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

Abstract

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. 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. 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 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-1cm (-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 2Gy 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). 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, thyroid, and lenses.