[en] Optically stimulated luminescence (OSL) using aluminium oxide crystals (Al_2O_3:C) is a dosimetry technique, already validated in radiation therapy. The aim of this study was to characterize the OSL detectors in terms of energy dependence using monochromatic beams in the low-medium energy range (25-85 keV); and to evaluate their potential for experimental dosimetry in therapeutic applications at these energies. The OSL system is composed of a multichannel reader and alumina crystals (Al_2O_3:C, 0.09 mm"3) that are remotely read by laser light. The OSL signal is directly linked to the absorbed dose. Irradiations in were performed at 8 energy points from 25 to 90 keV using a synchrotron source. Absolute OSL dose measurements were also performed at 80 keV at 2 cm depth in water equivalent phantoms (1-8 Gy range). The detectors have been read over 300 s to collect all the light available from the trapped electrons. The OSL detector show a lower energy dependence (≤ 10%) in the 25 to 50 keV range than at higher energies (∼ 45% from 50 to 90 keV). OSL is a reproducible absolute dosimetry technique at 80 keV (σ≤5 %). The field size has no other influence on the OSL signal than the one due to phantom scatter output factors. We demonstrated that the OSL energy dependence decreases with the beam energy. The conventional models of OSL response in function of beam energy and delivered dose were confronted to our results. The next step of this study is to use OSL for beam penumbra characterisation, where conventional detectors exhibit a severe energy dependence due to low energy spectra. In vivo dosimetry applications in low-medium energy radiotherapy are foreseen due to the good reproducibility in OSL signal for absolute dose measurements. (authors)

[en] The effects on shielding needs of a 15 Mv Mevatron-20 and a 10 Mv clinac 18 accelerator are discussed in the light of recent TVL measurements

[en] It is pointed out that method used for accelerator calibration should be consistent with that used to calculate treatment planning dosage

[en] The question of the number of radii which are necessary to accurately determine the average tissue--air ratio (TAR) to be used in ⁶⁰Co rotational radiation therapy treatment planning was studied using actual patient contours. It was found that 12 radii adequately determine the average TAR for clinical purposes. Key words: TAR, ⁶⁰Co, rotational therapy

[en] The question of the number of radii which are necessary to accurately determine the average tissue-air ratio (TAR) to be used in ⁶⁰Co rotational radiation therapy treatment planning was studied using actual patient contours. It was found that 12 radii adequately determine the average TAR for clinical purposes

[en] Theoretically, partial deuteration of body water should allow significantly increased neutron penetration in tissue. To evaluate the possible usefulness of partially deuterated water in neutron capture therapy (NCT), neutron flux density distributions were measured in a 23 x 16.5 cm (length x diameter) cylinder for incident thermal and epithermal neutron beams, at 20 and 40 at. % deuteration of water. Relative to neutron flux densities in nondeuterated water, flux densities increased significantly with increasing depth and increasing levels of deuteration. For example, at a depth of 6 cm, flux density was increased approx.20% to 50% for 20 to 40 at. % deuteration. In a clinical situation, this would increase tumor dose by approx.30%. Further benefits include the reduced hydrogen neutron capture and the chemical radioprotective effects of partial deuteration for photon radiation

[en] A new type of radiation dosimeter using the photoacoustical effect is described. The photoacoustical radiation dosimeter (PARD) is capable of directly measuring the energy absorbed in the detecting element. For a completely absorbing element, the energy fluence rate in the radiation beam is measured. It is thus a calorimetric dosimeter. Since the energy sensor can be calibrated with another form of energy, it has the potential for being an absolute radiation dosemeter. Measurements were made using 50 to 100 kVp x rays with exposure rates at the detector of 2.6 x 10^-6 C/kg/s (10 mR/s) to 5 x 10^-5 C/kg/s (200 mR/s). The minimum measurable exposure rate at 90 kVp is 5 x 10^-7 C/kg/s (2 mR/s). For a given x-ray spectrum, the PARD has a linear response with radiation intensity and an inverse response with chopping frequency. With appropriate design parameters, we believe the PARD may be used to measure any photon energy or any type of radiation particle

[en] All radiotherapy photon beams are accompanied to some extent by secondary electrons which originate in interactions with source hardware, collimator, shadow tray, and/or the air through which the beam passes. Skin sparing, the shape of the dose buildup curve, and the depth of the dose maximum are all influenced by this electron ''contamination.'' The present study of a ⁶⁰Co source employs a flat ion chamber to measure dose buildup curves in polystyrene at source distances of 72 to 200 cm, with an open beam or a filter of Lucite, Cu, Pb-loaded acrylic, or Ba- or Pb-loaded nonbrowning glass placed 57 cm from the source, using 5 X 5, 20 X 20, and 35 X 35-cm² beams as defined at 80 cm SSD. The effect of electron generation in the air was studied by placing a He-gas-filled plastic bag in the beam. A value of about 12% is estimated for the lowest relative dose obtainable with a polystyrene phantom in a ''clear'' ⁶⁰Co gamma-ray beam of 1-cm diameter

[en] Scanning film densitometry routinely used for obtaining dosimetric information about therapy treatment beams is subject to several sources of inaccuracies. The most significant of these are described and appropriate methods of testing are presented. This establishes the need for adequate acceptance testing followed by a quality assurance program if these devices are to be used to provide accurate relative dose information over extended periods of time

[en] Section 4 of ICRU Report No. 30 contains information on determining the absorbed dose from exposure. Table 4.1 lists the f factor for relating absorbed dose to exposure for photons from 10 keV to 2 MeV under conditions of charged particle equilibrium for water, bone, and muscle. Upon inspection, one notices that although the water values have not changed significantly, the muscle values differ by as much as 6% from previous tables in ICRU Report Nos. 17 and 24. A recomputation of the data indicates that errors exist in the published values. Corrected f factors for photons from 10 keV to 2 MeV are calculated in this communication