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Proton Therapy for Spinal Chordomas and Chondrosarcomas
© 2018 Elsevier Inc. All rights reserved. Please note that the copyright for the original figures submitted by the contributors is owned by Contributors.
General Comments
Chordomas and chondrosarcomas are quite uncommon, with an estimated annual incidence of ∼1320 chondrosarcomas and ∼300 chordomas in the United States. Accordingly, the clinical outcome data for different management strategies are quite modest and data from randomized clinical trials are virtually nonexistent.
A multidisciplinary team with expertise in managing these rare tumors is favored. The primary treatment strategy for chondrosarcoma and chordoma of the spine has been and remains surgery, provided tumor-negative margins are achieved, although recent evidence suggests a role for definitive radiation for selected patients who decline surgery in anatomic locations such as the upper sacrum where the morbidity associated with surgery is unacceptable to some patients. Obtaining pathologically clear margins for sarcomas that have extended into the extraosseous paravertebral tissue/structures is difficult in a high proportion of patients, even for experienced oncologic surgeons, provided reasonable levels of function are preserved. This is a particularly grievous problem when there has been extension into the vertebral canal with displacement of the dura and/or the cord. This latter situation inevitably means a positive or extraordinarily close margin and eradication of the sarcoma cells on the dura is not easy. Because of these issues with tumor eradication, the natural inclination is to combine surgery and radiation therapy to treat these patients.
The potential morbidity associated with surgery in the skull base, spine and paraspinal regions can be significant. En bloc resection resulting in negative margins is challenging because of the tumor proximity to vital and delicate structures such as spinal cord, nerve roots, brainstem, and cranial nerves. The ultimate surgical goal is to achieve the best possible eradication of the tumor while preserving neurological function. The same normal structures that pose difficulty for resection are also a problem for the radiation oncologist, because the dose limitations offered by the delicate structures in close proximity to the target region make it hard to deliver the high dose of radiation therapy necessary to control these tumors. Important technological advances in radiation oncology have enabled conformal delivery of high-dose radiation therapy, translating into decreased normal tissue toxicity and at the same time enabling local disease control.
For medically or technically inoperable patients, or patients who want to forgo surgery, high-dose definitive radiation therapy using modern technology achieves a useful tumor control probability (TCP), with decreasing efficacy in patients with tumors larger than 500 cc.
General Considerations
Surgery
Type of resection and margin status are important prognostic factors for the local control (LC) of chordomas and chondrosarcomas. Unfortunately, the difficult and intricate anatomical territory makes it hard to achieve tumor-negative margins and the intraoperative and postoperative complication rates are as high as 46%.
En bloc resection is favored in the spine because this type of surgical resection leads to superior LC. Boriani et al. found that en bloc resection played an important role in decreasing local recurrence rates and also improved survival.
Margin status is thought to influence the risk of local recurrence; however, in the presence of radiation therapy, patients with contaminated margins may have similar rates of LC and survival as patients with negative margins. Schwab et al. focused on sacral chordomas treated with wide negative margins versus contaminated margins ; in the presence of radiation therapy, there was no difference in LC or survival rates for patients with sacral chordomas treated with wide versus contaminated margins. Delivering sufficient dose is essential to providing adequate LC—the dose of radiation therapy should be higher than 60 Gy; the effective dose for microscopically positive margins is generally 66–70 Gy and for gross residual disease >70 Gy.
Intralesional resections of spine chordomas are associated with inferior LC. Rotondo et al. reported rates of local and locoregional control for intralesional resection versus en bloc of 55% versus 72% ( P = .016) and 53% versus 70% ( P = .033), respectively. Ozaki et al. presented the outcome of a series of 26 chondrosarcomas managed by intralesional surgery. Out of these, 18 were of the axial skeleton and 8 were located in the extremities. The rate of relapse-free survival at 20 years was 7%, in contrast to 64% for patients whose margins were negative. Local regrowth was observed in 7 of 7 patients treated by curettage and in 14 of 19 patients following attempted radical resection. Radiation was employed in 4 of the 26 intralesional cases; the doses were 15, 30, 60, and 60 Gy. Of these, there was LC in one patient with sacral chondrosarcoma following excision and 60 Gy. Shives et al. described the outcome of 19 patients treated surgically at Mayo Clinic for chondrosarcoma of the spine; the procedure was described as intralesional or extralesional with contaminated margins in all patients. Five patients also received radiation, only one of whom received ≥50 Gy. No patient received chemotherapy. Local failure developed in 14 of these 19 patients. That is, inadequate surgery for low-grade chondrosarcomas was not inevitably followed by local regrowth. In fact, five patients are listed as NED at more than 60 months after treatment. Although, this was true in their experience, even for tumors categorized as chondrosarcoma grade 1, ideal management is negative margin resection, combined with radiation if wide or negative margins are not achieved.
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