Nuclear Medicine Resources Manual

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CHAPTER 6. RADIONUCLIDE THERAPY

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Female and male patients should be told what precautions, if any, are

necessary if they wish to conceive, or father, a child subsequent to the therapy.

A minimum of six months should be observed before conception.

(b) Therapy procedure — low doses (below discharge level)

Iodine-131 therapy doses are obtainable in liquid form or in capsules.

Because of the significantly greater radiation hazards from liquid sources, the

comments below assume the use of capsules. In addition to the general advice

given above, the following points should be considered when designing the

treatment protocol:

—Patients should be given written information about the therapy, and in

particular instructions for when they return home.

—When patients are first brought in, they should be asked if they fully

understand the procedure. If not, the procedure should be explained to

them in simple terms.

—Patients should be asked to wear gowns and gloves (in case of contami-

nation).

—The procedure should be explained carefully to the patient.

—The capsule should be placed in a plastic cup to avoid handling.

—The patient is required to swallow the capsule without chewing, followed

by a drink of water.

—The patient should place the plastic cup and gloves in a waste bag.

The patient may then leave, after any subsequent restrictions are clearly

understood. These restrictions may include:

—Flushing the toilet twice after urinating, for the first 72 hours after

therapy;

—Maintaining a safe distance (1 m) from children or pregnant women for a

few days.

The procedure for administering high doses is the same as for low doses

except that the therapy should be administered in the patient’s room.

Patients with thyroid cancer will have a very low iodine uptake, and a

high proportion (often more than 95%) of the dose will be excreted, generally

in the 72

hours following administration. While most excretion occurs in the

urine, significant contamination can occur in saliva, with less in sweat and

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441

faeces. Until the dose is fully absorbed from the gut, vomiting can cause a

major contamination problem. To deal with these problems, the following

measures can be considered:

(1) A prophylactic anti-emetic should be given prior to, or immediately after,

the dose is administered.

(2) All linen, mattresses and pillows used by the patient must remain in the

patient’s room until checked for contamination; pillows in particular may

be significantly contaminated.

(3) The therapist should check with the local regulatory authority for any

requirements relating to discharge of radioactive human waste in the

sewer. The simplest precaution is to tell the patient to flush the toilet at

least twice after urinating. Even then there may still be a requirement (in

some countries) to connect the toilet to a storage tank, where the waste

may decay for some weeks before discharge to the sewer.

(4) If the patient is incontinent, or confused, a bladder catheter should be

inserted prior to dose administration.

(5) To stimulate excretion, patients should be advised to drink freely, and

void frequently.

(6) Salivary excretion can be stimulated by sucking or chewing confectionary.

(7) The patient’s food must be served on disposable plates, and with

disposable cutlery because of the potential for high salivary contami

nation.

These precautions may usually be discontinued after 72 hours.

(d) Inpatient therapy procedures (MIBG)

The above precautions also apply to MIBG therapy, although there are

some extra issues to be considered and the rate of excretion will vary according

to the degree of tumour retention. The precautionary period for excreta

control might need to be extended.

The patient information should also be varied, with an example given

below.

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SPECIMEN PATIENT INFORMATION SHEET

Introduction

1. This is a short information sheet to help you understand the restrictions

that will be placed on you after undergoing treatment using radioactive iodine.

2. There are several precautions that you and your family must observe both

during the time you are in hospital and after you have been discharged. These

precautions must be discussed fully with you; they are outlined below to ensure

that they are clear. The radioactive treatment cannot be administered unless

you understand these restrictions and sign a consent form by which you agree

to adhere to them.

3. There will be a telephone within the room that may be used for incoming

calls. In an emergency, the nursing staff can arrange for you to make an outside

call.

Radioactivity and radiation

4. The treatment involves the administration of radioactive iodine, which

will be attached to a non-radioactive label called MIBG specifically designed to

adhere to the appropriate tumour.

5. Since you will become radioactive and will emit radiation after the

treatment, you will be required to remain within the radionuclide treatment

room until you are advised that it is safe to leave. This consists of a side room,

shower/bath and toilet. You will excrete a considerable amount of radioactive

iodine in urine, faeces, sweat, saliva and nasal mucous. It is very important that

these substances are not allowed to contaminate other people, or areas outside

the room.

