Identifying predictors for late toxicity following stereotactic body radiotherapy for localised prostate cancer
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Embargo End Date
2027-01-27
ICR Authors
Authors
Ratnakumaran, R
Document Type
Thesis or Dissertation
Date
2026-01-27
Date Accepted
Abstract
Stereotactic body radiotherapy (SBRT) is emerging as a standard-of-care option for localised prostate cancer. However, concerns remain regarding treatment-related toxicity, particularly urinary side-effects. This thesis utilises data from the PACE studies to identify predictors for toxicity following prostate SBRT. The relationship between acute and late toxicity was first examined in PACE-B, in those treated with SBRT and conventional or moderately hypofractionated radiotherapy (CRT/MHRT). Using multivariable logistic regression, grade ≥2 acute urinary and bowel toxicity were shown to be strongly associated with subsequent grade ≥2 late urinary and bowel toxicity in both treatment arms. Next, a novel surrogate urethral model (SUM) was developed and trained using MRI-delineated urethras (MDU) onto CT planning scans, with the aim to facilitate dose–toxicity modelling. Despite geometric differences between SUM and ‘true’ MDU, urethral dose–volume parameters were similar, with no clinical significant difference. Toxicity modelling was performed to identify predictors for late urinary toxicity in the PACE-B SBRT cohort. No association was observed between dose to urinary substructures and late urinary toxicity; however, higher baseline urinary symptom scores and baseline urinary medication use were independently predictive for CTCAE grade ≥2 urinary toxicity at two years .Further modelling was performed to identify predictors of late sexual dysfunction. Among SBRT patients with good baseline erectile function, higher crura Dmax and D2% were associated with a minimal clinically important decline in EPIC-26 sexual function at 12 months, with new dose constraints suggested. Next, to investigate the differences in toxicity observed between SBRT platforms, planning dosimetry was compared between CyberKnife (CK) and conventional linac-based SBRT. Interestingly, despite lower urinary toxicity, CK-SBRT planning dose to urinary substructures was higher. Finally, Two-year late toxicity outcomes from PACE-C, comparing SBRT with MHRT in higher-risk patients were analysed, showing worse urinary side-effects with SBRT, but no difference in bowel side-effects.
Citation
2026
DOI
Source Title
Publisher
Institute of Cancer Research (University Of London)
ISSN
eISSN
Collections
Research Team
Clinic Acad RT Huddart