Management of Radiation Oncology Patients with Implanted Cardiac Pacemakers

AAPM REPORT NO. 45 Management of Radiation Oncology Patients with Implanted Cardiac Pacemakers Published for the American Association of Physicists in Medicine by the American Institute of Physics AAPM REPORT NO. 45 Management of Radiation Oncology Patients with Implanted Cardiac Pacemakers REPORT OF TASK GROUP 34 Members J. R. Marbach, Chair M. R. Sontag J. Van Dyk A. B. Wolbarst Reprinted from MEDICAL PHYSICS, Vol. 21, Issue 1, January 1994 July 1994 Published for the American Association of Physicists in Medicine by the American Institute of Physics DISCLAIMER: This publication is based on sources and information believed to be reliable, but the AAPM and the editors disclaim any warranty or liability based on or relating to the contents of this publication. The AAPM does not endorse any products, manufacturers, or suppliers. Nothing in this publication should be interpreted as implying such endorsement. Further copies of this report ($10 prepaid) may be obtained from: American Institute of Physics c/o AIDC P.O. Box 20 Williston, Vermont 05495-0020 (800) 488-2665 (802) 862-0095 International Standard Book Number: 1-56396-380-9 International Standard Serial Number: 0271-7344 © 1994 by the American Association of Physicists in Medicine All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopy- ing, recording, or otherwise) without the prior written permission of the publisher. Published by the American Institute of Physics 500 Sunnyside Blvd., Woodbury, NY 11797 Printed in the United States of America Management of radiation oncology patients with implanted cardiac pacemakers: Report of AAPM Task Group No. 34 J. R. Marbach Cancer Therapy and Research Center, San Antonio, Texas 78229 M. R. Sontag Duke University Medical Center, Durham, North Carolina 27710 J. Van Dyk Ontario Cancer Institute, Toronto, Ontario M4X 1K9, Canada A. B. Wolbarsta) Environmental Protection Agency, Washington, D.C. 20460 (Received 12 May 1992; accepted for publication 4 October 1993) Contemporary cardiac pacemakers can fail from radiation damage at doses as low as 10 gray and can exhibit functional changes at doses as low as 2 gray. A review and discussion of this potential problem is presented and a protocol is offered that suggests that radiation therapy patients with implanted pacemakers be planned so as to limit accumulated dose to the pacemaker to 2 gray. Although certain levels and types of electromagnetic interference can cause pacemaker malfunction, there is evidence that this is not a serious problem around most contemporary radiation therapy equipment. Key words: radiation oncology, pacemakers, treatment protocol, complications I. INTRODUCTION them for longer periods of time. Since cancer incidence increases with age, this further suggests that significant It is estimated that in 1986 more than 100 000 cardiac numbers of patients could present for therapy with pace- pacemaker implants were performed in the United States makers. and that there were at least 500 000 pacemaker implanted Task group 34 was formed by the Radiation Therapy patients. 1 Committee of the American Association of Physicists in Cardiac pacemakers are either extrinsically or intrinsi- Medicine in 1985 with the charge to determine the effects cally attached to the heart muscle (outside or inside the of radiation on implanted pacemakers in patients undergo- heart). If, during open heart surgery, it is determined that ing radiation therapy and to formulate a set of guidelines a patient requires pacing, the leads are attached to the for the management of these patients. A preliminary guide- heart at that time and the pacemaker is usually fitted into line was formulated early and informally disseminated the patient’s upper abdomen. If surgery is not required, throughout the radiation oncology community. 4 then the pacemaker leads are intrinsically attached to the The interaction of a complex electronic cardiac pace- apex of the right ventricle by passing them through an maker with the radiation environment encountered in the opening in the subclavian vein. The pacemaker is then clinical radiation therapy setting is not a trivial one to placed under the skin on top of either pectoral muscle, predict. Many variables can have a profound effect on these usually laterally near either axilla. On occasion, a pace- interactions and particularly on the resulting behavior in maker is located underneath a breast for cosmetic reasons. the pacemaker. Thus, an optimum set of recommendations In 1992, it is estimated that 168 000 new cases of lung, is difficult to determine based on available experimental cancer were diagnosed in the United States.2 In addition, and theoretical data. Since the potential risk to an individ- an estimated 180 000 new breast cancers were discovered ual patient is high, while the overall population risk is low, as well. we are left to suggest precautions that will seem too con- As with most cancers, treatment of lung and breast tu- servative for some. The alternative is either a demand on mors depends somewhat on