ABR TMP cheat sheet

TG-51 absorbed-dose-to-water formalism: D_w^Q = M · N_D,w^60Co · k_Q · P_Q, where P_Q = P_ion · P_TP · P_pol · P_elec; photon reference geometry is 10 × 10 cm² at 100 cm SSD with the reference depth near 10 cm for 6 MV.

TMR(d, FS) is defined at fixed SAD and is independent of SSD; PDD depends on both SSD and field size, and TMR = (PDD/100) · [(SSD + d_max)/(SSD + d)]².

Mayneord F factor for changing SSD: F = [(SSD₂ + d_max)/(SSD₁ + d_max)]² × [(SSD₁ + d)/(SSD₂ + d)]²; PDD₂ = PDD₁ × F.

Equivalent square field for collimator scatter: side = 4A/P (four times area divided by perimeter); square-field output and depth-dose data are then used for rectangular fields.

Fractionation: BED = n·d·(1 + d/(α/β)); EQD2 = BED/(1 + 2/(α/β)); α/β is about 10 Gy for tumor and 3 Gy for late-responding normal tissue.

Convolution-superposition computes TERMA from primary fluence and deposits it with a dose-spread kernel; pencil-beam algorithms lose accuracy in lung, bone, and small fields where lateral electronic disequilibrium dominates.

Gamma index combines dose-difference and distance-to-agreement criteria; typical IMRT/VMAT patient-specific QA is 3%/3 mm with a 10% dose threshold and a passing rate above 95% of evaluated points.

Plan metrics: Paddick conformity index = (TV_PIV)²/(TV × PIV); ICRU-83 homogeneity index = (D2 − D98)/D50; gradient index = volume of half the prescription isodose divided by PIV.

Electron beam energy from depth-dose: E₀ (MeV) ≈ 2.33 × R50 (cm); therapeutic range R90 ≈ E₀/4 in centimeters of water, and surface dose rises with increasing energy.

TG-142 output tolerances relative to baseline: daily constancy ±3%, monthly calibration ±2%, annual calibration ±1% for both photons and electrons.

Reference chamber correction: P_TP = [(273.15 + T)/295.15] × (760/P), with T in degrees Celsius and P in mm Hg; reference conditions are 22 °C and 760 mm Hg.

Ion recombination correction P_ion is obtained by the two-voltage method: measure charge at the normal bias and at half bias, take the ratio, and apply the standard TG-51 quadratic solution.

Radiation and mechanical isocenter coincidence is verified with the Winston-Lutz test (marker plus small field over multiple gantry, collimator, and couch angles); tolerance is about 1 mm.

MLC tests: picket-fence imaging detects leaf position and calibration drift; IMRT leaf positioning accuracy tolerance is 1 mm, and the dosimetric leaf gap compensates for rounded leaf ends and transmission.

TG-142 energy constancy tolerance is ±2% for photons and ±3% for electrons, assessed from the ratio of chamber readings at two depths in a fixed phantom.

Daily mechanical checks: lasers and ODI agree with isocenter to ±2 mm, gantry/collimator digital readouts to ±1°, and couch position to ±2 mm and ±1°.

VMAT and IMRT delivery verification uses machine log files or dynalog files to confirm gantry speed, dose rate, and MLC trajectory, plus an independent dose recalculation agreeing within 3%/3 mm.

End-to-end testing with an anthropomorphic phantom validates the full chain from imaging and contouring through planning, transfer, setup, and delivery, including heterogeneity and small-field effects.

TG-43 dose formalism: D(r,θ) = S_k · Λ · [G(r,θ)/G(r₀,θ₀)] · g(r) · F(r,θ), where Λ is the dose rate constant, g the radial dose function, and F the anisotropy function.

Air kerma strength units: 1 U = 1 μGy·m²/h = 1 cGy·cm²/h; source strength is measured in a well chamber calibrated against a traceable standard, with verification within ±3% of the vendor assay.

