Evaluation of Potential Interchangeability Between CBCT and Calypso® for Target Localization During Prostate RT Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/j38609963

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  • Introduction: In today's radiological quest to pacify and eliminate cancer, it has become conventional in cancer treatment facilities to implement advanced guidance or target localization systems with the goal of maximizing accuracy of radiation dose delivery to a tumor while simultaneously minimizing normal tissue complication. At the Oregon Health & Science University, prostate cancer patients can be treated with radiation therapy using real-time target monitoring with the aid of the Calypso® System. Clinical protocol allows for verification of Calypso-based patient localization with a cone-beam computed tomography (CBCT) scan. While CBCT is presumed to be the "gold standard" for patient alignment and target localization, both CBCT and the Calypso System are independently commissioned and calibrated for clinical use. This thesis utilizes inferential statistics to evaluate the potential for interchangeability between CBCT and the Calypso system for patient alignment and target localization during prostate cancer external beam radiotherapy. Hypothesis: We hypothesize that the difference in means of target displacements from isocenter recorded by CBCT and Calypso is less than 1 mm, the smallest increment of movement possible on the patient couch and thus the threshold of mechanical positioning accuracy, in the vertical (AP), longitudinal (SI), and lateral directions (LR). Methods and Materials: A cohort of 120 prostate cancer patients aligned with Calypso and treated on a clinical linear accelerator with multiple fractions (N=1,118) of external-beam radiation therapy formed the basis for this study. Corresponding CBCT verification shifts of Calypso positioning were recorded and tested for practical equivalence at a tolerance of ±1 mm using Equivalence Testing or a Two One Sided Test (TOST). Populations of independently recorded vertical, longitudinal, and lateral displacement values were evaluated to determine if values recorded by sequential Calypso-CBCT localizations could be empirically considered as equivalent. Result: Our study finds that the positions reported in all three axes (superior-inferior, anterior-posterior, and left-right) by Calypso and CBCT during target localization can be considered practically equivalent when tested to a tolerance of ±1 mm. Conclusion: With this result, we claim that CBCT and Calypso are interchangeable technologies for the purpose of aligning prostate cancer patients. Nonetheless, further assessments must be performed to determine the clinical implications of the current finding. Caveat: We warn all readers not to accept our claims through faith, but rather by means of a rigorous in house study confirming our findings as well as through collaborations and discussions between radiation team members within their department prior to integrating our claims in construction of or modification to existing clinical protocols and/or practices.
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