Verification of patient set-ups using the electronic portal imaging system

Abstract

While set-up uncertainties in patient positioning may result in inadequate treatment of the tumor, increasing the likelihood of local tumor recurrence, some non-target tissues may be over-irradiated. Random and systematic set-up errors were investigated using DRR (Digitally Reconstructed Radiograph) images of the plans of 15 lung, 21 head-neck, 10 pancreatic, 15 breast, 4 stomach and 33 pelvic region cancer patients treated with three-dimensional conformal radiotherapy technique in our clinic. The highest systematic set-up error was 5.29 mm medial-lateral in lung cancer patients, cranio-caudal with 5.53 mm in patients with head and neck cancer, medial-lateral with 4.22 mm in patients with gastric cancer, and medial-lateral with 6.20 mm in patients with pancreatic cancer. in the anterior-posterior direction with 5.02 mm in regional cancers and 7.0 mm in the anterior-posterior direction in breast cancer patients. The highest random set-up error was medial-lateral with 5.98 mm in lung cancer patients, anterior-posterior with 9.05 mm in patients with head and neck cancer, medial-lateral with 4.52 mm in patients with gastric cancer, and 6.00 mm in cranio-caudal and pelvic in patients with pancreatic cancer. It was in the cranio-caudal direction with 9.79 mm in regional cancers and in the cranio-caudal direction with 5.96 mm in breast cancer patients. Clinically, pre-treatment and weekly electronic portal imaging were found to be sufficient to control treatment area accuracy in all cancer cases.