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Dynamic Arc Technique Improves Delivery Accuracy of Stereotactic Body Radiation Therapy (SBRT) for Spine

L Huang

L Huang*, T Djemil, S Chao, J Suh, P Xia, Cleveland Clinic Foundation, Cleveland, OH

SU-E-T-418 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To investigate whether delivery accuracy can be improved with volumetric intensity modulated arc (VMAT), a hybrid dynamic arc therapy (HA) with fixed beam IMRT when compared to fixed beam IMRT alone for spine SBRT.

Methods: Ten spine patients who underwent SBRT treatment using fixed beam IMRT were randomly chosen from an IRB approved registry. All cases were replanned with VMAT and HA techniques. The VMAT plans were created using the Pinnacle 9.0 with four 120 degree coplanar arcs and 120 segments. HA plans and clinical IMRT plans were created from Brainlab iplan. All HA plans used one 360 dynamic arc and 5-7 IMRT fixed beams, consisting 150-180 segments. All clinically IMRT plans used 7-9 fixed IMRT beams with 200-250 segments. All VMAT and HA plans were similar or better than clinical IMRT plans, meeting clinical objectives. All thirty plans were delivered with the same linear accelerator and measured with a 2D ion chamber array. The gamma index (GI) (3mm/3% and 2mm/2%) was used to test the delivery accuracy for each plan.

Results: For the three delivery techniques, VMAT, HA, and IMRT, the average GI of 3mm/3% were 98.9±0.6%, 96.5±2.7%, and 92.6±1.1%, respectively. The average GI of 2mm/2% were 92.3±2.4%, 90.4±2.1%, and 82.0±2.2%, respectively. There is no significant difference on delivery accuracy between the VMAT plans and HA plans(P =0.09 for GI (3mm/3%) and P=0.229 for GI(2mm/2%)). There is a significant difference (P<0.05) on delivery accuracy between VMAT (or HA) and IMRT plans based on GI of 3mm/3% and 2mm/2% criteria.

Conclusions Dynamic arc techniques improve delivery accuracy of stereotactic body radiation therapy for the spinal lesions. VMAT or HA is a better choice than fixed beam IMRT with improved delivery accuracy.

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