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Purpose The aim of this study was to examine current practice patterns in pediatric total body irradiation (TBI) techniques among COG member institutions. Methods and Materials Between November 2019 and February 2020, a questionnaire containing 52 questions related to the technical aspects of TBI was sent to medical physicists at 152 COG institutions. The questions were designed to obtain technical information on commonly used TBI treatment techniques. Another set of 9 questions related to the clinical management of patients undergoing TBI was sent to 152 COG member radiation oncologists at the same institutions. Results Twelve institutions were excluded because TBI was not performed in their institutions. A total of 88 physicists from 88 institutions (63% response rate) and 96 radiation oncologists from 96 institutions (69% response rate) responded. The anterior-posterior/posterior-anterior (AP/PA) technique was the most common technique reported (49 institutions [56%]); 44 institutions (50%) used the lateral technique, and 14 (16%) used volumetric modulated arc therapy or tomotherapy. Midplane dose rates of 6 to 15 cGy/min were most commonly used. The most common specification for lung dose was the midlung dose for both AP/PA techniques (71%) and lateral techniques (63%). Almost all physician responders agreed with the need to refine current TBI techniques, and 79% supported the investigation of new TBI techniques to further lower the lung dose. Conclusions There was no consistency in the practice patterns, methods for dose measurement, and reporting of TBI doses among COG institutions. The lack of standardization precludes meaningful correlation between TBI doses and clinical outcomes including disease control and normal tissue toxicity. The COG radiation oncology discipline is currently undertaking several steps to standardize the practice and dose reporting of pediatric TBI using detailed questionnaires and phantom-based credentialing for all COG centers.

PURPOSE/OBJECTIVE(S) Central (CLT) and ultracentral (UCLT) lung tumors can be at higher risk for treatment related mortality following stereotactic body radiation therapy (SBRT) and the preferred dose and fractionation is unclear. We assessed the toxicity and outcomes of patients with CLT and UCLT who underwent definitive five-fraction SBRT. MATERIALS/METHODS We reviewed the charts of patients with either CLT or UCLT managed with SBRT from June 2010-April 2019. CLT were defined as gross tumor volume within 2 cm of either the proximal bronchial tree, trachea, mediastinum, aorta, or spinal cord. UCLT were defined as GTV abutting any of these structures. Toxicity was graded by the Common Terminology Criteria for Adverse Events version 5.0. Propensity score matching was performed for gender, performance status, and history of prior lung cancer. Survival outcomes evaluated by Cox regression and Kaplan-Meier estimation. RESULTS Within this cohort of 83 patients, the median age was 73.1 years with a median follow up of 29.9 months. All patients underwent 5 fraction SBRT, with dose range of 50-60 Gy. Most patients had T1 tumors (68.7%) and 43 (51.8%) were considered UCLT. In 20 (50%) patients with CLT, the proximal bronchial tree was the closest central structure while the aorta was the closest structure in 16 (37.2%) of UCLT patients. Grade 2+ toxicity was similar between the two groups, 11 (27.5%) for CLT and 13 (30.2%) (P = 0.78) for UCLT patients. Furthermore, there was no difference in grade 3 toxicity with 3 (7.5%) CLT and 4 (9.3%) UCLT patients (P = 0.77) and no observed grade 4+ events. There was no difference in crude local failure (5% vs 7.0%) (P = 0.34) or recurrence rates (22.5% vs 9.3) (P = 0.09). Multivariate analysis adjusting for gender, performance status, prior lung cancer, history of diabetes, history of heart disease, and prescription volume revealed UCLT to be associated with worse overall survival (OS) (P = 0.02) but not freedom from progression (FFP). Using propensity score match pairing, 29 match pairs were generated finding UCLT to correlate with reduced non-cancer related survival (NC-OS) and OS, but not FFP. CONCLUSION Definitive 5 fraction SBRT yielded similar toxicity profiles for CLT and UCLT. Despite no difference in FFP, UCLT were associated with worse (NC-OS) and OS.

