3013 - Evaluation of In-Vivo Dose Delivery in Lung SBRT Using a Novel, Automated Offline Adaptive Radiotherapy Assessment Software

Purpose/Objective(s): ChartCheck Adaptive (CCA) is a novel, offline adaptive radiotherapy (ART) assessment software, which allows quantitative evaluation of delivered dose by performing Monte Carlo (MC) dose calculation on synthetic CT scans created from daily CBCTs. Dose-tracking during radiotherapy is especially important in SBRT, as changes in patient anatomy or set-up for even a single fraction may be clinically significant and require plan modifications for the remainder of a treatment course. We explored the clinical feasibility of CCA for in-vivo dose tracking by comparing target and OAR DVH metrics from treatment plans calculated with Varian Eclipse Acuros XB (AXB) vs. those calculated on synthetic CTs for a series of patients receiving lung SBRT.

Materials/Methods: 21 patients treated with lung SBRT were included in the analysis; lesions were grouped by lung location, specifically “peripheral” (= 2 cm from pleura), central (=2 cm from mediastinum) or “island” (= 2 cm from both). Treatment data was imported by CCA to perform synthetic CT generation and MC dose calculation. Results were compared to AXB dose calculations on original treatment planning CTs. Differences between original and synthetic generated plans for target (ITV and PTV) coverage and adjacent OAR dose metrics were calculated.

Results:

CCA proved consistent at deforming CBCT images into synthetic CTs for MC dose calculation for targets in all three lung locations. PTV and ITV D95% calculated on synthetic scans were consistently less than the original plan (-9.0±8.0% and -3.1±4.3%, for PTV and ITV, respectively; p< 0.05). Except for lung dose, OAR metrics calculated from synthetic scans were estimated to be slightly higher than planned.

Conclusion: CCA provides real-time, reliable information regarding delivered dose in patients receiving lung SBRT using an efficient, automated workflow. Additional investigations will allow greater understanding of the specific differences observed between recalculated and planned dose for target volumes and OARs – refining the ability of CCA to help ensure safe and effective delivery of SBRT. To our knowledge, this is the first study of the application of CCA in patients receiving lung SBRT.

DVH Metric	Difference (%) between original AXB and MC dose calculation on Synthetic CTs
	ALL	Peripheral	Central	Island
SpinalCord D0.03cc = 28Gy	1.1±5.0%	-0.4±4.3%	3.9±2.9%	1.8±0.0%
Esophagus D0.03cc = 38Gy	2.6±4.2%	1.2±3.0%	4.5±5.8%	2.8±3.7%
Heart D0.03cc = 38Gy	6.6±9.4%	10.1±7.2%	4.4±9.9%	1.4±10.8%
GreatVes D0.03cc = 53Gy	8.2±12.4%	12.1±16.6%	6.1±7.2%	4.6±4.1%
Bronchus D0.03cc = 50Gy	2.1±9.1%	3.4±11.0%	5.2±5.5%	-0.5±6.2%
Chestwall D0.03cc = 57Gy	3.2±4.7%	3.6±4.8%	2.4±3.1%	2.7±5.0%
Lungs V13.5Gy = 37%	-3.6±5.3%	-2.9±3.9%	-9.7±3.9%	-1.9±3.1%
PTV_50 D95% = 100%	-9.0±8.0%	-11.1±10.6%	-6.2±2.9%	-7.9±3.4%
ITV D95% = 100%	-3.1±4.3%	-6.1±0.5%	-6.5±3.5%	-3.1±5.3%