Role of Imaging and Multidisciplinary Approach
Improvements in treatment outcomes have led to an increase in the number of long-term cancer survivors (survivorship). This requires careful monitoring of the long-term effects of both the disease and the treatment itself. Such patients are managed by a multidisciplinary team (tumour boards) comprising oncologists, surgeons, radiologists, pathologists, and other specialists.
The primary tasks of diagnostic radiology in oncology include:
- Screening — examination of asymptomatic individuals for the early detection of cancer (proven to reduce mortality, as seen in breast and colorectal cancer).
- Diagnosis — initial detection and characterization of the neoplasm.
- Staging (staging) — assessment of local and systemic disease spread.
- Treatment response assessment — monitoring the efficacy of ongoing therapy.
- Surveillance (surveillance) and restaging in case of suspected recurrence.
Anatomical Imaging Techniques
These methods evaluate the physical dimensions, density, and structure of tissues. The choice of optimal strategy depends on the tumor type and location, clinical indications, and cost.
- Computed Tomography (CT). The mainstay (mainstay) imaging modality in oncology. Based on X-ray attenuation. It provides submillimeter isotropic resolution, allows whole-body scanning in seconds, and generates multiplanar 3D reconstructions. The main drawback is radiation exposure. Its scale of application is vast: for example, in the UK, out of 5 million annual CT scans, half are performed for oncological indications.
- Magnetic Resonance Imaging (MRI). Utilizes the absorption of radiofrequency waves by hydrogen nuclei. It provides superior soft-tissue contrast resolution without ionizing radiation. Limitations include the effects of a strong magnetic field and tissue heating (especially in high-field systems).
- Ultrasound (US). An accessible, radiation-free method based on the attenuation of sound waves. Its main drawback is strong operator dependency.
- Radiography. An inexpensive and accessible method, but with extremely limited spatial resolution.
Functional Imaging Techniques
These methods visualize biological processes within the tumor, which is critically important for modern personalized medicine.
- Diffusion-Weighted MRI (DW-MRI): evaluates water molecule diffusion, serving as a surrogate marker of tumor cellularity (tumour cellularity).
- Dynamic Contrast-Enhanced MRI and CT: analyze contrast agent (gadolinium or iodine) kinetics. They help quantitatively assess vascular permeability (vascular leakage), perfusion, and angiogenesis.
- BOLD-Contrast MRI: based on the paramagnetic effect of deoxyhemoglobin, serving as a marker of hypoxic blood volume in tissues.
- 18F-Fluorodeoxyglucose PET (18F-FDG PET): evaluates the uptake of an endogenous glucose analog, demonstrating the metabolic activity of cancer cells. It is frequently combined with CT or MRI for precise anatomical localization, though it is characterized by high cost, radiation exposure, and lower spatial resolution.
Evolution of Treatment: Targeted and Immunotherapy
Understanding tumor clonal evolution has driven the development of molecularly targeted therapies. Diagnostic radiology helps assess the efficacy of these advanced approaches:
- Targeted therapy: blocks specific molecules. Examples include bevacizumab (VEGF inhibitor), trastuzumab (HER-2 blocker in breast and gastric cancer), cetuximab (EGFR inhibitor in RAS wild-type colorectal cancer), as well as agents for non-small cell lung cancer with crizotinib (ALK gene rearrangements) or gefitinib (EGFR mutations).
- Immunotherapy: aims to neutralize immunosuppressive mechanisms, enabling the body to fight cancer on its own. Antibodies against CTLA4 (ipilimumab) and PD1 (nivolumab) are used, licensed for advanced melanoma and lung cancer.
Briefly: answers to topical questions
Which international system is used to classify the anatomical staging of most solid tumors?
In the cited sources, anatomical tumor staging is based on the AJCC/UICC TNM system. The following prefixes are used:
- cTNM — clinical assessment;
- iTNM — imaging-based assessment;
- pTNM — pathomorphological assessment;
- yTNM — restaging after treatment;
- rTNM — restaging in case of disease recurrence.
What standardized criteria are used by radiologists to objectively assess the response of solid tumors to treatment on CT?
RECIST criteria (Response Evaluation Criteria in Solid Tumours) are used to objectively assess the response of solid tumors to treatment. They include the following categories:
- Complete Response (Complete Response, CR) — complete disappearance of all target lesions.
- Partial Response (Partial Response, PR) — at least a 30% decrease in the sum of the longest diameters of target lesions.
- Stable Disease (Stable Disease, SD) — changes do not meet the criteria for partial response or progression.
- Progressive Disease (Progressive Disease, PD) — at least a 20% increase in the sum of the longest diameters of target lesions, or the appearance of new lesions.
What are the absolute contraindications to the intravenous administration of gadolinium-based contrast agents in MRI?
The source states that gadolinium-based contrast agents should be completely avoided in severe renal impairment due to the risk of nephrogenic systemic fibrosis (NSF). Concomitant inflammatory processes, blood phosphate levels, the type of contrast agent, and its cumulative dose are also cited as risk factors.
Which specific radiopharmaceuticals, besides 18F-FDG, are used in PET-CT for staging prostate cancer?
The following are used for PET-CT in prostate cancer:
- 68Ga-PSMA or 18F-PSMA — PSMA PET-CT has higher sensitivity compared to multiparametric MRI and 11C-choline PET-CT;
- 11C-choline — not recommended for routine initial staging and the detection of lymph node metastases; used to evaluate lipid metabolism and detect recurrences.
Which medical specialties are mandatory members of a multidisciplinary oncology tumor board?
A multidisciplinary oncology tumor board must include the following medical specialists:
- Oncologists — the primary specialists in the treatment of malignancies;
- Pediatric oncologists — mandatory participants if the patient is under 18 years of age;
- Radiation therapist — specialist in radiation therapy;
- Neurosurgeon — mandatory participant in cases of nervous system tumors.
If necessary, specialists from other fields may be invited to participate in the tumor board.
The tasks of imaging in oncology are easily remembered by the acronym SD-SOS: Screening, Diagnosis, Staging, Response Assessment, Restaging (and surveillance).
Class and exam questions
Why is computed tomography considered the primary modality in oncology?
CT combines high clinical availability, cost-effectiveness, and excellent spatial resolution. Modern scanners are capable of scanning the entire body in a matter of seconds, creating precise volumetric reconstructions.
What is the fundamental difference between functional and anatomical imaging?
Anatomical methods (X-ray, US, standard CT and MRI) show only the structure and dimensions of the tumor. Functional methods (PET, DW-MRI, perfusion studies) visualize biological processes: cell density, glucose metabolism, angiogenesis, and hypoxic zones.
How do imaging methods aid in targeted therapy?
Functional imaging (such as dynamic contrast-enhanced MRI) allows for the assessment of vascular permeability and angiogenesis. This serves as an early marker of how effectively anti-angiogenic drugs (such as VEGF inhibitors) are working, even before the tumor physically decreases in size.
What else to study on this topic
- Cancer epidemiology: incidence statistics and economic burden.
- Principles of action of targeted drugs: multikinase and mTOR inhibitors in renal cell carcinoma.
- Mechanisms of tumor evasion from the immune system and targets for immunotherapy.
- Locoregional treatment: interventional oncology and modern radiation therapy modalities (IMRT, stereotactic radiotherapy).
- Specifics of 18F-FDG PET/CT use in various histological tumor types.
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