6. You may ONLY use the toilet, shower and washing facilities within the

radionuclide room. You are not allowed out of the room, except for a scan.

Meals

7. Your meals will be supplied on disposable plates and with disposable

cutlery. Waste may not be thrown away by anyone on the ward. You will be

provided with an electric kettle, coffee powder and tea bags so that you may

make your own drinks. There is also a small refrigerator in the room to keep

6.2. SAFETY PRINCIPLES

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milk or other cold drinks that you may like. If you have a preference for a

particular drink, you should bring it with you.

Personal belongings

8. Money: It is not advisable to bring more money than you think you will

require into the ward. If you would like the nursing staff to buy you daily

newspapers, please give them some cash prior to the initiation of your

treatment. If you are likely to have much excess money, it is wise to ask the

nursing staff to lock it away until it is time for you to go home. The nurses will

discuss this with you.

9. Clothes: Any clothes that you wear may become contaminated with

radioactive iodine. Ideally, clothes worn while in the ward should be suitable

for laundering in a washing machine; they should be taken home in a polythene

bag and washed in a machine. Towels and flannels may also become contami

nated and must be machine washed.

10. Other personnel belongings: It is advisable not to bring too many

personal belongings into hospital, since anything you handle could become

contaminated. Books, CDs and DVDs generally remain free of contamination.

General precautions

11. You will be required to start taking some tablets prior to the adminis-

tration of the radioactive iodine-MIBG treatment. If you are on any medica-

tions, including nose drops, eye, ear, throat or cough drops or tablets, you must

inform your doctor since they could prevent the radioactive treatment from

acting efficiently.

12. It is important for you to drink as much fluid as possible, as this helps to

keep the radiation dose to the bladder to a minimum, thus preventing a

possible cystitis. It is also important not to be constipated, since this will lead to

the stomach and bowel becoming unnecessarily irradiated. As a result the

residual whole body activity will remain high for a longer period, possibly

delaying your discharge.

13. You should use disposable tissues rather than handkerchiefs, if possible,

since nasal mucous tends to have a high radioactive content. These tissues must

be disposed of in the macerator.

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14. Bed linen: Should this require changing, the used linen should be placed

in a bag and left within the suite. It must not be sent to the laundry. Any

radioactive contamination can normally be washed out in one washing machine

cycle, but this must be done under the control of a physicist.

15. Rubbish must be kept within the suite until checked for contamination.

This may involve storage prior to incineration in a licensed incinerator or

storage until ‘complete’ decay of the contamination.

16. You may only leave the suite for the purpose of a scan or in an emergency.

On leaving the room you should put on protective clothing (i.e. plastic aprons,

shoes and gloves) and remove it on re-entry to the suite. In an emergency this

may not be feasible if time is crucial.

Visitors

17. It is permitted for you to have visitors, provided that they comply with the

regulations and that neither children nor pregnant women visit you at any time.

18. Visitors should respect the maximum visiting time as displayed on the

door. They should keep as far away from you as possible. Under no circum

stances should visitors eat, drink, smoke or use the toilet facilities in the

treatment room.

Discharge

19. There are different levels of remaining activity at which the hospital is

allowed to discharge you depending on your home circumstances and on your

means of transport home. After two or three days (possibly longer, depending

on the estimate of residual activity), the activity remaining within you will be

measured and you will then be advised as to how many more days it may be

necessary for you to stay. Once you have been discharged, we may have to

request you to observe certain restrictions such as not going to the cinema or

mixing with children. These restrictions are dependent on the level and rate at

which the radioactive iodine-MIBG has been passing out of you.

20. In the event of an emergency, the nuclear medicine department should be

contacted immediately (be sure to include contact information).

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6.2.9. Pure beta emitters and mixed beta/gamma emitters

6.2.9.1. Pure beta emitters

Beta emitters such as

186

Re,

169

Er,

166

Ho,

Sr and

P generally

require consideration only at the time of administration, with little if any

hazard afterwards, although higher energy beta emissions can cause

measurable bremsstrahlung X ray radiation exterior to the patient.

