Linear Accelerator Decommissioning

End-of-life retirement of a megavoltage radiotherapy linac. Unique among diagnostic-imaging decommissioning because photon beams above ~10 MV produce neutron activation in the treatment head and surrounding gantry parts. Cool-down and physicist survey are non-negotiable parts of the file. Plan a year ahead — rushed linac decommissioning is regulatorily fraught and operationally expensive.

Radiation-activated materials

Linacs operating above ~10 MV (and in practice many ~6 MV machines at high duty cycle) produce neutrons via photonuclear interactions. Treatment head, primary collimator, target, flattening filter, multi-leaf collimator (MLC), wedges, and the immediately surrounding gantry can carry residual radioactivity from short- to medium-half-life isotopes after final beam-off. Activation gradient drops sharply with distance from the central axis but is detectable for weeks to years on the most-activated parts.

Decommissioning protocol

Final treatment cessation — last patient, beam-off, document beam-off date for the file.
Cool-down period — typically 6–12 months of beam-off time before major disassembly, allowing activated materials to decay toward release limits. Some target / collimator components require longer cool-down or radioactive-waste disposal regardless.
Physicist activation survey — Qualified Medical Physicist surveys all potentially activated components with calibrated instrumentation. Survey-of-record forms part of the regulatory file.
Disassembly with radiation-safety oversight — high-activation parts (target, primary collimator, MLC leaves, flattening filter) released only after extended cool-down, or shipped to low-level radioactive-waste (LLRW) disposal as needed.
Klystron / magnetron / waveguide handling — these are not generally activated but are heavy, vacuum-sealed, and contain hazardous materials (SF6, beryllium windows on some tubes, tungsten / heavy-metal shielding). Specialty handling.
Concrete vault survey — vault walls surveyed for residual activation; release for repurposing or demolition documented.
State / NRC license amendment — radiation-producing-machine registration cancelled; if isotope sources were ever co-located (brachy afterloader, calibration sources), NRC / Agreement-State license amended separately.

Resale and parts recovery

MLC — current-generation MLC heads (HD120, Millennium 120, Agility) have meaningful refurb value if leaf-position calibration history is clean and activation has decayed.
Klystron / magnetron — long-lead-time consumables; heat-aged units have limited resale, but rebuilders exist.
Imaging chain (kV OBI, MV imager, CBCT panel) — flat-panel detectors and kV imaging components hold resale value.
PerfectPitch / 6 DoF couch — couch assemblies have meaningful aftermarket interest.
Mechanical gantry / counterweight assemblies — primarily scrap, with selected rebuild use.

Parts-recovery timing is cool-down-gated: dismount happens after activation clearance.

Data sanitization

HDDs / SSDs on the linac control console, IGRT planning station, and OIS / R&V interface destroyed or certified-erased per HIPAA.
ARIA / MOSAIQ patient-record migration completed before workstation retirement.
Treatment-planning-system (Eclipse, Monaco, RayStation, Pinnacle) data archived per state retention.

Vault and facility

Concrete vault — typically retained for the next linac or repurposed (storage, conventional clinical use). Release survey is the documentation handoff; some vault repurposing requires deeper concrete-coring activation samples.
Maze / shielding door — door is reusable; documented for the file.
HVAC and cooling water — capacity usually retained.
Cabling, R&V network, anaesthesia infrastructure — retained per next-system requirements.

Special platforms

MR-Linac (Unity, MRIdian) — combines linac and MRI decommissioning. Cryogen handling and activation cool-down both apply. See also MRI decommissioning.
TomoTherapy / Radixact — ring-gantry geometry, MVCT detector with its own activation profile.
CyberKnife — compact 6 MV linac on robotic arm; activation profile lighter than C-arm 18 MV but cool-down still applies.
Gamma Knife — sealed-source platform, not an activated-material decommissioning. Cobalt-60 sources are returned to the vendor; this is sealed-source disposal under NRC Part 35.600, not radioactive-machine release.
Proton therapy — distinct decommissioning, with cyclotron / synchrotron, beamline, and gantry-room activation; specialty vendors only.

Vendors

Specialist radiation-oncology decommissioning companies handle activation management, LLRW manifesting, and survey documentation. Varian and Elekta service arms sometimes partner with third parties or coordinate trade-in / removal as part of replacement-system contracting.