Abstract.  A new monolithic silicon DE-E telescope was evaluated in un-modulated and modulated 100 MeV proton beams used for hadron therapy. Compared to a classical microdosimetry detector, which provides only one-dimensional information on lineal energy of charged particles, this detector system provides two-dimensional information on lineal energy and particle energy based on energy depositions, collected in coincidence, within the DE and E stages of the detector.  We investigated the possibility to use the information obtained with the DE-E telescope to determine the relative biological effectiveness (RBE) at defined location within the proton beam. An RBE matrix based on established in-vitro V79 cell survival data was developed to link the output of the device directly to RBE(a), the RBE in the low-dose limit, at various depths in a homogeneous polystyrene phantom. In the spread-out Bragg peak (SOBP) of a 100 MeV proton beam, the RBE(a) increased from 3.8 at the proximal SOBP to a maximum value of 4.9 at the distal edge.  The DE-E telescope, with its high spatial resolution, has potential applications to biologically-weighted hadron treatment planning as it provides a compact and portable means for estimating the RBE in rapidly changing hadron radiation fields within phantoms. Additional applications in radiation protection are also possible and are discussed. 

Abstract: This work provides information pertaining to the performance of Silicon-On-Insulator (SOI) microdosimeters in heavy ion radiation fields. SOI microdosimeters have been previously tested in light ion radiation fields for both space and therapeutic applications, however their response has not been established in high energy, heavy ion radiation fields which are experienced in space. Irradiations were completed at the NASA Space Radiation Laboratory at BNL using 0.6 GeV/u Fe and 1.0 GeV/u Ti ions. Energy deposition and lineal energy spectra were obtained with this device at various depths within a Lucite phantom along the central axis of the beam. The response of which was compared with existing proportional counter data to assess the applicability of SOI microdosimeters to future deployments in space missions.

Abstract: Measurements were performed to assess the dose equivalent outside a primary proton treatment field, using a silicon-on-insulator
SOI microdosimeter. The SOI microdosimeter was placed on the surface of an anthropomorphic phantom and dose equivalents were determined as a function of lateral distance from a typical passively scattered and modulated prostate treatment field. Measurements were also completed within a polystyrene plate phantom as a function of depth for a distance of 5 cm from the field edge, as function of lateral distance from field edge at two different depths, and as a function of distance from the distal edge on the central beam axis. The dose equivalent at the surface of the anthropomorphic phantom decreases from 3.9 to 0.18 mSv/Gy when the lateral distance from the proton field edge increases from 2.5 to 60 cm. Measurements along the proton depth dose distribution at a constant distance of 5 cm from the primary field edge indicate a decrease in dose equivalent as a function of depth, with a 38% decrease relative to the surface dose at a depth of 5 cm in polystyrene. Measurements completed as a function of lateral distance from the primary field at two separate depths within polystyrene illustrate a convergence of the dose equivalent at approximately 20 cm from the primary field edge. Past the distal edge of the spreadout Bragg peak dose equivalents decrease exponentially for increasing distance, with an initial value of 1.6 mSv/Gy at 0.6 cm from the distal edge. Silicon microdosimetry measurements were also compared with published results obtained utilizing different measurement techniques. This study demonstrates the applicability of SOI microdosimetry in determining the dose equivalent outside proton treatment fields, and provides valuable information on the dose equivalent both at the surface and at depth experienced by prostate cancer patients treated with protons.

Abstract: Semiconductor planar processing technology has spurned the development of novel radiation detectors with applications in space, high energy physics, medical diagnostics, radiation protection and cancer therapy. The ANSTO heavy ion microprobe, which allows a wide range of ions to be focused into spot sizes of a few micrometers in diameter, has proven to be an essential tool for characterising these detectors using the Ion Beam Induced Charge (IBIC) imaging technique. The use of different ions and the wide range of available energies on the heavy ion microprobe, allows the testing of these devices with ionising particles associated with different values of linear energy transfer (LET). Quadruple coincidence measurements have been used to map the charge collection characteristics of a monolithic DE–E telescope. This was done through simultaneous measurement of the spatial coordinates of the microbeam relative to the sample and the response of both detector elements. The resulting charge collection maps were used to better understand the functionality of the device as well as to ascertain ways in which future device designs could be modified to improve performance.

Abstract: The development of microdosimeters and particle telescopes is important for risk assessment in space and aviation applications. The charge collection properties of a monolithic particle telescope, suitable for both microdosimetry and fluence based approaches, were studied using an ion microprobe.

