SU‐E‐T‐364: Investigation of the PMLC Delivery Accuracy for MERT On An Artiste Linac

Purpose: To verify the delivery accuracy of energy‐intensity modulated electron radiotherapy (MERT) using the existing photon multileaf collimator (pMLC) on the Artiste linac. Methods: Phase space data for 6, 9, 12 and 15 MeV electron beams of the Artiste accelerator, as an input source for our in‐house Monte Carlo (MC)‐based dose calculation/optimization planning code for MERT, were first commissioned by comparing measured PDD and dose profiles for pMLC‐shaped fields of 3 × 3 cm²and 10 × 10 cm². MC calculated dose was then calibrated for each of the energies by comparing with chamber measurements for pMLC‐delivered electron beam and further verified at a different SSD setup. An energy‐intensity modulated electron plan was generated for a breast treatment on a breast phantom at a 60 cm SSD and recalculated with a solid water phantom and later delivered to the phantom through ten pMLC segments ‐ ‐each associated one of above energies and a specific monitor unit. Film measurement for the plan was done at the depth of 1.5 cm. The measured 2D dose distribution was then compared with calculations to verify the plan. Results: Comparisons between measured PDDs and dose profiles, and MC calculations for the various energies showed good agreement (within 2%/2mm). The verification measurement for MC dose calculation calibration at different SSDs was within 2% of the calculated values for all energies. The measured 2D dose distribution of the MERT plan was consistent with the calculations in low‐medium dose regions while in high dose regions, there existed some discrepancy. Conclusion: With pMLC shaped fields, MC dose calculations agreed with measured PDDs and dose profiles at various depths. The measured dose distribution of a breast plan showed good agreement in low‐medium dose regions while the discrepancy in high dose regions remains to be investigated.