ESTRO 2024 - Abstract Book

S3220

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

Stereotactic body radioablation (SBRT of ventricular tachycardia (VT) is a recent non-invasive technique for patients refractory to other treatment options, commonly radiofrequency catheter ablation. This type of treatment requires, among other things, high dose rate, intrafraction control of the position of the fiduciary and management of the patient's breathing using the gating technique. The high dose required (30 Gy in 1 fraction with the VMAT technique) pushes the machine to its limits and the quality assurance process must be adapted to the present case.

Material/Methods:

The detector used to control the delivered dose is the Delta4®. The simulation of the patient's breathing is possible thanks to an in-house system, setting in motion a platform on which the VARIAN RPM box is placed. The measurement of the absolute dose as close as possible to the treatment conditions is then analyzed on the Scandidos® software, the median dose and the gamma index score are recorded. Several treatment plans were planned on Eclipse with a number of arcs ranging from 6 to 11. The desired effect is to highlight a difficulty for the Linac to deliver dose below a given arm speed.

Results:

We observe that the 6 half-arcs treatment plans are not correctly delivered by the machine. Median dose deviations of up to 6% and gamma pass rates below the usual criterion (>95% for 3%/3mm). For plans with a larger number of arcs, an improvement in the value of the median dose and the gamma pass rate is observed, gradually with an increase in the arc number. For the 10 arc ballistic we find median dose results oscillating around zero.