The preliminary comparison of the reconstructed doses with electronic portal imaging device (EPID) and dynalogs files for in vivo phantom dosimetry

Objective: To study the difference of the constructed doses between electronic portal imaging device (EPID) and dynalogs files of linac for in vivo phantom dosimetry. Methods: Twelve pelvic patients treated with volumetric modulated arc therapy (VMAT) plans were selected and the information of each plan was copied to the 'Cheese' phantom to recalculate the doses before delivered on Varian RapidArc Linac. The 'Cheese' phantom was placed on the isocenter and the electronic portal image (EPI) formed by the EPID was sent to EPIgray software to reconstruct the actual delivered doses. Meanwhile, dynalogs files were respectively imported to the Mobius software to reconstruct the actual delivered doses too. The point dose in the center of each VMAT plan (the center of the effective sensitive volume of ionization chamber) was measured by the A1SL ionization chamber. At the same time, the dose of sensitive volume of ionization chamber from treatment planning system (TPS) was recorded. Results: The relative deviation between the dose from TPS and the measurement results by the ionization chamber was 1.13%. The difference between the reconstructed doses of EPID-based or the 'dynalogs file'-based with the measurement results by the ionization chamber was not statistically significant (P > 0.05). Conclusions: The two methods of dose reconstruction can provide reference for in vivo dosimetry of VMAT. (authors)