Geometric shifting of the porta hepatis during posthepatectomy radiotherapy for biliary tract cancer.

Purpose: To evaluate geometric shifting of the porta hepatis induced by liver regeneration during radiotherapy (RT) after partial hepatectomy for biliary tract cancer.
Methods and Materials: Between August 2004 and August 2005, the study enrolled 10 biliary tract cancer patients who underwent hemihepatectomy or more extensive surgery and were scheduled to receive postoperative RT. All patients received 4500 cGy RT in 25 fractions with concurrent 5-fluorouracil. Before RT and in the third and fifth weeks during RT, the liver volume was determined using CT, and geometric location of the porta hepatis was determined using a conventional simulator.
Results: The liver volume increase during RT was 246.6 +/- 118.2 cm(3). The overall actual shifting length of the porta hepatis was 9.8 +/- 2.5 mm, with right and left hepatectomy causing a 10.1 +/- 1.7 mm shift to the right or 9.2 +/- 4.3 mm shift to the left, respectively. The actual shifting length of the porta hepatis was proportional to the increase in liver volume during RT (r = 0.742, p = 0.014).
Conclusion: The results of this study have demonstrated that the porta hepatis can be shifted by liver regeneration after partial hepatectomy. We recommend an additional RT margin or adaptive RT (repeat planning at several intervals during the treatment course) to avoid exclusion of the porta hepatis from the RT target volume after partial hepatectomy for biliary tract cancer.