Development and Commissioning of a Protocol for Intracavitary High Dose Rate Brachytherapy Treatment In a Murine Cervical Cancer Model
Abstract
Purpose
This study seeks to establish a protocol for intracavitary HDR brachytherapy treatment in a murine cervical cancer model mimicking patient treatment procedure. This procedure includes the use of large-bore simulation CT imaging and clinical treatment planning software, as well as commercial remote afterloaders.
Methods
A mouse HDR treatment planning and delivery protocol was developed, emulating clinical workflow including applicator placement verification through cervical marker, simulation CT scans, and treatment planning. Three mice were implanted with commercial 17-Gauge interstitial titanium needles commissioned for intracavitary transvaginal implants in mice. CT reconstruction kernel selection was investigated to optimize accurate tissue and material mapping. The need for dose calculation heterogeneity corrections, comparing a homogeneous water-based calculation model (TG-43) against a model-based dose calculation algorithm (MBDCA) employing heterogeneity corrections (AcurosBV), was compared. Treatment plans were created to deliver 400 cGy to two reference points located 5 mm laterally from the source midline. CT reconstruction kernel influence on the MBDCA dose at the two reference points was evaluated on the Qr40 (CT calibration curve, iMAR), Br56, and Hr44 (iMAR) kernels.
Results
Successful needle placement and localization were verified through gauze saturated with contrast (Omnipaque 350) placed into the vagina to mark the cervix and further verified through necropsy with the brachytherapy needle still in place. For the three implanted mice, the average (range) percent difference between TG-43 and MBDCA dose at reference points was 2.5% (1.8%-3.4%). CT reconstruction kernel showed little impact on the dose evaluated at the reference points with the largest percent difference between kernels within each mouse ranged from 0.9%-2%.
Conclusion
A protocol for intracavitary, clinically-mimicking HDR treatments of a murine cervical cancer model was successfully developed. Dose calculations employing heterogeneity corrections are recommended for optimal dosimetric accuracy. We show that the calculated MBDCA dose is generally agnostic to CT reconstruction kernel.