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Purpose The complexity of the modern Stereotactic Body Radiation Therapy (SBRT) techniques requires comprehensive quality assurance programs, to ensure the right treatment to the patient. Dosimetry of small radiation fields is a challenge especially for radiotherapy centres starting to work on this issue. The matter to be discussed here concerns the need of detailed measurement procedures and cross checks to be paired to the usual recommendations on detectors and correction factors. Materials and Methods The presented work involved 24 Italian radiotheraphy centres, with the specific purpose to minimize systematic errors in output factor measurements over different radiotherapy centres. Using the unshielded silicon diode IBA Razor, reference curves for the relative signal ratio (RSR) as a function of beam size were created for each Linac family. Results With this study we have demonstrated consistency of small field dosimetry on all the centres involved, moreover all radiotherapy centres using Razor are allowed to compare measurements amongst each other and centres with values deviating more than 5% from the reference curve are advised to repeat their measurements. With this procedure, some critical issues were detected from two centres in RSR measurements, that, if implemented into the own treatment planning system, would induce an unwanted overdosage larger than 5%. Conclusions The proposed approach could allow one to envision high-skilled therapy centres providing support to those featuring minor experience and could represent an important strategy for the clinical implementation of emerging technologies at high quality levels. The methodology adopted exploits crowd knowledge methods which could be applied in others areas of radiation dosimetry.

Purpose The increasing interest in SBRT treatments encourages the use of flattening filter free (FFF) beams. Aim of this work was to evaluate the performance of the PTW60019 microDiamond detector under 6 MV and 10MVFFF beams delivered with the EDGE accelerator (Varian Medical System, Palo Alto, USA). A flattened 6 MV beam was also considered for comparison. Methods Short term stability, dose linearity and dose rate dependence were evaluated. Dose per pulse dependence was investigated in the range 0.2–2.2 mGy/pulse. MicroDiamond profiles and output factors (OFs) were compared to those obtained with other detectors for field sizes ranging from 40 × 40 cm2 to 0.6 × 0.6 cm2. In small fields, volume averaging effects were evaluated and the relevant correction factors were applied for each detector. Results MicroDiamond short term stability, dose linearity and dependence on monitor unit rate were less than 0.8% for all energies. Response variations with dose per pulse were found within 1.8%. MicroDiamond output factors (OF) values differed from those measured with the reference ion-chamber for less than 1% up to 40 × 40 cm2 fields where silicon diodes overestimate the dose of ≈3%. For small fields (

Purpose To assess the capability of different types of detectors to measure relative output factors (OF) at high dose per pulse by comparison with alanine dosimeters, which are independent of dose rate. Methods Measurements were made in 9 MeV and 7 MeV electron beams produced by a Novac7 accelerator for intraoperative radiotherapy. Applicators with diameter of 10-7-6-5 and 4 cm were used. The dose per pulse varied from about 30 mGy, for the 10 cm reference applicator, to about 70 mGy, for the 4 cm applicator. Five types of plane-parallel ionization chambers (PTW Advanced Markus, Markus and Roos, IBA PPC40 and PPC05), two types of silicon diodes (PTW 60017 and IBA EFD3G) and a PTW 60019 microDiamond were considered. For the ionization chambers, correction factors for ion recombination effects were determined for each applicator using a modified two-voltage-analysis method that includes the free-electron component. Results Reference OF values were determined by alanine dosimeters with a standard combined uncertainty of 0.8%. Deviations from the reference OFs were generally within 1.5% for all the detectors, hence within the 95% confidence interval of alanine measurements. Larger deviations of up to about 2% obtained in a few cases are consistent with a 0.7% long-term reproducibility of OF measurements. Conclusions Comparison with alanine measurements demonstrated that all the detectors considered in this work can be used to measure OFs in high dose-per-pulse electron beams with an accuracy better than 2%, provided that appropriate corrections for ion recombination effects are applied when using ionization chambers.

The Italian National Institute of Ionizing Radiation Metrology (ENEA-INMRI) has designed and built a graphite calorimeter that, in a water phantom, has allowed the determination of the absorbed dose to water in medium-energy x-rays with generating voltages from 180 to 250 kV. The new standard is a miniaturized three-bodies calorimeter, with a disc-shaped core of 21 mm diameter and 2 mm thickness weighing 1.134 g, sealed in a PMMA waterproof envelope with air-evacuated gaps. The measured absorbed dose to graphite is converted into absorbed dose to water by means of an energy-dependent conversion factor obtained from Monte Carlo simulations. Heat-transfer correction factors were determined by FEM calculations. At a source-to-detector distance of 100 cm, a depth in water of 2 g cm-2, and at a dose rate of about 0.15 Gy min-1, results of calorimetric measurements of absorbed dose to water, D w, were compared to experimental determinations, D wK, obtained via an ionization chamber calibrated in terms of air kerma, according to established dosimetry protocols. The combined standard uncertainty of D w and D wK were estimated as 1.9% and 1.7%, respectively. The two absorbed dose to water determinations were in agreement within 1%, well below the stated measurement uncertainties. Advancements are in progress to extend the measurement capability of the new in-water-phantom graphite calorimeter to other filtered medium-energy x-ray qualities and to reduce the D w uncertainty to around 1%. The new calorimeter represents the first implementation of in-water-phantom graphite calorimetry in the kilovoltage range and, allowing independent determinations of D w, it will contribute to establish a robust system of absorbed dose to water primary standards for medium-energy x-ray beams. © 2016 Institute of Physics and Engineering in Medicine.

