(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: SBRT liver requires précised dose delivery to the targets. Liver is a soft tissue organ, relative position between multi-targets can vary from CT Simulation on treatment couch. It is often unable to align each of 2-3 targets satisfactorily using a single isocenter setup. The current study evaluated the impact of the distance and location to the setup deviation among multi-targets.
Methods: 10 out of 35 (recently treated) liver SBRT patients had 2-3 targets. These 10 patients had either implanted fiducials or residual TACE as surrogates for image guided SBRT. Respiratory motions were managed by gating or expiratory breath-hold. Multi-targets positional deviations from planning CT were measured on pretreatment CBCT. Distance between two targets was determined between their centers of mass. Target locations were categorized to eight sub-segments based on a transverse plane through the bifurcation of the main portal vein (Couinaud system).
Results: In 23 targets, 6-7 targets were involved in each of V, VI, VIII, VIII segment. 1-4 targets were involved in each of I, II, III, IV segment. In 55 target-pairs, the target distance ranged 4.8-14.7 cm. Positional deviations ranged 0.0-1.1 cm in lateral (x), 0.0-1.0 cm in anterior-posterior (y), and 0.0-1.1 cm in superior-inferior (z) direction (total n=165). There were no associations between target distance and positional deviations (x, y, z) (R =0.4). For target distance < 5.5 cm, 95% positional deviations were within 0.5 cm. For target distance > 5.5 cm, 53% positional deviation were greater or equal to 0.5 cm. large deviations were observed in targets in segment VI, II, III.
Conclusion: Multi-targets in liver may not be aligned satisfactorily using a single isocenter setup, if distance between targets was greater than 5.5 cm. Larger deviation was likely to occur for targets located at peripheral lobes.
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