Main Session
Sep
30
PQA 07 - Genitourinary Cancer, Patient Safety, Nursing/Supportive Care
3372 - Investigating Effects of Film Digitization Methods on IROC SRS Head Phantom Credentialing Results
Presenter(s)
Michael Yang, BS - MD Anderson Cancer Center, Houston, TX
M. Yang1, P. E. Alvarez2, T. M. Briere3, R. Lin4, S. Kry4, and M. Glenn1; 1MD Anderson Cancer Center, Houston, TX, 2MD Anderson Cancer Center, Houston, TX, United States, 3MD Anderson Cancer Cancer, Houston, TX, 4The University of Texas MD Anderson Cancer Center, Houston, TX
Purpose/Objective(s):
To assess differences in relative film dosimetry when using a charged-couple device (CCD) camera versus a flatbed scanner to read irradiated films. This study aims to determine if these differences in image processing affect the outcome of the IROC SRS phantom irradiations.Materials/Methods:
20 anthropomorphic SRS head phantoms were retrospectively analyzed. These phantoms were sent to multiple institutions for treatment planning and irradiation of a single target to approximately 30 Gy. Each phantom contained two thermoluminescent dosimeters (TLD) located within the target volume and two radiochromic films for dosimetry (coronal and sagittal planes). The films were digitized using both a CCD camera to obtain intensity values and a flatbed scanner to obtain reflectance values. The films were registered to the radiation treatment plan using points physically cut into the film. A dose calibration was applied using fourth degree polynomial curves fit to data from scans on the CCD and flatbed scanner of a set of calibration films. The phantom film doses were then normalized to the average TLD dose, and a dose map was obtained for each film. Gamma analysis was performed comparing the film and planned doses with a 5% dose difference and 3 mm distance-to-agreement criteria and threshold of 85% pixels passing for both the scanned and CCD-captured films.Results:
On average the gamma pass rates for the two systems were 93.9% and 97.4% for the flatbed scanner and CCD camera respectively. The film scanned on the flatbed scanner had on average a -3.60 ± 4.69% percent difference in gamma pass rate when compared to the CCD camera. A paired t-test confirmed a statistically significant difference between gamma results obtained from the scanner and CCD camera (p < 0.05). All 20 phantoms passed the 85% threshold when digitized on the CCD camera, whereas 2 cases failed the criteria when using the flatbed scanner.Conclusion:
The flatbed scanner shows potential to be more discriminating when judging SRS phantom results. This could be due to resolution differences and an increased ability to detect localized dosimetric errors (e.g. hot and cold spots), as seen by the decrease in average pass rate. Future work will seek to identify specific performance factors between these film digitization systems for broader use with IROC Houston phantom services.