Evaluation of novel modified tangential irradiation technique for breast cancer patients using dose-volume histograms.
OBJECTIVE
We have previously reported that entire axillary lymph node regions could be irradiated by the modified tangential irradiation technique (MTIT). In this study, MTIT was compared with a conventional irradiation technique (CTIT) using dose-volume histograms to verify how adequately MTIT covers the breast and axillary lymph node region and the extent to which it involves the lung and heart.


METHODS
Forty-four patients with early-stage breast cancer were treated by lumpectomy, axillary dissection, and postoperative radiotherapy. Twenty-two patients were treated with MTIT and 22 with CTIT. In 25 patients, the breast tumor was on the left and in 19 on the right. During axillary dissection, surgical clips were left as markers at the border of the axillary lymph node region. MTIT was planned by setting the dorsal edge of the radiation field on a lateral-view simulator film at the dorsal edge of the humeral head and the cranial edge of the radiation field at the caudal edge of the humeral head. CTIT was planned to ensure radiation of the breast tissue without considering the axillary region. In this study, all patients underwent computed tomography, and the CT data were transmitted on-line to a radiotherapy planning system, in which the dose-distribution computed tomography images and dose-volume histograms were calculated by defining the breast, axillary region (levels I, II, and III), lung, and heart region.


RESULTS
Dose-volume histogram analysis demonstrated that breast tissue was radiated with an 86.5-100% volume (median 96.5%) by MTIT and an 83-100% volume (median, 95%) by CTIT at >95% of the isocenter dose. The axillary lymph node regions at Levels I, II, and III were irradiated with 84-100% (median, 94.5%), 59-100% (median, 89%), and 70-100% (median, 89.5%) volumes, respectively, by MTIT and with 2-84% (median, 38%), 0-53% (median, 15%), and 0-31% (median, 0%) volumes, respectively, by CTIT at >70% of the isocenter dose. The ipsilateral lung was irradiated with a 5-22% volume (median, 11.5%) by MTIT and 5-15% volume (median 9%) by CTIT at >90% of the isocenter dose. In all 25 left-sided breast cancer patients, the volumes irradiated with an 80% isocenter dose were <30 cm(3).


CONCLUSIONS
The results of our study demonstrated that the breast tissue was sufficiently irradiated with both CTIT and MTIT planning, the axillary lymph node areas irradiated by MTIT were much wider than those irradiated by CTIT at all levels, and the lung and heart volumes irradiated by MTIT were small.
Department of Radiology, Keio University School of Medicine and Tokyo Metropolitan Hiroo Hospita, Tokyo, Japan.
Atsuya
A
Takeda
Naoyuki
N
Shigematsu
Tadashi
T
Ikeda
Osamu
O
Kawaguchi
Shoji
S
Kutsuki
Ryochi
R
Ishibashi
Etsuo
E
Kunieda
Toshiaki
T
Takeda
Kazuhiko
K
Takemasa
Hisao
H
Ito
Takashi
T
Uno
Hiromitsu
H
Jinno
Atsushi
A
Kubo
D000328:Adult; D000368:Aged; D001365:Axilla; D001943:Breast Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D003131:Combined Modality Therapy; D005260:Female; D006801:Humans; D008197:Lymph Node Excision; D015182:Lymphatic Irradiation / Q000379:methods*; D015412:Mastectomy, Segmental; D008875:Middle Aged; D011878:Radiotherapy / Q000379:methods; D011879:Radiotherapy Dosage