Dosimetry of ionising radiation is a well-established and mature branch of physical sciences with many applications in medicine and biology. In particular radiotherapy relies on dosimetry for optimisation of cancer treatment and avoidance of severe toxicity for patients. Several novel developments in radiotherapy have introduced new challenges for dosimetry with small and dynamically changing radiation fields being central to many of these applications such as stereotactic ablative body radiotherapy and intensity modulated radiation therapy. There is also an increasing awareness of low doses given to structures not in the target region and the associated risk of secondary cancer induction. Here accurate dosimetry is important not only for treatment optimisation but also for the generation of data that can inform radiation protection approaches in the future. The article introduces some of the challenges and highlights the interdependence of dosimetric calculations and measurements. Dosimetric concepts are explored in the context of six application fields: reference dosimetry, small fields, low dose out of field, in vivo dosimetry, brachytherapy and auditing of radiotherapy practice. Recent developments of dosimeters that can be used for these purposes are discussed using spatial resolution and number of dimensions for measurement as sorting criteria. While dosimetry is ever evolving to address the needs of advancing applications of radiation in medicine two fundamental issues remain: the accuracy of the measurement from a scientific perspective and the importance to link the measurement to a clinically relevant question. This review aims to provide an update on both of these.

http://iopscience.iop.org/article/10.1088/0031-9155/61/14/R167/pdf

Dosimetry of ionising radiation in modern radiation oncology

Design of Pulse Oxirrieters J.G. Webster (Editor), 1n:stitute of Physics Publishing, Bristol and Philadelphia, 1997, ISBN: 0-7503-0467-7,244 pages, $99. Noninvasive monitoring of arterial oxygen saturation by means of pulse oximeters (PO) is currently a routine procedure in a wide variety of medical disciplines. In the USA alone, clinicians use scores of different PO models. The effectiveness of PO medical applications requires from both users and biomedical engineers an extremely high level of understanding of such diverse fields of 1 knowledge as physiology. PO principles and design, and algorithms for the calculation of blood oxygen saturation. As one who has been involved in field of biomedical optics and engineering for more than 15 years, I can say that this book is a complete guide to understanding, using, and designing the PO. It is difficult to overestimate the value of this book for biomedical engineers and for all those who needs to know the technical workings of this instrument. Design of Pulse Oximeters provides complete coverage of the field-from basic principles (chapters 2-4) and techniques (chapters 5-8) to signal-processing algorithms and calibration (chapters 9-10). Supplemented with an abundance of figures, tables, and equations, the book is easy to read and clear in understanding. Well edited, it leaves the impression that it was written by one author, which is a rarity among multi-authored texts. There is no doubt that Design of Pulse Oximeters will be a valued source on pulse oximetry. It will be piwticularly useful for graduate students, biomedical technicians, and instrument designers as the essential reference that encompasses the entire field of pulse oximehy. Unfortunately, the theoretical chapters (4 and 9) are slightly weaker than the others. Spcnding a few pages to describe Beer’s law, the authors then say almost nothing about the role of the scattering processes and the current state of research in this area. They bypass the diffusion lheory of blood particles (A. Ishimary, “Wave propagation and Scattering in Random Media,” Academic Press, New York, 1978) and modern experimental results. There is nothing in these chapters about optical properties of tissues under compression that contain blood, which is very important for the understanding of motion artifact. This interference (noise) is a significant concern in the real-world use of pulse oximeters for patient monitoring. As a previous study has shown, the optomechanical effects of blood circulation can be used, in principle, to mitigate motion artifact (V. Grimblatov, “Optomechanical Effect of Tissue Blood Circulation Under Compression,” Proc. SPIE, Vol. 3253, 1997). I believe that a wider theoretical description of the photoplethysmographic aspects of pulse oximetry would make the bookmore useful for scientists as well as instrument developers. Of course, this note does not affect the obvious advantages of the book. To my knowledge, this is the best book to date dedicated to pulse oximetry. It will remain an important reference for many years to come. -Valentin Grimblatov, Ph.D. Department of Biomedical Engineering Columbia-Presbyterian Medical Center

Shielding Techniques For Radiation Oncology Facilities

Investigating in-field and out-of-field neutron contamination in high-energy medical linear accelerators based on the treatment factors of field size, depth, beam modifiers, and beam type.

