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.
International journal of radiation oncology, biology, physics (Impact Factor: 4.26). 07/2009; 74(4):1276-82. DOI: 10.1016/j.ijrobp.2009.02.028
Source: PubMed


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).
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(1)-weighted [standard and fat-suppressed] and T(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(CT)) with >or=95% of the reference dose. The percentage of MRCT-defined CTV (CTV(MRCT)) receiving >or=95% of the reference dose was measured.
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(CT) was 97.1% (range, 95.3%-100.0%) and of CTV(MRCT) was 96.5% (range, 89.0%-100.0%).
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(MRCT) by CTV(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.

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    • "Direct visualization of the target volumes is especially important when considering boosts to the target volume, which both modalities do not allow with high tissue-contrast. MR guidance is potentially useful for on-line highcontrast visualization of the tumour bed in postoperative RT, or for tumour detection in a preoperative setting (Sabine et al 2005, Whipp and Halliwell 2008, Kirby et al 2009, Lee et al 2010, Giezen et al 2011). However, apart from developing novel targeting techniques, it is of great importance to investigate the induced effects of the magnetic field itself on the dose distribution. "
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    ABSTRACT: The UMC Utrecht MRI/linac (MRL) design provides image guidance with high soft-tissue contrast, directly during radiotherapy (RT). Breast cancer patients are a potential group to benefit from better guidance in the MRL. However, due to the electron return effect, the skin dose can be increased in presence of a magnetic field. Since large skin areas are generally involved in breast RT, the purpose of this study is to investigate the effects on the skin dose, for whole-breast irradiation (WBI) and accelerated partial-breast irradiation (APBI). In ten patients with early-stage breast cancer, targets and organs at risk (OARs) were delineated on postoperative CT scans co-registered with MRI. The OARs included the skin, comprising the first 5 mm of ipsilateral-breast tissue, plus extensions. Three intensity-modulated RT techniques were considered (2× WBI, 1× APBI). Individual beam geometries were used for all patients. Specially developed MRL treatment-planning software was used. Acceptable plans were generated for 0 T, 0.35 T and 1.5 T, using a class solution. The skin dose was augmented in WBI in the presence of a magnetic field, which is a potential drawback, whereas in APBI the induced effects were negligible. This opens possibilities for developing MR-guided partial-breast treatments in the MRL.
    Full-text · Article · Aug 2013 · Physics in Medicine and Biology
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    • "Because the position at preoperative imaging is different from the planning CT, there may be a geographic miss in estimation of tumor bed. Some studies suggest that breast MR identically positioned with planning CT provides more precise information on tumor bed localization [6,8]. However, the additional imaging study for radiotherapy planning to localize the tumor bed is not always available. "
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    ABSTRACT: Localization of the tumor bed of breast cancer is crucial for accurate planning of boost irradiation. Lumpectomy cavity and surgical clips provide localizing information about tumor bed. However, defining the tumor bed is often difficult because of presence of unclear lumpectomy cavity and lack of certain information such as absence of surgical clips. In the present study, we evaluated the feasibility of initial diagnostic PET-CT in localization of the tumor bed using deformable image registration (DIR). We selected twenty-five patients who had an initial diagnostic PET-CT performed and underwent breast-conserving surgery with surgical clips in tumor bed. In every individual patient, two target volumes were separately delineated on planning CT; 1) target volume based on surgical clips with a margin of 1 cm (TVclip) and 2) tumor volume based on 90% of maximum SUV on PET-CT registered by DIR (TVPET). The percent of TVPET in TVclip (Vin) was calculated and distance between center points of two volumes (Dcenter) was also measured. Mean Dcenter between two volumes was 1.4 cm (range, 0.33 -- 2.53). Mean Vin was 94.8% (range, 60.9-100) and 100% in 18 out of 25 patients. When compared to the center of TVclip, the center of TVPET tended to be located posteriorly (mean 0.3 cm, standard deviation 0.6), laterally (mean 0.3cm, standard deviation 0.8) and inferiorly (mean 0.4 cm, standard deviation 0.9). Initial diagnostic PET-CT can be one of the possible references to localize the tumor bed in breast cancer radiotherapy.
    Full-text · Article · Jul 2013 · Radiation Oncology
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    • "Recently, Kirby et al showed that MRI allowed a higher conformity index (CI at 0.89) when compared with CT scan. Even though MRI is of interest for CTV delineation, it is not readily accessible and when available, it is often performed in the prone position whereas treatments are performed in the supine position [17,18]. Further evaluations are needed to clearly define the role of either 3D-US or PET-CT or MRI in contouring LC. "
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    ABSTRACT: Accurate localisation of the lumpectomy cavity (LC) volume is one of the most critical points in 3D-conformal Partial breast irradiation (3D-APBI) treatment planning because the irradiated volume is restricted to a small breast volume. Here, we studied the role of the placement of surgical clips at the 4 cardinal points of the lumpectomy cavity in target delineation. Forty CT-based 3D-APBI plans were retrieved on which a total of 4 radiation oncologists, two trainee and two experienced physicians, outlined the lumpectomy cavity. The inter-observer variability of LC contouring was assessed when the CTV was defined as the delineation that encompassed both surgical clips and remodelled breast tissue. The conformity index of tumour bed delineation was significantly improved by the placement of surgical clips within the LC (median at 0.65). Furthermore, a better conformity index of LC was observed according to the experience of the physicians (median CI = 0.55 for trainee physicians vs 0.65 for experienced physicians). The placement of surgical clips improved the accuracy of lumpectomy cavity delineation in 3D-APBI. However, a learning curve is needed to improve the conformity index of the lumpectomy cavity.
    Full-text · Article · Dec 2009 · Radiation Oncology
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