the staging as well as the cell pacemaker manufacturers to redesign their devices for a type of the disease and, to some extent, the condition of the small percentage of patients or a recommendation that will individual patient. Therapy involves the use of surgery, prove too high a risk to these special patients we are ad- radiation, or chemotherapy or, often, a combination of two dressing. or all three. However, in 1990, 47% of all cancers were at Cardiac pacemakers have found increasingly wide- least partially managed with radiation therapy.3 spread use in the management of heart block and brady- Thus, it is safe to assume that over 150 000 new cancer cardia since the early 1960s when synchronized pacemak- patients a year in the United States could present for radi- ers were developed. These so-called demand pacemakers ation to that part of the anatomy that could include an stimulate the heart only when the heart itself does not implanted cardiac pacemaker. Further, the majority of function at the proper beating rate. Early devices utilized pacemaker implants are in older patients who now utilize conventional bipolar transistors and, by comparison to to- 85 Med. Phys. 21 (1), January 1994 0094-2405/94/21(1)/85/6/$1.20 © 1994 Am. Assoc. Phys. Med. 85 86 Marbach et al.: Task Group Report No. 34: Radiation patients with pacemakers 86 day’s designs, relatively unsophisticated circuits. The de- B. Permanent interference velopment of integrated circuits, large-scale integrated cir- Permanent interference can result in either total mal- cuits (LSI), and eventually very-large-scale integrated function or permanent erratic behavior. If sources of elec- circuits (VLSI) was rapidly implemented by all pacemaker tromagnetic interference cause the computer to be repro- manufacturers. These devices, along with microcomputer grammed, the pacemaker will function improperly for that technology, make today’s pacemaker extremely sophisti- ‘specific patient. The malfunction is permanent unless the cated. device is reprogrammed correctly. The contemporary cardiac pacemaker uses If the pacemaker is exposed to a sufficient dose of ion- complimentary-metal-oxide silicon (CMOS) and other izing radiation, individual chip components will fail, caus- sensitive transistor devices in VLSI arrangements to result ing various malfunctions. Minimal radiation damage can in very small (3-5 cm diam) units. These can be pro- sometimes anneal out of these components and the device grammed to fit each individual’s changing pacing needs, can return to apparent normal function, but in general, with self-contained batteries that can last for 10 yr or more. once a radiation damage-induced failure occurs, the pace- The basic function of the pacemaker is to sense, through maker must be considered permanently damaged.6,7 leads connected to the heart muscle, the electrical activity of the heart and, if necessary stimulate electrically, through those same leads, the heart into performing Its normal iii. EXPECTED ENVIRONMENT IN RADIATION pumping function. The sensitivity and response of the THERAPY pacemaker can be adjusted to fit the individual’s needs The various sources of electromagnetic noise in a typical through computer programming. This is accomplished re- radiation oncology department include the following: motely by “talking” to the pacemaker through a simple (l) Motor noise from couch drive motors, air compres- radio-frequency transmitter using a special device placed sors, x-ray tube rotors, and cooling pumps. near the patient’s chest over the implanted pacemaker. The (2) Transformer noise from x-ray transformers and same device allows evaluation of the pacemaker function power supplies. and the general condition of the patient’s heart. This in- (3) Microwave leakage from magnetrons, klystrons and formation is sometimes sent over a telephone connection to waveguide assemblies, and low frequency (< 500 a physician’s office by the patient. Hz) noise from beam pulse forming circuits. Since no known regulation or guide exists for determin- ing and/or controlling these environments, there is little II. POTENTIAL PACEMAKER MALFUNCTIONS quantitative information available on the levels of noise to Failure of a pacemaker constitutes either not pacing the be expected around these types of equipment. Treatment heart as required or pacing it erratically or inappropriately. and simulator couches usually use dc motors for speed Lack of pacing will occur if the electronics fail catastroph- control at relatively low voltages and power levels and are ically. Erratic or inappropriate pacing can occur if the usually located within metal frames that afford some computer becomes deprogrammed due to selective damage shielding. Water pumps are usually in the main structure to parts of the chips. If noise is coupled into the circuitry of the accelerator which also act as a shield, and are usu- directly, or through the leads, the pacer might be improp- ally running continuously under constant load which at erly reprogrammed or may lose programming capability.

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