ESTRO 2022 - Abstract Book

S1090

Abstract book

ESTRO 2022

B. Stewart-Thomson 1

1 The Clatterbridge Cancer Centre, Physics, Liverpool, United Kingdom

Purpose or Objective This study will investigate whether patients with a middle or lower-third oesophageal tumour will benefit from lower organ at risk (OAR) doses with a 4D-CT planning scan compared with a 3D-CT planning scan. The SCOPE studies have previously highlighted the benefits of a 4D-CT for patients with conformal treatment plans. This study aims to determine if this benefit extends to middle-third oesophageal patients and, whether there is an additional benefit with using a more precise planning method of intensity-modulated radiotherapy (IMRT) such as volumetric modulated arc therapy (VMAT). Materials and Methods At our centre, 3D scans are acquired during free-breathing, without any monitoring of a patients breathing cycle. A 4D scan requires a regular breathing cycle, which is monitored prior to scan acquisition to determine the patient’s suitability; this ensures the patient is able to take regular, consistent breaths for the duration of treatment delivery. Patients included in this study had previously been dual-scanned in 3D and 4D and clinical plans were created using the 4D-CT scan, taking breathing motion into account. At our centre, 4D-CT patients are treated with a reduced PTV margin (0.5cm vs 1.0cm for 3D-CT). For this study, the 3D and 4D datasets were anonymised, and the 3D scan was contoured by one of three clinicians, the 4D scan having been contoured previously. New treatment plans were created retrospectively for the 3D and 4D scans separately which allowed dosimetric comparison of OAR doses and target volumes. Results Analysis of the results shows there is a dosimetric benefit to planning with 4D-CT scans for both middle and lower-third oesophagus patients with significant reductions in heart, lung and spinal canal doses – as shown in table 1. In addition to this, there is a reduction in overall target volume size using a 4D-CT – as shown in table 2. Further research is required with a larger sample size to determine if these results can be replicated. table 1

table 2

Conclusion There is a statistically significant benefit for patients with a middle or lower third oesophageal tumour to have a 4D-CT acquired for radiotherapy planning to reduce PTV volume and OAR doses. This study has shown the dosimetric benefit of reducing OAR doses using VMAT with the acquisition of a 4D-CT compared with a 3D-CT. This research has been expanded