Superficial radiation therapy (SRT) is a nonsurgical treatment that uses low-energy X-rays to destroy skin cancer cells and treat certain other skin conditions, including keloids. It works by delivering radiation that penetrates only a few millimeters into the skin, killing abnormal cells in the upper layers while leaving deeper tissues unharmed. SRT is most commonly used for basal cell carcinoma and squamous cell carcinoma, the two most common types of non-melanoma skin cancer.
How SRT Works
SRT delivers external radiation using photons in the range of 50 to 150 kilovolts, which is far less powerful than the radiation used for cancers deeper in the body. Even at the upper end of its energy range (around 200 kilovolts), the beam penetrates through the outer skin layers and dermis but stops before reaching muscle, bone, or other structures underneath. This shallow penetration is what makes the treatment “superficial” and is also why it’s limited to conditions that sit near the skin’s surface.
A newer version called image-guided superficial radiation therapy (IGSRT) pairs the radiation with a built-in high-frequency ultrasound. The ultrasound scans the skin at a frequency optimized for viewing tissue up to about 6 millimeters deep, which lets the clinician see the tumor’s exact edges and depth before and during each session. This means the radiation dose can be adjusted in real time to match the actual size of the lesion rather than relying solely on what’s visible on the surface.
Who It’s Used For
SRT is FDA-cleared for treating non-melanoma skin cancers, specifically basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and squamous cell carcinoma in situ. It’s also cleared for recurrent keloid scars that haven’t responded to other treatments.
National Comprehensive Cancer Network (NCCN) guidelines position radiation therapy as an option when surgery isn’t feasible or desirable. That includes people who have medical conditions making surgery risky, such as certain heart conditions or blood clotting disorders that complicate wound healing. It also includes people who simply prefer a non-surgical approach. For squamous cell carcinoma, the NCCN notes that considerations of function, cosmetic outcome, and patient preference may all be valid reasons to choose radiation over the knife, particularly for tumors on the face, ears, or nose where scarring matters.
SRT is not appropriate for melanoma. It’s designed for cancers that stay in the superficial layers of the skin, and melanoma requires different treatment strategies because of its tendency to spread deeper and to other parts of the body.
How Effective Is SRT?
Modern SRT produces cure rates of roughly 93% to 100% for non-melanoma skin cancers, depending on the study and follow-up period. When researchers tracked outcomes over longer timeframes, the 5-year cure rates were 94.4% for basal cell carcinoma and 92.7% for squamous cell carcinoma. At 15 years, those numbers dropped to 84.8% and 78.6%, respectively, reflecting the fact that some cancers do eventually return.
The image-guided version appears to improve on these numbers. A retrospective study of 2,880 lesions treated with IGSRT found 2-year recurrence rates of just 0.7% overall, with 1.1% for BCC and 0.8% for SCC. Multiple meta-analyses have found IGSRT statistically superior to traditional SRT across all cancer subtypes. Some studies have even shown IGSRT to be clinically equivalent to Mohs micrographic surgery, which is widely considered the gold standard surgical treatment for skin cancer, at two years of follow-up.
SRT Compared to Mohs Surgery
Mohs surgery involves cutting away the cancer layer by layer, examining each layer under a microscope until no cancer cells remain. It’s highly effective and remains the first-line recommendation for many skin cancers, especially high-risk ones. But it’s a surgical procedure that requires local anesthesia, creates a wound that needs healing, and sometimes leaves a noticeable scar.
SRT offers a different tradeoff. There’s no cutting, no stitching, and no surgical wound. This matters most for people who are on blood thinners, have compromised immune systems, or have tumors in cosmetically sensitive areas like the tip of the nose or eyelid. It also appeals to older patients who want to avoid the stress and recovery time of surgery. The downside is that SRT requires multiple visits rather than the single (sometimes two-day) procedure of Mohs, and long-term cure rates beyond five years tend to be slightly lower than what surgery achieves.
What Treatment Looks Like
A full course of SRT typically involves multiple sessions spread over several weeks. Each appointment, including setup, takes roughly an hour, though the actual radiation delivery is only a few minutes. The treatment is painless during delivery. You sit or lie still while a small applicator is positioned over the lesion, and the machine sends the X-ray beam to the targeted area.
With IGSRT, the clinician performs an ultrasound scan at each visit to check how the tumor is responding and adjusts the radiation energy accordingly. The machine offers energy settings in precise increments, and dose-depth tables guide the selection so that the beam reaches the bottom of the tumor without going unnecessarily deeper. This adaptive approach is one reason the image-guided technology has shown better recurrence rates than older SRT devices.
Side Effects and Healing
Because the radiation targets only the top layers of skin, side effects are localized to the treatment area. The most common reaction is radiation dermatitis, which looks and feels similar to a sunburn. On lighter skin, the area turns red; on darker skin, it may appear noticeably darker than the surrounding area. You may also experience itching, dryness, peeling, or mild swelling.
In some cases, the skin can blister or develop moist, weeping patches, particularly in areas where skin folds trap moisture, like near the ears or along the jawline. These reactions tend to peak toward the end of the treatment course or shortly after the final session. Most mild symptoms begin improving within a few weeks of finishing treatment, though the skin can remain sensitive for up to a month. Full healing sometimes takes longer, depending on the size and location of the treated area.
Serious complications are uncommon. The low-energy beam doesn’t reach deep enough to damage underlying structures, so the risks associated with conventional radiation therapy (fatigue, damage to internal organs) don’t apply here.
SRT for Keloid Scars
Keloids are raised, thickened scars that grow beyond the boundaries of the original wound. They’re notoriously difficult to treat because they tend to come back after surgical removal. SRT is used as an add-on therapy immediately after a keloid is surgically cut out, with the goal of preventing regrowth. The radiation is typically delivered in a small number of sessions shortly after excision.
Results for keloids are less consistent than for skin cancer. One cohort study following patients for 24 months found that 35% remained keloid-free, while 65% experienced some degree of recurrence. That recurrence rate is still an improvement over surgery alone for stubborn keloids, which can recur in up to 80% or more of cases without any adjuvant therapy. SRT is generally reserved for keloids that have already failed other treatments like steroid injections or silicone sheeting.