Dose verification in lung SBRT and implications with the clinical implementation of Acuros

Abstract

The currently used standard in radiotherapy for dose calculation is AAA. Although more accurate and faster calculation engines are present, such as AcurosXB (Varian Medical Systems), the switch from AAA to AXB has not been made. Despite many previous studies, the implications on the dose are not ambiguously clear. This Master’s thesis, in cooperation with Beldart, LOC Limburg and Maastro Clinic, focusses on the dose reporting and evaluation of lung SBRT. The dose of PTV and OAR in SBRT plans was verified and evaluated for AAA and the two dose reporting methods of AXB: dose-to-water and dose-to-medium (AXBW and AXBM). Firstly, the dose differences of AAA, AXBW and AXBM were examined by recalculating 60 SBRT-plans. The absolute percentage difference for PTV and OAR were compared. Next, the dose (AAA), was verified with the Virtual Water Dose Verification Phantom with an adjustable hydrogel tumor. The dose maps of the TPS were evaluated and compared at tumor center and at lung-soft tissue transition with radiochromic films. The dose at tumor center was verified with L-α-alanine. Although the recalculations concluded an overestimation of AAA (5,6%) in comparison to AXB, the results in three phantom tests did not confirm this. The three individual phantom cases showed that dose differences are affected by several parameters, of which the surrounding tissue distribution is the most important. Further refining of the phantom is necessary, to minimize uncertainties and further evaluate the dose differences of the algorithms.