Respiratory organ motion and dosimetric impact on breast and nodal irradiation.
OBJECTIVE
To examine the respiratory motion for target and normal structures during whole breast and nodal irradiation and the resulting dosimetric impact.


METHODS
Four-dimensional CT data sets of 18 patients with early-stage breast cancer were analyzed retrospectively. A three-dimensional conformal dosimetric plan designed to irradiate the breast was generated on the basis of CT images at 20% respiratory phase (reference phase). The reference plans were copied to other respiratory phases at 0% (end of inspiration) and 50% (end of expiration) to simulate the effects of breathing motion on whole breast irradiation. Dose-volume histograms, equivalent uniform dose, and normal tissue complication probability were evaluated and compared.


RESULTS
Organ motion of up to 8.8mm was observed during free breathing. A large lung centroid movement was typically associated with a large shift of other organs. The variation of planning target volume coverage during a free breathing cycle is generally within 1%-5% (17 of 18 patients) compared with the reference plan. However, up to 28% of V(45) variation for the internal mammary nodes was observed. Interphase mean dose variations of 2.2%, 1.2%, and 1.4% were observed for planning target volume, ipsilateral lung, and heart, respectively. Dose variations for the axillary nodes and brachial plexus were minimal.


CONCLUSIONS
The doses delivered to the target and normal structures are different from the planned dose based on the reference phase. During normal breathing, the dosimetric impact of respiratory motion is clinically insignificant with the exception of internal mammary nodes. However, noticeable degradation in dosimetric plan quality may be expected for the patients with large respiratory motion.
Qi
X Sharon
XS
Department of Radiation Oncology, University of Colorado Denver, Aurora, USA. xiangrong.qi@ucdenver.edu
White
Julia
J
Rabinovitch
Rachel
R
Merrell
Kenneth
K
Sood
Amit
A
Bauer
Anderson
A
Wilson
J Frank
JF
Miften
Moyed
M
Li
X Allen
XA
D000328:Adult; D000368:Aged; D001940:Breast / Q000033:anatomy & histology; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D005260:Female; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006321:Heart / Q000033:anatomy & histology; D006801:Humans; D008168:Lung / Q000033:anatomy & histology; D015182:Lymphatic Irradiation; D015412:Mastectomy, Segmental; D008875:Middle Aged; D009068:Movement; D009929:Organ Size; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D012119:Respiration; D012189:Retrospective Studies; D018709:Statistics, Nonparametric; D047368:Tumor Burden