Pacemaker and radiotherapy in breast cancer: is targeted intraoperative radiotherapy the answer in this setting?
Mohammed RS Keshtgar
0
David J Eaton
2
Claire Reynolds
2
Katharine Pigott
2
Tim Davidson
0
Benjamin Gauter-Fleckenstein
1
Frederik Wenz
1
0
The Breast Unit, Academic Department of Surgery, Royal Free and University College Medical School
,
Pond Street, London NW3 2QG
,
UK
1
Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg
,
Mannheim
,
Germany
2
Department of Radiotherapy, Royal Free Hospital
,
London
,
UK
We present the case of an 83 year old woman with a cardiac pacemaker located close in distance to a subsequently diagnosed invasive ductal carcinoma of the left breast. Short range intraoperative radiotherapy was given following wide local excision and sentinel node biopsy. The challenges of using ionising radiation with pacemakers is also discussed.
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Background
Ionising radiation (IR) has been reported to interfere
with modern cardiac pacemakers (PM), which are
equipped with complementary metal oxide
semiconductor circuitry (CMOS) [1]. In 1994, the American
Association of Physicists in Medicine (AAPM) stated that a
cardiac pacemaker can fail at radiotherapy doses as low
as 10 Gy, and even doses of 2 Gy could lead to
significant functional changes. This resulted in guidelines
suggesting that the dose to the PM should be limited to
2 Gy [2].
The cardiac conditions which lead to the implantation
of a PM are typically sick sinus syndrome, high grade
atrio-ventricular (AV) blockade IIb, type mobitz, or total
AV-blockade III. Patients suffering from high grade
AVblockade depend highly on external functional cardiac
pacing since cardiac output is directly related to left
ventricular pump function and heart rate. Arrhythmia
results in inconstant and insufficient ventricular filling
and decreased ventricular ejection fraction. This, in
combination with a very low heart rate (3050 bpm),
gives rise to very low cerebral, coronary, intestinal,
pulmonary and renal perfusion pressure, leading to
ischemia. The patients at highest risk from pacemaker
dysfunction are those who are absolutely dependent on
their PM, who are without a sufficient escape rhythm.
Cardiac pacemakers are programmed to sense
bradycardia and to pace the heart through implanted metal
coil leads which are not sufficiently shielded against
radiation.
Modern PMs contain CMOS circuitry and random
access memory (RAM), in addition to the battery and leads
capable of sensing and pacing the heart. The CMOS is
capable of signal amplification and improves device reliability
and energy consumption. RAM is the programmable
part of the device, holding information about
patientrelated anti-bradycardia pacing, detection settings and
frequency thresholds. It contains a small amount of
energy which is highly volatile. Some cases have been
reported wherein no obvious damage to the device was
found following irradiation, but the RAM had been
entirely erased [3].
CMOS circuitry is built from metal-oxide-semiconductor
field effect transistors. The metal oxide used in the CMOS
is polycrystalline silicon (Si) and silicon dioxide (SiO2) is
used as insulation. Energy deposition during
radiotherapy using ionising radiation can result in excess
electron holes in the electron valence band and electrons
can leave their valence band (tunnelling). This can result
in aberrant electrical pathways and reprogramming of the
devices. Possible effects on the PM include altered
sensitivity, amplitude changes, telemetry and programming
defects (even preventing reprogramming), adjustment
of function or loss of function for seconds, days or
permanently.
Several cases have been reported where the threshold
programming was deleted or the devices failed at low
doses [1]. Therefore, in cases where the PM is close to
the treatment fields for external beam radiotherapy
(EBRT), adjustments may be necessary. These include
modification of the field size and shape, moving the PM
surgically out of the field or even withholding
radiotherapy in some cases.
An alternative to EBRT for these patients might be
intraoperative radiotherapy (IORT). The TARGIT
trialists group has reported the result of a randomised
controlled trial with this technique, which has confirmed
the safety and efficacy [4].
Case presentation
An 83 year old female patient presented with a two week
history of a self detected lump in the upper outer
quadrant of the left breast. Clinically there was a 15 mm
suspicious lump in the left breast, mammography did not
reveal any abnormality (R1) and ultrasound scan
findings were consistent with the diagnosis of breast cancer
(U5). Clinical and ultrasound examination of the axilla
was unremarkable. Core biopsy of the lesion confirmed
the diagnosis of invasive ductal carcinoma.
During review of her past medical history, it was
noted that in 1996 she had a cardiac PM inserted for
persistent sinus bradycardia. In 2003 this was replaced
with a St. Jude Medical dual chamber PM (St. Jude
Medical Inc., St. Paul, MN, USA). The pacemaker was
progr (...truncated)