Comprehensive radiotherapy for pediatric Ewing Sarcoma: Outcomes of a prospective proton study

BACKGROUND AND PURPOSE

Patients with Ewing Sarcoma (EWS) are treated with multimodality therapy which includes radiation therapy (RT) as an option for local control. We report on the efficacy after proton radiation therapy (PRT) to the primary site for localized and metastatic EWS.

MATERIALS AND METHODS

Forty-two children with EWS (33 localized, 9 metastatic) treated between 2007 and 2020 were enrolled on 2 prospective registry protocols for pediatric patients undergoing PRT. PRT was delivered by passive scatter (74 %), pencil-beam scanning (12 %) or mixed technique (14 %). Treated sites included the spine (45 %), pelvis/sacrum (26 %), skull/cranium (14 %), extraosseous (10 %), and chest wall (5 %). Median radiation dose was 54 Gy-RBE (range 39.6-55.8 Gy-RBE). Patients with metastatic disease received consolidative RT to metastatic sites (4 at the time of PRT to the primary site, 5 after completion of chemotherapy). Median follow-up time was 47 months after PRT.

RESULTS

The 4-year local control (LC), progression-free survival (PFS), and overall survival (OS) rates were 83 %, 71 %, and 86 %, respectively. All local failures (n = 6) were in-field failures. Tumor size ≥ 8 cm predicted for inferior 4-year LC (69 % vs 95 %, p = 0.04). 4-year PFS and OS rates were not statistically different in patients with localized versus metastatic disease (72 % vs 67 %, p = 0.70; 89 % vs 78 %, p = 0.38, respectively).

CONCLUSION

In conclusion, LC for pediatric patients with EWS treated with PRT was comparable to that of historical patients who received photon-RT. Tumor size ≥ 8 cm predicted increased risk of local failure. Patients with metastatic disease, including non-pulmonary only metastases, received radiation therapy to all metastatic sites and had favorable survival outcomes.

Surface guided radiotherapy practice in paediatric oncology: a survey on behalf of the SIOPE Radiation Oncology Working Group

INTRODUCTION

Surface guided radiotherapy (SGRT) is increasingly being implemented to track patient's surface movement and position during radiation therapy. However, limited information is available on the SGRT use in paediatrics. The aim of this double survey was to map SIOPE (European Society for Paediatric Oncology)-affiliated centres using SGRT and to gain information on potential indications, observed, or expected benefits.

METHODS

A double online survey was distributed to 246 SIOPE-affiliated radiotherapy (RT) centres. Multiple choices, yes/no, and open answers were included. The first survey (41 questions) was active from February to March 2021. A shortened version (13 questions) was repeated in March 2023 to detect trends in SGRT use within the same community.

RESULTS

Respectively, 76/142 (54%) and 28/142 (20%) responding centres used and planned to use SGRT clinically, including 4/34 (12%) new centres since 2021. Among the SGRT users, 33/76 (43%) already applied this technology to paediatric treatments. The main benefits of improved patient comfort, better monitoring of intrafraction motion, and more accurate initial patient set-up expected by future users did not differ from current SGRT-users (P = .893). Among non-SGRT users, the main hurdles to implement SGRT were costs and time for installation. In paediatrics, SGRT is applied to all anatomical sites.

CONCLUSION

This work provides information on the practice of SGRT in paediatrics across SIOPE-affiliated RT centres which can serve as a basis for departments when considering the purchase of SGRT systems.

ADVANCES IN KNOWLEDGE

Since little information is available in the literature on the use of SGRT in paediatrics, the results of this double survey can serve as a basis for departments treating children when considering the purchase of an SGRT system.

ESTRO-SIOPE guideline: Clinical management of radiotherapy in atypical teratoid/rhabdoid tumors (AT/RTs)

BACKGROUND AND PURPOSE

Treatment of patients with atypical teratoid/rhabdoid (AT/RT) is challenging, especially when very young (below the age of three years). Radiotherapy (RT) is part of a complex trimodality therapy. The purpose of this guideline is to provide appropriate recommendations for RT in the clinical management of patients not enrolled in clinical trials.

MATERIALS AND METHODS

Nine European experts were nominated to form a European Society for Radiotherapy and Oncology (ESTRO) guideline committee. A systematic literature search was conducted in PubMed/MEDLINE and Web of Science. They discussed and analyzed the evidence concerning the role of RT in the clinical management of AT/RT.

RESULTS

Recommendations on diagnostic imaging, therapeutic principles, RT considerations regarding timing, dose, techniques, target volume definitions, dose constraints of radiation-sensitive organs at risk, concomitant chemotherapy, and follow-up were considered. Treating children with AT/RT within the framework of prospective trials or prospective registries is of utmost importance.

CONCLUSION

The present guideline summarizes the evidence and clinical-based recommendations for RT in patients with AT/RT. Prospective clinical trials and international, large registries evaluating modern treatment approaches will contribute to a better understanding of the best treatment for these children in future.

Engaging carers in neuropsychological rehabilitation for brain cancer survivors: The "I'm aware: Patients And Carers Together" (ImPACT) program

BACKGROUND

Cognitive impairment is a common late effect in child and adult brain cancer survivors (BCS). Still, there is a dearth of research aimed at therapeutic interventions and no standard treatment options for most BCS.

OBJECTIVE

To describe 1) a novel neuropsychological rehabilitation program for BCS - the "I'm aware: Patients And Carers Together" (ImPACT) program, and 2) two studies that aim to assess the feasibility of the ImPACT program in child and adult BCS, respectively. The program adapts the holistic neuropsychological approach pioneered by Leonard Diller and Yehuda Ben-Yishay to an outpatient setting.

