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Measurements of KV XVI CBCT Dose Profiles in Phantom Using Gafchromic XRQA2 Film

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T Giaddui

T Giaddui1*, Y Cui2, J Galvin1, Y Yu1, Y Xiao1, (1) Thomas Jefferson University, Philadelphia, PA, (2) Duke University Medical Center, Durham, NC.

SU-E-I-9 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To measure CBCT dose profiles inside phantom using Gafchromic XRQA2 film.

Methods:Gafchromic XRQA2 film (International Specialty Products, Wayne, NJ) whole sheets were placed between slabs of the IMRT head and torso free point phantom, model 002H9K (Computerized Imaging Reference Systems, Inc, Norfolk, Virginia). Doses were acquired during chest and head imaging protocols of the Volume Imager (XVI) mounted on the Elekta linar accelerator (Elekta, Crawley, UK). Scanned films were analyzed using ImageJ (National Institute of Health, Bethesda, MD).

Results:For the Chest protocol (full trajectory), dose ranged between 1.25 and 2.11 cGy, with average dose of 1.78 cGy. Here, the dose increased over the first 3 cm from the right surface of the phantom, it then leveled off, with average fluctuation of around 5% (within uncertainty level, with the exception of few points where a fluctuation of 24% was observed). Dose eventually started to drop in the left side of the phantom till it reached its lowest value. For the head and neck protocol (trajectory is 200°), dose ranged between 0.02 and 0.13 cGy, with average value of 0.09 cGy. The dose was more or less uniform from the right surface of the phantom till its center (it fluctuated within uncertainty level of 20 to 40% and even higher at some low dose points) and then started to increase from almost the center of the phantom until it reached its highest value near the left surface.

Conclusion:Full trajectory protocol led to uniform dose distribution in the middle part of the phantom and doses were less near surfaces. However, for a protocol with a trajectory of 200° degree, the dose was uniform in one part of the phantom and showed increase in the other part, consistent with the start/stop angle of the gantry. Measured dose fluctuated mostly within uncertainty levels.

Funding Support, Disclosures, and Conflict of Interest: This project is funded, in part, under a grant with the Pennsylvania Department of Health. The Department specifically declaims responsibility for any analyses, interpretations or conclusions

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