Pacemaker and radiotherapy in breast cancer: is targeted intraoperative radiotherapy the answer in this setting?

Radiation Oncology, Aug 2012

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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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. - 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)


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Mohammed RS Keshtgar, David J Eaton, Claire Reynolds, Katharine Pigott, Tim Davidson, Benjamin Gauter-Fleckenstein, Frederik Wenz. Pacemaker and radiotherapy in breast cancer: is targeted intraoperative radiotherapy the answer in this setting?, Radiation Oncology, 2012, pp. 128, 7, DOI: 10.1186/1748-717X-7-128