METHODS

Two feasibility studies are described: 1) A single-armed study with 15 child BCS (10-17 years) (ImPACT Child); and 2) a randomized waitlist-controlled trial with 26 adult BCS (>17 years) (ImPACT Adult). In both studies, patients will undergo an 8-week program together with a cohabiting carer. Primary outcomes (i.e., cognitive and neurobehavioral symptoms), and secondary outcomes (i.e., behavioral and psychological symptoms, e.g., quality of life, fatigue) will be assessed at four time points: pre-, mid-, and post intervention, and 8 weeks follow-up. Adult waitlist controls will be assessed at equivalent time points and will be included in the intervention group after all study assessments. Semi-structured interviews will be conducted at follow-up.

EXPECTED OUTCOMES

Results will provide feasibility data in support of future larger scale trials.

DISCUSSION

The findings could potentially improve the management of cognitive impairment in BCS and transform available services. The program can be delivered in-person or remotely and harnesses existing resources in patients' lives.

Linear energy transfer-inclusive models of brainstem necrosis following proton therapy of paediatric ependymoma

Background and Purpose

Radiation-induced brainstem necrosis after proton therapy is a severe toxicity with potential association to uncertainties in the proton relative biological effectiveness (RBE). A constant RBE of 1.1 is assumed clinically, but the RBE is known to vary with linear energy transfer (LET). LET-inclusive predictive models of toxicity may therefore be beneficial during proton treatment planning. Hence, we aimed to construct models describing the association between brainstem necrosis and LET in the brainstem.

Materials and methods

A matched case-control cohort (n = 28, 1:3 case-control ratio) of symptomatic brainstem necrosis was selected from 954 paediatric ependymoma brain tumour patients treated with passively scattered proton therapy. Dose-averaged LET (LET_d) parameters in restricted volumes (L_50%, L_10% and L_0.1cm³, the cumulative LET_d) within high-dose thresholds were included in linear- and logistic regression normal tissue complication probability (NTCP) models.

Results

A 1 keV/µm increase in L_10% to the brainstem volume receiving dose over 54 Gy(RBE) led to an increased brainstem necrosis risk [95% confidence interval] of 2.5 [0.0, 7.8] percentage points. The corresponding logistic regression model had area under the receiver operating characteristic curve (AUC) of 0.76, increasing to 0.84 with the anterior pons substructure as a second parameter. 19 [7, 350] patients with toxicity were required to associate the L_10% (D > 54 Gy(RBE)) and brainstem necrosis with 80% statistical power.

Conclusion

The established models of brainstem necrosis illustrate a potential impact of high LET regions in patients receiving high doses to the brainstem, and thereby support LET mitigation during clinical treatment planning.

Neurocognitive function and health-related quality of life in a nationwide cohort of long-term childhood brain tumor survivors

Background

Childhood brain tumor survivors are at high risk of late effects, especially neurocognitive impairment. Limited data are available examining neurocognitive function and associations with quality of life (QoL) in childhood brain tumor survivors. Our aim was to examine neurocognitive function in childhood brain tumor survivors, and associations with QoL and symptom burden.

Methods

Five-year survivors of brain tumors over the age of 15 were identified in the Danish Childhood Cancer Registry (n = 423). Eligible and consenting participants completed neuropsychological tests and questionnaires assessing QoL, insomnia, fatigue, anxiety, and depression. Survivors treated with radiation (n = 59) were statistically compared with survivors not treated with radiation (n = 102).

Results

In total, 170 survivors participated (40.2% participation rate). Sixty-six percent of the survivors who completed neurocognitive tests (n = 161) exhibited overall neurocognitive impairment. Survivors treated with radiation, especially whole-brain irradiation, exhibited poorer neurocognitive outcomes than survivors not treated with radiation. Neurocognitive outcomes for survivors treated with surgery were below normative expectations. Furthermore, a number of survivors experienced significant fatigue (40%), anxiety (23%), insomnia (13%), and/or depression (6%). Survivors treated with radiation reported lower quality of life (QoL) and higher symptom burden scores than survivors not treated with radiation; particularly in physical functioning, and social functioning with symptoms of fatigue. Neurocognitive impairment was not associated with QoL or symptom burden.

Conclusions

In this study, a majority of the childhood brain tumor survivors experienced neurocognitive impairment, reduced QoL, and high symptom burden. Although not associated with each other, it is apparent that childhood brain tumor survivors experience not only neurocognitive dysfunction but may also experience QoL impairments and significant symptom burden.

P09.02.B Engaging Parents in Neuropsychological Rehabilitation for Childhood Cancer Survivors: The I’M aware: Patients And Carers Together (ImPACT) Program

Background

Cognitive impairment is the most common late effect in childhood cancer survivors (CCS). A third are likely to experience impairments in skills such as attention, processing speed, memory, and executive function. Neurobehavioral impairments are also observed in CCS (e.g., apathy) and may underlie cognitive impairment. Although these problems can impair quality of life, scholastic achievement and long-term socioeconomic outcomes, there is a dearth of research on interventions to treat cognitive impairment in CCS. Cognitive rehabilitation studies in CCS have focused primarily on computerized cognitive training and meta-cognitive strategy training, but with limited effects and poor study designs. They have lacked four key elements: 1) transfer of learning to real-world functional outcomes; 2) awareness training to enhance compensatory strategy use, particularly since CCS may experience neurological unawareness preventing the optimal application of strategies; 3) inclusion of parents that could enhance transfer of learning to the home; and 4) recognition of the inter-related nature of cognitive, neurobehavioral, and psychological functions. A novel, context-sensitive neuropsychological rehabilitation program has been developed for CSS to address these missing elements - the “I’M aware: Patients and Carers Together (ImPACT)” program - based on an evidenced-based approach pioneered at NYU Hospital in the US. In this protocol, the feasibility, acceptability, and preliminary efficacy of the ImPACT program (8 x 1 hour sessions) will be evaluated.

