Predicting changes in dose distribution to tumor and normal tissue when correcting for heterogeneity in radiotherapy for lung cancer.
OBJECTIVE
The purposes of this study were to examine dose alterations to gross tumor volume (GTV) and lung using heterogeneity corrections and to predict the magnitude of these changes.


METHODS
Three separate conformal plans were generated for 37 patients with lung cancer: plan 1 corrected for heterogeneity, plan 2 did not correct for heterogeneity, and plan 3 used identical beams and monitor units from plan 2 but with heterogeneous calculations. Plans 1 and 2 were normalized to the 95% isodose line. Mean dose (MeanDGTV), maximum dose (MaxDGTV), and minimum dose (MinDGTV) to GTV and V20 were compared between plans 1 and 3. For each patient, the amount of lung in all beam paths of plan 3 was quantified by a density correction factor and correlated with the percent change.


RESULTS
The median percent change in MeanDGTV, MaxDGTV, and MinDGTV between plan 3 and plan 1 was -4.7% (-0.1% to -19.1%, P < 0.0001), -5.59% (0.16% to -31.86%, P < 0.0001), and -4.88% (2.90% to -24.88%, P < 0.0001), respectively. The median V20 difference was -1% (1% to -8%). The density correction factor correlated with larger differences in MeanDGTV on univariate analysis.


CONCLUSIONS
Heterogeneity correction lowers the dose to GTV by 5%. This difference can be correlated with the density correction factor.
Chang
Daniel
D
Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, Florida 32610-0385, USA.
Liu
Chihray
C
Dempsey
James F
JF
Palta
Jatinder R
JR
Kopea
Jill
J
Louis
Debbie
D
Morris
Christopher
C
Chopra
Rahul
R
Olivier
Kenneth R
KR
D000704:Analysis of Variance; D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology / Q000532:radiotherapy*; D018288:Carcinoma, Small Cell / Q000473:pathology / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D009367:Neoplasm Staging; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D013909:Thorax / Q000528:radiation effects*; D014057:Tomography, X-Ray Computed