Stereotactic Body Radiation Therapy Planning For Pancreas Cancer Under Real Time Ultrasound Monitoring

Stereotactic Body Radiation Therapy (SBRT) allows for high doses of radiation to be delivered to the pancreas tumor over 3-5 days with limited toxicity. Nevertheless, motion of the pancreas caused by patient respiration introduces major uncertainty during SBRT. Ultrasound guidance is a non-ionizing, real-time and cost effective technique for intra-fractional monitoring. However, placement of an ultrasound probe on the abdomen may limit the selection of beam angles. This study investigated the clinical radiation treatment with and without the ultrasound probe in place. Four pancreatic SBRT cases were randomly selected and IRB approval was obtained. A transabdominal 4D probe was scanned and fused to the abdominal surface of patient CT as a virtual simulation. Both intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) were planned on the fused CT. During planning, angles of the beams were selected to be more than 45 degrees away from the central axis of the probe. Planning prescription and constraints were set as in the clinically treated plan. Planning target volume (PTV) was prescribed with a total dose of 33 Gy in 5 fractions. Major constraints for PTV and organs at risk (OAR) include percentage volume receiving 33 Gy (V33) for PTV, V42.9 for PTV, V20 and V15 for proximal duodenum, proximal stomach, and proximal bowel. Planning results were assessed with our institution pancreas SBRT protocol and compared with the clinically treated plans. All plans including IMRT and VMAT delivery passed all protocol criteria. The average V33 of the PTV was 92.6±2.1% for virtual simulation plans and 92.1±2.1% for clinically treated SBRT plans. The average V20 and V15 from virtual simulation for proximal duodenum (3.4% and 9.6%), proximal stomach (0.3% and 2.1%), and proximal bowel (0.3% and 2.6%) all passed protocol specification. No statistically significant difference (p> 0.05) in the protocol criteria was found between the plan with and without probe. Table 1 summarizes the planning result comparison. SBRT IMRT and VMAT planning was successfully completed while avoiding placement of an abdominal ultrasound probe. Therefore, no planning quality compromise is required for pancreas SBRT treatment delivery under real-time ultrasound monitoring.Poster Viewing Abstracts 3480; Table 1Planning result comparison for virtual simulation plan and clinically treated plan.PTVproximal duodenumproximal stomachproximal bowelV33V42.9V20V15V20V15V20V15Virtual simulation plan with probe [%]92.60.33.49.60.22.80.42.6Clinically treated plan [%]92.10.41.810.20.42.10.52.4p value0.720.700.830.760.810.780.911.00 Open table in a new tab