Quantitative assessment of irradiated lung volume and lung mass in breast cancer patients treated with tangential fields in combination with deep inspiration breath hold (DIBH).
OBJECTIVE
Comparison of the amount of irradiated lung tissue volume and mass in patients with breast cancer treated with an optimized tangential-field technique with and without a deep inspiration breath-hold (DIBH) technique and its impact on the normal-tissue complication probability (NTCP).


METHODS
Computed tomography datasets of 60 patients in normal breathing (NB) and subsequently in DIBH were compared. With a Real-Time Position Management Respiratory Gating System (RPM), anteroposterior movement of the chest wall was monitored and a lower and upper threshold were defined. Ipsilateral lung and a restricted tangential region of the lung were delineated and the mean and maximum doses calculated. Irradiated lung tissue mass was computed based on density values. NTCP for lung was calculated using a modified Lyman-Kutcher-Burman (LKB) model.


RESULTS
Mean dose to the ipsilateral lung in DIBH versus NB was significantly reduced by 15%. Mean lung mass calculation in the restricted area receiving ≤ 20 Gy (M(20)) was reduced by 17% in DIBH but associated with an increase in volume. NTCP showed an improvement in DIBH of 20%. The correlation of individual breathing amplitude with NTCP proved to be independent.


CONCLUSIONS
The delineation of a restricted area provides the lung mass calculation in patients treated with tangential fields. DIBH reduces ipsilateral lung dose by inflation so that less tissue remains in the irradiated region and its efficiency is supported by a decrease of NTCP.
Zurl
Brigitte
B
University Clinic of Therapeutic Radiology and Oncology, Medical University of Graz, Graz, Austria. brigitte.zurl@klinikum-graz.at
Stranzl
Heidi
H
Winkler
Peter
P
Kapp
Karin Sigrid
KS
D000328:Adult; D000368:Aged; D001822:Body Burden; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D007103:Immobilization / Q000379:methods; D008168:Lung / Q000000981:diagnostic imaging* / Q000528:radiation effects*; D008875:Middle Aged; D009038:Motion; D011835:Radiation Protection / Q000379:methods*; D011859:Radiography; D011874:Radiometry; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000379:methods*; D015656:Respiratory Mechanics