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Radiotherapy equipment represents one of the most sophisticated applications of physics and engineering in medicine, and understanding these systems means grasping how energy transfer, imaging technology, and precision engineering work together to destroy cancer cells while preserving healthy tissue. You're being tested on more than just what each machine does—exams want you to understand the underlying physics of radiation delivery, the trade-offs between different treatment modalities, and how imaging and planning systems integrate to achieve therapeutic precision.
When you encounter questions about radiotherapy, think in terms of radiation source type, delivery mechanism, and targeting strategy. Each piece of equipment solves a specific clinical problem: How do we get enough radiation to the tumor? How do we avoid damaging healthy tissue? How do we verify we're hitting the right spot? Don't just memorize device names—know what principle each component demonstrates and how they work as an integrated system.
These are the workhorses of radiotherapy—the machines that actually produce and deliver therapeutic radiation. The key distinction is the type of radiation produced and how it interacts with tissue.
Compare: LINACs vs. Proton Therapy—both deliver external beam radiation, but X-rays deposit dose along their entire path while protons stop at the Bragg peak. If an FRQ asks about minimizing radiation to healthy tissue in pediatric cases, proton therapy is your go-to example.
When external beams can't achieve the desired dose distribution, radiation sources can be placed directly at the tumor site. This approach maximizes tumor dose while exploiting the inverse square law to protect surrounding tissues.
Compare: External beam (LINAC) vs. Brachytherapy—external beam treats from outside with fractionated doses over weeks, while brachytherapy delivers radiation from within, achieving high local doses in fewer sessions. Know this distinction for questions about treatment planning trade-offs.
Precision radiotherapy depends on conforming the radiation field to irregular tumor shapes. These components modify the beam geometry and intensity to maximize tumor coverage while creating steep dose gradients at tissue boundaries.
Compare: Standard collimation vs. IMRT—conventional fields deliver uniform intensity across shaped apertures, while IMRT varies intensity within each field. IMRT questions often focus on treating tumors adjacent to spinal cord or parotid glands where dose gradients must be steep.
Accurate radiation delivery requires knowing exactly where the tumor is—both during planning and at each treatment session. These systems bridge diagnostic imaging and therapeutic delivery.
Compare: CT Simulator vs. IGRT—simulation imaging happens once during planning, while IGRT imaging occurs at every treatment session. This distinction matters for questions about managing patient motion and anatomical changes during a treatment course.
These systems ensure that the prescribed dose is both optimally designed and accurately delivered. Treatment planning translates clinical intent into machine instructions, while dosimetry verifies execution.
Compare: Treatment Planning Systems vs. Dosimetry Systems—TPS designs the plan computationally, while dosimetry systems physically measure whether the plan executes correctly. Exam questions may ask about the role of each in preventing treatment errors.
| Concept | Best Examples |
|---|---|
| External beam radiation sources | LINAC, Gamma Knife, Proton therapy systems |
| Internal radiation delivery | Brachytherapy devices |
| Beam shaping technology | Multileaf collimators, IMRT equipment |
| Pre-treatment imaging | CT simulators |
| Real-time treatment verification | IGRT systems |
| Dose optimization software | Treatment planning systems |
| Quality assurance measurement | Dosimetry systems |
| Bragg peak physics | Proton therapy systems |
Which two radiotherapy modalities both deliver external beam radiation but differ fundamentally in how dose is deposited along the beam path? Explain the physical principle behind this difference.
A patient has a tumor wrapped around the spinal cord. Which beam delivery technology would best create a concave dose distribution, and what component makes this possible?
Compare the roles of CT simulation and IGRT in a typical radiotherapy course. At what point in treatment does each occur, and what problem does each solve?
Why does brachytherapy achieve high tumor doses with minimal exposure to surrounding tissues? Identify the physical law that explains this advantage.
If an FRQ asks you to describe quality assurance in radiotherapy, which two system categories would you discuss, and how do their functions differ in ensuring treatment accuracy?