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Precision required for dose-escalated treatment of spinal metastases and implications for image-guided radiation
Matthias Guckenberger1, Juergen Meyer, Juergen Wilbert
1Department of Radiation Oncology, University of Wuerzburg, Wuerzburg, Germany. guckenberg_m@klinik.uni-wuerzburg.de
Introduction:
To evaluate the precision required in dose-escalated IMRT treatment of spinal metastases and paraspinal tumors.
Methods:
In IMRT treatment plans of nine patients with spinal metastases (n=7) and paraspinal tumors (n=2) translational patient positioning errors (0-10mm) and rotational errors (0-7.5 degrees ) were simulated. The dose to the spinal cord (D5(spine)) resulting from these simulations was evaluated and NTCP for spinal cord necrosis was calculated. All patient set-up errors observed during treatment were simulated and the influence on D5(spine) was investigated.
Results:
To keep the dose distribution to the spinal cord within +/-5% (+/-10%) of the prescribed dose, maximum tolerable errors of 1mm (2mm) in the transversal plane, 4mm (7mm) in superior-inferior direction and maximum rotations of 3.5 degrees (5 degrees ) were calculated on average. The translational and rotational component of clinically observed set-up errors increased D5(spine) by 23+/-14% and 3+/-2% on average, respectively.
Conclusion:
Steep dose gradients of IMRT planning require very high precision. In selected patients correction of both translational and rotational errors may be beneficial.
