Assessment of parotid gland dose changes during head and neck cancer radiotherapy using daily megavoltage computed tomography and deformable image registration.
OBJECTIVE
To analyze changes in parotid gland dose resulting from anatomic changes throughout a course of radiotherapy in a cohort of head-and-neck cancer patients.


METHODS
The study population consisted of 10 head-and-neck cancer patients treated definitively with intensity-modulated radiotherapy on a helical tomotherapy unit. A total of 330 daily megavoltage computed tomography images were retrospectively processed through a deformable image registration algorithm to be registered to the planning kilovoltage computed tomography images. The process resulted in deformed parotid contours and voxel mappings for both daily and accumulated dose-volume histogram calculations. The daily and cumulative dose deviations from the original treatment plan were analyzed. Correlations between dosimetric variations and anatomic changes were investigated.


RESULTS
The daily parotid mean dose of the 10 patients differed from the plan dose by an average of 15%. At the end of the treatment, 3 of the 10 patients were estimated to have received a greater than 10% higher mean parotid dose than in the original plan (range, 13-42%), whereas the remaining 7 patients received doses that differed by less than 10% (range, -6-8%). The dose difference was correlated with a migration of the parotids toward the high-dose region.


CONCLUSIONS
The use of deformable image registration techniques and daily megavoltage computed tomography imaging makes it possible to calculate daily and accumulated dose-volume histograms. Significant dose variations were observed as result of interfractional anatomic changes. These techniques enable the implementation of dose-adaptive radiotherapy.
Lee
Choonik
C
Department of Radiation Oncology, M. D. Anderson Cancer Center Orlando, 1400 South Orange Avenue, Orlando, FL 32806, USA. Choonik.Lee@orhs.org
Langen
Katja M
KM
Lu
Weiguo
W
Haimerl
Jason
J
Schnarr
Eric
E
Ruchala
Kenneth J
KJ
Olivera
Gustavo H
GH
Meeks
Sanford L
SL
Kupelian
Patrick A
PA
Shellenberger
Thomas D
TD
Mañon
Rafael R
RR
D000465:Algorithms; D003528:Carcinoma, Adenoid Cystic / Q000000981:diagnostic imaging / Q000532:radiotherapy; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging / Q000532:radiotherapy; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D010306:Parotid Gland / Q000000981:diagnostic imaging / Q000528:radiation effects*; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated; D036542:Tomography, Spiral Computed