Exhibit Hall | Forum 5
Purpose: Intraocular cancers are optimally treated with eye plaque brachytherapy (EPB). While it is critical to ensure the exact strength and positions of the radioactive seeds for accurate treatment, current quality assurance (QA) practice according to the AAPM TG129 only dictates the plaque assembly be visually inspected due to the lack of an effective and practical technique to measure seed radioactivity distribution. Unlike the general trend in external beam radiotherapy, the advancement of plaque therapy lags behind in terms of intensity modulated delivery. We developed a fast, low-cost radio-luminescent imaging method to verify the seed activity distribution for differential loading. Without it, we must assume correct loading without verification, but errors could occur.
Methods: We constructed a proof-of-concept system consisting of a thin scintillator sheet coupled to a camera/lens system. A loaded plaque can be placed directly on the scintillator surface with the radioactive seeds facing the scintillator. The camera system is on the opposite side of the scintillator collecting the radioluminescent signal generated by the plaque. The predicted dose distribution out of the scintillator plane (to be imaged by the camera) was calculated using Monte Carlo simulation with the planned plaque loading pattern. Quantitative comparisons of measured (76.4 µm/pixel) and calculated dose distributions were performed by gamma analysis, similar to IMRT QA.
Results: Data analyses showed high gamma (3%/0.3mm, relative, global, 20% threshold) passing rates with correct seed loadings and significantly reduced passing rates with incorrect loadings, indicating that possible errors may be detected. The measurement and analysis only require a few minutes, significantly shorter than the time to assay the extra verification seeds the physicist already must perform as recommended by TG129.
Conclusion: Radio-luminescent QA can be used to facilitate and assure the implementation of intensity modulated, customized plaque loading. It has the potential to crucially advance EPB.
Funding Support, Disclosures, and Conflict of Interest: This research is supported by a Stanford Cancer Center internal grant.