Author: Mateb Ali Alghamwa, Haya Aljuaid, Siyong Kim, Tianjun Ma, William Song 👨🔬
Affiliation: Virginia Commonwealth University 🌍
Purpose: The integration of Plastic Scintillation Detectors (PSDs) into 0.35T MR-Linac systems represents a significant advancement in radiotherapy, offering substantial benefits due to their tissue-equivalent material and small size. This study characterizes and validates experimental methodologies for extracting Cerenkov Radiation (CR) from PSD signals, a critical step toward improving measurement accuracy in radiotherapy settings.
Methods: A 1 mm BluePhysics detector was employed using three methods. The first method, Underwood Cross Calibration, quantifies the CR Extraction (CRE) of both CR channel (chCR) and PSD channel (chPSD) signals by considering the known output factor measurement of a 3.32 cm x 3.32 cm field size and comparing it to the ratio of two different field sizes (3.32 cm x 3.32 cm and 9.96 cm x 9.96 cm). The second method, the loop method, involves a single field size of 9.96 cm x 9.96 cm and utilizes varying numbers of optical fiber loops (from 0 to 5 loops), with the CRE calculated from the slope between chPSD and chCR charges. The third method measures the optical fiber alone with the sensitive volume outside the field, determining the CRE by comparing signal readings from chPSD and chCR.
Results: The Underwood Cross Calibration method measured an CRE of 0.9996. The loop method, after plotting a linear curve between chPSD and chCR charges, calculated an CRE of 1.0045 from the slope. The fiber only method measured and calculated an CRE of 1.013.
Conclusion: Three methods for removing radiation contamination were applied to the BluePhysics PSD in a 0.35T MR-Linac environment. The CRE values obtained across all three methods demonstrate different methodologies for CR removal. The results of all CRE measurements and calculations were within ±1. The loop method seemed most practical due to its simplicity, error resistance, and minimal dependency on exact outputs or machine variations.