Target delineation error assessment for patients treated to the larynx with VMAT : a quantitative study performed at a local Maltese radiotherapy department

Abstract

Introduction: Target volume delineation error (Σdelin) affects the accuracy of radiation therapy, but it is often not incorporated in studies measuring the Planning Target Volume (PTV) margin. The aim of this study was to assess the impact of Σdelin on the PTV margin for patients receiving treatment with Volumetric-Modulated Arc Therapy (VMAT) to the larynx in a radiotherapy department.

Methods: Six clinical oncologists were asked to delineate the Clinical Target Volume (CTV) of five patients receiving treatment to the larynx with VMAT. Van Herk’s formula was used to measure the PTV margin based on target volume delineation error. All data were collected and analysed to measure the Σdelin and the PTV margin.

Results: The PTV margin based on Σdelin was 5.6 mm, 11.1 mm, and 4.5 mm, in the left-right (X), superior-inferior (Y) and anterior-posterior (Z) directions respectively. The standard deviation (SD) in the X and Z direction was 3.47 mm, and the SD in the Y direction was 6.92 mm.

Conclusion: The PTV margin calculated based on the evaluation of Σdelin was considerably larger than the margin currently used (5mm). If the resulting margin was implemented it would increase radiation induced side-effects.