Radiation Oncology Physicist
Board-certified clinical medical physicist (American Board of Radiology / American Board of Medical Physics) embedded in a radiation-oncology department. Known contractually as the Qualified Medical Physicist (QMP). Responsible for linac commissioning and quality assurance, treatment-planning system validation, radiation safety, patient-specific plan QA, and the day-to-day machine-calibration discipline that underpins every treatment delivered. Reports to the radiation oncology department chair; works in constant collaboration with radiation oncologists, dosimetrists, and biomed engineering.
Daily responsibilities
- Daily / weekly / monthly / annual linac QA per AAPM TG-142 — output constancy, flatness / symmetry, MLC position, couch position, kV/MV imaging alignment, end-to-end testing.
- Patient-specific plan QA — IMRT / VMAT / SRS / SBRT plan verification against treatment-planning-system predictions using phantom + diode / film / portal imaging.
- Treatment-planning-system commissioning and validation — beam-data collection, beam-model tuning, small-field dosimetry for SRS cones.
- Commissioning of new linacs and platform upgrades — TrueBeam, TrueBeam STx, Versa HD, Synergy S commissioning spans weeks.
- SRS / SBRT commissioning — small-field dosimetry (TRS-483 protocol), end-to-end test, imaging-chain verification.
- Radiation safety — vault shielding verification, area surveys, incident investigation.
- Patient dose reporting and dose-accumulation tracking.
- Educator role — radiation oncology resident and therapist continuing education.
- Accreditation — ACR accreditation, ROILS incident reporting, peer-review chart-checks.
What they evaluate when equipment decisions come up
- MLC resolution — HD120 2.5 mm vs Millennium 120 5 mm vs Agility 5 mm. Fine-leaf MLC is the SRS / SBRT differentiator.
- FFF beam availability — flattening-filter-free beams on TrueBeam / STx / Edge and Versa HD support high-dose-rate SRS.
- 6DoF couch — Varian PerfectPitch on TrueBeam STx / Edge, Hexapod on Elekta.
- Imaging chain — kV / kV / CBCT / MV / SGRT integration. IGRT quality.
- Treatment-planning system compatibility — Eclipse (Varian), Monaco (Elekta), RayStation, Pinnacle (Philips). Beam-model migration discipline.
- Adaptive workflow — Halcyon Ethos, Unity MR-linac adaptive capabilities.
- Commissioning complexity — weeks of physicist time per new install; platform choice affects go-live date.
- Service contract response — a linac down for days has real clinical impact on patients mid-course.
Decision drivers
- Clinical-technique capability — can the platform deliver the treatments the department wants to offer (SRS, SBRT, adaptive, hypofractionation, MR-guided)?
- TG-142 compliance posture — platforms with well-understood QA workflows (TrueBeam) have lower QA-labor overhead than novel platforms.
- End-to-end accuracy — SRS clinical programs demand sub-millimeter accuracy validated end-to-end.
- TPS / OIS ecosystem — Varian ARIA + Eclipse is a deep ecosystem; switching to Elekta Monaco + MOSAIQ is a substantial re-commissioning event.
- Peer reputation — platform choice affects recruitment and scientific-credibility of the program.