Radiosurgery for spinal malignant tumors

Abstract

Background: Radiosurgery is a special treatment method that employs highly focused radiation to destroy tumors with high precision in a single session. A broad base of scientific evidence already exists for the radiosurgical treatment of brain metastases. Recent advances in medical technology now allow radiosurgery to be extended to the spine as well.

Methods: Selective literature review based on a PubMed search using the search terms stereotaxis, radiosurgery, stereotactic radiotherapy, accuracy, quality assurance, spine, spine metastasis, pain, Novalis, CyberKnife, Synergy, and robotics. We also present and analyze our own data as an illustration of the application of spinal radiosurgery.

Results: The literature search identified 20 scientific original publications and one recent review. The data indicate that, within the specific constraints of the method, radiosurgery can arrest the growth of up to 96% of spinal metastases. Durable pain relief can be achieved in patients with tumor-associated pain syndromes. The morbidity of spinal radiosurgery is low, with a less than 1% risk of myelopathy.

Conclusions: Spinal radiosurgery is an independent, essentially noninvasive method of treatment. Different types of radiosurgical treatment apparatus are available. For properly selected patients, radiosurgery offers a good chance of therapeutic success with relatively rare complications.

Keywords: cancer treatment; medical technology; quality of life; radiation therapy; surgery.

Figure 1

(a) Radiation over segments of a circle in radiotherapy with a moving source. Three arc segments are schematically depicted; in practice, 9 to 15 arc segments are usually used. (b) Radiation with stationary fields. The diagram shows three stationary fields shaped by a multileaf collimator. In practice, 7 to 13 stationary fields with multileaf collimation are usually used. Figures 1(a) and 1(b) correspond to treatment with gantry-based systems such as Novalis and Synergy. (c) Radiation with multiple microstationary fields according to the CyberKnife concept. The diagram shows 14 such fields, shaped by a cylindric collimator. In practice, 150 to 350 fields of this type are usually used.

Figure 2

Axial CT section through a 10^th thoracic vertebra containing a metastasis of undifferentiated sarcoma. CyberKnife radiosurgery was performed; the target was defined as the involved area of the skeletal structures. The red line indicates the target volume. The radiosurgical dose was 35 Gy in the center of the tumor and 22.8 Gy at the 65% isodose line (green line). The 60%, 50%, and 40% isodose lines are shown in yellow, while the 30%, 20%, and 10% isodose lines are shown in white. The dose distribution was calculated with a special planning algorithm (inverse planning principle, Monte Carlo simulation). This method yields not only the dose within the tumor, but also a protective value for the spinal cord. The low water content of pulmonary tissue, through which part of the applied radiation passes, was also taken into account.

Figure 3

The radiation exposure of normal tissue as a function of tumor volume. The parameter V10 designates the volume of tissue (in cm³) that is exposed to a dose of 10 Gy or higher. The diagram is based on data from 70 patients with solitary spinal metastases who were treated radiosurgically with the CyberKnife. The tumor volume is the volume (in cm³) of the spinal metastases treated. The blue line represents a polynomial fitting function of these two parameters; the shaded area corresponds to the 95% confidence interval.

Figure 4

(a) Intramedullary metastasis of breast carcinoma at the C2 vertebral level, causing incipient quadriparesis. (b) Complete remission of the clinical manifestations and subtotal radiological remission of the metastasis upon follow-up 4 weeks after treatment. (Contrast-enhanced sagittal MR images.)

Figure 5

(a) Metastasis of breast carcinoma in the right side of the sacrum causing radicular pain. (b) Complete remission of clinical manifestations and radiological remission of the metastasis as seen in a follow-up study 3 months after treatment. (c) Another follow-up study 11 months after treatment shows recalcification of the area that originally harbored the metastasis. (PET-CT images in (a), (b), and (c).)

Figure 6

Local tumor control rate of radiosurgery of solitary cerebral and spinal metastases. The brain metastases were treated radiosurgically with either the Leksell Gamma Knife or the CyberKnife, while the spinal metastases were treated with the CyberKnife. Kaplan-Meier curves for recurrence-free survival are shown. The recurrence-free survival 18 months after treatment was 94% to 96% in all three groups. (No significant differences between groups were found with the Cox proportional hazard model.)