Author: Kaile Li 👨🔬
Affiliation: Alexander T. Augusta Miliary Medical Center 🌍
Purpose: To develop a experimental method in observation of beam profile transfer model in intensity modulated radiotherapy (IMRT).
Methods: A picket fence plan was generated in Eclipse treatment planning system from Varian Medical System with 6MV beam with and without flattening filter free (FFF) setting for a Varian Truebeam LINAC. The open beam profile was first recorded in portal dosimetry setting and comparison was done and showing the difference between this profile with a gamma analysis method, and then two plans with two energy beam were delivered with picket fence setting. Two dose profiles were recorded in the portal dosimetry system. Then the gamma analysis was executed again, the two matrices of the gamma analysis results were used for the evaluation of profile variation effect on the multi-leaf collimator (MLC) IMRT plan.
Results: For 6MV and 6MV FFF photon beam, two profiles with difference at 3.4% for open field setting and 27.0% for picket fence setting delivery for gamma setting at dose difference at 2% and distance to agree at 2mm. The maximum gamma value was 10 and 6.93; average gamma was 7.43 and 2.7; average dose difference was 3.3 to 0.87 at calibration unit. Similarly, the comparison of 10MV and 10MV FFF photon beam at picket fence setting delivery, the comparison gamma less less than 1 value was 10%, maximum gamma was 10, average gamma was 3.73, average dose difference was 1.2 calibration unit.
Conclusion: A profile variation effect on MLC based IMRT plan was measured and analyzed, this provides a composition approach to evaluate the profile variation in an IMRT plan. And it could be set as a reference procedure of profile effect in IMRT QA. Future development will be injecting arbitrary formats of profile variation into the planning system and predict the clinical effect of the profile variation.