risk coefficients for organs at risk of second cancer incidence were taken from the Biological Effects of Ionization Radiation VII report. Alternative risk models including linear exponential model and linear plateau model were also examined. The predicted absolute lifetime risk distributions were visualized together with images of the patient anatomy.

RESULTS

The risk distributions of second cancer for the two patients were visually presented. The risk distributions varied with tissue, dose, dose-risk model used, and the risk distribution could be similar to or very different from the dose distribution.

CONCLUSIONS

Our method provides a convenient way to directly visualize and evaluate the risks of radiogenic second cancer in organs and tissues of the human body. In the future, visual assessment of risk distribution could be an influential determinant for treatment plan scoring.

Dosimetric Comparison and Potential for Improved Clinical Outcomes of Paediatric CNS Patients Treated with Protons or IMRT

Background: We compare clinical outcomes of paediatric patients with CNS tumours treated with protons or IMRT. CNS tumours form the second most common group of cancers in children. Radiotherapy plays a major role in the treatment of many of these patients but also contributes to late side effects in long term survivors. Radiation dose inevitably deposited in healthy tissues outside the clinical target has been linked to detrimental late effects such as neurocognitive, behavioural and vascular effects in addition to endocrine abnormalities and second tumours. Methods: A literature search was performed using keywords: protons, IMRT, CNS and paediatric. Of 189 papers retrieved, 10 were deemed relevant based on title and abstract screening. All papers directly compared outcomes from protons with photons, five papers included medulloblastoma, four papers each included craniopharyngioma and low grade gliomas and three papers included ependymoma. Results: This review found that while proton beam therapy offered similar clinical target coverage, there was a demonstrable reduction in integral dose to normal structures. Conclusions: This in turn suggests the potential for superior long term outcomes for paediatric patients with CNS tumours both in terms of radiogenic second cancers and out-of-field adverse effects.

The physics of proton therapy

The physics of proton therapy has advanced considerably since it was proposed in 1946. Today analytical equations and numerical simulation methods are available to predict and characterize many aspects of proton therapy. This article reviews the basic aspects of the physics of proton therapy, including proton interaction mechanisms, proton transport calculations, the determination of dose from therapeutic and stray radiations, and shielding design. The article discusses underlying processes as well as selected practical experimental and theoretical methods. We conclude by briefly speculating on possible future areas of research of relevance to the physics of proton therapy.

Inter-Institutional Comparison of Personalized Risk Assessments for Second Malignant Neoplasms for a 13-Year-Old Girl Receiving Proton versus Photon Craniospinal Irradiation

Children receiving radiotherapy face the probability of a subsequent malignant neoplasm (SMN). In some cases, the predicted SMN risk can be reduced by proton therapy. The purpose of this study was to apply the most comprehensive dose assessment methods to estimate the reduction in SMN risk after proton therapy vs. photon therapy for a 13-year-old girl requiring craniospinal irradiation (CSI). We reconstructed the equivalent dose throughout the patient’s body from therapeutic and stray radiation and applied SMN incidence and mortality risk models for each modality. Excluding skin cancer, the risk of incidence after proton CSI was a third of that of photon CSI. The predicted absolute SMN risks were high. For photon CSI, the SMN incidence rates greater than 10% were for thyroid, non-melanoma skin, lung, colon, stomach, and other solid cancers, and for proton CSI they were non-melanoma skin, lung, and other solid cancers. In each setting, lung cancer accounted for half the risk of mortality. In conclusion, the predicted SMN risk for a 13-year-old girl undergoing proton CSI was reduced vs. photon CSI. This study demonstrates the feasibility of inter-institutional whole-body dose and risk assessments and also serves as a model for including risk estimation in personalized cancer care.