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Title: The effective application of dynamic arc radiotherapy
Author: Boylan, Christopher James
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2013
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Volumetric modulated arc therapy (VMAT) is a technique for the delivery of intensity modulated radiotherapy (IMRT) whereby the linear accelerator (linac) delivers dose continuously while rotating around the patient. VMAT has gained attention due to its ability to produce complex dose distributions, deliverable in a much shorter treatment time than IMRT. The purpose of this thesis was to investigate the clinical application of VMAT, and to identify any benefits over IMRT in the areas of treatment planning, delivery, and imaging. A VMAT planning strategy was developed which demonstrates that complex dynamic arc deliveries can be sequenced from static, IMRT-based control points. For prostate patients, the VMAT solution demonstrated superior sparing of critical structures compared to IMRT plans. A further comparison of VMAT and IMRT was performed with the development of an automated planning methodology, which aimed to reduce the impact of planner bias. Applied over a series of nasopharynx patients, the technique showed that VMAT achieved an improvement in parotid sparing compared to IMRT.To investigate the limitations on the delivery of VMAT plans, a software emulator was produced to accurately simulate linac motion. The emulator was used to determine 'ideal' linac parameters for a range of VMAT plans. Leaf speed was found to be a limiting factor for the achievable plan complexity, along with the availability of continuous variable dose rate (CVDR). For a commercial CVDR system, experiments confirmed the improved delivery efficiency, and an improvement in dosimetric accuracy compared to the binned dose rate (BDR) system.An independent dose calculation methodology was developed for VMAT, such that accurate pre-treatment plan QC can be performed. It was found that the accuracy of a Monte Carlo simulation was improved when accounting for the effects of realistic linac motion. Finally, the impact of MV scatter on simultaneously-acquired cone beam CT images was investigated, and a scatter correction methodology was developed and validated.This thesis shows that VMAT can offer an alternative to static-field IMRT, provided that knowledge of the limitations of dynamic linac motion are accounted for within planning. Results suggest that modern linac designs (i.e. faster MLC speed, and a higher, continuously-variable dose rate) are required to achieve robust delivery of complex plans. The workflow benefits of VMAT can also be optimised through the use of independent dose calculations incorporating delivery characteristics, and through the use of image guidance from CBCT scans acquired during treatment.
Supervisor: Rowbottom, Carl; Mackay, Ranald Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: radiotherapy ; optimisation