RATIONALE: Diagnostic procedures, such as multifunctional magnetic resonance imaging and CT scans, may help reduce normal tissue damage in patients undergoing radiation therapy for cancer.

PURPOSE: This clinical trial is studying how well radiation therapy planning techniques work in reducing damage to normal tissue in women undergoing breast-conserving surgery for ductal breast carcinoma.

OBJECTIVES:

• To improve precision of tumor bed localization and definition of clinical target volume, and to reduce normal tissue irradiation in women undergoing partial breast or breast boost radiotherapy.
• To test whether post-operative MRI improves the precision of tumor bed delineation after wide-local excision in comparison with the current standard CT scan/clip method.
• To determine the impact of tumor position within the excision specimen upon the localization of clinical target volume in relation to the tumor bed.
• To compare theoretical non-target tissue exposure from partial breast irradiation planned in the supine and prone (face-down) positions.

OUTLINE: Patients undergo planned breast-conservation surgery and placement of titanium clips to the four radial, the deep, and superficial margins of the excision cavity (for localization of tumor bed).

Within 2 weeks after surgery, patients undergo supine radiotherapy-planning CT scan as standard analysis. Patients then undergo a radiotherapy-planning CT scan in the prone position. Patients complete a linear analogue questionnaire after both scans designed to assess patient comfort and anxiety in each position. Patients then undergo multifunctional MRI (including dynamic contrast-enhancement MRI and diffusion-weighted MRI) of the ipsilateral breast in the prone position (≥ 3 weeks after surgery). If suspicious lesions ≥ 5 mm are found on MRI, patients are referred for a second-look ultrasound with biopsy (if lesion visible on ultrasound); where suspicious lesions are seen only on MRI, patients undergo MRI-guided biopsy. Lesions < 5 mm are included in the whole-breast radiotherapy treatment.

DISEASE CHARACTERISTICS:

• Planning to undergo breast-conserving surgery (BCS)* for unifocal ductal carcinoma in situ (DCIS) or grade 1-2 invasive ductal carcinoma (IDC) of the breast NOTE: *Patients who have underwent BCS and have titanium clips placed according to this protocol are eligible for this study.
• No T4d or multifocal disease (as defined on mammography or ultrasound)
• No G3 disease
• Hormone receptor status not specified

PATIENT CHARACTERISTICS:

Inclusion criteria:

• Female
• Menopausal status not specified

Exclusion criteria:

• Cup size DD or greater
• Ferromagnetic implants (exclude participation in MRI)
• Claustrophobia (exclude participation in MRI)
• Gadolinium allergy

PRIOR CONCURRENT THERAPY:

• No prior surgery to ipsilateral breast
• No prior neoadjuvant chemotherapy