Target volume definition for upper abdominal irradiation using CT scans obtained during inhale and exhale phases

Purpose: To evaluate the clinical utility of a treatment-planning technique involving the use of CT images obtained during both the static exhalation phase and static inhalation phase (two-phase planning). Methods and Materials: Ten patients with pancreatic or liver tumors underwe nt CT scanning under static exhale and inhale conditions, after a period of mild ventilation. By setting image positions differently, we were able to treat the two-phase images as one dataset, Each gross tumor volume (GTV) wa s contoured separately and the mixed GTV was used for the two-phase treatme nt planning. Treatment plans were constructed to compare the two-phase plan s with the plans constructed using static exhalation images, The shift of t he center of the GTV and kidneys and the minimum dose of GTV were then calc ulated, Results: The shift of the GTV ranged from 2.6 to 27.3 mm and that of the ki dneys from 2.2 to 24 mm, In some patients whose treatment was planned using exhalation planning, the minimum dose of GTV at inhalation was less than 9 0% of the isocenter dose. Conclusion: Two-phase planning is a simple technique that can visualize tum or and organ movement simultaneously using CT. It further defines adequate field margins around the tumor and prevents unexpected radiation exposure t o critical organs. Routine use of this technique for upper abdominal irradi ation is recommended. (C) 2000 Elsevier Science Inc.