Successful Treatment of Infantile Fibrosarcoma Spinal Metastasis by Chemotherapy and Stereotactic Hypofractionated Radiotherapy
A previously healthy 8-month-old boy presented with a 3×3 cm mass in the right lower leg, which was surgically excised. Pathological analysis confirmed the diagnosis of infantile fibrosarcoma and the surgical margin was not clear. His parents refused reexcision but accepted monitoring by regular imaging. However, a mass was detected again in the same area two years after surgery. Therefore, the patient then underwent complete excision, and recurrent sarcoma was confirmed histologically. After the second resection, the patient had monthly follow-up and no evidence of disease was observed on an ongoing one year.\nA surveillance whole-body fludeoxyglucose positron emission tomography scan conducted 3 years after the initial presentation demonstrated a recurrent mass in the right lower leg, one micrometastatic lesions at the left proximal fibula and another macrometastasis in the 4th lumbar vertebral column, respectively. Lumbar spine magnetic resonance imaging (MRI) revealed a contrast-enhancing lesion of 1.6 cm in the posterior aspect of the 4th lumbar vertebral column without spinal canal compression (). To preserve right lower leg, debulking surgery of the recurrent lesion was performed, and the histological features were found to be consistent with recurrent sarcoma with rhabomyosarcomatous differentiation. Two weeks after the surgery, the patient started to receive chemotherapy with a VAC regimen composed of vincristine (1.5 mg/m2), dactinomycin (0.045 mg/kg), and cyclophosphamide (2.2 g/m2) for a total of 44 weeks treatment course.\nGiven the potential risk of spinal pathologic fracture and myelopathy, radiotherapy was chosen to treat the 4th lumbar vertebral metastatic lesion. Cyberknife® hypofractionated radiotherapy was decided due to the solitary nature of the metastasis and fewer sessions are needed, which would decrease the frequency of general anesthesia for radiotherapy. The patient was immobilized in a vacuum mattress. Fused enhanced computed tomography (CT) (Accuray) and MRI scans were used in the treatment planning. The delineation of the gross tumor volume (GTV) and the organs at risk was carried out on the planning CT. Given the potential risk of kyphosis and scoliosis by asymmetric irradiation of the spine, the whole involved vertebra was contoured as the GTV. Clinical target volume was equal to the GTV and no margin was added to obtain the planning target volume (PTV), which was 8.84 mL. No fiducial or other markers were implanted to localize the irradiated area. A total of 26 Gy was prescribed to the 75% isodose line, covering 92.64% of the PTV with a maximal spinal cord dose of 744.26 cGy (). Cyberknife® stereotactic body radiotherapy was performed on the 15th, 16th, 19th, and 20th of October 2009 with a mean procedure time of 83 min (range 56 min to 128 min). The radiotherapy course was conducted in a manner concomitant with the first cycle of chemotherapy. During the radiotherapy, immobilization was aided by general anesthesia, and X-sight spine tracking (Accuray Inc.) was used to minimize setup error.\nThe patient tolerated the anesthesia and immobilization well and remained still during the radiotherapy. Up to the date of this report, i.e., 33 months after radiotherapy, the patient remains neurologically stable and 23% reduction in tumor volume was achieved on the surveillance MRI scans (). No acute radiation toxicity was found.