Common radionuclides and half-lives: Ir-192 = 73.8 days, I-125 = 59.4 days, Pd-103 = 17.0 days, Cs-131 = 9.7 days; Ir-192 photons average roughly 380 keV.

Gynecologic Point A is 2 cm lateral to the tandem and 2 cm superior to the external cervical os along the intrauterine applicator; ICRU 38 bladder and rectal reference points remain in use for reporting.

Combined EBRT plus image-guided brachytherapy targets (EQD2, α/β = 10 for tumor, 3 for organs at risk): HR-CTV D90 ≥ 85 Gy, bladder D2cc ≤ 90 Gy, rectum D2cc ≤ 70–75 Gy.

Permanent prostate implant dosimetry by TG-137: postimplant D90 of at least 100% of the prescribed dose and V100 of at least 95% are accepted adequacy benchmarks for monotherapy.

High-dose-rate daily QA: timer accuracy within ±1% for intervals over 1 second, source position within ±1 mm of intended location, functional emergency retraction, and a calibrated survey meter.

Emergency procedure for a stuck source: use long forceps and a shielded container, manually retract the source, monitor with a survey meter, and restrict access until the room is verified clear.

CT simulation protocol: slice thickness of 2–3 mm through the target volume, scan extent sufficient for matching and dose calculation, flat couch top, indexed immobilization, and external isocenter markers.

Hounsfield units are converted to electron density by stoichiometric calibration using tissue-equivalent inserts; the density phantom is scanned annually and after major CT service.

Four-dimensional CT sorts images by respiratory phase or amplitude and defines the internal target volume; artifacts include blurring, duplication, and phase mismatch at irregular breathing.

Cone-beam CT has degraded Hounsfield accuracy from scatter and truncation, so it is used for setup and monitoring rather than primary dose calculation unless calibrated with a density phantom.

Magnetic resonance simulation requires assessment of geometric distortion from gradient nonlinearity and B0 inhomogeneity; AAPM TG-284 covers geometry, QA phantoms, and distortion correction.

PET/CT contributes metabolic target information; SUV depends on injected activity, uptake time, and reconstruction, and respiratory motion causes mismatch between PET and CT datasets.

DICOM radiotherapy objects: CT (image), RTSTRUCT (contours), RTPLAN (beams and MLC), RTDOSE (dose grid), RTIMAGE (portal/DRR images), and RTRECORD (delivered treatment).

Image-guided radiotherapy options include planar kV/kV imaging, CBCT, ultrasound, electromagnetic transponders, and surface imaging; each adds setup accuracy with a different dose and workflow cost.

NCRP Report 151 shielding: transmitted dose P = (W · U · T)/d² and barrier thickness = TVL · log₁₀(1/B), where B is the required attenuation factor for workload W, use factor U, occupancy T, and distance d.

Dose limits: occupational effective dose 50 mSv per year, public 1 mSv per year, and public-area ambient rate at or below 0.02 mSv per hour in any hour (NCRP), with ALARA applied below all limits.

Linear accelerator leakage must average no more than 0.1% and never exceed 0.2% of the useful beam dose rate; secondary barriers are designed for leakage plus patient-scattered radiation.

Primary barriers block the useful beam for workloads with the specified use factor (often 0.25 for walls and 1.0 for the floor in a four-field arrangement); secondary barriers account for leakage and scatter with use factor 1.

AAPM TG-100 applies failure mode and effects analysis prospectively: each step receives severity, occurrence, and detectability scores, and the risk priority number is their product, guiding mitigation priority.

AAPM TG-263 standardizes structure and plan nomenclature, while DICOM-RT, HL7, and IHE-RO profiles support interoperable exchange between planning, record-and-verify, and oncology information systems.

Incident learning is supported by RO-ILS and TG-100 methods; a facility radiation safety officer administers the radioactive materials license under 10 CFR Part 35 in NRC or Agreement State jurisdictions.

Radioactive sources and waste are held in storage until decay to background, conventionally estimated as ten half-lives; packages are surveyed and wipe-tested on receipt and before disposal.