Abstract
Background and purpose: Fast and reliable tumor localization is an important part of today's radiotherapy utilizing new delivery techniques. This proof-of-principle study demonstrates the use of a method called herein 'stochastic triangulation' for this purpose. Stochastic triangulation uses very short imaging arcs and a few projections. Materials and methods: A stochastic Maximum A Posteriori ...
Abstract
Background and purpose: Fast and reliable tumor localization is an important part of today's radiotherapy utilizing new delivery techniques. This proof-of-principle study demonstrates the use of a method called herein 'stochastic triangulation' for this purpose. Stochastic triangulation uses very short imaging arcs and a few projections. Materials and methods: A stochastic Maximum A Posteriori (MAP) estimator is proposed based on an uncertainty-driven model of the acquisition geometry and inter-/intra-fractional deformable anatomy. The application of this method was designed to use the available linac-mounted cone-beam computed tomography (CBCT) and/or electronic portal imaging devices (EPID) for the patient setup based on short imaging arcs. For the proof-of-principle clinical demonstration, the MAP estimator was applied to 5 CBCT scans of a prostate cancer patient with 2 implanted gold markers. Estimation was performed for several (18) very short imaging arcs of 5 degrees with 10 projections resulting in 90 estimations. Results: Short-arc stochastic triangulation led to residual radial errors compared to manual inspection with a mean value of 1.4 mm and a standard deviation of 0.9 mm (median 1.2 mm, maximum 3.8 mm) averaged over imaging directions all around the patient. Furthermore, abrupt intra-fractional motion of up to 10 mm resulted in radial errors with a mean value of 1.8 mm and a standard deviation of 1.1 mm (median 1.5 mm, maximum 5.6 mm). Slow periodic intra-fractional motions in the range of 12 mm resulted in radial errors with a mean value of 1.8 mm and a standard deviation of 1.1 mm (median 1.6 mm, maximum 4.7 mm). Conclusion: Based on this study, the proposed stochastic method is fast, robust and can be used-for inter- as well as intra-fractional target localization using current CBCT units. (C) 2013 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 106 (2013) 241-249
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