Radiation therapy of the breast

Impact of radiation therapy and treatment monitoring

Adjuvant radiation therapy effectively reduces the rate of local recurrence by controlling residual disease foci after breast-conserving surgery. However, prior irradiation or surgical intervention significantly complicates image interpretation. Background tissue contrast enhancement normalizes only 3–6 months after the completion of radiation therapy.

Furthermore, a history of irradiation is a major risk factor. In patients who received mantle field radiation therapy (mantle radiotherapy) for lymphoma in their second or third decade of life, the risk of developing breast cancer by age 40–45 reaches 13–20%. Since the sensitivity of standard mammography is low in this group, using MRI is critical for screening.

Dynamic contrast-enhanced CT (DCE-CT) data may also be considered when planning radiation therapy: its parameters serve as a marker of the tumor hypoxic environment, which directly correlates with radiation resistance.

The role of MRI in staging and diagnosis

Contrast-enhanced MRI is the most accurate tool for determining the true size of invasive cancer. The method allows for the detection of occult multifocal lesions in the same breast (about 16% of cases) or additional foci in the contralateral breast (about 4%).

MRI is of particular importance in lobular carcinoma (lobular carcinoma). Due to infiltrative growth associated with the loss of the E-cadherin adhesion molecule, this type of cancer is difficult to measure using ultrasound or mammography. In half of such patients, MRI shows a more extensive lesion than initially suspected.

Any suspicious findings require histological verification. The surgical plan should not be changed until malignancy of the new foci is confirmed. For this, targeted second-look ultrasound (second-look ultrasound) is used. If no ultrasound equivalent is found, the probability of cancer decreases, but MRI-guided biopsy is still indicated if the MRI picture is suspicious.

Controversial points: Despite logical expectations, clinical trials (such as COMICE and MONET) have not proven that preoperative MRI reduces the rate of re-excision or improves long-term outcomes in breast-conserving surgery.

Assessment of response to neoadjuvant chemotherapy (NAC)

NAC is prescribed for locally advanced, triple-negative breast cancer, high-grade tumors, or in the presence of lymph node metastases. MRI is recognized as the gold standard for monitoring response to such therapy.

The method records positive dynamics earlier than other imaging modalities: a decrease in size, lower contrast uptake intensity, or a shift in the enhancement pattern toward a more benign appearance is noted. Successful NAC can downstage the disease (downstage), allowing approximately 59% of women initially threatened with mastectomy to undergo breast-conserving surgery.

Dynamic contrast-enhanced CT (DCE-CT) and nuclear medicine

DCE-CT assesses microvascular changes associated with angiogenesis. Vascular permeability in tumors is typically higher than in healthy tissues. The method is accessible and inexpensive, but is associated with a high radiation dose and cannot always clearly differentiate malignant processes from inflammation due to parameter overlap.

Nuclear medicine methods are based on the uptake of specific isotopes (e.g., 18F-FDG for PET or 99mTc-MIBI). They are used for local staging, searching for occult primary tumors in dense breast tissue, and detecting recurrences, although they have not yet become widespread routine clinical practice.

Breast implant imaging

MRI surpasses ultrasound and mammography in assessing implant integrity, boasting a sensitivity and specificity exceeding 90%. The procedure is performed without contrast (unless malignancy is suspected), in the prone position using a dedicated coil.

In intracapsular rupture, the silicone is contained by the fibrous capsule. On T2-weighted images, this manifests as specific signs:

• The linguini sign (linguini sign) or wavy line sign — a floating elastomer shell.
• The key-hole sign (key-hole).
• The salad oil sign (salad oil sign) — bright droplets of water-like material.

Extracapsular rupture, where silicone extends beyond the capsule, can also be successfully diagnosed using ultrasound (visualizing free silicone or granulomas).

Class and exam questions

What else to study on this topic

• Application of shear-wave elastography to increase ultrasound specificity
• Use of the ACR BI-RADS standardization system
• Efficacy of digital breast tomosynthesis (DBT) and contrast-enhanced spectral mammography (CESM)
• Preoperative lesion localization and the impact of breast density on diagnostics
• Interventional radiology: vacuum-assisted biopsy (VAB) and percutaneous excision

Other topics in the "Diagnostic Radiology in Oncology" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.