Clinical controversies: proton therapy for pediatric tumors

Integrating Systemic Therapies into the Multimodality Therapy of Patients with Craniopharyngioma

OPINION STATEMENT

The integration of targeted therapy into the multimodal management of craniopharyngiomas represents a significant advancement in the field of neuro-oncology. Historically, the management of these tumors has been challenging due to their proximity to vital brain structures, necessitating a delicate balance between tumor control and the preservation of neurological function. Traditional treatment modalities, such as surgical resection and radiation, while effective, carry their own set of risks, including potential damage to surrounding healthy tissues and the potential for long-term side effects. Recent insights into the molecular biology of craniopharyngiomas, particularly the discovery of the BRAF V600E mutation in nearly all papillary craniopharyngiomas, have paved the way for a targeted systemic treatment approach. However, advances have been limited for adamantinomatous craniopharyngiomas. The success of BRAF/MEK inhibitors in clinical trials underscores the potential of these targeted therapies not only to control tumor growth but also to reduce the need for more invasive treatments, potentially minimizing treatment-related complications. However, the introduction of these novel therapies also brings forth new challenges, such as determining the optimal timing, sequencing, and duration of targeted treatments. Furthermore, there are open questions regarding which specific BRAF/MEK inhibitors to use, the potential need for combination therapy, and the strategies for managing intolerable adverse events. Finally, ensuring equitable access to these therapies, especially in healthcare systems with limited resources, is crucial to prevent widening healthcare disparities. In conclusion, targeted therapy with BRAF/MEK inhibitors holds great promise for improving outcomes and quality of life for patients with BRAF-mutated craniopharyngiomas. However, additional research is needed to address the questions that remain about its optimal use and integration into comprehensive treatment plans.

Clinical Insight on Proton Therapy for Paediatric Rhabdomyosarcoma

This paper offers an insight into the use of Proton Beam Therapy (PBT) in paediatric patients with rhabdomyosarcoma (RMS). This paper provides a comprehensive analysis of the literature, investigating comparative photon-proton dosimetry, outcome, and toxicity. In the complex and multimodal scenario of the treatment of RMS, clear evidence of the therapeutic superiority of PBT compared to other modern photon techniques has not yet been demonstrated; however, PBT can be considered an excellent treatment option, in particular for young children and patients with specific primary sites, such as the head and neck area (and especially the parameningeal regions), genito-urinary, pelvic, and paravertebral regions. The unique depth-dose characteristics of protons can be exploited to achieve significant reductions in normal tissue doses and may allow an escalation of tumour doses and greater sparing of normal tissues, thus potentially improving local control while at the same time reducing toxicity and improving quality of life. However, access of children with RMS (and more in general with solid tumors) to PBT remains a challenge, due to the limited number of available proton therapy installations.

Proton therapy and limited surgery for paediatric and adolescent patients with craniopharyngioma (RT2CR): a single-arm, phase 2 study

BACKGROUND

Compared with photon therapy, proton therapy reduces exposure of normal brain tissue in patients with craniopharyngioma, which might reduce cognitive deficits associated with radiotherapy. Because there are known physical differences between the two methods of radiotherapy, we aimed to estimate progression-free survival and overall survival distributions for paediatric and adolescent patients with craniopharyngioma treated with limited surgery and proton therapy, while monitoring for excessive CNS toxicity.

METHODS

In this single-arm, phase 2 study, patients with craniopharyngioma at St Jude Children's Research Hospital (Memphis TN, USA) and University of Florida Health Proton Therapy Institute (Jacksonville, FL, USA) were recruited. Patients were eligible if they were aged 0-21 years at the time of enrolment and had not been treated with previous radiotherapeutic or intracystic therapies. Eligible patients were treated using passively scattered proton beams, 54 Gy (relative biological effect), and a 0·5 cm clinical target volume margin. Surgical treatment was individualised before proton therapy and included no surgery, single procedures with catheter and Ommaya reservoir placement through a burr hole or craniotomy, endoscopic resection, trans-sphenoidal resection, craniotomy, or multiple procedure types. After completing treatment, patients were evaluated clinically and by neuroimaging for tumour progression and evidence of necrosis, vasculopathy, permanent neurological deficits, vision loss, and endocrinopathy. Neurocognitive tests were administered at baseline and once a year for 5 years. Outcomes were compared with a historical cohort treated with surgery and photon therapy. The coprimary endpoints were progression-free survival and overall survival. Progression was defined as an increase in tumour dimensions on successive imaging evaluations more than 2 years after treatment. Survival and safety were also assessed in all patients who received photon therapy and limited surgery. This study is registered with ClinicalTrials.gov, NCT01419067.

FINDINGS

Between Aug 22, 2011, and Jan 19, 2016, 94 patients were enrolled and treated with surgery and proton therapy, of whom 49 (52%) were female, 45 (48%) were male, 62 (66%) were White, 16 (17%) were Black, two (2%) were Asian, and 14 (15%) were other races, and median age was 9·39 years (IQR 6·39-13·38) at the time of radiotherapy. As of data cutoff (Feb 2, 2022), median follow-up was 7·52 years (IQR 6·28-8·53) for patients who did not have progression and 7·62 years (IQR 6·48-8·54) for the full cohort of 94 patients. 3-year progression-free survival was 96·8% (95% CI 90·4-99·0; p=0·89), with progression occurring in three of 94 patients. No deaths occurred at 3 years, such that overall survival was 100%. At 5 years, necrosis had occurred in two (2%) of 94 patients, severe vasculopathy in four (4%), and permanent neurological conditions in three (3%); decline in vision from normal to abnormal occurred in four (7%) of 54 patients with normal vision at baseline. The most common grade 3-4 adverse events were headache (six [6%] of 94 patients), seizure (five [5%]), and vascular disorders (six [6%]). No deaths occurred as of data cutoff.

INTERPRETATION

Proton therapy did not improve survival outcomes in paediatric and adolescent patients with craniopharyngioma compared with a historical cohort, and severe complication rates were similar. However, cognitive outcomes with proton therapy were improved over photon therapy. Children and adolescents treated for craniopharyngioma using limited surgery and post-operative proton therapy have a high rate of tumour control and low rate of severe complications. The outcomes achieved with this treatment represent a new benchmark to which other regimens can be compared.

FUNDING

American Lebanese Syrian Associated Charities, American Cancer Society, the US National Cancer Institute, and Research to Prevent Blindness.

