Isosurvival testing of bar ridge filters for wobbled neon ion beams

An extensive series of experiments has been performed to test new bar filters. The filters were constructed to produce constant cell survival across the spread Bragg peak region in preparation for phase III therapeutic trials with the magnetically wobbled neon-ion beam. Three different filter designs (designed 3E1, 3E2, and 3E3) were studied. Each design produced a different slope in the spread peak region of the Bragg ionization curve. From analysis of the data, it was decided to construct a series of filters at 1-cm increments from 4 to 14 cm using the 3E3 design. The general conclusion of this analysis was that the design producing the flattest slope (3E3) produced the most constant cell survival across the peak region in the clinically important dose range. Survival data obtained in the proximal-peak position of the Bragg curves for the already completed 3E3 filters have been useful in developing RBE tables for the upcoming phase III trials. Proximal peak RBEs are used along with other data, including cell survival measurements as a function of depth after a single exposure, to determine the physical doses to be delivered to the patients