Implanted Devices Part I + tx planning

Implanted Cardiac Pacemakers- what do they do and when

provide small electrical stimuli during brachycardia when electrical activity of the heart is slow

what is the order of the electrical stimuli provided by ICP

1-5 V

what do implanted cardiac defribrillators do?

generate a large amount of electrical energy in a single output to defribilate the heart

what voltage is applied by ICD

700 V

what do Implanted cardiac defribilators prevent and treat

cardiac arrest

tachycardia, brachycardia, ventricular and atrial fibrilation

what kinds of malfunctions can occur during or after RT

permanent damage

soft error

transient interference

electromagnetic interference

permanent damage malfunction results from and how

accumulate dose

circuitry is degraded in proportion to the accumulated dose

what does permanent damage result in

decreased output amplitude

increase current drain

erroneous or failed sensor operation

permanent damage and increase current drain effect

not obvious and can lead to sudden failure months after RT

what is an example of erroneous or failed sensor operation with permanent damge

failed heartbeat sensoring

what are soft errors caused by and what does this upset

neutrons upset memory or logic circuits

what changes with soft errors

changes in stored memory values

changes in micro processor circuitry

what may not be functionally recoverable

soft errors

resets in soft errors

device resets to default parameters

reset can be delayed for hours or weeks after RT

what does transient interference result from

high dose rate x=rays

what kind of damage does transient interference cause

not permanent damage unless accumulated dose is high

effects of transient interference

innapropriate sensing of device

non-existent pacing output

reset

what does the inappropriate sensing of devices in transient interference lead to

ICD shock

electromagnetic interference are _________ and of _____________ in nature

minimal and transiet in nature

electromagnetic interference effect on ICPS (4)

may sense the field as myocardial inhibition of output

inappropriate re-programming

fixed pacing

output triggering

electromagnetic interference effect on ICDs

possible reprogramming

transient effect

risks for CIED dependent patients if their implanted devices are irradiated

palpitations

shortness of breath

vertigo

syncope

decrease in heart rate and BP

V tach or V fib

cardiopulmonary resuscitation may be required followed by temporal external pacing

prohibition of life saving intervention from ICD

even in the transient malfunction setting what can occur

patient condition can deteriorate to life threatening cardiac event

what are the conditions that have motivated the need for updated cardiac device management guidelines

average life expectancy increased to 78.1 years

number of CIED pts receiving RT is steadily increasing

briefly detail the heart rate society's 2017 recommendation for rad exposure to cardiac implanted devices

avoid >10 MV beams

5 Gy dose threshold

summarize the TG-34 literature review

reccomended a dose threshold of 2 Gy

did not discuss ICDs

what did TG 34 literature state about modern CMOs

modern CMOs are less susceptible to EMF interference but exponentially more sensitive to radiation induced malfunction

what did TG 34 literature view say about memory chip sensitivity

memory chips are sensitive to RT damage especially in neutron presence

what is a soft errir

signal or datum is wrong

what did the TG 203 review say about doses causing CIED malfunction

potential errors from doses as low as 15 cGy

what did Tg 203 review say about errors not reported

no report for errors for CIED exposed to

what errors were reported by TG 203 review

multiple error reports due to 18 MV photons beams and

error reports for tg 203 for 18 MV photon beams and

proximity to CIED

tg 203 report ICD Vs ICP sensitivity

defribilators are more sensitive to radiation damage than pacemakers

according to the grant study, which type of radiation treatment produces more errors or malfunctions in cardiac devices

high let energies >10 MV and neutrons/protons/carbons

protocol for low risk, intermediate, and high risk patients (5)

audio visual monitoring of the Pt

restrict imaging CIED

nanodot measurement

ICD: program tachycardia or use magnet (if pt has a defribilator, use the magnet to disable the tachycardia function)

resuscitation protocol

what is the purpose of a donut magnet used in conjunction with a defribilator in RT?

TG 203 reccomendations for SIM (3)

remove CIED from scan if anatomy is not needed for RT

avoid prolonged imaging with high dose rate

use helical scats with pitch>1

prolonged imaging with high dose rate during sim may result in

oversensing

TG 203 reccomendations for TM planning

contour CIED

minimize dose and dose rate during planning

design beam arrangement to avoid direct radiation entrance

use non neutron producing energy

avoid hard wedges

TG 203 planning, where should the CIED pulse generator be kept?

CIED pulse generator should be >5 cm from treatment and imaging fields

non-neutron producing energt

>10 mv or electron

what should the cummulative dose to CIED be (TG 203)

why should hard wedges be avoided

scatter from a physical wedge significantly increases the dose outside field

for an 18 MV beam compare neutron dose from a hard wedge to a open beam

6.5 times higher

what distance from the field edge should the TPS not be used for dose to CIED estimation

greater than 3 cm from field edge

what are artifacts

loss of image data caused by high density implants

loss of image data is caused by

photon starvation

streaking artifact throughout the image complicates

delineation of soft tissue OARs

how is dose downstream as a result of prostheses and why

reduced dose dowstream target due to prosthesis attenuation

what can occur near prosthesis

local hot or cold spots

how is dose distribution proximal to the hip prosthesis (before entering it) tissue-prosthesis interface

there is a local hotspot around the high z prosthesis due to backscatter from secondary electrons

for photon beams commonly used in RT, the dose _____ at the entrance region of the tissue/metal interface may be

increases

high as 130%

how is dose distribution modified by hip prosthesis

in the prosthesis the beam is attenuated by high z material

where should nanodot dosimetry be done

on the device site closest to the radiation beams

how far from the field edge should the TPS calculations not be used

greater than 3 cm from field edge

outside 3 cm from field edge, the TPS calcs should not be used, what should be used instead

Tg-36 or TG-158

what can be said about dose 10 cm from the field edge

dose is about 1% and increases with field size

tomo mlcs

mlcs move independently and produce a minimum field size of 1 × 1 cm at iso

this type of machine can produce energies at any depth without degraders

synchrotron

Megavoltage treatment rooms are generally constructed as a maze to prevent radiation from reaching the door. What is the source of this radiation?

the patient