Impact of stringent tolerance criteria on verification of absorbed dose distributions and evaluation through inhomogeneous media

Abstract

Advances of radiation delivery devices have increased the complexity of the radiation oncology treatments. Herewith, outcome of the treatment, as well as patient safety, strongly depend on the consistency of absorbed dose delivery. Both can be ensured by comprehensive system of verification of calculated absorbed dose distributions. Standard method is evaluation of calculated absorbed dose distribution according to gamma method, using a 2-D detector and a homogeneous phantom, to obtain measured dose distribution. Purpose of this research was to investigate the influence of tolerance criteria on gamma passing rate. Additionally, the agreement in heterogeneous phantom was analysed. Absorbed dose calculations were performed using systems Monaco and XiO. Detector with 1020 ionization chambers in homogeneous phantom and semi-anthropomorphic phantom was used for measurements. Absorbed dose distributions of around 3500 patients were analysed using gamma method. In homogeneous phantom, average gamma passing rates were within tolerance for 3 %/2 mm. For measurements in heterogeneous media, the highest average gamma passing rate was obtained for small volumes of medium treatment complexity (γ¯=93.84%), while large volumes of treatment with low complexity yielded the lowest gamma passing rates (γ¯= 83.22%).

Keywords

• pre-treatment absorbed dose verification
• tolerance criteria
• inhomogeneous media
• calculation algorithm
• patient safety