Conventionally-fractionated image-guided intensity modulated radiotherapy (IG-IMRT): a safe and effective treatment for cancer spinal metastasis

Abstract

Background: Treatments for cancer spinal metastasis were always palliative. This study was conducted to investigate the safety and effectiveness of IG-IMRT for these patients.

Methods: 10 metastatic lesions were treated with conventionally-fractionated IG-IMRT. Daily kilovoltage cone-beam computed tomography (kV-CBCT) scan was applied to ensure accurate positioning. Plans were evaluated by the dose-volume histogram (DVH) analysis.

Results: Before set-up correction, the positioning errors in the left-right (LR), superior-inferior (SI) and anterior-posterior (AP) axes were 0.3 +/- 3.2, 0.4 +/- 4.5 and -0.2 +/- 3.9 mm, respectively. After repositioning, those errors were 0.1 +/- 0.7, 0 +/- 0.8 and 0 +/- 0.7 mm, respectively. The systematic/random uncertainties ranged 1.4-2.3/3.0-4.1 before and 0.1-0.2/0.7-0.8 mm after online set-up correction. In the original IMRT plans, the average dose of the planning target volume (PTV) was 61.9 Gy, with the spinal cord dose less than 49 Gy. Compared to the simulated PTVs based on the pre-correction CBCT, the average volume reduction of PTVs was 42.3% after online correction. Also, organ at risk (OAR) all benefited from CBCT-based set-up correction and had significant dose reduction with IGRT technique. Clinically, most patients had prompt pain relief within one month of treatment. There was no radiation-induced toxicity detected clinically during a median follow-up of 15.6 months.

Conclusion: IG-IMRT provides a new approach to treat cancer spinal metastasis. The precise positioning ensures the implementation of optimal IMRT plan, satisfying both the dose escalation of tumor targets and the radiation tolerance of spinal cord. It might benefit the cancer patient with spinal metastasis.

Figure 1

The maximum, minimum and mean dose of the 10 metastatic lesions (PTV) in treatment plans and the average level.

Figure 2

The maximum dose of the spinal cord in treatment plans and the average level.

Figure 3

The homogeneity index/dose conformity index and the average level in treatment plans (1, 2, 3..10 represented the number of the IMRT plans, respectively).

Figure 4

A representative IMRT plan with radiation isodose curves. The PTV (red region) was covered by the 95% curve of the prescription dose (the green line), and the dose of the adjacent cord was less than 49 Gy. (a: transverse section and b: sagittal section).

Figure 5

Comparison of the simulated effects of the positioning errors with/without CBCT-based online set-up correction in the LR, SI and AP axes on the irradiation dose of the spinal cord with the actual plan (red and orange line: isocenter moving left/right in LR axis, yellow and deep green lines: isocenter moving superior/inferior in SI axis, blue and purple lines: isocenter moving anterior/posterior in AP axis, respectively; and the green line was the actual DVH of the cord). (a: the simulated and actual DVHs of the cord and b: the simulated and actual maximum dose of 5% volume of the cord).