Purpose: Most brachytherapy planning systems are based on a dose calculation algorithm that assumes an infinite scatter environment surrounding the target volume and applicator. Dosimetric errors from this assumption are negligible. However, in intraoperative high-dose-rate brachytherapy (IOHDR) where treatment catheters are typically laid either directly on a tumor bed or within applicators that may have little or no scatter material above them, the lack of scatter from one side of the applicator can result in underdosage during treatment. This study was carried out to investigate the magnitude of this underdosage. Methods: IOHDR treatment geometries were simulated using a solid water phantom beneath an applicator with varying amounts of bolus material on the top and sides of the applicator to account for missing tissue. Treatment plans were developed for 3 different treatment surface areas (4 × 4, 7 × 7, 12 × 12 cm2), each with prescription points located at 3 distances (0.5 cm, 1.0 cm, and 1.5 cm) from the source dwell positions. Ionization measurements were made with a liquid-filled ionization chamber linear array with a dedicated electrometer and data acquisition system. Results: Measurements showed that the magnitude of the underdosage varies from about 8% to 13% of the prescription dose as the prescription depth is increased from 0.5 cm to 1.5 cm. This treatment error was found to be independent of the irradiated area and strongly dependent on the prescription distance. Furthermore, for a given prescription depth, measurements in planes parallel to an applicator at distances up to 4.0 cm from the applicator plane showed that the dose delivery error is equal in magnitude throughout the target volume. Conclusion: This study demonstrates the magnitude of underdosage in IOHDR treatments delivered in a geometry that may not result in a full scatter environment around the applicator. This implies that the target volume and, specifically, the prescription depth (tumor bed) may get a dose significantly less than prescribed. It might be clinically relevant to correct for this inaccuracy.

Purpose: To determine whether a dose-response relationship exists between the biologic effective dose (BED) at Point A and the bladder and rectum and the clinical outcomes in our experience with external beam radiotherapy (EBRT) and high-dose-rate brachytherapy in the treatment of cervical carcinoma. Methods and Materials: This was a retrospective study. A total of 49 patients with cervical cancer were treated with a combination of EBRT (median 45 Gy, range 41.4–50.4) and high-dose-rate brachytherapy (median 18 Gy; range 18–19, in two fractions). Twenty-three patients received concomitant cisplatin-based chemotherapy. The cumulative BEDs were calculated at Point A (BED 10 ) and at bladder and rectal reference points (BED 3 ) using the linear-quadratic equation. The BED 10 values, after incorporating a time factor (BED 10 tf) in the formula, were also calculated. Results: In patients treated with RT alone, the local failure rate was 10% (1 of 10) and 19% (3 of 16) in patients receiving a BED 10 >89 Gy 10 or 10 to Point A, respectively ( p = 0.2). The corresponding local failure rates were 20% (3 of 15) and 0% (0 of 8) in patients treated with concomitant chemotherapy ( p = 0.3). In patients treated with RT alone, the local failure rate was 7.7% (1 of 13) and 23% (3 of 13) in patients with a BED 10 tf >64 Gy 10 or 10 ( p = 0.1), respectively. The median BED 3 values at the rectal and bladder point was 95.5 Gy 3 and 103.6 Gy 3, respectively. Only 1 case of Grade 2 late rectal toxicity (2%) and no late bladder toxicity occurred. Conclusion: In patients treated with RT alone, a BED 10 >89 Gy and a BED 10 tf >64 Gy indicated a trend toward a better local control rate. This difference was not observed in patients receiving chemotherapy. A BED 3 3 was associated with negligible late toxicity. Although the BED 10 in our study was about 10–15 Gy 10 less than that in the published data, the 4-year local control rate of 80% and 83% and disease-free survival rate of 75% and 70% with and without chemotherapy, respectively, compare well with the rates in other studies in the literature.