Pretreatment Patient-specific Quality Assurance Research Articles

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

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.

Patient Specific Pre-Treatment QA Verification Using an EPID Approach

A software program [MU-EPID], has been developed to perform patient specific pre-treatment quality assurance (QA) verification for intensity modulated radiation therapy (IMRT) using fluence maps measured with an electronic portal imaging device (EPID). The software converts the EPID acquired images of each IMRT beam, to fluence maps that are equivalent to those calculated by the treatment planning system (TPS). The software has the capability to process Varian, Elekta and Siemens EPID DICOM images. In the present investigation, several IMRT plans for different treatment sites were used to validate the software using the Varian a-Si 1000 EPID with the Pinnacle TPS. A total of 20 IMRT plans of different treatment sites were analyzed. Isodose distributions, dose profiles, dose volume histograms (DVH's) and gamma analysis comparisons were performed to evaluate the accuracy of our method. A gamma index analysis of the isocenter coronal plane was done for each plan and showed an average of 97.44% of gamma passing rate using a 3% and 3 mm gamma criterion. Isodose, DVH and dose profile comparisons were conducted between the original calculated plan and the measured reconstructed plan from the EPID images processed through the MU-EPID software. The results suggest that MU-EPID can be used clinically for patient specific IMRT QA, providing a comprehensive 3D dosimetric evaluation through DVH comparison as well as an option for a 2D gamma analysis.

EP-1486: Gantry angle dependence pre-treatment patient-specific quality assurance and gamma index variation study

EP-1486: Gantry angle dependence pre-treatment patient-specific quality assurance and gamma index variation study

SU-E-T-134: Patient Specific Quality Assurance of RapidArc Pre Treatment Plans Using Semiflex 0.125 Cc Ionization Chamber.

To evaluate the Patient specific pre-treatment quality assurance for hundred RapidArc plans using semiflex (0.125cc) ionization chambers. Absolute point dose were measured for head and neck, thorax and abdomen cases using semiflex (0.125 cc) ionization chamber. Verification plan was created for each treatment plan in eclipse 8.6 treatment planning system with the semiflex ionization chamber and the octavius phantom. Measurements were performed on a Varian Clinac2100C/D linear accelerator equipped with a millennium 120 leaf collimator. All the results were compared with the fluence measurements using 2D Seven29 ion chamber array combined with octavius phantom. Positive absolute mean dose variation of 0.56 % was observed with thorax cases with a standard deviation (SD) of ± 1.13 between the plans with a range of -1.78% to 2.70%. Negative percentage dose errors were found with head and neck and abdomen cases, with a mean variation of -0.43 % (SD ± 1.50), (range -3.25 % to 2.85 %) and -0.35 % (SD ± 1.48), (range -3.10 % to 2.65 %) for head and neck and abdomen cases respectively. Relative dose measurements with 2D array agreed well with the TPS calculate for all the cases. The maximum percentage value failed in gamma analysis was found to be 4.95, 4.75, and 4.88 for head and neck, thorax, and abdomen cases respectively. In all the cases analysed the percentage dose points failed the gamma criteria was less than 5%. On the basis of the studies performed it can be concluded that the semiflex ionization chamber having a volume of 0.125cc can be used efficiently for measuring the pre-treatment quality assurance of RapidArc plans for all the sites. The results provide an overall accuracy when compared to fluence measurement done using 2D array seven29.