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Feasibility of Using Quantitative Cone Beam CT for Proton Adaptive Planning

W Jingqian

W Jingqian1*, T Tsui2 , J Wei3 , Q Wang1 , X Zhang1 , Z Wen1 , X Zhu1 , S Frank1 , H Li1 , L Zhu2 , (1) UT MD Anderson Cancer Center, Houston, TX, (2) Georgia Institute of Technology, Atlanta, GA,(3) Landauer Medical Physics , Newnan, GA


SU-E-J-135 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

To investigate the feasibility of using scatter corrected cone beam CT (CBCT) for proton adaptive planning.
Phantom study was used to evaluate the CT number difference between the planning CT (pCT), quantitative CBCT (qCBCT) with scatter correction and calibrated Hounsfield units using adaptive scatter kernel superposition (ASKS) technique, and raw CBCT (rCBCT). After confirming the CT number accuracy, prostate patients, each with a pCT and several sets of weekly CBCT, were investigated for this study. Spot scanning proton treatment plans were independently generated on pCT, qCBCT and rCBCT. The treatment plans were then recalculated on all images. Dose-volume-histogram (DVH) parameters and gamma analysis were used to compare between dose distributions.
Phantom study suggested that Hounsfield unit accuracy for different materials are within 20 HU for qCBCT and over 250 HU for rCBCT. For prostate patients, proton dose could be calculated accurately on qCBCT but not on rCBCT. When the original plan was recalculated on qCBCT, tumor coverage was maintained when anatomy was consistent with pCT. However, large dose variance was observed when patient anatomy change. Adaptive plan using qCBCT was able to recover tumor coverage and reduce dose to normal tissue.
It is feasible to use quantitative CBCT (qCBCT) with scatter correction and calibrated Hounsfield units for proton dose calculation and adaptive planning in proton therapy.

Funding Support, Disclosures, and Conflict of Interest: Partly supported by Varian Medical Systems

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