ESTRO 2024 - Abstract Book

S3356

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

Both devices display field size dependence in smaller field sizes. Octavius 1500MR tends to underestimate the dose, while Octavius 1600MR overestimates it. The observed deviations are caused by the volume averaging effect and density variations [10]. The most significant deviations occur for field sizes smaller than the recommended values. All clinical tests were successfully completed. The Octavius Detector 1500 MR demonstrated compatibility with the standard 95% pass rate when employing a 3%/3mm gamma criterion, and a 90% pass rate using a 2%/2mm gamma criterion for different targets (Fig.1). Deliberately introduced positional errors of 5 mm were all identified by the Octavius system, with a significant reduction in Gamma percentage. With the standard parameters, the Gamma test was not sensitive to uniform small changes in MU (and dose).

Octavius 1500MR

Octavius 1600MR

Additional information

Additional information

Test

Max Deviation Error

Max Deviation Error

Short-term reproducibility

0.20%

0.09%

-

0.10%

0.06%

-

Biggest deviation for 2MU

Dose linearity

0.43%

0.23%

-

0.95%

0.37%

Dose-per-pulse dependence

0.13%

0.12%

-

0.36%

0.24%

-

Biggest deviation for PRF up to 115 MU/min

Dose

rate

0.25%

0.14%

-

0.77%

0.54%

dependence

Field

size

Biggest deviation for small field sizes

Biggest deviation for small field sizes

4.0%

1.5%

2.1%

1.6%

dependence

Biggest deviation in cryostat and table position

Biggest deviation in cryostat and table position

Angular response

0.97%

0.47%

1.14%

0.57%

Table 1. Maximum deviation (%) for each dosimetry test for Octavius 1500MR and Octavius 1600MR arrays. All test results were acceptable for clinical use.