implanted devices part II

how is dose distribution modified by hip prostheses at the exit of the prosthetic material for energies less than or equal to 10 MV and why does this occur

PDD is increased slightly from backscatter from the metal into soft tissue

how is dose distribution effected by prostheses at the exit of prosthetic material for energies greater than 10 MV and why

PDD increases greatly from increase pair production and neutron production in the metal

how is dose distribution modified by hip prostheses distally to prosthesis beyond d-max

at d-max beyond the prosthesis, both 6 MV and 18 MV depth dose curves are reduced but parallel to the curve

what increases distally to prosthesis beyond dmax

broad beam squares PPD is increased

increased lateral scatter (increases dose to lateral surrounding tissue)

historical studies have not show significant complicatins from treating through metal so why worry (2)

historical data comes from 4 field box with 65 Gy prescription

dose escalation in current prostate treatment in 80 gy

bone necrosis TD 5/5

52 Gy

bone necrosis TD 50/5

65 Gy

tg 63 recommendations on how to manage prostheses

avoid direct entry through prosthesis

contour prosthesis and overide its density

contour artifact and override its density

minimize weighting of beams that go through prosthesis to reduce hotspots

employ monte carlo algorithms

physician awareness

artifact should be contoured and assigned what HU

soft tissue HU

why should monte carlo algorithms be used

most accurately determines hot spot so actual dose distribution is known

ignoring the presence of prosthesis can result in?

reduction of a 4 field target dose by 5-10% due to attenuation

when treating a patient with 18 MV how is the proximity of treatment field to the cardiac device related to rad induced malfunction

unrelated

how is DD affected proximally to prosthesis

hot spot in tissue surrounding the prosthesis

what is a soft error

an error where the signal or datum is wrong

what are the conditions that have motivated the need for updated cardiac device management guidelines (4)

increased life expectancy

increased patients with implanted devices that use RT

increased radiation sensitivity of newer devices

older guidelines did not discuss defribilators

what is there no clarification on for the heart rate society's 2017 recommendations for radiation exposure to cardiac implanted devices

no clarification on cumulative dose effects or resolution between vendor specific dose thresholds and HRS threshold or verifying dose assessment

what disrepancies were summarized in TG 203 literature review

large direspancies in dose levels from previous model (15 cGy to 150 Gy)

what is the purpose of using a donut magnet with a defribilator and RT

during RT, the device may see radiation as cardiac activity and deliver a shock

the magnet on the defribillator disables the tachycardia function

ICP vs ICD sensitivity

ICDs are more sensitive to radiation induced malfunction