Managing radiotherapy patients with implanted cardiac devices (implantable cardiac pacemakers and implantable cardioverter‐defibrillators) has been a great practical and procedural challenge in radiation oncology practice. Since the publication of the AAPM TG‐34 in 1994, large bodies of literature and case reports have been published about different kinds of radiation effects on modern technology implantable cardiac devices and patient management before, during, and after radiotherapy. This task group report provides the framework that analyzes the potential failure modes of these devices and lays out the methodology for patient management in a comprehensive and concise way, in every step of the entire radiotherapy process.
Recent improvements to the functionality and stability of implantable pacemakers and cardioverter‐defibrillators involve changes that include efficient battery power consumption and radiation hardened electrical circuits. Manufacturers have also pursued MRI‐compatibility for these devices. While such newer models of pacemakers and cardioverter‐defibrillators are similar in construction to previously marketed devices – even for the recent MRI‐compatible designs currently in clinical trials – there is increased interest now with regard to radiation therapy dose effects when a device is near or directly in the field of radiation. Specifically, the limitation on dose to the device from therapeutic radiation beams is being investigated for a possible elevation in limiting dose above 200 cGy. We present here the first‐ever study that evaluates dosimetric effects from implantable pacemakers and implantable cardioverter‐defibrillators in high energy X‐ray beams from a medical accelerator. Treatment plan simulations were analyzed for four different pacemakers and five different implantable cardioverter‐defibrillators and intercompared with direct measurements from a miniature ionization chamber in water. All defibrillators exhibited the same results and all pacemakers were seen to display the same consequences, within only a a±1.8% deviation for all X‐ray energies studied. Attenuation, backscatter, and lateral scatter were determined to be −13.4%, 2.1% and 1.5% at 6 MV, and −6.1%, 3.1% and 5.1% at 18 MV for the defibrillator group. For the pacemaker group, this research showed results of −15.9%, 2.8% and 2.5% at 6 MV, and −9.4%, 3.4% and 5.7% at 18 MV, respectively. Limited results were discovered from scattering processes through computer modeling. Strong verification from measurements was concluded with respect to simulating attenuation characteristics. For IP and ICD leads, measured dose changes were less than 4%, existing as attenuation processes only, and invariant with regard to X‐ray energy.PACS number: 87.53.Bn, 87.53.Dq, 87.53.Tf, 87.66.Jj
PURPOSEThe undesirable production of secondary neutrons by cancer radiotherapy linear accelerators has been demonstrated to cause softerrors in nearby electronics through the %(n, a)'Li reaction. The "B is a component in the BPSG used as a dielectric material in some IC fabrication processes. XNTRODUCTIONBaumann el ai first reported the potential for thermal neutrons to cause soft-errors in some integrated circuits (IC) [I]. In this scenario, neutrons that are in thermal equilibrium with their surroundings (i.e., those with kinetic energq. of approximately 0.025 eV at 25OC) interact with 1°5 found in the lower inter-metal dielectric layers of an IC, resulting in the production of 7Li and a particles in the immediate vicinity of the active circuitry. Subsequent interaction of these charged species with the IC leads to soft-errors. For some ICs with normal terrestrial exposure to thermal neutrons, this mechanism has been identified as the dominant cause of soft-errors 121. Other authors have also reported measurements of soft-errors caused by this mechanism [3].In most developed countries, linear accelerators (linacs) are used for cancer radiotherapy treatment (figure 1). This equipment accelerates a beam of electrons to high energies (3 -20 MV) and directs them at a high atomic number target, typically tungsten. The bremmstrahlung X-rays produced in this interaction are filtered, collimated and directed to the patient's tumor. When operated at an electron beam energy greater than -9MV, a flux of energetic photoneutrons is produced as an undesirable byproduct. These energetic neutrons are moderated or absorbed by the shielding materials in the linac and the construction materials of the treatment FIGURE 1. A TYPICAL 18 MV LINAC USED FOR THE TREATMENT OF CANCEROUS TUMORS.room. Unabsorbed neutrons quickly reach thermal equilibrium with the environment and are available for a host of nuclear reactions that are much more probable with a low energy incident particle, A typical radiation safety survey has characterized the thermal neutron flux near the entrance to the treatment room maze at I mSv h i ' 141. EXPERIMENTAL METHODOLOGYAn experiment to determine the potential for soft-errors in electronics operating in the vicinity of a linac was undertaken. A total of 10 small S U M S (SI), known to be sensitive to thermal neutron induced soft-errors, were continuously monitored while being exposed to the ambient flux approximately 50 cm from the linac beam's iso-center. Each SRAM was alternately exposed a) without shielding, b) shielded from electromagnetic interference (EMI), c) shielded from thermal neutrons, or d) held outside the treatment room as a control. Shielding from thermal neutrons was accomplished by surrounding the memory on all sides with a minimum of 2 cm of dry boric acid. A total of 4 soft-errors were detected in the S1 devices during these exposures, 3 from the unshielded memories and 1 from an EM1 shielded memory. No errors were detected from any device shielded from thermal neutrons or outside the treat...
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