Abstract: An ion-counting nanodosemeter (ND) yielding the distribution of radiation-induced ions in a low-pressure gas within a millimetric, wall-less sensitive volume (SV) was equipped with a silicon microstrip telescope that tracks the primary particles, allowing correlation of nanodosimetric data with particle position relative to the SV. The performance of this tracking ND was tested with a broad 250 MeV proton beam at Loma Linda University Medical Center. The high-resolution tracking capability made it possible to map the ion registration efficiency distribution within the SV, for which only calculated data were available before. It was shown that tracking information combined with nanodosimetric data can map the ionisation pattern of track segments within 150 nm-equivalent long SVs with a longitudinal resolution of 5 tissue-equivalent nanometers. Data acquired in this work were compared with results of Monte Carlo track structure simulations. The good agreement between ‘tracking nanodosimetry’ data acquired with the new system and simulated data supports the application of ion-counting nanodosimetry in experimental track-structure studies.

Abstract: Microdosimetry spectra obtained experimentally utilizing a Silicon-On-Insulator (SOI) microdosimeter within biological materials, was used to provide information on secondary radiation spectra at tissue boundaries. Comparative GEANT4 simulations of the experimental conditions were also conducted.

Abstract: The goal of this project is to develop and test in space a solid-state microdosimeter to directly assess astronaut risk to an unknown mixed radiation field. The instrument is rugged, has low power (< 1.25W), has low mass, and utilizes low voltages (± 5V). A microdosimeter can determine in real time dose equivalent in sieverts which is the regulatory quantity used to evaluate risk and limits of radiation exposure. The lineal energy spectrum that it measures can be multiplied by lineal-energy-dependent regulatory quality factors to determine dose equivalent. An early version of the instrument (MIDN on MidSTAR-I) has been designed and built for inclusion in the MidSTAR-1 USNA student built satellite to be launched in late fall 2006. The instrument is now undergoing test and minor modifications. The DoD Space Experiment Review Board (SERB) has also identified the MIDN instrument as a candidate for inclusion on the International Space Station as an express rack payload for radiation shielding studies.

Abstract: In hadron therapy the spectra of secondary particles can be very broad in type and energy. The most accurate calculations of tissue equivalent (TE) absorbed dose and biological effect can be achieved using Monte Carlo (MC) simulations followed by the application of an appropriate radiobiological model. The verification of MC simulations is therefore an important quality assurance (QA) issue in dose planning. We propose a method of verification for MC dose calculations based on measurements of either the integral absorbed dose or the spectra of deposited energies from single secondary particles in non-TE material detectors embedded in a target of interest (phantom). This method was tested in boron neutron capture therapy and fast neutron therapy beams.

Abstract: As we move into the new millennium, it is important that we improve our understanding of radiation effects on humans and nanoelectronic systems. This understanding is essential in a number of areas including radiation therapy for cancer treatment and extended human presence in outer space. Nanodosimetry in low-pressure gases enables measurement of the energy deposition of ionizing radiation on a scale equivalent to the dimensions of the DNA molecule. This is extremely important for not only biological applications but also electronic applications, as the effect of radiation on nanoelectronics needs to be determined before they are installed and deployed in complex radiation fields. However, before nanodosimetry can be widely applied, further investigation is required to link the output of gas-based nanodosimeters to the actual effect of the radiation on a biological or electronic system. The purpose of this research is to conduct nanodosimetric measurements of proton radiation fields at the proton accelerator of Loma Linda University Medical Center (LLUMC) and to develop a Monte Carlo simulation system to validate and support further developments of experimental nanodosimetry. To achieve this, measured ion cluster size distributions are compared to the output from the Monte Carlo simulation system that simulates the characteristics of the LLUMC beam line and the performance of the nanodosimeter installed on one of LLUMC’s proton research beam lines. As we move into the new millennium, it is important

Abstract: We present two methods of independently mapping the dimensions of the sensitive volume in an ion-counting nanodosimeter. The first method is based on a calculational approach simulating the extraction of ions from the sensitive volume, and the second method on probing the sensitive volume with 250 MeV protons. Sensitive-volume maps obtained with both methods are compared and systematic errors inherent in both methods are quantified.

Abstract: The microdosimetric spectra derived by silicon microdosimeter in a proton radiation field traversing heterogeneous structures were simulated using the GEANT4 toolkit.

