Four-dimensional dosimetry validation and study in lung radiotherapy using deformable image registration and Monte Carlo techniques.
Thoracic cancer treatment presents dosimetric difficulties due to respiratory motion and lung inhomogeneity. Monte Carlo and deformable image registration techniques have been proposed to be used in four-dimensional (4D) dose calculations to overcome the difficulties. This study validates the 4D Monte Carlo dosimetry with measurement, compares 4D dosimetry of different tumor sizes and tumor motion ranges, and demonstrates differences of dose-volume histograms (DVH) with the number of respiratory phases that are included in 4D dosimetry. BEAMnrc was used in dose calculations while an optical flow algorithm was used in deformable image registration and dose mapping. Calculated and measured doses of a moving phantom agreed within 3% at the center of the moving gross tumor volumes (GTV). 4D CT image sets of lung cancer cases were used in the analysis of 4D dosimetry. For a small tumor (12.5 cm3) with motion range of 1.5 cm, reduced tumor volume coverage was observed in the 4D dose with a beam margin of 1 cm. For large tumors and tumors with small motion range (around 1 cm), the 4D dosimetry did not differ appreciably from the static plans. The dose-volume histogram (DVH) analysis shows that the inclusion of only extreme respiratory phases in 4D dosimetry is a reasonable approximation of all-phase inclusion for lung cancer cases similar to the ones studied, which reduces the calculation in 4D dosimetry.
Huang
Tzung-Chi
TC
Department of Biomedical Imaging and Radiological Sciences, National Yang Ming University, Taiwan.
Liang
Ji-An
JA
Dilling
Thomas
T
Wu
Tung-Hsin
TH
Zhang
Geoffrey
G
D003198:Computer Simulation; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted; D011874:Radiometry; D011880:Radiotherapy Planning, Computer-Assisted