ESTRO 2024 - Abstract Book

S3189

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

Nierer, L., Kamp, F., Reiner, M., Corradini, S., Rabe, M., Dietrich, O., ... & Landry, G. (2022). Evaluation of an anthropomorphic ion chamber and 3D gel dosimetry head phantom at a 0.35 T MR-linac using separate 1.5 T MR scanners for gel readout. Zeitschrift für Medizinische Physik, 32(3), 312-325.

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Multi-Institutional Study of a New Plastic Scintillator Detector for Photon Small Field Dosimetry

Sergio Panzuela Pérez 1 , Mario Gallego Castro 1 , Jose Macias Jaen 1 , Marziyeh Tahmasbi 2 , Miguel Capela 3 , Tania Santos 3 , Josefina Mateus 3 , Tiago Ventura 3 , Maria Do carmo Lopes 3 1 Hospital Virgen Macarena, Medical Physics, Sevilla, Spain. 2 University of Medical Sciences, Medical Sciences, Ahvaz, Iran, Islamic Republic of. 3 Instituto Portugues de Oncologia Coimbra Francisco Gentil, Medical Physics, Coimbra, Portugal

Purpose/Objective:

The present study shows the suitability of a new plastic scintillator detector, BluePhysics model 10 (BP10), for small field dosimetry of photon beams in conventional linear accelerators (linac) without the need of small field output correction factors.

Material/Methods:

BP10 is a new plastic scintillator sensor consisting of a core material of fluorescent doped polystyrene and a cladding material of acrylic. Cerenkov effect is taken into account by placing an identical second fiber next to the transport plastic optical fiber. Thus, by means of the Adjacent Channel (ACR) method, BP10 takes into account the proportion of Cerenkov signal to be subtracted. To characterize this detector, the ACR, monitor unit linearity, dose rate constancy and sensitivity tests have been performed with 6MV and 6FFF of two different linear accelerators: a TrueBeam STx linac at the Portuguese Oncology Institute of Coimbra, Portugal (IPOCFG), and a VersaHD linac with an APEX micro multi-leaf collimator (μ-MLC) at the Hospital Virgen Macarena of Sevilla, Spain (HUVM). Output factors (OF), beam profiles and percentage depth doses (PDD) have been measured and compared against the microdiamond detector, SRS diode and radiochromic film.

Results:

The obtained ACR values show a nearly constant dependency with the beam energy. BP10 shows a perfect lineal relationship with the MU and a variation in the dose rate constancy ≤ 0.5% for 100MU and ≤ 4% for 5 MU. Its dose response sensitivity at energy 6MV is 78.8 nC/Gy, which is higher than most detectors. Beam Profiles of 0.5x0.5cm 2 and 1x1cm 2 fields and PDDs of 0.5x0.5cm 2 (not shown) and 1x1cm 2 fields are comparable with those obtained by a microdiamond detector; 1D-gamma analysis shows that 100% of the points meet the 2%/2mm criteria. OFs of square shaped fields, from 0.5cm to 12cm field size, and elongated fields, with one field size fixed to 1cm and the other