Photon Irradiation for Spinal Chordomas and Chondrosarcomas

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Introduction

Chordoma is a rare malignancy arising from remnants of the embryonic notochord at an estimated incidence of <1 per 100,000 and a median age at diagnosis of 59 years. Most chordomas present in the spine, either the mobile spine (53%) or the sacral/coccygeal spine (47%), as opposed to cranial, extra-axial, or other sites. Overall survival rates for chordoma have been reported to be 68% at 5 years and 40% at 10 years.

Chondrosarcoma is a type of sarcoma that produces a cartilaginous matrix. It is also rare, with an estimated annual incidence of 1 in 200,000. About 7%–10% occur in the mobile spine and 5% in the sacrum.

Although chordoma and chondrosarcoma are often considered to be slow growing, both tumors, even when of low malignant grade, can cause significant morbidity and mortality when located in the spine. Traditional treatment approaches include surgery, either en bloc or intralesional resection, and radiotherapy. En bloc resection with wide margins is superior to intralesional resection in achieving local control and cure, but such tumor-free surgical margins can be difficult to achieve in the spine without significant morbidity in some cases because of tumor proximity to the spinal cord and vertebral arteries. Therefore, additional therapy is needed for durable local control in cases of incomplete resection.

Radiation therapy has been given for spinal chordomas and chondrosarcomas in preoperative, adjuvant, and definitive settings. Radiation modalities include external beam radiotherapy with photons or charged particles such as protons and cobalt, and intraoperative plaque brachytherapy.

Herein, we discuss and review photon external beam radiation for spinal chordomas and chondrosarcomas. There are no randomized control trials to demonstrate the optimal use of radiotherapy in this setting but rather retrospective series predominately limited to fewer than 50 patients. Photon radiotherapy, administered as stereotactic radiosurgery in conventional fractionation or hypofractionated schemes, may improve local tumor control and patient survival.