Extravasation and surface contamination of beta emitters must be

avoided. Administration must only be performed in a room designed for

unsealed radionuclide use; in particular, all surfaces should be free of gaps and

easily washable. Following administration the injection site must be checked

for spilt or leaked radionuclides by swabbing and checking the swab with a beta

detector.

In the case of

Sr, most of the unbound strontium will be excreted in the

urine, normally within 48 hours of administration. Patients should be advised to

flush the toilet twice after voiding. Precautions must be taken if staff or

relatives come into contact with urine, for example if the patient is incontinent

or catheterized, in which case gloves must be worn and properly disposed of.

Similarly,

P is largely excreted in the urine, with some in the faeces.

Patients should again be advised to flush the toilet twice after voiding for the

first 48 hours.

The patient must be given written instructions covering the need to wash

hands following toilet use, cleaning up any spilt urine, flushing toilets and the

washing of any clothing that may be urine contaminated. The instructions

should also include contact names and phone numbers in case of an emergency.

6.2.9.2. Emitters of both beta and gamma radiations

Samarium-153 and

188

Re produce some gamma emission but this is not

normally a significant safety problem. Staff and patient should be advised to

remain at a distance of 1 m until discharge.

6.2.10. Precautions following death of a therapy patient

Procedures should be put in place for the safe disposal of the bodies of

patients who have received therapeutic doses. This may include labelling,

contamination avoidance and notification of the staff who may have to handle

the body. These procedures will obviously depend on the radiopharmaceutical

involved, the dose and the time since administration.

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Cremation may usually be undertaken with negligible hazard to

crematorium operators or members of the public at the normal doses used for

therapy, although some radionuclides may be present in significant quantities

in the ashes. The local regulatory authority should be contacted for advice.

If a post-mortem or embalming is to be performed, then advice from the

radiation safety officer must be sought, as there could be a significant contami

nation and radiation hazard, especially with

131

Ward staff in particular should be provided with instructions for dealing

with the death of a radionuclide therapy patient.

6.2.10.1. Procedures

The nuclear medicine department must be notified as soon as possible

after a death. Only a minimum of laying out procedures should be attempted

(e.g. replacement of false teeth) and the sheet in which the body is wrapped

should be clearly labelled as containing a radioactive body. The label should be

clearly visible to all those handling the body. The body should be removed from

the ward to the mortuary as soon as possible after death, without attempting to

remove any of the radioactive material, and placed in, if possible, the centre

section of the body storage refrigerator. This is to minimize any radiation

exposure to staff who may be working in the mortuary.

6.2.10.2. Mortuary procedures

Exposure of individuals to radiation emitted by radioactive materials

retained in or on a corpse can be reduced by:

(a) Working quickly to reduce the time of exposure;

(b) Working, where necessary, behind adequate shielding;

removal of highly contaminated tissues such as the thyroid.

6.2.10.3. Autopsies: General comments

If a corpse contains less than 150 MBq (4 mCi) of colloidal

Y, 300 MBq

(8 mCi) of

P or 450 MBq (12 mCi) of

131

I, the procedures normally observed

during autopsy are adequate for the examination unless such examinations are

carried out frequently.

If, however, a corpse contains radioactivity in excess of the levels given

above, the pathologist should be informed of the radiation levels likely to be

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447

encountered and of the hazards involved. The methods employed and the

precautions adopted should be chosen accordingly.

Occasionally corpses are assigned to medical schools for dissection or are

to be transported overseas. Any hazards to persons involved in these

operations or the need for compliance with international transport regulations

depend on several factors relating to the nature of the radioactive sources. In

most instances the issue is resolved by keeping the corpse in appropriate cold

storage until twenty half-lives of radioactive decay have passed.

If it is known that the radioactive material used for treatment will be

selectively absorbed in a particular organ, for example

131

I in the thyroid, the

organ should be excised before the examination proceeds and removed from

the work area. It may later be disposed of with the body.

If it is known that radioactive material used for treatment will be

distributed in particular body fluids, these should be drained off, using suitable

equipment, before the examination proceeds. These fluids may often be safely

disposed of via the sewerage system. The equipment should later be decontam

inated by thorough rinsing in a detergent solution followed by washing in

running water.

