Class solution development and imaging considerations for spinal SABR

Abstract

Background: Stereotactic Ablative Body Radiotherapy (SABR) is a recent but rapidly emerging treatment option for both malignant and benign spine tumours. The principle behind the use of SABR, is to treat target volumes with high radiation doses and steep dose gradients, which help to achieve highly conformal dose distributions and spare healthy tissue. Objectives: The primary aim of this research project is to develop a SABR class solution for patients with spinal tumours. This class solution has to meet all the constraints and objectives as de ned by the clinical protocol. A second part of the project deals with the suitability of the Clinical Target Volume (CTV) to Planning Target Volume (PTV) margin and immobilisation techniques. These will be assessed through an audit of previously treated SABR patients. Research Design: Both parts of this project can be considered to be retrospective studies since they involved scans of patients which had been treated in the past. A comparative evaluation and an iterative optimisation research strategy were used for the development of the SABR class solution. For the second part of the project, a comparative evaluation approach was used to analyse intra-fractional motion in SABR patients. Results and Conclusions: A double arc VMAT SABR class solution was developed which successfully met the requirements de ned by the clinical protocol. Special attention was given to optimising target coverage, sparing organs at risk, and reducing the number of Monitor Units used throughout the treatment. The suitability of the CTV to PTV margin was also assessed. It was recommended that a margin of 3 mm is used. Furthermore, it was advised that a 6 degree-offreedom couch is used when treating spinal SABR patients.