Dose distribution analysis of axillary lymph nodes for three-dimensional conformal radiotherapy with a field-in-field technique for breast cancer.
OBJECTIVE
We previously reported that most of axillary regions could be irradiated by the modified tangential irradiation technique (MTIT). The purpose of this study was to determine whether the three-dimensional conformal radiotherapy (3D-CRT) with a field-in-field technique improves dosimetry for the breast and axillary nodes.


METHODS
Fifty patients with left-sided breast cancer were enrolled. With MTIT, we planned the radiation field to be wider in the cranial direction than the standard tangential fields to include the axillary regions. With 3D-CRT, a field-in-field technique was used to spare the heart and contralateral breast to the extent possible by applying the multileaf collimator manually. Dose-volume histograms were compared for the breast, axillary region, heart, lung, and other normal tissues.


RESULTS
There were no significant differences in the percent volume of the breast receiving >90% of the prescribed dose (V90) between MTIT and 3D-CRT. The mean V90 of the level I to III axillary regions were increased from 93.7%, 48.2%, and 41.3% with MTIT to 97.6%, 85.8%, and 82.8% with 3D-CRT. 3D-CRT significantly reduced the volume of the heart receiving >30 Gy (mean, 7.6 vs. 15.9 mL), the percent volume of the bilateral lung receiving >20 Gy (7.4% vs. 8.9%), and the volume of other normal tissues receiving >107% of the prescribed dose (0.1 vs. 2.9 mL).


CONCLUSIONS
The use of 3D-CRT with a field-in-field technique improves axillary node coverage, while decreasing doses to the heart, lungs, and the other normal tissues, compared with MTIT.
Ohashi
Toshio
T
Department of Radiology, Keio University, School of Medicine, Tokyo, Japan.
Takeda
Atsuya
A
Shigematsu
Naoyuki
N
Fukada
Junichi
J
Sanuki
Naoko
N
Amemiya
Atsushi
A
Kubo
Atsushi
A
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001365:Axilla; D001822:Body Burden; D001943:Breast Neoplasms / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008198:Lymph Nodes / Q000528:radiation effects*; D008875:Middle Aged; D011874:Radiometry; D020266:Radiotherapy, Conformal / Q000379:methods*; D012062:Relative Biological Effectiveness; D018570:Risk Assessment / Q000379:methods*