Place of CT in the management algorithm for patients with breast cancer
Computed tomography is critical at the stage of preparing patients with breast cancer for radiation therapy. The radiation therapy process is strictly regulated and includes several steps where CT technologies are involved:
- Imaging for planning. For precise determination of the irradiation volume, CT topometry is performed. The obtained scans are often fused (fusion) with MRI or PET results for the most accurate contouring of the tumor and critical organs.
- Plan verification. Before starting irradiation, the calculated data are checked using virtual CT or a traditional X-ray simulator.
- Monitoring during treatment. To verify the correct patient positioning directly on the treatment couch, megavoltage imaging or cone-beam kV-CT (Cone beam kV CT) is used.
Why CT is not suitable for primary screening?
The breast consists predominantly of adipose and glandular tissue, which have an extremely narrow range of X-ray attenuation. Computed tomography, which generates relatively hard X-ray radiation, does not provide optimal soft-tissue contrast for the early detection of carcinomas.
Diagnostics requires strict imaging parameters, which are implemented in digital mammography:
- The use of a special target and filter combination (most commonly molybdenum/molybdenum), providing a low-energy radiation spectrum (peaks at 17.5 and 19.6 keV).
- An extremely small focal spot (0.3 mm for routine imaging and 0.1 mm for magnification imaging) to detect microcalcifications around 100 µm in size.
- Short exposure time (less than 1 second) to eliminate motion unsharpness.
CT scanners cannot provide such high spatial resolution with an acceptable radiation dose to the glandular tissue.
Alternative high-tech methods
To obtain more detailed information about the breast structure and the extent of the tumor process, in addition to standard mammography in mediolateral oblique (MLO) and craniocaudal (CC) projections, the following are used:
- Advanced mammography. Includes digital breast tomosynthesis (creation of pseudo-3D images) and contrast-enhanced spectral mammography.
- MRI. The method has maximum sensitivity to invasive forms of cancer. MRI is effectively used to monitor tumor response to neoadjuvant chemotherapy, allowing surgeons to plan breast-conserving surgeries.
- Radionuclide studies. These include positron emission mammography (PEM) and mammo-scintigraphy, based on the accumulation of specific radiopharmaceuticals by the tumor (e.g., 99mTc-MIBI).
MRI as an alternative to CT in implant assessment
If a patient needs to evaluate the condition of silicone endoprostheses, computed tomography is also not the method of choice. Magnetic resonance imaging is recognized as the most accurate tool (surpassing ultrasound and mammography).
The examination is performed in the prone position using a dedicated coil; contrast administration is not required (unless malignancy is suspected). On T2-weighted images, MRI reliably detects intracapsular rupture, visualizing the floating shell of the implant inside the silicone (“linguine”, “wave”, or “salad oil” signs).
The role of CT technologies in complex irradiation methods
During intensity-modulated radiation therapy (IMRT), radiation beams are shaped to match the complex contour of the tumor while their intensity is varied. This allows delivering a high dose to the target while sparing healthy tissues.
One of the technologies for implementing IMRT is tomotherapy. In this case, a megavoltage X-ray source is mounted in the device based on the principle of a CT scanner: the radiation intensity is modulated while the patient moves through the gantry aperture. Since the breast shifts with respiration, 4D planning is used for control.
Class and exam questions
Is CT used for breast cancer screening?
No, it is not used. The primary method for population-based screening of women and early detection of neoplasms is digital mammography, which reliably reduces mortality.
In what cases is a CT scan performed in mammology?
Computed tomography is critically necessary at the radiation therapy preparation stage for 3D planning, contouring irradiation volumes, and checking patient positioning during treatment sessions.
Which method is best suited to search for an X-ray-negative tumor in dense breasts?
In cases of high mammographic density, MRI is indicated. Nuclear medicine methods (PET or mammo-scintigraphy) may also be used, but they are less frequently applied in routine practice.
What else to study on this topic
- Technical features of digital mammography (target/filter combinations, effect of compression)
- MRI semiotics of breast implant ruptures
- Principles and stages of intensity-modulated radiation therapy (IMRT)
- Interventional radiology in mammology: biopsies and percutaneous excision
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