Radiotherapy is a collection of versatile treatment modalities that includes brachytherapy and external-beam radiation.
The clinical effects of radiotherapy include acute and late skin changes:
Acute effects include an inflammatory reaction and desquamation.
Late effects include fibrotic changes and atrophy of skin adnexa.
Radiation-induced malignancy is a rare but serious side effect, which presents at a median of 10 years after treatment.
Radiotherapy is indicated for selected benign, proliferative diseases after more conservative measures have failed.
Radiotherapy is a valuable option for primary or adjuvant therapy for malignant skin disease.
The first documented use of radiation as a therapeutic treatment was for a cutaneous malignancy, in a patient with squamous cell cancer of the nose, in 1900. Over the next century, radiotherapy was widely used in the treatment of both malignant and benign disorders of the skin, in both adults and children. As the long-term consequences of radiotherapy became evident, particularly the risk of radiation-induced malignancy, its use in the treatment of benign diseases declined, particularly in children. Radiotherapy continues to have a small but important role in the management of benign proliferative diseases of the skin, but is more commonly used as a valuable adjunct or alternative to surgery for both premalignant and malignant lesions.
There are several choices for radiation modalities, some commonly available and others only in specialized centers. The selection is made on the basis of the anatomic location and size of the target, tumor biology, the nature of critical surrounding structures, and availability. In particular, with respect to the cutaneous targets, the depth of the lesion plays a large role in determining the optimal therapy.
High-energy photons, in the form of γ- or X-rays, are most commonly produced by a linear accelerator (LINAC) and are available in a spectrum of energies. Incident radiation deposits its energy as it passes through matter, becoming attenuated as a function of depth and the density of the tissue. Higher energy beams deliver increased doses at depth in tissue, and proportionally less at the surface (often referred to as “skin sparing”). Lower energy radiation deposits the dose primarily at the target surface, sparing deeper tissue. The most commonly available treatment energies in general oncology practice are in the megavoltage range (6 to 18 megavolts),1 depositing their dose at a range practical for the treatment of internal targets in human tissue. Such beams were designed to relatively spare surface structures such as skin in the interest of delivering a higher dose to deeper target structures and sparing the skin from toxicity. This is in contrast to lower radiation energy beams in the kilovoltage range (commonly referred to as “superficial radiation therapy”), which are often more appropriate for cutaneous targets. Figure 200-1A shows the depth dose curves demonstrating the absorption of X-rays as a function of their energy.
Depth dose distributions. ...