Evaluation of the setup errors in patients with head and neck cancer (HNC) in external radiation therapy with electronic portal imaging device (EPID)

Background: Nowadays, radiotherapy is one of the most important methods in cancer treatment. One of the most important in radiotherapy process is treatment verification. The main objective of this study was to determine the setup errors in patients with head and neck cancer (HNC) in external radiation therapy with an in-room electronic portal imaging device (EPID).Methods: 20 patients with (HNC) were investigated in this study. Simulation process was carried out with thermoplastic mask for individual patients. Three radio-opaque markers were implanted on the surface of the masks. CT simulation with 120 kV, 130 mAs and 3 mm slice thickness was performed. Every patient was planned individually with Prowess treatment planning system to deliver sufficient dose to the tumor and less dose to the normal organs. Portal images were acquiring by using an in-room EPID device. All images were acquiring with 6 MV photon beam with 2 monitor units (MU) at the first, 6th and 11th day of the treatment session. Portal images were compared with reference images (digitally reconstructed radiograph-DRR).Results: A total of 60 images were gathered acquired during first three weeks of treatment session for 20 HNC patients. The mean displacement in the x, y and z directions were 1.1 mm (ranged from -4.5 to +6.7 mm), 0.9 mm (ranged from -2.1 to 5.1 mm) and 1.3 mm (ranged from -2.0 to +5.8 mm), respectively. 85, 95 and 90 percent of displacements were within 5 mm in x, y and z directions, respectively.Conclusion: The EPID technique was effective for evaluation of patient s setup errors during the treatment sessions.

Evaluation of the setup errors in patients with head and neck cancer (HNC) in external radiation therapy with electronic portal imaging device (EPID) Keywords:

Setup errors , Head and neck cancer , Radiotherapy , EPID technique