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Purpose: To develop an external quality control procedure for CyberKnife(®) beams. This work conducted in Nancy, has included a test protocol initially drawn by the medical physicist of Nancy and Lille in collaboration with Equal-Estro Laboratory., Materials and Methods: A head and neck anthropomorphic phantom and a water-equivalent homogeneous cubic plastic test-object, so-called "MiniCube", have been used. Powder and solid thermoluminescent dosimeters as well as radiochromic films have been used to perform absolute and relative dose studies, respectively. The comparison between doses calculated by Multiplan treatment planning system and measured doses have been studied in absolute dose. The dose distributions measured with films and treatment planning system calculations have been compared via the gamma function, configured with different tolerance criteria., Results: This work allowed, via solid thermoluminescent dosimeter measurements, verifying the beam reliability with a reproducibility of 1.7 %. The absolute dose measured in the phantom irradiated by the seven participating centres has shown an error inferior to the standard tolerance limits (± 5 %), for most of participating centres. The relative dose measurements performed at Nancy and by the Equal-Estro laboratory allowed defining the most adequate parameters for gamma index (5 %/2mm--with at least 95 % of pixels satisfying acceptability criteria: γ<1). These parameters should be independent of the film analysis software., Conclusion: This work allowed defining a dosimetric external quality control for CyberKnife(®) systems, based on a reproducible irradiation plan through measurements performed with thermoluminescent dosimeters and radiochromic films. This protocol should be validated by a new series of measurement and taking into account the lessons of this work., (Copyright © 2013 Société française de radiothérapie oncologique (SFRO). Published by Elsevier SAS. All rights reserved.)

Purpose: To investigate if the regular use of kV-CBCT notably increases the dose delivered to tumor and surrounding healthy tissues., Material and Methods: Images were obtained using a Varian equipment (OBI version 1.3, 645 to 650 projections in 370 degrees to acquire image), and patients were irradiated at source-tumor distance: 100cm. In vivo measurements were performed using radio-thermoluminescent dosimeters Harshaw-TLD700H (TLD) at skin (anterior-posterior and lateral axis crossing the rotation axis), with a fourth TLD group under the table thanks to a retrolaser. TLD's were calibrated at the kV-CBCT effective energy (64 keV), and the method validated using an anthropomorphic phantom, in which Gafchromic EBT films were also inserted., Results: The phantom study showed that the dose distribution depends on the phantom position relative to the axis and that the doses measured at the phantom surface using TLD and films (good agreement) were maximum at the entrance of the anterior-posterior axis. Their arithmetic mean was equal, or a slightly greater than doses measured at mid-thickness of the phantom and at the level of the rectum (OAR). In vivo measurements performed on the five first patients (125 kV-CBCT) yield a mean skin dose per kV-CBCT varying from 5.8+/-0.1 to 7.3+/-0.2 cGy on the anterior-posterior axis. Lateral skin doses vary from 3.4+/-0.2 to 4.5+/-0.2 cGy., Conclusion: Doses delivered by repeated kV-CBCT are not negligible. They should be taken into account, but questions about the RBE to be applied to kilovoltage X-rays are raised.

Patient dosimetry related to two bone densitometer units from different manufacturers (LUNAR IQ and HOLOGIC 4500A) were evaluated using the parallel beam technique and thermoluminescence from Ca (SO4)/Dy. The radiation dose measured for a phantom of 18 cm in thickness was 0,11 mGy (+/- 0,004) at a maximum current of 3 mA for the LUNAR IQ unit in the high-resolution mode. The radiation dose is 0,28 mGy (+/- 0,011) for the HOLOGIC 4500A unit used at 2,5 mA in the high resolution-mode. These results obtained by thermoluminescence of the Ca (SO4)/Dy are in favor of the LUNAR IQ unit. However, dosimetry must be weighted against image quality.

The methods of surveillance of coronary angiography or angioplasty operators vary from team to team. The choice of method implies evaluation of the level of exposition of unprotected areas. The usual methods of surveillance by dosimetry may be complemented by an electronic device used for industrial radiological protection against X and Gamma rays. This instrument emits a sound each time a micro sievert is detected: the operator perceives the photons of diffused rays. The value of protective screens is then directly audible. This instrument does not detect X rays with an energy of less than 50 KeV but there is a good correlation with results measured by thermoluminescent dosimetry. The measurement of irradiation were noted at three points on the body before and after the use of complementary protection which certain operators hesitated to use before this study. The results confirmed the value of these protections: the suspended lead screen reduced cervical irradiations by a factor of 15 and that of the left wrist by 8. Lower down, a flexible lead skirt reduced irradiation of the ankle by a factor of 19. These results underestimate the efficacy of the screen as low energy X rays were not measured and are even more easily absorbed by the screens.

Although the Imatron is based on a technology different from that of conventional CT scanners, its physical principle is comparable. For this reason dosimetric studies were carried out in the same manner that is by employing small thermoluminescent dosimeters. The results obtained with this technique for the four specific protocols of the Imatron indicated surface doses between 0.7 and 15.7 cGy and between 0.1 and 7.2 cGy at surface of the slice. The weakest doses were recorded during cardiac exams for which this type of CT scanner was designed and developed. This highest doses were delivered for scans of the head region.

The authors carried out routine measurements in vivo, and emphasise their value in radiotherapy. After reviewing the objectives of in vivo measurements in general, and showing the problems posed by routine measurements, they describe the technique of measurement using thermoluminescent dosimeters and the problems associated with their use in patients treated with the aid of a 5.5 MV linear accelerator. Results based upon 232 routine measurements made it possible to establish a correlation between the dose delivered and the expected dose. Under optimal functional conditions, almost all the deviations seen were less than 5% whilst higher deviations occurred when the apparatus showed signs of instability. They conclude that routine in vivo measurements are extremely useful in ensuring that planned treatment is carried out in a satisfactory manner and also in the early detection of potential faults in equipment.

This paper recalls the main concepts of dosimetry which are useful when assessing the collective dose to the patient from medical X-ray examinations. It describes the general protocol which has been followed in measuring dose associated to each x-ray exam (anthropomorphic phantom, in vivo measurement) and gives some results about the variations of parameters such as the mAs, the kVp and the fluoroscopy screening time. As far as the gonadal dose and the effective dose equivalent are concerned a first evaluation is given per type of examination carried out in France in 1982.

The authors recall the functional principles of thermoluminescent dosimeters: heating, apparatus for measuring the emitted light, circulation of nitrogen, reference source. They take this opportunity to stress the essential role played by the circulation of nitrogen over the dosimeters which equilibrates the temperature of the photo multiplier, reduces the emission of unwanted light, prevents the combustion of dust or other possible impurities and finally improves the reproductibility of the measurements even for high dosod for finding the optimum working conditions for the heating apparatus of the planchette in the most simple T.L.D. readers and in those where the heating apparatus of the planchette has a pre-heating phase. They then study the dosimetric properties of lithium borate incorporated in thin teflon discs (type DLB. 0.13 and 0.4). This shows itself to be very interesting for certain uses because it is a solid dosimeter which does not require annealing between two measurements. The reproductibility of the measurements obtained with this material, the stability of its response relative to the delay between radiation and reading (fading), its response relative to the absorbed dose plus the nature and the energy of the rays, are presented with the usual reservations made for this type of dosimetry. The authors conclude by citing a few applications where they have been able to achieve a satisfactory result with the aid of lithium borate.