Evaluation of commercial devices for patient specific QA of stereotactic radiotherapy plans

Abstract

Stereotactic radiotherapy (SRT) methods have become common for the treatment of small tumors in various parts of the body. Small field dosimetry has a unique set of challenges when it comes to the pre‐treatment validation of a radiotherapy plan that involves film dosimetry or high‐resolution detectors. Comparison of commercial quality assurance (QA) devices to the film dosimetry method for pre‐treatment evaluation of stereotactic radiosurgery (SRS), fractionated SRT, and stereotactic body radiation therapy treatment plans have been evaluated in this study. Forty stereotactic QA plans were measured using EBT‐XD film, IBA Matrixx Resolution, SNC ArcCHECK, Varian aS1200 EPID, SNC SRS MapCHECK, and IBA myQA SRS. The results of the commercial devices are compared to the EBT‐XD film dosimetry results for each gamma criteria. Treatment plan characteristics such as modulation factor and target volume were investigated for correlation with the passing rates. It was found that all detectors have greater than 95% passing rates at 3%/3 mm. Passing rates decrease rapidly for ArcCHECK and the Matrixx as criteria became more strict. In contrast, EBT‐XD film, SNC SRS MapCHECK, and IBA myQA SRS passing rates do not decline as rapidly when compared to Matrix Resolution, ArcCHECK, and the EPID. EBT‐XD film, SNC SRS MapCHECK, and IBA myQA SRS maintain greater than 90% passing rate at 2%/1 mm and greater than 80% at 1%/1 mm. Additionally, the ability of these devices to detect changes in dose distribution due to MLC positioning errors was investigated. Ten VMAT SBRT/SRS treatment plans were created with 6 MV FFF or 10 MV FFF beam energies using Eclipse 15.6. A MATLAB script was used to create two MLC positioning error scenarios from the original treatment plan. It was found that errors in MLC positioning were most reliably detected at 2%/1 mm for high‐resolution detectors and that lower‐resolution detectors did not consistently detect MLC positioning errors.

Systematic evaluation of spatial resolution and gamma criteria for quality assurance with detector arrays in stereotactic radiosurgery

“…This result is consistent with a similar recent study comparing various detector arrays against film dosimetry. 24 The Fourier analysis in the present work (see Figure 3 ) shows that the detector spacing in the SRS MapCHECK is sufficient for the investigated SRS fields. This highlights the importance of a small distance to agreement (DTA) value for high‐resolution detector arrays when altering the dose difference (DD) to detect errors.…”

“…Data from another study on SRS deliveries on target volumes of sizes 0.43–161.13cmm is also included to depict the trend. 24 This trend is indicative of the complexity behind the influencing factors, which may include treatment plan and delivery as well as measuring technique. Figure 8 , however, helps underline the role of the Nyquist theory on MLC error detectability, whereby an optimal detector spacing should preferably lie within the boundaries defined by the vertical dotted lines.…”

Dosimetric Systems in Pre-Treatment QA for Stereotactic Treatments: Correlation Agreements and Target Volume Dependency

“…For both the gamma criteria used. James S et al, [ 19 ] also observed better gamma agreement with EBT XD film compared EPID. They reported average gamma agreement of 96.7% and 95.9% for EBT XD and EPID respectively.…”

Assessing the sensitivity and suitability of a range of detectors for SIMT PSQA

“…James et al. 24 compared commercial quality assurance (QA) devices (EBT‐XD film, IBA Matrixx Resolution, SNC ArcCHECK, Varian aS1200 EPID, SNC SRS MapCHECK, and IBA myQA SRS) to film dosimetry for pre‐treatment evaluation of stereotactic radiosurgery (SRS), fractionated SRT, and stereotactic body radiation therapy treatment plans. Their work compared gamma pass rates for a set of forty plans as well as two plans containing MLC positioning error scenarios.…”