Customized computed tomography-based boost volumes in breast-conserving therapy: use of three-dimensional histologic information for clinical target volume margins.
OBJECTIVE
To determine the difference in size between computed tomography (CT)-based irradiated boost volumes and simulator-based irradiated volumes in patients treated with breast-conserving therapy and to analyze whether the use of anisotropic three-dimensional clinical target volume (CTV) margins using the histologically determined free resection margins allows for a significant reduction of the CT-based boost volumes.


METHODS
The CT data from 49 patients were used to delineate a planning target volume (PTV) with isotropic CTV margins and to delineate a PTV(sim) that mimicked the PTV as delineated in the era of conventional simulation. For 17 patients, a PTV with anisotropic CTV margins was defined by applying customized three-dimensional CTV margins, according to the free excision margins in six directions. Boost treatment plans consisted of conformal portals for the CT-based PTVs and rectangular fields for the PTV(sim).


RESULTS
The irradiated volume (volume receiving > or =95% of the prescribed dose [V(95)]) for the PTV with isotropic CTV margins was 1.6 times greater than that for the PTV(sim): 228 cm(3) vs. 147 cm(3) (p < .001). For the 17 patients with a PTV with anisotropic CTV margins, the V(95) was similar to the V(95) for the PTV(sim) (190 cm(3) vs. 162 cm(3); p = NS). The main determinant for the irradiated volume was the size of the excision cavity (p < .001), which was mainly related to the interval between surgery and the planning CT scan (p = .029).


CONCLUSIONS
CT-based PTVs with isotropic margins for the CTV yield much greater irradiated volumes than fluoroscopically based PTVs. Applying individualized anisotropic CTV margins allowed for a significant reduction of the irradiated boost volume.
Hanbeukers
Bianca
B
Department of Radiation Oncology, MAASTRO Clinic, Dr. Tanslaan 12, Maastricht, The Netherlands.
Borger
Jacques
J
van den Ende
Piet
P
van der Ent
Fred
F
Houben
Ruud
R
Jager
Jos
J
Keymeulen
Kristien
K
Murrer
Lars
L
Sastrowijoto
Suprapto
S
van de Vijver
Koen
K
Boersma
Liesbeth
L
D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005260:Female; D006801:Humans; D015412:Mastectomy, Segmental; D008875:Middle Aged; D009367:Neoplasm Staging; D019736:Prostheses and Implants; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D019233:Retreatment; D012189:Retrospective Studies; D047368:Tumor Burden