Measurements of neutron streaming through penetrations in biological shields are being carried out at JET fusion device by means of thermoluminescence (TL) detectors with the objective to validate the neutronics codes and nuclear data widely applied in ITER nuclear analyses in a real fusion environment. TLDs response due to the neutron component of the radiation field is related to the neutron fluence in a well-defined neutron energy spectrum. Therefore, a TLDs calibration in real fusion radiation fields is necessary to allow neutron fluence from TL measurements at JET to be more precisely calculated. Hence, a MCP-N and MCP-7 TLDs produced at the IFJ PAN in Kraków were calibrated at the ENEA facilities of Frascati and Casaccia laboratories. The obtained results have been analysed and new calibration factors are proposed. The detection system based on TLDs developed and calibrated for JET experiments can then be generally applied not only to fusion neutron fields, but also to ITER to monitor the neutron fluence outside the biological shield. © 2018

Purpose: To investigate the feasibility of using the ratio of dose-area product at 20 cm and 10 cm water depths (DAPR20,10) as a beam quality specifier for radiotherapy photon beams with field diameter below 2 cm. Methods: Dose-area product was determined as the integral of absorbed dose to water (Dw) over a surface larger than the beam size. 6 MV and 10 MV photon beams with field diameters from 0.75 cm to 2 cm were considered. Monte Carlo (MC) simulations were performed to calculate energy-dependent dosimetric parameters and to study the DAPR20,10 properties. Aspects relevant to DAPR20,10 measurement were explored using large-area plane-parallel ionization chambers with different diameters. Results: DAPR20,10 was nearly independent of field size in line with the small differences among the corresponding mean beam energies. Both MC and experimental results showed a dependence of DAPR20,10 on the measurement setup and the surface over which Dw is integrated. For a given setup, DAPR20,10 values obtained using ionization chambers with different air-cavity diameters agreed with one another within 0.4%, after the application of MC correction factors accounting for effects due to the chamber size. DAPR20,10 differences among the small field sizes were within 1% and sensitivity to the beam energy resulted similar to that of established beam quality specifiers based on the point measurement of Dw. Conclusions: For a specific measurement setup and integration area, DAPR20,10 proved suitable to specify the beam quality of small photon beams for the selection of energy-dependent dosimetric parameters. © 2017 Associazione Italiana di Fisica Medica

Purpose: To study EBT3 GafChromic film in low-energy protons, and for comparison purposes, in a reference 60Co beam in order to use it as a calibrated dosimetry system in the proton irradiation facility under construction within the framework of the Oncological Therapy with Protons (TOP)-Intensity Modulated Proton Linear Accelerator for RadioTherapy (IMPLART) Project at ENEA-Frascati, Italy. Methods: EBT3 film samples were irradiated at the Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali di Legnaro, Italy, with a 5 MeV proton beam generated by a 7 MV Van de Graaff CN accelerator. The nominal dose rates used were 2.1 Gy/min and 40 Gy/min. The delivered dose was determined by measuring the particle fluence and the energy spectrum in air with silicon surface barrier detector monitors. A preliminary study of the EBT3 film beam quality dependence in low-energy protons was conducted by passively degrading the beam energy. EBT3 films were also irradiated at ENEA-National Institute of Ionizing Radiation Metrology with gamma radiation produced by a 60Co source characterized by an absorbed dose to water rate of 0.26 Gy/min as measured by a calibrated Farmer type ionization chamber. EBT3 film calibration curves were determined by means of a set of 40 film pieces irradiated to various doses ranging from 0.5 Gy to 30 Gy absorbed dose to water. An EPSON Expression 11000XL color scanner in transmission mode was used for film analysis. Scanner response stability, intrafilm uniformity, and interfilm reproducibility were verified. Optical absorption spectra measurements were performed on unirradiated and irradiated EBT3 films to choose the most sensitive color channel to the dose range used. Results: EBT3 GafChromic films show an under response up to about 33% for low-energy protons with respect to 60Co gamma radiation, which is consistent with the linear energy transfer dependence already observed with higher energy protons, and a negligible dose-rate dependence in the 2–40 Gy/min range. Short- and long-term scanner stabilities were 0.5% and 1.5%, respectively; film uniformity and reproducibility were better than 0.5%. Conclusions: The main purpose of this study was to implement EBT3 dosimetry in the proton low-energy radiobiology line of the TOP-IMPLART accelerator, having a maximum energy of 7 MeV. Low-energy proton and 60Co calibrated sources were used to investigate the behavior of film response vs to be written in italicum dose. The calibration in 5 MeV protons is currently used for dose assessment in the radiobiological experiments at the TOP-IMPLART accelerator carried out at that energy value.

