Validation of the Elekta Synergy Platform Linac at 6 MV Photon Beam using PRIMO Monte Carlo Software

The objective was to validate the initial beam parameters of the Davao Doctors Hospital's 6 MV Elekta Synergy Platform linac, which performs to the specification of the commissioning data per our records using the gamma-index analysis toolkit integrated inside PRIMO software.

In PRIMO, a sequence of optimization processes is performed, in which the measured and simulated percent depth dose (PDD) and lateral beam profiles at various depths are compared, using the stringent gamma-index passing rate at 1%/1 mm criteria (GPR11). Using four fields of sizes 3 cm × 3 cm, 4 cm × 4 cm, 5 cm × 5 cm, and 10 cm × 10 cm, the dose is calculated on a water phantom measuring 16.2 cm × 16.2 cm × 30.0 cm. In addition, one field of size 20 cm × 20 cm is used on a 50.0 cm × 50.0 cm × 30.0 cm water phantom with a bin size of 0.2 cm × 0.2 cm × 0.2 cm at a source-surface distance of 100.0 cm.

For PDD and beam profiles comparison at the largest field size, the 6.5 MeV initial electron beam energy, 0.25 MeV full-width-half-maximum energy, 0.20 cm focal spot size, and 3° beam divergence tuned configuration yield GPR11 values of 94.0% and 97.7% (PRIMO PDD and lateral beam profile at 200 mm scan depth, respectively) with a statistical uncertainty of 2.9%. For lower field sizes, the GPR11 values are consistent at more than 90% for the PDD, whereas GPR11 values of 80.3% and 70.6% for the lateral beam profiles (at 15 mm and 200 mm scan depths) at 10 cm × 10 cm and 5 cm × 5 cm, respectively. The percentage difference between the measured and simulated PDD _20,10 ratios of not more than 2.45% is observed in all field settings.

These tuned beam parameters are remarkably in agreement with the suggested beam parameters listed on the PRIMO website for the 6 MV Elekta linac which was optimized with a different set of measurements.