Improving tumour target coverage in spine stereotactic radiotherapy
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Embargo End Date
ICR Authors
Authors
Page, S
Document Type
Thesis or Dissertation
Date
2024-01-16
Date Accepted
Abstract
Spine stereotactic body radiotherapy (SBRT) has high rates of local control. Local
control failure rates are higher in cases with epidural disease and radioresistant
histologies. A limiting factor is the proximity of the spinal cord and the competing risk
of radiation myelitis. The overlap of the target and spinal cord planning margins is
often a deciding factor in target coverage and epidural dose. The aim of this thesis
was to develop solutions to improve target coverage in spine SBRT.
Chapter 2-4 were designed as a step-wise approach to developing spine SBRT on the
MR-linac platform for the purposes of utilising adaptive radiotherapy to improve target
coverage. Chapter 2 developed an imaging protocol with observer analysis of image
structure clarity relevant to spine SBRT. Chapter 3 explored the capabilities of the
platform and software to generate spine SBRT radiotherapy plans of equal quality and
matching clinical goals compared to CyberKnife (Accuray, Sunnyvale), the current
radiotherapy platform used at RMH. Chapter 4 simulated an online adaptive MR-linac
workflow to show that standard spine SBRT workflows exceed the reported dose to
the spinal cord by up to 27% in up to 80% of cases. Adaptive MR-linac workflows
achieved small gains in PTV coverage we seen in a 3/5 of cases.
Chapter 5 and 6 looked at positioning patients for CyberKnife based treatments in the
prone setup to improve target coverage in posteriorly based vertebral tumours. 15
cases were retrospectively replanned in Chapter 5 to identify patient anatomical
factors to guide a prospective study in chapter 6. The incomplete study was unable to
show a benefit from prone treatment to improve PTV coverage to allow
recommendations for clinical adoption.
Chapter 7 utilised data from prior chapters to calculate spine planning risk volume
(PRV) margins around the spinal cord. Reduced margins are expected to reduce the
overlap of target and spinal cord planning volumes and improve coverage. A 1.75mm
MR-linac spine PRV was recommended which is a reduction on current RMH margins
and importantly was a markedly smaller margin than other standard radiotherapy
platforms. A smaller CyberKnife supine PRV margin was achieved but in the prone
position a smaller margin could not be recommended.
Citation
2024
DOI
Source Title
Publisher
Institute of Cancer Research (University Of London)
ISSN
eISSN
Collections
Research Team
Lung Radiotherapy