2989 - Direct-to-Unit Adaptive Celiac Plexus Radiation Therapy

B. Guevara¹, A. Rezaei¹, T. Arsenault¹, R. Woods¹, G. C. Pereira¹, R. Kashani¹, A. T. Price², and L. E. Henke²; ¹University Hospitals, Seidman Cancer Center, Case Western Reserve University, Cleveland, OH, ²Department of Radiation Oncology, University Hospitals Seidman Cancer Center, Case Western Reserve University, Cleveland, OH

Purpose/Objective(s): Celiac plexus SBRT (CP-RT 25Gy/1fx) is an effective method of palliative pain relief for patients suffering from celiac axis tumor invasion. Standard complex/SBRT radiotherapy (RT) workflows for simulation and planning delay time to pain relief during end-of-life care. We propose a sim free, direct-to-unit (DTU) adaptive radiotherapy (ART) approach, using a diagnostic CT (dxCT) pre-plan and online adaptation for final plan construction to enable same-day radiation oncology consult and CP-RT. We aimed to demonstrate that hCBCT imaging enables this DTU, adaptive CP-RT workflow in silico with acceptable plan quality. Materials/

Methods: Five patients with abdominal malignancies were imaged on a HyperSight CBCT (hCBCT) solution on a c-arm linear accelerator as part of a prospective imaging clinical trial. Next, existing patient-specific dxCTs were used to generate CP-RT pre-plans. A radiation oncologist contoured initial pre-plan organ-at-risk (OARs; stomach, duodenum, small and large bowel, liver, kidneys, spinal cord) and targets. The CP-RT target (PTV25Gy) was defined as a 5mm ant-left/right rind around the aorta from the level of T12 to L2. An additional 5mm isotropic expansion was used to create the PTV20Gy. A semi-automated ART planning template developed for CP-RT was then applied. After pre-plan construction, to simulate a sim-free, DTU workflow, hCBCTs were injected into a CT-guided ART emulator environment as the primary dataset, with contours propagated from the registered dxCT. Contours were updated as needed to reflect the treatment anatomy and positioning. A standard online ART workflow was utilized for predicted and final adaptive plan calculation. Dosimetric statistics for each clinical goal were compared between predicted and final plans.
Results: DTU adaptive CP-RT plans were successfully created for all 5 patients and met all clinical goals. Table 1 shows comparative PTV coverage and OAR sparing of predicted and final ART plans. Without adaptation, predicted plans were infeasible for clinical use; 3/5 patients had non deliverable predicted plans. In contrast, all ART plans were clinically deliverable and met clinical goals.
Conclusion: DTU ART for CP-RT is dosimetrically feasible. Adaptation is a critical component for DTU CP-RT to achieve deliverable plans. This approach could reduce treatment delay for cancer-related celiac pain. A prospective pilot clinical trial is in development.

Abstract 2989 - Table 1: Clinical Goals for Targets and OARs comparison between Adapted and Predicted Plans

	Clinical Goal (Priority)	PLAN
		Average Adapted	Average Predicted
PTV25OPT	V100 (2)	97.1	66.6
PTV20OPT	V100 (2)	95.2	76.4
Cord	D1cc<11Gy (1)	7.3	6.9
Stomach	V11Gy<1cc (3)	0.5	0.8
	V15 Gy<0.03 cc (1)	0.0	0.0
	V12 Gy <5cc (1)	0.2	0.3
Duodenum	V11Gy<1cc (3)	0.8	0.0
	V15 Gy<0.03 cc (1)	0.0	0.0
	V12 Gy <5cc (1)	0.1	0.0
Small Bowel	V11Gy<1cc (3)	0.8	5.4
	V15 Gy<0.03 cc (1)	0.0	0.5
	V12 Gy <5cc (1)	0.1	3.3
Large Bowel	V11Gy<1cc (3)	2.2	0.1
	V15 Gy<0.03 cc (1)	0.0	0.0
	V12 Gy <5cc (1)	0.0	0.0
Kidneys	Dmean<5.5Gy (3)	3.7	3.2