K Yang*, S Sharma, A Ju, East Carolina University, Greenville, NC

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  K Yang

PO-GePV-T-64 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: In electron beam therapy, skin collimation that conforms to the patient surface can be used to minimize the penumbra. However, accurate in-vivo dosimetry is challenging, particularly for small and irregular fields. Plastic scintillating fiber detector is well-known for small dimension and water-equivalence for high-energy electron beams, and thus fewer beam perturbations. The objective of this study was to quantify and compare its output performance on the surface.

Methods: The Exradin W1 plastic scintillation detector was mounted on a solid water phantom. The circular-shaped lead cutouts were placed on the surface with the center of the opening aligned with the detector. Each channel of the scintillation detector was connected to an electrometer and the raw signals were recorded simultaneously. The Cherenkov Light Ratio parameters were also determined for each electron energy in the calibration process. The ion-chamber (Exradin A16) readings were also measured with the same configuration as comparison.

Results: Both Channel1 (green, mainly scintillation light) and Channel2 (blue, mainly Cherenkov light) signals increase when skin collimation size decreases, while the ratio of Channel1 versus Channel2 remains relatively stable when changing opening diameters (coefficient of variation<0.009). The Cherenkov-corrected relative output monotonically decreases when skin collimation diameter decreases, and the maximum relative output reduces to 0.792 with the highest 18 MeV electron energy and smallest 2 cm diameter.

Conclusion: We have calibrated and used a plastic scintillator to determine surface dose. The relative output performance was in good agreement with other types of detectors in small electron radiation fields.

Keywords

Scintillators, Electron Therapy, Surface Dose

Taxonomy

TH- Radiation Dose Measurement Devices: scintillators

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