Nataliya Kovalchuk

Purpose/objectives To evaluate dosimetric differences between auto‐planned volumetric modulated arc therapy (VMAT) total body irradiation (TBI) technique and two‐dimensional radiotherapy using anterior‐posterial/posterio‐anterial beams (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 source to skin distance (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 planned target volume (PTV) D90% ≥ 100% of prescription. VMAT‐TBI PTV D90% significantly increased (7.1% ± 2.9%, p < .001) compared to the 2D technique, whereas no differences were observed in global D max ( p < .2) and PTV V110% ( p < .4). Compared to the 2D plans, significant decreases in the D mean to the lungs (−25.6% ± 11.5%, p < .001) and lungs‐1 cm (−34.1% ± 10.1%, p < .001) were observed with the VMAT plans. The VMAT technique also enabled decrease of dose to other organs: kidneys D mean (−32.5% ± 5.0%, p < .001) and lenses D max (−5.3% ± 8.1%, p = .03); and in addition, for 2 Gy prescription: testes/ovaries D mean (−41.5% ± 11.5%, p < .001), brain D mean (−22.6% ± 5.4%, p = .002), and thyroid D mean (−18.2% ± 16.0%, p = .03). Conclusions Superior lung sparing with improved target coverage and similar global D max were observed with the VMAT plans as compared to 2D plans. In addition, VMAT‐TBI plans provided greater dose reductions in gonads, kidneys, brain, thyroid, and lenses.