ABSTRACT
This chapter covers the physical principles of the different radiotherapy treatment modalities used to treat skin cancer, including both brachytherapy and external beam radiotherapy. Each modality has specific advantages so the choice can be optimized for a given clinical scenario.
Brachytherapy techniques use radioactive sources placed close to, or inside, the volume to be treated. The most common radioactive source is iridium-192, usually contained within a high dose rate (HDR) brachytherapy machine. Superficial lesions can be treated using surface applicators, flaps, or individual molds, whilst deeper lesions are better suited to interstitial techniques. The recent development of electronic brachytherapy is also discussed.
External beam radiotherapy uses either electron or photon beams directed at the patient from outside the body. Electrons and low energy kilovoltage x-rays (divided into superficial and orthovoltage energies) have been used in the treatment of skin cancer for many years. Megavoltage photons have not been widely utilized in the past, but modern advanced techniques such as volumetric arc therapy (VMAT) mean that they can be very effective in complex cases for larger treatment volumes.
