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.

This dissertation addresses the issue of robustness in proton therapy treatment planning for cancer treatment. Proton therapy is considered to be advantageous in treating most childhood cancers and certain adult cancers, including those of the skull base, spine and head and neck. Protons, unlike X-rays, have a finite range highly dependent on the electron density of the material they are traversing, resulting in a steep dose gradient at the distal edge of the Bragg peak. These characteristics, together with advancements in computation and technology have led to the ability to plan and deliver treatments with greater conformality, sparing normal tissue and organs at risk. Radiotherapy treatment plans aim to meet set dosimetric constraints, and meet them at every fraction. Plan robustness is a measure of deviation between the delivered dose distribution and the planned dose distribution. Due to the same characteristics that make protons advantageous, conventional means of using margins to create a Planning Target Volume (PTV) to ensure plan robustness are inadequate. Additional to this, without a PTV, a new method of analysing plan quality is required in proton therapy. My original contribution to the knowledge in this area is the demonstration of how site- and centre- specific robustness constraints can be established. Robustness constraints can be used both for proton plan analysis and to identify patients that require plans of greater individualisation. I have also used the daily volumetric imaging from patients previously treated with conventional radiotherapy to quantify range uncertainty from inter- and intra-fraction motion. These new methods of both quantifying and analysing the change in proton range in the patient can aid in the choice of beam directions, provide input into a multi- criteria optimisation algorithm or can be used as criteria to determine when adaptive planning may be required. This greater understanding in range uncertainty better informs the planner on how best to balance the trade-off between plan conformality and robustness in proton therapy. This research is directly relevant to furthering the knowledge base in light of HM Government pledging £250 million to build two proton centres in England, to treat NHS patients from 2018. Use of methods described in this dissertation will aid in the establishment of clear and pre-defined protocols for treating patients in the future.