Pre-irradiation Dose Research Articles

Intrafraction organ movement in adaptive MR-guided radiotherapy of abdominal lesions – dosimetric impact and how to detect its extent in advance

IntroductionMagnetic resonance guided radiotherapy (MRgRT) allows daily adaptation of treatment plans to compensate for positional changes of target volumes and organs at risk (OARs). However, current adaptation times are relatively long and organ movement occurring during the adaptation process might offset the benefit gained by adaptation. The aim of this study was to evaluate the dosimetric impact of these intrafractional changes. Additionally, a method to predict the extent of organ movement before the first treatment was evaluated in order to have the possibility to compensate for them, for example by adding additional margins to OARs.Materials & methodsTwenty patients receiving adaptive MRgRT for treatment of abdominal lesions were retrospectively analyzed. Magnetic resonance (MR) images acquired at the start of adaptation and immediately before irradiation were used to calculate adapted and pre-irradiation dose in OARs directly next to the planning target volume. The extent of organ movement was determined on MR images acquired during simulation sessions and adaptive treatments, and their agreement was evaluated. Correlation between the magnitude of organ movement during simulation and the duration of simulation session was analyzed in order to assess whether organ movement might be relevant even if the adaptation process could be accelerated in the future.ResultsA significant increase in dose constraint violations was observed from adapted (6.9%) to pre-irradiation (30.2%) dose distributions. Overall, OAR dose increased significantly by 4.3% due to intrafractional organ movement. Median changes in organ position of 7.5 mm (range 1.5–10.5 mm) were detected within a median time of 17.1 min (range 1.6–28.7 min). Good agreement was found between the range of organ movement during simulation and adaptation (66.8%), especially if simulation sessions were longer and multiple MR images were acquired. No correlation was determined between duration of simulation sessions and magnitude of organ movement.ConclusionIntrafractional organ movement can impact dose distributions and lead to violations of OAR tolerance doses, which impairs the benefit of daily on-table plan adaptation. By application of simulation images, the extent of intrafractional organ movement can be predicted, which possibly allows to compensate for them.

Distributed Optical Fiber-Based Radiation Detection Using an Ultra-Low-Loss Optical Fiber

The combination of an ultra-low-loss optical fiber sensitive to ionizing radiation and an optical time domain reflectometer (OTDR) is investigated to explore the feasibility of a single-ended distributed radiation detector. The peculiarity of the tested fiber resides in its regenerative high radiation-induced attenuation (RIA) response in the infrared spectrum (1310 nm), which returns to a low value once the irradiation has ended, combined to its sensitivity, highly increasing with the dose rate. In this work, only some sections of the fiber line were irradiated with 100 kV X-rays at room temperature, to prove the spatially resolved radiation detection capabilities of the system. The transient RIA response of the fiber was characterized at different pre-irradiation doses. A pre-irradiation treatment was shown to stabilize the optical fiber response, improving its RIA vs. dose rate linearity and repeatability. This improved response, in terms of radiation quantification, comes at the cost of a lower detection threshold. This work lays the bases for a distributed radiation detector, with some capabilities in dose rate evaluation.

Characterizing a PTW microDiamond detector in kilovoltage radiation beams.

The aim of this work was to characterize the dosimetric properties of the PTW microDiamond (60019) single crystal synthetic diamond detector (DD) in kilovoltage x-ray beams. The following characteristics were addressed in this study: required preirradiation dose, dose-rate linearity, energy dependence, and percent depth dose response of the DD. UWADCL x-ray beams, characterized by NIST-traceable ionization chambers, were used in this study. Preirradiation dose required by the DD, in order to stabilize the detector's response to within 0.1%, was quantitated. Dose-rate dependence was also investigated using the UW250-M and UW50-M beams, where the dose rate was varied by changing the tube current. and calibration coefficients for all the available M series beams at UWADCL were obtained to determine the energy dependence of the DD, Diode E, Diode P, and P11 parallel-plate ionization chamber. A custom-built water tank was utilized to measure the percent depth dose (PDD) response of the DD, Diode E, Diode P, and P11 chamber in UW250-M, UW100-M, and UW50-M beams. The measured PDD response of the detectors was compared with the simulated PDD data using EGSnrc Monte Carlo code. A 1.5Gy dose-to-water or air-kerma was found to be sufficient for the given DD's response to stabilize to within 0.1% in all of the beams used in this study. The dose-rate dependence parameter, Δ, was found to be 1.00±0.02 and 1.016±0.05 for the UW250-M and UW50-M beams, respectively. Relative to the Co calibration coefficients, the DD was found to under-respond relative to calculated absorbed dose to water response and over-respond relative to the calculated air-kerma response in the M-series beams. Agreement of 1.5% was found between the measured PDD values and Monte Carlo simulated PDD values for UW250-M, UW100-M, and UW50-M beams. In order to stabilize the response, the DD needs a preirradiation dose, which is unique to every DD. A linear relationship between detector response and dose rate was found within the evaluated uncertainty. An energy dependence of the DD was studied, which is more pronounced in the low-energy beams and can be partially attributed to the metal contact material around the sensitive volume of the DD. Overall, the DD was found to be suitable for kilovoltage x-ray dosimetry.

