TU-AB-201-06: Evaluation of Electromagnetically Guided High- Dose Rate Brachytherapy for Ablative Treatment of Lung Metastases
Purpose: The advent of electromagnetic navigation bronchoscopy has enabled minimally invasive access to peripheral lung tumors previously inaccessible by optical bronchoscopes. As an adjunct to Stereotactic Ablative Radiosurgery (SABR), implantation of HDR catheters can provide focal treatments for multiple metastases and sites of retreatments. The authors evaluate a procedure to deliver ablative doses via Electromagnetically-Guided HDR (EMG-HDR) to lung metastases, quantify the resulting dosimetry, and assess its role in the comprehensive treatment of lung cancer. Methods: A retrospective study was conducted on ten patients, who, from 2009 to 2011, received a hypo-fractionated SABR regimen with 6MV VMAT to lesions in various lobes ranging from 1.5 to 20 cc in volume. A CT visible pathway was delineated for EM guided placement of an HDR applicator (catheter) and dwell times were optimized to ensure at least 98% prescription dose coverage of the GTV. Normal tissue doses were calculated using inhomogeneity corrections via a grid-based Boltzmann solver (Acuros_BV_1.5.0). Results: With EMG-HDR, an average of 83% (+/−9% standard deviation) of each patient’s GTV received over 200% of the prescription dose, as compared to SABR where the patients received an average maximum dose of 125% (+/−5%). EMG-HDR enabled a 59% (+/−12%) decrease in the aorta maximum dose, a 63% (+/−26%) decrease in the spinal cord max dose, and 57% (+/−23%) and 70% (+/−17%) decreases in the volume of the body receiving over 50% and 25% of the prescription dose, respectively. Conclusion: EMG-HDR enables delivery of higher ablative doses to the GTV, while concurrently reducing surrounding normal tissue doses. The single catheter approach shown here is limited to targets smaller than 20 cc. As such, the technique enables ablation of small lesions and a potentially safe and effective retreatment option in situations where external beam utility is limited by normal tissue constraints.