The goal of this clinical trial is to learn if high-dose radiotherapy can provide sustained disease relief in moderate to severe, treatment resistant Hidradenitis suppurativa patients; could include any of the following: any sex/gender, and those greater then 18 years old. The main question[s] it aims to answer are:

Outcome measure 1: Will radiotherapy change the number of inflammatory nodules, abscesses, and draining sinus tracts in the treated axilla compared with the untreated axilla? Outcome measure 2: Will radiotherapy positively change a patient's quality of life, pain levels and symptom burden?

Participants will receive radiotherapy to one axilla affected by hidradenitis suppurativa. The contralateral axilla will not receive radiotherapy and will continue receiving the standard treatment regimen.

Participants will...

• Attend a baseline dermatology skin evaluation, complete multiple surveys and an optional participation in a biopsy
• Attend multiple radiation sessions over 5 weeks
• Attend 2 follow up visits with dermatology for skin evaluation, complete follow up surveys, and an optional biopsy.

This is a prospective, non-randomized, split-body interventional study enrolling adults with moderate to severe hidradenitis suppurativa involving bilateral axillary disease of comparable severity. Each participant will receive radiotherapy to one axilla, while the contralateral axilla will serve as an untreated within-subject control.

Radiotherapy will be delivered to a total dose of 45 Gy in 15 fractions (3 Gy per fraction), administered three times per week over approximately five weeks.

Patients will continue stable background HS therapies during the study period. Dermatologic assessments, lesion counts, physician global assessment scores, and patient-reported outcomes will be collected at baseline, during treatment, and at 4 and 12 weeks following completion of radiotherapy. Long-term safety and disease outcomes will be assessed by chart review for up to two years post-treatment. An optional punch biopsy sub-study will evaluate histologic changes associated with treatment response.

Inclusion Criteria:

• Male or female subjects between the age of 18 or older with moderate or severe HS (Hurley Stage II or III) with bilateral axillary disease of approximately equivalent disease severity will be included.
• Patients on topical and/or systemic HS medications for at least 1 month will continue maintenance treatment throughout the study period as per standard of care.
• Patients willing and able to provide informed consent

Exclusion Criteria:

• Pregnancy - Women of childbearing potential must use trial approved birth control and obtain a negative pregnancy test 7 days prior to radiotherapy CT simulation.
• Severe autoimmune conditions including lupus, scleroderma and mixed connective tissue disease
• Poorly controlled diabetes per physician discretion, HIV, Hepatitis B/C.
• Prior therapeutic radiotherapy.
• Active malignancy.
• Contraindication to radiotherapy as determined by treating radiation oncologist.
• Patients who began new systemic treatment for their HS <1 month prior to enrollment in trial
• History of photosensitivity disorders or prior radiation sensitization syndromes
• Any contraindication to radiotherapy as determined by the treating radiation oncologist.