Skin cancer is the most frequently diagnosed cancer globally, broadly categorized into non-melanoma skin cancers (NMSC) and melanoma. While surgical excision remains the primary treatment for most skin cancers, radiation therapy (RT) offers a powerful, non-invasive alternative or supplement. The decision to use radiation depends heavily on the cancer type, location, and the patient’s overall health. In certain situations, radiation is the preferred method to achieve a cure while preserving function and appearance.
Non-Melanoma Skin Cancers: Primary Role of Radiation
Basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) are the most common NMSCs, and radiation therapy is a highly effective primary treatment option for both. This approach provides excellent cure rates, often comparable to surgery, particularly when lesions are superficial or confined to the skin’s surface. Radiation is often chosen as the initial treatment when surgery might lead to significant cosmetic or functional impairment.
Specific tumor locations often necessitate radiation use to ensure the best possible outcome without disfigurement. Areas like the eyelids, nose, lips, and ears present challenges for surgical reconstruction due to complex anatomy. Radiation allows physicians to precisely target cancerous cells while sparing delicate nearby structures, maintaining the patient’s appearance and sensory function.
Radiation is also required for patients who are poor candidates for surgery due to advanced age or co-morbidities that increase surgical risk. For large or irregularly shaped tumors where achieving clear surgical margins is uncertain, radiation offers a non-surgical path to tumor eradication. This treatment is often delivered in a series of small, daily doses, minimizing stress compared to an invasive procedure.
High-Risk and Advanced Cancers: The Adjuvant Role
Beyond its use as a primary curative approach, radiation therapy frequently serves an adjuvant role, meaning it is delivered after surgery to eliminate microscopic residual disease. This post-operative approach aims to reduce the risk of local recurrence and improve long-term control, particularly in cancers with aggressive features. The need for adjuvant therapy is determined by specific pathological characteristics identified after tumor removal.
Merkel cell carcinoma (MCC), a rare but highly aggressive neuroendocrine tumor, almost always requires adjuvant radiation following surgical removal of the primary tumor and involved lymph nodes. Even when surgical margins appear clear, the high rate of local and regional recurrence associated with MCC makes post-operative radiation a standard component of the treatment protocol. This treatment targets the tumor bed and regional lymphatics to prevent the cancer from returning.
For high-risk NMSCs, such as advanced SCC, certain pathological features strongly indicate the need for adjuvant radiation. These features include positive or close surgical margins, suggesting residual disease. Furthermore, the presence of perineural invasion, where cancer cells track along nerves, is a powerful predictor of recurrence that necessitates post-operative radiation to sterilize the nerve pathway.
Melanoma, a cancer arising from pigment-producing cells, typically involves radiation only in specific high-risk or advanced scenarios, rather than as a routine post-operative measure. Adjuvant radiation may be employed for patients with very large primary tumors, extensive lymph node involvement, or extracapsular extension. In advanced, metastatic disease, radiation also serves a palliative function, shrinking tumors in sites like the brain or bone to alleviate pain and neurological symptoms.
Delivery Methods and Treatment Planning
Radiation treatment begins with a detailed planning process, often called simulation, where medical physicists and oncologists precisely map the tumor area and depth. This planning ensures the radiation dose is delivered accurately to the cancerous tissue while minimizing exposure to surrounding healthy structures. Specialized imaging techniques define the treatment volume and calculate the specific energy and trajectory of the radiation beams.
Several methods are used to deliver radiation, chosen based on the tumor’s characteristics. Superficial Radiation Therapy (SRT) uses low-energy X-rays that penetrate only a few millimeters into the skin. Electronic brachytherapy involves placing a small radioactive source temporarily near or directly on the skin lesion, delivering a highly concentrated dose over a short distance. Both SRT and brachytherapy are preferred for many skin cancers because they limit dose exposure to the underlying cartilage and bone.
For deeper or more advanced tumors, External Beam Radiation Therapy (EBRT) using higher-energy beams from a linear accelerator may be required to achieve sufficient depth penetration. The treatment is typically fractionated, meaning the total dose is broken up into small, daily treatments delivered over several weeks. This fractionation allows healthy cells time to repair themselves between sessions, reducing side effects and improving the therapeutic ratio.