Characterization of a prototype MR-compatible Delta4 QA-system in a 1.5 tesla MR-linac

Abstract

To perform patient plan-quality assurance (QA) on the newly installed MR-Linac (MRL) there was a need for having an MR-compatible QA-device. An MR compatible device (MR-Delta4) was developed together with Scandidos AB (Uppsala, Sweden). 
 
 The basic characteristics of the detector response such as short-term-reproducibility, dose linearity, field size dependency, dose rate dependency, dose-per-pulse dependency and angular dependency were investigated for the Clinical Delta4PT as well as for the MR compatible version. All tests were performed with both devices on a conventional linac and the MR compatible device was tested on the MRL as well.
 
 No statistically significant differences were found in short term reproducibility (< 0.1%), dose linearity (≤ 0.5%), field size dependency (< 2.0% for field sizes larger than 5x5 cm2), dose rate dependency (< 1.0%) and angular dependency for all phantom/linac combinations. Dose-per-pulse dependency (< 0.8%) was found to be significantly different between the 2 devices. This difference can be explained by the fact that the diodes of the Clinical Delta4PT have been irradiated with a much larger dose than the MR-Delta4PT ones. The absolute difference between the devices (< 0.5%) was found to be small, so no clinical impact is expected.
 
 For both devices, the results were consistent with characteristics of the Delta4PT device reported in literature (Bedford et al. (2009), Sadagopan et al. (2009)).
 
 We found that the characteristics of the MR compatible Delta4 phantom are found to be comparable to the clinical used one. Also the found characteristics do not differ from previous reported characteristics of the commercially available non-MR compatible Delta4PT phantom. Therefor the MR compatible Delta4 was found to be safe and effective for use in the 1.5 Tesla magnetic field of the Elekta MR-Linac&#13.