Practice Patterns of Pediatric Total Body Irradiation Techniques: A Children's Oncology Group Survey.

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.

Higher Reported Lung Dose Received During Total Body Irradiation for Allogeneic Hematopoietic Stem Cell Transplantation in Children With Acute Lymphoblastic Leukemia Is Associated With Inferior Survival: A Report from the Children's Oncology Group.

PURPOSE: To examine the relationship between lung radiation dose and survival outcomes in children undergoing total body irradiation (TBI)-based hematopoietic stem cell transplantation (HSCT) for acute lymphoblastic leukemia on the Children's Oncology Group trial. METHODS AND MATERIALS: TBI (1200 or 1320 cGy given twice daily in 6 or 8 fractions) was used as part of 3 HSCT preparative regimens, allowing institutional flexibility regarding TBI techniques, including lung shielding. Lung doses as reported by each participating institution were calculated for different patient setups, with and without shielding, with a variety of dose calculation techniques. The association between lung dose and transplant-related mortality, relapse-free survival, and overall survival (OS) was examined using the Cox proportional hazards regression model controlling for the following variables: TBI dose rate, TBI fields, patient position during TBI, donor type, and pre-HSCT minimal residual disease level. RESULTS: Of a total of 143 eligible patients, 127 had lung doses available for this analysis. The TBI techniques were heterogeneous. The mean lung dose was reported as 904.5 cGy (standard deviation, ±232.3). Patients treated with lateral fields were more likely to receive lung doses ≥800 cGy (P < .001). The influence of lung dose ≥800 cGy on transplant-related mortality was not significant (hazard ratio [HR], 1.78; P = .21). On univariate analysis, lung dose ≥800 cGy was associated with inferior relapse-free survival (HR, 1.76; P = .04) and OS (HR, 1.85; P = .03). In the multivariate analysis, OS maintained statistical significance (HR, 1.85; P = .04). CONCLUSIONS: The variability in TBI techniques resulted in uncertainty with reported lung doses. Lateral fields were associated with higher lung dose, and thus they should be avoided. Patients treated with lung dose <800 cGy in this study had better outcomes. This approach is currently being investigated in the Children's Oncology Group AALL1331 study. Additionally, the Imaging and Radiation Oncology Core Group is evaluating effects of TBI techniques on lung doses using a phantom.

Cardiac-Sparing Whole Lung IMRT in Patients With Pediatric Tumors and Lung Metastasis: Final Report of a Prospective Multicenter Clinical Trial.

PURPOSE: A prospective clinical trial was conducted for patients undergoing cardiac sparing (CS) whole lung irradiation (WLI) using intensity modulated radiation therapy (IMRT). The 3 trial aims were (1) to demonstrate the feasibility of CS IMRT with real-time central quality control; (2) to determine the dosimetric advantages of WLI using IMRT compared with standard anteroposterior (AP) techniques; and (3) to determine acute tolerance and short-term efficacy after a protocol-mandated minimum 2-year follow-up for all patients. METHODS AND MATERIALS: All patients underwent a 3-dimensional chest computed tomography scan and a contrast-enhanced 4-dimensional (4D) gated chest computed tomography scan using a standard gating device. The clinical target volume was the entire bilateral 3-dimensional lung volume, and the internal target volume was the 4D minimum intensity projection of both lungs. The internal target volume was expanded by 1 cm to get the planning target volume. All target volumes, cardiac contours, and treatment plans were centrally reviewed before treatment. The different cardiac volumes receiving percentages of prescribed radiation therapy (RT) doses on AP and IMRT WLI plans were estimated and compared. RESULTS: The target 20 patients were accrued in 2 years. Median RT dose was 15 Gy. Real-time central quality assurance review and plan preapproval were obtained for all patients. WLI using IMRT was feasible in all patients. Compared with standard AP WLI, CS IMRT resulted in a statistically significant reduction in radiation doses to the whole heart, atria, ventricles, and coronaries. One child developed cardiac dysfunction and pulmonary restrictive disease 5.5 years after CS IMRT (15 Gy) and doxorubicin (375 mg/m2). The 2- and 3-year lung metastasis progression-free survival was 65% and 52%, respectively. CONCLUSIONS: We have demonstrated the feasibility of WLI using CS IMRT and confirmed the previously reported advantages of IMRT, including superior cardiac protection and superior dose coverage of 4D lung volumes. Further studies are required to establish the efficacy and safety of this irradiation technique.