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Dosimetry of Modulated Electron Radiation Therapy Using Fricke Gel Dosimeter

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M Abdel Gawad

M Abdel Gawad1*, O Desouky2 , M Elgohary1 , M Hassaan1 , A Eldib1,3 , M Emam1 , C Ma3 , (1) Al Azhar University, Cairo Egypt,(2) National center for radiation research and technology-Egyptian atomic energy, Cairo,Egypt ,(3) Fox Chase Cancer Center, Philadelphia, PA,USA.


SU-D-213-6 (Sunday, July 12, 2015) 2:05 PM - 3:00 PM Room: 213

Modulated electron radiation therapy (MERT) has been proposed as an effective modality for treatment of superficial targets. MERT utilizes multiple beams of different energies which are intensity modulated to deliver optimized dose distribution. Energy independent dosimeters are thus needed for quantitative evaluations of MERT dose distributions and measurements of absolute doses delivered to patients. Thus in the current work we study the feasibility of Fricke gel dosimeters in MERT dosimetry.

Batches of radiation sensitive Fricke gel is fabricated and poured into polymethyl methacrylate cuvettes. The samples were irradiated in solid water phantom and a thick layer of bolus was used as a buildup. A spectrophotometer system was used for measuring the color changes (the absorbance) before and after irradiation and then we calculate net absorbance. We constructed calibration curves to relate the measured absorbance in terms of absorbed dose for all available electron energies. Dosimetric measurements were performed for mixed electron beam delivery and we also performed measurement for segmented field delivery with the dosimeter placed at the junction of two adjacent electron beams of different energies. Dose measured by our gel dosimetry is compared to that calculation from our precise treatment planning system. We also initiated a Monte Carlo study to evaluate the water equivalence of our dosimeters. MCBEAM and MCSIM codes were used for treatment head simulation and phantom dose calculation. PDDs and profiles were calculated for electron beams incident on a phantom designed with 1cm slab of Fricke gel.

The calibration curves showed no observed energy dependence with all studied electron beam energies. Good agreement was obtained between dose calculated and that obtained by gel dosimetry. Monte Carlo results illustrated the tissue equivalency of our Gel dosimeters.

Fricke Gel dosimeters represent a good option for the dosimetric quality assurance prior to MERT application.

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