Interstitial photodynamic therapy (I-PDT) has been shown promising results in the treatment of locally advanced head-and-neck cancer (LAHNC). In this therapy, systemic administration of a light sensitive drug is followed by insertion of multiple laser fibers to illuminate the tumor and its margins. Image-based pretreatment planning is employed to compute light delivery to the complex LAHNC anatomy. However, tumor shape deformation during treatment could negatively impact the capacity to deliver the planned light dose to tumor and margins. This paper presents a novel computational method designed for calculating deformed tumor shape, in seconds, to allow for real time update of the treatment planning. The new method utilizes implanted fiducial markers (FM) and their registration during therapy. This new, deformed tumor shape is calculated by solving the inverse problem of what would have resulted in the corresponding FM displacements. The computational method is studied on spheres of variable sizes and demonstrated on computed tomography (CT) reconstructed LAHNC model. Results of this study demonstrate an average error of less than 1 mm in predicting the deformed tumor shape, where 1 mm is typically the order of uncertainty in distance measurements using CT imaging and high-quality ultrasound imaging. This study further demonstrates that the deformed shaped can be calculated in a few seconds, making the proposed method clinically relevant.
Ye Han, Emily Oakley, Gal Shafirstein, Yoed Rabin, Levent Burak Kara. (2016). Reconstruction of a deformed tumor for treatment planning of interstitial photodynamic therapy: A computational feasibility study. The 14th International Symposium Computer Methods in Biomechanics and Biomedical Engineering. Tel Aviv, Israel, September 20-22, 2016.