Proton Beam Irradiation in the Treatment of Sacral Chordomas

Purpose/Objective(s): This retrospective analysis details outcomes in regards to overall survival, local control rate, and morbidity for sacral chordoma patients treated with fractionated proton radiotherapy at the Loma Linda University Proton Treatment Center over the past decade. Materials/Methods: Twenty patients with sacral chordoma tumors without distant metastases at presentation were included in this analysis, all of whom had a minimum follow up time of at least 12 months. Patients completed treatment between October 1994 and October 2004. The mean age at initiation of treatment was 60.8 years. Ten patients presented after disease recurrence or progression from a prior surgical resection, while the remaining patients presented after their initial surgery. Some patients underwent multiple resections prior to study entry. Eleven patients presented after a gross complete resection while nine patients presented after an incomplete resection, defined as gross residual seen intraoperatively or identified by imaging studies. 3D-conformal proton irradiation was utilized in all patients. Nine patients underwent a mixed beam course, with the use of photon irradiation first (mean dose of 49 Gy), followed by proton irradiation to a boost field. Daily fractions of 1.8 Cobalt-Gray equivalent (CGE) were used to deliver a total dose that ranged from 66.6–81 CGE, with a mean dose of 73.8 CGE. Results: The mean follow up time was 63.1 months. Follow up revealed a 5 year actuarial local control rate of 60% and a 5 year actuarial overall survival of 80%. The 5 year actuarial disease free survival was 60%, while the 5 year actuarial distant disease free survival was 75%. Distant metastases were seen involving the liver, lungs, and thoracic spine. To determine the impact of the extent of surgery prior to initiation of radiation therapy, patients were stratified into two groups. For patients who underwent a gross total resection, the 5 year actuarial local control rate was 90% compared to 29% for those had an incomplete resection (p = 0.0242). The 5 year actuarial disease free survival was 90% in the gross total resection group compared to 29% for incomplete resection patients (p = 0.0279). A statistically significant 5 year actuarial overall survival benefit was not found (89% for gross total resection patients versus 73% for incomplete resection) (p = 0.60). The median time to recurrence was 86 months for those who received a gross total resection versus 44 months for those who received a partial resection. The 5 year actuarial distant control rate was 100% for gross total resection and 40% for subtotal resection. A trend toward significance was seen (p = .0843). Using the RTOG/EORTC Late Radiation Morbidity Scoring Schema, only one patient experienced a grade 3 complication, which involved the bone. The most common toxicity involved skin complications, with five patients reporting grade 1 or 2 morbidity. No late rectal complications were reported. Conclusions: The results of this study verify the importance of a complete resection prior to proton radiation treatment. Significant local control and disease free survival benefits were seen among patients who underwent a gross total resection compared to those who had an incomplete resection. The safety of delivering high doses of radiation was noted in this study, with only one case of grade 3 late morbidity and no cases of grade 4 morbidit