The Effect of CT Dose Reduction on Proton Therapy Dose Calculation

In adaptive proton therapy, a CT scan is acquired in each treatment session to enable detection of and correction for changes in the anatomy which would otherwise cause significant changes to the dose distribution. This CT is not used to delineate lesions or tissues at risk, it is only used to compute proton stopping powers for dose calculations. Because a treatment typically involves 30 to 40 treatment sessions, the total dose associated with these CT-scans is significant, in particular, if 4D CT is used to account for breathing effects. We hypothesized that the signal-to-noise ratio provided by conventional CT protocols is higher than needed for this application. To verify this hypothesis and enable a patient dependent reduction of the CT dose, a CT dose reduction simulation tool is developed to simulate lower-dose CT scans from an existing standard-dose scan. The simulated lower-dose scans are then used for treatment planning and the results are compared with that of the standard dose scan. The preliminary results show that the dose reduction by a factor up to 10 does not have a significant effect on proton dose distribution.

Publication year:2020

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