First clinical investigation of CBCT and deformable registration for adaptive proton therapy of lung cancer

Publication date: Available online 4 February 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Catarina Veiga, Guillaume Janssens, Ching-Ling Teng, Thomas Baudier, Lucian Hotoiu, Jamie R. McClelland, Gary Royle, Liyong Lin, Lingshu Yin, James Metz, Timothy D. Solberg, Zelig Tochner, Charles B. Simone, James McDonough, Boon-Keng Kevin Teo
PurposeAn adaptive proton therapy workflow using cone-beam computed tomography (CBCT) is proposed. It consists of an online evaluation of a fast range-corrected dose distribution based on a virtual CT (vCT). This may be followed by more accurate offline dose recalculation on the vCT which may trigger a rescan CT (rCT) for replanning.Methods and MaterialsThe workflow was tested retrospectively on twenty consecutive lung cancer patients. A diffeomorphic Morphons algorithm was used to generate the lung vCT, by deforming the average planning CT (pCT) onto the CBCT. An additional correction step was applied to account for anatomical modifications that cannot be modeled by deformation alone. A set of clinical indicators for replanning were generated based on water equivalent thickness (WET) and dose statistics, and compared to those obtained on a rCT. The fast dose approximation consisted of warping the initial planned dose onto the vCT based on changes in WET. Potential under/over-ranges were assessed as variation in WET at the target's distal surface.ResultsThe range-corrected dose from the vCT reproduced similar clinical indicators as the rCT. The workflow performed well under different clinical scenarios: atelectasis, lung reinflation and different types of tumor response. Between vCT and rCT, we found a difference in the measured 95% percentile of the over-ranges distribution of 3.4±2.7mm. The limitations of the technique consisted of inherent uncertainties of deformable registration and drawbacks of CBCT imaging. The correction step was adequate when gross errors occurred but could not recover subtle anatomical or density changes in tumors with complex topology.ConclusionsA proton therapy workflow based on CBCT provided similar clinical indicators as rCT on lung patients with considerable anatomical changes.

Teaser

Accurate patient positioning and routine computed tomography (CT) scans are critical components of proton therapy. Cone-beam CT (CBCT) has recently become available as an alternative to verification CT. This study describes the first clinical investigation of CBCT and deformable registration in adaptive lung proton therapy.


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