Purpose: The aim of in vivo skin dosimetry was to measure the absorbed dose to the skin during radiotherapy, when treatment planning calculations cannot be relied on. It is of particularly importance in hypo‐fractionated stereotactic modalities, where excessive dose can lead to severe skin toxicity. Currently, commercial diodes for such applications are with water equivalent depths ranging from 0.5 to 0.8 mm. In this study, we investigate a new detector for skin dosimetry based on a silicon epitaxial diode, referred to as the skin diode. Method: The skin diode is manufactured on a thin epitaxial layer and packaged using the “drop‐in” technology. It was characterized in terms of percentage depth dose, dose linearity, and dose rate dependence, and benchmarked against the Attix ionization chamber. The response of the skin diode in the build‐up region of the percentage depth dose (PDD) curve of a 6 MV clinical photon beam was investigated. Geant4 radiation transport simulations were used to model the PDD in order to estimate the water equivalent measurement depth (WED) of the skin diode. Measured output factors using the skin diode were compared with the MOSkin detector and EBT3 film at 10 cm depth and at surface at isocenter of a water equivalent phantom. The intrinsic angular response of the skin diode was also quantified in charge particle equilibrium conditions (CPE) and at the surface of a solid water phantom. Finally, the radiation hardness of the skin diode up to an accumulated dose of 80 kGy using photons from a Co‐60 gamma source was evaluated. Results: The PDD curve measured with the skin diode was within 0.5% agreement of the equivalent Geant4 simulated curve. When placed at the phantom surface, the WED of the skin diode was estimated to be 0.075 ± 0.005 mm from Geant4 simulations and was confirmed using the response of a corrected Attix ionization chamber placed at water equivalent depth of 0.075 mm, with the measurement agreement to within 0.3%. The output factor measurements at 10 cm depth were within 2% of those measured with film and the MOSkin detector down to a field size of 2 × 2 cm2. The dose–response for all detector samples was linear and with a repeatability within 0.2%. The skin diode intrinsic angular response showed a maximum deviation of 8% at 90 degrees and from 0 to 60 degree is less than 5%. The radiation sensitivity reduced by 25% after an accumulated dose of 20 kGy but after was found to stabilize. At 60 kGy total accumulated dose the response was within 2% of that measured at 20 kGy total accumulated dose. Conclusions: This work characterizes an innovative detector for in vivo and real‐time skin dose measurements that is based on an epitaxial silicon diode combined with the Centre for Medical Radiation Physics (CMRP) “drop‐in” packaging technology. The skin diode proved to have a water equivalent depth of measurement of 0.075 ± 0.005 mm and the ability to measure doses accurately relative to reference detectors.

PURPOSE:To characterize a new air vented ionization chamber technology, suitable to build detector arrays with small pixel pitch and independence of sensitivity on dose per pulse.METHODS:The prototype under test is a linear array of air vented ionization chambers, consisting of 80 pixels with 3.5 mm pixel pitch distance and a sensitive volume of about 4 mm(3). The detector has been characterized with (60)Co radiation and MV x rays from different linear accelerators (with flattened and unflattened beam qualities). Sensitivity dependence on dose per pulse has been evaluated under MV x rays by changing both the source to detector distance and the beam quality. Bias voltage has been varied in order to evaluate the charge collection efficiency in the most critical conditions. Relative dose profiles have been measured for both flattened and unflattened distributions with different field sizes. The reference detectors were a commercial array of ionization chambers and an amorphous silicon flat panel in direct conversion configuration. Profiles of dose distribution have been measured also with intensity modulated radiation therapy (IMRT), stereotactic radiosurgery (SRS), and volumetric modulated arc therapy (VMAT) patient plans. Comparison has been done with a commercial diode array and with Gafchromic EBT3 films.RESULTS:Repeatability and stability under continuous gamma irradiation are within 0.3%, in spite of low active volume and sensitivity (∼200 pC/Gy). Deviation from linearity is in the range [0.3%, -0.9%] for a dose of at least 20 cGy, while a worsening of linearity is observed below 10 cGy. Charge collection efficiency with 2.67 mGy/pulse is higher than 99%, leading to a ±0.9% sensitivity change in the range 0.09-2.67 mGy/pulse (covering all flattened and unflattened beam qualities). Tissue to phantom ratios show an agreement within 0.6% with the reference detector up to 34 cm depth. For field sizes in the range 2 × 2 to 15 × 15 cm(2), the output factors are in agreement with a thimble chamber within 2%, while with 25 × 25 cm(2) field size, an underestimation of 4.0% was found. Agreement of field and penumbra width measurements with the flat panel is of the order of 1 mm down to 1 × 1 cm(2) field size. Flatness and symmetry values measured with the 1D array and the reference detectors are comparable, and differences are always smaller than 1%. Angular dependence of the detector, when compared to measurements taken with a cylindrical chamber in the same phantom, is as large as 16%. This includes inhomogeneity and asymmetry of the design, which during plan verification are accounted for by the treatment planning system (TPS). The detector is capable to reproduce the dose distributions of IMRT and VMAT plans with a maximum deviation from TPS of 3.0% in the target region. In the case of VMAT and SRS plans, an average (maximum) deviation of the order of 1% (4%) from films has been measured.CONCLUSIONS:The investigated technology appears to be useful both for Linac QA and patient plan verification, especially in treatments with steep dose gradients and nonuniform dose rates such as VMAT and SRS. Major limitations of the present prototype are the linearity at low dose, which can be solved by optimizing the readout electronics, and the underestimation of output factors with large field sizes. The latter problem is presently not completely understood and will require further investigations.

