Tumor Bed Delineation for Partial Breast and Breast Boost Radiotherapy Planned in the Prone Position: What Does MRI Add to X-ray CT Localization of Titanium Clips Placed in the Excision Cavity Wall?
- Department of Academic Radiotherapy, Royal Marsden NHS Foundation Trust, Sutton (United Kingdom)
- Joint Departments of Radiotherapy and Physics, Institute of Cancer Research, Sutton (United Kingdom)
- Department of Clinical Magnetic Resonance, Institute of Cancer Research, Sutton (United Kingdom)
Purpose: To compare tumor bed (TB) volumes delineated using magnetic resonance imaging plus computed tomography and clips (MRCT) with those delineated using CT and clips (CT/clips) alone in postlumpectomy breast cancer patients positioned prone and to determine the value of MRCT for planning partial breast irradiation (PBI). Methods and Materials: Thirty women with breast cancer each had 6 to 12 titanium clips secured in the excision cavity walls at lumpectomy. Patients underwent CT imaging in the prone position, followed by MRI (T{sub 1}-weighted [standard and fat-suppressed] and T{sub 2}-weighted sequences) in the prone position. TB volumes were delineated separately on CT and on fused MRCT datasets. Clinical target volumes (CTV) (where CTV = TB + 15 mm) and planning target volumes (PTV) (where PTV = CTV + 10 mm) were generated. Conformity indices between CT- and MRCT-defined target volumes were calculated (ratio of the volume of agreement to total delineated volume). Discordance was expressed as a geographical miss index (GMI) (where the GMI = the fraction of total delineated volume not defined by CT) and a normal tissue index (the fraction of total delineated volume designated as normal tissue on MRCT). PBI dose distributions were generated to cover CT-defined CTV (CTV{sub CT}) with {>=}95% of the reference dose. The percentage of MRCT-defined CTV (CTV{sub MRCT}) receiving {>=}95% of the reference dose was measured. Results: Mean conformity indices were 0.54 (TB), 0.84 (CTV), and 0.89 (PTV). For TB volumes, the GMI was 0.37, and the NTI was 0.09. Median percentage volume coverage of CTV{sub CT} was 97.1% (range, 95.3%-100.0%) and of CTV{sub MRCT} was 96.5% (range, 89.0%-100.0%). Conclusions: Addition of MR to CT/clip data generated TB volumes that were discordant with those based on CT/clips alone. However, clinically satisfactory coverage of CTV{sub MRCT} by CTV{sub CT}-based tangential PBI fields provides support for CT/clip-based TB delineation remaining the method of choice for PBI/breast boost radiotherapy planned using tangential fields.
- OSTI ID:
- 21276922
- Journal Information:
- International Journal of Radiation Oncology, Biology and Physics, Vol. 74, Issue 4; Other Information: DOI: 10.1016/j.ijrobp.2009.02.028; PII: S0360-3016(09)00244-2; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0360-3016
- Country of Publication:
- United States
- Language:
- English
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