ESTRO 2024 - Abstract Book

S3202

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

542

Digital Poster

In-vivo micro-dosimetry in modern radiation therapy (RT) treatment

Sree Bash Chandra Debnath 1,2 , Didier Tonneau 3 , Carole Fauquet 3 , Agnes Tallet 4 , Marjorie Ferre 4 , Julien Darreon 4

1 Aix-Marseille University, Physics, Marseille, France. 2 Lasers, Plasmas et Procédés Photoniques - LP3, Physics- UMR 7341, Marseille, France. 3 Aix-Marseille University, Physics- CINaM-UMR 7325, Marseille, France. 4 Institut Paoli Calmettes, Radiation Therapy, Marseille, France

Purpose/Objective:

Due to its compact size, robustness, and high sensitivity, optical fiber-based scintillating dosimetry has been a promising technique for small-field radiation dosimetry [1,2,3]. Despite several advantages, a Cerenkov contamination could lead to dose perturbation, thus limiting its application. This study is focused on Cerenkov-free in-vivo micro-dosimetry techniques to evaluate dose measurements at in-vivo conditions.

Material/Methods:

A novel infrared inorganic scintillating device (IR-ISD) has been used to evaluate in-vivo dose measurements and dose distributions. The device is composed of sensitive infrared (IR) scintillating materials (emitting range ~ 1470 nm) integrated into an optical fiber, and an IR-photon counter (AUREA TECHNOLOGY©) to measure the dose image at the output of the detector. The measurement of the internal dose has been performed under 320KV- 192Ir Brachytherapy (BT) source in the hospital provided by Elekta microSelectron HDR-V2 afterloader. Overall measurements were performed using IBATM blue phantoms and solid water slabs by following TG43U1 recommendations for BT treatment that allows dose distribution with high precision according to international standards (IAEA, AAPM, etc.). Cerenkov measurements were performed at different distances (0.2 cm to 8 cm) from the radioactive source for different dose rates. The IR-ISD system performances were also investigated in terms of dose stability, dose linearity, dose rate proportionality, dose distributions, scintillation stability, and energy dependency. Dwell times were measured and calculated by IR-ISD for several constant and random dwell times selected by the operators at the machine at different dwell positions. Finally, a comparison between the IR- ISD measurements and results obtained from the TG43 reference Dataset has been presented.

Results:

IR-ISD system measurements demonstrated excellent linear behavior (R2 = 1) for the investigated dose rates at 0.5 cm and 8 cm distances from the source, respectively. Standard deviation (1σ) remains within 0.025% of signal magnitude, and no Cerenkov signal was monitored till 0.2 cm of source-to-detector distance. Scintillation stability of 0.45% is achieved, and afterglow stays less than 0.85% of the total signal. Symmetrical behavior of the dose rate was observed at different radiation planes. The measured dwell times were found to be acceptable with the planned dwell times that matched with 0.09% average accuracy for the constant dwell times and 0.25% average accuracy for random dwell times in different dwell positions.