Purpose: Aim of the present work is to evaluate the synthetic single crystal diamond Schottky photodiode developed at the laboratories of “Tor Vergata” University in Rome in a new dosimeter configuration specifically designed for offline wireless in vivo dosimetry (IVD) applications. Methods: The new diamond based dosimeter, single crystal diamond detector (SCDD-iv), consists of a small unwired detector and a small external reading unit that can be connected to commercial electrometers for getting the detector readout after irradiation. Two nominally identical SCDD-iv dosimeter prototypes were fabricated and tested. A basic dosimetric characterization of detector performances relevant for IVD application was performed under irradiation with 60Co and 6 MV photon beams. Preirradiation procedure, response stability, short and long term reproducibility, leakage charge, fading effect, linearity with dose, dose rate dependence, temperature dependence, and angular response were investigated. Results: The SCDD-iv is simple, with no cables linked to the patient and the readout is immediate. The range of response with dose has been tested from 1 up to 12 Gy; the reading is independent of the accumulated dose and dose rate independent in the range between about 0.5 and 5 Gy/min; its temperature dependence is within 0.5% between 25 and 38 °C, and its directional dependence is within 2% from 0° to 90°. The combined relative standard uncertainty of absorbed dose to water measurements is estimated lower than the tolerance and action level of 5%. Conclusions: The reported results indicate the proposed novel offline dosimeter based on a synthetic single crystal diamond Schottky photodiode as a promising candidate for in vivo dosimetry applications with photon beams.

Background: PET/CT has recently been shown to be a viable alternative to traditional post-infusion imaging methods providing good quality images of 90Y-laden microspheres after selective internal radiation therapy (SIRT). In the present paper, first we assessed the quantitative accuracy of 90Y-PET using an anthropomorphic phantom provided with lungs, liver, spine, and a cylindrical homemade lesion located into the hepatic compartment. Then, we explored the accuracy of different computational approaches on dose calculation, including (I) direct Monte Carlo radiation transport using Raydose, (II) Kernel convolution using Philips Stratos, (III) local deposition algorithm, (IV) Monte Carlo technique (MCNP) considering a uniform activity distribution, and (V) MIRD (Medical Internal Radiation Dose) analytical approach. Finally, calculated absorbed doses were compared with those obtained performing measurements with LiF:Mg,Cu,P TLD chips in a liquid environment. Results: Our results indicate that despite 90Y-PET being likely to provide high-resolution images, the 90Y low branch ratio, along with other image-degrading factors, may produce non-uniform activity maps, even in the presence of uniform activity. A systematic underestimation of the recovered activity, both for the tumor insert and for the liver background, was found. This is particularly true if no partial volume correction is applied through recovery coefficients. All dose algorithms performed well, the worst case scenario providing an agreement between absorbed dose evaluations within 20%. Average absorbed doses determined with the local deposition method are in excellent agreement with those obtained using the MIRD and the kernel-convolution dose calculation approach. Finally, absorbed dose assessed with MC codes are in good agreement with those obtained using TLD in liquid solution, thus confirming the soundness of both calculation approaches. This is especially true for Raydose, which provided an absorbed dose value within 3% of the measured dose, well within the stated uncertainties. Conclusions: Patient-specific dosimetry is possible even in a scenario with low true coincidences and high random fraction, as in 90Y–PET imaging, granted that accurate absolute PET calibration is performed and acquisition times are sufficiently long. Despite Monte Carlo calculations seeming to outperform all dose estimation algorithms, our data provide a strong argument for encouraging the use of the local deposition algorithm for routine 90Y dosimetry based on PET/CT imaging, due to its simplicity of implementation. © 2017, The Author(s).

A systematic study of the PTW microDiamond (MD) output factors (OF) is reported, aimed at clarifying its response in small fields and investigating its suitability for small field reference dosimetry. Ten MDs were calibrated under 60Co irradiation. OF measurements were performed in 6 MV photon beams by a CyberKnife M6, a Varian DHX and an Elekta Synergy linacs. Two PTW silicon diodes E (Si-D) were used for comparison. The results obtained by the MDs were evaluated in terms of absorbed dose to water determination in reference conditions and OF measurements, and compared to the results reported in the recent literature. To this purpose, the Monte Carlo (MC) beam-quality correction factor, , was calculated for the MD, and the small field output correction factors, , were calculated for both the MD and the Si-D by two different research groups. An empirical function was also derived, providing output correction factors within 0.5% from the MC values calculated for all of the three linacs. A high reproducibility of the dosimetric properties was observed among the ten MDs. The experimental values are in agreement within 1% with the MC calculated ones. Output correction factors within +0.7% and -1.4% were obtained down to field sizes as narrow as 5 mm. The resulting MD and Si-D field factors are in agreement within 0.2% in the case of CyberKnife measurements and 1.6% in the other cases. This latter higher spread of the data was demonstrated to be due to a lower reproducibility of small beam sizes defined by jaws or multi leaf collimators. The results of the present study demonstrate the reproducibility of the MD response and provide a validation of the MC modelling of this device. In principle, accurate reference dosimetry is thus feasible by using the microDiamond dosimeter for field sizes down to 5 mm. © 2017 Institute of Physics and Engineering in Medicine.

