ESTRO 2024 - Abstract Book

S3317

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

2253

Digital Poster

SRS/SBRT patient-specific QA device comparison: Electronic QA devices vs film dosimetry

Tamir Shacham, Dan Epstein, Daphne Levin

Assuta Medical Centers, Radiotherapy, Tel Aviv, Israel

Purpose/Objective:

Patient-specific QA is an essential part of the SBRT and SRS treatment chain, where large doses per fraction are delivered. The standard patient-specific QA at our institution includes an absolute point dose measurement with an appropriate ion chamber, as well as film dosimetry, which is considered the gold standard due to its high resolution. However, film dosimetry is time consuming and expensive. Electronic QA devices claim to be film-equivalent in terms of resolution and accuracy, less labor intensive, and more cost effective. In this study we compared two electronic QA devices to radiochromic film. The aim of the study was to determine whether accuracy of QA measurements performed by different electronic QA devices is, indeed, equivalent to that of radiochromic film.

Material/Methods:

Ten SBRT and SRS treatment plans of previously treated patients were measured with radiochromic films (Ashland) and with two electronic QA devices: MapCHECK (SunNuclear) and MyQA SRS (IBA). All measurements were performed in the coronal plane and compared to films with gamma criteria of 95% pass rates for 3mm/3%, 2mm/2% and 1mm/3%, which are the commonly used criteria clinically. We then averaged the readings from each device for all 10 patients for each gamma criterion and compared them to the same average for film.

Results:

Films and electronic devices all had gamma pass rates at or exceeding 95% for the 3mm/3%, and 2mm/2% criteria. For the 1mm/3% criterion MyQA and MapCheck had pass rates of 94.16% and 98.31% respectively, compared to film: 90.56%.

At the most stringent criterion (1mm/1%) both electronic devices gave higher pass rates than film: 77.86% and 87.6% for MyQA SRS and MapCHECK, respectively, vs 58.84% for film.

Conclusion:

Both MapCHECK and MyQA SRS electronic devices provide good agreement with film for the less stringent gamma criteria tested. At more stringent criteria the electronic devices gave higher pass rates than film, and the difference increased with tighter tolerances.