RapidArc – Inverse Planning, Dose Calculation and Clinical Application
Thesis DisciplineMedical Physics
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Volumetric modulated arc therapy delivers highly conformal radiotherapy treatments to cancer patients in a continuous arc whilst dynamically varying the multi-leaf collimator (MLC) position, dose rate and rotational angular velocity. The present master’s thesis seeks to develop a better understanding of delivering treatment in this manner, ranging from progressive resolution inverse optimisation, class solutions, clinical application and the ability of dose calculation algorithms to model such a complex modality.
A progressive resolution based class solution for inverse planning has been developed, outlining contouring, field set-up and optimisation. This class solution was then applied to 10 prostate patients and subjected to an inter-comparative planning study with static gantry intensity-modulated radiotherapy. The results of this justification study showed the presented class solution produces plans that are generally and directly comparable with previously published data. Following this result, the class solution was applied to a previously uninvestigated clinical site (treatment of prostate bed following radical prostatectomy) in an effort to solve persistent clinical problems involving target volumes and dose escalation. The results of this secondary study provisionally showed the feasibility of treating prostate beds with rotational intensity-modulated techniques whilst maintaining the integrity of the target volumes and escalating the delivered dose.
The potential for improving the accuracy of the dose calculation analytic anisotropic algorithm for volumetric modulated plans was also investigated, through configuration of two independent algorithms containing beam data taken with either the linac jaws or MLCs defining the field. The two algorithms were inter-compared in virtual water phantoms and against physical verification measurements. The configuration process has shown to be sensitive to depth dose data but not beam profiles. Furthermore, the two algorithms show no significant difference and therefore it is recommended that beam be taken with the jaws defining the field.