Cancer radiotherapy equipment as a cause of soft-errors in electronic equipment

Abstract

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...

Effect of different total ionizing dose sources on charge loss from programmed floating gate cells

“…The main difference between protons/ -rays and X-rays has important implication for testing of FG memories against ionizing radiation effects. If devices are intended for ground use, they are likely to be subjected to larger fluxes of relatively low energy photons, such as X-rays: typical applications in this sense are security controls, even if the hardness of devices intended for medical applications is becoming of interest in last years [30]. For converse, if the devices are intended for space use, Co source should be the best choice, since it closely follows degradation induced by protons, which are the main responsible for TID effects.…”

Clinical Concerns and Strategies in Radiation Oncology

“…However, neutrons can only be produced by x-ray beams operating above 8.04 MV. The flux of thermal neutrons created by an 18 MV x-ray beam of a radiotherapy linear accelerator has been observed to have caused a high rate of soft errors in integrated circuits that contain 10 B compounds (Wilkinson et al, 2005). These memory-loss effects can be removed entirely if 6 MV x-rays are used alternatively.…”

Application of polymer composite material for radiation protection of infusion pumps

“…[6][7][8][9][10][11][12]. Research regarding the effects of radiation on medical devices previously focused on implantable cardiac devices, but recently, infusion pumps have also been studied with similar results.…”

“…Thus, the internal circuit of an infusion pump should not be directly exposed to radiation since the memory chips can be damaged [10], which would disrupt function. Risk of damage seems to be increased by radiotherapy settings that contain boron-10 compounds and radiotherapy linear accelerators [11]. Another finding was that battery life may be reduced when exposed to radiation [12].…”