Measurement of Radiotherapy Setup Errors in IMRT and VMAT - Treated Head and Neck Cancer Patients on a Ring - Based LINAC

Abstract

Objective: Our study aimed quantify the magnitude of setup errors in intensity - modulated radiotherapy (IMRT) and Volumetric Arc therapy treated Head and Neck cancer patients and recommend appropriate PTV margin. Materials and Methods: 65 patients with head and neck cancer at Father Muller Medical College who underwent radical or postoperative radiotherapy with bilateral neck irradiation were planned and treated with IMRT or VMAT technique. All Patients underwent image - guided radiotherapy (IGRT) with daily cone beam computed tomography (CBCT). The 3D displacements, systematic and random errors were calculated and PTV expansion was determined using Van Herk’s formula. Results: Mean 3D displacement was 0.219 cm in the vertical direction, 0.215 cm in the horizontal direction and 0.218 cm in the longitudinal direction. Conclusion: Daily CBCT allows the planning target volume (PTV) expansion to be reduced. The newly derived clinical target volume (CTV) - PTV margin for our linear accelerator is 0.219 cm, 0.215 cm, and 0.218 cm in the vertical, horizontal and longitudinal directions, respectively.