Improved Organ Sparing Using Auto-Planned Stanford Volumetric Modulated Arc Therapy for Total Body Irradiation (VMAT-TBI) Technique

Purpose/Objectives: To evaluate dosimetric differences between auto-planned Volumetric Modulated Arc Therapy (VMAT) Total Body Irradiation (TBI) technique and 2D AP/PA TBI technique. Methods: Ten pediatric patients treated with VMAT-TBI on Varian c-arm linac were included in this study. VMAT-TBI plans were generated using our in-house developed and publicly shared auto-planning scripts. For each VMAT-TBI plan, a 2D AP/PA plan was created replicating the institution’s clinical setup with the patient positioned at extended SSD with a compensator to account for differences in patient thickness, 50%-transmission daily lung blocks and electron chest-wall boosts prescribed to 50% of the photon prescription. Clinically relevant metrics were analyzed and compared between the VMAT and 2D plans. Results: All VMAT-TBI plans achieved PTV D90%≥100% of prescription. VMAT-TBI PTV D90% significantly increased (6.2%±2.4%, p<0.001) compared to the 2D technique, whereas no differences were observed in global Dmax (p<0.2) and PTV V110% (p<0.4). Compared to the 2D plans, significant decreases in the Dmean to the lungs (-25.6%±11.5%, p<0.001) and lungs-1cm (-34.1%±10.1%, p<0.001) were observed with the VMAT plans. The VMAT technique also provided additional sparing to other organs: for 12Gy prescription, kidneys Dmean of 64.7%±3.3%; for 2Gy prescription, testes/ovaries (Dmean of 31.6%±10.7%), brain (Dmean of 74.8%±1.6%) and thyroid (Dmean of 72.5±3.5%). Conclusions : Superior lung sparing with improved target coverage and similar global Dmax were observed with the VMAT plans as compared to 2D plans. In addition, VMAT-TBI plans provided greater dose reductions in gonads, kidneys, brain, and thyroid.