Complex external-beam radiotherapy technologies, such as intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT), provide a means of delivering dose distributions which conform tightly to target volumes, while also sparing nearby organsat-riskorgans at risk (Bortfeld 2006, Otto 2008). These techniques are particularly suitable for treatmentthe treatment of the cancer of the head and neck, where target volumes may lie in close proximity to dose sensitive organs such as the spinal cord, the parotid glands, the eyes, or the optic nerves.
Steep dose gradients are often necessary to ensure the coverage of the target, while simultaneously minimizing the dose to the organs-at-riskorgans at risk. Thorough commissioning of these techniques before clinical implementation and a quality assurance (QA) programme following implementation are therefore critically important, since planning or delivery errors could potentially result in a poor treatment outcome: if the dose delivered to the tumour is lower than planned, then the likelihood of local control oflocally controlling the tumour will be reduced, while a higher than expected dose delivered to an organ-at-riskorgan at risk may lead to increased toxicity. A QA programme may include regular pre-treatment verification measurements on individual treatment plans, as well as periodic auditaudits of the technique itself (Clark et al 2009).