Comparison of spinal Stereotactic Body Radiotherapy (SBRT) planning techniques: intensity-modulated radiation therapy, modulated arc therapy, and helical tomotherapy

Stereotactic body radiotherapy (SBRT) delivers a highly conformal, hypofractionated radiation dose to a small target with minimal radiation applied to the surrounding areas. Therefore, using the proper treatment planning techniques for SBRT is important. Intensity modulation techniques, such as static intensity-modulated radiation therapy (IMRT), modulated arc therapy (mARC), and helical tomotherapy (HT), are useful for spinal SBRT because of a rapid dose fall-off and spinal cord avoidance. This study compared the planning characteristics for hypofractionated spinal SBRT administered using 3 treatment techniques. The factors evaluated for spinal SBRT planning were dose coverage, cord avoidance, target conformity, homogeneity, and dose spillage. Target coverage was 82.74% ± 3.35%, 80.92% ± 0.81%, and 85.01% ± 7.27% for IMRT, mARC, and HT, respectively. HT was therefore a powerful technique with respect to target coverage. The spinal cord dose for HT (mean, 1763.96 cGy; standard deviation [SD], 164.48) was significantly different from those for mARC (mean, 1991.75 cGy; SD, 248.00) and IMRT (mean, 2053.24 cGy; SD, 164.48). In addition, the partial spinal cord volume at 2000 cGy for HT (mean, 0.12 cc, SD, 0.01) was significantly different from those for IMRT and mARC (0.50 ± 0.10 cc and 0.56 ± 0.25 cc, respectively). The conformity index was 1.30 ± 0.12, 1.08 ± 0.05, and 1.36 ± 0.23 for IMRT, mARC, and HT planning, respectively. mARC showed the highest conformity (p = 0.000). HT used a narrow field fan beam and exhibited remarkable improvement of target coverage and cord dose, offering an important benefit to spinal SBRT. mARC had the highest target conformity and better high- and intermediate-dose spillage than HT and IMRT did, respectively. These planning techniques have different advantages. In the case of spine SBRT, HT should be used for cord avoidance. In some cases, such as for a short treatment duration when the patient is considered to be in a poor general condition, mARC can be used.