ESTRO 2024 - Abstract Book

S3276

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

1635

Digital Poster

In vivo dosimetry - keeping my finger on the pulse

Agnieszka Walewska 1 , Paulina Wesołowska 1 , Magdalena Dobrzynska 2 , Pawel Franciszek Kukolowicz 1

1 Maria Sklodowska-Curie National Research Institute of Oncology, Medical Physics Department, Warsaw, Poland. 2 National Centre for Nuclear Research, Particle Acceleration Physics and Technology Devision, Otwock, Poland

Purpose/Objective:

Precise and safe radiotherapy, resulting in the accurate delivery of the planned dose, is of particular importance for achieving the expected treatment effect. The aim of this work is to introduce the in vivo film detector (IVFD) designed for dose measurement for dynamic techniques and to present the results performed with this detector.

Material/Methods:

The detector, (Figure 1), was made of PLA using a Flash Forge Guider II 3D printer (100% fill). The detector has the shape of a cylinder with an outer diameter of 22 mm. It consists of two parts: a film overlay and a thin base with a centrally placed cylindrical air space in between, which allows the placement of two Gafchromic films (Ashland Inc., USA). The optimal thickness of the overlay was chosen based on the consistency of the dose measured with the in vivo detector and the Markus chamber. The influence of the in vivo detector on the dose distribution was evaluated by comparing the dose distributions for VMAT plans prepared with and without the detector for two H&N plans calculated on an anthropomorphic phantom - statistics routinely used in our clinic for plan evaluation were compared. The IVFD was then used to verify the doses calculated in the Eclipse treatment planning system (AAA, v. 15.6) for plans prepared on two different phantoms These were: the solid water phantom (single field) and the semi anthropomorphic phantom (full treatment plans). The dose value from the TPS was read using in-house-developed “ROI” software, which allows the calculation of the average dose from selected ROI in a film plane around the point defined in the treatment planning system (Fig. 1). A circular ROI of 1 cm diameter was selected for comparison with the measured dose.