Material and Methods

Phase One will consist of semi-structured interviews with 5 to 10 CCS and their parents in order to review and refine procedures for the ImPACT program. In Phase Two, twenty participants will be randomized to a wait-list control (WLC) or intervention group. WLCs will not receive the intervention immediately, but will serve as the control comparison group. Measures of self- and parent-reported cognition, neurobehavioral function, and global function will be administered pre- and post- intervention, and 9 weeks later (or equivalent time points for WLCs).

Results

Results of this project will provide vital data in support of a future large-scale trial.

Conclusion

Findings could have implications for the management of cognitive and neurobehavioral impairment in CCS that could transform the nature of services provided to CCS. The program can be delivered remotely or in-person and harnesses existing supports in the child’s life to promote real-world functioning.

QUARTET: A SIOP Europe project for quality and excellence in radiotherapy and imaging for children and adolescents with cancer

The European Society for Paediatric Oncology (SIOPE) Radiation Oncology Working Group presents the QUARTET Project: a centralised quality assurance programme designed to standardise care and improve the quality of radiotherapy and imaging for international clinical trials recruiting children and adolescents with cancer throughout Europe. QUARTET combines the paediatric radiation oncology expertise of SIOPE with the infrastructure and experience of the European Organisation for Research and Treatment of Cancer to deliver radiotherapy quality assurance programmes for large, prospective, international clinical trials. QUARTET-affiliated trials include children and adolescents with brain tumours, neuroblastoma, sarcomas including rhabdomyosarcoma, and renal tumours including Wilms' tumour. With nine prospective clinical trials and two retrospective studies within the active portfolio in March 2022, QUARTET will collect one of the largest repositories of paediatric radiotherapy and imaging data, support the clinical assessment of radiotherapy, and evaluate the role and benefit of radiotherapy quality assurance for this cohort of patients within the context of clinical trials.

Systematic Review: Sleep Disorders Based on Objective Data in Children and Adolescents Treated for a Brain Tumor

Background

Tumors of the central nervous system (CNS) are the most common solid childhood malignancy. Over the last decades, treatment developments have strongly contributed to the improved overall 5-year survival rate, which is now approaching 75%. However, children now face significant long-term morbidity with late-effects including sleep disorders that may have detrimental impact on everyday functioning and quality of life. The aims of this study were to (1) describe the symptoms that lead to polysomnographic evaluation; (2) describe the nature of sleep disorders diagnosed in survivors of childhood CNS tumor using polysomnography (PSG); and (3) explore the association between tumor location and diagnosed sleep disorder.

Methods

An extensive literature search following the Preferred Reporting Items for Systematic Review and Meta-Analysis guidelines (PRISMA) was conducted. Inclusion criteria were children and adolescents diagnosed with a CNS tumor age <20 years having a PSG performed after end of tumor treatment. The primary outcome was sleep disorder confirmed by PSG.

Results

Of the 1,658 studies identified, 11 met the inclusion criteria. All the included articles were appraised for quality and included in the analysis. Analyses indicated that sleep disorders commonly occur among childhood CNS tumor survivors. Symptoms prior to referral for PSG were excessive daytime sleepiness (EDS), fatigue, irregular breathing during sleep and snoring. The most common sleep disorders diagnosed were sleep-related breathing disorders (i.e., obstructive sleep apnea) and central disorders of hypersomnolence (i.e., narcolepsy).

Conclusion

Our findings point to the potential benefit of systematically registering sleep disorder symptoms among CNS tumor patients together with tumor type and treatment information, so that at-risk patients can be identified early. Moreover, future rigorous and larger scale controlled observational studies that include possible modifiable confounders of sleep disorders such as fatigue and obesity are warranted.

Clinical Trial Registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021243866, identifier [CRD42021243866].

Treatment plan comparison of proton vs photon radiotherapy for lower-grade gliomas

Background and purpose

Patients with lower-grade gliomas are long-term survivors after radiotherapy and may benefit from the reduced dose to normal tissue achievable with proton therapy. Here, we aimed to quantify differences in dose to the uninvolved brain and contralateral hippocampus and compare the risk of radiation-induced secondary cancer for photon and proton plans for lower-grade glioma patients.

Materials and methods

Twenty-three patients were included in this in-silico planning comparative study and had photon and proton plans calculated (50.4 Gy(RBE = 1.1), 28 Fx) applying similar dose constraints to the target and organs at risk. Automatically calculated photon plans were generated with a 3 mm margin from clinical target volume (CTV) to planning target volume. Manual proton plans were generated using robust optimisation on the CTV. Dose metrics of organs at risk were compared using population mean dose-volume histograms and Wilcoxon signed-rank test. Secondary cancer risk per 10,000 persons per year (PPY) was estimated using dose-volume data and a risk model for secondary cancer induction.

