Help me draft a prior authorization support letter for [insurance company / payer] for a patient needing [procedure — e.g. uterine fibroid embolization / genicular artery embolization / prostate artery embolization / hyperbaric oxygen therapy / DVT treatment].

Clinical summary: [paste clinical notes, diagnosis codes, failed prior treatments, physician recommendation]

The letter should: clearly state medical necessity, reference clinical guidelines and evidence, note failure of conservative treatments where applicable, and be formatted for insurance review. Professional, thorough, clinically grounded.