PURPOSE:Proton radiography (PR) and proton computed tomography (PCT) can be used to measure proton stopping power directly. However, practical and cost effective proton imaging detectors are not widely available. In this study, the authors investigated the feasibility of proton imaging using a silicon diode array.METHODS:A one-dimensional silicon diode detector array (1DSDA) was aligned with the central axis (CAX) of the proton beam. Polymethyl methacrylate (PMMA) slabs were used to find the correspondence between the water equivalent thickness (WET) and 1DSDA channel number. Two-dimensional proton radiographs were obtained by translation and rotation of a phantom relative to CAX while the proton nozzle and 1DSDA were kept stationary. A PCT image of one slice of the phantom was reconstructed using filtered backprojection.RESULTS:PR and PCT images of the PMMA cube were successfully acquired using the 1DSDA. The WET of the phantom was measured using PR data. The resolution and maximum error in WET measurement are 2.0 and 1.5 mm, respectively. Structures down to 2.0 mm in size could be resolved completely. Reconstruction of a PCT image showed very good agreement with simulation. Limitations in spatial resolution are attributed to limited spatial sampling, beam collimation, and proton scatter.CONCLUSIONS:The results demonstrate the feasibility of using silicon diode arrays for proton imaging. Such a device can potentially offer fast image acquisition and high spatial and energy resolution for PR and PCT.

PurposeIn radiotherapy, uncertainties due to small field measurements (SFM) introduce systematic errors to the treatment process and the development of new dosimeters for quality assurance programs is a challenge. In this work we analyze the behavior of seven detectors measuring output factors of 6MV photon beam.MethodsThe dosimeters employed are: a single cristal diamond detector (SCCD) developed at the University of Rome Tor Vergata, a silicon diode developed within the project MAESTRO, a IBA Razor silicon diode, A1SL and A26 Exradin ion chambers, an EBT3 Gafchromic film and the Exradin W1 Scintillator.Diamond sensitive volume is a cylinder 2.2mm in diameter and 1μm thick. MAESTRO diode is 2×2mm2 active area. Razor sensitive volume is a cylinder 0.6 mm in diameter and 0.02 mm thick. A16 and A1Sl have a collecting volume of 0,015cc and 0,053cc. The W1 is an optical fiber with an active volume of 0.002cc. All measurements were performed in a water phantom, with detector positioned at the isocenter (SSD=90cm, d=10cm), MAESTRO diode being sandwiched in solid water to obtain an equivalent experimental setup.ResultsThese measurements are challenging due to the absence of charged particle equilibrium conditions, detector size and positioning problems. They are in good agreement among each other, especially GAF, Razor, W1 and SCDD. Maximum deviations reported are related to the field 0.8×0.8cm2 for MAESTRO and chambers data with respect to EBT3: around 15% (A1SLvsEBT3), 16% (MAESTROvsEBT3). Razor and W1 show a deviation around 3% with respect to SCDD.ConclusionIn this work measurements made with a variety of detectors are compared. These study show the possibility to choose different detectors for SFM and that smaller ion chambers are still not competitive with solid state detectors. Silicon, diamond and optical fiber dosimeters show a similar behavior with minor discrepancies for the smallest field.

