RT-11 * MINIMAL ACUTE TOXICITIES FOLLOWING HIGH-DOSE PROTON THERAPY FOR SPINAL TUMORS

Abstract

Purpose/Objective(s): Proton therapy for spinal malignancies permits the opportunity to minimize toxicities by using posterior proton beams and positioning distal range anterior to spinal target volume. This approach to proton treatment significantly limits dose to anterior visceral structures, including esophagus, bowel and bladder. This study seeks to determine whether this dosimetric advantage of proton therapy impacts clinical outcomes in terms of acute toxicities. Materials/Methods: All patients consecutively treated for a spinal malignancy on the prospective Proton Collaborative Group registry at a single proton center were reviewed. Cases receiving concurrent cranial irradiation or chemotherapy prior to or during proton therapy were excluded. All patients were treated either in the supine or prone position using left and right posterior oblique beam angles with distal edge placed anterior to the planning target volume to ensure at least 95% prescription coverage. Treatments were delivered at 1.8 CGyE/fraction. All patients were evaluated on a weekly basis and acute toxicities were prospectively graded in the electronic medical records using the Common Terminology Criteria for Adverse Events version 4.0. Results: Nineteen patients were treated with proton therapy to the spine. Median age was 49 (range 12-74); 3 patients were less than 21 years old. 5 patients had chordoma/chondrosarcoma (dose range 70.4-75.8 CGyE); 1 patient had sarcoma (66.3 CGyE); 5 patients had a WHO grade II ependymoma (54.2-59.6 CGyE); 4 patients had a WHO grade I myxopapillary ependymoma (52.3-59.6 CGyE); 3 patients had benign or malignant peripheral nerve sheath tumor (57.9-59.8 CGyE); and, 1 patient had hemangioma (50.5 CGyE). 16 patients developed grade 1 dermatitis. Grade 2 desquamation was observed in 2 patients (11%), all of whom were treated to 72 CGyE, and grade 3 desquamation was observed in 1 patient (5%), treated to 75.8 CGyE. 2 patients (11%), all of whom were treated to >72 CGyE, developed grade 1 diarrhea. Two patients (10%), both of whom were treated to >72 CGyE, developed grade 1 urinary frequency. Two patients (10%) reported grade 1 fatigue. Aside from desquamation, no grade >2 acute toxicities were observed. Conclusions: Proton therapy to > 50 CGyE for spinal tumors is well tolerated, with no grade >2 non-dermatologic acute toxicities and grade 1 acute GI and GU toxicities only in patients treated to >72 CGyE. Dermatologic toxicities were observed in all patients, but severe only in patients treated to >72 CGyE.