ESTRO meets Asia 2024 - Abstract Book

S345

Physics – Quality assurance and auditing

ESTRO meets Asia 2024

Hafiz M Zin 1 , N Diyana Afrina 2 , Ahmad Taufek Abdul Rahman 3 , Ngie Min Ung 2 , Kwan Hong Ng 2

1 Advanced Medical & Dental Institute, Universiti Sains Malaysia, Penang, Malaysia. 2 Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia. 3 Faculty of Applied Science, Universiti Teknologi MARA, Selangor, Malaysia

Purpose/Objective:

Modern radiotherapy uses linac with digital control system to adjust and monitor dynamic radiotherapy treatment parameters especially the multileaf collimators (MLCs) to deliver highly conformal technique. There is a potentially greater risk for errors to be missed due to variability of the sophisticated treatment techniques different linac modalities and the techniques used to verify the treatment. National dosimetry audits can maintain and improve standards of radiotherapy treatment on a larger geographic scale. However, the audit can be highly resource extensive because of the complexity of the treatment and the dosimeters required. This work presents the development of a novel linac-dependent method to verify complex radiotherapy treatment remotely using EPID validated log data from different models of linac.

Material/Methods:

A computer algorithm was developed to extract and verify the treatment parameters from the logged data during beam delivery from different generations of digital linac from different vendors. A picket fence test was performed using EPID to validate the log data measured. IMRT treatment was also delivered whilst the log data were collected. Comparison between the prescribed and the tracked parameters was performed by calculating the discrepancy of the tracked parameters and the resulting fluence with the prescribed data. Fluence was also measured using PTW 1500 2D array detector. Nine radiotherapy centres across Malaysia participated in this audit by electronically returning the log data and EPID images recorded remotely on-site as per the instructions provided.

Results:

The range of errors for the MLC positions tracked using log data compared to the EPID measurement is between 0.1 to 0.8 mm for centres that participated in the study. The percentage gamma pass rates of the radiation fluence constructed using the tracked beam delivery parameters are between 94% to 99% at 2% and 2 mm gamma criteria. The values correlate with the percentage of MLC positions that exceed 1 mm errors during treatment delivery at each centre of between 0.5% to 2.8%. The results from the log data agree with the measurements validated with EPID and the 2D array detector. However, the sensitivity of the error measurements varies between different linac generations and vendors.

Conclusion:

The method provides a more detailed analysis of linac performance such as MLC position errors, and may potentially significantly reduce the time required to perform the verification. Hence the technique is suitable for remote audit purpose encompassing different linac machines and IMRT techniques used. The technique significantly reduces the time required to perform an IMRT audit and provides valuable performance metrics of IMRT treatment accuracy remotely.

Keywords: Radiotherapy, Audit, Log Data