| dc.description.abstract | The accuracy in radiotherapy is very important since it is irreversible treatment and it
partially depends on patient’s set up on each fraction of treatment. Developing unique
margins by assessing set up errors will provide better treatment. The aim of this study
was to evaluate set up errors in three-dimensional conformal radiation therapy for head
and neck region using an electronic portal imaging device and to de ne the Clinical
Target Volume (CTV) to Planning Target Volume (PTV) margin in Varian 2300CD unit
at Apeksha Hospital, Maharagama, Sri Lanka. Head and neck patients (n=101) immobilized
with thermoplastic masks and data were collected from July 2021 to July 2022
for this study. Transitional errors of all directions were collected using 303 pairs of
orthogonal portal images to calculate systematic errors and random errors. The margins
for CTV to PTV were calculated using three di erent margins recipes. The calculated
population systematic and random errors for the Anteroposterior (AP), Superioinferior
(SI) and Mediolateral (ML) directions are 0.13 cm, 0.1 cm, 0.08 cm and 0.22 cm, 0.21 cm,
0.19 cm respectively. All the margins were calculated from the three recipes are less
than 0.5 cm. Therefore, this study shows that 0.5 cm margin is safe for head and neck
patients who receive treatment from Varian 2300CD unit at Apeksha Hospital. This
study recommends to maintain their own CTV to PTV margins by institute to minimize
unnecessary radiation dose for surrounding tissues and organs at risk (OARs). In addition,
the e ectiveness of the immobilization devices should be analyzed during the treatment. | en_US |
