Aswin John Solomon, Precision oncologist, Longevity physician, Nutrivention pioneer, shared a post on LinkedIn:
“Inside the Linac: How Therapeutic Beams Are Actually Made
What people think: “Radiation comes from a machine.” It doesn’t. It’s engineered electron acceleration at microwave frequencies.
The Core Idea –
Linac converts microwave energy into high-energy electrons, and electrons into therapeutic photons. So an energy transfer, which is Precisely controlled.
Step 1: Pulse Coordination
Everything starts with synchronization. The modulator fires microsecond pulses.
Electron gun and RF source must be perfectly timed. If timing drifts – energy spread increases – beam quality degrades. This is precision RF engineering.
Step 2: RF Acceleration (The Real Magic)
Electrons travel through copper cavities. Oscillating microwave fields give them repeated “kicks.” Each cavity adds energy.
Surfing a perfectly timed electromagnetic wave. If the phase is missed – no acceleration.
Microwave Power Sources
There are two main systems:
- Klystron – high-power amplifier which is stable, scalable and used in large systems.
- Magnetron – compact microwave generator, which is used in smaller systems.
Power stability directly impacts beam output consistency.
S-Band vs X-Band (Board Favorite)
S-Band: 2-4 GHz
Standard medical linacs.
X-Band: 8-12 GHz
Shorter wavelength – more compact systems.
Higher frequency – smaller accelerating structures.
Compact doesn’t mean weaker – it’s just engineered differently.
The 270° Achromatic Bend
Electrons don’t go straight to the patient. They are bent 270° by magnets.
But why? It’s because:
- Energy selection
- Beam focusing
- Penumbra control
Achromatic design ensures electrons of slightly different energies still converge at the same focal spot. This improves the beam sharpness.
Photon Production
High-energy electrons hit tungsten. Bremsstrahlung dominates. In result we get forward-directed megavoltage photon beam. it’s therapeutic energy range typically is 6-15 MV.
Why MV Photons Are Different from Diagnostic X-Rays?
In diagnostic there’s low energy, so there’s photoelectric dominant. In therapeutic there’s high energy, so there’s compton dominant. We get skin sparing due to dose buildup.
In a nutshell different physics – different goals.
Imagine pushing a swing at exactly the right moment.
Each push would make it go higher. That’s RF acceleration. Then you slam the swing into a metal plate. Light would come out. That would be your treatment beam.
The Board Pearl
Microwave frequency determines structure size. Bending magnets determine beam sharpness. Target interaction determines photon production.
Three engineering domains – one clinical beam.
One Sentence to Remember
A linac is a microwave-powered electron accelerator designed to convert RF energy into precisely shaped megavoltage photon beams.”
Other articles about Linac on OncoDaily.