Dose-escalated volumetric modulated arc therapy for total marrow irradiation: A feasibility dosimetric study with 4DCT planning and simultaneous integrated boost.

Abstract

To evaluate the planning feasibility of dose-escalated total marrow irradiation (TMI) with simultaneous integrated boost (SIB) to the active bone marrow (ABM) using volumetric modulated arc therapy (VMAT), and to assess the impact of using planning organs at risk (OAR) volumes (PRV) accounting for breathing motion in the optimization. Five patients underwent whole-body CT and thoraco-abdominal 4DCT. A planning target volume (PTV) including all bones and ABM was contoured on each whole-body CT. PRV of selected OAR (liver, heart, kidneys, lungs, spleen, stomach) were determined with 4DCT. Planning consisted of 9-10 full 6 MV photon VMAT arcs. Four plans were created for each patient with 12Gy prescribed to the PTV, with or without an additional 4Gy SIB to the ABM. Planning dose constraints were set on the OAR or on the PRV. Planning objective was a PTV Dmean<110% of the prescribed dose, a PTV V110%<50%, and OAR Dmean≤50-60%. PTV Dmean<110% was accomplished for most plans (n=18/20), while all achieved V110%<50%. SIB plans succeeded to optimally cover the boost volume (median ABM Dmean=16.3Gy) and resulted in similar OAR sparing compared to plans without SIB (median OAR Dmean=40-54% of the ABM prescribed dose). No statistically significant differences between plans optimized with constraints on OAR or PRV were found. Adding a 4Gy SIB to the ABM for TMI is feasible with VMAT technique, and results in OAR sparing similar to plans without SIB. Setting dose constraints on PRV does not impair PTV dosimetric parameters.