[en] During the first phase of the pion interaction the requirements of a tissue-equivalent material are identical to those for other heavy charged particles and could be met by conventional materials. During the third phase the major requirement is that the same charged particle spectrum should be produced following nuclear spallation. Measurements of the spectra emitted following pion capture on light nuclei, particularly carbon and oxygen, have consistently shown significant differences (Mechtersheimer et al 1978, Klein et al, 1979). In carbon there are greater numbers of charged particles produced and their mean energies are higher. The implication of this is that an equivalent material would require an identical elemental composition to that of tissue. A further complication arises from the mechanism of pion capture in the second phase. It was originally suggested (Fermi and Teller 1947) that pion capture probabilities were solely dependent on atomic number, but more recent work (Jackson et al 1982) has shown that pion capture is influenced by molecular effects. Therefore, in addition to an identical elemental composition, a truly tissue-equivalent material for pions would require an identical molecular structure. (U.K.)

No abstract available

[en] In order to use negative pions for the treatment of large deep-seated tumors in radiotherapy, it is necessary to produce depth-dose distributions tailored to specific shapes. We present here a method of beam shaping which utilizes a fluid-filled piston having a programmable, computer-controlled, time-dependent thickness. The fluid alters the residual range of the pions such that predetermined depth-dose distributions can be obtained. Changing from one distribution to another can be accomplished simply and rapidly without access to the treatment room. Depth-dose distributions which are flat over a range in depth up to 10 cm have been produced. Distributions tailored to produce flat effective dose versus depth have also been obtained

No abstract available

[en] Treatment planning for conventional radiations is based on the assumption that the effect of a combination of doses at any location in the treatment field in a multibeam plan will be equivalent to that of a single dose made up of the total sum of the doses delivered to that location. This is obviously valid for conventional low linear-energy-transfer (LET) radiations when the dose contributions from various beam components are associated with the same relative biological effectiveness (RBE) value of unity. However, this is not the case for the new generation of charged particle beams whose RBEs have been shown to vary significantly with depth. A concept of effective dose, defined as the mathematical product of physical dose and RBE value evaluated for an effect level, is developed for the treatment planning of these high-LET particle radiations. Based on radiobiological results in mixed radiation experiments, it is shown that these effective doses are linearly additive like physical doses and hence, can be used directly for general treatment planning using linear algorithms already developed for the use of physical doses. This is illustrated using examples of simplified one-dimensional plans for the TRIUMF pion beam. Key words: LET, treatment planning, effective doses, pions, heavy ions, RBE

[en] An absolute dose determination has been made for the negative pion beam at TRIUMF using an ionization chamber. The relationship required to convert the ionization per unit mass, J/M, measured by the chamber to dose in tissue is D = J/M WrF where W, r and F are calculated quantities: W is the average energy expended in the gas per ion pair produced; r is the ratio of dose in the wall material to dose in the gas; F is the ratio of dose in tissue to dose in wall material. Experimentally, the ionization per unit mass was measured in a parallel plate chamber as a function of pressure for various gases with carbon, aluminum and TE-A150 electrodes. The pressure dependence of J/M measured for methane and carbon dioxide with carbon electrodes was compared to the behaviour predicted by the calculation. Qualitatively, the prediction was confirmed: the ionization per unit mass for CO₂ decreases more dramatically with increased pressure than for CH₄. Therefore pion capture in the gas is significant and the energy released to charged secondaries per pion capture on oxygen is less than for carbon. Quantitatively, the percentage change is larger than predicted. The value of J/M extrapolated to zero pressure and the appropriate values calculated for W and r enabled a determination of the absolute dose in carbon with an estimated accuracy of ±5%. The ionization created with aluminum electrodes was compared to that for carbon in order to estimate the dose in aluminum

No abstract available

[en] The biological equivalent dose profile of the pion beam was predicted with one parameter (γ) using physical dose and pion star density. The value of the relative biological effectiveness (RBE) at each depth was given as a linear function of pion star density (PSD): RBE = 1.0 + γPSD, assuming (i) the mixed beam lesion additivity model and (ii) the linear relationship between the ratio of high LET dose to total dose and pion star density. The predicted depth-survival curve fitted well with the pooled biological data of the gel technique using Chinese hamster cells (CHO). The predicted RBE were consistent with previously published results through the flat dose peak, except at the decreasing portion of the dose profile. The practical usefulness of this model in clinical treatment is stressed. (author)

No abstract available

[en] It can be shown that the values of the radiation weighting factors, w_R, recommended in ICRP Publication 60 for high energy neutrons and protons are over conservative. The approximation obtained by the rule recommended in Paragraph (A14) of Publication 60 is generally inadequate for high energy radiation. In order to determine appropriate w_R values in the high energy region, several criteria are here analysed. Modifications of the recommended values are proposed for neutrons of energy above 100 MeV and for protons above 10 MeV. The w_R value for muons is confirmed to be practically equal to unity. Sets of values intended for use with negative and positive pions are determined. (author)