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Purpose: To analyze the patient specific IMRT QA results at our institution over the past 3 years and evaluate the procedures and methods of our IMRT QA program. Methods: 1466 patient specific IMRT QAs were performed at our institution from March 2009 to December 2011. The passing criteria for each IMRT QA are that 90% of all evaluated points must have a gamma =1.0. The gamma is calculated using the TPS calculated planar dose as reference and the reference value is 90% of the maximum dose in the plane. A dose threshold of 10% is used in order to remove very low dose points from the calculation. The planar dose and the measurements are computed and obtained using the actual beam angles. The measurements were performed on Varian linacs equipped with Millennium 80, Millennium 120 and High‐Definition 120 MLC. Results: The IMRT QA results were analyzed with respect to the linac, treatment site, number of beams, IMRT vs. TOMO vs. VMAT, and number of control points. The overall average gamma index value was 96.85% (±1.5%). Head and Neck had the lowest gamma index (95.97%) while brain had the highest (97.85%). Conclusions: After evaluation of 700 patients, it can be determined that there are significant variations in the average measured gamma value based on treatment site, number of beams, machine type, and number of control points. This work provides a foundation for future analysis of possible underlying issues in the gamma value deviations for each comparison.

Purpose: IMRT patient specific QA is often used across institutions to provide a quantitative measure of the accuracy by which a treatment plan is delivered. The aim of this project is to evaluate the performance of four commercially available devices while varying the acceptance criteria of dose difference and distance to agreement (DTA). Methods: Ten VMAT and 10 static field IMRT plans were evaluated. All the plans were optimized using the Pinnacle v9.2. Measurements were performed on a Varian 2100CD linac equipped with millennium 80MLC. The gamma index was chosen as the primary metric for the evaluation of the agreement between the planned and measured dose distributions. The gamma index was calculated for each plan using 10% and 20% dose thresholds, 3%/3mm, 2%/2mm. The analysis was performed for the composite plans as well as field‐by‐field using the software provided with each IMRT QA systemResults: Octavius II showed higher passing gammas for 3%3mm and 2%2mm compared to the other detectors in all the IMRT field‐by‐field comparison. In the IMRT true composite plans, the gamma index values (3%/3mm) were: 89.5, 87.3, 89.2, 88.8 for Delta4, IBA Matrixx, Octavius4D and PTW Octavius II, respectively. For the same IMRT plans with the beams delivered with the gantry in the upright position, the gamma indices were 89.5, 98.4, 94.0, 100. For the VMAT plans, the gamma index values were 93.7, 95.0, 91.2, and 97.5. The gamma index values from the evaluation of the VMAT plan using a dose threshold of 20% were 91.8, 95.1, 88.6, and 97.3, respectively. Conclusion: The detectors response is very similar for the three treatment techniques examined. Stricter gamma index criteria reduced the passing rate of the plans by about 20%. The differences between the detectors did not show any trend depending on method, site, or mode of delivery.

Purpose: All radiation therapy departments have a need for a quick and accurate verification of their treatment plans ranging from conventional, brachytherapy, to IMRT. The aim of this study is to perform an inter‐comparison of different commercially available Monitor Unit (MU) secondary/independent software. Methods: In this study, four independent MU verification software were examined (IMSure, DIAMOND, MuCheck, and Radcalc) as quality assurance tools for RTP systems. An inter‐comparison of the treatment plans of 13 patients was performed using those MU verification software. All the plans were generated using the Pinnacle v9.2 treatment planning system. The treatment techniques include VMAT, MLC‐based step‐and‐shoot IMRT and Conventional Conformal plans for different treatment sites (breast, head and neck, chest, pelvis, abdomen, and brain). The parameters that had to be adjusted after importing the treatment plans into the different software were the average SSD and effective depth. Results: The average percent differences between the MUs provided by the Pinnacle and the RadCalc, ImSure and DIAMOND software were found to be −1.7%, −1.9% and 3.4%, respectively. The variation of the percent differences among the individual patients were 2.9% (−7.2 − 2.5), 3.7% (−7.2 − 3.7) and 7.0% (−9.9 – 16.2) for RadCalc, ImSure and DIAMOND, respectively. Conclusion: Importing the files from the Pinnacle RTP system was equally easy for all the software. It was found that Radcalc was the software that required the minimum changes/interventions when inserting the average SSD and effective depth. However, the Radcalc was the slower among the examined software in computing the MUs of the different beams for the VMAT technique. Overall, the variation of the MU calculations between the examined software was found to be very similar indicating that their ability to be used as quality assurance tools of the calculations provided by the RTP systems is equivalent.

Purpose: To investigate the dosimetric effects of delivering a VMAT plan optimized for a straight‐beam linac on a bent‐beam linac. Methods: When a linac is unavailable to treat, it is common practice to transfer patients to another machine that has been dosimetrically matched. The purpose of this study was to evaluate the changes in the dose to organs at risk (OAR) and planned target volumes (PTV) due to a patient transfer from Clinac 600C/D to Clinac 23EX. The former is a straight beam machine (no bending magnet) and the latter has an achromatic bending magnet. Both machines are equipped with 120 Millennium MLCs. Nine VMAT plans (three treatment sites) originally optimized for the Clinac 600C/D were recalculated for the Clinac 23EX. Each plan was recomputed with the Pinnacle3 treatment planning system to deliver the same dose to the same treatment volume using the same number of monitor units for the entire treatment regime. To quantify the variations, the dose volume histograms (DVHs) for each plan, V50, mean and maximum dose to the OARs and PTV were compared. Results: The V50 of the OARs in the recalculated plan for the Clinac 23EX increased by an average of 15.2% (STD=15.1%). The increases on the maximum and mean dose to the OARs were on average 2.9±1.4% and 5.9±2.7% respectively. The maximum and mean PTV doses also increased for all of the 9 patients by 2.3±1.2% and 2.5±1.0%. Conclusions: The results indicated that the delivery of a VMAT plan for Clinac 600C/D on Clina c23EX will increase the dose to the PTVs and OARs. In cases where a patient is transferred to another machine for a single or small number of fractions, changes in dose distribution may be clinically insignificant; otherwise dosimetric evaluation of the transferred treatment to on another machine is highly recommended.