4D-CT-based target volume definition in stereotactic radiotherapy of lung tumours: Comparison with a conventional technique using individual margins
Received 27 March 2009; received in revised form 24 August 2009; accepted 25 August 2009. published online 27 September 2009.
Abstract
Purpose
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.
Material and methods
Two different PTVs were defined: PTVconv 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 PTV4D 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 40.7cm3 (31%) (p<0.001). A significant inverse correlation was found for the motion vector and the amount of inclusion of PTV4D in PTVconv (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.
ABSTRACT