XRT TO DEVICE

Received a phone call from Dr. _______ of Radiation Oncology at Texas
Oncology. 

They are planning on XRT to the patient. 

The patient has a _______  and he has a history of ______

I spoke with Medtronic and in reviewing the manufacturer's literature, "Average
dose rates at the device of less than 1cGy/min are unlikely to produce device
interference."  Medtronic also recommends "pacemaker patients who can tolerate
asynchronous operation may have a magnet secured over their pacemaker or have
the pacing mode programmed to an asynchronous pacing mode such as DOO, VOO, or
AOO." 

In regards to the possibility of device operational errors (memory errors), "the
use of photon beams < 10 MV will greatly reduce the neutron flux and
consequently, the probability of any of these errors [electrical reset, errors
in device functionality, errors in diagnostic data etc] occuring.  Photon beams
at 6 MV or electron beams that do not produce neutrons cannot cause these
errors."  Of note, an electrical reset does not indicate damage to the device;
however, a reset requires device interrogation." 

Medtronic also recommends to NOT expose the device to high doses of direct or
scattered radiation.  An accumulated dose of radiation exceeding the recommended
values to the device circuits may damage to the device.  As the patient has an
Medtronic Adapta DC-PPM, the recommended dose limit from the manufacturer is 500
cGy.  If the XRT has an expected dose limit of > 500 cGy, then the manufacturer
recommends to consider moving the device to an alternative location to reduce
the dose.   Pacing lead extenders maybe used to extend the exisiting lead to the
new implantation location. 

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In reviewing the non-manufacturer literature, there is an excellent review
article (Hurkmans, Coen "Management of radiation oncology patients with a
pacemaker or ICD:  A new comprehensive practical guideline in the Netherlands"
Radiat Oncol 2012; 7: 198) - the risk of malfunction generally increases with
dose and malfunction.  In general, doses of radiation < 2Gy is categorized as
low risk.  In the paper, they cite that "For the majority of patients the CIED
dose will be lower than 2 Gy."

As far as weighing the risk of relocating the device vs keeping the device in
the current location,  "There was consensus that it would not be needed nor
feasible to either adapt the treatment, relocate the CIED or ECG monitor all
patients that receive a CIED dose of more than 2 Gy."  If the dose was > 10 Gy,
adaptation of the radiation therapy treatment vs an alternative location of
device would be a consideration. 

The paper also supplies a management algorithm, and if we apply this algorithm
to this patient, if the dose of radiation < 10 Gy, given his pacemaker dependent
status, he would be categorized based on this paper as an intermediate risk, and
recommendations would be to:

        1.  Audiovisual monitoring of the patient is mandatory
        2.  Crashcart present during radiation therapy
                -External pacing capabilities
        3.  Weekly device checks
        4.  According to the above radiation oncology journal paper, "trained
            staff with cardiology expertise can be present wtihin 10 minutes (if
            not, patients should be referred to another institute)"

Post radiation therapy, the recommended follow up pacemaker check intervals are
1 month, 3 months, and then 6 months. 

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Thus, if the expected dose is > 10 Gy (Hurkmans et et) or >500 cGy (Medtronic
direct manufacturer) --> can consider adaptation of radiation vs moving device.