VERIFYING THE POSITIONING OF THE MANTLE FIELDS BY ON-LINE PORTAL IMAGING SYSTEM

On-line imaging system was used to verify patients positioning during mantle field irradiation. A total of 65 portal images was evaluated. Daily reproducibility and global accuracy of the treatment were studied separately. Only small day-to-day variations were found with the mean value less than 3 mm. The SD is 1.88 mm for craniocaudal and 1.85 mm for lateral deviations. Deviations more than 5 mm was seen 7% for craniocaudal, 11.5% for lateral movement. It implies that treatment reproducibility is achieved successfully. However in the assessment of global accuracy, deviations more than 5 mm was found to be 20% for craniocaudal, 18% for lateral movement. The SD of global accuracy is 2.93 mm for craniocaudal and 2.96 mm for lateral deviations. This large deviations is caused by the contribution of technical factors such as block construction, block fixation.