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Investigation of a PRESAGE Three-Dimensional Dosimetry Protocol That Allows for Internal Calibration

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M Carroll

M Carroll*, H Lee , S Venkataraman , G Ibbott , UT MD Anderson Cancer Center, Houston, TX


SU-I-GPD-T-457 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: A preliminary study of a novel PRESAGE® 3D dosimeter formulation with a stable temporal dose signal, large dynamic range, and low fractionation sensitivity has demonstrated potential for a single device calibration system offering efficiency and improved dose accuracy. This study investigated the radiological properties of the dosimeter and compared a dose analysis to one using a conventional calibration method.

Methods: Modified PRESAGE was manufactured in-house and cast into cuvettes (1x1x4cm³) which were irradiated to 0-12Gy. Dose sensitivity was measured by the change in optical density (ΔOD) relative to dose. Additional cuvettes were irradiated with a uniform 4Gy field and the baseline ΔOD was recorded and subtracted. These were then re-irradiated to 0-12Gy and the dose response was compared to the single irradiation cuvettes. Signal fading while refrigerated (<3°C) was measured over 5 days to ensure temporal stability and to determine optimal readout window. Next, two cylindrical dosimeters were irradiated using a preliminary commissioning test (AP:PA). One cylinder used single device calibration while the second followed a conventional method of calibration using a separate dosimeter.

Results: Signal fading within the first 12hrs was 6-15% ΔOD. Between 12-48hrs, signal fading stabilized to ~1% ΔOD/day which was ideal for subsequent readouts. The dosimeters showed a linear response both when irradiated once (R2>0.999) and re-irradiated (R2>0.997). The ΔOD of the re-irradiated dosimeters agreed within 2% of single irradiations. The 3D gamma passing rate (3%/3mm and 10% dose threshold) of the re-irradiated cylindrical PRESAGE was 98.9% after a fading correction while the conventionally calibrated dosimeter was 98.4%.

Conclusion: Using this PRESAGE formulation and strict protocols, a single device has been shown to improve dosimetric accuracy compared to conventional methods. This demonstrates a promising new and efficient calibration method. Further studies are warranted to reproduce these results using more complex beam deliveries.

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