Abstract
Pretreatment quality assurance (QA) is a major concern in complex radiation therapy treatment plans like intensity modulated radiation therapy (IMRT). Present study considers the variations in gamma index for gantry dependent pretreatment verification and commonly practiced zero gantry angle verifications for ten prostate IMRT plans using two commercial medical linear accelerators (Varian 2300 CD, Varian Clinac iX). Two verification plans (the one with all fields at the actual treatment angles and one with all fields merged to 0 degree gantry angles) for all the patients were generated to obtain dose fluence mapping using amorphous silicon electronic portal imaging device (EPID). The gamma index was found depend on gantry angles but the difference between zero and the nonzero treatment angles is in the confidence level for clinical acceptance. The acceptance criteria of gamma method were always satisfied in both cases for two machines and are stable enough to execute the patient specific pretreatment quality assurance at 0 degree gantry angle for prostate IMRTs, where limited number of gantry angles are used.
Highlights
Modern cancer treatments using radiation therapy is mostly employed with multileaf optimized plans as in intensity modulated radiation therapy
Patient specific pretreatment quality assurance (QA) should be better done at the treatment angles, if an on-board electronic portal imaging device (EPID) is available
Pretreatment plan verifications using EPID are preferred to be in gantry angle dependent positions but it was shown that such requirement is not strictly necessary
Summary
Modern cancer treatments using radiation therapy is mostly employed with multileaf optimized plans as in intensity modulated radiation therapy. Pretreatment quality assurance in complex treatment techniques like intensity modulated radiation therapy is carried out using electronic portal imaging devices attached to the medical linacs. This ensures the accuracy of treatment plan generated using commercial planning systems for complex IMRT treatments. Pretreatment quality verification is advisable in all IMRT treatment plans to compare the beam fluence maps delivered using continuous motion of multileaf collimators (MLC). It requires virtually no time for patient set-up or postprocessing to obtain useful data with a fast image acquisition which is stored in digital for further analysis [5,6,7,8]
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