Role of radiotherapy in the treatment of lentigo maligna and lentigo maligna melanoma-a systematic review

Background: Radiotherapy is one of the non-surgical treatments for lentigo maligna (LM) and lentigo maligna melanoma (LMM). Several studies reported an array of radiation regimens. In this review, we aim to discuss the effectiveness of different radiation regimens in terms of the calculation of the biologically effective dose (BED) value compared to clinical outcomes. Methods: The literature search was from July 24, 2024 until August 11, 2024 through PubMed, Cochrane Library, and Scopus using the keywords lentigo maligna, lentigo maligna melanoma, Hutchinson, radiotherapy, Grenz ray, X-ray, and radiation therapy. Any studies that had confirmed the diagnosis of LM/LMM clinically or histopathologically and were written in English were included, except review articles, single case reports, editorials, letters, and book chapters. Quality assessment was accomplished by using the Newcastle-Ottawa Quality Assessment Scale (NOS). The BED value was divided into late and early depending on tissue response using the formula (BED) = n d 1 + d/(α/β). LM was considered late-responding tissue due to low α/β ratio (0.6-2.5). We compared the BED value with specific clinical outcomes, including complete response rate (CRR), clinical regression, local recurrence, metastatic progression, and chronic skin toxicity. Results: Ten studies (988 patients) primarily from Europe and North America evaluated radiotherapy for LM/LMM, mostly in elderly females (mean age 71.9 years). X-rays (10-250 kV) were used with BED values ranging from 17-587 Gy (early-responding) and 28-1,584 Gy (late-responding). Higher BED values shortened regression time. CRR was >87% across all studies. Local recurrence rate (LRR) was 0-7% with 20-250 kV (BED 103-162 Gy<inf>3</inf>) and 3-31% with 10-20 kV (BED 433-920 Gy<inf>3</inf>). Metastasis was rare (0-2%). Cosmetic outcomes were good to excellent, though high BED was linked to chronic skin toxicities. Conclusions: Higher BED values with different energy of X-ray utilization were generally associated with better CRR, lower LRR, better control of metastasis, and promising cosmetic results, though careful consideration is required to minimize complications. However, limitations such as inconsistent and incomplete data might introduce bias and affect the credibility of these conclusions. © AME Publishing Company, Taiwan Society for Therapeutic Radiology and Oncology.