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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Available from: Anna M Kirby, Oct 06, 2015
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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.
    Physics in Medicine and Biology 08/2013; 58(17):5917-5930. DOI:10.1088/0031-9155/58/17/5917 · 2.76 Impact Factor
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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.
    Radiation Oncology 07/2013; 8(1):163. DOI:10.1186/1748-717X-8-163 · 2.55 Impact Factor
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    • "Definition of the lumpectomy cavity is a critical step in treatment planning for irradiation of the intact breast, breast boost, and for partial breast irradiation. Multiple studies have shown the limitations of single modality imaging with interobserver differences in lumpectomy cavity definition [1] [2] [3] [4]. CT-based imaging is commonly used for breast treatment planning; but the limited soft tissue contrast of CT can result in poor visualization of the lumpectomy site in patients with dense breast parenchyma, small lumpectomy cavities, or a prolonged delay between surgery and treatment planning [2] [3]. "
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    ABSTRACT: Accurate lumpectomy cavity definition is critical in breast treatment planning. We compared contouring lumpectomy cavity volume and cavity visualization score (CVS) with CT versus 3T MRI. 29 patients were imaged with CT and 3T MRI. Seven additional boost planning sets were obtained for 36 image sets total. Three observers contoured the lumpectomy cavity on all images, assigning a cavity visualization score (CVS ) of 1 to 5. Measures of consistency and agreement for CT volumes were 98.84% and 98.62%, for T1 MRI were 95.65% and 95.55%, and for T2 MRI were 97.63% and 97.71%. The mean CT, T1 MRI, and T2 MRI CVS scores were 3.28, 3.38, and 4.32, respectively. There was a highly significant difference between CT and T2 scores (P < .00001) and between T1 and T2 scores (P < .00001). Interobserver consistency and agreement regarding volumes were high for all three modalities with T2 MRI CVS the highest. MRI may contribute to target definition in selected patients.
    04/2011; 2011:246265. DOI:10.4061/2011/246265
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