IG-SRT is best suited for early to moderate-stage tumors – those that are not extremely large or deeply infiltrative. For very large tumors (for example, a basal cell carcinoma that covers a big section of the face or scalp, several centimeters across) or ones that have grown deep into tissue (beyond the skin into cartilage, muscle, bone), a combination approach or surgery might be more appropriate. Why? Large areas would require radiating a lot of skin, which can lead to more significant side effects and potential healing issues; also, extremely deep tumors might not be adequately reached by superficial X-rays alone. IG-SRT penetrates a few millimeters, so if a tumor extends deeper than about 5-6 mm, we can sometimes compensate by treating from different angles or using a slightly higher energy, but it has its limits. Deep invasion often signals a higher risk situation too, which might be better managed with surgery and possibly traditional radiotherapy. That said, a tumor doesn’t have to be tiny to use IG-SRT – we commonly treat lesions in the 1 to 2 cm diameter range (or a bit larger) effectively. It’s when you get to very large sizes (say, >5 cm) that radiation becomes more complex. In radiation oncology, there are techniques to cover large areas, but with IG-SRT specifically, treating something huge would mean many overlapping fields and potentially a less uniform dose. In those cases, sometimes a referral to a radiation oncology center for a different technique or a surgical debulking followed by radiation might be considered. As for deep tumors – if, for instance, a squamous cell has invaded to the level of muscle, Mohs surgery or excision to remove that bulk and possibly followed by radiation is often recommended.
In sum, IG-SRT is ideal for localized, skin-limited tumors. For very large surface area tumors or very deep ones, we may say surgery is the first-line and perhaps use radiation (IG-SRT or other modalities) as adjunct or backup. We evaluate each case individually – using ultrasound to gauge depth helps a lot in making that call. If the ultrasound shows it’s beyond what superficial radiation can cover, we’ll advise accordingly. But for most “typical” cases that dermatologists see (which are caught before they become massive), IG-SRT is fine. Truly huge or deeply invasive cases are more rare and often are managed in a multi-disciplinary way. So, if your tumor falls into that atypical category, we’d likely lean toward other treatments. Otherwise, for anything up to moderately large and within the skin layers, IG-SRT can be appropriate.
