# Radiation Oncology/Physics/Isotopes

* Front Page: Radiation Oncology | RTOG Trials | Randomized Trials
A listing of useful isotopes in Radiation Oncology
    See also: Unsealed sources
Periodic table

## Overview

Listed in order of increasing atomic number (Z).
Sealed Sources :
| Radionuclide | Source | Half-life | Gamma | Energy | HVL (mm Pb) |
| Co-60 | Neutron absorption | 5.3 years | 13.1 | Gamma: 1.25 MeV | 11 |
| Sr-90 | Fission product | 28.8 years | | Beta (Sr-90): 546 keV Beta (Y-90): 940 keV | |
| Pd-103 | Neutron absorption Proton absorption | 17 days | 1.5 | X-ray: 21 keV | 0.008 |
| I-125 | Neutron absorption | 60 days | 1.4 | X-ray: 28 keV | 0.028 |
| Cs-131 | | 9.7 days | | X-ray: ~30 keV | |
| Cs-137 | Fission product | 30 years | 3.3 | Gamma: 662 keV | 6.5 |
| Ir-192 | Neutron absorption | 74 days | 4.7 | Gamma: 380 keV | 2.5 |
| Au-198 | Neutron absorption | 2.7 days | 2.4 | Gamma: 412 keV | 2.5 |
| Ra-226 | Uranium ore | 1622 years | 8.2 | Gamma: 830 keV | 8 |
Unsealed Sources :
| Radionuclide | Source | Half-life | Energy |
| P-32 | Neutron absorption | 14.3 days | Beta: 695 keV |
| Sr-89 | Fission product | 50 days | Beta: 1.46 MeV |
| Y-90 | Sr-90 daughter | 64 hours | Beta: 940 keV |
| I-131 | Fission product | 8 days | Beta: 806 keV |
| Sm-153 | Neutron absorption | 47 hours | Beta: 810 keV |
* 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, $^{60}$Co->$^{60}$Ni (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. $^{103}$Pd -> $^{103}$Rh, 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. $^{125}$I -> $^{125}$Te, 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 $^{137}$Cs -> $^{137}$Ba. 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%) $^{192}$Ir->$^{192}$Pt and electron capture (5%) $^{192}$Ir->$^{192}$Os. 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