Effects of bolus thickness and use frequency on skin dose in postmastectomy intensity-modulated radiotherapy / 中国辐射卫生

ABSTRACT

Objective To investigate the effects of bolus thickness and use frequency on skin dose in postmastectomy intensity-modulated radiotherapy. Methods We retrospectively reviewed 20 cases receiving postmastectomy fixed-field intensity-modulated radiotherapy, to analyze the homogeneity index (HI) and conformity index (CI) of the target volume and the skin dose (Dmax, Dmean, and Dmin) of radiotherapy plans with 0.5 cm-thick bolus or 1 cm-thick bolus alone at a use frequency of 5 F, 10 F, 15 F, 20 F, and 25 F versus a combination of 0.5 cm and 1 cm-thick bolus, and fit the relationship between skin dose and bolus use frequency. Results As the bolus use frequency increased, the skin dose increased, the hot spot of the target volume decreased, and the low-dose volume decreased. The HI of the target volume with the 1 cm bolus was better than that with the 0.5 cm bolus at all use frequencies (P < 0.05), and HI decreased with the increase of bolus use frequency. For both 0.5 cm and 1 cm bolus, the CI of the target volume increased initially and then decreased, reaching the maximum value at a frequency of around 15 F; the CI showed significant differences only at 20 F and 25 F between the two types of bolus (P < 0.05). The skin Dmax and Dmean were significant higher with the 0.5 cm bolus than with the 1 cm bolus (P < 0.05). The equation for the relationship between skin dose (D) and bolus use frequency (F) was D = A × F + B × F2 + C. The Dmax and HI with the combination of 0.5 cm bolus (6 F) plus 1 cm bolus (8 F) fell between those with the 0.5 cm bolus (15 F) and those with the 1 cm bolus (15 F) (P < 0.05). Conclusion In postmastectomy fixed-field intensity-modulated radiotherapy, skin dose can be calculated based on bolus use frequency. Mixed use of bolus may be more suitable than use of 0.5 cm bolus or 1 cm bolus alone.