Late Toxicity After 3-Dimensional External Beam Radiotherapy Among Children With Cancer: A Systematic Review

Radiotherapy has evolved from 2-dimensional conventional radiotherapy (2D-RT) to 3-dimensional planned radiotherapy (3D-RT). Because 3D-RT improves conformity, an altered late health outcomes risk profile is anticipated. Here, we systematically reviewed the current literature on late toxicity after 3D-RT in children treated for cancer. PubMed was searched for studies describing late toxicity after 3D-RT for childhood cancer (below 21 y). Late toxicity was defined as somatic health outcomes occurring ≥90 days after treatment. We identified 13 eligible studies, describing most frequently head/neck area tumors. Included studies reported on crude frequencies of late toxicities including subsequent tumors and conditions of organ systems. Three studies offered a global assessment of the full spectrum of late toxicity; one study compared toxicities after 2D-RT and 3D-RT. Incidence rates were typically not provided. Heterogeneity in study characteristics, small study sizes and short follow-up times precluded multivariable modeling and pooling of data. In conclusion, among the first pediatric cohorts treated with 3D-RT, a broad variety of late toxicity is reported; precise estimates of incidence, and contributions of risk factors are unclear. Continued systematic evaluation of well-defined health outcomes in survivors treated with 3D-RT, including proton therapy, is needed to optimize evidence-based care for children with cancer and survivors.

Current approaches to management of bone sarcoma in adolescent and young adult patients

Bone tumors are a group of histologically diverse diseases that occur across all ages. Two of the commonest, osteosarcoma (OS) and Ewing sarcoma (ES), are regarded as characteristic adolescent and young adult (AYA) cancers with an incidence peak in AYAs. They are curable for some but associated with unacceptably high rates of treatment failure and morbidity. The introduction of effective new therapeutics for bone sarcomas is slow, and to date, complex biology has been insufficiently characterized to allow more rapid therapeutic exploitation. This review focuses on current standards of care, recent advances that have or may soon change that standard of care and challenges to the expert clinical research community that we suggest must be met.

New aspects and innovations in the local treatment of renal and urogenital pediatric tumors

Local treatment plays a key role for patients' outcome in tumors of the urogenital tract in children. Despite a great variety of different etiologies, the specific localization of pediatric urogenital tumors renders several characteristic demands to the treating personnel. Surgery and radiotherapy are the main elements of local treatment in this group of neoplasms. Numerous new guidelines and innovative technical developments of surgery and radiotherapy have recently been integrated into treatment concepts for pediatric urogenital tumors. Due to the broadness of the field it is not possible to give a full overview over all aspects. Therefore, this article highlights the most important innovations and new guidelines of surgery and radiotherapy of pediatric urogenital tumors.

A comparative study on dispersed doses during photon and proton radiation therapy in pediatric applications

The Monte Carlo method was employed to simulate realistic treatment situations for photon and proton radiation therapy for a set of Oak Ridge National Laboratory (ORNL) pediatric phantoms for 15, 10, 5 and 1-year olds as well as newborns. Complete radiotherapy situations were simulated using the previously developed NRUrad input code for Monte Carlo N-Particle (MCNP) code package. Each pediatric phantom was irradiated at five different positions, namely, the testes, colon, liver, left lung and brain, and the doses in targeted organs (Dt) were determined using the track length estimate of energy. The dispersed photon and proton doses in non-targeted organs (Dd), namely, the skeleton, skin, brain, spine, left and right lungs were computed. The conversion coefficients (F = Dd/Dt) of the dispersed doses were used to study the dose dispersion in different non-targeted organs for phantoms for 15, 10, 5 and 1-year olds as well as newborns. In general, the F values were larger for younger patients. The F values for non-targeted organs for phantoms for 1-year olds and newborns were significantly larger compared to those for other phantoms. The dispersed doses from proton radiation therapy were also found to be significantly lower than those from conventional photon radiation therapy. For example, the largest F values for the brain were 65.6% and 0.206% of the dose delivered to the left lung (P4) for newborns during photon and proton radiation therapy, respectively. The present results demonstrated that dispersion of photons and generated electrons significantly affected the absorbed doses in non-targeted organs during pediatric photon therapy, and illustrated that proton therapy could in general bring benefits for treatment of pediatric cancer patients.

Radiobiological effectiveness difference of proton arc beams versus conventional proton and photon beams

This paper aims to demonstrate the difference in biological effectiveness of proton monoenergetic arc therapy (PMAT) compared to intensity modulated proton therapy (IMPT) and conventional 6 MV photon therapy, and to quantify this difference when exposing cells of different radiosensitivity to the same experimental conditions for each modality. V79, H1299 and H460 cells were cultured in petri dishes placed in the central axis of a cylindrical and homogeneous solid water phantom of 20 cm in diameter. For the PMAT plan, cells were exposed to 13 mono-energetic proton beams separated every 15° over a 180° arc, designed to deliver a uniform dose of higher LET to the petri dishes. For the IMPT plans, 3 fields were used, where each field was modulated to cover the full target. Cells were also exposed to 6 MV photon beams in petri dishes to characterize their radiosensitivity. The relative biological effectiveness of the PMAT plans compared with those of IMPT was measured using clonogenic assays. Similarly, in order to study the quantity and quality of the DNA damage induced by the PMAT plans compared to that of IMPT and photons, γ-H2AX assays were conducted to study the relative amount of DNA damage induced by each modality, and their repair rate over time. The clonogenic assay revealed similar survival levels to the same dose delivered with IMPT or x-rays. However, a systematic average of up to a 43% increase in effectiveness in PMAT plans was observed when compared with IMPT. In addition, the repair kinetic assays proved that PMAT induces larger and more complex DNA damage (evidenced by a slower repair rate and a larger proportion of unrepaired DNA damage) than IMPT. The repair kinetics of IMPT and 6 MV photon therapy were similar. Mono-energetic arc beams offer the possibility of taking advantage of the enhanced LET of proton beams to increase TCP. This study presents initial results based on exposing cells with different radiosensitivity to other modalities under the same experimental conditions, but more extensive clonogenic and in-vivo studies will be required to confirm the validity of these results.

Child Proton Beam Therapy: A qualitative study of parental views on treatment and information sources

INTRODUCTION

Proton Beam Therapy (PBT) is often described as an advanced mode of radiotherapy. Whilst PBT offers an equivalent chance of cure to conventional radiotherapy, it is said to offer a theoretical reduction in long term side effects. NHS patients have had access to PBT since 2008 and approximately 65% of the 1144 approved referrals have been for paediatric cases. Yet, there is little research on how parents in these paediatric cases perceive their child's PBT and the information sources they encounter.

METHODS

This is a qualitative inquiry informed by in-depth interviews carried out with 27 parents of children treated with PBT.

RESULTS

Parents primarily frame PBT as a form of radiation but one which is better than alternatives. Whilst medical professionals do play a role, wider sources of information - such as other families and the internet - are important to both initial decision-making and treatment/recovery experiences.

CONCLUSION

Parents are faced with the challenge of a 'fragmented expertise' which comes with the 'novelty' of the radiation therapy, the 'rare' nature of the tumours and the remote location of clinical specialists.

