Dermatologists achieve cure rates as high as 98% when treating nonaggressive NMSC using SRT for basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) in select patient populations. SRT is relatively simple to administer, with little impact to underlying healthy tissue. It can be used on any skin surface area and causes minimal scarring. It poses fewer risks than surgery, which is particularly relevant for patients who are elderly or at high risk with significant comorbidities.

• Recently published guidelines address available SRT technology, selecting which patients and tumor types are ideally suited to this treatment, the risks and benefits of treatment, and clinician techniques.
• For NMSC on lower extremities, SRT is often more advantageous than a surgical option.
• Better cosmesis can be achieved using SRT instead of surgical treatment, which is particularly important for facial NMSC lesions.

Modern SRT devices offer the advantage of relative simplicity, utilizing low energy photon x-rays operating at variable peak voltages of 50 -100 kilovoltage peaks (kVp). The dose delivery is planned and calibrated. The unit automatically stops when the appropriate cumulative amount of radiation is delivered. The SRT is easily administered to target the lesion. The radiation provided is indirect and penetrates to a depth of approximately 5 mm and does not impact the underlying healthy tissue.

• Available Technology: the SRT-100 system is Food and Drug Administration approved for total body treatment of NMSC and keloids. The cure rate was 98% for patients with primary nonaggressive NMSC treated with the SRT-100 [1].
• Tumor types most commonly treated with SRT: are BCC and SCC. While the tumor site may be any skin surface area, SRT offers a cosmetic advantage for tumor sites such as the scalp, eyelid, external ear canal and helix, and nasal ala as the procedure leaves minimal scarring.

It is important to differentiate between SRT used by dermatologists and procedures performed by radiation oncologists (e.g., electron beam, brachytherapy, and electronic brachytherapy) [2,3].

2019 Consensus Guidelines Note the Following:

• SRT provides more energy and deeper penetration than grenz-ray (GR) treatment [3].
• Brachytherapy differs from SRT by using radioactive sources within or directly adjacent to the tumor and has a lower cure rate for NMSC [3].
• Electron beam therapy (EBT) differs from SRT by using a medical linear accelerator and has a lower cure rate for NMSC [3].
• SRT offers better cosmesis and is more cost effective compared to both brachiotherapy and EBT [3].

• For larger tumors, SRT may present a simpler option than extensive surgery and reconstruction (skin grafting). It presents a minimally higher risk of recurrence than surgery.
• SRT is clearly more beneficial for many NMSC on lower extremities.
• SRT has particularly favorable cosmetic benefits on alar rim of nose and periorbital area.
• Important factors to consider are treatment margins for BCC and SCC.
• According to 2019 Consensus Group guidelines, the initial measurement should be size of lesion plus 2-5 mm margin around lesion.

• Patient who are poor surgical candidates, or elderly with significant comorbidities are likely better candidates for SRT, which offers lower risks than surgery.
• SRT does not require that patients stop anticoagulants and can be used safely in patients with poor circulation.
• It is well-suited for those who cannot perform wound care, have significant fear of surgery, or concerns about scarring.
• Contraindications for SRT include having a pacemaker or defibrillator within the treatment area or having had previous radiation therapy to the area of concern.
• Complications from SRT are rare. Temporary erythema is experienced by most patients, lasting for 7-14 days, and is usually related to the radiation dose. Hyperpigmentation occurs rarely for NMSC patients, but more often when SRT is used to treat keloids in Fitzpatrick type V-VI patients. Radiation dermatitis occurs occasionally; when it occurs, it is mild.
• There is insufficient evidence to support or refute specific topical therapies for the prevention or management of radiation-involved skin changes during the actual treatment period.