**6. Activation products medical uses**

Remembering what we want for a radioisotopes to be safely used in medicine, Natural decay series has had a very bad performance. For example, 226Ra was used in Medicine until users realized that its daughter was 222Rn, a gas. Since 226Ra was encapsulated in stainless steel tubes the accumulation of Radon from Radium decay inside the tube, cause the gaseous pressure to increase in a non controlled way, so more than 10 years after its encapsulation, the gas pressure was so high as to break the capsule and escape. So as 222Rn is a radioactive gas and it half life is not short (almost 4 days), contamination was hard to contain, so Radium use was declined.

Fig. 10. Radium Tubes.

Activation products from Cyclotrons are in general of short half life, so the control can be focus in the energy users can handle. In such a way, we can say activation products can be tailored to our needs. But medical uses are little complicated. Nuclear Medicine consist in mix the radioisotope with a pharmaceutical product which is characterized by the organ they are going to address the isotope. What Nuclear Medicine really needs is to send the radioisotope to get inside the organ we want to study, and as the radioisotope is inside a molecule that can be metabolized by this organ, this metabolization function can be easily watch and measure with the appropriate radiation detectors. The name "radiopharmaceuticals" refers to the metabolically stable combination of a biochemical molecule to which radioisotope in bind that act as the vehicle through which, organ of interest can be reach. There are several mechanism for the radioisotope to join the address molecule such as:

1. Ionic compound: In which the radioisotopes determine the metabolic route to be follow as in 131I to thyroid uses, because thyroid likes iodine and do not distinguish between different isotopes of the same element iodine.

**Yttrium-90** 90Y 39 2.67d β- - 2.280 (100%) **Iodine-131** 131I 53 8.02 d γ, β- 364 (81%) 0.807 (100%)

In the table above we can see some radioisotopes that say they are parent or daughter in a

In Nuclear Medicine environment, sometimes is useful to have a regular provision of radioisotopes for studies to be performed without the restrictions of providers time dependences, for example when studies has to be done anytime of the day in emergency conditions. If physician suspects an infection in a patient admitted in Emergency Room, it will be of utmost usefulness to have Nuclear Medicine images done with appropriate radiopharmaceuticals to solve the question about the most effective treatment to be offer to the patient. Either way, sometimes in Cardiology it is of high importance to know about percentage of isquemic muscle, but patient has not the luxury of time to undergo a catheterism, so it is more effective and quick to have Nuclear Medicine images and cine of the heart. In many cases like this, have a good availability of radiotracers make the

This is the reason why radioisotopes generators have become so popular beside the fact that in countries like Venezuela where there is no nuclear production, sometime become very hard to warranty a regular supply. A radioisotopes generator is a device in which you can contain a pair father/daughter in which the daughter is the product of interest for studies purposes and father only come to generate the full amount of daughter needed. Due to the short half life we need for the radioisotope to be safe handle in hospital conditions, it would be useful to find a pair father and daughter that warranty the in time provision of radioisotope needed. During the generator useful life father has to decay completely to the useful daughter so it can be easily recharged, disposed or returned to provider. Such pair

1. Father has to have long enough half life (physical) such as to overcome travel time from provider to user. In this way father will be generating enough amount of daughter that can be extract in site for studies and will continue generating daughter to fulfill the

3. Daughter has to decay in a sufficient short life be secure for image acquisition and

4. Father and daughter have to have different chemical characteristics so the can be easily separate to be sure the daughter is so pure to be safe for human applications and there

Table 3. Common Isotopes Used in Nuclear Medicine for diagnostic studies or therapy

**mode** 

**Photons energy** 

β **energy** 

**Isotope Symbol Z T1/2 Decay** 

differences between a correct and opportune answer or a misdiagnosis.

Therapy:

procedure.

**7. Generators** 

generator, but what is a generator?

must that accomplish some conditions like:

needs for its entire useful time.

radiation protection of patient

2. Father must be shipped in pyrogen free condition

are no traces of the father in the injection solution.


Imaging:


Therapy:

60 12 Chapters on Nuclear Medicine

2. Isotopic Exchange: In which the radioactive isotope goes to replace the stable isotope of

3. Incorporation: In which radioisotope get inside the molecule but not interacting with the chemical compound, so it did not change its structure neither biochemical nor

4. Coprecipitation: In which radionuclide is precipitated in the same reaction with the chemical compound. Many are the radioisotopes that can be combined with different molecules to be address to different parts of human body with diagnostic or therapeutic

> **Photons Energy**

(193%)

**Krypton-81m** 81mKr 36 13.1s IT 190 (68%) - Refrigerant

(191%)

**Technetium-99m** 99mTc 43 6.01h IT 140 (89%) - Pulmonary ventilation studies. **Indium-111** 111In 49 2.80d EC 171 (90%) 245 (94%) Brain studies, infection and colon

**Iodine-123** 123I 53 13.3 h EC 159 (83%) - Gamma emitter: diagnosis of

**Xenon-133** 133Xe 54 5.24d β- 81 (31%) 0.364 (99%) Studies of pulmonary function

**Carbon-11** 11C 6 20.39m β+ -- 0.96 (100%) PET: Studies of brain physiology:

(94%)

**Nitrogen-13** 13N 9 9.965m β+ -- 1.2 (100%) PET: Cardiology **Oxygen-15** 15O 8 122.24s β+ -- 1.8 (100%) PET: Cardiology and cancer

**Cooper-67** 67Cu 29 2.6 d β− -- 0.56 (100%) Beta emitter therapy

**Germanium-68** 68Ge 32 271 d EC -- 0.1 (100%) 68Ga generator parent

**Gallium-68** 68Ga 31 68 min β+ -- 1.90 (100%) PET: tumor detection, daughter

300 (17%)

0.58(39%)

**β energy Uses** 

0.664 (97%) PET: Cancer detection and

3.379 (95%) Tracer in positron emission

167 (10%) Diagnostic aid in the form of

in 68Ge generator

monitoring of treatment progress, in flurodexoxiglucose. (FDG) Tracer in flurothymidine (FLT) and fluromisonidazole (F-MISO), and 18F-choline

> SPECT: Tumor imaging, infections localization

> > tomography

transit studies.

thyroid function, without the beta radiation of I-131.

and organic blood flow.

thallous chloride TI 201

epileptic focus, dementia, etc

detection

genetic studies: copper metabolism: Wilson's and Menke's diseases. PET: tumours, and therapy.

purposes, so we can group them as in the table below:

**Z T1/2 Decay** 

**Gallium-67** 67Ga 31 3.26d EC 93 (39%) 185 (21%),

**mode**

it own species

Imaging:

physical properties

**Isotope Symb**

**ol** 

**Fluorine-18** 18F 9 109.77m β+ 511

**Rubidium-82** 82Rb 37 1.27m β+ 511

**Thallium-201** 201Tl 81 3.04d EC 69-83\*

**Cooper-64** 64Cu 29 13 h β+ -- 0.65 (61%)


Table 3. Common Isotopes Used in Nuclear Medicine for diagnostic studies or therapy procedure.

In the table above we can see some radioisotopes that say they are parent or daughter in a generator, but what is a generator?