Results

CTV coverage (V95%>98%) was similar for the two treatment modalities. Mean dose (D_mean) to the uninvolved brain was significantly reduced from 21.5 Gy (median, IQR 17.1–24.4 Gy) with photons compared to 10.3 Gy(RBE) (8.1–13.9 Gy(RBE)) with protons. D_mean to the contralateral hippocampus was significantly reduced from 6.5 Gy (5.4–11.7 Gy) with photons to 1.5 Gy(RBE) (0.4–6.8 Gy(RBE)) with protons. The estimated secondary cancer risk was reduced from 6.7 PPY (median, range 3.3–10.4 PPY) with photons to 3.0 PPY (1.3–7.5 PPY) with protons.

Conclusion

A significant reduction in mean dose to uninvolved brain and contralateral hippocampus was found with proton planning. The estimated secondary cancer risk was reduced with proton therapy.

Delineation atlas of the Circle of Willis and the large intracranial arteries for evaluation of doses to neurovascular structures in pediatric brain tumor patients treated with radiation therapy

BACKGROUND

Survivors of pediatric brain tumors are susceptible to neurovascular disease after radiotherapy, with dose to the chiasm or Circle of Willis (CW) as risk factors. The aims of this study were to develop a delineation atlas of neurovascular structures, to investigate the doses to these structures in relation to tumor location and to investigate potential dose surrogates for the CW dose.

MATERIAL AND METHODS

An atlas of the CW, the large intracranial arteries and the suprasellar cistern (SC) was developed and validated. Thirty proton plans from previously treated pediatric brain tumor patients were retrieved and grouped according to tumor site: 10 central, 10 lateralized, and 10 posterior fossa tumors. Based on the atlas, neurovascular structures were delineated and dose metrics (mean dose (D_mean) and maximal dose (D_max)) to these structures and the already delineated chiasm were evaluated. The agreement between dose metrics to the CW vs. chiasm/SC was investigated. The minimal Hausdorff distance (HD_min) between the target and SC was correlated with the SC D_mean.

RESULTS

The median D_mean/D_max to the CW were 53 Gy(RBE)/55 Gy(RBE) in the central tumors, 18 Gy(RBE)/25 Gy(RBE) in the lateralized tumors and 30 Gy(RBE)/49 Gy(RBE) in the posterior fossa tumors. There was a good agreement between the D_max/D_mean to the CW and the SC for all cases (R²=0.99), while in the posterior fossa group, the CW D_max was underestimated when using the chiasm as surrogate (R²=0.76). Across all patients, cases with HD_min < 10 mm between the target and the SC received the highest SC D_mean.

CONCLUSION

The pattern of dose to neurovascular structures varied with the tumor location. For all locations, SC doses could be used as a surrogate for CW doses. A minimal distance larger than 10 mm between the target and the SC indicated a potential for neurovascular dose sparing.

A national study on the inter-observer variability in the delineation of organs at risk in the brain

BACKGROUND

The Danish Neuro Oncology Group (DNOG) has established national consensus guidelines for the delineation of organs at risk (OAR) structures based on published literature. This study was conducted to finalise these guidelines and evaluate the inter-observer variability of the delineated OAR structures by expert observers.

MATERIAL AND METHODS

The DNOG delineation guidelines were formed by participants from all Danish centres that treat brain tumours with radiotherapy. In a two-day workshop, guidelines were discussed and finalised based on a pilot study. Following this, the ten participants contoured the following OARs on T1-weighted gadolinium enhanced MRI from 13 patients with brain tumours: optic tracts, optic nerves, chiasm, spinal cord, brainstem, pituitary gland and hippocampus. The metrics used for comparison were the Dice similarity coefficient (Dice), mean surface distance (MSD) and others.

RESULTS

A total of 968 contours were delineated across the 13 patients. On average eight (range six to nine) individual contour sets were made per patient. Good agreement was found across all structures with a median MSD below 1 mm for most structures, with the chiasm performing the best with a median MSD of 0.45 mm. The Dice was as expected highly volume dependent, the brainstem (the largest structure) had the highest Dice value with a median of 0.89 whereas smaller volumes such as the chiasm had a Dice of 0.71.

CONCLUSION

Except for the caudal definition of the spinal cord, the variances observed in the contours of OARs in the brain were generally low and consistent. Surface mapping revealed sub-regions of higher variance for some organs. The data set is being prepared as a validation data set for auto-segmentation algorithms for use within the Danish Comprehensive Cancer Centre - Radiotherapy and potential collaborators.

Associations between patient-reported outcomes and radiation dose in patients treated with radiation therapy for primary brain tumours

•

Higher radiation doses to the brain may negatively affect quality of life.

•

Higher radiation doses to the brain may negatively affect patient-reported cognition.

•

Patients with fatigue had received higher dose to certain areas in the brain.

Aim

This study aimed to explore associations between radiation dose and patient-reported outcomes in patients with a primary non-glioblastoma brain tumour treated with radiation therapy (RT), with a focus on health-related quality-of-life (HRQoL) and self-reported cognitive function.

Methods

In this cross-sectional study, 78 patients who had received RT for a non-glioblastoma primary brain tumour, underwent neuropsychological testing and completed questionnaires on HRQoL, cognitive function, fatigue, depression, anxiety and perceived stress. The study explores the association between HRQoL scores, self-reported cognitive function and radiation doses to total brain, brainstem, hippocampus, thalamus, temporal lobes and frontal lobes. In addition, we examined correlations between neuropsychological test scores and self-reported cognitive function.

Results

The median time between RT and testing was 4.6 years (range 1–9 years). Patients who had received high mean radiation doses to the total brain had low HRQoL scores (Cohen’s d = 0.50, p = 0.04), brainstem (d = 0.65, p = 0.01) and hippocampus (d = 0.66, p = 0.01). High mean doses to the total brain were also associated with low scores on self-reported cognitive functioning (Cohen’s d = 0.64, p = 0.02), brainstem (d = 0.55, p = 0.03), hippocampus (d = 0.76, p < 0.01), temporal lobes (d = 0.70, p < 0.01) and thalamus (d = 0.64, p = 0.01). Self-reported cognitive function correlated well with neuropsychological test scores (correlation range 0.27–0.54.)

Conclusions

High radiation doses to specific brain structures may be associated with impaired HRQoL and self-reported cognitive function with potentially negative implications to patients’ daily lives. Patient-reported outcomes of treatment-related side-effects and their associations with radiation doses to the brain and its sub-structures may provide important information on radiation tolerance to the brain and sub-structures.

Inter-clinician delineation variation for a new highly-conformal flank target volume in children with renal tumors: A SIOP-Renal Tumor Study Group international multicenter exercise

BACKGROUND AND PURPOSE

Recently, the SIOP-RTSG developed a highly-conformal flank target volume definition for children with renal tumors. The aims of this study were to evaluate the inter-clinician delineation variation of this new target volume definition in an international multicenter setting and to explore the necessity of quality assurance.

MATERIALS AND METHODS

Six pediatric renal cancer cases were transferred to ten radiation oncologists from seven European countries ('participants'). These participants delineated the pre- and postoperative Gross Tumor Volume (GTVpre/post), and Clinical Target Volume (CTV) during two test phases (case 1-2 and 3-4), followed by guideline refinement and a quality assurance phase (case 5-6). Reference target volumes (TVref) were established by three experienced radiation oncologists. The Dice Similarity Coefficient between the reference and participants (DSCref/part) was calculated per case. Delineations of case 5-6 were graded by four independent reviewers as 'per protocol' (0-4 mm), 'minor deviation' (5-9 mm) or 'major deviation' (≥10 mm) from the delineation guideline using 18 standardized criteria. Also, a major deviation resulting in underestimation of the CTVref was regarded as an unacceptable variation.

RESULTS

A total of 57/60 delineation sets were completed. The median DSCref/part for the CTV was 0.55 without improvement after sequential cases (case 3-4 vs. case 5-6: p = 0.15). For case 5-6, a major deviation was found for 5/18, 12/17, 18/18 and 4/9 collected delineations of the GTVpre, GTVpost, CTV-T and CTV-N, respectively. An unacceptable variation from the CTVref was found for 7/9 participants for case 5 and 6/9 participants for case 6.

CONCLUSION

This international multicenter delineation exercise demonstrates that the new consensus for highly-conformal postoperative flank target volume delineation leads to geometrical variation among participants. Moreover, standardized review showed an unacceptable delineation variation in the majority of the participants. These findings strongly suggest the need for additional training and centralized pre-treatment review when this target volume delineation approach is implemented on a larger scale.

Variation in relative biological effectiveness for cognitive structures in proton therapy of pediatric brain tumors

BACKGROUND

Clinically, a constant value of 1.1 is used for the relative biological effectiveness (RBE) of protons, whereas in vitro the RBE has been shown to vary depending on physical dose, tissue type, and linear energy transfer (LET). As the LET increases at the distal end of the proton beam, concerns exist for an elevated RBE in normal tissues. The aim of this study was therefore to investigate the heterogeneity of RBE to brain structures associated with cognition (BSCs) in pediatric suprasellar tumors.

MATERIAL AND METHODS

Intensity-modulated proton therapy (IMPT) plans for 10 pediatric craniopharyngioma patients were re-calculated using 11 phenomenological and two plan-based variable RBE models. Based on LET, tissue dependence and number of data points used to fit the models, the three RBE models considered the most relevant for the studied endpoint were selected. Thirty BSCs were investigated in terms of RBE and dose/volume parameters.

RESULTS

For a representative patient, the median (range) dose-weighted mean RBE (RBE_d) across all BSCs from the plan-based models was among the lowest (1.09 (1.02-1.52) vs. the phenomenological models at 1.21 (0.78-2.24)). Omitting tissue dependency resulted in RBE_d at 1.21 (1.04-2.24). Across all patients, the narrower RBE model selection gave median RBE_d values from 1.22 to 1.30.

CONCLUSION

For all BSCs, there was a systematic model-dependent variation in RBE_d, mirroring the uncertainty in biological effects of protons. According to a refined selection of in vitro models, the RBE variation across BSCs was in effect underestimated when using a fixed RBE of 1.1.

Spatial Agreement of Brainstem Dose Distributions Depending on Biological Model in Proton Therapy for Pediatric Brain Tumors

Purpose

During radiation therapy for pediatric brain tumors, the brainstem is a critical organ at risk, possibly with different radio-sensitivity across its substructures. In proton therapy, treatment planning is currently performed using a constant relative biological effectiveness (RBE) of 1.1 (RBE_1.1), whereas preclinical studies point toward spatial variability of this factor. To shed light on this biological uncertainty, we investigated the spatial agreement between isodose maps produced by different RBE models, with emphasis on (smaller) substructures of the brainstem.

Methods and Materials

Proton plans were recalculated using Monte Carlo simulations in 3 anonymized pediatric patients with brain tumors (a craniopharyngioma, a low-grade glioma, and a posterior fossa ependymoma) to obtain dose and linear energy transfer distributions. Doses and volume metrics for the brainstem and its substructures were calculated using a constant RBE_1.1, 4 phenomenological RBE models with varying (α/β)_x parameters, and with a simpler linear energy transfer-dependent model. The spatial agreement between the dose distributions of constant RBE_1.1 versus the variable RBE models was compared using the Dice similarity coefficient.

Results

The spatial agreement between the variable RBE dose distributions and RBE_1.1 decreased with increasing isodose levels in all patient cases. The patient with ependymoma showed the greatest variation in dose and dose volumes, where V_50Gy(RBE) in the brainstem increased from 32% (RBE_1.1) to 35% to 49% depending on the applied model, corresponding to a spatial agreement (Dice similarity coefficient) between 0.79 and 0.95. The remaining patients showed similar trends, however, with lower absolute values due to lower brainstem doses.

Conclusions

All phenomenological RBE models fully enclosed the isodose volumes of the constant RBE_1.1, and the volumes based on variable RBE spatially agreed. The spatial agreement was dependent on the isodose level, where higher isodose levels showed larger expansions and less agreement between the variable RBE models and RBE_1.1.

ETMR-01. TREATMENT OUTCOME OF TWO CASES WITH HIGH-GRADE NEUROEPITHELIAL TUMOR WITH BCOR ALTERATION

INTRODUCTION

High grade neuroepithelial tumor with BCOR exon 15 internal tandem duplication (HGNET BCOR) is a recently described tumor entity of the central nervous system (CNS) with a distinct methylation profile and characteristic genetic alteration. We report the outcome of two cases after 1st line multimodality therapy.

MATERIAL AND METHOD

A 7 year old girl with a ventricular tumour and a 6 year old boy with a tumour in the occipital region with infiltration of the transverse and sigmoid sinus were both diagnosed based on histology and methylation with HGNET-BCOR. No spinal or liquor dissemination were found at diagnosis in both cases. Treatment consisted of radical resection of the tumour. In the case of the lesion with sinus infiltration residual tumour in the vessel could not be removed. Both children were postoperatively treated with radiotherapy (craniospinal 36 Gy and boost to 54 Gy), concomitant Vincristin and adjuvant Cisplatin, Lomustine and Vincristine.

RESULTS

The girl developed a local recurrence at the primary tumour site 18 months after diagnosis. Reoperation showed the same histology. Start of 2nd line chemotherapy with Temozolomid and Irinotecan is being discussed. The boy with sinus infiltration developed seven months after diagnosis multiple liver, lung and bone metastasis. Biopsy of a liver lesion showed HGNET-BCOR. He was treated with Temozolomid, Irinotecan and died nine months after diagnosis.

CONCLUSION

We report two cases with failure after 1st line treatment for HGNET-BCOR. To our knowledge HGNET-BCOR with development of hematological disease dissemination is a rare finding.

GCT-65. INCIDENCE AND OUTCOME OF INTRACRANIAL MALIGNANT GERM CELL TUMOURS DIAGNOSED IN WESTERN DENMARK IN THE LAST DECADE

INTRODUCTION

Intracranial malignant germ cell tumours (iGCT) are rare brain tumours mainly diagnosed in children and younger adults.

MATERIAL AND METHODS

A retrospective analysis was performed by chart review of patients treated for iGCT in the northern and central region of Denmark. Teratoma only patients were not included in the study.

RESULTS

20 patients with iGCT were diagnosed from 2008–2019 in Western Denmark. The cumulative incidence was 1.05 per 100.000. The yearly incidence was 0.1 per 100.000. Mean age at diagnosis was 18 years (range 8–36 years), 17 were males and 3 were females. 13 patients presented with germinoma and 7 patients with non germinomateous germ cell tumours (NGGCT). Three patients had disseminated disease, two with germinoma and one with NGGCT. All patients had received radiotherapy and 18 patients were treated with multidrug chemotherapy including platinum and etoposide before irradiation. Two patients experienced recurrent disease, both non disseminated at diagnosis, one patient with germinoma and one patient with NGGCT. Both received salvage treatment including high dose chemotherapy with stem cell transplantation and reirradiation. Two NGGCT patients died, one patient after development of an anaplastic astrocytoma in the radiation field five years after radiotherapy and one patient after intracranial hemorraghe 18 months after salvage treatment for recurrent disease. Overall survival was 90%, 100% for GCT and 71% for NGGCT.

CONCLUSION

The outcome of patients with iGCT in Western Denmark was comparable to the literature. A nationwide study of epidemiology and outcome of iGCT in Denmark is planned.

A rapid review of evidence and recommendations from the SIOPE radiation oncology working group to help mitigate for reduced paediatric radiotherapy capacity during the COVID-19 pandemic or other crises

OBJECTIVE

To derive evidence-based recommendations for the optimal utilisation of resources during unexpected shortage of radiotherapy capacity.

METHODS AND MATERIALS

We have undertaken a rapid review of published literature on the role of radiotherapy in the multimodality treatment of paediatric cancers governing the European practise of paediatric radiotherapy. The derived data has been discussed with expert paediatric radiation oncologists to derive a hierarchy of recommendations.

RESULTS

The general recommendations to mitigate the potential detriment of an unexpected shortage of radiotherapy facilities include: (1) maintain current standards of care as long as possible (2) refer to another specialist paediatric radiotherapy department with similar level of expertise (3) prioritise use of existing radiotherapy resources to treat patients with tumours where radiotherapy has the most effect on clinical outcome (4) use chemotherapy to defer the start of radiotherapy where timing of radiotherapy is not expected to be detrimental (5) active surveillance for low-grade tumours if appropriate and (6) consider iso-effective hypofractionated radiotherapy regimens only for selected patients with predicted poor prognosis. The effectiveness of radiotherapy and recommendations for prioritisation of its use for common and challenging paediatric tumours are discussed.

CONCLUSION

This review provides evidence-based treatment recommendations during unexpected shortage of paediatric radiotherapy facilities. It has wider applications for the optimal utilisation of facilities, to improve clinical outcome in low- and middle-income countries, where limited resources continue to be a challenge.

OptimalTTF-1: Enhancing tumor treating fields therapy with skull remodeling surgery. A clinical phase I trial in adult recurrent glioblastoma

BACKGROUND

Preclinical studies suggest that skull remodeling surgery (SR-surgery) increases the dose of tumor treating fields (TTFields) in glioblastoma (GBM) and prevents wasteful current shunting through the skin. SR-surgery introduces minor skull defects to focus the cancer-inhibiting currents toward the tumor and increase the treatment dose. This study aimed to test the safety and feasibility of this concept in a phase I setting.

METHODS

Fifteen adult patients with the first recurrence of GBM were treated with personalized SR-surgery, TTFields, and physician's choice oncological therapy. The primary endpoint was toxicity and secondary endpoints included standard efficacy outcomes.

RESULTS

SR-surgery resulted in a mean skull defect area of 10.6 cm2 producing a median TTFields enhancement of 32% (range 25-59%). The median TTFields treatment duration was 6.8 months and the median compliance rate 90%. Patients received either bevacizumab, bevacizumab/irinotecan, or temozolomide rechallenge. We observed 71 adverse events (AEs) of grades 1 (52%), 2 (35%), and 3 (13%). There were no grade 4 or 5 AEs or intervention-related serious AEs. Six patients experienced minor TTFields-induced skin rash. The median progression-free survival (PFS) was 4.6 months and the PFS rate at 6 months was 36%. The median overall survival (OS) was 15.5 months and the OS rate at 12 months was 55%.

CONCLUSIONS

TTFields therapy combined with SR-surgery and medical oncological treatment is safe and nontoxic and holds the potential to improve the outcome for GBM patients through focal dose enhancement in the tumor.

[Tumor treating fields in cancer treatment in Denmark]

Tumor treating fields (TTFields) is a new non-invasive approach to cancer treatment. TTFields is low-intensity (1-5 V/m), intermediate frequency (150-200 kHz) alternating electric fields delivered locally to the tumour to selectively kill dividing cells and disrupt cancer growth. TTFields has proven safe and effective for newly diagnosed glioblastoma and is currently being tried for multiple other tumours. This review presents an introduction to TTFields, covering the main indications, the application method, the mechanism of action, the clinical results and the perspectives for implementation in Danish cancer treatment.

Radiation doses to brain substructures associated with cognition in radiotherapy of pediatric brain tumors

Background: Several brain substructures associated with cognition (BSCs) are located close to typical pediatric brain tumors. Pediatric patients therefore have considerable risks of neurocognitive impairment after brain radiotherapy. In this study, we investigated the radiation doses received by BSCs for three common locations of pediatric brain tumor entities. Material and methods: For ten patients in each group [posterior fossa ependymoma (PFE), craniopharyngioma (CP), and hemispheric ependymoma (HE)], the cumulative fraction of BSCs volumes receiving various dose levels were analyzed. We subsequently explored the differences in dose pattern between the three groups and used available dose response models from the literature to estimate treatment-induced intelligence quotient (IQ) decline. Results: Doses to BSCs were found to differ considerably between the groups, depending on their position relative to the tumor. Large inter-patient variations were observed in the ipsilateral structures of the HE groups, and at low doses for all three groups. IQ decline estimates differed depending on the model applied, presenting larger variations in the HE group. Conclusion: While there were notable differences in the dose patterns between the groups, the extent of estimated IQ decline depended more on the model applied. This inter-model variability should be considered in dose-effect assessments on cognitive outcomes of pediatric patients.

Towards proton arc therapy: physical and biologically equivalent doses with increasing number of beams in pediatric brain irradiation

Background: Proton arc therapy may improve physical dose conformity and reduce concerns of elevated linear energy transfer (LET) and relative biological effectiveness (RBE) at the end of the proton range, while offering more degrees of freedom for normal tissue sparing. To explore the potential of proton arc therapy, we studied the effect of increasing the number of beams on physical and biologically equivalent dose conformity in the setting of pediatric brain tumors. Material and methods: A cylindrical phantom (Ø = 150 mm) with central cylindrical targets (Ø = 25 and 30 mm) was planned with increasing number of equiangular coplanar proton beams (from 3 to 36). For four anonymized pediatric brain tumor patients, two 'surrogate' proton arc plans (18 equiangular coplanar or sagittal beams) and a reference plan with 3 non-coplanar beams were constructed. Biologically equivalent doses were calculated using two RBE scenarios: RBE_1.1; and RBE_LET, the physical dose weighted by the LET. For both RBE scenarios, dose gradients were assessed, and doses to cognitive brain structures were reported. Results: Increasing the number of beams resulted in an improved dose gradient and reduced volume exposed to intermediate LET levels, at the expense of increased low-dose and low-LET volumes. Most of the differences between the two RBE scenarios were seen around the prescription dose level, where the isodose volumes increased with the RBE_LET plans, e.g. up to 63% in the 3-beam plan for the smallest phantom target. Overall, the temporal lobes were better spared with the sagittal proton arc surrogate plans, e.g. a mean dose of 3.9 Gy compared to 6 Gy in the reference 3-beam plan (median value, RBE_1.1). Conclusion: Proton arc therapy has the potential to improve dose gradients to better spare cognitive brain structures. However, this is at the expense of increased low-dose/low-LET volumes, with possible implications for secondary cancer risks.

