(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: study reported the first clinical application of electron plastic scintillating detector (e-PSD) for real-time dose measurement of a patient with scalp cutaneous lymphoma treated with electron beam radiotherapy.
Methods: Solid water phantom based calibrations were performed for the e-PSDs (Angiodynamics, USA) and TLD-100 (Thermo Scientific, USA). The e-PSD, TLDs, and calibrated PTW34045 parallel plate ion chamber (PTW, Germany) were used to measure 200cGy at the standard setup (i.e. 100cm SSD, 10x10 cm2, measured at Dmax) for electron beams with energies ranged from 6MeV to 18MeV. Energy specific dose calibration factors were applied to e-PSD for clinical measurements. The patient was treated with 30Gy in 15 fractions using 9MeV electron beam using 1cm customized bolus. e-PSDs and TLDs were placed under the bolus at the field center and on the field edge during CT simulation and treatments. Two measurements (once a week) were acquired throughout the treatment and compared with the planned doses.
Results: The average measurements of all the energies for TLDs and ion chamber were 197.5±2.9cGy and 196.3±3.7cGy. For 6MeV, 9MeV, 12MeV, 15MeV, and 18MeV, e-PSD measurements were 198.3±5.8 cGy, 199.1±4.6cGy, 199.8±3.5cGy, 198.9±4.4cGy, 199.9±3.7cGy, respectively. The expected patient doses at the field center and edge were 205.2cGy and 202.4cGy, respectively. In-vivo treatment dose measurements with e-PSDs at the center and edge were 211.6±1.5cGy and 208.3±1.1cGy, respectively while TLDs at the center and edge were 210.9±2.7cGy and 207.4±0.6cGy, respectively. The difference between e-PSD measurements and expected doses ranged from 0.3% to 2.4%.
Conclusion: Phantom based calibration for PSD is highly recommended before clinical applications. The e-PSD demonstrated accurate and reproducible real-time dose tracking capability for all clinical electron energies. The e-PSD is recommended for surface dose measurement with its high spatial resolution and water equivalence.
Keywords
In Vivo Dosimetry, Electron Therapy, Optical Dosimetry
Taxonomy
TH- External Beam- Electrons: dose measurement
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