This clinical study tests a new device called **DaRT** (Diffusing Alpha-Emitters Radiation Therapy) for people with skin cancer, specifically Cutaneous Squamous Cell Carcinoma (SCC), who have weakened immune systems. The study will have up to 28 participants. It involves placing a small source of radiation directly inside the tumor for 14-21 days to see if it shrinks or disappears. The main goals are to see how well the tumors respond and to check the safety of the treatment. Participants will be monitored for up to 12 months to see how long they live without the cancer getting worse and to track any side effects. Participants need to be 18 or older, able to have multiple CT scans, and willing to use birth control if needed. The study is not suitable for people with certain medical conditions or those who have had recent cancer treatments.

• Study lasts up to 12 months.
• Radiation source is placed for 14-21 days.
• Participants must have regular check-ups and tests.