Exhibit Hall | Forum 7
Purpose: Spine alignment is crucial yet can be challenging in multi-isocenter spine SBRT due to the complex dose distribution and large dose gradient around the cord at the field junction. Predicting the dosimetric impact of setup uncertainty can help guide planning and patient setup. In this study we use an in-house script to prospectively evaluate the dosimetric impact of uncertainty on the spinal cord and cauda.
Methods: RAdiotherapy Dose Accumulation Routine (RADAR) is a script developed for automatic dose accumulation. RADAR accounts for registration and setup uncertainties in the composite dose by introducing perturbations in the spatial dose accumulation. We used RADAR in five spine cases where each received concurrent SBRT in 3 or 5 fractions to two adjacent targets planned with separate isocenters. Setup uncertainties between adjacent isocenters due to change in spine curvature or local deformation were simulated in RADAR using perturbations of incremental radius. RADAR calculated the composite dose distributions and dose to the cord or cauda and compared with the original plan sum.
Results: The maximum dose to cord or cauda remained similar to the planned values with 1mm 3D spatial uncertainty, and it started to rise by 380cGy up to 946cGy when increasing the SI shift between two isocenters from 2mm to 6mm and keeping 1mm or 2mm AP and LR shift. Dose to cord or cauda at the field junction appeared to be relatively insensitive to SI shift between the 2 isocenters except for one case which saw an increase of more than 800cGy over 6mm SI shift.
Conclusion: This study illustrates the feasibility of using an automated dose accumulation script to predict the dosimetric impact to the spinal cord from setup uncertainties which could ultimately help design treatment plans as well as set a reliable action threshold for patient setup and treatment.
Funding Support, Disclosures, and Conflict of Interest: This work is partially funded by NIH/NCI Cancer Center Support Grant/Core Grant P30 CA008748
Not Applicable / None Entered.