Objective: The aim was to evaluate the parameters that influence the incidental presence of whole liver detected by simulation computed tomography (simCT) while irradiation in breast cancer patients and to evaluate the factors predicting the presence of the liver in simCT scanning and defining the inferior border in simCT.
Subjects and methods: We analyzed simCT radiotherapy (RT) planning images of 327 patients with breast cancer. During the evaluation, whether the entire liver was included in the simCT scanning and the level of the vertebra where the inferior border of the simCT scan passed were investigated. Left (L) and right (R) lung, L and R breast, and heart volume were recorded so that they would reflect the internal volume of the thorax. From the simCT images, anteroposterior (A-P) distance at the jugular notch level, A-P and R-L lateral distances at manubriosternal joint alignment, A-P and R-L lateral distances at xiphisternal joint alignment were measured. The predictive value of these measurements and volumes on whether the liver was present in simCT were determined by receiver operating characteristic (ROC) curve analysis.
Results: The liver was included in 72 (22%) out of 327 simCT scans. ROC analysis was applied to the whole group; bilateral lung volume (P < 0.001), bilateral lung + heart volume (P < 0.001), xiphisternal angle R-L lateral distance (P = 0.009), manubriosternal angle A-P distance (P = 0.49), R breast volume (P = 0.007), and L breast volume (P < 0.001) were associated with the visualization of liver. A total of 37 of 72 patients, whose inferior level of the simCT sections passed below L1, had entire liver visualization. The cutoff value of xiphisternal joint R-L lateral distance was found as 31.55 cm, and its sensitivity and specificity were calculated as 81%, and 60%, respectively.
Conclusion: Through R-L lateral measurement taken from the midaxillary line at the level of the xiphisternal joint, we showed that liver would be present in simCT with a sensitivity of 81% at L1 level in those 31.55 cm and above.
Keywords: Breast cancer; liver; radiation therapy; radiation-induced liver toxicity.