ESTRO 2024 - Abstract Book

S3359

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

and 2mm in x direction resulting in 8 different profiles. Two different types of 3DCT were created: one as an average of all 10 phases and one using only the phases from 40 to 60% of the breath profile with a total of 16 3DCT. A single arc with 6MV and 900 MU was planned on the 3DCT scan motionless and this plan was translated to the others 16 3DCT. For the plans calculated on the average CT, the acquisitions were performed in free breath, while for the plans calculated on the phases from 40 to 60%, treatment gating was set. Gamma evaluation was performed with 2% of dose and 2mm on DTA tolerance limit and 10% threshold.

Results:

The gamma passing-rate (GP) value decrease with the introduction of respiratory movements and worsen in the case of gating on the contrary the mean gamma values increase. The mean of the GP and the mean value of the gamma for all the breath profiles considered are: 88.2±6.3 % and 0.5±0.1 in the case of free breath, 93±1.6% and 0.44± 0.04 in the case of gating treatment (Figure)

Delta4 phantom not moving presents values of 95.8% and 0.42 for gamma passing rate and mean gamma value respectively. The differences are statistically significant (p=0.031). On the other hand, there is no statically significant differences found in the case where at the respiratory movement in z axis, movements in y and x directions were added.

Conclusion:

The delivery with respiratory gating is a treatment modality that requires high precision. The difficulty of treat at certain stages with high accuracy is reduced for regular, smaller movements. The RGSC System , despite follows movements in one direction (antero-posterior), does not involve worsening during the delivery in case the movements are also in other directions.

Keywords: Gating treatment , Quality assurance

References: