Radiation Oncology/Physics/Isotopes

A listing of useful isotopes in Radiation Oncology
 * See also: Unsealed sources

Periodic table

Overview
Listed in order of increasing atomic number (Z).


 * Preparation overview
 * Spent nuclear reactor: Cs-137, Sr-90
 * Neutron bombardment in nuclear reactor: Co-60, Ir-192
 * Proton bombardment in cyclotron: C-11, N-13, O-14 (short half-life positron emitters)
 * Elution of metastable daughter: Tc-99m

Phosphorus
P, Z = 15
 * P-32

Half life: 14.29 days Decay: B minus to S-32 B energy: 0.5MeV

Cobalt
Co, Z = 27
 * Co-60: Half life 5.263 yrs. Gamma energy 1.25 MeV (avg)
 * Beta decay, 60Co->60Ni (stable). Gamma rays produced: 1.17 MeV, 1.33 MeV. Beta: 0.32 MeV (99%) and 1.48 MeV (1%) Emax.
 * Clinical use: cobalt teletherapy, brachytherapy (remote afterloading), Gamma Knife radiosurgery
 * Clinical form: teletherapy source (1-2 cm diameter, Co-60 in stainless steel capsule), brachytherapy (in stainless steel capsule)

Strontium
Sr, Z = 38
 * Sr-89 Half-life 50.6 days
 * Source: byproduct of nuclear fission
 * Energy beta 1.46 MeV


 * Sr-90 Half-life 28.5 years; in secular equilibrium with daughter Y-90 (half-life 64 hours)
 * Source: byproduct of nuclear fission. Present in significant amounts in spent nuclear waste
 * Energy: beta (Sr-90) 546 keV, beta (Y-90) 940 keV
 * Dose rate: ~1 Gy/sec at surface, ~5 cGy/sec at 4mm (lens)
 * Clinical use: As applicator for superficial skin and ophthalological cancers
 * Toxicity: Seen by body as calcium, and deposited into bone. Bone marrow toxicity

Yttrium
Y, Z = 39
 * Y-90: pure beta emitter, average energy 0.94 MeV, tissue penetration 2.5 mm, maximum range 1.1 cm. Half life 64.2 hrs.
 * Clinical use: hepatic microsphere therapy; Zevalin in NHL

Palladium
Pd, Z = 46
 * Pd-103: Avg 0.021 MeV (21 keV) x-rays. Half life 17.0 days.
 * Produced from stable Pd-102 by absorption of a neutron
 * Decays via electron capture. 103Pd -> 103Rh, which undergoes internal conversion and emits characteristic X-rays (range: 20-23 keV). Auger electrons also emitted.
 * Clinical use: interstitial brachytherapy (prostate)
 * Clinical form: seed model 200 (Theragenics Corp) - 4.5 mm x 0.8 mm; two graphite pellets plated with Pd-103 in titanium tube. Lead marker between pellets allows for identification on X-rays.

Iodine
I'', Z = 53
 * I-125: Avg 0.028 MeV (28.5 keV) x-rays. Half life 59.4 days.
 * Produced from Xe-124 by absorption of a neutron
 * Decays by electron capture. 125I -> 125Te, which undergoes internal conversion 93% of time (to 27.3 keV, 31.4 keV x-rays; avg 28.5 keV) and produces gamma ray (35 keV) 7% of time
 * Commercially available as small "seed" sources


 * I-131
 * Clinical use: thyroid cancer, Bexxar for NHL

Cesium
Cs, Z = 55
 * Cs-137: gamma 0.662 MeV. Half life 30.07 yrs.
 * Produced from fission of uranium U-235 in nuclear reactors. It is one of the major fission byproducts, and accounts for most of the radioactivity in spent radioactive fuel (and from nuclear contamination after accidents such as Chernobyl). Some is extracted for commercial uses
 * Decays by beta decay 137Cs -> 137Ba. Gamma rays from metastable Ba-137 produced (93.5%) - 0.662 MeV
 * Decay correction ~2%/year
 * Clinical use: interstitial and intracavitary brachytherapy
 * Clinical form: needles or tubes; ceramic microspheres or powders encapsulated in stainless-steel. Beta and low energy x-rays absorbed by tube, so source acts as a pure gamma emitter.
 * Lifecycle of Cs-137 in the U.S.

Iridium
Ir (Z=77)
 * Ir-192: gamma, avg E 0.37 MeV. Half life 74.2 days
 * Produced from stable Ir-191 by absorption of a neutron in a nuclear reactor
 * Decays by beta decay (95%) 192Ir->192Pt and electron capture (5%) 192Ir->192Os. Complex energy spectrum (0.1 - 1.1 MeV, average 0.37 MeV)
 * Decay correction ~1%/day
 * Clinical use: interstitial brachytherapy (HDR)
 * Clinical form: alloy of 30% Ir and 70% Pt. Thin flexible wires. Nylon ribbons containing Ir-192 seeds
 * Available in variety of air kerma strengths (1.4-7.2 U commonly, up to 72 U)

Gold
Au, Z=79
 * Au-198

Radium
Ra, Z = 88
 * Ra-226: gamma, 1.2 MeV avg. Half life 1600 yrs
 * No longer as prevalent for medical use due to decay into radon gas