Room: Exhibit Hall | Forum 7
Purpose: to develop a Monte Carlo based treatment planning system (TPS) for bioluminescent tomography (BLT) guided small animal radiation treatment.
Methods: EGSnrc was used to model the small animal irradiator with integrated onboard CBCT and BLT. The X-ray source, beam hardening filter and collimators were modeled in BEAMnrc. The modeling accuracy was validated by comparing simulated PDD and transverse profiles against EBT2 film measurements in a solid water phantom. A five-material heterogeneity phantom was used to acquire the relationship used to convert the CBCT intensity to true CT numbers used in DOSXYZnrc dose calculation. Calculation results were converted to radiation beam on time for treatment delivery. To test the TPS, a nude mouse with prostate tumor (2 weeks after inoculation with 5x10â?µ LNCaP cell stably expressing luciferase) received BLT guided RT. The tumor target was identified in the reconstructed BLT, then added 1mm margin as the PTV. Twenty Gy (225 kVp, 13mA) dose was prescribed to the tumor center and 5Gy each delivered from anterior, posterior, left lateral and right lateral, respectively.
Results: differences between simulation and film measurement was < 4% for PDD within 4cm depth for all except 1mm collimator (5.8%), and < 1.5% for dose within the transverse profile plateau for all collimators. The prostate tumor was measured 5mm Ã— 4mm Ã— 4mm in BLT. An 8mm collimator was used for irradiation of all fields which sufficiently cover the PTV. Dose calculation shows 100% prescribed dose covers the entire PTV, while hot regions in bones reached 54Gy.
Conclusion: BLT can reliably localize the tumor target and therefore provide image guidance for precision focal irradiation. After the PTV is determined in BLT, Monte Carlo TPS then provide accurate dose distribution in three dimension. Radiation delivery to the tumor target will be confirmed by histology in the ongoing study.