Foundations of Medical Physics: Radiotherapy Techniques
Welcome to this module on Radiotherapy, a cornerstone of cancer treatment. We will explore two primary modalities: Brachytherapy and External Beam Radiotherapy (EBRT). Understanding these techniques is crucial for competitive exams like AIIMS, as they represent fundamental applications of physics in medicine.
Brachytherapy: Radiation from Within
Brachytherapy, derived from the Greek word 'brachys' meaning 'short distance,' is a form of radiotherapy where a sealed radioactive source is placed directly inside or very close to the tumor. This allows for a high dose of radiation to be delivered to the target volume while minimizing exposure to surrounding healthy tissues.
Brachytherapy allows for a higher radiation dose to be delivered directly to the tumor while significantly reducing the dose to surrounding healthy tissues due to the rapid fall-off of radiation with distance.
External Beam Radiotherapy (EBRT): Radiation from Outside
External Beam Radiotherapy (EBRT) is the most common form of radiation therapy. In EBRT, a machine located outside the body directs high-energy beams of radiation towards the cancerous tumor. The goal is to damage the DNA of cancer cells, preventing them from growing and dividing.
The fundamental difference between Brachytherapy and EBRT lies in the source of radiation. Brachytherapy uses sealed radioactive sources placed inside the body, close to the tumor. EBRT uses external machines to project radiation beams through the body's surface to reach the tumor. This distinction impacts dose distribution, treatment planning, and patient experience.
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| Feature | Brachytherapy | External Beam Radiotherapy (EBRT) |
|---|---|---|
| Radiation Source | Sealed radioactive isotopes placed internally | External machine (e.g., LINAC) |
| Delivery Method | Direct contact or very close proximity to tumor | Beams pass through body surface |
| Dose Gradient | Steep dose fall-off with distance | More gradual dose fall-off, requires careful planning |
| Targeting Precision | Extremely high for localized tumors | High, with advanced techniques |
| Typical Applications | Prostate, cervix, breast, skin | Wide range of cancers, including lung, brain, head & neck |
Key Concepts for AIIMS Preparation
When preparing for AIIMS, focus on the physical principles behind these techniques. For brachytherapy, understand isotopes used (e.g., Iodine-125, Cesium-137, Iridium-192), dose rate variations (LDR vs. HDR), and the concept of 'source strength.' For EBRT, grasp the generation of photons and electrons, beam modifiers (collimators, wedges), dose calculation algorithms, and the importance of immobilization devices. Understanding the trade-offs between dose conformity, tumor coverage, and organ-at-risk sparing is paramount.
Remember: Brachytherapy is like a precise internal laser, while EBRT is like a powerful external spotlight. Both aim to eliminate cancer cells, but their delivery mechanisms and physical principles differ significantly.
Learning Resources
Provides a comprehensive overview of brachytherapy, its types, and common applications for cancer treatment.
An official fact sheet explaining the process, technology, and benefits of external beam radiation therapy.
A technical paper detailing the physics principles behind brachytherapy, suitable for advanced understanding.
While specific courses vary, this link points to a typical introductory lecture on radiation therapy physics, often covering EBRT and brachytherapy basics.
An article discussing the role of physics in modern radiotherapy, offering insights into advanced techniques.
A patient-focused explanation of brachytherapy, covering its purpose, procedures, and potential side effects.
The American Association of Physicists in Medicine (AAPM) website offers extensive resources and publications on radiation therapy physics.
Provides a clear, concise overview of radiation therapy, including EBRT and brachytherapy, from a reputable medical institution.
Explains advanced EBRT techniques like IMRT and VMAT, which are crucial for understanding modern radiation delivery.
Search for channels dedicated to medical physics exam preparation on YouTube; they often have detailed explanations of radiotherapy principles.