High-energy electron beams generated by linear accelerators, typically in the range 6 to 20 MeV, are used in small field sizes for radiotherapy of localized superficial tumors. Unshielded silicon diodes (Si-D) are commonly considered suitable detectors for relative dose measurements in small electron fields due to their high spatial resolution. Recently, a novel synthetic single crystal diamond diode (SCDD) showed suitable properties for standard electron beams and small photon beams dosimetry. The aim of the present study is twofold: to characterize 6 to 15 MeV small electron beams shaped by using commercial tubular applicators with 2, 3, 4 and 5 cm diameter and to assess the dosimetric performance under such irradiation conditions of the novel SCDD dosimeter by comparison with commercially available dosimeters, namely a Si-D and a plane-parallel ionization chamber. Percentage depth dose curves, beam profiles and output factors (OFs) were measured. A good agreement among the dosimeters was observed in all of the performed measurements. As for the tubular applicators, two main effects were evidenced: (i) OFs larger than unity were measured for a number of field sizes and energies, with values up to about 1.3, that is an output 30% greater than that obtained at the 10 × 10 cm 2 reference field; (ii) for each diameter of the tubular applicator a noticeable increase of the OF values was observed with increasing beam energy, up to about 100% in the case of the smaller applicator. This OF behavior is remarkably different from what typically observed for small blocked fields having the same size and energy as those used in this study. OFs for tubular applicators depend considerably on the field size, so interpolation is unadvisable to predict the linear accelerator output for such applicators whereas reliable high-resolution detectors, as the silicon and diamond diodes used in this work allow OF measurements with uncertainties of about 1%. © 2013 Institute of Physics and Engineering in Medicine. Printed in the UK & the USA.

Purpose New promising detectors are available for measuring small field size output factors (OFs). This study focused on a multicenter evaluation of two new generation detectors for OF measurements on CyberKnife systems. Methods PTW-60019 microDiamond and W1 plastic scintillation detector (PSD) were used to measure OFs on eight CyberKnife units of various generations for 5–60 mm fixed cones. MicroDiamond and PSD OF were compared to routinely used silicon diodes data corrected applying published Monte Carlo (MC) factors. PSD data were corrected for Cerenkov Light Ratio (CLR). The uncertainties related to CLR determination were estimated. Results Considering OF values averaged over all centers, the differences between MC corrected diode and the other two detectors were within 1.5%. MicroDiamond exhibited an over-response of 1.3% at 7.5 mm and a trend inversion at 5 mm with a difference of 0.2%. This behavior was consistent among the different units. OFs measured by PSD slightly under-responded compared to MC corrected diode for the smaller cones and the differences were within 1%. The observed CLR variability was 2.5% and the related variation in OF values was 1.9%. Conclusion This study indicates that CyberKnife microDiamond OF require corrections below 2%. The results are enhanced by the consistency observed among different units. Scintillator shows a good agreement to MC corrected diode but CLR determination remains critical requiring further investigations. The results emphasized the value of a multi-center validation over a single center approach.

This report presents the results of the first international comparison of primary measurement standards of absorbed dose to water for the medium-energy X-ray range. Three of the participants (VSL, PTB, LNE-LNHB) used their existing water calorimeter based standards and one participant (ENEA) recently developed a new standard based on a water-graphite calorimeter. The participants calibrated three transfer chambers of the same type in terms of absorbed dose to water (N Dw) and in addition in terms of air kerma (NK ) using the CCRI radiation qualities in the range 100 kV to 250 kV. The additional NK values were intended to be used for a physical analysis of the ratios N Dw/NK . All participants had previously participated in the BIPM.RI(I)-K3 key comparison of air kerma standards. Ratios of pairs of NMI's NK results of the current comparison were found to be consistent with the corresponding key comparison results within the expanded uncertainties of 0.6 % - 1 %. The N Dw results were analysed in terms of the degrees of equivalence with the comparison reference values which were calculated for each beam quality as the weighted means of all results. The participant's results were consistent with the reference value within the expanded uncertainties. However, these expanded uncertainties varied significantly and ranged between about 1-1.8 % for the water calorimeter based standards and were estimated at 3.7 % for the water-graphite calorimeter. It was shown previously that the ratios N Dw/NK for the type of ionization chamber used as transfer chamber in this comparison were very close (within less than 1 %) to the calculated values of (μ̄en/ρ)w,a d, the mean values of the water-to-air ratio of the mass-energy-absorption coefficients at the depth d in water. Some of the participant's results deviated significantly from the expected behavior. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Purpose Evaluating the level of agreement of measurements by different types of ionization chambers and solid state detectors in IORT electron beams with high dose per pulse. Methods Two electron beams (R50 2.59 and 3.05 cm) by a Novac7 Hitesys linac were used. Absorbed dose to water (Dw) and output factors (OF) were determined for the reference applicator of diameter 10 cm and the clinical applicators of diameter from 4 to 7 cm. The dose per pulse ranged between 29 and 77 mGy. Six types of plane parallel ionization chambers (PTW Markus, Advanced Markus and Roos; IBA PPC05, PPC40 and NACP02) were utilized. OF measurements were also made using a PTW microDiamond type 60019 and silicon diodes PTW type 60017 and IBA-EFG-3D. The IAEA TRS-398 dosimetry protocol was applied except for the saturation corrections applied to the ionization chambers that were determined according to [1] . Results The PPC05 and the Advanced Markus chambers exhibited the lowest ion recombination effects, being the corrections to be applied lower than 0.5% and 1.5%, respectively. Corrections larger than 15% were obtained for the Roos, the and PPC40 and the NACP02. Agreement among ionization chamber OF values was generally better than 1.5% except for the largest chambers in the smallest beams, where beam non uniformity likely caused dose underestimation, and for some discrepancies relevant to the Markus and the NACP02 chambers. OF values obtained using the solid state detectors typically agreed within 1.5%, while differences from PPC05 and Advanced Markus OFs were within 2%. Dw measurements by means of different ionization chambers agree to each other within the stated uncertainties (2.5%, 1SD). Conclusions Results of this work show that, at the high dose per pulse of NOVAC7 beams, dosimetry based on ionimetric measurements is feasible, if ion recombination effects are properly taken into account, and the studied solid state detectors are suitable for relative dosimetry.

