Adjuvant radiation of the axilla for skin cancer - evolution of a technique

Phase II and retrospective data show that adjuvant radiotherapy to the axilla improves local control in skin cancers such as melanoma, squamous cell carcinoma and Merkel cell carcinoma. Optimisation of the volume treated, dose and fractionation patterns are essential in order to avoid long term toxicities to nearby dose sensitive structures in survivors. Traditionally this has been planned with plain film simulation and a certain percentage of treatment toxicity has been accepted as inevitable to deliver appropriate treatment. The recent advent of CT planning has enabled a better understanding of the origin of toxicity based on the amount of normal structures actually in the treated volume. Other variables such as the differences in individual patient anatomy and the differences between the prescribing radiation oncologists' understanding of the anatomy of the axilla and volumes, such as clinical target volume and planning target volume, have also been discovered when compared with plain film simulation. Case studies are presented which suggest causes of toxicity and techniques of optimization based on CT planning which differ with other variables such as patient anatomy and dose-volume histograms of relevant structures.. Baseline parameters that outline a standard treatment plan based on CT planning are offered that should assist in minimising toxicity and maximising the treatment efficacy. This could also be offered as a template so that inter-doctor and inter-centre variations are kept to a minimum. The latter is important in ensuring there is standardisation of treatment particularly when it is imperative to maintain consistency of treatment volumes in multi-centre clinical trials