Abstract
We investigated the feasibility of measuring daily fiducial length on cone-beam computed tomography (CBCT) images to assess the variation in daily tumor motion for pancreatic SBRT. Motion data for fifty pancreatic SBRT patients with fiducials were analyzed retrospectively to determine the tumor motion statistics. We also performed a phantom study which involved motion analysis of three gold fiducials placed around a solid target inside the Quasar Phantom as a function of variable tumor motion and breathing period. The end-exhalation CT-50 images were compared with the CBCT images acquired prior to treatment delivery on a TrueBeam STx linear accelerator. Sinusoidal tumor motion and patients’ breathing files acquired from a Varian-RPM system were used to simulate patients’ breathing patterns. The fiducial length was measured to determine its correlation with tumor motion. Patient tumor motions along the superior-inferior (SI), anterior-posterior (AP), and left-right (LR) directions were found to be 0.7 ± 0.4 cm, 0.2 ± 0.3 cm, and 0.1 ± 0.2 cm, respectively. Average breathing period was 4.3 ± 0.8 seconds. For sinusoidal and patients’ breathing patterns, a significant correlation was observed between the fiducial length and tumor motions with R2 of 0.99. However, fiducial length was found to be independent of the variation in breathing periods. This work suggests that measuring the fiducial length on daily CBCT images could provide quantitative daily tumor motion for fiducial-based pancreatic SBRT. A timely decision to modify the motion management strategy could be made prior to daily treatment delivery.
Highlights
Stereotactic Body Radiation Therapy (SBRT) of abdominal targets such as pancreatic and liver cancers has shown to be an effective treatment modality that could achieve high local control and reduced toxicity [1]-[6]
We investigated the feasibility of measuring daily fiducial length on cone-beam computed tomography (CBCT) images to assess the variation in daily tumor motion for pancreatic SBRT
This work suggests that measuring the fiducial length on daily CBCT images could provide quantitative daily tumor motion for fiducial-based pancreatic SBRT
Summary
Stereotactic Body Radiation Therapy (SBRT) of abdominal targets such as pancreatic and liver cancers has shown to be an effective treatment modality that could achieve high local control and reduced toxicity [1]-[6]. Motion study provides insight on tumor motion during 4-dimensional (4D) Computed Tomography (CT) simulation, variations in inter- and intra-fractional target motion result in the loss of targeting accuracy and reproducibility compared to the original treatment plan [2] [7]. Several studies [7] [8] discussed the applicability of the motion study data acquired during 4D-CT simulation over the course of treatment delivery. Regarding the SBRT technique of abdominal targets, tumor motion over the treatment course is susceptible to the variability of abdominal filling, patient setup, and therapy/disease-related progression due to tight setup margins. It is important to evaluate the daily variation of tumor motion prior to beam delivery, and compare the daily tumor motion to the reference 4D-CT motion data in order to ensure the adequacy of the plan delivery
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