Abstract

The feasibility of soft-tissue matching in cone-beam computed tomography (CBCT) guidance for liver cancer patients is investigated and its equivalence to fiducial-marker matching on determining patient setup corrections has been studied. On the Elekta Synergy machine, daily CBCT volumetric images were acquired after setup with silver rings (SRs) in liver. The SRs were served as fiducial markers in our study. The CBCT images without SRs in liver were then obtained by digitally removing the SRs in each projection image using photoshop CS4.Considering fiducial-marker matching as a standard, the patient setup errors were compared between two two matching methods. A total of 90 datasets of volumetric images for 10 patients were used in the comparison. Pearson coefficient of correlation for the setup errors was as follows: R² = 0.718, 0.724, 0.785 in the LR, AP and SI directions, respectively. A Bland-Altman analysis showed no significant trends. The percentage of errors within a ±3 mm tolerance was respectively 95.56%, 95.83%, 91.11%. The p-value (paired permutation test) are respectively 0.1217, 0.919 and 0.7685 in the three cardinal directions and are all greater than 0.05. So, the null hypothesis cannot be refused, that is to say. Two methods have no significant difference. CBCT guidance using soft-tissue is an equivalent method for on-line image-guided radiotherapy for liver-cancer patients when compared to CBCT guidance using fiducial markers. It is feasible to implement CBCT image guidance using soft-tissue matching method clinically.

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