4D-CT-based target volume definition in stereotactic radiotherapy of lung tumours: comparison with a conventional technique using individual margins.
OBJECTIVE
To investigate the dosimetric benefit of integration of 4D-CT in the planning target volume (PTV) definition process compared to conventional PTV definition using individual margins in stereotactic body radiotherapy (SBRT) of lung tumours.


METHODS
Two different PTVs were defined: PTV(conv) consisting of the helical-CT-based clinical target volume (CTV) enlarged isotropically for each spatial direction by the individually measured amount of motion in the 4D-CT, and PTV(4D) encompassing the CTVs defined in the 4D-CT phases displaying the extremes of the tumour position. Tumour motion as well as volumetric and dosimetric differences and relations of both PTVs were evaluated.


RESULTS
Volumetric examinations revealed a significant reduction of the mean PTV by 4D-CT from 57.7 to 40.7 cm(3) (31%) (p<0.001). A significant inverse correlation was found for the motion vector and the amount of inclusion of PTV(4D) in PTV(conv) (r=-0.69, 90% confidence limits: -0.87 and -0.34, p=0.007). Mean lung dose (MLD) was decreased significantly by 17% (p<0.001).


CONCLUSIONS
In SBRT of lung tumours the mere use of individual margins for target volume definition cannot compensate for the additional effects that the implementation of 4D-CT phases can offer.
Department of Radiation Oncology, University of Heidelberg, Heidelberg, Germany. holger.hof@med.uni-heidelberg.de
Holger
H
Hof
Bernhard
B
Rhein
Peter
P
Haering
Annette
A
Kopp-Schneider
Jürgen
J
Debus
Klaus
K
Herfarth
D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000601:surgery*; D009068:Movement; D016634:Radiosurgery; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012119:Respiration; D036542:Tomography, Spiral Computed