Dosimetric evaluation of a commercial proton spot scanning Monte-Carlo dose algorithm: comparisons against measurements and simulations.

Dosimetric evaluation of a commercial proton spot scanning Monte-Carlo dose algorithm: comparisons against measurements and simulations.

Phys Med Biol. 2017 Jul 27;:

Authors: Saini J, Maes D, Egan A, Bowen SR, St James S, Janson M, Wong T, Bloch C

Abstract
PURPOSE: RaySearch Americas Inc. (NY) has introduced a commercial Monte Carlo dose algorithm (RS-MC) for routine clinical use in proton spot scanning. In this report, we provide a validation of this algorithm against phantom measurements and simulations in GATE/GEANT4 software package. We also compared the performance of RayStation analytical algorithm (RS-PBA) against the RS-MC algorithm. Methods: A beam model (G-MC) for spot scanning gantry at our proton center was implemented in the GATE software package. The model was validated against measurements in a water phantom and was used for benchmarking the RS-MC. Validation of RS-MC was performed in a water phantom by measuring depth doses and profiles for three SOBP beams with normal incidence, a SOBP with oblique incidence, and a SOBP with a range shifter and large air gap. RS-MC was also validated against measurements and simulations in heterogeneous phantoms created by placing lung or bone slabs in a water phantom. Lateral dose profiles near the distal end of the beam were measured with a diamond detector and compared to G-MC simulations, RS-MC and RS-PBA. Finally, RS-MC and RS-PBA were validated against measured dose distributions in an Alderson-Rando (AR) phantom. Measurements were made using Gafchromic film in the AR phantom and compared to doses using RS-PBA and RS-MC algorithms. Results: For SOBP depth doses in a water phantom, all three algorithms matched the measurements to within +/-3% at all points and range within 1mm. The RS-PBA algorithm showed up to a 10% difference in dose at the entrance for beam with range shifter and >30cm air gap while RS-MC and G-MC were always within 3% of the measurement. For an oblique beam incident at 45 degree, RS-PBA algorithm showed up to 6% local dose differences and broadening of distal penumbra by 5mm. Both RS-MC and G-MC accurately predicted the depth dose to within +/-3% and distal penumbra to within 2mm. In an anthropomorphic phantom, the gamma index (dose tolerance=3%, Distance-to-agreement=3mm) was greater than 90% for 6 out of 7 planes using the RS-MC, and 3 out 7 for RS-PBA. Conclusions: RS-MC algorithm demonstrated improved dosimetric accuracy over RS-PBA in presence of homogenous, heterogeneous and anthropomorphic phantoms. The computation performance of RS-MC was similar to RS-PBA algorithm. For complex disease sites like breast, head and neck, and lung cancer, the RS-MC algorithm will provide significantly more accurate treatment planning. .

PMID: 28749373 [PubMed - as supplied by publisher]

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