A dosimetric comparison of IORT techniques in limited-stage breast cancer.
OBJECTIVE
For intraoperative radiotherapy (IORT) during breast-conserving treatment four different techniques have been addressed: interstitial brachytherapy, an inflatable balloon with a central high-dose-rate source (MammoSite), a miniature orthovolt system (Intrabeam), and linac-based electron radiotherapy (IOERT). The dosimetric properties of these methods are compared.


METHODS
Planning target volumes (PTVs) of the same size but of different shapes are assumed, corresponding to the technique's specific situs. Dose distributions for the PTVs and for surrounding tissues are demonstrated by dose-volume histograms and a list of physical parameters. A dose inhomogeneity index (DII) is introduced to describe the deviation of a delivered from the prescribed dose, reaching its minimal value 0 in case of perfect homogeneity.


RESULTS
In terms of DII, IOERT reaches the lowest value followed by the MammoSite, the Intrabeam and interstitial implants. The surrounding tissues receive the smallest average dose with IOERT, closely followed by the orthovolt system.


CONCLUSIONS
When comparing simplified geometric figures, IOERT delivers the most homogeneous dose distributions. However, in clinical reality PTVs often present asymmetric shapes instead of ideal geometries. Due to a strictly centric dose fall-off, any system with a round central applicator will have technical limits. During IOERT margin-directed applicator guidance is possible and interstitial brachytherapy allows for polygonal dose shaping. These techniques seem to be superior for asymmetric PTV irradiation.
Nairz
Olaf
O
Department of Radio-Oncology, Salzburger Landeskliniken and Paracelsus Private Medical University (PMU), Salzburg, Austria.
Deutschmann
Heinz
H
Kopp
Michael
M
Wurstbauer
Karl
K
Kametriser
Gerhard
G
Fastner
Gerd
G
Merz
Florian
F
Reitsamer
Roland
R
Menzel
Christian
C
Sedlmayer
Felix
F
D001943:Breast Neoplasms / Q000532:radiotherapy* / Q000601:surgery*; D006801:Humans; D007430:Intraoperative Care / Q000379:methods*; D015412:Mastectomy, Segmental / Q000379:methods*; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016896:Treatment Outcome