Click here to


Are you sure ?

Yes, do it No, cancel

Potential of Treating Multiple Targets with a Single-Isocenter in Spinal SRS/SBRT

X Wang*, G Zhao , J Sutton , A Ghia , J Li , M McAleer , UT MD Anderson Cancer Center, Houston, TX


(Wednesday, 8/1/2018) 10:00 AM - 10:30 AM

Room: Exhibit Hall | Forum 9

Purpose: To investigate the advantage and feasibility of using single-isocenter to treat two targets separated by a vertebra in spinal SRS/SBRT.

Methods: Eight patient cases were identified based on criteria of having two targets separated by one vertebra in the T- or L-spine region and prescribed with same fractions. Original clinical (two-isocenter) plan was generated with each target having its own isocenter. A new single-isocenter plan was constructed in this study for dosimetric comparison. DVHs of both targets and critical organs were examined to compare the quality of two plans with special attention to Dmin of GTV (local control), Dmax of cord/cauda (cord injury) and dose gradient between GTV and cord. To confirm the single-isocenter plan can be safely delivered, we retrospectively examined the treatment CBCT data for setup accuracy.

Results: There are slight difference in DVHs between single-isocenter and two-isocenter plans with both satisfy the clinical requirements. Considering two most important parameters: Dmin to GTV and Dmax to cord/cauda, half of the cases show the single-isocenter plan is slightly worse. However, the largest under dose of Dmin or over dose of Dmax from the single-isocenter plan is 0.9 Gy, clinically insignificant. The setup data also confirms our ability to reliably set up three contiguous vertebrae in submillimeter accuracy in the T- and L-spine region. There are ~20% MU saving in single-isocenter plan. Most importantly, it eliminates the treatment session and resources required for the extra isocenter.

Conclusion: Single-isocenter plan was show to be comparable to the two isocenter plan in target coverage and normal tissue sparing, but could reduce the total treatment time/session by half. This provides significant benefits in patient convenience, comfort, throughput, and staffing resource. Lower half of spinal column was recommended with this approach with the use of advanced immobilization, IGRT and 6-degree couch.


Not Applicable / None Entered.


Not Applicable / None Entered.

Contact Email