The objective of this study was to investigate the feasibility and safety of delivering a third course of radiation to patients with multiply recurrent metastatic disease to the spine.
Between 2009 and 2011, 10 patients received a third course of radiation to spinal metastases at Memorial Sloan–Kettering Cancer Center using image-guided intensity-modulated radiation therapy (IMRT). Patient and tumor characteristics, dosimetry details, and outcomes were obtained using retrospective chart review. Spinal imaging was performed prior to treatment and at regular follow-up intervals. The cumulative biologically effective dose (BED) to the spinal cord and cauda equina was calculated and was normalized to 2 Gy equivalents (Gy2/2). Toxicity and local control were assessed.
The median time between the first and second courses of radiation was 18.5 months and the median time between the second and third courses was 11.5 months. The median follow-up from the third course of radiation was 12 months and the median overall survival was 13 months. Pain or neurological symptoms were improved in 80% of patients. The median spinal cord maximum dose normalized BED (nBED) for the whole cohort was 70.73 Gy2/2 (range 51.9–101.7 Gy2/2). The median dose to 5% of the spinal cord D05 nBED for the entire cohort was 59.4 Gy2/2. Acute toxicity was most commonly fatigue and dermatitis, with 1 patient experiencing Grade 3 fatigue and 1 patient Grade 3 dermatitis. Late toxicity was limited to 2 cases of Grade 1 dysphagia. There was 1 case of Grade 1 neuropathy and 1 case of Grade 2 neuropathy. The crude rate of local control was 80% with 1 in-field failure and 1 marginal failure.
In this cohort of patients, a third course of IMRT to the spine was well tolerated with no significant late toxicities. Used as salvage therapy for select patients, a third course of radiation is a safe and effective treatment strategy.
Abbreviations used in this paper:BED = biologically effective dose; D05 = dose to 5% of the target; D80 = dose to 80% of the target; Dmax = maximum dose; IMRT = intensity-modulated radiation therapy; nBED = normalized BED; PTV = planning target volume; SBRT = stereotactic body radiation therapy.
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