156 Annual Report 2008

Electronic X-ray Sources for Brachytherapy (ESB) by M.S apa, M.Traczyk [VII.4]

Recent years have witnessed a new wave of Parameter PRS 400 Xoft Axxent interest in X-ray machines built for oncology Anode bias 50 kV 50 kV radiotherapy [1,2]. Progress in materials science and Anode current 40 µA 300 µA 10 cm long rigid 20 x 5 mm capsule technology has made it possible to develop new types Probe pipe, ext. dia 3.2 at the end of a of X-ray tubes specially designed for brachytherapy dimensions i.e. to irradiate tumors from inside. mm flexible cable Dissipated power 2 W 15 W To be useful for brachytherapy, the construction of Cooling Natural Water an X-ray tube must enable its target (anode) to enter Several thousand Lifetime A few hours the to-be-irradiated object. Besides, it must emit hours radiation isotropically over the whole 4-pi solid angle. Applicator dia 1.5…5 cm 3…7 cm Currently two approaches are followed: Applicator shape Sphere Sphere, ellipsoid  X-ray tube with needle-like anode, Since both solutions have some advantages and some disadvantages, one may expect that ESB sources  miniature X-ray tube that might be placed will be further developed. completely inside the to-be-irradiated tumor. In 2008 our team: The idea of an X-ray tube with a needle-like anode ! for brachytherapy was brought to the market by Analyzed new developments in construction of Photoelectron Corporation in the early ’90s of the last EBS sources and the operational parameters attained century as the Photoelectron Radiation System in published solutions. This work was aimed at (PRS400) aimed at brachytherapy of brain tumors [1]. finding ways to improve the operational parameters of the Polish Photon Needle developed by us during previous years and helping us to prepare a proposal for the LAXT project (Low-energy Accelerator with X- Ray Tube, a part of the Detectors and Accelerators project). ! Extended our engineering and manufacturing base as regards high-voltage electronics circuitry for X-ray tube power supply, which helped to increase the anode voltage of the tube. ! Looked for optimum X-ray energy spectra from the point of view of some selected brachytherapy treatments. ! Optimized X-ray tube construction details from the Fig. 1 Two approaches to brachytherapy performed with the help point of view of some selected brachytherapy of electronic X-ray sources. treatments.

The Xoft company developed new X-ray tubes for brachytherapy at the beginning of this century (Xoft [1] M.Dinsmore et al ., “A new miniature x - ray Axxent). This miniature (2 mm dia, 10 mm long) tube source for interstitial radiosurgery: Device operates at the end of a thin (1.5 mm dia) flexible high description”, Med. Phys. Vol. 23 No 1 (1996) 45 voltage cable [2]. [2] D.Johnson, I.Rutel, and S.Ahmad, “Xoft Axxent Both sources have been FDA-certified for Electronic Brachytherapy System. A Clinical applications in clinical practice to brachytherapy of Implementation Experience”, Med. Phys. Vol. 35 tumors in all medically justified cases. Their basic No 6 (2008) 2734 properties are compared below: