Factors Associated With Acute Toxicity in Pediatric Patients Treated With Proton Radiation Therapy: A Report From the Pediatric Proton Consortium Registry

PurposeLimited prospective information regarding acute toxicity in pediatric patients receiving proton therapy (PT) exists. In this study, Pediatric Proton Consortium Registry (PPCR) data was analyzed for factors associated with development of acute toxicity in children receiving passively scattered or pencil beam scanning PT.Methods and MaterialsPediatric patients treated with PT and enrolled on the PPCR from 2016 to 2017 at 7 institutions were included. Data were entered on presence versus absence of acute general, cardiac, endocrine, eye, gastrointestinal, genitourinary, hematologic, mouth, musculoskeletal, neurologic, psychological, respiratory, and skin toxicities before (baseline) and at the end of PT (acute). Associations between patient and treatment variables with development of acute toxicity were assessed with multivariable modeling.ResultsOf 422 patients included, PT technique was passively scattered in 241 (57%), pencil beam scanning in 180 (43%), and missing in 1 (<1%) patient. Median age was 9.9 years. Daily anesthesia for treatment was used in 169 (40%). Treatments were categorized as craniospinal irradiation (CSI; n = 100, 24%), focal central nervous system PT (n = 157, 38%), or body PT (n = 158, 38%). Passively scattered PT was associated with increased risk of hematologic toxicity compared with pencil beam scanning PT (odds ratio [OR]: 3.03; 95% confidence interval [CI], 1.38-6.70; P = .006). There were no other differences toxicities between PT techniques. Uninsured patients had increased risk of GI (OR: 2.71; 95% CI, 1.12-6.58; P = .027) and hematologic toxicity (OR: 10.67; 95% CI, 2.68-42.46; P <.001). Patients receiving concurrent chemotherapy were more likely to experience skin (OR: 2.45; 95% CI, 1.23-4.88; P = .011), hematologic (OR: 2.87; 95% CI, 1.31-6.25; P = .008), GI (OR: 2.37; 95% CI, 1.33-4.21; P = .003), and mouth toxicities (OR: 2.03; 95% CI, 1.10-3.73; P = .024). Patients receiving 49 to 55 Gy were more likely to experience skin (OR: 2.18; 95% CI, 1.06-4.44; P = .033) toxicity than those receiving <49 Gy.ConclusionsThe PPCR registry highlights broad differences in acute toxicity rates in children receiving PT, and identifies opportunities for improvements in prevention, monitoring, and treatment of toxicities.     

Bronchial Stenosis in Central Pulmonary Tumors Treated With Stereotactic Body Radiation Therapy

PurposeStereotactic body radiation therapy (SBRT) in lung tumors has an excellent local control due to the high delivered dose. Proximity of the proximal bronchial tree (PBT) to the high dose area may result in pulmonary toxicity. Bronchial stenosis is an adverse event that can occur after high dose to the PBT. Literature on the risk of developing bronchial stenosis is limited. We therefore evaluated the risk of bronchial stenosis for tumors central to the PBT and correlated the dose to the bronchi.Methods and MaterialsPatients with a planning tumor volume (PTV) ≤2 cm from PBT receiving SBRT (8 × 7.5 Gy) between 2015 to 2019 were retrospectively reviewed. Main bronchi and lobar bronchi were manually delineated. Follow-up computed tomography scans were analyzed for bronchial stenosis and atelectasis. Bronchial stenosis was assessed using Common Terminology Criteria for Adverse Events Version 4.0 (CTCAEv4). Patient, tumor, dosimetric factors and survival were evaluated between patients with and without stenosis using uni- and multivariate and Kaplan-Meier analysis.ResultsFifty-one patients were analyzed with a median age of 70 years and World Health Organization (WHO) performance status ≤1 in 92.2%. Median follow-up was 36 months (interquartile range [IQR], 19.6-45.4) and median overall survival 48 months (IQR 21.5-59.3). In 15 patients (29.4%) bronchial stenosis was observed on follow-up computed tomography scan. Grade 1 stenosis was seen in 21.6% (n = 11), grade 2 in 7.8% (n = 4). No grade ≥3 stenosis was observed. Median time to stenosis was 9.6 months (IQR 4.4-19.2). Patients who developed stenosis had significantly larger gross tumor volume with a median of 19 cm³(IQR 7.7-63.2) versus 5.2 cm³ (IQR 1.7-11.3, P <.01). Prognostic factors in multivariate analysis for stenosis were age (P = .03; odds ratio [OR] 1.1), baseline dyspnea (P = .02 OR 7.7), and the mean lobar bronchus dose (P = .01; OR 1.1).ConclusionsLow-grade (≤2) lobar bronchial stenosis is a complication in approximately one-third of patients after SBRT for lung tumors with a PTV ≤2 cm from PBT. Prognostic risk factors were age, baseline dyspnea and mean dose on a lobar bronchus.     

Patterns of Failure Among Patients With Low-grade Glioma Treated With Proton Radiation Therapy

PurposeProton treatment may be a useful radiation therapy modality for long-term surviving patients with glioma to reduce normal tissue toxicities. Photon studies demonstrate that most low-grade glioma (LGG) failures occur within the radiation field, supporting the use of more conformal treatment plans, yet it is unclear whether this can be translated to proton radiation therapy (PRT). Our objective is to examine our institutional experience to determine patterns of failure in patients with LGG with respect to the volume irradiated with PRT.Methods and materialsPatients with World Health Organization 2007 grade I to II or isocitrate dehydrogenase 1–positive mutation grade III LGG treated with PRT between 2005 and 2015 were retrospectively reviewed. Patients with documented local recurrences on magnetic resonance imaging after receipt of PRT underwent a comparison with the initial treatment plan dosimetry to evaluate patterns of failure. A total of 141 patients were included in the final cohort.ResultsThe median follow-up time was 46.7 months (range, 2.8-144 months), and 5-year overall survival was 84%. The median PRT dose delivered was 54 Gy (relative biological effectiveness) (range, 45-60 Gy). There were 42 failures after PRT (30%). The median time to progression after treatment was 32.7 months (range, 4.8-93.6 months). Thirty-one patients (74%) failed in-field (defined as within the 95% isodose volume), 5 patients (12%) failed out-of-field, and 5 patients (12%) had marginal failures (defined as within the 50%-95% isodose volume). The 5-year freedom from progression after PRT was 60.1% (95% confidence interval, 48.7-70.0). The 5-year cumulative incidence of overall survival was 33% among those with recurrence after PRT and 96% among those without recurrence after PRT (P < .001).ConclusionsOf the patients with LGG who had documented failures after PRT, most recurred within the radiation field with few marginal failures, indicating that even with PRT, which often can have steeper dose gradients, coverage is adequate. Survival was poor for patients whose tumors recurred.     

Radiation Therapy for Pediatric Brain Tumors using Robotic Radiation Delivery System and Intensity Modulated Proton Therapy

PurposeThis study recruited 2 centers with expertise in treating pediatric brain tumors with robotic radiation delivery system photon therapy and proton therapy, respectively, to study the plan quality and dose deposition characteristics of robotic radiation delivery system photon therapy and intensity modulated proton therapy (IMPT) plans.Methods and MaterialsA total of 18 patients clinically treated with the robotic radiation delivery system were planned with IMPT. Cases were planned per the standard of care of each institution but respected the same planning objectives. The comparison included 3 aspects: plan quality, dose fall-off characteristics around the target volume, and the volume of the high-, intermediate-, and low-dose baths.ResultsAll robotic radiation delivery system and IMPT plans met the planning objectives. However, IMPT significantly reduced the maximum dose to organs at risk away from the planning target volume (PTV), such as the cochlea and eye (P < .05), and the mean dose to the normal brain (P < .05). No statistically significant difference was observed in the maximum dose to the optical pathway and brain stem. Robotic radiation delivery system plans demonstrated a sharper dose fall-off within 5 mm around the PTV (P < .05), whereas IMPT significantly lowered the dose to the normal tissue beyond 10 mm from the PTV (P < .05). The robotic radiation delivery system offers a smaller high-dose bath whereas IMPT offers a smaller low-dose bath (P < .05). However, the difference in intermediate dose is not statistically significant.ConclusionsIn general, robotic radiation delivery system plans exhibit reduced high-dose exposure to normal tissue, and IMPT plans have considerably smaller volumes of low-dose exposure with differences in medium-range dose baths increasingly favoring protons as tumor size increases.     

Adjuvant Systemic Therapy in Patients With Early-Stage NSCLC Treated With Stereotactic Body Radiation Therapy

Introduction

Stereotactic body radiation therapy (SBRT) is commonly used to treat nonsurgical patients with early-stage NSCLC. There are no prospective data on the role of adjuvant chemotherapy in this setting.

Mathematical Modelling for Patient Selection in Proton Therapy

Proton beam therapy (PBT) is still relatively new in cancer treatment and the clinical evidence base is relatively sparse. Mathematical modelling offers assistance when selecting patients for PBT and predicting the demand for service. Discrete event simulation, normal tissue complication probability, quality-adjusted life-years and Markov Chain models are all mathematical and statistical modelling techniques currently used but none is dominant. As new evidence and outcome data become available from PBT, comprehensive models will emerge that are less dependent on the specific technologies of radiotherapy planning and delivery.