Rationale for the method in oncology
The application of DCE-CT is based on the method's ability to record microvascular changes accompanying angiogenesis. The permeability surface-area product (permeability surface-area product) in normal tissues is generally lower than in tumor lesions.
The parameters obtained during scanning are positively associated with angiogenesis markers and negatively with hypoxia markers. This allows them to use them to assess the fundamental biological processes of cancer formation. Patients with malignant neoplasms usually exhibit high perfusion rates. At the same time, there is a pronounced variability of parameters not only between different types of tumors, but also within the same neoplasm, reflecting the complex biological nature of cancer.
Although the method helps differentiate benign and malignant lesions (e.g., in the lungs, intestines, or pancreas), it has a major limitation. There is an overlap of data between malignant and inflammatory processes, as vascular changes in inflammation are non-specific.
Risk stratification and prognosis
In clinical practice, DCE-CT serves as an important predictive tool:
- Evaluation of chemotherapy: perfusion parameters show how well the drug is delivered to the tumor tissue (drug delivery). For example, in pancreatic cancer, a low baseline volume transfer constant ($K^{trans}$) predicts a poor response to gemcitabine treatment.
- Evaluation of radiation therapy: blood flow acts as a marker of the hypoxic environment, which is directly linked to radioresistance. For instance, colorectal cancer with low baseline blood flow responds poorly to chemoradiotherapy, metastasizes to lymph nodes more frequently, and has a worse prognosis.
- Surgery and adjuvant therapy: in locally advanced squamous cell carcinoma of the head and neck, baseline blood flow and permeability indices of the primary lesion are independent predictors of recurrence.
Clinical trials and anti-angiogenic therapy
One of the main applications of the method is early-phase clinical trials of anti-angiogenic drugs (e.g., bevacizumab) and vascular disrupting agents (vascular disrupting agents). DCE-CT acts as a direct imaging biomarker of drug action.
Analysis of parametric maps before and after treatment allows for a clear visualization of pharmacodynamics. For example, 48 hours after bevacizumab administration, maps of the initial area under the curve (IAUGC90) visualize a sharp drop in metastasis perfusion.
Depending on the drug and the type of solid tumor, a successful response to therapy is usually manifested by a decrease in regional blood flow (BF) and blood volume (BV), or an increase in mean transit time (MTT). In patients with oropharyngeal squamous cell carcinoma, a decrease in these parameters during chemotherapy (cisplatin + 5-fluorouracil) is observed only in the treatment-responder group.
DCE-CT vs. DCE-MRI: pros and cons
Dynamic MRI (DCE-MRI) works on a similar principle: serial scanning is performed during contrast administration (usually low-molecular-weight gadolinium chelates at a dose of 0.1 mmol/kg). Paramagnetic ions shorten T1 relaxation time, enhancing the signal.
Advantages of CT perfusion:
- Wide availability of equipment and low cost.
- Ease of standardizing protocols across clinics.
Disadvantages of CT perfusion:
- Significant radiation exposure (up to 28.7 mSv), requiring weighing benefits against carcinogenesis risks.
- Lack of robust data on the link between an acute drop in vascularity and long-term patient outcomes.
Advantages of MRI perfusion:
- Complete absence of ionizing radiation (allows repeated procedures for monitoring).
- High signal-to-noise and contrast-to-noise ratio.
- However, the reproducibility of DCE-MRI is lower due to differences in scanners, injection protocols (e.g., 1 minute of baseline and up to 10 minutes of data collection), and the kinetic calculation models used.
Briefly: answers to topical questions
What scanning phases are included in the standard multiphasic CT liver perfusion protocol?
The minimum standard for multiphasic liver CT includes unenhanced and arterial phases, and the complete protocol may be supplemented by portal venous and delayed phases.
- Unenhanced phase (unenhanced) — pre-contrast scanning.
- Arterial phase (arterial phase) — usually relatively late, e.g., at 18 seconds after contrast entry into the aorta; hepatic veins are not contrasted in this phase.
- Portal venous phase (portal phase) — hepatic veins fill with contrast and become radiopaque.
- Delayed phase (delayed phase) — used for specific indications, such as diagnosing hemangiomas and cholangiocarcinomas.
Class and exam questions
Why can perfusion parameters vary significantly in different areas of the same tumor?
This is due to the complexity of malignant tumor biology. The tumor is heterogeneous: areas of active angiogenesis, zones of inflammation, and regions of pronounced hypoxia coexist within it.
Can DCE-CT accurately distinguish cancer from severe inflammation?
Doing this definitively is challenging. There is an overlap of parameters between inflammatory and tumor processes due to the non-specific nature of vascular changes.
How do macromolecular MR contrasts differ from low-molecular-weight ones?
Low-molecular-weight contrasts (less than 1 kDa) rapidly diffuse from vessels into the extracellular space. Macromolecular contrasts (greater than 30 kDa) are retained in the vascular bed for significantly longer.
How dangerous is the radiation exposure in perfusion CT?
The effective dose for a chest or abdomen scan is 13.7–28.7 mSv. The lifetime risk of developing radiation-induced cancer from a single such scan is estimated to be approximately 1 in 1,000.
What else to study on this topic
- Kinetic models for calculating the volume transfer constant ($K^{trans}$)
- Interpretation of parametric maps: regional blood flow (BF) and blood volume (BV)
- Pharmacodynamics of vascular disrupting agents
- Calculation of the initial area under the gadolinium concentration curve (IAUGC90)
- Scanning protocols: assessment of contrast uptake and washout
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