6.2.10.4. Cremation

No special precautions are necessary for the cremation of corpses

containing not more than 1000 MBq (30 mCi) of

131

Sr or 400 MBq

(10

mCi) of

Transport of a corpse containing radioactive materials should be

considered in accordance with the requirements of local legislation covering

the transport of radioactive materials.

6.2.11. Cardiac or respiratory arrest, or transfer of a therapy patient for

medical reasons

Resuscitation of patients containing radioactive material for radiotherapy

or therapeutic nuclear medicine purposes poses special problems.

The general principles to be followed in all cases are that the patient’s

welfare is paramount and possible radiation exposure to staff should not be

considered a barrier to resuscitation, as, for the short times involved, the

potential radiation exposure will be small.

6.2.11.1. Patients treated with

131

Attention should be paid to the following points:

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(a) Do NOT apply direct mouth-to-mouth resuscitation.

(b) Staff involved in resuscitation should wear disposable gloves.

far as is practicable, be kept to one side for examination by nuclear

medicine staff. This particularly applies to airways, masks, endotracheal

tubes, etc.

(d) Notify the Department of Nuclear Medicine immediately.

6.2.11.2. Transfer to intensive care or the coronary care unit

Attention should be paid to the following points:

(a) If a transfer is required, the fact that the patient may still contain

radioactive material should not interfere with the management of the

case.

(b) In the case of patients treated with

131

I for whom intubation, catheteri-

zation or use of a nasogastric tube may be necessary, staff should wear

gowns and gloves when handling the patient.

possible by means of absorbent pads, and the pads held in a contaminated

waste bag for examination by nuclear medicine staff.

(d) Any suction bottles or urine bags used must not be discarded until

checked for contamination.

6.2.11.3. Examination of staff involved in resuscitation or handling of the patient

Staff who have been directly involved with the patient will need, for their

own safety and peace of mind, to be assessed as to their potential radiation

exposure, however small. This will include the best possible estimation of

radiation exposure, and, where

131

I is involved, administration of Lugol’s iodine

as soon as possible to block thyroid uptake of any absorbed contaminant, if

necessary, and subsequent measurement of any thyroidal accumulation of

131

BIBLIOGRAPHY TO SECTION 6.2

UNITED STATES NUCLEAR REGULATORY COMMISSION, Release of Patients

Administered Radioactive Materials, NRC Regulatory Guide No. 39, USNRC,

Washington, DC (1997).

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449

6.3. DOSIMETRY AND MATHEMATICAL MODELS IN

RADIOPHARMACEUTICAL THERAPY

6.3.1. Introduction

Most radiopharmaceutical therapies are based on the amounts of radio-

activity given, with adjustments made for body weight or surface area.

However, radiopharmaceutical toxicity is dependent upon the radiation

absorbed dose to critical normal organs; measurement of the radiation

absorbed dose provides an optimal estimation of potential toxicity. This section

will provide an overview of the methods used to estimate radiation absorbed

dose. In most cases, the critical normal organ is the haematopoietic system.

In order to evaluate potential toxicity to other organs, mathematical

models to describe biodistribution are important.

6.3.2. Rationale

Calculation of the radiation absorbed dose to organs permits a more

accurate prediction of toxicity and side effects than assessments of toxicity

based on the amounts of radioactivity administered. It therefore follows that

maximization of the dose delivery to tumours may be achieved by the accurate

calculation of the radiation dose to critical organs (usually the haematopoietic

system).

Dosimetry is carried out in deciding the maximum safe amount of

131

I that

can be administered to patients with thyroid carcinoma. In order to determine

the radiation absorbed dose to the haematopoietic system, serum and whole

body measurements are typically carried out.

6.3.3. Indications

Dosimetry is carried out to permit determination of the radiation

absorbed dose to critical normal organs, calculation of the safe amount of

radioactivity that may be administered and calculation of the radiation

absorbed dose to the tumour.

6.3.4. Procedure

For all calculations, it is mandatory to measure a known amount of radio-

activity in a manner identical to that used for patient or sample measurement

so that estimates of counts per unit radioactivity may be made.