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Cumulative Dose Measurements in Fractionated Radiotherapy with Alanine Detectors

A Al-Karmi

Anan M. Al-Karmi*, Ahmad A. Dawabsheh , Department of Physics, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia


SU-K-205-5 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 205

Purpose: We developed a radiation detector containing the amino acid alanine as a dosimeter. The detector successfully provided single measurements of low-dose ranges typical for single-fraction irradiation often given to patients in a course of radiotherapy. The objective of this study is to use the same detector to make multiple measurements in a row and investigate the detector’s response with cumulative doses.

Methods: The detector was prepared by filing high purity L-α-alanine powder into a tissue-equivalent polymethylmethacrylate (PMMA) plastic tube. Next, the detector was placed at the geometric center of a radiation field at 9.6 cm depth in a solid water phantom and then irradiated to a dose of 2 Gy on a CLINAC with 6 and 18 MV photon beams of 15x15 cm² field size and 100 cm source-surface distance (SSD). After irradiation, an X-band electron paramagnetic resonance (EPR) spectrometer was used to detect signals from the radicals generated in irradiated alanine. The peak-to-peak amplitude of the central line of the spectrum represented the absorbed dose in alanine. The irradiation was repeated on the same detector to achieve several cumulative dose values. The consistency between measurements was verified by comparing the difference between the final reading minus the reading made just prior to the irradiation.

Results: A good consistency between alanine measurements was found within ±3%. The detector dose response curve showed good linear behavior with linear regression coefficient of 0.9997 and with no dependence on the photon beam energy. From this individualized calibration curve, a calibration factor in Gy per EPR signal was generated for the detector.

Conclusion: The alanine detector can be used in vivo to measure cumulative doses from the accrual of daily fractional radiation measurements during a radiotherapy course. The detector provides a permanent record of exposure and can be preserved in archival storage.

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