Purpose The high dose per pulse of electron beams produced by some mobile accelerators for intraoperative radiotherapy can affect output factor (OF) measurements, since the dose rate increases by a factor larger than two from the reference to the smallest radiation field. Aim of this work was to assess the capability of different types of detectors to measure OFs at high dose per pulse by comparison with alanine dosimeters, which are independent of dose rate. Methods Measurements were made in 9 and 7 MeV electron beams produced by a Novac 7 accelerator. PMMA cylindrical applicators with diameter of 100 mm (reference field), 70 mm, 60 mm, 50 mm and 40 mm were used. The dose per pulse varied from about 30 mGy, for the 100 mm applicator, to about 70 mGy, for the 40 mm applicator. OFs were determined using four types of plane-parallel ionization chambers (PTW Advanced Markus and Roos, IBA PPC40 and PPC05), two types of silicon diodes (PTW 60017 and IBA 3FG-3D), a PTW microDiamond and alanine dosimeters. Ionization chamber signals were corrected for ion recombination effects using a modified two-voltage-analysis method that includes the free-electron component. Results A fairly good agreement was found between OFs measured by the three types of solid-state detectors and those measured by alanine. Differences were generally below 1% and maximum discrepancies around 2%. For the Advanced Markus and the PPC05 chambers differences from alanine results were below 1.7%. For the Roos and the PPC40 chambers agreement with alanine was within 2.3% down to the 50 mm applicator, while differences of several percent were found for the smallest applicator, most likely due to volume averaging effect. The variation of ion recombination correction factor with field size was below 1% for the Advanced Markus and the PPC05 chambers and up to about 10% for the Roos and the PPC40 chambers. Conclusions Comparison with alanine measurements demonstrated that all the detectors considered in this work can be used to measure OFs in high-dose-per-pulse electron beams with an accuracy of 2%, provided that appropriate corrections for ion recombination effects are applied when using ionization chambers.

Purpose The aim of the present work was to evaluate small field size output factors (OFs) using the latest diamond detector commercially available, PTW-60019 microDiamond, over different CyberKnife systems. OFs were measured also by silicon detectors routinely used by each center, considered as reference. Methods Five Italian CyberKnife centers performed OFs measurements for field sizes ranging from 5 to 60 mm, defined by fixed circular collimators (5 centers) and by Iris ™ variable aperture collimator (4 centers). Setup conditions were: 80 cm source to detector distance, and 1.5 cm depth in water. To speed up measurements two diamond detectors were used and their equivalence was evaluated. MonteCarlo (MC) correction factors for silicon detectors were used for comparing the OF measurements. Results Considering OFs values averaged over all centers, diamond data resulted lower than uncorrected silicon diode ones. The agreement between diamond and MC corrected silicon values was within 0.6% for all fixed circular collimators. Relative differences between microDiamond and MC corrected silicon diodes data for Iris ™ collimator were lower than 1.0% for all apertures in the totality of centers. The two microDiamond detectors showed similar characteristics, in agreement with the technical specifications. Conclusions Excellent agreement between microDiamond and MC corrected silicon diode detectors OFs was obtained for both collimation systems fixed cones and Iris ™ , demonstrating the microDiamond could be a suitable detector for CyberKnife commissioning and routine checks. These results obtained in five centers suggest that for CyberKnife systems microDiamond can be used without corrections even at the smallest field size.

The purpose of this study was to compare the dosimetric properties of small field electron beams shaped by circular Cerrobend blocks and stainless steel tubular applicators. Percentage depth dose curves, beam profiles, and output factors of small‐size circular fields from 2 to 5 cm diameter, obtained either by tubular applicators and Cerrobend blocks, were measured for 6, 10, and 15 MeV electron beam energies. All measurements were performed using a PTW microDiamond 60019 premarket prototype. An overall similar behavior between the two collimating systems can be observed in terms of PDD and beam profiles. However, Cerrobend collimators produce a higher bremsstrahlung background under irradiation with high‐energy electrons. In such irradiation condition, larger output factors are observed for tubular applicators. Similar dosimetric properties are observed using circular Cerrobend blocks and stainless steel tubular applicators at lower beam energies. However, Cerrobend collimators allow the delivery of specific beam shapes, conformed to the target area. On the other hand, in high‐energy irradiation conditions, tubular applicators produce a lower bremsstrahlung contribution, leading to lower doses outside the target volume. In addition, the higher output factors observed at high energies for tubular applicators lead to reduced treatment times. PACS number: 87.53.Bn, 87.55.Qr, 87.56.Fc

