| dc.description.abstract | A set-up error is defined as any deviation between the predetermined and actual treatment positions, and is
determined by measuring the displacement of the treatment field position by comparing the treatment image to its
reference image. Dose distribution in the target volume is dependent on setup margins. It is important to assess the
setup errors for each radiotherapy unit to reduce the treatment errors. The aim of this study was to evaluate the
systematic and random setup errors using electronic portal imaging device (EPID) for pelvic tumour patients
treated by 3D-CRT (conformal radiotherapy) and also to assess set-up margin. 115 pelvic tumour patients were
included in this study in which 1150 portal images were assessed. The displacements between DRR (digitally
reconstructed radiograph) and the portal images were measured in the direction of right to lateral, superior to
inferior in anterior images by matching rigid bony landmarks. Moreover, the displacements between anterior to
posterior and superior to inferior were measured in lateral images. The estimated systematic errors were 0.242,
0.255 cm in right to lateral and superior to inferior direction in anterior images, and 0.227, 0.220 cm in anterior
to posterior and superior to inferior in lateral images. The estimated random errors were 0.404, 0.367 cm in right
to lateral and superior to inferior in anterior images, 0.313, 0.337 cm in anterior to posterior and superior to
inferior in lateral images. The determined margins for CTV to PTV based on ICRU were 0.4711, 0.4465, 0.3870,
0.4026 cm in the order of the above mentioned directions. A 0.5 cm safety margin is suggested for all pelvic tumour
patients treated with 3D-CRT in Varian 2300CD linear accelerator unit, Apeksha Hospital, Maharagama. | en_US |
