ESTRO 2024 - Abstract Book

S3304

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

The employ of a solid water phantom is particularly advantageous to assemble the measurement setup, that becomes easier without loss in data accuracy.

Data show that RC and RD detectors are suitable for relative measurements in Tomotherapy. Larger deviation were found for ionization chamber results, probably due to the volume averaging effect. Correction factors for the new generation detectors here investigated are needed

Keywords: multicentric research, tomotherapy, output factor

References:

Alfonso R, Andreo P, Capote R, et al. International Atomic Energy Agency (IAEA). Dosimetry of Small Static Fields Used in External Beam Radiotherapy: An International Code of Practice for Reference and Relative Dose Determination. IAEA TRS-483. Vienna: International Atomic Energy Agency. 2017.

2054

Digital Poster

The impact of linac x-ray target replacement on megavoltage photon small-field dosimetry

Mohammed Ghazal 1,2 , Hamza Benmakhlouf 1,2

1 Karolinska University Hospital, Medical Radiation Physics and Nuclear Medicine, Stockholm, Sweden. 2 Karolinska Institute, Oncology-Pathology, Stockholm, Sweden

Purpose/Objective:

It is a common practice to replace x-ray targets in linear accelerators (linac) as part of a maintenance program. This is due to the target being continuously bombarded by high energy electrons to produce x-rays, and with time, this results in an instable dose output and change in the x-ray characteristics (1). Small-field dosimetry is most sensitive to target replacement. It was shown that differences in small-field output factors (OF) between linacs might be due to variation in spot sizes characterized by differences in target wear over time (2). Also, it was shown that correction factors for OF, proposed by TRS-483 (3), are affected by the spot size of the beam (4). Common practice dictates that extensive verification measurements should be performed after x-ray target replacement (1). In this work, the impact of linac x-ray target replacement on small-field dosimetry is investigated in terms of: OF, lateral dose profiles and dosimetric leaf gap (DLG) of the multileaf collimators (MLCs).

Material/Methods:

Lateral dose profile- and OF measurements were performed in water using three small-field detectors: IBA Razor diode (profiles and OF), PTW microSilicon diode (OF) and PTW microDiamond (OF). Investigated field-sizes were: 0.6