[Internal target volume definition using four-dimensional CT and dosimetric evaluation for hepatocellular carcinoma].
OBJECTIVE
Accurate definition of target volume is difficult in three-dimensional conformal radiotherapy (3D CRT) for liver tumors because of the wide moving extent of tumors with respiration. This study was to define individualized internal target volume (ITV) using four-dimensional computed tomography (4D-CT), and compare planning target volumes (PTVs) and dose distribution of 3D planning with 4D planning for hepatocellular carcinoma (HCC).


METHODS
Seven primary HCC patients received 4D-CT scanning. Gross tumor volumes (GTVs) and clinical target volumes (CTVs) were contoured on all 10 respiratory phases of CT images. The 3D and 4D treatment plans were made for each patient using different PTVs, namely, PTV-3D derived from a single CTV plus conventional margins; PTV-4D derived from ITV-4D which encompassing all 10 CTVs plus setup margins (SM). The two plans were designed at the 20% respiratory phase CT images using 3D treatment planning system and compared with respect to PTVs, dose distribution to normal tissues, normal tissue complication probability. The prescription dose and design of irradiating fields were identical for both plans.


RESULTS
The average PTV was (417.6+/-197.7) cm(3) in 3D plan and (331.9+/-183.1) cm(3) in 4D plan, decreased by 20.50% (12.60%-34.40%). PTV coverage and dose uniformity were similar in the 2 plans. 4D plans spared more normal liver, kidney, stomach, and small intestine than 3D plans, especially for the liver. The V30 and V40 of the liver were lower in 4D plans than in 3D plans (33.59% vs. 38.77%, 22.62% vs. 27.32%); the mean dose to normal liver was decreased from 24.13 Gy to 21.5 Gy; liver complication probability was decreased from 21.57% to 15.86%. Without increasing the normal tissue complication probability, the prescription dose was higher in 4D plans than in 3D plans [(54.86+/-2.79) Gy vs. (50.57+/-1.51) Gy], increased by 9.72% (4%-16%).


CONCLUSIONS
The 3D plans have pitfalls of geometric miss or over coverage of target volume. The 4D plans can accurately definite target volume to spare more normal tissues and make dose escalation as compared with 3D CRT.
Xi
Mian
M
State Key Laboratory of Oncology in South China, Guangzhou, Guangdong, 510060, P. R. China.
Liu
Meng-Zhong
MZ
Deng
Xiao-Wu
XW
Liu
Hui
H
Huang
Xiao-Yan
XY
Zhang
Li
L
Li
Qiao-Qiao
QQ
Hu
Yong-Hong
YH
Cai
Ling
L
Cui
Nian-Ji
NJ
D000328:Adult; D000368:Aged; D006528:Carcinoma, Hepatocellular / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D007668:Kidney / Q000528:radiation effects; D008099:Liver / Q000528:radiation effects; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods; D012119:Respiration; D014057:Tomography, X-Ray Computed / Q000379:methods*