Abstract: Conformal proton radiation therapy requires accurate prediction of the Bragg peak position. Protons may be more suitable than conventional x rays for this task since the relative electron density distribution can be measured directly with proton computed tomography has its own limitations, which need to be carefully studied before this technique can be introduced into routine clinical practice. In this work, we have used analytical relationships as well as the Monte Carlo simulation tool level observed in proton CT images of a cylindrical water phantom with embedded tissueequivalent density inhomogeneities, which were generated based on well with predictions based on Tschalar’s theory of energy loss straggling. The relationship between phantom thickness, initial energy, and the relative electron density resolution was systematically investigated to estimate the proton dose needed to obtain a given density resolution. We show that a reasonable density resolution can be achieved with a relatively small dose, which is comparable to or even lower than that of x-ray CT. sCTd. However, proton CTGEANT4 to study the principal resolution limits of proton CT.

Abstract:  Many new techniques for delivering radiation therapy are being developed for the treatment of cancer. One of these, proton therapy, is becoming increasingly popular because of the precise way in which protons deliver dose to the tumor volume. In order to achieve this level of precision, extensive treatment planning needs to be carried out to determine the optimum beam energies, energy spread (which determines the width of the spread-out Bragg peak), and angles for each patient’s treatment. Due to the level of precision required and advancements in computer technology, there is increasing interest in the use of Monte Carlo calculations for treatment planning in proton therapy. However, in order to achieve optimum simulation times, nonelastic nuclear interactions between protons and the target nucleus within the patient’s internal structure are often not accounted for or are simulated using less accurate models such as analytical or ray tracing. These interactions produce high LET particles such as neutrons, alpha particles, and recoil protons, which affect the dose distribution and biological effectiveness of the beam. This situation has prompted an investigation of the importance of nonelastic products on depth dose distributions within various materials including water, A-150 tissue equivalent plastic, ICRP (International Commission on Radiological Protection) muscle, ICRP bone, and ICRP adipose. This investigation was conducted utilizing the GEANT4.5.2 Monte Carlo hadron transport toolkit.

Abstract: The irradiation of various tissue-like materials by therapeutic proton beams was simulated using Monte Carlo. The contribution of inelastic reaction products to the depth-dose distribution was determined. The use of silicon microdosimeters for verifying Monte Carlo calculations was also investigated. The importance of these studies to Monte Carlo-based treatment planning systems is emphasized.

Abstract: Purpose: Microdosimetric measurements were performed at Massachusetts General Hospital to assess the dose equivalent external to passively delivered proton fields for various clinical treatment scenarios.  Method and Materials: Treatment fields evaluated included a prostate cancer field, cranial and spinal medulloblastoma fields, an ocular melanoma field, and a field for an intracranial stereotactic treatment.  Measurements were completed with patient-specific configurations of clinically relevant treatment settings using a silicon-on-insulator microdosimeter that was placed on the surface of and at various depths within a homogeneous Lucite phantom.  The dose equivalent and average quality factor was assessed as a function of both lateral displacement from the treatment field edge and distance downstream of the beam’s distal edge. Results: Dose equivalent values ranged from 8.3-0.3mSv/Gy (2.5-60cm lateral displacement) for a typical prostate cancer field, 10.8-0.58mSv/Gy (2.5-40cm lateral displacement) for the cranial medulloblastoma field, 2.5-0.58mSv/Gy (5-20cm lateral displacement) for the spinal medulloblastoma field, and 0.5-0.08mSv/Gy (2.5-10cm lateral displacement) for the ocular melanoma field.  Measurements of external field dose equivalent for the stereotactic field case exhibited differences as high as 50% depending on the modality of beam collimation.  Average quality factors derived from this work ranged from 2-7, with the value dependent on the position within the phantom in relation to the primary beam. Conclusions: This work provides a valuable and clinically relevant comparison of the external field dose equivalents for various passively scattered proton treatment fields.

Abstract: Evaluation and monitoring of the cancer risk from space radiation exposure is a crucial requirement for the success of long-term space missions. One important task in the risk calculation is to properly weigh the various components of space radiation dose according to their assumed contribution to the cancer risk relative to the risk associated with radiation of low ionization density. Currently, quality factors of radiation both on the ground and in space are defined by national and international commissions based on existing radiobiological data and presumed knowledge of the ionization density distribution of the radiation field at a given point of interest. This approach makes the determination of the average quality factor of a given radiation field a rather complex task. In this contribution, we investigate the possibility to define quality factors of space radiation exposure based on nanodosimetric data. The underlying formalism of the determination of quality factors on the basis of nanodosimetric data is described, and quality factors for protons and ions (helium and carbon) of different energies based on simulated nanodosimetric data are presented. The value and limitations of this approach are discussed.