Purpose: To characterize a synthetic diamond dosimeter (PTW Freiburg microDiamond 60019) in high dose-per-pulse electron beams produced by an Intra Operative Radiation Therapy (IORT) dedicated accelerator. Methods: The dosimetric properties of the microDiamond were assessed under 6, 8 and 9 MeV electron beams by a NOVAC11 mobile accelerator (Sordina IORT Technologies S.p.A.).The characterization was carried out with dose-per-pulse ranging from 26 to 105 mGy per pulse. The microDiamond performance was compared with an Advanced Markus ionization chamber and a PTW silicon diode E in terms of dose linearity, percentage depth dose (PDD) curves, beam profiles and output factors. Results: A good linearity of the microDiamond response was verified in the dose range from 0.2 Gy to 28 Gy. A sensitivity of 1.29 nC/Gy was measured under IORT electron beams, resulting within 1% with respect to the one obtained in reference condition under 60Co gamma irradiation. PDD measurements were found in agreement with the ones by the reference dosimeters, with differences in R50 values below 0.3 mm. Profile measurements evidenced a high spatial resolution of the microDiamond, slightly worse than the one of the silicon diode. The penumbra widths measured by the microDiamond resulted approximately 0.5 mm larger than the ones by the Silicon diode. Output factors measured by the microDiamond were found within 2% with those obtained by the Advanced Markus down to 3 cm diameter field sizes. Conclusions: The microDiamond dosimeter was demonstrated to be suitable for precise dosimetry in IORT applications under high dose-per-pulse conditions. © 2015 Associazione Italiana di Fisica Medica.

A project dedicated to stereotactic body radiotherapy (SBRT) dosimetric aspects started in the framework of the Italian Association of Medical Physics (AIFM) SBRT working group. Its main objectives are manifold but sharing the knowledge between different clinics is the one of the most important. More than 30 centres, equipped with Varian, Elekta, Siemens or CyberKnife linac were enrolled. The project was divided in several work-packages, the first one evaluated the relative measurements with detectors routinely used by individual centers and in the following different detectors run in various centre. Each centre in the same work-package performed dose profile of field size ranging from 0.6 × 0.6 cm 2 to 5.0 × 5.0 cm 2 , and relative output factors (ROF) measurements with a diamond or silicon diode or scintillator detector. In workpackage-1 ROF values measured in the first phase were compared with the ones measured with a microdiamond showing a higher inter-center consistency with this dosimeter compared to routine detectors. In workpackage-2 a silicon diode of new generation was used also to develop a mathematical relation from multicentric experimental data, which describes and predicts the ROF as a function of effective field size for TrueBeam Varian and Elekta linacs. Workpackage-3 used a plastic scintillator for TPR20, 10 and ROF; the latter showed a greater variability. Workpackage-4 used diamond and plastic scintillator with Cyberknife beams, to evaluate if microDiamond could be a suitable alternative to silicon diodes for OF determination and to validate the feasibility of using the scintillator as a reference detector in consideration of the CerenkovLightRatio and experimental uncertainties. The results of the study for all the detectors emphasized the usefulness of a multi-center validation over a single center approach.

This paper summarizes the progress on the construction of a graphite calorimeter for the measurement of absorbed dose to water Dw in medium-energy filtered x-ray qualities, as part of the EMRP- funded project "Metrology for radiotherapy using complex radiation fields" (MetrExtRT, http://radiotherapy- emrp.eu/). The design and the construction of a new primary standard for absorbed dose to water (Dw) is shown, together with a presentation of the preliminary estimates of conversion factors, calculated by Monte Carlo using the EGSnrc code, and heat-transport calculations resulting from COMSOL simulations. The vacuum-gap-insulated calorimeter core has a thickness of 2 mm and a diameter of 20 mm. The graphite calorimeter is embedded in a PMMA waterproof sleeve and can be positioned at the desired measurement depth in a water phantom. Once completed, the new calorimeter will participate in an international comparison with other existing standards of absorbed dose to water for medium energy x-rays.

This paper is intended to give information about the on-going work of the MetrExtRT research project concerned with the dosimetric metrology of modern external beam radiotherapy. It started on the 1st of June 2012 for duration of 36 months and covers the study medium- and high-energy X-rays, high-energy electrons, electronic brachytherapy and scanned proton and carbon ion beams. The project concerns all the steps of traceability from the primary standards through to verification of the dose in and around the tumour, namely: developing new primary standards of absorbed dose to water; studying new detectors and improving the knowledge of the characteristics of existing detectors, useable for quality control and in vivo dosimetry, and publishing guide lines of good practice on their use. MetrExtRT gathers 10 partners that are all National Metrology Institutes (NMI) or Designated Institutes (DI) as represented by the list of authors, two Researcher Excellence Grants (REG) for the development of passive gel dosimetry (Universite d'Auverge – France) and diamond detectors (Tor Vergata University - Italy) and up to now 12 collaborators from industry, oncology centres and universities.

A chemical vapour deposition diamond detector fabricated at Rome ‘Tor Vergata’ University was investigated for its applicability as transfer dosimeter in radiotherapy photon beams with small field sizes. The detector consists of a single crystal diamond with a very small sensitive volume (0.004 mm3). The detector showed a measurement repeatability of 0.1% and a long term reproducibility of 0.4%. Monte Carlo simulations revealed a response dependence on the photon beam energy of about 2% from the 60Co quality to 10 MV photon beam. The calculated detector response was found to be independent of field size within 0.5% from 10 cm × 10 cm to 2 cm × 2 cm beam size for both 6 MV and 10 MV photon beams, increasing in smaller field sizes. Dw values obtained by the diamond detector were found to be in agreement with Dw values obtained by a small volume ionization chamber in photon beams with field size down to 2 cm × 2 cm.

