ESTRO 2024 - Abstract Book

S4945

Physics - Quality assurance and auditing

ESTRO 2024

automated extraction and analysis of extensive datasets, thereby enhancing the efficiency and accuracy of the process.

Keywords: SBRT, dose prescription

References:

[1] ICRU report 50: Prescribing, recording, and reporting photon beam therapy. 1993.

[2] ICRU report 91: Prescribing, Recording, and reporting of Stereotactic Treatments with Small Photon Beams. 2017.

3185

Digital Poster

Retrospective analysis of output data for ten linear accelerators at Northern Ireland Cancer Centre

Hannah L Marshall, James Robinson, Raymond B King, Conor K McGarry, Christina E Agnew

Belfast Health and Social Care Trust, Radiotherapy Physics, Belfast, United Kingdom

Purpose/Objective:

Monitoring the output of linear accelerators, through an established quality assurance programme, is crucial in ensuring consistent and accurate delivery of dose to patients. The monitor chamber, in the head of a linear accelerator, is responsible for calibrating this dose. Previous studies have presented data suggesting that the response of the monitor chamber degrades with age, resulting in an output plateau with time 1,2 . Additionally, several studies 2,3,4 analysed trends in outputs over time, with reported data on both sealed and unsealed monitor chambers. This work aimed to further probe the response of sealed monitor chambers over time, through the retrospective analysis of output data obtained over a period of up to 11.5 years.

Material/Methods:

Weekly output data for ten Varian TrueBeam (Varian Medical systems, Palo Alto, CA) linear accelerators was analysed. Over this period, several monitor chamber replacements were made, allowing evaluation of chamber performance with age. The maximum chamber age for which data was obtained was 6 years. The unadjusted output was calculated to observe the expected growth of accelerator output over time, as demonstrated in previous studies 1,2 . Annual percentage variation in output was determined for each unique monitor chamber-linear accelerator combination. Additionally, the frequency of required adjustments to the output with chamber age was investigated.

Results: