Introduction/Background US imaging due to its limited cost is under intense investigation as base for dose adaptation in cervical cancer brachytherapy. This work test inter/intra-observer uncertainties between MR and TRUS imaging defining maximum tumor width before first BT application in a prospective cohort of cervical cancer patients undergoing IGABT.

Methodology 110 consecutive cervical cancer patients were included. Before first BT implant underwent MR and TRUS scan with no applicator in place. Images were independently analyzed by three examiners, blinded to the other’s results. With clinical information at hand, maximum tumor width was measured on preBT TRUS and MR (figure.1). Quantitative agreement analysis was undertaken. Intra-class correlation coefficient (ICC), Passing-Bablok and Bland Altman plots were used to evaluate the intra/inter-observers agreement.

Results Average difference between HRCTV_MR and HRCTV_TRUS was 1.3±3.2 mm (p<0.001); 1.1±4.6 mm (p=0.01) and 0.7±3 mm (p=0.01). Error was less than 3 mm in 79%, 82% and 80% of the measurements for the three observers, respectively. Intra-observer ICC was 0.96 (CI 95% 0.94–0.97), 0.93 (CI 95% 0.9–0.95) and 0.96 (CI 95% 0.95–0.98) respectively. Inter-observer ICC for HRCTV_MR width measures was 0.92 (CI 95% 0.89–0.94) with no difference among FIGO stages. Inter-observer ICC for HRCTV_TRUS was 0.86 (CI 95% 0.81–0.9). For FIGO stage I/II, ICC HRCTV_TRUS values were comparable to respective HRCTV_MR values. For larger tumors HRCTV_TRUS inter-observer ICC values were lower than respective HRCTV_MR although remaining acceptable (table 1).

Conclusion TRUS is equivalent to MR in assessing preBT tumor maximum width in cervical cancer FIGO stage I/II. In advanced stages TRUS is slightly inferior to MR.

Disclosure Nothing to disclose.

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Abstract EP288 Figure 1