Four-dimensional treatment planning for stereotactic body radiotherapy.
OBJECTIVE
To investigate the influence of tumor motion on the calculation of four-dimensional (4D) dose distributions of the gross tumor volume (GTV) in pulmonary stereotactic body radiotherapy.


METHODS
For 7 patients with eight pulmonary tumors, a respiratory-correlated 4D-computed tomography study was acquired. The internal target volume was the sum of all tumor positions in the planning 4D-computed tomography study, and a 5-mm margin was used for generation of the planning target volume. Three-dimensional (3D) treatment plans were generated with a dose prescription of 3 x 12.5 Gy to the planning target volume enclosing the 65% and 80% isodose. After model-based nonrigid image registration, the 4D dose distributions were calculated.


RESULTS
No significant difference was found in the dose to the GTV with the tumor in the end-exhalation, end-inhalation, or mid-ventilation phase of the breathing cycle. The high-dose region was confined to the solid tumor, and lower doses were delivered to the surrounding pulmonary tissue of lower density. This nonstatic, variant dose distribution increased the 4D dose to the GTV by 6.2%, on average, compared with calculations using on a static dose distribution during the breathing cycle. The 4D accumulation resulted in a biologic effective dose (BED) of 143 +/- 8 Gy and 106 +/- 4 Gy to the GTV in the plan-65% and plan-80%, respectively. The dose to the ipsilateral lung was not different between the 3D and 4D dose calculations or between plan-65% and plan-80%.


CONCLUSIONS
In this study, the dose to the GTV was not decreased or blurred in the 4D plan compared with the 3D plan. The 3D doses to the GTV, internal target volume, and dose at the isocenter were good approximations of the 4D dose calculations. The 3D dose at the planning target volume margin underestimated the 4D dose significantly.
Guckenberger
Matthias
M
Department of Radiation Oncology, Julius-Maximilians University, Wuerzburg, Germany. guckenberg_m@klinik.uni-wuerzburg.de
Wilbert
Juergen
J
Krieger
Thomas
T
Richter
Anne
A
Baier
Kurt
K
Meyer
Juergen
J
Flentje
Michael
M
D005240:Feasibility Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy* / Q000556:secondary; D009068:Movement; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D012062:Relative Biological Effectiveness; D012119:Respiration; D047368:Tumor Burden