lecture 6- dose reduction to patients

work in progress

nuc med thyroid scan dose

0.14 mSv

Tc-99m cardiac diagnostic dose

11 mSv

F-18 FDG PET/CT study dose

14 mSv

in nuclear imaging, a patient’s radiation exposure depends on…

RP physical half life and photon energy, biological distribution, and kinetics of localization/excretion

per the NRC, the administration of radiopharmaceuticals must be ___ the dosage ordered by the physician

+/- 20%

diagnostic imaging/uptake dosage

standard dosages established in institutional procedures

therapy ordered dosages

written directive from physician

residual radioactivity (amount leftover in syringe) should be…

measured post injection and deducted from original measurement

standard adults dosages

either standard dosages or weight-based dosages

children dosages

weight-based

adults w variant pathology dosages

e.g. reduced dosages for pt w transplant kidney

critical organs

the part of the body that is most susceptible to radiation damage resulting from the specific exposure conditions under consideration

once RPs are taken into the body, radiation effects depend on…

anatomic distribution, duration of retention in body

duration of RP retention in the body depends on

pathological conditions of pt, chemical nature of drug, biological half life

internally deposited radionuclides may ___ in and disproportionally ___ certain organs.

concentration in, irradiate

physical half life: the longer the half life…

the more dose to the patient

biological half life: different pathologies will result in…

different biological responses

average bio responses can be obtained from…

population stats; patients w advanced disease states will have slower clearance

energy of emissions: the higher the energy…

the more dose to the patient

alpha and beta have ___ dose concern

internal

gamma has ___ dose concern

external

methods for reducing pt dose

adjust mA & kVp settings based on weight of pt for lowest possible CT dose

remove pt from room when doing tube warm-up to reduce dose from scatter

lead aprons while CT runs

CT related methods to reduce dose

decrease tube voltage (kVp), decrease tube current and exposure time (mAs), increase pitch, use automatic tube current modulation

PET related methods to reduce dose

optimize/minimize injected dose FDG

encourage frequent hydration/voiding

use 3D PET acquisition mode

use time of flight (TOF) info in image reconstruction

increase duration of acquisition time per bed position

administering the right activity of the right isotope is the…

most essential way to reduce patient dose

for therapy doses, how should you check correct dosage?

review written directive, double check isotope setting on dose calibrator, have another tech verify dose before administration

administering therapy doses: techs must wear gloves if

handling radioactivity

administering therapy doses: encourage patients to…

drink plenty of fluids, increase fluid consumption; for thyroid, patients encouraged to consume sour candies

placing a foley catheter helps to..

reduce patient dose for inpatients receiving high dose therapy

a misadministration of radioactive material can have several causes, including what?

dose varies more than 20%, dose given to wrong pt, wrong route of admin, results in dose of 5 rem to pt or 50 to skin/organ

all misadministrations at Vanderbilt are reported to…

the state (TDEC-DRH)

a written report of a misadministration must include…

licensee/registrant’s name, name of physician, brief description of event, why event occurred, effect on individual, actions taken/planned to take, certification that individual was notified

if fetal dose is over 1,000 mrem…

minimal increased risk of carcinogenesis, miscarriage, organogenesis

childhood cancer is rare- for every 1000 mrem a child receives, there is an increased….

incidence risk of 0.06%, or 1/1667 children

if fetal dose is under 1000 mrem…

its doubtful that any significant risk exists to the fetus

estimated fetal dose in mrem: Ga-67

early: 1800

3 mon: 3800

6 mon: 3400

9 mon: 2500

estimated fetal dose in mrem: Tc-99m mibi

early: 1700

3 mon: 1300

estimated fetal dose in mrem: Tc99m Mag 3

early: 1500

estimated fetal dose in mrem: Tc99m pertechnetate

early: 1200

3 mon: 2400

6 mon: 1500

9 mon: 1000

for pregnant/breastfeeding patients getting therapy…

must have a written statement, urine pregnancy tests

urine pregnancy test is required when

RP could potentially result in a fetal dose of 5000 mrem or more (e.g. I-131 therapy)

breast feeding patients should be advised of risks of

continued breastfeeding before diagnostic and therapeutic NM procedures

(breastfeeding) increased radiation doses will result in two ways:

will uptake in breast tissue (overactive), go to baby through consumption of breast milk and from being close to mother’s body

babies should not be allowed to receive an effective dose of

100 mrem

risk to benefit ratio

benefits outweigh the risk in purposeful exposure scenarios

ICRP guidelines (simplified) regarding risk-to-benefit ratio

1 proper radiation use in medicine is doing more good than harm

2 specified proc. w specified objective is justified

3 application of procedure to pt should be justified

always defer to physician for what questions?

radiation effects questions; techs should only explain how procedure is done

therapeutic procedures; a ___ must be completed by physician

includes signature of pt and physician

if patients will give members of the public dose of 100 mrem or more at release…

homegoing instructions are required

examples of homegoing instructions

extra distance b/w self/others, sleep in separate bed, flush toilet several times after use, drive separately/sit in back seat