Evaluation of geometric changes of parotid glands during head and neck cancer radiotherapy using daily MVCT and automatic deformable registration

• Published in: Radiotherapy and oncology 2008-10, Vol.89 (1), p.81-88
• Main Authors: Lee, Choonik, Langen, Katja M, Lu, Weiguo, Haimerl, Jason, Schnarr, Eric, Ruchala, Kenneth J, Olivera, Gustavo H, Meeks, Sanford L, Kupelian, Patrick A, Shellenberger, Thomas D, Mañon, Rafael R
• Format: Article
• Language: English
• Subjects: Algorithms; Daily MVCT; Deformable image registration; Head and neck cancer; Head and Neck Neoplasms - radiotherapy; Hematology, Oncology and Palliative Medicine; Humans; Parotid Gland - diagnostic imaging; Parotid Gland - radiation effects; Parotid gland changes; Radiation Dosage; Radiotherapy Planning, Computer-Assisted - methods; Tomography, Spiral Computed
• ISSN: 0167-8140; 1879-0887
• DOI: 10.1016/j.radonc.2008.07.006

Abstract Background and purpose To assess and evaluate geometrical changes in parotid glands using deformable image registration and megavoltage CT (MVCT) images. Methods A deformable registration algorithm was applied to 330 daily MVCT images (10 patients) to create deformed parotid contours. The accuracy and robustness of the algorithm was evaluated through visual review, comparison with manual contours, and precision analysis. Temporal changes in the parotid gland geometry were observed. Results The deformed parotid contours were qualitatively judged to be acceptable. Compared with manual contours, the uncertainties of automatically deformed contours were similar with regard to geometry and dosimetric endpoint. The day-to-day variations (1 standard deviation of errors) in the center-of-mass distance and volume were 1.61 mm and 4.36%, respectively. The volumes tended to decrease with a median total loss of 21.3% (6.7–31.5%) and a median change rate of 0.7%/day (0.4–1.3%/day). Parotids migrated toward the patient center with a median total distance change of −5.26 mm (0.00 to −16.35 mm) and a median change rate of −0.22 mm/day (0.02 to −0.56 mm/day). Conclusion The deformable image registration and daily MVCT images provide an efficient and reliable assessment of parotid changes over the course of a radiation therapy.