Evaluation of coplanar partial left breast irradiation using tomotherapy-based topotherapy.
OBJECTIVE
To investigate the use of topotherapy for accelerated partial breast irradiation through field-design optimization and dosimetric comparison to linear accelerator-based three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiation therapy (IMRT).


METHODS
Hypothetical 3-cm lumpectomy sites were contoured in each quadrant of a left breast by using dosimetric guidelines from the National Surgical Adjuvant Breast and Bowel Project B-39/Radiation Therapy Oncology Group 0413 protocol. Coplanar intensity-modulated topotherapy treatment plans were optimized by using two-, three-, four-, five-, and seven-field arrangements for delivery by the tomotherapy unit with fixed gantry angles. Optimized noncoplanar five-field 3D-CRT and IMRT were compared with corresponding topotherapy plans.


RESULTS
On average, 99.5% +/- 0.5% of the target received 100% of the prescribed dose for all topotherapy plans. Average equivalent uniform doses ranged from 1.20-2.06, 0.79-1.76, and 0.10-0.29 Gy for heart, ipsilateral lung, and contralateral lung, respectively. Average volume of normal breast exceeding 90% of the prescription and average area of skin exceeding 35 Gy were lowest for five-field plans. Average uniformity indexes for five-field plans using 3D-CRT, IMRT, and topotherapy were 1.047, 1.050, and 1.040, respectively. Dose-volume histograms and calculated equivalent uniform doses of all three techniques illustrate clinically equivalent doses to ipsilateral breast, lung, and heart.


CONCLUSIONS
This dosimetric evaluation for a single patient shows that coplanar partial breast topotherapy provides good target coverage with exceptionally low dose to organs at risk. Use of more than five fields provided no additional dosimetric advantage. A comparison of five-field topotherapy to 3D-CRT and IMRT for accelerated partial breast irradiation illustrates equivalent target conformality and uniformity.
McIntosh
Alyson
A
Department of Radiation Oncology, University of Virginia, Charlottesville, VA 22908, USA.
Read
Paul W
PW
Khandelwal
Shiv R
SR
Arthur
Douglas W
DW
Turner
A Benton
AB
Ruchala
Kenneth J
KJ
Olivera
Gustavo H
GH
Jeswani
Sam
S
Sheng
Ke
K
D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D003198:Computer Simulation; D006801:Humans; D015412:Mastectomy, Segmental; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D036542:Tomography, Spiral Computed / Q000379:methods*