Abstract: Stereotactic Radiation Therapy (SBRT) has been implemented for re-iradiation of recurrent or second primary cancers of the head and neck to improve the therapeutic ratio in this difficult scenario. We reviewed our experience at a single institution. After IRB approval, a database of patients receiving re-irradiation was queried. Patients were excluded if receiving conventionally fractionated radiotherapy (RT), non-squamous histology, were enrolled on non-published clinical trials, or metastatic disease. All patients were seen in a multi-disciplinary clinic and/or reviewed in multi-disciplinary tumor board. All patients were ineligible for or refused surgical intervention. Patients were simulated with thermoplastic masks and 2 mm cuts on CT scan with and without contrast. Additional imaging including PET and/or MRI were fused. Gross tumor volume (GTV) was delineated and expanded 2-3 mm for the planning target volume. Elective nodes were not targeted. Minimum dose to PTV was 90% of prescription, with 110 - 130% prescription allowed within GTV/PTV. SBRT was delivered every other day for 5 fractions, with daily cone beam CT imaging, and 6 degree of freedom couch correction. Locoregional control (LRC), progression free survival (PFS), and overall survival (OS) were calculated from the end of RT and estimated via Kaplan-Meier method and comparisons made via log-rank test. Multi-variate cox regression model of OS was performed. Acute (during within three months from completion of treatment) and late (three or more months from completion of treatment) grade 3-5 CTCAE toxicities were collected. A total of 76 patients were available for analysis, with a median follow up of 31.5 months for patients alive at last contact, and 12 months for the entire cohort. Median age was 66 (range 36 – 92) with a median RT interval of 29.5 months (range 5 -315). Median dose of initial RT was 70 Gy (range 44 – 79.2 Gy). The majority of patients were former smokers (n=45, 59.2%), followed by never smokers (n=20, 26.3%), and current smokers (n=11, 14.5%). There were 56 men (73.7%) and 20 women (26.3%). Performance status was zero (n=22, 28.9%) and 1-2 (n=54, 71.1%), with 50 patients being recurrent (65.8%) and 26 having a second primary (34.2%). All patients were treated with 5 fractions to a median dose of 40 Gy (range 25 – 40 Gy). Systemic therapy was utilized in 29 patients (38.2%), primarily concurrently (n=27). Concurrent systemic therapy was cisplatin (n=20, 26.3%), cetuximab (n=4, 5.3%), or immunotherapy (n=3, 3.9%). Median gross tumor volume (GTV) was 11.42 cc (range 0.93 – 58.31 cc). Acute grade 3-4 toxicity was seen in 5 patients (6.6%), consisting of feeding tube in 2, aspiration pneumonia in 1, tracheostomy in 1, and stroke in 1. Actuarial rates for the entire cohort at 1 and 2-years for LRC were 43.5% and 33.3%, for PFS, 40.6% and 31.1%, and OS 49.6% and 33.1%. On univariate analysis median GTV, treatment site (nasopharynx/base of skull/neck/skin vs other), and recurrence were prognostic for OS. On multivariate analysis, GTV (HR 1.037, 95% CI 1.018 – 1.056, p < 0.001) and recurrent disease (HR 0.344, 95% CI 0.194 – 0.609, p < 0.001). For the subset of patients (n=26) with a GTV ≤ 11.4 cc and recurrent disease, 2-year OS was 80.1% with a median OS of 37 months. Of 73 patients followed for more than 3 months post treatment, 15 (20.5%) developed a late grade 3-4 toxicity, including feeding tubes in 7, aspiration pneumonia in 3, soft tissue necrosis in 3, or a cranial neve deficit in 3. SBRT for re-irradiation for patients with smaller, recurrent squamous cell carcinomas of the head and neck had the best performance. While severe acute toxicities are low, additional studies are needed to improve survival and decrease the risk of late toxicity. [ABSTRACT FROM AUTHOR]
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