The appropriate correction factors have been determined to enable plane-parallel ionization chambers to be calibrated using a 60Co photon beam with a known air kerma rate. These factors refer to different calibration conditions and to different types of plane-parallel chambers. The main purpose of these correction factors is to allow calibration procedures more widely practicable than those based on the use of an electron beam of sufficiently high energy. The condition required to apply the correction factors is that the characteristics of the chambers to be calibrated are the same as those reported for the chambers considered in the investigation. To this end the types of chambers investigated were among the most widely used plane-parallel chambers commercially available.

A new diamond detector to perform absorbed-dose- to-water measurement in radiotherapy photon beams with small field sizes is being developed in the framework of the EURAMET/EC FP7 project “External Beam Cancer Therapy”. An objective of the project is to obtain detectors capable of ensuring traceability of absorbed dose measurements in radiotherapy photon beams with field size down to 1 cm x 1 cm. To this end the CVD diamond detectors up to now developed were found not adequate. The present project requires detectors with high spatial resolution, good stability and low energy dependence. Diamond detectors were chosen for their high spatial resolution and good tissue equivalence (Z = 6). The detector studied in this work is based on a single crystal CVD diamond with dimensions 3 mm x 3 mm x 0.5 mm on which 0.2 μm electrodes were thermally evaporated. Particular care was addressed to ensure the tissue-equivalence of the detector by using appropriate materials. A thorough analysis of the priming procedure, stability and signal reproducibility was carried out in a Co-60 gamma beam at dose rates in the range from 0.3 Gy min− 1 to 1.38 Gy min− 1. Moreover the detector response was studied by Monte Carlo calculations as a function both of the beam quality, from Co-60 to 10 MV photon beams, and field size, from 10 cm x 10 cm to 1 cm x 1 cm. The perturbation due to the non-water equivalence of electrodes was also determined by Monte Carlo simulations.

This paper outlines the joint research project “Increasing cancer treatment efficacy using 3D brachytherapy” co-funded in the FP7, according to the iMERA-Plus Grant Agreement No. 217257 between the EC and EURAMET e. V. (European Association of National Metrology Institutes). The project brings together the capabilities of ten major European National Metrology Institutes in the ionizing radiation field and it is focused on the targeted programme “Health”. It aims at establishing across Europe a more accurate metrological basis in brachytherapy by developing methods for the direct measurement of the quantity absorbed dose to water in brachytherapy dosimetry with an uncertainty on the dose delivered to the target volume less than 5% (k=1) at clinical level. In fact, in the current brachytherapy practice, the procedures to determine the absorbed dose imparted to the patient are affected by an uncertainty that could reduce the treatment success. Most of this uncertainty is due to a lacking metrology. No absorbed-dose primary standards are so far available to assure direct traceability in dosimetry of brachytherapy sources. In order to optimize the brachytherapy treatments there is also a need for more accurate dosimetry with high spatial resolution. The present research project is expected to increase the accuracy of brachytherapy to a level comparable to that typical of radiotherapy with external accelerator beams.

Introduction, material and method A work package of the European metrological joint research project (JRP) entitled ‘‘Metrology for radiotherapy using complex radiation fields – MetrExRT” is aimed at studying radiation qualities, measurement conditions and beam quality index suitable for dosimeter calibration in terms of Dw in the conditions of the IAEA protocol 398 for medium-energy X-rays. A survey was undertaken among European end users and calibration labs to select the most relevant beam qualities for dosimeter calibrations and international comparison. It is also aimed at gathering information about the use of medium energy X-rays for therapy. Two electronic questionnaires were circulated, one for the end users, and one for the calibration labs (32 and 9 answers respectively). Results and Conclusions Most of the X-ray generators of the end users were bought before 2000. High voltages lie between 7.5 and 300 kV while for treatment the range is between 10 and 250 kV. Addition filtration is up to 1 mm Cu (150 kV). Dose rates lie between 0.3 and 25 Gy/min, about 80% of the dose rates are below 5 Gy/min and about 10% are below 0.5 Gy/min. Concerning therapeutic indications, 54% are for contact therapy (rectum; skin; eyes; gynecology; etc.), 11% for intra-operative (breast; etc.), benign diseases are also treated. The largest numbers of treatments per year for a given service were found for contact therapy and benign diseases (from 50 to more than 500). Radiation qualities for calibration are chosen mainly in ISO 4037 and IEC 61267 and 60731. The calibration lab facilities cover the range of high voltage used for treatments. Radiation qualities are similar to those mentioned above, as it might have been foreseen, CCRI qualities are more used by metrological labs. Absorbed dose to water for 60Co is mentioned by the end users. The dose rates available at calibration labs are low compare to most of those used for the treatments. This suggests that saturation effect has to be studied to introduce a correction factor if needed. A comparison of the treatment spectra with the ones used by calibration labs will be shown. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.

