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Title: Dosimetric investigation of image-guided radiotherapy for prostate cancer using cone-beam computed tomography
Author: Ariyaratne, Hemal
ISNI:       0000 0004 7231 2716
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2018
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Objectives: 1. To survey the current practice of image-guided radiotherapy (IGRT) for prostate cancer in the United Kingdom. 2. To validate a practical dose calculation strategy on cone-beam computed tomography (CBCT) 3. To assess the effect of CBCT verification imaging frequency on actual dose delivered to target volume and organs at risk during a course of image-guided radiotherapy for prostate cancer. 4. To compare the dosimetric effects of reduction of CTV-PTV margin with daily imaging. / Material and Methods: 59 radiotherapy centres in the United Kingdom were included in an online survey of IGRT practice. The survey covered details of verification strategy during prostate radiotherapy, with specific questions on imaging frequency. A validation study of the CBCT dose calculation strategy was evaluated on 37 fractions using Bland-Altman plots. The study technique was compared to the density-override technique. A pilot comparison of CTV coverage with bone matching to soft tissue matching was performed. For the principal dosimetric analysis, 844 cone-beam CT (CBCT) images from 20 patients undergoing radical prostate radiotherapy were included. Patients received a dose of 74 Gy in 37 fractions using 7-field intensity-modulated radiotherapy. Target volume and organs at risk were contoured manually on each CBCT image. A daily online CBCT verification schedule was compared with a protocol of day 1-3 followed by weekly imaging. 3 mm, 5 mm, and 7 mm CTV-PTV margins were compared for daily imaging. / Results: CBCT is the principal verification imaging modality in the UK for prostate cancer, used by 66% of centres. There is no consensus on optimal imaging schedule, with 2 main strategies used. These are the daily online schedule and the day 1-3 followed by weekly schedule. Use of CBCT contours on planning CT showed good agreement with the density-override technique, provided multifield IMRT was used. There were clear drops in target coverage if a bone match strategy was used in comparison to soft tissue matching. 90% of patients had improved target coverage with daily online in comparison to weekly online soft tissue match. A median of 37 fractions achieved CTV coverage with daily imaging compared with 34 fractions with a weekly online protocol. 80% of patients had a reduction in rectal dose with the daily protocol. Margin reduction to 5 mm with adequate target coverage was feasible with daily imaging. / Conclusions: Daily online CBCT verification improves CTV coverage and reduces rectal dose during IGRT for prostate cancer. Daily CBCT imaging allows reduction of CTV-PTV margin for radiotherapy.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available