Room: AAPM ePoster Library
Following the installation of the new Halcyon™ (Varian Medical Systems) treatment machines (O-Ring Design) to replace our c-arm linacs 2100C on which we practiced stereotactic treatments, we wanted to verify that we could perform dosimetrically identical treatments without non-coplanar beams.
We therefore randomly selected five patients treated in our radiotherapy centers during 2018. We performed dosimetry optimization with the Halcyon machine modeled in our treatment planning software (ECLIPSE V15.6) and we compared, in terms of quality of coverage index, conformity index (RTOG, Lomax, Paddick) and homogeneity index, to the dosimetry planned on the initial machine (Linac 2100 C).
In parallel to this, we carried out a whole set of mechanical and dosimetric tests to completely characterize our new accelerator and know its mechanical and dosimetric limits. Daily monitoring of these tests is carried out and enriches our QA database.
The pre-treatment checks of the treatment plans planned on Halcyon were then compared to those initially carried out on the C-arm linac to check that they were deliverable and compliant with our validation criteria (Gamma 3%-3mm; minimum 97% of the points which meet this criteria).
The plans generated with the Halcyon show the Lomax conformity index (0.94±0.04 vs 0.83±0.08), Paddick conformity index (0.88±0.04 vs 0.69±0.13) and quality of coverage indices significantly higher than those of the C-arm linac 2100 C (96%±0.01 vs 92.3%±0.03).
Halcyon pre-treatment quality assurance tests strictly comply with all of our validation criteria and encourage us to become more restrictive on these criteria.
These new treatment machines offered by Varian seem very efficient and allow all types of treatments, even if the manufacturer offers in its catalog machines dedicated to stereotactic treatments.
Validation, Stereotactic Radiosurgery, Dosimetry