Table 1. Baseline Patient and Treatment Characteristics.

Characteristics	N (%)
Age, years (mean ± standard deviation)	64.4 ± 10.2
Sex
Male	18 (26%)
Female	51 (74%)
Smoking Status (n=66, 96%)
Never – less than 10 pack years	15 (22%)
Greater than 10 pack year	51 (74%)
HPV status (n=30, 43%)
Positive	17 (57%)
Negative	13 (45%)
Primary Site in Oropharynx
Tonsil	26 (38%)
Base of Tongue	32 (46%)
Other or NOS	11 (16%)
Prior Treatment
Prior Full Dose Radiotherapy	69 (100%)
Prior Surgery	18 (26%)
Prior Chemotherapy	44 (64%)
Recurrence Treatment Site
Base of Tongue	23 (33%)
Cervical Lymph Nodes	10 (15%)
Base of Skull	6 (9%)
Other*	30 (43%)
Second Primary¥	14 (20%)
SBRT Treatment Volume, cc, mean (range)	45 (2.5-345.1)
SBRT Dose, Gy, mean (range)	40.9 Gy (15-50)

^*Other sites: tonsil, hypopharynx, nasopharynx, parotid, other oropharynx.

^¥Fourteen patients (20.3%) had been previously diagnosed and treated with squamous cell carcinoma of the head and neck and presented with OPSCC as a second primary lesion. Of these, 5 patients were treated for laryngeal squamous cell carcinoma (SCC), 3 patients were treated for oral cavity SCC, and 3 were treated for OPSCC. Thirteen (92.9%) of the patients with second primary tumors were smokers, for the remaining 1 patient smoking status was unknown.