SU‐E‐T‐379: Evaluation of An EPID‐Based System for Daily Dosimetry Check by Comparison with a Widely‐Used Ionization Chamber‐Based Device

Abstract

Purpose: To examine the feasibility of using Varian's EPID‐based Machine Performance Check (MPC) system to track daily machine output through comparison with Sun Nuclear's DailyQA3 (DQA) device. Methods: Daily machine outputs for two photon energies (6 and 16MV) and five electron energies (6, 9, 12, 16, 20MeV) were measured for one month using both MPC and DQA. Baselines measurements for MPC were taken at the start of the measurement series, while DQA baselines were set at an earlier date. In order to make absolute comparisons with MPC, all DQA readings were referenced to the average of the first three DQA readings in that series, minimizing systematic differences between the measurement techniques due to baseline differences. In addition to daily output measurements, weekly averages were also calculated and compared. Finally, the electron energy dependence of each measurement technique was examined by comparing energy‐specific measurements to the average electron output of all energies each day. Results: For 6 and 16MV photons, the largest absolute percent differences between MPC and DQA were 0.60% and 0.73%, respectively. Weekly averages were within 0.17% and 0.23%, respectively. For all five electron energies, the greatest absolute percent differences between MPC and DQA for each energy ranged from 0.49%–0.83%. Weekly averages ranged from 0.07%–0.28%. DQA energy‐specific electron readings matched the average electron output within 0.29% for all days and all energies. MPC energy‐specific readings matched the average within 0.21% for 9–20MeV. However, 6MeV showed a larger distribution about the average with four days showing a difference greater than 0.30% and a maximum difference of 0.51%. Conclusion: MPC output measurements correlated well with the widely‐used DQA3 for most beam energies, making it a reliable back up technique for daily output monitoring. However, MPC may display an energy dependence for lower electrons energies, requiring additional investigation.

Report of AAPM Task Group 219 on independent calculation‐based dose/MU verification for IMRT

“…Reports and scientific publications that describe the accuracy of independent IMRT dose or monitor unit calculation software, whether developed in-house or commercial products, are scarce. Most publications deal with static (step-and shoot) or dynamic IMRT delivery based on a multileaf collimator or VMAT, [43][44][45] and only a few of them with advanced treatment techniques performed with a robotic linac 46 and TomoTherapy. 47 Nevertheless, the commercial vendor list (Table 2) reveals that these tools are clinically applied for verifying IMRT or VMAT.…”

Is it still necessary to perform measured based pre‐treatment patient‐specific QA for SRS HyperArc treatments?

“…It performs a full recalculation of dose on the patient CT and allows for quality assurance of the treatment plan by offering a "delivered dose" calculation, generated using the M3D model and treatment machine's log files. 18,19 In a recent study, Hasse et al 20 investigated the possibility to use M3D dose calculation software to reduce the number of physical measurements and the required amount of on-site personnel, during corona virus disease, while maintaining patient safety.…”

“…M3D was validated for a variety of radiation therapy techniques, IMRT/VMAT/TomoTherapy, demonstrating to be a safely pre-treatment calculation-based verification system. [19][20][21][22][23][24] However, there is a lack of investigation regarding the appropriateness of M3D as patient-specific pre-treatment verification system for stereotactic brain radiation treatment with a high dose in a single fraction.…”

“…Mobius3D (M3D) is the Varian (Varian Medical Systems Inc., Palo Alto, California, USA) solution of a secondary independent and log file based dose verification system. It performs a full recalculation of dose on the patient CT and allows for quality assurance of the treatment plan by offering a “delivered dose” calculation, generated using the M3D model and treatment machine's log files 18,19 …”

Evaluating Mobius3D Dose Calculation Accuracy for Small-Field Flattening- Filter-Free Photon Beams

“…To overcome these limitations, various pretreatment QA methods have been proposed using innovative devices and algorithms. [9][10][11][12][13][14][15][16][17][18][19] Among these, dose-volume histogram (DVH)-based patient-specific QA has emerged in recent years. The DVH-based method enables the calculation of dose distributions in the patient domain, where tissue inhomogeneity is considered.…”