SU‐E‐T‐133: Assessing IMRT Treatment Delivery Accuracy and Consistency On a Varian TrueBeam Using the SunNuclear PerFraction EPID Dosimetry Software

Abstract

Purpose: To assess if the TrueBeam HD120 collimator is delivering small IMRT fields accurately and consistently throughout the course of treatment using the SunNuclear PerFraction software. Methods: 7‐field IMRT plans for 8 canine patients who passed IMRT QA using SunNuclear Mapcheck DQA were selected for this study. The animals were setup using CBCT image guidance. The EPID fluence maps were captured for each treatment field and each treatment fraction, with the first fraction EPID data serving as the baseline for comparison. The Sun Nuclear PerFraction Software was used to compare the EPID data for subsequent fractions using a Gamma (3%/3mm) pass rate of 90%. To simulate requirements for SRS, the data was reanalyzed using a Gamma (3%/1mm) pass rate of 90%. Low‐dose, low‐ and high gradient thresholds were used to focus the analysis on clinically relevant parts of the dose distribution. Results: Not all fractions could be analyzed, because during some of the treatment courses the DICOM tags in the EPID images intermittently change from CU to US (unspecified), which would indicate a temporary loss of EPID calibration. This technical issue is still being investigated. For the remaining fractions, the vast majority (7/8 of patients, 95% of fractions, and 96.6% of fields) are passing the less stringent Gamma criteria. The more stringent Gamma criteria caused a drop in pass rate (90 % of fractions, 84% of fields). For the patient with the lowest pass rate, wet towel bolus was used. Another patient with low pass rates experienced masseter muscle wasting. Conclusion: EPID dosimetry using the PerFraction software demonstrated that the majority of fields passed a Gamma (3%/3mm) for IMRT treatments delivered with a TrueBeam HD120 MLC. Pass rates dropped for a DTA of 1mm to model SRS tolerances. PerFraction pass rates can flag missing bolus or internal shields. Sanjeev Saini is an employee of Sun Nuclear Corporation. For this study, a pre‐release version of PerFRACTION 1.1 software from Sun Nuclear Corporation was used.

Report of Task Group 201 of the American Association of Physicists in Medicine: Quality management of external beam therapy data transfer

“…IMRT QA may be a clinical surrogate for items 3 and 9, if done with an absolute dosimetry measurement. All the tests in Table IV are manual checks, with the possible exception of the control point comparison that could be performed with the tools in references 47–49 . See Appendix A4 for use case examples.…”

“…As of the writing of this report, computer programs to perform the tasks described above have been developed by several institutions. [43][44][45] Such programs are starting to become commercially available [47][48][49] and manufacturers should work toward making them become standard clinical software.…”

“…In‐house software applications could be written to extract these values and compare them. Some commercial systems are starting to provide similar functionality 47–49 …”

“…All the tests in Table IV are manual checks, with the possible exception of the control point comparison that could be performed with the tools in references. [47][48][49] See Appendix A4 for use case examples.…”