In a medical linear accelerator, the primary and secondary collimators are generally made of high atomic weight metals. The energy of the x-rays generated by accelerated electrons exceeds ...

Investigation of the effects of different composite materials on neutron contamination caused by medical LINAC

Medical linear accelerators (linacs) are the most frequently applied radiation therapy machines in the locoregional treatment of cancers by producing either high-energy electron or photon beams. However, with high-energy photons (>8 MeV), interaction of these photons with different high-Z nuclei of materials in components of the linac head unavoidably generates neutrons. On the other hand, the average energy of these generated neutrons has almost the highest radiation-weighting factor. Therefore, the produced neutrons should not be neglected. There are various tools for the measurement of neutron dose/fluence generated in a megavoltage linac, including thermoluminescent dosimeters, solid-state nuclear track detectors, bubble detectors, activation foils, Bonner sphere systems, and ionization chamber pairs. In this review article, each of the above-mentioned dosimetric methods will be described in detail.

Different Methods of Measuring Neutron Dose/Fluence Generated During Radiation Therapy with Megavoltage Beams.

High-energy linacs produce secondary particles such as neutrons (photoneutron production). The neutrons have the important role during treatment with high energy photons in terms of protection and dose escalation. In this work, neutron dose equivalents of 18 MV Varian and Elekta accelerators are measured by thermoluminescent dosimeter (TLD) 600 and TLD700 detectors and compared with the Monte Carlo calculations. For neutron and photon dose discrimination, first TLDs were calibrated separately by gamma and neutron doses. Gamma calibration was carried out in two procedures; by standard 60Co source and by 18 MV linac photon beam. For neutron calibration by (241)Am-Be source, irradiations were performed in several different time intervals. The Varian and Elekta linac heads and the phantom were simulated by the MCNPX code (v. 2.5). Neutron dose equivalent was calculated in the central axis, on the phantom surface and depths of 1, 2, 3.3, 4, 5, and 6 cm. The maximum photoneutron dose equivalents which calculated by the MCNPX code were 7.06 and 2.37 mSv.Gy(-1) for Varian and Elekta accelerators, respectively, in comparison with 50 and 44 mSv.Gy(-1) achieved by TLDs. All the results showed more photoneutron production in Varian accelerator compared to Elekta. According to the results, it seems that TLD600 and TLD700 pairs are not suitable dosimeters for neutron dosimetry inside the linac field due to high photon flux, while MCNPX code is an appropriate alternative for studying photoneutron production.

Neutron dose measurements of Varian and Elekta linacs by TLD600 and TLD700 dosimeters and comparison with MCNP calculations.

Medical diagnostic equipment, like diagnostic radiology and mammography require a dosimeter with high accuracy for dosimetry of the diagnostic X-ray beam. Ionization chambers are suitable instruments for dosimetry of diagnostic-range X-ray beams because of their appropriate response and high reliability. This work introduces the design and fabrication of a new parallel plate ionization chamber with a PMMA body, graphite-coated PMMA windows (0.5 mm thick) and a graphite-foil central electrode (0.1 mm thick, 0.7 g/cm 3 dense). This design improves upon the response characteristics of existing designs through the specific choice of materials as well as the appropriate size and arrangement of the ionization chamber components. The results of performance tests conducted at the Secondary Standard Dosimetry laboratory in Karaj-Iran demonstrated the short and long-term stability, the low leakage current, the low directional dependence, and the high ion collection efficiency of the design. Furthermore, the FLUKA Monte Carlo simulations confirmed the low effect of central electrode on this new ionization chamber response. The response characteristics of the parallel plate ionization chamber presented in this work makes the instrument suitable for use as a standard dosimeter in laboratories.

Investigation and performance tests of a new parallel plate ionization chamber with double sensitive volume for measuring diagnostic X-rays

