We previously determined that the predicted risk of radiogenic second cancer in the bladder and rectum after proton arc therapy (PAT) was less than or equal to that after volumetric modulated arc therapy (VMAT) with photons, but we did not consider the impact of margin size on that risk.
The current study was thus conducted to evaluate margin size's effect on the predicted risks of second cancer for the two modalities and the relative risk between them. Seven treatment plans with margins ranging from 0 mm in all directions to 6 mm posteriorly and 8 mm in all other directions were considered for both modalities. We performed risk analyses using three risk models with varying amounts of cell sterilization and calculated ratios of risk for the corresponding PAT and VMAT plans. We found that the change in risk with margin size depended on the risk model but that the relative risk remained nearly constant with margin size, regardless of the amount of cell sterilization modeled. We conclude that while margin size influences the predicted risk of a second cancer for a given modality, it appears to affect both modalities in roughly equal proportions so that the relative risk between PAT and VMAT is approximately equivalent.
Written by:
Rechner LA, Howell RM, Zhang R, Newhauser WD. Are you the author?
Department of Radiation Physics, Graduate School of Biomedical Sciences, The University of Texas Health Science Center Houston, Houston, TX 77030, USA; Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Reference: Phys Med Biol. 2012 Dec 7;57(23):N469-79.
doi: 10.1088/0031-9155/57/23/N469
PubMed Abstract
PMID: 23154795
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