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SU‐E‐T‐233: Commissioning of An Implantable Dosimeter for External Beam Radiation Therapy
Author(s) -
Buzurovic I,
Showalter T,
Dicker A,
Cao J,
Xiao Y,
Yu Y,
Harrison A
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612183
Subject(s) - dosimeter , reproducibility , imaging phantom , dosimetry , nuclear medicine , ionization chamber , materials science , irradiation , dose profile , absorbed dose , calibration , biomedical engineering , optics , medicine , physics , chemistry , nuclear physics , ion , quantum mechanics , ionization , chromatography
Purpose: To commission a Dose Verification System (DVS) with permanently implanted in vivo dosimeters. To acquire and evaluate sufficient data for establishing standard of quality in a clinical setting.Methods: DVS is permanent implantable wireless radiation sensor based on MOSFET for absolute dose measurements. To evaluate characteristics of dosimeter, following tests were performed: temperature dependence, reproducibility, field size dependence, post‐irradiation signal drift, dependence on average dose‐rate, linearity test, angular dependence, dose‐rate dependence, irradiation depth dependence and a multiple reading effect. Dosimeter is not currently calibrated for use in kV range. Nonetheless, effects of conebeam CT(CBCT) imaging to dosimeter were investigated. Phantom studies were performed in both air and water using an Elekta Synergy‐S Beam‐Modulator linear accelerator. Results: DVS dosimeters have been calibrated to be used at 37C. Reproducibility tests were performed at room temperature. Readings were −3.2% low (SD=2.5%, or 5.06cGy for 200cGy delivered). Same tests in water at human body temperature showed 1.5% absolute difference, with a similar deviation (SD=2.85%). It was observed that measurement signal decayed significantly with time post‐irradiation, from +3% after 0.5min to −3.5% after 10min. Dose linearity was within 2% for absorbed total dose of 75Gy. Signal rapidly decayed after total dose of 82Gy. Angular dependence was −0.3% (SD=2.31%). Readings decreased with increase in depth, about 0.3%/cm. No filed size and dose‐rate difference were observed. Average dose reading due to CBCT imaging using the pelvis protocol was 7.89cGy (SD=1.46cGy) Conclusions: Extensive acceptance and commissioning measurements have shown considerable post‐radiation signal drift, temperature dependence, reproducibility variation, and rotational isotropy. This process confirmed manufacturerˈs stated performance and provided baseline QA necessary to implement DVS clinically. System is currently implemented with ±7% tolerance. Dosimeter can be used to quantify dose at depth, as well as to evaluate adherence between dose from treatment plan and daily delivery.