Pretreatment Patient Specific Quality Assurance and Gamma Index Variation Study in Gantry Dependent EPID Positions for IMRT Prostate Treatments

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.

A comprehensive study of the mechanical performance of gantry, EPID and the MLC assembly in Elekta linacs during gantry rotation

“…[7][8][9] Moreover, linear accelerator (linac) rotation can affect gantry-mounted accessories such as the electronic portal imaging device (EPID), since the EPIDsupporting arm is not mechanically perfect and rigidly attached. With the growing application of EPIDs in preand post-treatment dosimetry verification, [10][11][12][13][14][15] realtime dosimetry verification 16,17 and real-time tumour tracking for intrafraction motion management in modern radiotherapy, [18][19][20] it is essential to characterize and account for the mechanical system imperfections of linacs.…”

Investigation of the mechanical performance of Siemens linacs components during arc: gantry, MLC, and electronic portal imaging device

“…Moreover, linac rotation can affect gantry-mounted accessories such as the electronic portal imaging device (EPID), since the EPID supporting arm is not mechanically perfect and rigidly attached. With the growing application of EPIDs in pretreatment and posttreatment dosimetry verification, 21 – 26 real-time dosimetry verification, 27 , 28 and real-time tumor tracking for intra-fraction motion management in modern radiotherapy, 29 – 31 it is essential to characterize and account for the mechanical system imperfections of linacs.…”