Biological Equivalent Dose Of The Road Model For Flash Radiotherapy

Ultra-high dose rate in radiotherapy (FLASH) has been shown to increase the therapeutic index with markedly reduced normal tissue toxicity and the same or better tumor cell killing. In previous study, we developed the Rotational direct Aperture optimization with a Decoupled ring-collimator (ROAD) to achieve simultaneous ultrafast delivery and complex dose modulation. This study investigates the biological gain of the ROAD model based on a radiolytic oxygen depletion model proposed by Pratx et al 2019. The ROAD design includes a fast-rotating slip ring Linac and a decoupled ring-collimator with 75 pre-shaped multi-leaf collimator (MLC) modules, with the ring-source rotates at 1 rps clockwise while the ring-collimator rotating at 1 rps counterclockwise. The X-ray source is triggered when the source is aligned with individual MLCs, achieving 150 equal-angular beams for one full arc. For each ROAD plan, the oxygen tension was computed voxelwise using a spatiotemporal model that took into account of the cell respiration, tissue diffusion, and radiolytic oxygen depletion. The oxygen enhancement ratio and the biological equivalent dose (BED) were computed based on the transient oxygen tension at each control point. The ROAD plans were compared with Volumetric Modulated Arc Therapy (VMAT) plans on both the physical dose and the BED, of a brain, a lung, a prostate, and a head and neck cancer patient. The ROAD plans can be delivered within 1s, achieving 112 Gy/s average per-beam dose rate. Table 1 reports the statistics of the physical dose and the BED of ROAD and VMAT plans. The BED of VMAT plans is equivalent to its physical dose. For physical dose, the average PTV homogeneity is 0.956 and 0.955 for VMAT and ROAD respectively, and differences in the average OAR mean and max physical dose are within 2% of the prescription dose. For the BED, ROAD plans reduced the R50 and integral dose by 48% and 21% respectively, compared with VMAT. The average reduction of OAR mean and max BED of ROAD from VMAT were 2.78 Gy and 8.29 Gy, respectively. The ROAD method achieved comparable physical dosimetry and superior BED compared with state-of-the-art VMAT.Abstract 3223; Table 1Statistics of the physical dose and the BED in VMAT and ROAD plans. The BED of VMAT plans is equivalent to its physical dose.CaseMethodR50Integral Dose (Gy·cm3)OAR Dmean (Gy)OAR Dmax (Gy)Dose ConformityGBMphysical doseVMAT4.612.351.693.961.00ROAD4.842.541.593.491.01BEDROAD2.172.091.543.060.95LNGphysical doseVMAT4.1573.894.5915.720.98ROAD3.2070.764.6515.120.98BEDROAD1.6254.223.6610.170.95PRTphysical doseVMAT2.8339.284.8721.130.96ROAD2.8539.624.5620.400.96BEDROAD1.4730.343.3113.290.95H&Nphysical doseVMAT2.23113.7121.7748.331.15ROAD2.14111.7020.7147.031.14BEDROAD1.5488.6413.2929.450.97 Open table in a new tab