ESTRO 2024 - Abstract Book

S3352

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

M. L. Jensen, B. Julsgaard, R. M. Turtos et al., High-resolution three-dimensional dosimetry in clinically relevant volumes utilizing optically stimulated luminescence, Medical Physics, In production, DOI: 10.1002/mp.16796.

M. Sadel, J. Gajewski, U. Sowa et al., 3D dosimetry based on LiMgPO 4 OSL silicone foils: Facilitating the verification of eye-ball cancer proton radiotherapy, Sensors 21 (2021).

2585

Digital Poster

Commissioning of a novel 3 mm diameter cone for the ZAP-X system using a microSilicon detector

Katrin Saße 1 , Karina Albers 1 , Peter Douglas Klassen 2 , Neelan J. Marianyagam 3 , Georg Weidlich 4 , M. Bret Schneider 4 , Steven D. Chang 3 , John R. Adler 4 , Björn Poppe 1 , Hui Khee Looe 1 , Daniela Eulenstein 5 1 Carl von Ossietzky University, Universitiy Clinic for Medical Radiation Physics, Oldenburg, Germany. 2 Bonifatius Hospital Lingen, ZAP-X Zentrum Lingen, Lingen, Germany. 3 Standfort University School of Medicine, Neurosurgery, Palo Alto, USA. 4 ZAP Surgical, ZAP, San Carlos, USA. 5 PTW Freiburg, PTW, Freiburg, Germany

Purpose/Objective:

The ZAP-X is gyroscopic radiosurgery system for brain lesions with a 3 MV linac and circular collimators of diameters between 4 mm and 25 mm. To treat smaller lesions in early-stage pathologies that are nowadays detected using advanced imaging techniques, small collimators matching the anatomical targets are required. For this purpose, a novel 3 mm diameter cone was developed. In this study, this novel collimator has been characterized dosimetrically using a commercial microSilicon detector (PTW Freiburg, Germany) and radiochromic EBT3 films (Ashland, USA). To allow better understanding of the small field perturbation effects associated with the detector in this very small field, comprehensive investigations were performed using Monte Carlo simulations. Thereby, the associated small field output correction factors were derived for these very small collimator sizes.

Material/Methods:

The diameter of the sensitive volume of the microSilicon detector is 1.5 mm. During the measurements, the detector is positioned with its axis parallel to the beam’s axis in a MP3-XS water phantom (PTW Freiburg, Germany). The profile measurements for the 3 mm cone were performed using the detector at a source-to-surface-distance (SSD) of 450 mm at five different depths (7, 50, 100, 200, and 250 mm). The output ratios were measured at a SSD of 443 mm in 7 mm water depth. Additionally, the profiles and output factors were also measured using radiochromic EBT3 films. For the Monte Carlo simulations, a virtual photon fluence source was derived from 2D measured dose distributions acquired with EBT3 films according to the methods described in (Delfs et al, Blum et al). The implemented virtual sources were verified by comparing the simulated dose profiles with the measurements.

The detector perturbation factors were studied by modifying the detector’s model stepwise according to a previous work (Weber et al). By taking the ratios of the simulated deposited energies in two subsequent steps, normalized to