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Patient SRS Plans Verification of the New O-Ring System (Halcyon™)

D NGUYEN1*,J FARAH3, F JOSSERAND PIETRI2, M KHODRI1, (1) Radiotherapy centers of ORLAM group, MACON,FR, (2) Radiotherapy centers of ORLAM group, LYON,FR, (3) Vision RT Ltd, LONDON,UK


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Six Halcyon™ (Varian, USA) O-ring Linacs have been installed at our centers. The present work aims to validate the Anisotropic Analytical Algorithm v15.6 (AAA) algorithm for stereotactic radiosurgery (SRS) with these machines.

Eclipse™ version 15.6 was used to generate 20 different SRS plans using AAA algorithm and a calculation grid of 1 mm. The target volume was varied from 0.1cc, 0.5cc, 1cc and 2cc considering five different modulation levels (very low, low, Normal, Moderate and Very High) achieved using the aperture shape controller function. Measurements on Halcyon 2.0 were performed using a 2D SRS MapCHECK® detector with StereoPHAN (Sun Nuclear, USA). Additionally, 10 SRS patients’ treatment plans treated on Halcyon were randomly selected to benchmark the TPS in clinically realistic conditions.
SNC Patient™ software V8.3 (Sun Nuclear) was used to perform a global gamma index with 1%/1mm and 0.5%/0.5mm criteria and a 5% threshold.

First when considering the 20 test plans, the mean passing rates of the global gamma index analysis were ?global = 99.48 ±0.46% ?global = 97.27±1.38% for the 1%/1mm and 0.5%/0.5mm criteria, respectively. When investigating the effect of tumour size, ?global at 0.5%/0.5 mm quickly increased from 70.78 ± 2.66% for 0.1cc tumour to 97.4 ± 1.31% for 0.5cc, 95.98 ± 1.04% for 1cc and up to 98.3 ± 0.69% for the largest tumour of 2cc. Meanwhile, modulation proved to have lower impact on ?global at 0.5%/0.5 mm which ranged from 90.6 ± 14.2% for VeryLow modulation to 91.5 ± 12.5% for VeryHigh modulation. This result was further confirmed with 10 realistic patient plans and tumour shaped with global gamma index 0.5%/0.5mm achieved on Halcyon of 90.35 ± 6.72%.

The study proved that SRS patients can benefit from fast and accurate delivery on Halcyon™ using AAA planning algorithm

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