IMPLICATIONS FOR PRACTICE

This article will prove useful for practitioners dealing with parents and care givers of children undergoing proton therapy, and is especially valuable and timely for practitioners based in the newly installed proton centres in the UK. Two high energy proton centres are expected to become fully operational in the UK by the end of 2020. Understanding parents' experiences and perspectives can help avoid undue anxiety and lead to service improvements and overall satisfaction.

Research progress on mechanism and dosimetry of brainstem injury induced by intensity-modulated radiotherapy, proton therapy, and heavy ion radiotherapy

Radiotherapy (RT) is an effective method for treating head and neck cancer (HNC). However, RT may cause side effects during and after treatment. Radiation-induced brainstem injury (BSI) is often neglected due to its low incidence and short survival time and because it is indistinguishable from intracranial tumor progression. It is currently believed that the possible mechanism of radiation-induced BSI includes increased expression of vascular endothelial growth factor and damage of vascular endothelial cells, neurons, and glial cells as well as an inflammatory response and oxidative stress. At present, it is still difficult to avoid BSI even with several advanced RT techniques. Intensity-modulated radiotherapy (IMRT) is the most commonly used therapeutic technique in the field of RT. Compared with early conformal therapy, it has greatly reduced the injury to normal tissues. Proton beam radiotherapy (PBT) and heavy ion radiotherapy (HIT) have good dose distribution due to the presence of a Bragg peak, which not only results in better control of the tumor but also minimizes the dose to the surrounding normal tissues. There are many clinical studies on BSI caused by IMRT, PBT, and HIT. In this paper, we review the mechanism, dosimetry, and other aspects of BSI caused by IMRT, PBT, and HIT.Key Points• Enhanced MRI imaging can better detect radiation-induced BSI early.• This article summarized the dose constraints of brainstem toxicity in clinical studies using different techniques including IMRT, PBT, and HIT and recommended better dose constraints pattern to clinicians.• The latest pathological mechanism of radiation-induced BSI and the corresponding advanced treatment methods will be discussed.

Paediatric image-guided radiation therapy: determining and evaluating appropriate kilovoltage planar exposure factors for the Varian on-board imager

INTRODUCTION

Kilovoltage (kV) orthogonal imaging is commonly used for image-guided radiation therapy (IGRT) in paediatrics. Paediatrics have an increased sensitivity to radiation. Exposure factors need to be optimised so that imaging dose is kept as low as reasonably achievable (ALARA).

METHODS

A table of low-dose IGRT radiographic exposure factors for paediatric IGRT was determined through a phantom study. Four anatomical sites, head and neck, thorax, abdomen and pelvis, were investigated. The table was evaluated against standard manufacturer pre-sets. Dose was evaluated in terms of system-reported entrance surface air kerma (ESAK). Qualified participants volunteered to perform offline image matching in a further phantom study, recording misalignments detected and providing subjective assessments of image quality using an electronic survey tool. A statistical comparison of matching accuracy was conducted.

RESULTS

Twelve radiation therapists or radiation oncologists completed the image matching task and survey. The low-dose exposure table reduced imaging dose by 20-94% compared to manufacturer pre-sets. No significant difference was observed in the accuracy of image matching (head and neck P = 0.82, thorax P = 0.15, abdomen P = 0.33, pelvis P = 0.59). Participant image exposure preference was largely equivocal.

CONCLUSIONS

Optimising radiographic exposures in paediatric IGRT is feasible, logical and therefore reasonably achievable. Implementation of the low-dose exposure table presented in this study should be considered by paediatric radiotherapy departments wishing to image gently without compromising the potential to detect set up errors. Further study using a contrast detail phantom and contrast to noise image analysis software is recommended.

The role of proton therapy in pediatric malignancies: Recent advances and future directions

Proton radiotherapy has promised an advantage in safely treating pediatric malignancies with an increased capability to spare normal tissues, reducing the risk of both acute and late toxicity. The past decade has seen the proliferation of more than 30 proton facilities in the United States, with increased capacity to provide access to approximately 3,000 children per year who will require radiotherapy for their disease. We provide a review of the initial efforts to describe outcomes after proton therapy across the common pediatric disease sites. We discuss the main attempts to assess comparative efficacy between proton and photon radiotherapy concerning toxicity. We also discuss recent efforts of multi-institutional registries aimed at accelerating research to better define the optimal treatment paradigm for children requiring radiotherapy for cure.

Proton therapy in the most common pediatric non-central nervous system malignancies: an overview of clinical and dosimetric outcomes

Radiation therapy represents an important approach in the therapeutic management of children and adolescents with malignant tumors and its application with modern techniques – including Proton Beam Therapy (PBT) – is of great interest. In particular, potential radiation-induced injuries and secondary malignancies – also associated to the prolonged life expectancy of patients – are still questions of concern that increase the debate on the usefulness of PBT in pediatric treatments. This paper presents a literary review of current applications of PBT in non-Central Nervous System pediatric tumors (such as retinoblastoma, Hodgkin Lymphoma, Wilms tumor, bone and soft tissues sarcomas). We specifically reported clinical results achieved with PBT and dosimetric comparisons between PBT and the most common photon-therapy techniques. The analysis emphasizes that PBT minimizes radiation doses to healthy growing organs, suggesting for reduced risks of late side-effects and radiation-induced secondary malignancies. Extended follow up and confirms by prospective clinical trials should support the effectiveness and long-term tolerance of PBT in the considered setting.

Radiation-Induced DNA Damage Cooperates with Heterozygosity of TP53 and PTEN to Generate High-Grade Gliomas

Glioblastomas are lethal brain tumors that are treated with conventional radiation (X-rays and gamma rays) or particle radiation (protons and carbon ions). Paradoxically, radiation is also a risk factor for GBM development, raising the possibility that radiotherapy of brain tumors could promote tumor recurrence or trigger secondary gliomas. In this study, we determined whether tumor suppressor losses commonly displayed by patients with GBM confer susceptibility to radiation-induced glioma. Mice with Nestin-Cre-driven deletions of Trp53 and Pten alleles were intracranially irradiated with X-rays or charged particles of increasing atomic number and linear energy transfer (LET). Mice with loss of one allele each of Trp53 and Pten did not develop spontaneous gliomas, but were highly susceptible to radiation-induced gliomagenesis. Tumor development frequency after exposure to high-LET particle radiation was significantly higher compared with X-rays, in accordance with the irreparability of DNA double-strand breaks (DSB) induced by high-LET radiation. All resultant gliomas, regardless of radiation quality, presented histopathologic features of grade IV lesions and harbored populations of cancer stem-like cells with tumor-propagating properties. Furthermore, all tumors displayed concomitant loss of heterozygosity of Trp53 and Pten along with frequent amplification of the Met receptor tyrosine kinase, which conferred a stem cell phenotype to tumor cells. Our results demonstrate that radiation-induced DSBs cooperate with preexisting tumor suppressor losses to generate high-grade gliomas. Moreover, our mouse model can be used for studies on radiation-induced development of GBM and therapeutic strategies. SIGNIFICANCE: This study uncovers mechanisms by which ionizing radiation, especially particle radiation, promote GBM development or recurrence.

