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Dosimetric Evaluation of An SRS MapCHECK for SBRT QA

F Mostafaei*, S Lin , J Salazar , A Webb , Y Lee , R Hamilton , Y Kim , Department of Radiation Oncology, University of Arizona, Tucson, AZ


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: A new commercially available two-dimensional diode detector array called “SRS MapCHECK� has a higher spatial resolution compared to the conventional MapCHECK®2 (1.75 mm vs. 7.07 mm). Clinical QA data from these two devices for small fields in SBRT treatment plans were compared.

Methods: Absolute dose measurements of SRS MapCHECK was validated using an ionization chamber and Gafchromic EBT3 films. Gamma analysis was also performed using an in-house MATLAB program to compare measurements between SRS MapCHECK and film. Eleven clinical SBRT treatment plans (59 volumetric modulated arc fields in total) were selected for PTV volume between 0.53 - 15.53 cc and QA was performed for each field using these two devices. The QA results were evaluated using various Gamma passing criteria of 3%/3 mm, 2%/2 mm, 2%/1 mm and 1%/1 mm.

Results: For a clinical treatment plans, ionization chamber and film measurements agreed with the doses calculated in a treatment planning system (RayStation 8A, RaySearch, Inc., New York, NY) to within 1-1.5 % and with 98.2% of Gamma passing rate (2%/2mm). For 59 clinical SBRT fields, the average Gamma passing rates between SRS MapCHECK and MapCHECK®2 were 99.7% vs. 99.2% (3%/3mm), 98.2% vs. 95.1% (2%/2mm), 93.6% vs. 67.1% (2%/1mm) and 88.2% vs. 60.6% (1%/1mm). The average number of active diode detector points between SRS MapCHECK and MapCHECK®2 was 396 vs. 26 for SBRT fields.

Conclusion: SRS MapCHECK QA was validated using an ionization chamber and films. Due to the higher resolution of the diode detector arrays, for SBRT treatment fields SRS MapCHECK demonstrated more reliable QA result than MapCHECK®2.


Stereotactic Radiosurgery, Quality Assurance


Not Applicable / None Entered.

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