Radionuclide Therapy

Question 1

What radionuclide is used for SIRT?

Answer 1

Y-90

Question 2

What type of radionuclide emitter is used for SIRT? (gamma, alpha, beta?)

Answer 2

Beta

Question 3

What are the administration routes for radionuclides?

Answer 3

IV injection or infusion, oral, intracavitary, intra-arterial.

Question 4

What properties determine the absorbed dose in the patient for radionuclide therapy?

Answer 4

The distribution within body, patient size, patient biology, uptake & retention, along with physical radiation properties.

Question 5

What is the maximum deviation aimed for from the prescribed activity in radionuclide therapy?

Answer 5

5%

Question 6

What are the limitations of radionuclide therapy?

Answer 6

Potentially small workload in terms of patients, but large in terms of time & cost.

No agent is entirely selective to desired target – get uptake by other tissues, e.g. Ca. thyroid treatments

Patient-specific dose calculations are difficult due to inhomogeneous dose deposition and individual physiology affecting behaviour of agent

Radiation is not risk free - IR(ME)R requires a ‘net benefit’

Dose Limiting Factor = normal tissue toxicity e.g. myelotoxicity due to bone irradiation

Question 7

What are the properties of a diagnostic radionuclide?

Answer 7

Short effective half life: order of study

No particulate emission: EC or IT

Mid gamma energy: 100 - 300 keV, high yield

High target / background ratio

Question 8

What are the properties of a therapeutic radionuclide?

Answer 8

Ideally beta particles, alpha particles (charged particles). – beta or alpha decay.

Longer half life to give more dose (not too long – roughly days (diagnostic = hours)).

Price is low – funding & expense

Radionuclide & radiochemical purity – all activity in right nuclide & chemical form. (I-131 with MIBG – if some of free iodine isn’t connected to MIBG will be a radiochemical impurity)

Ideally emits gamma rays for imaging – brem, etc.

Question 9

Is a high or low LET useful for therapy?

Answer 9

High

Question 10

What is the energy of an alpha particle?

Answer 10

< 7.5 MeV

Question 11

What is the energy of an auger electron?

Answer 11

< 10 keV

Question 12

What is the energy of a conversion electron?

Answer 12

< 100 keV

Question 13

What is the energy of a beta particle?

Answer 13

< 1000 keV

Question 14

What is the range of an alpha particle?

Answer 14

< 0.07 mm (cell diameter)

Question 15

What is the range of an auger electron?

Answer 15

< 0.01 mm (cell nucleus)

Question 16

What is the range of a conversion electron?

Answer 16

< 0.14 mm (few cells)

Question 17

What is the range of a beta particle?

Answer 17

< 4.4 mm (many cells)

Question 18

On a time activity curve, what does the area under the curve represent?

Answer 18

Amount of dose deposited in tissue.

Longer half life = bigger area = more dose.

Question 19

How many disintegrations per second is 1 MBq?

Answer 19

1 million per second.

Question 20

What is P-32 orthophosphate used to treat?

Answer 20

Myeloproliferative disorders

Question 21

What is used to treat bone pain palliation?

Answer 21

Strontium [89Sr] chloride

Samarium [153Sm] EDTMP

Question 22

What is used to treat bone metastases?

Answer 22

Radium-223 Chloride

Question 23

What is 90Y or 186Re Colloid used to treat?

Answer 23

Joint arthritis, inflammations & effusions.

Question 24

What is used to treat thyrotoxicosis or thyroid cancer?

Answer 24

Radioiodine [131I] NaI

Question 25

Describe P-32 therapy.

Answer 25

Treats myeloproliferative disease (eg polycythaemia vera) where too many blood cells produced and blood gets thick, often associated with bone marrow hyperactivity.

IV injection 111-222 MBq (chosen by clinical assessment).

Costs ~ £400. (varies as air fare from Poland is shared by hospitals using it)

Taken up in haemopoetic (blood forming) tissue and reduces cell viability & proliferation (radiation injury to cell precursors and bone marrow)

Physical Half Life = 14 days.

