ABR Rule of thumb

Average photon energy of a bremsstrahlung beam

Approximately one-third of the maximum/nominal energy.

Co-60 photon energies

1.17 and 1.33 MeV.

Average Co-60 photon energy

~1.25 MeV.

Co-60 dmax

~0.5 cm.

6 MV dmax for 10×10 cm²

~1.5 cm.

10 MV dmax for 10×10 cm²

~2.4 cm.

18 MV dmax for 10×10 cm²

~3.3 cm.

PDD at 10 cm for Co-60, 10×10 cm²

~55%.

PDD at 10 cm for 6 MV, 10×10 cm²

~65%.

PDD at 10 cm for 10 MV, 10×10 cm²

~75%.

PDD at 10 cm for 18 MV, 10×10 cm²

~80%.

TMR at 10 cm for 6 MV

~0.78.

TMR at 10 cm for 10 MV

~0.85.

TMR at 10 cm for 18 MV

~0.90.

Approximate attenuation rate for 6 MV

~3% per cm.

Approximate attenuation rate for 10 MV

~2.5% per cm.

Approximate attenuation rate for 18 MV

~2% per cm.

Surface dose for Co-60

~50%.

Surface dose for 6 MV

~25%.

Surface dose for 10 MV

~23%.

Surface dose for 18 MV

~20%.

Scatter at 1 m from phantom

~1/1000 of primary beam.

MV f-factor in air, conversion for Roentgent to cGy

0.876 cGy/R.

MV f-factor in tissue, conversion for Roentgen to cGy

~0.97 cGy/R.

I-125 exposure rate constant

1.45 R cm2/mCi-hr

Ir-192 exposure rate constant

4.69 R cm2/ mCi-hr

Physical wedge out-of-field scatter

~2.5% of central axis dose.

Dynamic wedge out-of-field scatter

~1.0% of central axis dose.

Dose 10 cm outside field at dmax

~1% of central axis dose.

Dose 30 cm outside field at dmax

~0.2% of central axis dose.

Intraleaf MLC leakage

~2%.

Interleaf MLC leakage

~3%.

MLC end leakage

~15%.

LINAC head leakage limit

0.1% of central axis dose at 1 m.

Neutron head leakage 10 MV

~0.01%.

Neutron head leakage 18 MV

~0.15%.

6 MeV electron dmax

~1.2 cm.

9 MeV electron dmax

~1.9 cm.

12 MeV electron dmax

~2.1 cm.

20 MeV electron dmax

~2.5 cm.

6 MeV electron surface dose

~80%.

12 MeV electron surface dose

~90%.

20 MeV electron surface dose

~95%.

6 MeV electron x-ray contamination

~1%.

12 MeV electron x-ray contamination

~2%.

20 MeV electron x-ray contamination

~5%.

Lead thickness to stop electrons

Approximately E0(MeV)/2 in mm of lead.

Electron practical range Rp

Approximately E/2 in cm of water.

Electron therapeutic range R80/R90

Approximately E/3 in cm of water.

Electron R50 relation to Energy

R50 ≈ E/2.33 in cm.

Electron penumbra trend with energy

Penumbra generally increases with energy.

Proton range uncertainty common estimate

~3.5% of range plus 1–3 mm.

70 MeV proton range in water

~4 cm.

100 MeV proton range in water

~7.7 cm.

130 MeV proton range in water

12.3 cm

150 MeV proton range in water

~17.7 cm.

190 MeV proton range in water

~23.8cm

200 MeV proton range in water

~26 cm.

230 MeV proton range in water

~33 cm.

250 MeV proton range in water

~38 cm.

Proton calibration protocol often referenced

IAEA TRS-398; AAPM TG-185 for proton reference dosimetry.

LDR dose rate at prescription point

0.5–2 Gy/hr.

HDR dose rate at prescription point

12Gy/hr

Ir-192 half-life

73.8 days.

Ir-192 daily decay rule

~1% per day (~0.94% exact).

HDR source replacement interval

About every 3 months.

approximate dose from Cs-137 to Ir-192

Ir-192 = D(Cs-137) * 0.65

Time 1 m from exposed HDR source to occupational limit

Order of ~1 hour, depending on source strength.

Definition of 1 U, equivalent units

1 cGy*cm2/hr

TG-43 geometry function purpose

Accounts for inverse-square and source geometry effects.

TG-43 radial dose function purpose

Accounts for attenuation and scatter along transverse plane.

TG-43 anisotropy function purpose

Accounts for angular dose variation around source.

I-125 half-life

~59.4 days.

Pd-103 half-life

~17 days.

Cs-131 half-life

~9.7 days.

Cs-137 half-life

~30.2 years.

Co-60 half-life

~5.27 years.

Ra-226 half-life

1600 yrs

Au-198 half-life

2.7 days

I-125 average photon energy

~28 keV.

Pd-103 average photon energy

~21 keV.

Cs-131 average photon energy

~30 keV.

Ir-192 average photon energy

~380 keV.

Au-198 energy

420 keV

Cs-137 energy

660 keV

Ra-226 energy

830 keV

Co-60 photon energies

1250 keV

I-125 patient release limit

less than 1 mR/hr at 1 m.

Pd-103 patient release limit

less than 3 mR/hr at 1 m.

I-131 patient release limit

less than 7 mR/hr at 1 m.

Sealed source leak test removal threshold

More than 185 Bq (0.005 μCi) leakage.

Brachy medical event

Wrong patient, site, or radionuclide; total dose 20%, single fraction 50%

Teletherapy medical event

wrong patient, site; total dose differs by 20% (3+fx); total dose differs by 10% (-3fx)

Point A vs Point B

Point A from tandem, point b from midline

Occupational dose limit

50 mSv/year.

Pregnancy occupational dose limit

5 mSv for entire pregnancy.

Public dose limit

1 mSv/year.

Average occupational exposure in U.S. radiation worker

~2 mSv/year.

Average annual background + medical exposure

~4–5 mSv/year.

Radon annual contribution

~1 mSv/year.