National Cancer Institute Workshop on Proton Therapy for Children: Considerations Regarding Brainstem Injury

PURPOSE

Proton therapy can allow for superior avoidance of normal tissues. A widespread consensus has been reached that proton therapy should be used for patients with curable pediatric brain tumor to avoid critical central nervous system structures. Brainstem necrosis is a potentially devastating, but rare, complication of radiation. Recent reports of brainstem necrosis after proton therapy have raised concerns over the potential biological differences among radiation modalities. We have summarized findings from the National Cancer Institute Workshop on Proton Therapy for Children convened in May 2016 to examine brainstem injury.

METHODS AND MATERIALS

Twenty-seven physicians, physicists, and researchers from 17 institutions with expertise met to discuss this issue. The definition of brainstem injury, imaging of this entity, clinical experience with photons and photons, and potential biological differences among these radiation modalities were thoroughly discussed and reviewed. The 3 largest US pediatric proton therapy centers collectively summarized the incidence of symptomatic brainstem injury and physics details (planning, dosimetry, delivery) for 671 children with focal posterior fossa tumors treated with protons from 2006 to 2016.

RESULTS

The average rate of symptomatic brainstem toxicity from the 3 largest US pediatric proton centers was 2.38%. The actuarial rate of grade ≥2 brainstem toxicity was successfully reduced from 12.7% to 0% at 1 center after adopting modified radiation guidelines. Guidelines for treatment planning and current consensus brainstem constraints for proton therapy are presented. The current knowledge regarding linear energy transfer (LET) and its relationship to relative biological effectiveness (RBE) are defined. We review the current state of LET-based planning.

CONCLUSIONS

Brainstem injury is a rare complication of radiation therapy for both photons and protons. Substantial dosimetric data have been collected for brainstem injury after proton therapy, and established guidelines to allow for safe delivery of proton radiation have been defined. Increased capability exists to incorporate LET optimization; however, further research is needed to fully explore the capabilities of LET- and RBE-based planning.

Evolving Radiotherapy Techniques in Paediatric Oncology

AIMS

Childhood cancer is rare and survival of childhood cancer has increased up to 80% at 5 years after diagnosis. Radiotherapy is an important element of the multimodal treatment concept. However, due to growing tissue, children are particularly sensitive to radiation-related side-effects and the induction of secondary malignancies. However, radiotherapy techniques have continuously progressed. In addition, modern treatment concepts have been improved in order to minimise long-term effects. Today, radiotherapy is used for various tumour types in childhood, such as sarcomas and tumours of the central nervous system.

MATERIALS AND METHODS

External beam therapy with either photons or protons and brachytherapy are predominantly used for the treatment of childhood tumours. Technical developments and features, as well as clinical outcomes, for several tumour entities are presented.

RESULTS

The development of radiotherapy techniques, as well as risk-adapted therapy concepts, resulted in promising outcome regarding tumour control, survival and therapy-related side-effects. It is assumed that proton therapy will be increasingly used for treating children in the future. However, more data have to be collected through multi-institutional registries in order to strengthen the evidence.

CONCLUSION

The development of radiotherapy techniques is beneficial for children in terms of reducing dose exposure. As compared with other modern and highly conformal techniques, particularly proton therapy may achieve high survival rates and tumour control rates while decreasing the risk for side-effects. However, clinical evidence for modern radiotherapy techniques is still limited today. An optimal patient triaging with the selection of the most appropriate radiation technique for each individual patient will be an important goal for the future.

Early Axial Growth Outcomes of Pediatric Patients Receiving Proton Craniospinal Irradiation

Guidelines on proton craniospinal irradiation (p-CSI) target volume selection in children are lacking. We examined the impact of target volume selection on growth of children receiving p-CSI at a institution. Records of 58 patients who received p-CSI were reviewed. Median age at treatment initiation was 8 years (range, 2 to 18 y). Spinal target volumes included whole vertebral body (WVB) in 67% and partial vertebral body (PVB) in 33%. Height z-scores before and after p-CSI were assessed using Centers for Disease Control and Prevention stature-for-age charts. Maximal Cobb angle and height z-score change were compared for WVB versus PVB p-CSI using a t test. Among 93% of patients with detailed data, median follow-up was 19 months (range, 2 to 58 mo) after radiation therapy initiation. Quantitative growth evaluations were available for 64% of patients. Median change in height z-score was -0.5 (range, -2.1 to +0.7) after treatment, representing a decrease (P<0.001) in age-adjusted height. WVB patients had significantly greater reduction in height z-score versus PVB patients (P=0.004) but no difference in Cobb angle change (P>0.05). Despite reluctance surrounding its use in younger patients, PVB p-CSI was associated with similar spinal curvature and less growth suppression as compared with WVB p-CSI; a trial comparing WVB versus PVB in children may be warranted.

Comparing Photon and Charged Particle Therapy Using DNA Damage Biomarkers

Treatment modalities for cancer radiation therapy have become increasingly diversified given the growing number of facilities providing proton and carbon-ion therapy in addition to the more historically accepted photon therapy. An understanding of high-LET radiobiology is critical for optimization of charged particle radiation therapy and potential DNA damage response. In this review, we present a comprehensive summary and comparison of these types of therapy monitored primarily by using DNA damage biomarkers. We focus on their relative profiles of dose distribution and mechanisms of action from the level of nucleic acid to tumor cell death.

Auditory Outcomes in Patients Who Received Proton Radiotherapy for Craniopharyngioma

PURPOSE

Compared to photon-based radiotherapy, protons deliver less radiation to healthy tissue resulting in the potential reduction of late complications such as sensorineural hearing loss (SNHL). We report early auditory outcomes in children treated with proton radiotherapy (PRT) for craniopharyngioma.

METHOD

Conventional frequency (CF = 0.25-8.0 kHz) audiometry, extended high-frequency (EHF = 9.0-16.0 kHz) audiometry, distortion product otoacoustic emission (DPOAE) testing, and speech-in-noise (SIN) assessments were prospectively and longitudinally conducted on 74 children with a median of 2 post-PRT evaluations (range, 1-5) per patient. The median age at PRT initiation was 10 years, and median follow-up time was 2 years. Ototoxicity was classified using the Chang Ototoxicity Grading Scale (Chang & Chinosornvatana, 2010) and the American Speech-Language-Hearing Association (ASHA) criteria (ASHA, 1994). Comparisons were made between baseline and most recent DPOAE levels, with evidence of ototoxicity based on criterion reductions of ≥ 6 dB. The critical difference values for comparing SIN scores between two conditions (i.e., pre- and post-PRT) were used to determine a significant change between test scores.

