Improved organ sparing using auto‐planned Stanford volumetric modulated arc therapy for total body irradiation technique

Abstract

Purpose/objectivesTo 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.MethodsTen 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.ResultsAll 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 Dmax (p < .2) and PTV V110% (p < .4). Compared to the 2D plans, significant decreases in the Dmean 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 Dmean (−32.5% ± 5.0%, p < .001) and lenses Dmax (−5.3% ± 8.1%, p = .03); and in addition, for 2 Gy prescription: testes/ovaries Dmean (−41.5% ± 11.5%, p < .001), brain Dmean (−22.6% ± 5.4%, p = .002), and thyroid Dmean (−18.2% ± 16.0%, p = .03).ConclusionsSuperior 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, thyroid, and lenses.