Efficacy of proton therapy in children with high-risk and locally recurrent neuroblastoma

PURPOSE

Proton therapy is currently used in the management of pediatric tumors to decrease late toxicities. However, one of the criticisms of proton therapy is the limited data regarding efficacy on disease control. The purpose of this study was to examine local and distant control rates after proton therapy for neuroblastoma.

METHODS AND MATERIALS

Eighteen patients with high-risk (n = 16) and locally recurrent neuroblastoma (n = 2) were treated with curative intent and received proton therapy to the primary site and up to three post-induction MIBG-avid metastatic sites. Primary sites (n = 18) were treated to 21-36 Gy (relative biological effectiveness [RBE]), and metastatic sites (n = 16) were treated to 21-24 Gy (RBE). Local control and survival rates were calculated using the Kaplan-Meier method.

RESULTS

With a median follow-up of 60.2 months, two- and five-year local control rates at the irradiated primary site were 94% and 87%, respectively. No failures at irradiated distant metastatic sites were observed. The five-year progression-free survival (PFS) was 64%, and the five-year overall survival (OS) was 94%. The extent of surgical resection was not associated with local control, PFS, or OS. No radiation-related nephropathy or hepatopathy was reported.

CONCLUSIONS

Excellent local control was achieved using proton therapy to the primary and post-induction MIBG-positive distant sites. The predominant site of failure is progression in post-induction non-MIBG-avid distant sites. Although proton therapy provides high rates of local control with acceptable toxicity for neuroblastoma, further advances in systemic therapy are needed for the improved control of systemic disease.

[Tumor treating fields in cancer treatment in Denmark]

Tumor treating fields (TTFields) is a new non-invasive approach to cancer treatment. TTFields are low-intensity (1-5 V/m), intermediate frequency (150-200 kHz) alternating electric fields delivered locally to the tumour to selectively kill dividing cells and disrupt cancer growth. TTFields has proven safe and effective for newly diagnosed glioblastoma and is currently being tried for multiple other tumours. This review presents an introduction to TTFields, covering the main indications, the application method, the mechanism of action, the clinical results and the perspectives for implementation in Danish cancer treatment.

Dosimetric comparison of five different techniques for craniospinal irradiation across 15 European centers: analysis on behalf of the SIOP-E-BTG (radiotherapy working group). Acta Oncol 2018;57:1240-1249. [PMID: 29698060 DOI: 10.1080/0284186x.2018.1465588]

PURPOSE

Conventional techniques (3D-CRT) for craniospinal irradiation (CSI) are still widely used. Modern techniques (IMRT, VMAT, TomoTherapy^®, proton pencil beam scanning [PBS]) are applied in a limited number of centers. For a 14-year-old patient, we aimed to compare dose distributions of five CSI techniques applied across Europe and generated according to the participating institute protocols, therefore representing daily practice.

MATERIAL AND METHODS

A multicenter (n = 15) dosimetric analysis of five different techniques for CSI (3D-CRT, IMRT, VMAT, TomoTherapy^®, PBS; 3 centers per technique) was performed using the same patient data, set of delineations and dose prescription (36.0/1.8 Gy). Different treatment plans were optimized based on the same planning target volume margin. All participating institutes returned their best treatment plan applicable in clinic.

RESULTS

The modern radiotherapy techniques investigated resulted in superior conformity/homogeneity-indices (CI/HI), particularly in the spinal part of the target (CI: 3D-CRT:0.3 vs. modern:0.6; HI: 3D-CRT:0.2 vs. modern:0.1), and demonstrated a decreased dose to the thyroid, heart, esophagus and pancreas. Dose reductions of >10.0 Gy were observed with PBS compared to modern photon techniques for parotid glands, thyroid and pancreas. Following this technique, a wide range in dosimetry among centers using the same technique was observed (e.g., thyroid mean dose: VMAT: 5.6-24.6 Gy; PBS: 0.3-10.1 Gy).

CONCLUSIONS

The investigated modern radiotherapy techniques demonstrate superior dosimetric results compared to 3D-CRT. The lowest mean dose for organs at risk is obtained with proton therapy. However, for a large number of organs ranges in mean doses were wide and overlapping between techniques making it difficult to recommend one radiotherapy technique over another.

SIOPE - Brain tumor group consensus guideline on craniospinal target volume delineation for high-precision radiotherapy

OBJECTIVE

To develop a consensus guideline for craniospinal target volume (TV) delineation in children and young adults participating in SIOPE studies in the era of high-precision radiotherapy.

METHODS AND MATERIALS

During four consensus meetings (Cambridge, Essen, Liverpool, and Marseille), conventional field-based TV has been translated into image-guided high-precision craniospinal TV by a group of expert paediatric radiation oncologists and enhanced by MRI images of liquor distribution.

RESULTS

The CTV_cranial should include the whole brain, cribriform plate, most inferior part of the temporal lobes, and the pituitary fossa. If the full length of both optic nerves is not included, the dose received by different volumes of optic nerve should be recorded to correlate with future patterns of relapse (no consensus). The CTV_cranial should be modified to include the dural cuffs of cranial nerves as they pass through the skull base foramina. Attempts to spare the cochlea by excluding CSF within the internal auditory canal should be avoided. The CTV_spinal should include the entire subarachnoid space, including nerve roots laterally. The lower limit of the spinal CTV is at the lower limit of the thecal sac, best visible on MRI scan. There is no need to include sacral root canals in the spinal CTV.

CONCLUSION

This consensus guideline has the potential to improve consistency of craniospinal TV delineation in an era of high-precision radiotherapy. This proposal will be incorporated in the RTQA guidelines of future SIOPE-BTG trials using CSI.