In vivo dosimetry in the treatment of localised pelvic malignancies with brachytherapy and stereotactic ablative radiotherapy

Clinical outcomes and the effect of inter-fraction OAR movement were analysed as part of the SPORT prostate SABR trial and an exploratory analysis of citrulline was performed.<br><br>Results<br>Outcomes following brachytherapy at the NICC were in keeping with international practice. The dosimetric effect of potential OAR movement between planning and treatment was greatest for the urethra in LDR prostate brachytherapy and for the rectum in HDR cervical brachytherapy.

Patients with higher risk tumour characteristics treated with LDR prostate brachytherapy demonstrated statistically significantly greater biochemical recurrence rates. Rates of freedom from biochemical/clinical failure (BCF) were lowest when the dominant intraprostatic lesion (DIL) was located in the anterior base and highest when the DIL was located in the posterior midgland, with a statistically significant increase in freedom from BCF when the DIL sector D90 was > 110%.

Analysis of the SPORT SABR trial demonstrated feasibility with acceptable toxicity. The positions of OARs at pre-fraction CBCT correlated better with gastrointestinal toxicities than at planning CT. Correlations of citrulline levels with late bowel toxicity suggested its potential as a predictive biomarker.<br><br>Conclusions<br>In vivo dosimetry has the potential to detect dosimetric discrepancies from the radiotherapy plan as a result of OAR movement during radiotherapy delivery.

It would be particularly beneficial in the detection of deviations in rectal dose during HDR cervical brachytherapy and prostate SABR, and deviations in urethral dose during LDR prostate brachytherapy.<br><br><i>Thesis is embargoed until 31 December 2026.</i>