A Computational Framework for Patient-Specific Dose Agreement Verification in CBCT-Guided Radiation Therapy

Abstract

Purpose: To develop a computational framework for patient-specific dose agreementverification in cone-beam CT (CBCT) -guided radiation therapy (RT) for esophageal cancer treatment. Materials/Methods: Ten esophageal cancer patients undergoing CBCT-guided RT (Total Dose = 50 - 60 Gy, Treatment Fraction(Fx) =25 - 30, 5 Fx/ week) were retrospectively studied, and treatment plan, planning CT (pCT), CBCT images prior to each treatment fraction, along with couch correction records were collected for each patient. Two computational experiments were designed to calculate (1) fractional dose without CBCT guidance, and (2) fractional dose distributions under CBCT-guided RT. In the first experiment, a series of virtual CT were generated by rigidly registering the pCT to each CBCT images, mimicking patient anatomy after initial patient setup through laser system and surface marker. The original treatment plan was then applied to compute the fractional dose distribution. In the second experiment, couch movement data, as guided by CBCT, were further incorporated to refine the final patient positioning and fractional dose distributions were calculated similarly. The total dose can be calculated by combining fractional doses with/without CBCT for every patient, simulating different clinical scenarios such as full CBCT utilization, missing 5, 10, 15, 20 CBCT throughout the treatment, and complete absence of CBCT, as in traditional methods different from image-guided radiation therapy (IGRT). For each scenario, 100-fold random combinations were performed, and calculated total dose was compared with the planned dose based on the following clinical evaluation metrices: PTV ´ D2%, PTV ´ D98%, Lung ´ Dmean, SpinalCord ´ Dmax, and Heart ´ V30. Results: Our framework successfully quantified the impact of CBCT utilization on patient-specific dosimetric outcome. PTV coverage decreased for every 5 missing fractions of CBCT utilization. Dose to organ at risk changes depending on the relative position of target area with respect to the organ at risk. Conclusion: The proposed method provides a computational framework to verify patientiv specific dose agreement in CBCT-guided esophageal cancer RT. Our methods can also be generalized to other IGRT modalities across various treatment sites.