Customized computed tomography-based boost volumes in breast-conserving therapy: use of three-dimensional histologic information for clinical target volume margins.

Abstract

PURPOSE:

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.

PATIENTS AND 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).

CONCLUSION:

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.

• Authors: Bianca Hanbeukers, Jacques Borger, Piet van den Ende, Fred van der Ent, Ruud Houben, Jos Jager, Kristien Keymeulen, Lars Murrer, Suprapto Sastrowijoto, Koen van de Vijver, Liesbeth Boersma
• Journal: International journal of radiation oncology, biology, physics (Int J Radiat Oncol Biol Phys) Vol. 75 Issue 3 Pg. 757-63 (Nov 01 2009) ISSN: 1879-355X [Electronic] United States
• PMID: 19304402 (Publication Type: Journal Article)

Topics

• Adult
• Aged
• Breast Neoplasms (diagnostic imaging, pathology, radiotherapy, surgery)
• Cone-Beam Computed Tomography (methods)
• Female
• Humans
• Mastectomy, Segmental
• Middle Aged
• Neoplasm Staging
• Prostheses and Implants
• Radiotherapy Dosage
• Radiotherapy Planning, Computer-Assisted (methods)
• Retreatment
• Retrospective Studies
• Tumor Burden