Room: Exhibit Hall
Purpose: Linac-based stereotactic body radiation therapy (SBRT) may be preferable for patients who cannot tolerate a long treatment time. We aim to compare treatment planning using CyberKnife and a linac-based system for para-aortic lymph node cases.
Methods: Three SBRT treatment plan optimizations on patients with tumor in para-aortic lymph nodes were performed. The same set of computed tomography (CT) images and contours was used for each patient in both modalities. The gross tumor volume (GTV) was contoured by a physician and planning target volume defined as PTV=GTV+3mm. 35Gy/5fxs was prescribed to the target. Cyberknife plans were optimized with Ray-tracing algorithm with synchrony respiratory tracking technique using Accuray MultiPlan 5.3, and linac-based SBRT optimizations were performed using Varian Eclipse 11.0. For the comparison, homogeneity index (HI) for GTV and PTV, total MUs, DVHs and dose distribution around the target were analyzed for each case.
Results: While both modalities can provide satisfactory target dose coverage, HI values were higher for CyberKnife than for linac planning in all cases. Also, the variation of PTV HI was small (<14%) in CK plans, where it was significantly larger (up to 179%) for linac-based plan between different patients. Maximum dose to the target was higher for CyberKnife, while the surrounding tissue received lower dose than the linac-based plan. However, dose to critical organs showed no significant difference. Total delivered MUs were higher in CyberKnife plans by 130% in average, but that depended on the target size.
Conclusion: Linac-based SBRT is less time consuming (~5 mins vs. ~50 mins) for patient setup, imaging and delivery with smaller MUs, while the planning quality is comparable to that of Cyberknife. The result provides a suggestion of treatment modality selection based on dosimetric object, patient condition, normal tissue sparing, respiratory motion management and clinical capacity.