Evaluation of the Flash effect in breast irradiation using TomoDirect: An investigational study

Flash is a specified function in tomodirect that enables beam expansion by opening additional leaves to the target. this study assessed the theoretical dose distribution resulting from flash in breast irradiation using tomodirect. a cylindrical phantom that enabled dose distribution of the breast was used for verifying the effect of planning target volume (ptv) contouring and flash. a total of 18 gy in 10 fractions were prescribed to the ptv. five ptvs were then created by contracting this contour by 0,1,2,3,4 and 5 mm,giving ptv-x. flash ±x is defined by opening x (number) of the leaves. the flash effect in the air was compared with each set-up error of 5,10 and 15 mm,respectively. the minimum ptv dose from ptv-1 to ptv-3 increased from 13.88 gy to 15.86 gy. in contrast,dmin in ptv-4 and ptv-5 was 17.80 gy in 98.88% of the prescription dose. without flash,when 5-,10- and 15-mm set-up errors applied in the ptv,relative doses of 87.88,23.73 and 7.94% were observed,respectively. however,in flash 3,which was equal to the usual air margin of 1.875 cm,a relative dose of 104.24% ± 0.30% was observed,irrespective of set-up errors (5 mm to 15 mm). flash opening is useful for countervailing set-up errors in breast cancer patients who receive breast irradiation with tomodirect. © the author 2015.