SU‐E‐T‐660: Does CMS XiO Electron Monte Carlo Model of a Siemens Artiste Linac Produce Accurate Dose Distribution for a Highly Irregular Electron Field?

Purpose: To evaluate the ability of CMS XiO Electron Monte Carlo algorithm (eMC) to accurately simulate irregularly shaped electron fields from a Siemens Artiste linear accelerator. Methods: Irregular electron fields where defined using a 1.5 cm thick Cerrobend cutout. For accuracy, the pattern was cut using a milling machine. eMC calculated planar dose distributions for 6, 9, 12, 15 and 18 MeV electron beams produced by Siemens Artiste linear accelerator were compared with measurements done with EBT Gafchromic films. All measurements and dose calculations were performed at the depth of maximum dose of the particular beam, at a standard SSD of 100 cm. The EBT films were scanned with Epson Perfection V7000 scanner. The red channel data of the 48 bit TIFF images was extracted, calibrated, corrected and analyzed with in‐house developed software. Results: The differences between eMC and the measurements were found to be within the gamma‐criteria of 2% dose and 2mm distance‐to‐agreement, including in the areas under the Cerrobend cutout. These differences decrease with increasing electron beam energy. Compared to the commonly used electron Pencil Beam algorithm, eMC produced significantly more accurate dose distributions for all regions of the irregular field, as well as under the cutout. Conclusions: The new CMS XiO eMC algorithm is capable of calculating dose distributions for highly irregular fields with an accuracy expected from photon beam calculation algorithms. Additional tests are under way to verify the performance of eMC for inhomogeneous medium and the calculation of dose output for a range of clinical electron fields.