Purpose:To study the suitability of a novel 1D silicon monolithic array for dosimetry of small radiation fields and for QA of high dose gradient treatment modalities (IMRT and SBRT).Methods:A 1D array composed of 4 monolithic silicon modules of 64 mm length and 1 mm pixel pitch was developed by IBA Dosimetry. Measurements were carried out for 6MV and 15MV photons on two commercial different linacs (TrueBeam and Clinac iX, Varian Medical Systems, Palo Alto, CA) and for a CyberKnife G4 (Accuray Inc., Sunnyvale, CA). The 1D array was used to measure output factors (OF), profiles and off axis correction factors (OACF) for the Iris CyberKnife variable collimator (5–60 mm). In addition, dose profiles (at the isocenter plane) were measured for multiple IMRT and SBRT treatment plans and compared with those obtained using EDR2radiographic film (Carestream Health, Rochester NY), a commercial 2D diode array and with the dose distribution calculated using a commercial TPS (Eclipse, Varian Medical Systems, Palo Alto, CA).Results:Due to the small pixel pitch of the detector, IMRT and SBRT plan profiles deviate from film measurements by less than 2%. Similarly, the 1D array exhibits better performance than the 2D diode array due to the larger (7 mm) pitch of that device. Iris collimator OFs measured using the 1D silicon array are in good agreement with the commissioning values obtained using a commercial stereotactic diode as well as with published data. Maximum deviations are < 3% for the smallest field (5 and 7.5mm) and below 1% for all other dimensions.Conclusion:We have demonstrated good performances of the array for commissioning of small photon fields and in patient QA, compared with diodes and film typically used in these clinical applications. The technology compares favorably with existing commercial solutionsThe presenting author is founded by a Marie Curie Early Initial Training Network Fellowship of the European Communitys Seventh Framework Programme under contract number (PITN‐GA‐2011‐289198‐ARDENT).The research activity is hosted by IBA Dosimetry, Gmbh.

New tools for dosimetry in external beam radiotherapy have been developed during last years in the framework of the collaboration among the University of Florence, INFN Florence and IBA Dosimetry.The first step (in 2007) was the introduction in dosimetry of detector solutions adopted from high energy physics, namely epitaxial silicon as the base detector material and a guard ring in diode design. This allowed obtaining state of the art radiation hardness, in terms of sensitivity dependence on accumulated dose, with sensor geometry particularly suitable for the production of monolithic arrays with modular design.Following this study, a 2D monolithic array has been developed, based on 6.3 x 6.3 cm(2) modules with 3 mm pixel pitch. This prototype has been widely investigated and turned out to be a promising tool to measure dose distributions of small and IMRT fields.A further linear at prototype has been recently design with improve spatial resolution (1 min pitch) and radiation hardness. This 24 cm long device is constituted by 4 x 64 mm long modules. It features low sensitivity changes with dose (0.2%/kGy) and dose per pulse (+/- 1% in the range 0.1-2.3 mGyfpulse, covering applications with flattened and untlattened photon fields). The detector has been tested with very satisfactory results as a tool for quality assurance of linear accelerators, with special regards to small fields, and proton pencil beams. In this contribution, the characterization of the linear array with untlattened MV X-rays, Co-60 radiation and 226 MeV protons is reported. (C) 2015 Elsevier B.V. All rights reserved.

Purpose:to demonstrate suitability of a novel silicon array for measuring the dose properties of highly conformal photon and proton beams.Methods:prototype under test is a 24cm long linear array prototype, although the underlying technology is suitable to construct 2D arrays as well. It is based on a 64pixels monolithic sensor with 1mm pixel pitch, made of epitaxial ptype silicon. Thanks to design modularity, more sensors can be placed side by side without breaking pixel pitch. Flattened and unflattened photon beams, as well as proton radiation from a cyclotron in pencil beam scanning mode, were considered. Measurements of beam characteristics as percentage depth doses, dose profiles, output factors and energy response, which are necessary to deliver radiation with high precision and reliability, were performed.Results:Dose rate independence with photons was verified in the dose per pulse range 0.03 to 2mGy. Results clearly indicate nondependence of the detector sensitivity both for flattened and unflattened beams, with a variation of at most 0.5percentage. OFs were obtained for field with a lateral size ranging from 0.8cm to 16cm and the results are in good agreement with ion chamber A1SL, max difference less than 1.5percentage. Field sizes and beam penumbra were measured and compared to EBT film results. Concerning proton beams, sensitivity independence on dose rate was verified by changing the beam current in the interval 2‐130Gy/s. Field sizes and beam penumbra measurements are in agreement with data taken with a scintillating 2D array with 0.5mm resolution IBA Lynx, and a better penumbra definition than an array of ionization chambers IBA MatriXX is reached.Conclusion:The device is a novel and valuable tool for QA both for photon and proton dose delivery. All measurements demonstrated its capability to measure with high spatial resolution many crucial properties of the RT beam.