RESULTS

At last evaluation, no patients had SNHL in the CF range, and 2 patients had SNHL (Chang Grade 1a) in the EHF range. Based on the ASHA criteria, a decrease in hearing was observed in 0 patients in the CF range alone, in 9 patients in the EHF range alone, and in 15 patients in both the CF and EHF ranges. DPOAE levels decreased at a faster rate at higher versus lower frequencies. For 41 evaluable patients, SIN perception did not decline over time (p = .6463).

CONCLUSION

At a median follow-up time of 2 years post-PRT, normal hearing was maintained within the CF range. However, subclinical decreases in hearing were observed, particularly in the EHF range and in the DPOAE level; thus, long-term follow-up is recommended to monitor for potential auditory late effects from PRT.

An Update From the Pediatric Proton Consortium Registry

Background/objectives

The Pediatric Proton Consortium Registry (PPCR) was established to expedite proton outcomes research in the pediatric population requiring radiotherapy. Here, we introduce the PPCR as a resource to the oncology community and provide an overview of the data available for further study and collaboration.

Design/methods

A multi-institutional registry of integrated clinical, dosimetric, radiographic, and patient-reported data for patients undergoing proton radiation therapy was conceived in May 2010. Massachusetts General Hospital began enrollment in July of 2012. Subsequently, 12 other institutions joined the PPCR and activated patient accrual, with the latest joining in 2017. An optional patient-reported quality of life (QoL) survey is currently implemented at six institutions. Baseline health status, symptoms, medications, neurocognitive status, audiogram findings, and neuroendocrine testing are collected. Treatment details of surgery, chemotherapy, and radiation therapy are documented and radiation plans are archived. Follow-up is collected annually. Data were analyzed 25 September, 2017.

Results

A total of 1,854 patients have consented and enrolled in the PPCR from October 2012 until September 2017. The cohort is 55% male, 70% Caucasian, and comprised of 79% United States residents. Central nervous system (CNS) tumors comprise 61% of the cohort. The most common CNS histologies are as follows: medulloblastoma (n = 276), ependymoma (n = 214), glioma/astrocytoma (n = 195), craniopharyngioma (n = 153), and germ cell tumors (n = 108). The most common non-CNS tumors diagnoses are as follows: rhabdomyosarcoma (n = 191), Ewing sarcoma (n = 105), Hodgkin lymphoma (n = 66), and neuroblastoma (n = 55). The median follow-up is 1.5 years with a range of 0.14 to 4.6 years.

Conclusion

A large prospective population of children irradiated with proton therapy has reached a critical milestone to facilitate long-awaited clinical outcomes research in the modern era. This is an important resource for investigators both in the consortium and for those who wish to access the data for academic research pursuits.

Radiobiological issues in proton therapy

BACKGROUND

The relative biological effectiveness (RBE) for particle therapy is a complex function of particle type, radiation dose, linear energy transfer (LET), cell type, endpoint, etc. In the clinical practice of proton therapy, the RBE is assumed to have a fixed value of 1.1. This assumption, along with the effects of physical uncertainties, may mean that the biologically effective dose distributions received by the patient may be significantly different from what is seen on treatment plans. This may contribute to unforeseen toxicities and/or failure to control the disease. Variability of Proton RBE: It has been shown experimentally that proton RBE varies significantly along the beam path, especially near the end of the particle range. While there is now an increasing acceptance that proton RBE is variable, there is an ongoing debate about whether to change the current clinical practice. Clinical Evidence: A rationale against the change is the uncertainty in the models of variable RBE. Secondly, so far there is no clear clinical evidence of the harm of assuming proton RBE to be 1.1. It is conceivable, however, that the evidence is masked partially by physical uncertainties. It is, therefore, plausible that reduction in uncertainties and their incorporation in the estimation of dose actually delivered may isolate and reveal the variability of RBE in clinical practice. Nevertheless, clinical evidence of RBE variability is slowly emerging as more patients are treated with protons and their response data are analyzed. Modelling and Incorporation of RBE in the Optimization of Proton Therapy: The improvement in the knowledge of RBE could lead to better understanding of outcomes of proton therapy and in the improvement of models to predict RBE. Prospectively, the incorporation of such models in the optimization of intensity-modulated proton therapy could lead to improvements in the therapeutic ratio of proton therapy.

Current Clinical Challenges in Childhood Ependymoma: A Focused Review

Ependymoma is a locally aggressive tumor with metastatic potential that arises in diverse locations throughout the brain and spine in children. Tumor and treatment may result in significant morbidity. Cure remains elusive for many patients owing to diverse biology and resistance to conventional therapy. The implementation of systematic postoperative irradiation in clinical trials during the past 20 years has increased the proportion of patients achieving durable disease control with excellent results, as measured by objective functional outcome measures. Clinical, pathologic, and molecular risk stratification should be used to refine treatment regimens for children with ependymoma to reduce the risk of complications associated with therapy and increase the rate of disease control in the setting of combined modality or more intensive therapy. This review covers standards of care and current clinical trials for children with ependymoma, emphasizing the history and evolution of treatment regimens during the past 20 years and the clinical questions they hoped to address.

Proton beam therapy for pediatric malignancies

Although major advances have been made in radiation techniques, concerns still exist about the treatment-related acute and long-term side effects. This issue is most notable in the pediatric population because of developing organs and tissues combined with longer life expectancies. Proton beam therapy has the advantage of a reduced dose of radiation with less scatter to normal tissue, which may lead to fewer adverse side effects.
AT A GLANCE: Many pediatric patients with cancer receive radiation therapy.Radiation treatments can cause significant acute and long-term side effects.Proton beam therapy reduces radiation scatter to normal tissues and may decrease acute and late toxicities.

Can We Spare the Pancreas and Other Abdominal Organs at Risk? A Comparison of Conformal Radiotherapy, Helical Tomotherapy and Proton Beam Therapy in Pediatric Irradiation

OBJECTIVES

Late abdominal irradiation toxicity during childhood included renal damage, hepatic toxicity and secondary diabetes mellitus. We compared the potential of conformal radiotherapy (CRT), helical tomotherapy (HT) and proton beam therapy (PBT) to spare the abdominal organs at risk (pancreas, kidneys and liver- OAR) in children undergoing abdominal irradiation.

METHODS

We selected children with abdominal tumors who received more than 10 Gy to the abdomen. Treatment plans were calculated in order to keep the dose to abdominal OAR as low as possible while maintaining the same planned target volume (PTV) coverage. Dosimetric values were compared using the Wilcoxon signed-rank test.

