SRT therapy, or superficial radiation therapy, is a nonsurgical treatment for nonmelanoma skin cancers, primarily basal cell carcinoma and squamous cell carcinoma. It uses low-energy X-rays that penetrate only the surface layers of skin, destroying cancer cells without cutting into tissue. Modern devices achieve local control rates above 99%, making SRT a well-established alternative to surgery for people who aren’t good surgical candidates or prefer to avoid it.
How SRT Works
Superficial radiation therapy delivers targeted, low-energy radiation directly to a skin cancer lesion. Unlike the deep-penetrating radiation used for internal cancers, SRT energy is calibrated to affect only the top few millimeters of skin. This means the radiation destroys cancerous cells at the surface while leaving deeper tissue, muscle, and bone unaffected.
Newer devices combine this radiation with ultrasound imaging, a version called image-guided SRT (IGSRT). The ultrasound lets the clinician visualize the tumor’s borders in real time before each dose, improving precision and helping ensure the full lesion is treated.
What SRT Treats
SRT is cleared to treat two types of nonmelanoma skin cancer: basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), including squamous cell carcinoma in situ. These are the two most common skin cancers, and both tend to stay localized in the skin’s upper layers, which is exactly where SRT’s energy is delivered. It is not used for melanoma or cancers that have spread to deeper structures.
Beyond skin cancer, SRT is also used for recurrent keloid scars, the thick, raised scars that grow beyond the boundaries of an original wound. When keloids keep coming back after surgical removal, radiation delivered on the same day as excision is the most effective approach. A review of over 70 studies found that surgery followed by radiation had a recurrence rate around 22%, compared to 37% for radiation alone. Starting radiation on the day of surgery produces the best results, which requires coordination between the surgeon and radiation team.
What a Treatment Course Looks Like
SRT is performed in a dermatology office, not a hospital. Each session typically lasts about 15 minutes, and you’ll come in multiple times per week over a course of 5 to 7 weeks. The radiation itself takes only seconds to minutes per session. There’s no anesthesia, no incision, and no stitches. Most patients describe the experience as painless during the actual treatment.
Because the treatment is spread across many small doses rather than one large one, it gives healthy tissue time to recover between sessions. The trade-off is the time commitment: you’re visiting the office regularly for over a month, compared to a single surgical procedure that might take a few hours.
Cure Rates and How SRT Compares to Surgery
The standard treatment for nonmelanoma skin cancer remains surgical excision, particularly Mohs micrographic surgery, which has long been considered the gold standard because the surgeon examines tissue margins in real time. But SRT’s numbers are competitive. The largest modern study, covering 2,917 early-stage nonmelanoma skin cancers, found an absolute local control rate of 99.3%, stable at follow-up intervals out to four years. A separate study confirmed a 99.7% control rate after an average treatment course of 7.5 weeks, with that rate holding steady at 99.6% for lesions followed beyond 12 months.
A comparative analysis published in Clinical and Translational Radiation Oncology found that image-guided SRT had a statistically superior two-year recurrence probability compared to Mohs surgery. That finding supports SRT not just as a backup option for people who can’t have surgery, but as a genuinely effective primary treatment for early-stage disease.
Side Effects and Recovery
The most common side effect is skin irritation in the treatment area. Your skin will likely turn red and may become sore during the treatment course. Some people develop scabbing, and bleeding is possible but rare. These reactions typically continue for a few weeks after your final session before gradually improving.
Hair in the treated area will fall out. In some cases, that hair loss is permanent. Long-term changes can include lighter skin color at the treatment site and the appearance of small visible veins. The treated skin becomes permanently more sensitive to sun exposure, so ongoing sun protection with high-SPF sunscreen or physical coverage is important.
Compared to surgical options, SRT avoids the risks that come with cutting: no wound healing complications, no scarring from sutures, and no need for skin grafts or flaps. Cosmetic outcomes are generally considered superior, which makes SRT particularly appealing for cancers on the face, ears, nose, or other highly visible areas.
Who SRT Is Best Suited For
SRT is most commonly recommended for people who have early-stage basal cell or squamous cell carcinoma and fall into one or more of these categories:
- Poor surgical candidates due to age, blood-thinning medications, or other health conditions that make surgery risky
- Cancers in cosmetically sensitive areas where a surgical scar would be especially noticeable
- Patient preference for a noninvasive approach when the cancer is caught early
It’s less suitable for larger, deeper, or aggressive tumors, and it isn’t appropriate for melanoma. Your dermatologist can determine whether a specific lesion’s size, type, and location make it a good candidate for SRT versus surgical removal.
A Note on Other Uses of “SRT”
If you searched “SRT therapy” in the context of mental health, you may have been looking for social rhythm therapy, more formally called interpersonal and social rhythm therapy (IPSRT). This is a completely different treatment designed for bipolar disorder. IPSRT works by helping people stabilize their daily routines, particularly sleep and wake times, meal schedules, and activity patterns, with the goal of strengthening the body’s internal clock. Disruptions to these rhythms can trigger mood episodes in people with bipolar disorder, so the therapy combines routine regulation with interpersonal skills work to reduce recurrence of depressive and manic episodes.