BELdART-SRS: First results of the Belgian national audits in intracranial stereotaxy

Abstract

BELdART has started its audit program for intracranial stereotaxy using a combination of L-α-alanine-EMR dosimetry and Gafchromic® EBT3 films. The audit consists of basic testing in water and in a RW3 slab phantom as well as an End-To-End testing of SRS delivery using the Stereotactic End-to-End Verification (STEEV) phantom (CIRS Inc., Norfolk, Virginia, USA) with a custom positioning system. In the end-to-end test, the dosimetry is performed in two different slices where two structures have been positioned: one slice contains an EBT3 film sheet and an alanine pellet with a target ≈ 2x2 cm² and one slice just contains an EBT3 film sheet with target ≈ 0.8x0.8 cm². Until now, 6 audits have been realized wherein 5 centers used frameless and 1 center framed SRS. Figure 1 shows the results for the basic tests where all the results are within 3% except one clinic deviated >3% for the test with SSD85. For the reference field, all the centers are within 1%. Table 2 and Table 3 show the alanine results and film results for the SRS delivery respectively. One clinic had a deviation >2% for the measured dose. For the film analysis for the gamma evaluation method with criteria 5%/1mm and 50% lower dose threshold the passing rate was >95%. The choice of the lower dose threshold is still under discussion. Framed SRS introduced some challenges regarding the fixation of the frame to the head phantom without physically drilling the head phantom. The audit procedure has still to be evaluated.