The primary purpose of this research trial is to study the safety of electron FLASH treatment for cutaneous lymphoma lesions. In addition, investigators will confirm the accuracy of dose and dose rate delivery of electron FLASH therapy using on-patient dosimetry measurements in combination with FAST camera imaging. Researchers will also determine the response rates of cutaneous lymphomas treated with a low radiation dose in a single fraction using electron UHDR treatments, followed by an assessment of radiation related skin toxicity.

Inclusion Criteria:

1. Histologic proof of cutaneous lymphoma.
2. The cutaneous lymphoma is not planned to be treated with definitive, higher dose radiotherapy therapy.
3. Participant is planned to receive a course of palliative radiation therapy at DHMC for a cutaneous lymphomas lesion located on an extremity (see appendix A) that can be encompassed in a field size no larger than 7.5 cm in diameter.
4. No prior history of radiotherapy to the site of planned treatment.
5. Patient agrees to discontinue topical therapy, including steroid creams or chemotherapy agents, to the index lesion 4 weeks prior to the radiation treatment.
6. Participant must be capable of providing informed consent or has an acceptable surrogate capable of providing consent on behalf of the participant.
7. Adults at least 18 years of age
8. Eastern Cooperative Oncology Group performance status of <3.
9. Women of childbearing potential (WOCBP): Premenopausal females who had at least one menstrual cycle in the past 12-months and capable to become pregnant, must have a negative serum beta-HCG pregnancy test result within seven days prior to start of treatment.
10. WOCBP who are sexually active must agree at study entry to use adequate methods of contraception during treatment.

Exclusion Criteria:

1. Prior radiotherapy to the site of treatment.
2. Index lesion UHDR treatment field is <5cm from the field edge of a synchronously treated CONV lesion.
3. Patient receiving prescribed hormonal therapies.
4. Patients with known NCI CTCAE V5.0 grade 3 or higher active systemic or cutaneous viral, bacterial, or fungal infection.
5. Patients with any serious underlying medical condition that would impair their ability to receive or tolerate the planned treatment and/or comply with study protocol.
6. Patients with dementia or altered mental status that would preclude understanding and rendering of informed consent process.