RESULTS

The dose distribution of 20 clinical cases with a median age of 8 years (range 1-14) were calculated with different doses to the PTV: 5 medulloblastomas (36 Gy), 3 left-sided and 2 right-sided nephroblastomas (14.4 Gy to the tumor + 10.8 Gy boost to para-aortic lymphnodes), 1 left-sided and 4 right-sided or midline neuroblastomas (21 Gy) and 5 Hodgkin lymphomas (19.8 Gy to the para-aortic lymphnodes and spleen). HT significantly reduced the mean dose to the whole pancreas (WP), the pancreatic tail (PT) and to the ipsilateral kidney compared to CRT. PBT reduced the mean dose to the WP and PT compared to both CRT and HT especially in midline and right-sided tumors. PBT decreased the mean dose to the ispilateral kidney but also to the contralateral kidney and the liver compared to CRT. Low dose to normal tissue was similar or increased with HT whereas integral dose and the volume of normal tissue receiving at least 5 and 10 Gy were reduced with PBT compared to CRT and HT.

CONCLUSION

In children undergoing abdominal irradiation therapy, proton beam therapy reduces the dose to abdominal OAR while sparing normal tissue by limiting low dose irradiation.

Proton therapy in paediatric oncology: an Irish perspective

BACKGROUND

Proton therapy (PT) is a radiotherapy treatment modality that uses protons, rather than conventional photons. PT is often used in paediatric oncology due to its reported capability to reduce acute and late adverse treatment effects. As PT is unavailable in Ireland, patients are referred abroad for treatment.

AIMS

To: (1) produce a descriptive study of Irish children referred abroad for PT, and (2) discuss the case for PT in general.

METHODS

A retrospective review of all children referred for PT before October 2015 was performed. Information was gathered regarding demographics, diagnosis, referral timeline, adverse effects attributable to PT, current status and cost. A review of the relevant literature was performed.

RESULTS

Seventeen children treated in Ireland have been referred abroad for PT. The largest number was in the 0-4 year old group. At initial diagnosis the median age was 4.8 years. The average cost per child was €37,312. Two patients suffered disease relapse. Four have encountered PT-related adverse effects.

CONCLUSION

Despite the fact that >100,000 patients worldwide have been treated with PT, the level of published evidence to support superiority over conventional treatment remains low. It is debated that randomised control trials in this area would be inconsistent with the principle of clinical equipoise. In contrast, there is a call for level 1 evidence to justify drastic changes in patient care, particularly in light of recent reports of unexpected toxicities. In time, careful evaluation, follow-up and clinical trials will likely support the preferential use of PT in children.

Pediatric Ependymoma

Over the past 150 years since Virchow's initial characterization of ependymoma, incredible efforts have been made in the classification of these tumors and in the care of pediatric patients with this disease. While the advent of modern neurosurgery and the optimization of radiation have provided significant gains, a more complex but incomplete picture of pediatric ependymomas has begun to form through a combination of international collaborations and detailed genetic and histologic characterizations. This review includes and synthesizes the clinical understanding of pediatric ependymoma and their developing molecular insight into what is truly a family of malignancies in which distinct members require different surgical approaches, radiation plans, and targeted therapies.

Patterns of Failure in Pediatric Rhabdomyosarcoma After Proton Therapy

PURPOSE

To report on the patterns of failure in children with rhabdomyosarcoma treated with proton therapy.

PATIENTS AND METHODS

Between February 2007 and November 2013, 66 children with a median age of 4.1 years (range, 0.6-15.3 years) diagnosed with nonmetastatic rhabdomyosarcoma were treated with proton therapy. Clinical target volume 1 was defined as the prechemotherapy tumor plus a 1-cm anatomically constrained margin. Clinical target volume 2 was defined as the postchemotherapy tumor (or tumor bed) plus a 0.5-cm anatomically constrained margin, further expanded to encompass potential pathways of spread, including soft tissue infiltrated with tumor at diagnosis.

RESULTS

Of the 66 children, 11 developed locally progressive disease at a median of 16 months (range, 14-32 months), for an actuarial 2-year local control rate of 88%. Among the children who progressed, median age and tumor size at diagnosis were 6.7 years (range, 0.6-16 years) and 6 cm (range, 2-8 cm), respectively. Of the recurrences, 64% and 36% were embryonal and alveolar, respectively. Disease progression was observed in 7 (64%) parameningeal, 2 (18%) head and neck (other), and 2 (18%) bladder/prostate subsites. At diagnosis, 8 of 11 patients who developed a recurrence were Intergroup Rhabdomyosarcoma Study stage 3, and all 11 were group III. Of the relapses, 100% (11 of 11) were confirmed as in-field within the composite 95% isodose line. One of the 11 patients (9%) developed a new simultaneous regional nodal recurrence outside of the previously treated radiation field.

CONCLUSION

Early data suggest that the sharp dosimetric gradient associated with proton therapy is not associated with an increased risk of marginal failure. Routine use of a 0.5- to 1-cm clinical target volume 1/2 margin with highly conformal proton therapy does not compromise local control in children diagnosed with rhabdomyosarcoma with unfavorable risk features.

A Cross-Sectional Cohort Study of Cerebrovascular Disease and Late Effects After Radiation Therapy for Craniopharyngioma

BACKGROUND

The study objective was to describe radiation-induced vascular abnormalities, stroke prevalence, and stroke risk factors in survivors of childhood craniopharyngioma.

PROCEDURE

Twenty survivors of childhood craniopharyngioma who received radiotherapy (RT) were included in the study. A clinical history, quality of life assessment, cognitive functioning assessment, magnetic resonance angiogram or computed tomography angiogram, fasting lipid profile, and fasting glucose or hemoglobin A1c test were obtained.

RESULTS

Median age at diagnosis was 10.3 years and median age at time of study was 29.0 years. Vascular abnormalities were detected in six (32%) of 19 patients' angiograms (vascular stenosis, decreased artery size, aneurysm, cavernoma, and small vessel disease). Five (25%) of 20 patients experienced a stroke after RT. Median time since RT was 27.8 versus 9.1 years in patients with versus without vascular abnormalities (P = 0.02). A low level of high-density lipoproteiin (HDL) was present in 100% (5/5) of patients who had a post-RT stroke as compared with 13% (2/15) of patients who did not have any post-RT stroke (P = 0.02). Previous stroke had occurred in 0% (0/5) of patients receiving growth hormone (GH) replacement at the time of study, compared to 40% (6/15) of patients who were not receiving GH replacement (P = 0.09).

CONCLUSIONS

Patients with craniopharyngioma treated with RT have a high prevalence of stroke and vascular abnormalities, particularly those with low HDL and longer duration of time since RT. There is a trend to suggest that continual GH replacement may reduce the risk of stroke. These patients should undergo careful monitoring and aggressive modification of stroke risk factors.

