MR guided adaptive radiotherapy for gynaecological cancer

Abstract

Introduction The gold standard treatment for locally advanced cervical cancer is concurrent chemo radiotherapy followed by image guided brachytherapy. This has led to improved survival outcomes; however, rates of long term toxicity remain high. There is evidence that the cervix and uterus can move during external beam radiotherapy, exceeding the CTV (clinical target volume) to PTV (planning target volume) margin in many patients. Aim The overall aim of the project is to assess causes and implications of target motion in cervix cancer to support the development of novel image guided radiotherapy. Method Chapters 1 to 3 are based on a retrospective cohort of patients who received external beam radiotherapy for cervical cancer, with scans at 3 time-points. The central sagittal slice is used to estimate motion at the uterine fundus. The correlation between motion and clinical outcomes is assessed. The cause of motion at the uterine fundus and cervix was also assessed qualitatively. Chapter 4 describes and quantifies intrafraction motion and is based on data from a prospective MR imaging study, with 10 patients who underwent 4 MR scans during radiotherapy. Axial sequences every two minutes for 10 minutes were contoured and the distance to agreement (DTA) calculated. Chapter 5 is an assessment of outcomes of a retrospective cohort of patients who received moderately hypofractionated palliative external beam radiotherapy for gynaecological cancer, a patient group that could be potentially the first cervix treatments on the MR-linac in our institution. Results A novel methodology to estimate motion of the uterine fundus was developed, and mean motion found to be greater that the CTV to PTV margin. There was no association between motion at the fundus and overall survival, progression free survival and toxicity, suggesting that fields could be shortened without detrimental effects. Interfraction motion at the uterine cervix was usually related to rectal changes or tumour shrinkage, motion at the uterine fundus is often related to bladder filling but rectal and small bowel changes as well as tumour shrinkage were also important causes. Intrafraction motion was mainly related to bladder filling at both the uterine fundus and cervix but rectal changes also led to cervix motion. The mean max DTA was 0.5cm, however the site of maximum motion varied between fractions. Moderately hypofractionated radiotherapy was found to be an effective palliative treatment for patients with gynaecological malignancies. Conclusions The work presented in this thesis has provided a rationale for novel adaptive radiotherapy techniques, as the current approaches are based on bladder filling changes, which does not address the causes of motion at the cervix. Palliative treatment is a sensible initial step to develop MR guided external beam radiotherapy

Date of Award	31 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Alan Mcwilliam (Supervisor), Peter Hoskin (Supervisor), Ananya Choudhury (Supervisor) & Marcel Van Herk (Supervisor)