Purpose/Objective(s): During the last decade silicon dosimeters have found a wide application in radiation therapy due to the dose escalation in the tumor volume which demands accurate quality assurance programs. Silicon devices offer higher spatial resolution and higher performances than other commercial dosimeters like ion chambers, which suffer of limited spatial resolution, and gafchromic films, which are not real time detectors. In this article a novel epitaxial silicon array is described to demonstrate its suitability for measuring the dose properties of photon beams used in stereotactic treatments, Intensity Modulated (IMRT), and Volumetric Modulated Arc Therapy (VMAT) . Materials/Methods: The linear array prototype studied in this work is based on a 64-pixels monolithic silicon sensor made of epitaxial p-type silicon. Array length and pitch are 64mm and 1mm respectively. Sensor design is modular, and more sensors can be placed side by side without breaking pixel pitch. The prototype has four sensors mounted on a printed circuit board and connected to an electrometer based on TERA06 chips. All the pixels of the two central modules are connected to readout electronics. Due to the limited number of readout channels of this prototype (180), only 26 channels have been selected from each external module, with 2mm pitch. A full dosimetric characterization of the detector was performed and the application of the device in the dosimetric verification of clinical plans were verified. Results: Accurate measurements of the dose characteristics of beams as percentage depth doses, beam profiles, output factors and energy response, which are necessary to deliver radiation with high precision and in a trusted manner, were performed. Dose rate independence was verified irradiating the device with flattened and unflattened beams, varying dose per pulse in the range 0.03-2mGy. Results clearly indicate non-dependence of the detector sensitivity on the dose rate in all explored ranges both for flattened and unflattened beams with a variation of at most 0.5%. OFs were obtained for field with a lateral size ranging from 0.8cm to 16cm and the results are in good agreement with ion chamber A1SL (max difference < 1.5%) Field sizes and beam’s penumbra were measured and compared to those of EBT film. Eventually measured dose’s profile were compared with ones predicted by Pinnacle and Monaco TPS showing an excellent characterization of high modulated profiles. Conclusions: The device is a novel and valuable tool for QA in IMRT, VMAT, and especially for stereotactic dose delivery. In fact, all measurements demonstrated the device’s capability to measure with high spatial resolution many crucial properties of the RT beams. Moreover they show the high temporal resolution capability of the detector readout system, which allows to investigate the temporal dose pattern of IMRT and VMAT deliveries. Author Disclosure: C. Talamonti: None. M. Zani: None. D. Menichelli: None. F. Friedl: None. M. Scaringella: None. M. Bruzzi: None. M. Bucciolini: None.

Intensity modulated radiotherapy poses specific constraints in dosimetry due to the occurrence of: small radiation fields with high dose gradients; variation in space and time of the dose rate; variation in space and time of the beam energy spectrum. Our goal is to develop a silicon device adequate for coping these strict conditions. To this purpose we have studied various Si materials in terms of their thickness, resistivity and conductivity type, to determine the best radiation tolerant material. Independence on accumulated dose, ensuring radiation tolerance and thus needing no recalibration, was achieved both with thin and epitaxial Si diodes. A monolithical device designed and manufactured by us on epitaxial p-type silicon has been characterized under an IMRT field for prostate treatment. Our device is characterized by much larger spatial resolution than conventional ones and ability to directly measure temporal variations in dose modulation during plan verification.

With the commissioning of the LHC in 2010 and upgrades expected in 2015, ATLAS and CMS are planning to upgrade their innermost tracking layers with radiation hard technologies. Chemical Vapor Deposition diamond has been used extensively in beam conditions monitors as the innermost detectors in the highest radiation areas of BaBar, Belle, CDF and all LHC experiments. This material is now being considered as a sensor material for use very close to the interaction region where the most extreme radiation conditions exist. Recently the RD42 collaboration constructed, irradiated and tested polycrystalline and single-crystal chemical vapor deposition diamond sensors to the highest fluences expected at the super-LHC. We present beam test results of chemical vapor deposition diamond up to fluences of 1.8×1016 protons/cm2 illustrating that both polycrystalline and single-crystal chemical vapor deposition diamonds follow a single damage curve. We also present beam test results of irradiated complete diamond pixel modules.