The factor Kwall to correct for photon attenuation and scatter in the wall of ionization chambers for 60Co air-kerma measurement has been traditionally determined by a procedure based on a linear extrapolation of the chamber current to zero wall thickness. Monte Carlo calculations by Rogers and Bielajew (1990 Phys. Med. Biol. 35 1065-78) provided evidence, mostly for chambers of cylindrical and spherical geometry, of appreciable deviations between the calculated values of Kwall and those obtained by the traditional extrapolation procedure. In the present work an experimental method other than the traditional extrapolation procedure was used to determine the Kwall factor. In this method the dependence of the ionization current in a cylindrical chamber was analysed as a function of an effective wall thickness in place of the physical (radial) wall thickness traditionally considered in this type of measurement. To this end the chamber wall was ideally divided into distinct regions and for each region an effective thickness to which the chamber current correlates was determined. A Monte Carlo calculation of attenuation and scatter effects in the different regions of the chamber wall was also made to compare calculation to measurement results. The Kwall values experimentally determined in this work agree within 0.2% with the Monte Carlo calculation. The agreement between these independent methods and the appreciable deviation (up to about 1%) between the results of both these methods and those obtained by the traditional extrapolation procedure support the conclusion that the two independent methods providing comparable results are correct and the traditional extrapolation procedure is likely to be wrong. The numerical results of the present study refer to a cylindrical cavity chamber like that adopted as the Italian national air-kerma standard at INMRI-ENEA (Italy). The method used in this study applies, however, to any other chamber of the same type.

1 CEA, LIST, DM2I, Laboratoire National Henri Becquerel LNE/LNHB, F-91191 Gif sur Yvette, France 2 Denmarks Tekniske Universitet, DTU, Bygning 101, DK-2800 Kongens Lyngby, Denmark 3 Physikalisch-Technische Bundesanstalt, PTB, Bundesallee 100, D-38116 Braunschweig, Germany 4 Universte d’Auvergne, UdA, France 5 VSL B.V., Thijsseweg 11, NL-2629 JA Delft, Netherlands 6 Slovak Institute of Metrology, SMU, Karloveska 63, SK-842 55 Bratislava, Slovakia, 7 National Physical Laboratory, NPL, GB-TW11 0LW Teddington, Middlesex, United Kingdom, 8 Radiation and Nuclear Safety Authority, STUK, Laippatie 4, FI-00880 Helsinki, Finland, 9 Magyar Kereskedelmi Engedelyezesi Hivatal, MKEH, Hatosag 1534 Budapest, P.f.: 919 Hungary 10 Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti, ENEA CR Casaccia, Via Anguillarese, 301, 00123 Roma, Italy 11 Cesky Metrologicky Institut Brno, CMI, Okruzni 30, 63800 Brno, Czech Republic 12 Universita degli Studi di Roma Tor Vergata,Dipartimento di Ingegneria Industriale, Via del Politecnico 1, 00133 Roma, Italy

Purpose: To investigate the dosimetric properties of synthetic single crystal diamond based Schottky diodes under irradiation with therapeutic electron beams from linear accelerators. Methods: A single crystal diamond detector was fabricated and tested under 6, 8, 10, 12, and 15 MeV electron beams. The detector performances were evaluated using three types of commercial detectors as reference dosimeters: an Advanced Markus plane parallel ionization chamber, a Semiflex cylindrical ionization chamber, and a p-type silicon detector. Preirradiation, linearity with dose, dose rate dependence, output factors, lateral field profiles, and percentage depth dose profiles were investigated and discussed. Results: During preirradiation the diamond detector signal shows a weak decrease within 0.7% with respect to the plateau value and a final signal stability of 0.1% (1σ) is observed after about 5 Gy. A good linear behavior of the detector response as a function of the delivered dose is observed with deviations below ±0.3% in the dose range from 0.02 to 10 Gy. In addition, the detector response is dose rate independent, with deviations below 0.3% in the investigated dose rate range from 0.17 to 5.45 Gy/min. Percentage depth dose curves obtained from the diamond detector are in good agreement with the ones from the reference dosimeters. Lateral beam profile measurements show an overall good agreement among detectors, taking into account their respective geometrical features. The spatial resolution of solid state detectors is confirmed to be better than that of ionization chambers, being the one from the diamond detector comparable to that of the silicon diode. A good agreement within experimental uncertainties was also found in terms of output factor measurements between the diamond detector and reference dosimeters. Conclusions: The observed dosimetric properties indicate that the tested diamond detector is a suitable candidate for clinical electron beam dosimetry. © 2013 American Association of Physicists in Medicine .[ http://dx.doi.org/10.1118/1.4774360]

The primary standard of absorbed dose to water established at ENEA for the Co-60 gamma-ray quality is based on a graphite calorimeter and an ionometric transfer system. This standard was recently improved after a more accurate assessment of some perturbation effects in the calorimeter and a modification of the water phantom shape and size. The conversion procedure requires two corresponding depths, one in graphite and one in water, where the radiation energy spectra must be the same. The energy spectra at the corresponding points were determined by a Monte Carlo simulation in water and graphite scaled phantoms. A thorough study of the calorimeter gap effect corrections was also made with regard to their dependence on depth and field size. A comparison between the ionization chamber calibration procedures based on the standards of absorbed dose to water and of air kerma was also made, confirming the consistency of the two methods.