VARIABILITY OF TARGET VOLUME DELINEATION IN CERVICAL ESOPHAGEAL CANCER

Purpose: Three-dimensional (3D) conformal radiation therapy (CRT) assu mes and requires the precise delineation of the target volume. To asse ss the consistency of target volume delineation by radiation oncologis ts, who treat esophageal cancers, we have performed a transCanada surv ey. Materials and Methods: One of three case presentations, including CT scan images, of different stages of cervical esophageal cancer was randomly chosen and sent by mail. Respondents were asked to fill in qu estionnaires regarding treatment techniques and to outline boost targe t volumes for the primary tumor on CT scans, using ICRU-50 definitions . Results: Of 58 radiation oncologists who agreed to participate, 48 ( 83%) responded. The external beam techniques used were mostly anterior -posterior fields, followed by a multifield boost technique. Brachythe rapy was employed by 21% of the oncologists, and concurrent chemothera py by 88%. For a given case, and the three volumes defined by ICRU-50 (i.e., gross tumor volume [GTV], clinical target volume [CTV], and pla nning target volume [PTV]) we determined: 1. The total length in the c ranio-caudal dimension; 2. the mean diameter in the transverse slice t hat was located in a CT slice that was common to all participants; 3. the total volume for each ICRU volume; and 4. the (5, 95) percentiles for each parameter. The PTV showed a mean length of 14.4 (9.6, 18.0) c m for Case A, 9.4 (5.0, 15.0) cm for Case B, 11.8 (6.0, 16.0) cm for C ase C, a mean diameter of 6.4 (5.0, 9.4) cm for Case A, 4.4 (0.0, 7.3) cm for Case B, 5.2 (3.9, 7.3) cm for Case C, and a mean volume of 320 (167, 840) cm(3) for Case A and 176 (60, 362) cm3 for Case C. The res ults indicate variability factors (95 percentile divided by 5 percenti le values) in target diameters of 1.5 to 2.6, and in target lengths of 1.9 to 5.0. Conclusion: There was a substantial inconsistency in defi ning the planning target volume, both transversely and longitudinally, among radiation oncologists. The potential benefits of 3D treatment p lanning with high-precision dose delivery could be offset by this inco nsistency in target-volume delineation by radiation oncologists. This may be particularly important for multicenter clinical trials, for whi ch quality assurance of this step will be essential to the interpretat ion of results. (C) 1998 Elsevier Science Inc.