A new miniature x‐ray source for interstitial radiosurgery: Device description

Abstract

A device that generates low-energy x rays at the tip of a needle-like probe was developed for stereotactic interstitial radiosurgery. Electrons from a small thermionic gun are accelerated to a final energy of up to 40 keV and directed along a 3 mm outside diameter drift tube to a thin Au target, where the beam size is approximately 0.3 mm. All high-voltage electronics are in the probe housing, connected by low-voltage cable to a battery-operated control box. X-ray output, which is nearly isotropic, consists of a bremsstrahlung spectrum and several lines between 7 and 14 keV, with characteristic radiation contributing 15% of the total energy output. To date, 14 patients with metastatic brain tumors have been treated with this device.

Guidelines for quality assurance in intra-operative radiation therapy

“…Specific miniaturised sources of X-rays can be used for IORT, that emit X-rays of low energy (V max = 50 kV for the sources currently in commerce) from the point of a probe inserted in a spherical applicator, resulting in a uniform dose distribution to the surface of the applicator 79,80 . The dose-rate is of around 0.5 -2 Gy/min at the surface of the applicator, with a strong gradient of dose (typically equal to 10-20% per mm from the surface, in function of the diameter of the applicator).…”

Quality Assurance and Commissioning

“…The probe tip consists of beryllium, transparent to X-rays above an energy of 10 keV, coated with nickel and titanium nitride, to give a durable and biocompatible surface. All of these materials will affect the characteristic spectrum of the source, to give an effective energy of approximately 20 kV for the probe only (Beatty et al 1996 ;Dinsmore et al 1996 ). With a spherical breast applicator attached, the beam will be hardened due to the additional material in the path of the radiation, which preferentially absorbs lower energy photons.…”

Dosimetry of a low-kV intra-operative X-ray source using basic analytical beam models

“…[1][2][3] The device [the 'Intrabeam' (Photoelectron Corp., Lexington MA)] is currently being trialed for the treatment of well-localised low-risk breast cancer. 12 Clinical evidence supports the concept of utilising local application of a 'boost' radiation dose to the tumour bed surrounding a surgical cavity post-resection.…”