Motion Likelihood Over Spine Radiosurgery Treatments—An Intrafraction Motion Analysis

Abstract

The maximum difference for target D90 between the reference plan and plans with applicator rotation was 0.2%, 24.2%, 30.8% for 1) circumferential, 2) anterior, and 3) lateral target, respectively. For bladder D 2cc , the maximum difference was 2.7%, 11.0%, 26.1% for 1), 2), and 3), respectively. Similarly, for rectum D 2cc , it was 3.2 %, 5.0%, 24.7%, for 1), 2), and 3), respectively. Compared to circumferential target, anterior and one-sided lateral target had larger differences. Dosimetric differences > 5% occurred at ! 15 degree rotation (or ! 2.6mm radial shift) for anterior target and ! 10 degree rotation (or !1.7mm radial shift) for lateral target. For the lateral target, there was a substantial difference between symmetric rotations clockwise and counter-clockwise rotations, while anterior and circumferential target dosimetry did not differ significantly between the two directions. Conclusion:We have demonstrated significant variation in the degree of impact based on location of tumor. In order to achieve a dosemtric deviation of less than 5%, rotational error must be limited to less than 10-15%. Quality assurance measures should be taken to avoid rotation between planning and treatment.

Evaluation of spine structure stability at different locations during SBRT

“…The mean time to SSH was longer than 6 min in all spine segments, giving a probable motion of less than 0.17 mm/min. Kim et al 23 evaluated the intra-treatment spinal motion pre-, mid-and post-treatment for cone beam CT (CBCT) and reported the potential magnitude of motion per unit time as 0.15 mm/min, which is in agreement with our results.…”