Introduction: The use of low energy isotopes such as  103 Pd in brachytherapy for the treatment of cancers  such as prostate, eye, head, neck, breast and cervix is increasing. In this regard, different models of Pd- 103  seeds  have  been  designed  and  manufactured  at  the  Agricultural,  Medical  and  Industrial  Research  School (AMIRS) of Atomic Energy Organization of Iran. In this research, the dosimetric parameters of  the second model of Pd-103 seed manufactured at AMIRS have been calculated and measured. Materials and Methods: The dosimetric parameters of the second Pd-103 seed manufactured at AMIRS  were determined according to TG-43U1 protocol using Monte Carlo calculations (MCNP4C computer  code)  and  measurements  performed  using  TLD-GR200A  dosimeters  in  a  Perspex  phantom.  The  parameters  include  dose  rate  constant,  geometry  function,  radial  dose  function,  anisotropy  function,  anisotropy factor and anisotropy constant.  Results:  It  was  found  that  by  using  MCNP4C  code  the  calculated  dose  rate  constant  in  water  and  Perspex  was  0.706±0.001 and  0.501±0.001  cGyh -1 U -1 , respectively.  Using  the  calculated  geometry  function,  the  radial  dose  function  and  the  anisotropy  function  were  determined  by  experimental  and  theoretical methods in water and Perspex phantom. Also, the calculated value of anisotropy constant in  water was equal to 0.88.  Discussion and Conclusion: A discrepancy of less than 10% between the calculated and the measured  values indicates a reasonable agreement between the simulation and the measurement method. Also, the  dosimetric parameters of this seed have been compared to the dosimetric parameters of the first Pd-103  seed  manufactured  at  AMIRS  and  some  other  seeds.  The  obtained  results  indicate  that  the  seeds  manufactured at AMIRS have acceptable dosimetric parameters suitable for brachytherapy applications.

http://ijmp.mums.ac.ir/article_7526_1a8c71d395704c29e7ea3f46bb927b5a.pdf

Determination of dosimetric parameters of the second model of pd-103 seed manufactured at agricultural, medical and industrial research school

Medical linear accelerators, besides the clinically high energy electron and photon beams, produce other secondary particles such as neutrons which escalate the delivered dose. In this study the neutron dose at 10 and 18MV Elekta linac was obtained by using TLD600 and TLD700 as well as Monte Carlo simulation. For neutron dose assessment in 2020 cm 2 field, TLDs were calibrated at first. Gamma calibration was performed with 10 and 18 MV linac and neutron calibration was done with 241 Am-Be neutron source. For simulation, MCNPX code was used then calculated neutron dose equivalent was compared with measurement data. Neutron dose equivalent at 18 MV was measured by using TLDs on the phantom surface and depths of 1, 2, 3.3, 4, 5 and 6 cm. Neutron dose at depths of less than 3.3cm was zero and maximized at the depth of 4 cm (44.39 mSvGy -1 ), whereas calculation resulted  in the maximum of 2.32 mSvGy -1 at the same depth. Neutron dose at 10 MV was measured by using TLDs on the phantom surface and depths of 1, 2, 2.5, 3.3, 4 and 5 cm. No photoneutron dose was observed at depths of less than 3.3cm and the maximum was at 4cm equal to 5.44mSvGy -1 , however, the calculated data showed the maximum of 0.077mSvGy -1 at the same depth. The comparison between measured photo neutron dose and calculated data along the beam axis in different depths, shows that the measurement data were much more than the calculated data, so it seems that TLD600 and TLD700 pairs are not suitable dosimeters for neutron dosimetry in linac central axis due to high photon flux, whereas MCNPX Monte Carlo techniques still remain a valuable tool for photonuclear dose studies.

Neutron dose evaluation of Elekta Linac at two energies (10 & 18 MV) by MCNP code and comparison with experimental measurements

One of the most important measures of therapeutic quality in Microbeam Radiation Therapy (MRT) is the Peak to Valley Dose Ratio (PVDR). This parameter is a criterion to evaluate ablation of cancerous cells and sparing of normal cells in tumor and in its surrounding region. The aim of this work is to study the influence of using gold and gadolinium nano-particles as contrast agents on dose distribution and PVDR when a phantom is irradiated by a typical micro-planar X-ray beam of European Synchrotron Radiation Facility (ESRF

A. Shahvar

Papers

Neutron dose measurements of Varian and Elekta linacs by TLD600 and TLD700 dosimeters and comparison with MCNP calculations.

Investigation and performance tests of a new parallel plate ionization chamber with double sensitive volume for measuring diagnostic X-rays

Determination of dosimetric parameters of the second model of pd-103 seed manufactured at agricultural, medical and industrial research school

Neutron dose evaluation of Elekta Linac at two energies (10 & 18 MV) by MCNP code and comparison with experimental measurements

Monte carlo simulation of dose absorption of nano-particles-labeled tissues used in x-ray microbeam radiation therapy