Multi-modality management of craniopharyngioma: a review of various treatments and their outcomes

Craniopharyngioma is a rare tumor that is expected to occur in ∼400 patients/year in the United States. While surgical resection is considered to be the primary treatment when a patient presents with a craniopharyngioma, only 30% of such tumors present in locations that permit complete resection. Radiotherapy has been used as both primary and adjuvant therapy in the treatment of craniopharyngiomas for over 50 years. Modern radiotherapeutic techniques, via the use of CT-based treatment planning and MRI fusion, have permitted tighter treatment volumes that allow for better tumor control while limiting complications. Modern radiotherapeutic series have shown high control rates with lower doses than traditionally used in the two-dimensional treatment era. Intracavitary radiotherapy with radio-isotopes and stereotactic radiosurgery may have a role in the treatment of recurrent cystic and solid recurrences, respectively. Recently, due to the exclusive expression of the Beta-catenin clonal mutations and the exclusive expression of BRAF V600E clonal mutations in the overwhelming majority of adamantinomatous and papillary tumors respectively, it is felt that inhibitors of each pathway may play a role in the future treatment of these rare tumors.

Treatment tolerance of particle therapy in pediatric patients

Curative treatment of pediatric cancer not only focuses on long-term survival, but also on reducing treatment-related side effects. Advantages of particle therapy are mainly due to their physical ability of significantly reducing integral dose.

METHODS

Between January 2009 and December 2012, we treated 83 pediatric patients (aged 21 and younger) at the Heidelberg Ion Therapy Center at University Hospital of Heidelberg (HIT). In total 56 patients (67%) received proton irradiation, while 25 (30%) patients were treated with carbon ions (C12). Two patients received both treatments (3%). Treatment toxicity was analyzed retrospectively and documented according to the CTCAE/RTOG classification. In a second step, treatment toxicity from ion therapy was analyzed in comparison to treatment toxicity during photon irradiation of a comparable historical group of 19 pediatric patients.

RESULTS

In all patients, particle therapy was tolerated well (median follow-up time 3.7 months), children (20 patients) with at least two follow-up visits showed a median follow-up time of 10.2 months. During the first two months patients mainly suffered from radiogenic skin reaction (63%), mucositis (30%), headache and dizziness (35%) as well as nausea and vomiting (13%). Severe toxicity reaction (grade II-IV) was only seen in patients who had intensive simultaneous chemotherapy or who had undergone several operations in the irradiated area before radiotherapy (18%). Treatment toxicity during ion therapy was comparable to treatment toxicity from photon irradiation of a historical group.

CONCLUSIONS

In comparison to conventional therapy, patients with particle therapy do not suffer from increased acute treatment-related toxicity during the first months. More experience with particle therapy will be needed during the next years to help to thoroughly evaluate the high potential of ion therapy.

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.

Predictive Risk of Radiation Induced Cerebral Necrosis in Pediatric Brain Cancer Patients after VMAT Versus Proton Therapy

Cancer of the brain and central nervous system (CNS) is the second most common of all pediatric cancers. Treatment of many of these cancers includes radiation therapy of which radiation induced cerebral necrosis (RICN) can be a severe and potentially devastating side effect. Risk factors for RICN include brain volume irradiated, the dose given per fraction and total dose. Thirteen pediatric patients were selected for this study to determine the difference in predicted risk of RICN when treating with volumetric modulated arc therapy (VMAT) compared to passively scattered proton therapy (PSPT) and intensity modulated proton therapy (IMPT). Plans were compared on the basis of dosimetric endpoints in the planned treatment volume (PTV) and brain and a radiobiological endpoint of RICN calculated using the Lyman-Kutcher-Burman probit model. Uncertainty tests were performed to determine if the predicted risk of necrosis was sensitive to positional errors, proton range errors and selection of risk models. Both PSPT and IMPT plans resulted in a significant increase in the maximum dose to the brain, a significant reduction in the total brain volume irradiated to low doses, and a significant lower predicted risk of necrosis compared with the VMAT plans. The findings of this study were upheld by the uncertainty analysis.

Role for radiation therapy in melanoma

Although melanoma is generally considered a relative radioresistant tumor, radiation therapy (RT) remains a valid and effective treatment option in definitive, adjuvant, and palliative settings. Definitive RT is generally only used in inoperable patients. Despite a high-quality clinical trial showing adjuvant RT following lymphadenectomy in node-positive melanoma patients prevents local and regional recurrence, the role of adjuvant RT in the treatment of melanoma remains controversial and is underused. RT is highly effective in providing symptom palliation for metastatic melanoma. RT combined with new systemic options, such as immunotherapy, holds promise and is being actively evaluated.

PET/CT-guided treatment planning for paediatric cancer patients: a simulation study of proton and conventional photon therapy

OBJECTIVE

To investigate the impact of including fluorine-18 fludeoxyglucose ((18)F-FDG) positron emission tomography (PET) scanning in the planning of paediatric radiotherapy (RT).

METHODS

Target volumes were first delineated without and subsequently re-delineated with access to (18)F-FDG PET scan information, on duplicate CT sets. RT plans were generated for three-dimensional conformal photon RT (3DCRT) and intensity-modulated proton therapy (IMPT). The results were evaluated by comparison of target volumes, target dose coverage parameters, normal tissue complication probability (NTCP) and estimated risk of secondary cancer (SC).

RESULTS

Considerable deviations between CT- and PET/CT-guided target volumes were seen in 3 out of the 11 patients studied. However, averaging over the whole cohort, CT or PET/CT guidance introduced no significant difference in the shape or size of the target volumes, target dose coverage, irradiated volumes, estimated NTCP or SC risk, neither for IMPT nor 3DCRT.

CONCLUSION

Our results imply that the inclusion of PET/CT scans in the RT planning process could have considerable impact for individual patients. There were no general trends of increasing or decreasing irradiated volumes, suggesting that the long-term morbidity of RT in childhood would on average remain largely unaffected.

ADVANCES IN KNOWLEDGE

(18)F-FDG PET-based RT planning does not systematically change NTCP or SC risk for paediatric cancer patients compared with CT only. 3 out of 11 patients had a distinct change of target volumes when PET-guided planning was introduced. Dice and mismatch metrics are not sufficient to assess the consequences of target volume differences in the context of RT.

Recommendations for the referral of patients for proton-beam therapy, an Alberta Health Services report: a model for Canada?

BACKGROUND

Compared with photon therapy, proton-beam therapy (pbt) offers compelling advantages in physical dose distribution. Worldwide, gantry-based proton facilities are increasing in number, but no such facilities exist in Canada. To access pbt, Canadian patients must travel abroad for treatment at high cost. In the face of limited access, this report seeks to provide recommendations for the selection of patients most likely to benefit from pbt and suggests an out-of-country referral process.

