Role of multiparametric MRI
Successful treatment planning begins with detailed imaging. For precise mapping of the prostate, multiparametric MRI (mpMRI) has been introduced into routine clinical practice. It combines several modalities, including T2-weighted imaging, dynamic contrast-enhanced (DCE) MRI, and diffusion-weighted imaging (DWI).
The DWI sequence plays a critical role as it directly reflects tissue cellularity. Comprehensive analysis of these data allows radiologists and radiation oncologists to identify the dominant intraprostatic lesion (DIL)—the most aggressive part of the tumor. Because the physiology of a malignant neoplasm is dynamic, sequential imaging (sequential imaging) is required to accurately account for all changes.
Biologically optimized therapy and brachytherapy
The main principle of modern planning is to maximize the radiation dose to the DIL zone and strictly limit the radiation load on the rest of the prostate. Special software calculates Dose Volume Histograms. They demonstrate two dose levels: the planning target volume (PTV) for the dominant nodule receives a proportionally higher dose compared to the non-dominant tissue.
Brachytherapy is often used to deliver high doses. Under general anesthesia, catheters are placed into the prostate. A huge advantage of this method is that radiation sources (e.g., radioactive iodine-125 isotope seeds, $^{125}I$) move together with the organ. This solves the problem of target motion and patient positioning. Specific proton-weighted MRI sequences have been developed for precise identification of iodine seed positions, whereas CT is preferred for localizing the applicators themselves.
Adaptive technologies and innovations
Pelvic organs are mobile, so the course of treatment requires regular adjustments. Adaptive radiation therapy (ART) allows modifying the plan directly during the treatment course under continuous MRI guidance. The most promising direction is the use of hybrid MR-Linac systems, which combine a linear accelerator and an MRI scanner for real-time target visualization during beam delivery.
If standard radiation therapy faces the problem of tumor hypoxia (which reduces treatment effectiveness), particle therapy with fast neutrons or carbon ions can be considered. These particles cause dense ionization and irreversible radiation damage even in oxygen-depleted tissues. The implementation of all these advanced techniques requires coordinated work by a multidisciplinary team, where radiation oncologists, medical physicists, and radiation therapists jointly monitor quality (QA) at every stage.
Radiomics and radiogenomics
Medical images today are viewed not just as pictures, but as sources of big data (big data). This field is called radiomics.
- Special algorithms extract quantitative characteristics from scans: shape, size, volume, intensity, and texture.
- These data are used to create predictive models of treatment outcomes.
- Radiogenomics goes even further, combining radiomic data from biological imaging with the genetic profile of the tumor for personalized patient treatment stratification.
To remember the three key prostate MRI sequences (T2, DWI, DCE), use the mnemonic: "Tissue, Motion (water/diffusion), Vessels (contrast)"—they identify the dominant lesion.
Class and exam questions
Why doesn't prostate mobility reduce irradiation accuracy in brachytherapy?
In brachytherapy, radiation sources are located directly inside the prostate. If the organ shifts, the applicators and radioactive seeds move with it, maintaining their exact position relative to the tumor.
What is a dominant intraprostatic lesion (DIL)?
This is the densest and most aggressive area of the tumor within the gland, identified using multiparametric MRI and requiring the delivery of a maximum, proportionally higher radiation dose.
What is the physical advantage of proton therapy?
Protons deposit the bulk of their energy at the end of their range (the Bragg peak). As a result, tissues located beyond the target volume are virtually spared from radiation.
Why are hybrid MR-Linac systems needed?
They combine a linear accelerator and an MRI in a single device, allowing real-time tumor visualization directly during the irradiation session for the most precise dose delivery.
What else to study on this topic
- Three-dimensional conformal radiation therapy (3D CRT) and its limitations for horseshoe-shaped targets.
- Intensity-modulated radiation therapy (IMRT) principles for sparing the brainstem and other critical structures.
- Image fusion: integration of CT, MRI, and PET data for contouring.
- Physics of electron beams and their application for superficial targets.
Master the entire topic in the "Diagnostic Radiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Radiation Therapy for Prostate Cancer" and 2,199 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 10 video lessons on the subject
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.