B. Wan1, M. D. Faye2, R. L. Ruo1, J. Wang3, V. Matassa1, A. Joseph1, S. Skamene4, M. Evans5, and C. R. Freeman1; 1McGill University Health Centre, Montreal, QC, Canada, 2Department of Radiation Oncology, McGill University Health Centre, Montreal, QC, Canada, 3Medical Physics Unit, McGill University Heath Centre, Montreal, QC, Canada, 4McGill University Health Centre, Division of Radiation Oncology, Montreal, QC, Canada, 5Cedars Cancer Centre, Department of Medical Physics, McGill University Health Centre, Montreal, QC, Canada
Purpose/Objective(s): To address technical challenges associated with total body irradiation (TBI) following a move to a new Cancer Centre in 2015, we developed a total body photon irradiation technique using multiple overlapping arcs (TBI-ARC) (Evans et al., 2015). The purpose of the work presented here was to compare our dosimetric data to Children’s Oncology Group (COG) radiotherapy guidelines for Stem Cell Transplantation, and the impact of this technique on treatment-related toxicities and survival outcomes. Materials/
Methods: We conducted a retrospective chart review of patients treated with the TBI-ARC technique at our institution between March 2015 and June 2023. Demographic data, pathological diagnosis, and radiation-related toxicities were extracted. Dosimetric data analyzed included dose and fractionation, Imaging and Radiation Oncology CORE (IROC) dose reporting points ratio compared to prescription, and average lung point dose. Results: Of the 138 patients treated using TBI-ARC, 82 (59%) were under 18 years old. 110 (80%) patients had a hematological malignancy. 51 (37%) of patients received a single 2Gy (n=46) or 3Gy (n=5) fraction, whereas 87 (63%) of patients received between 4Gy and 13.2Gy in two to eight fractions. 23 (17%) patients experienced any radiation-related toxicity during TBI, 14 (10%) of whom experienced multiple toxicities. These included nausea (15%, 20), parotitis (7%, 10), vomiting (5%, 7) and fatigue (2%, 3). Dosimetric data are presented on 105/139 patients (76%), 52 of whom received high dose TBI (13.2Gy/8Fx, 12Gy/6Fx, 12Gy/8Fx). Lung blocks were used in 36 patients treated with high dose TBI. The IROC dose reporting points ratio relative to prescription dose were: head (0.94 ± 0.06), neck (1.06 ± 0.06), mid-mediastinum (0.96 ± 0.06), lung with blocks (0.80 ± 0.07), lung without blocks (1.08 ± 0.07), umbilicus (0.99 ± 0.03), pelvis (0.98 ± 0.04), knee (1.07 ± 0.07) and ankle (1.15 ± 0.10). There was good compliance between the dose reporting points and the, with the majority of point doses within ± 10%. The highest concordance was recorded for the mid-mediastinum, umbilicus and pelvis points with 95.2%, 99% and 98% of patients respectively within ±10%; and the lowest concordance for the lung and ankle points with 40% and 59.1% of patients with greater than ±15% deviation. Lung dosimetric data were reported for 81 patients. The average lung point dose was concordant with DVH mean lung dose with a ratio of 1.03 ± 0.01. Conclusion: Our TBI-ARC technique as a technique, it has wide applicability and versatility and acceptable rates of acute radiation-related toxicities. Future steps include the analysis of subacute and late toxicities, disease control and survival. REFERENCES Evans, M. D., Ruo, R., Patrocinio, H. J., Poon, E., Freeman, C., Hijal, T., & Parker, W. (2016). Poster-42: TB-ARC: A Total Body photon ARC technique using a commercially available linac. Medical Physics, 43(8Part2), 4946-4946.