METHODS

The medline, embase, PubMed, and Cochrane databases were systematically searched for studies published between January 1990 and May 2014 that evaluated clinical outcomes after pbt. A draft report developed through a review of evidence was externally reviewed and then approved by the Alberta Health Services Cancer Care Proton Therapy Guidelines steering committee.

RESULTS

Proton therapy is often used to treat tumours close to radiosensitive tissues and to treat children at risk of developing significant late effects of radiation therapy (rt). In uncontrolled and retrospective studies, local control rates with pbt appear similar to, or in some cases higher than, photon rt. Randomized trials comparing equivalent doses of pbt and photon rt are not available.

SUMMARY

Referral for pbt is recommended for patients who are being treated with curative intent and with an expectation for long-term survival, and who are able and willing to travel abroad to a proton facility. Commonly accepted indications for referral include chordoma and chondrosarcoma, intraocular melanoma, and solid tumours in children and adolescents who have the greatest risk for long-term sequelae. Current data do not provide sufficient evidence to recommend routine referral of patients with most head-and-neck, breast, lung, gastrointestinal tract, and pelvic cancers, including prostate cancer. It is recommended that all referrals be considered by a multidisciplinary team to select appropriate cases.

Proton radiotherapy for pediatric tumors: review of first clinical results

Radiation therapy is a part of multidisciplinary management of several childhood cancers. Proton therapy is a new method of irradiation, which uses protons instead of photons. Proton radiation has been used safely and effectively for medulloblastoma, primitive neuro-ectodermal tumors, craniopharyngioma, ependymoma, germ cell intracranial tumors, low-grade glioma, retinoblastoma, rhabdomyosarcoma and other soft tissue sarcomas, Ewing’s sarcoma and other bone sarcomas. Moreover, other possible applications are emerging, in particular for lymphoma and neuroblastoma. Although both photon and proton techniques allow similar target volume coverage, the main advantage of proton radiation therapy is to sparing of intermediate-to-low-dose to healthy tissues. This characteristic could translate into clinical reduction of side effects, including a lower risk for secondary cancers. The following review presents the state of the art of proton therapy in the treatment of pediatric malignancies.

Critical combinations of radiation dose and volume predict intelligence quotient and academic achievement scores after craniospinal irradiation in children with medulloblastoma

PURPOSE

To prospectively follow children treated with craniospinal irradiation to determine critical combinations of radiation dose and volume that would predict for cognitive effects.

METHODS AND MATERIALS

Between 1996 and 2003, 58 patients (median age 8.14 years, range 3.99-20.11 years) with medulloblastoma received risk-adapted craniospinal irradiation followed by dose-intense chemotherapy and were followed longitudinally with multiple cognitive evaluations (through 5 years after treatment) that included intelligence quotient (estimated intelligence quotient, full-scale, verbal, and performance) and academic achievement (math, reading, spelling) tests. Craniospinal irradiation consisted of 23.4 Gy for average-risk patients (nonmetastatic) and 36-39.6 Gy for high-risk patients (metastatic or residual disease >1.5 cm(2)). The primary site was treated using conformal or intensity modulated radiation therapy using a 2-cm clinical target volume margin. The effect of clinical variables and radiation dose to different brain volumes were modeled to estimate cognitive scores after treatment.

RESULTS

A decline with time for all test scores was observed for the entire cohort. Sex, race, and cerebrospinal fluid shunt status had a significant impact on baseline scores. Age and mean radiation dose to specific brain volumes, including the temporal lobes and hippocampi, had a significant impact on longitudinal scores. Dichotomized dose distributions at 25 Gy, 35 Gy, 45 Gy, and 55 Gy were modeled to show the impact of the high-dose volume on longitudinal test scores. The 50% risk of a below-normal cognitive test score was calculated according to mean dose and dose intervals between 25 Gy and 55 Gy at 10-Gy increments according to brain volume and age.

CONCLUSIONS

The ability to predict cognitive outcomes in children with medulloblastoma using dose-effects models for different brain subvolumes will improve treatment planning, guide intervention, and help estimate the value of newer methods of irradiation.

Comparative effectiveness research in radiation oncology: assessing technology

Technological advances are a major contributor to rising costs in health care, including radiation oncology. Despite the large amount spent on new technologies, technology assessment remains inadequate, leading to potentially costly and unnecessary use of new technologies. Comparative effectiveness studies have an important role to play in evaluating the benefits and harms of new technologies compared with older technologies and have been identified as a priority area for research by the Radiation Oncology Institute. This article outlines the elements of effective technology assessment, identifies key challenges to comparative effectiveness studies of new radiation oncology technologies, and reviews several examples of comparative effectiveness studies in radiation oncology, including studies on conformal radiation, IMRT, proton therapy, and other concurrent new technologies.

New challenges in high-energy particle radiobiology

Densely ionizing radiation has always been a main topic in radiobiology. In fact, α-particles and neutrons are sources of radiation exposure for the general population and workers in nuclear power plants. More recently, high-energy protons and heavy ions attracted a large interest for two applications: hadrontherapy in oncology and space radiation protection in manned space missions. For many years, studies concentrated on measurements of the relative biological effectiveness (RBE) of the energetic particles for different end points, especially cell killing (for radiotherapy) and carcinogenesis (for late effects). Although more recently, it has been shown that densely ionizing radiation elicits signalling pathways quite distinct from those involved in the cell and tissue response to photons. The response of the microenvironment to charged particles is therefore under scrutiny, and both the damage in the target and non-target tissues are relevant. The role of individual susceptibility in therapy and risk is obviously a major topic in radiation research in general, and for ion radiobiology as well. Particle radiobiology is therefore now entering into a new phase, where beyond RBE, the tissue response is considered. These results may open new applications for both cancer therapy and protection in deep space.

Proton beam therapy: a fad or a new standard of care

PURPOSE OF REVIEW

Newer methods and advances in radiation therapy promise to reduce the risk of complications in children who require irradiation. They have secured the role of radiation therapy in the treatment of a variety of pediatric central nervous system and solid tumors and for young patients enrolled on clinical trials.

RECENT FINDINGS

Proton therapy is the latest advancement in radiation therapy. Its availability is increasing as new centers are built throughout the United States. Pediatric specialists should understand that proton therapy is in its pioneering stage of development and that advantages have not been quantitatively demonstrated. Proton therapy clearly reduces collateral radiation dose to normal tissue when compared with photon (X-ray)-based methods of irradiation and has the potential to selectively and safely escalate dose to high-risk tumors; however, research results are lacking in both of these areas, leading to some confusion among pediatric specialists with regard to indications and the need to refer patients for this limited resource and expensive form of radiation therapy.

SUMMARY

This review highlights a number of issues surrounding proton therapy in children and supports the use of proton therapy in clinical trials.