Clinical dosimetry in radiotherapy is a well known matter but high conformal radiotherapy modalities (Intensity Modulated Radiation Therapy (IMRT), stereotactic treatments with photons and protons, Intensity Modulated Proton Therapy (IMPT)) possess problems due to small radiation fields with high dose gradients, variation in space and time of the dose rate and variation in space and time of the beam energy spectrum.A modular dosimetric detector, adequate for 2D pre-treatment dose verifications, has been developed in the framework of the European Integrated project MAESTRO. The detector is a monolithic segmented sensor obtained by n-type implantation on a 50 mu thick epitaxial silicon p-type layer: this is later used to guarantee improved radiation hardness of the device against the accumulated dose. The detector is composed of a matrix of 21 x 21 pixels with a size of 2 x 2 mm(2) each and a 3 mm center-to-center distance.A full dosimetric characterization of the detector was performed with photon and proton beams and with gammas from a Co-60 unit. Results have been compared with those obtained with a Farmer and a CC13 Scanditronix/Welhoffer ion chamber as well as with the silicon matrix MapCHECK (TM). The first application of the MAESTRO prototype in the dosimetric verification of a clinical IMRT field is also reported. Results show that our modular detector represents a valuable tool for quality assurance in IMRT dose delivery and for high precision radiotherapy techniques. (C) 2011 Elsevier B.V. All rights reserved.

Hadron therapy for tumor treatment is nowadays used in several medical centres. The main advantage in using protons or light ions beams is the possibility of tightly shaping the radiation dose to the target volume. Presently the spatial accuracy of the therapy is limited by the uncertainty in stopping power distribution, which is derived, for each treatment, from the photon attenuation coefficients measured by X-ray tomography. A direct measurement of the stopping powers will help in reducing this uncertainty. This can be achieved by using a proton beam and a detection system able to reconstruct a tomography image of the patient.As a first step towards such a system an apparatus able to perform a proton transmission radiography (pCR) has been designed. It consists of a silicon microstrip tracker, measuring proton trajectories, and a YAG:Ce calorimeter to determine the particle residual energy. Proton beam and laboratory tests have been performed on the system components prototypes: the main results will be shown and discussed. (C) 2010 Elsevier B.V. All rights reserved.

A zero-bias thermally stimulated currents (ZB-TSC) study has been carried out on n-type magnetic Czochralski silicon diodes irradiated with neutrons in the (1MeV equivalent neutron) fluence range of Φ=1013–1015neq/cm2. In standard TSC, deep-level emissions can be analyzed as long as they are clearly distinguishable from the background current, which increases exponentially during the heating scan. On the contrary, in ZB-TSC this problem is overcome because background current is negligible. As an example, at Φ=1015neq/cm2, we found a maximal temperature of investigation with standard TSC close to ∼150K, while with ZB-TSC this value is higher than 250K. Moreover, ZB-TSC can be used to evidence the complex structured electric field profile due to charged defects in the irradiated material. Therefore, ZB-TSC results in a very useful tool to characterize radiation damage in heavily irradiated silicon detectors, permitting both to explore the whole band gap and to obtain information about the residual electric field profile. Our ZB-TSC measurements showed the presence of radiation-induced deep levels in the range 0.37–0.51eV, while no deeper levels were found.

Proton radiation therapy is a precise form of cancer therapy, which requires verification of the patient position and the accurate knowledge of the dose delivered to the patient. At present in the proton treatment centre, patients are positioned with X-ray radiography and dose calculations rely on the patient's morphology and electron densities obtained by X-ray computed tomography [U. Schneider, E. Pedroni, Med. Phys. 22 (1995) 353]. A proton imaging device can improve the accuracy of proton radiation therapy treatment planning and the alignment of the patient with the proton beam. Our collaboration has developed a pCR prototype consisting of a silicon microstrip tracker and a calorimeter to detect the residual energy [R. Shulte, et al., IEEE Trans. Nucl. Sci. 51 (2004) 866–872]. In this contribution we will show some results obtained testing the front-end board of the tracker and measurements performed at LNS (Laboratori Nazionali del Sud) and in LLUMC (Loma Linda University Medical Centre) using 60 and 200 MeV proton beams to test the calorimeter.