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Small Filed Dosimetry Using EXTRADIN W1 SCINTILLATOR

S Behinaein1*, J Darko2 , E Osei3 , D Bassi4 , (1) Grand River Hospital, Kitchener, ON, (2) Grand River Hospital, Kitchener, ON,University of Waterloo, Waterloo, ON (3) Grand River Hospital, Kitchener, ON, University of Waterloo, Waterloo, ON(4) University of Waterloo, Waterloo, ON


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: With a rapid increase in the number of precision radiotherapy, developing techniques to acquire reliable percent depth dose (PDD) for small fields become crucial. Experimental determination of small filed dosimetric data is cumbersome due to a number of challenges including source occlusion, high dose gradients, and detector volume averaging. In this study, we attempted to measure PDD and profile for 0.5 × 0.5 and 1×1 cm² using EXTRADIN-W1-SCINTILLATOR for 6x, 6FFF, 10x, and 10FFF photon energies.

Methods: The 1D-Scanner Water Tank by Sun Nuclear was used for PDD measurements. “Low Temperature Thermoplastic Pellets� was used to build a holder for the detector. The ideal characterizations of the W1-scintillator include; water equivalence, linear dose response, dose rate independence, energy independence in MV range and its 1 mm spatial resolution make it optimal for measuring small fields. The detector is paired with the SuperMAX Electrometer to effectively correct for Cherenkov radiation. To verify results of our PDD measurements, Monte Carlo simulation was performed for the same field size and geometry for a voxel size of 1 × 1 × 1 mm³ using EGSnrcMP Monte Carlo (MC).

Results: The measured d_max values using W1-scintillator for field size 0.5×0.5 cm² are 11, 8, 16, and 14 mm and the measured PDD at 10 cm (dd�₀) are 53.7, 47.1, 63.9, 60.6 for the 6x, 6fff, 10x, and 10fff energies respectively. Likewise, for 1 × 1 cm² measured d_max values are 12, 12, 19, and 17 and dd�₀ are 55.9, 52.7, 65.8, 62.3 for the 6x, 6fff, 10x, and 10fff energies respectively. We found a good agreement between our measured and MC simulated PDDs for both d_max and dd�₀ results with the difference less than 1% and 0.5% respectively.

Conclusion: Our results confirm that EXTRADIN-W1-SCINTILLATOR can be used effectively to measure PDDs for small fields.


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