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Towards CT Based Dose Calculation for Proton Beam Therapy of Ocular Melanoma: Calibration of a Serial Small Volume High Resolution CT Protocol to Match An Existing Proton Beam TPS Calibration Curve Combined with Atlas Based CT Artifact Reduction Method

M Mamalui*, R Dagan , M Rutenberg , Z Li , University of Florida/Radiation Oncology, Jacksonville, FL


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Ocular melanoma proton beam dose calculation is usually based on an ellipsoidal phantom like model and pencil beam approach. Patients have 3-4tantalum clips implanted around tumor. For the precision required in patient positioning and planning, a high resolution serial CT, not calibrated for proton dose calculation, is acquired in our institution. To use CT-based dose calculation, issue of large volume of target area occupied by tantalum artifact must corrected. Also, to calculate proton dose, we need another CT, using regular helical calibrated protocol that does not allow for precision localization of the clips. This work aims to design a simple method of correcting for the artifact caused by tantalum clips that does not involve acquiring another CT scan.

Methods: 10paired regular resolution helical CT protocol scans and serial high resolution ocular CT scans were segmented and the HUs analyzed to find an analytical dependence between the same structures in paired scans. This analytical dependence was used to ‘recalibrate’ high resolution CT HU numbers to match our stopping power vs HU calibration curve used for a regular proton dose calculation. Then, atlas of 16synthetic regular protocol CTs with varying ocular structure sizes were created using averaging of the existing CT scans. In-house program(MatlabTM) selects closest-candidate regular protocol CT from the atlas, based on the target patient’s ocular measurements. The program automatically identifies the areas of the ocular scan affected by artifact and replaces HUs with the numbers in the identified CT match.

Results: We ‘recalibrate’ serial high resolution ocular CT scan to match a regular protocol helical CT protocol, calibrated for proton dose calculation; atlas-based artifact reduction method allows using high resolution ocular patient CT for proton dose planning.

Conclusion: A simple method is designed to prepare specialized ocular protocol CT scan for proton dose calculation for ocular melanoma treatment.


Not Applicable / None Entered.


TH- External Beam- Particle therapy: Proton therapy - treatment planning/virtual clinical studies

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