BeldART-SRS encompasses mailed audits for intracranial Stereotactic Radiosurgery (SRS) in Belgium. The project is financed by Het Kankerplan/Plan Cancer and monitored by the College of Medicine-radiotherapy and the FOD Healthcare. All Belgian centres are offered the possibility to participate to the dosimetry audit without charge.
The audit consists of 2 parts:
1) Control of basic dosimetry in a water tank using alanine positioned with a 3D printed holder and in RW3 plates.
The water tank is used for testing in standard fields and the RW3 plates for testing in small fields.
2) End-to-end verification of plans delivered on a STEEV Stereotactic End-to-End Verification Phantom (CIRS Inc.)
BELdART uses a combination of alanine-EPR-dosimetry and radiochromic film dosimetry. 2 sets of structures in DICOM format are delivered to the participating clinic. 1 larger structure which is analysed with GAFchromicTM EBT3 films and alanine detectors and 1 smaller structure which is analysed with EBT3 film detectors only.
14 centres participated to the SRS program so far. 15 beams were audited for the basic tests and 17 beams for the SRS delivery. The project is still ongoing. The results of 2 centres are under discussion. 1 audit was not analysed due to technical issues.
EPR basic tests
The figure above shows the results for 15 beams. The results are corrected for the output of the day.The difference between measured and planned dose for the output in reference conditions was < 3% for all the centres except and 80% of them were within 1%. For the other tests in 10x10 cm² fields, 86% of the centres were within 2%. Only 1 centre had a dose difference higher than 3% for the test at SSD85.
For the small fields, All the centres were within 3% with 46% of them being within 1%. The uncertainty on the measurements was 1% (k=1).
EPR in the SRS phantom
The figure above shows the results for 17 beams for the alanine pellet placed in the middle of the larger PTV. The results of the measured daily output are also shown. 16 beams were delivered using a frameless technique and 1 centre(#6) used a framed technique.
70% of the centres had a dose difference <3% than the planned dose. Centre #9 had a dose difference of 4.5%. The uncertainty on the measurements was 1% (k=1).
The figure above shows the film results for 17 beams. 1 film was placed through the centre of the large target where also the alanine pellet was placed and another film was placed through the small target. 16 beams were delivered using a frameless technique and 1 centre(#6) used a framed technique.
We evaluated the films using 5%/1mm criteria (global) with 50% threshold. All of the films had a passing rate >95% except for the small lesion at centre #10.