SU-E-T-385: Use of a Plastic Scintillation Detector for Calibration of a P32 Dura Plaque

Abstract

Purpose: Radiochromic film has been used to calibrate 32P plaques, which are used to irradiate the dura for patients with sarcomas of the spine. Although this method has been successful, it is time consuming due to the characteristics of the film. A more efficient calibration method utilizing a miniature plastic scintillation detector has been investigated for this work. This new method provides an immediate readout which can be corrected with a factor to determine dose rate. Methods and Materials: The surface dose rate for a 1 cm2 flat 2.47 mCi 32P source was measured with radiochromic film. A calibration curve for the radiochromic film was determined using a 90Sr eye plaque of known output. A plastic 2 × 2 × 4 cm mini phantom with a channel through the long dimension to accommodate the plastic scintillation detector, which has a diameter of 5.0 mm and length of 23 mm, was used to measure the count rate at the surface of the 32P source. A multiplicative correction factor for the scintillation detector readout was determined by dividing the dose rate measured by radiochromic film by the count rate measured using the scintillation detector. Results: The radiochromic film measurements yielded a surface dose rate of 2.52 Gy/min. The scintillation detector yielded an average count rate of 2.3 × 106 counts/min. The correction factor from these measurements was determined to be 1.12 × 10‐6 Gy/min. Conclusion: The use of a plastic scintillation detector versus radiochromic film for the calibration of 32P plaques will greatly decrease the calibration time by providing an immediate readout of dose rate.