ESTRO 2024 - Abstract Book

S4736

Physics - Quality assurance and auditing

ESTRO 2024

Material/Methods:

One hundred thirty three (133) HyperArc (HA) SRS plans computed using the Eclipse v. 16.10 treatment planning system (TPS) were included in this study. Plans included 281 targets, with mean equivalent diameter of 1.5 cm (ranged: 0.3 cm to 3.9 cm). The number of targets per plan was 2.1 (range: 1 to 14). Sixty plans were used to treat multiple brain targets with a single-isocenter approach. Eclipse dose calculations were performed using the Acuros XB algorithm (dose to medium). Photon beams of 6 MV (6 plans) and 6 MV FFF (127 plans) from a Varian TrueBeam linac, equipped with a Millennium 120 multileaf collimator (MLC), were used. Two types of pre-treatment verification were performed for each HA SRS. First, an independent dose calculation using the PRIMO Monte Carlo software v. 0.3.64.1800 was performed. The simulations were automated using a set of scripts (PRIMO WatchDog v. 1.08, Feb. 23, 2022). PRIMO was used with the Dose Planning Method (DPM) simulation engine and with the Varian phase space files (version 2, Feb. 27, 2013). PRIMO was previously commissioned and validated by our group for independent dose calculation [Phys Med. 2022 Oct;102:19-26]. Second, each HA plan was mapped to the PTW Octavius 4D (O4D) system equipped with a PTW 1600 SRS detector. The Eclipse and PRIMO dose distributions were compared using the 3D gamma index analysis tool available in the PRIMO software. Gamma index evaluation was performed for the whole patient volume ( ‟ body”) and the planning target volumes (PTVs). The Eclipse dose distributions were compared to the measured ones with the O4D using the 3D gama index analysis tool available in the PTW Verisoft software. Gamma index analysis was performed for each type of verification using the criteria: 3% and 5% global dose difference, and distance-to-agreement of 1 mm. Gamma passing rates (GPRs) were calculated for the body and PTV structures for the Eclipse-PRIMO comparisons. For the Eclipse-O4D evaluations, GPRs were calculated using a 10% dose threshold of the maximum measured dose. Confidence limits (CLs) were calculated according to the methodology described in the AAPP TG 119 report.

Results:

Excellent mean 3D GPRs were collected for the 100 HA plans and for each verification method (Figure and Table). PRIMO-based verifications revealed 3 PTVs with 3%/1 mm GPR < 90%, which reported GPRs > 90% using the 5%/1 mm criteria. All O4D-based verifications resulted in GPR >90% regardless the gamma criteria used. CLs> 95% were obtained for all type of gamma index analyses.