Is helical tomotherapy accurate and safe enough for spine stereotactic body radiotherapy?

PURPOSE: We assessed the accuracy and safety of spine stereotactic body radiation therapy (SBRT) using helical tomotherapy (HT) via evaluating intrafractional patient movement.
METHODS: From July 2009 to April 2011, 22 patients with spine lesions received SBRT using HT, with a total of 61 fractions. To evaluate intrafractional movement, we compared post-treatment megavoltage CT scans with planning CT images and obtained translational [lateral (X), craniocaudal (Y), anterioposterior (Z)] offsets and total displacements (R). We analyzed the correlation of intrafractional motion with patient and treatment characteristics. We also analyzed dosimetric change to the target and spinal cord, resulting from intrafractional movement, in the three patients that showed the greatest R values.
RESULTS: Intrafractional movements were 0.7 ± 0.6 mm (X), 1.1 ± 0.7 mm (Y), 0.9 ± 0.6 mm (Z), and 1.8 ± 0.6 mm (R). This movement did not correlate with age, pain score, treatment time, or treatment site. Only patients with lower BMIs have a tendency to move more during treatment. Patient immobilization using wrapping form (thermoplastic mask and BodyFIX(®) system) resulted in less lateral movement and total displacement than others (0.498 ± 0.409 vs. 1.138 ± 0.637 mm, P < 0.001 for X; and 1.638 ± 0.691 vs. 1.976 ± 0.495 mm, P = 0.032 for R). However, this intrafractional motion did not affect the dose delivery to the target and spinal cord.
CONCLUSION: SBRT using HT can be a safe treatment modality for spine metastasis with enhanced targeting accuracy.