Pure beta (b-) particle emitter
Emax   = 1.71 MeV
Emean  = 0.7 MeV
(Beta gives off range of energies as has excess of neutrons – converts to proton & gives off beta and anti-neutrino, as energy gets less the anti-neutrino is carrying away more energy.  So need to know mean energy for dose calcs.)

Radiation Protection: Flush toilet twice for 2 days, Don’t donate blood for 2 weeks, given card explaining instructions.

Question 26

What are the 3 mechanisms involved in stopping an electron?

Answer 26

Bremstrahlung (Radiative)
Excitation (Collisional)
Ionisation (Collisional)

Question 27

Describe Ra-223 therapy.

Answer 27

Use to treat: Metastatic bone disease
Chemical form: Radium chloride
Physical half-life: 11 days
Principal radiation: alpha particles (small amount of beta and gamma (roughly 3%))
Route: i.v. 6 injections at 4 weekly intervals

Administration:
Draw up the Radium immediately prior to injection
55 kBq per kg patient weight (manufacturer informed as delivered the correct amount with a small amount of excess)
Check the cannula with 10ml saline (careful not to tissue)
Slow IV injection using syringe shield.
10ml flush of saline
Separate sharps bin - seperate radiation waste
Return in 4 weeks

Radiation Protection:
Flush toilet twice for 2 days
Don’t give blood for 2 days 
Given card wtih instructions on
Tiny amount of gamma - not bothered about proximity

Question 28

Describe the properties of I-131 therapy.

Answer 28

Chemical form: Sodium Iodide
Physical half-life: 8.02 days
Principal radiation: 606 keV beta (87%), 364 keV gamma (82%)
Made in: nuclear reactor as high atomic mass & decays by beta – as extra neutrons. Neutron bombardment, or fission product in reactor.
Administered activity: hyperthyroid ~ 400-550 MBq, ca. thyroid ~ 1– 5 GBq
Route: oral (capsule)
Uptake : Active Transport
Cost of capsule: £100 – 300

Question 29

Describe I-131 for thyrotoxicosis.

Answer 29

Dose given to damage cells to produce less hormone.
Over-active thyroid: High levels of circulating T4 and T3 hormones
Common symptoms: Increased metabolic rate, palpitations, sweating, weight loss, nervousness, cardiac and eye complications can occur

Treat with Carbimazole / Propylthiouracil
Long-term side effects of carbimazole (cardiotoxic)
If not cured by drug therapy, may prefer alternatives – surgery (remove part or whole of thyroid) or radioiodine (reduce function)

Out-patient therapy (usually)

Careful workup to allow proper radiation risk assessment (e.g. are patients caring for children, incontinent, in a nursing home)

Clinical follow-up required to assess response. Test blood levels of thyroid hormones & assess clinical symptoms. If not low enough, may need 2nd treatment (<10% patients), if too low -> give thyroxine tablets to replace hormones (often the aim). Usual practice is to give extra to reduce function to under par, then top up with hormones.

Radiation protection:
5-6 days avoid long exposures (>1 hr) of close contact with everyone (limit dose)
Up to 3 weeks avoid close contact with children & pregnant women
No blood samples/invasive procedures for 1 month
Carry instruction card for 1 month, 3 month for travelling abroad (radiation detectors at airports)

Question 30

Describe I-131 for thyroid cancer.

Answer 30

Purpose: Eliminate residual thyroid tissue after thyroidectomy.

Method: I-131 capsule
Patients stop taking medication or given thyrogen administration which raises Thyroid Stimulating Hormone (TSH) levels stimulating I-131 uptake and Thyroglobulin production

Radiation Protection:
In patient procedure with lead lined walls.
Avoid close prolonged contacted dependent on rate of activity dispersion (Effective half life (= physical + biological))
Given card to keep for 3 months.

Dose: 1.1 GBq – low risk, 3.7 GBq – high risk, 5.0 GBq – patients with known metastasis

Post ablation scan taken 6-9 months later.