ESTRO 2025 - Abstract Book

S316

Brachytherapy - Physics

ESTRO 2025

187

Digital Poster In vivo dosimetry of gynaecological brachytherapy: a phantom investigation Mintra Keawsamur 1 , Itsaraporn Konlak 1 , Taweap Sanghangthum 1 , Chulee Vannavijit 2 , Sakda Kingkaew 2 , Chatchumnan Nichakan 2 , Petch Alisanant 2 1 Radiology, Chulalongkorn University, Bangkok, Thailand. 2 Radiology, King Chulalongkorn Memorial Hospital, Bangkok, Thailand Purpose/Objective: The purpose of a treatment planning system is to calculate the radiation dose for patients receiving brachytherapy. Nonetheless, it cannot verify the precision of the dose, particularly for intracavitary brachytherapy, which can be remarkably difficult. Commercial phantoms cannot be attached to both applicators and detectors concurrently. This study aimed to design an in-house phantom for in vivo dosimetry of gynaecological brachytherapy using a Radio photoluminescence glass dosimeter(RPLGD) and to assess the dosimetric discrepancies between measurements obtained with RPLGD and calculations made by the treatment planning system in clinical settings. Material/Methods: A phantom was constructed in-house, comprising the glass dosimeter holder and the applicator holder. This holder was designed to adjust its axis to accommodate different anatomical points, which vary based on the patient's anatomy. Furthermore, the applicator holder has been designed for use with multiple applicator types in intracavitary brachytherapy. The clinical study aimed to evaluate discrepancies between the calculated and measured doses for six patients at multiple locations within the phantom, including point A, point B, bladder point, and rectal points. Results: The average dose discrepancy between the calculated and measured doses at point A was 1.99%, at the bladder point was 4.42%, and at the rectum point was 3.53%. All values were within 5% of the acceptable reference value agreement. The measured dosage at point B for the low dose deviates from the estimated dose by approximately 0.1 Gy. Conclusion: We suggest that in-vivo dosimetry utilizing the RPLGD in an in-house phantom for brachytherapy can precisely estimate the actual delivered dose for patient records through an accessory for the applicator in clinical practice. References: 1.Tanderup K, Beddar S, Andersen CE, Kertzscher G, Cygler JE. In vivo dosimetry in brachytherapy. Med Phys. 2013;40(7):070902. 2. Kim SY, Park JW, Park J, Yea JW, Oh SA. Fabrication of 3D printed head phantom using plaster mixed with polylactic acid powder for patient-specific QA in intensity-modulated radiotherapy. Sci Rep. 2022;12(1):17500. 3. Moon SY, Son J, Yoon M, Jeang E, Lim YK, Chung WK, et al. Applicability of Glass Dosimeters for In-vivo Dosimetry in Brachytherapy. Korean Phys. Soc. 2018;72(11):1320-5. 4. Van der Walt M, Crabtree T, Albantow C. PLA as a suitable 3D printing thermoplastic for use in external beam radiotherapy. Australas Phys Eng Sci Med. 2019;42(4):1165-76 Keywords: In-vivo dosimetry, Glass dosimeter, 3D printing