D2 retention behavior and microstructural evolution of W-2wt.%Y2O3 alloy during He-ion irradiation at high temperatures

In this study, we carried out the pre-irradiation of a dispersion-strengthened W-2wt.%Y2O3 alloy with good mechanical properties with high-energy Fe-ions instead of neutrons. The effect of this pre-irradiation on the D2 retention behavior of the alloy was investigated. A maximum of 1022 D/m2 was irradiated onto the samples using 5-keV D2 ions, and Fe pre-irradiation was carried out up to an ion fluence of 4 × 1018/m2 with 1 MeV energy. For comparison, commercial pure W was also studied. The Fe-ion pre-irradiation process increased the D2 retention in both pure W and the W–Y2O3 alloy. However, this D2 retention was independent of the pre-irradiation dose. In addition, the formation of He bubbles in the W–Y2O3 alloy caused by the irradiation at 1.8 × 1021 He/m2 and high temperatures of 773, 973, and 1173 K was also investigated. When the irradiation dose exceeded 1.5 × 1020 He/m2, visible He bubbles were formed, and He bubbles grew and void swelling increased with an increase in the irradiation dose. Compared to pure W, the W–Y2O3 alloy showed suppressed void swelling. This can be attributed to the dispersion of vacancies and He atoms due to the He irradiation.

Surface modification of SiO2 nanoparticles with PDMAEMA brushes and Ag nanoparticles as antifungal coatings using electron beam assisted synthesis

A model functional, stable and dispersible silver nanoparticles (AgNPs) immobilized on polymeric brushes grafted silica nanoparticle is proposed as antimicrobial additive for coating applications. The aim of this work is to modify silica nanoparticles (SiO2NPs) with poly 2-(dimethyl amino) ethyl methacrylate (PDMAEMA) brushes for template synthesis and immobilization of AgNPs using electron beam assisted grafting and reduction reactions. The PDMAEMA moieties were grafted onto vinyltrimethoxysilane (VTMS) modified SiO2NPs using pre-irradiation and peroxidation grafting approaches. Several grafting parameters, i.e., pre-irradiation doses, DMAEMA monomer concentrations, reaction times and temperatures, were studied to optimize degree of grafting (DG). AgNPs were constructed on the SiO2NPs through the grafted PDMAEMA brushes as polymer shell template. AgNPs were successfully created on SiO2NPs-VTMS-PDMAEMA by electron-induced reduction reaction. DG of the PDMAEMA on SiO2NPs-VTMS was confirmed by gravimetric measurement, FTIR, TGA, TEM, FE-SEM. The nanostructure information and AgNPs immobilization were revealed by UV–Vis, TEM, SEM-EDX and XRD. The optimized grafting degree to obtain desirable appearance was 190%. The AgNPs (6 ± 2 nm) on SiO2NPs-VTMS-PDMAEMA exhibited the characteristic UV-vis absorbance of spherical Ag nanoarchitecture around 418 nm. The AgNPs immobilized SiO2NPs-VTMS-PDMAEMA efficiently inhibited the growth of fungi, i.e., Aspergillus niger and Syncephalatrum racemosum found on building materials.

Влияние малых доз гамма-излучения на оптические свойства наноструктурированного кремния, полученного методом металл-стимулированного химического травления in situ

Влияние малых доз гамма-излучения на оптические свойства наноструктурированного кремния, полученного методом металл-стимулированного химического травления in situ

Immobilization of antimicrobial and anti-quorum sensing enzymes onto GMA-grafted poly(vinyl chloride) catheters

Catheter-associated infections still represent a challenging thread because of the likelihood of biofilm formation. The aim of this work was the surface modification of catheters to immobilize lysozyme and acylase under mild conditions while preserving antimicrobial and anti-quorum sensing performances. Glycidyl methacrylate (GMA) was grafted onto poly(vinyl chloride) (PVC) catheters by a pre-irradiation method. The effects of monomer concentration, pre-irradiation dose, reaction time, monomer concentration and reaction temperature were investigated. The grafting process was monitored using FTIR-ATR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and swelling data. Lysozyme was directly immobilized onto PVC-g-GMA maintaining the hydrolytic activity, which hindered Staphylococcus aureus adhesion. For acylase immobilization, the PVC-g-GMA catheters were reacted with ethylenediamine and glutaraldehyde in order to facilitate acylase covalent binding. Free acylase in solution demonstrated notably capability to act as quorum sensing inhibitor, as observed using Chromobacterium violaceum as biosensor, by degrading a wide variety of acylated homoserine lactones (AHLs), including those produced by Pseudomonas aeruginosa and Acinetobacter baumannii. Acylase-immobilized PVC-g-GMA catheters were challenged against degradation of AHLs and the activity monitored using both the biosensor and HPLC-MS. Relevantly, the functionalized catheters completely degraded all tested AHL signals, opening new ways of preventing biofilm formation on medical devices.

Dosimetric characterization of a single crystal diamond detector in X-ray beams for preclinical research

The aim of this study was to investigate a single crystal diamond detector, the microDiamond detector from PTW (PTW-Freiburg, Freiburg, Germany), concerning the particular requirements in the set-up and energy range used in small animal radiotherapy (RT) research (around 220kV). We tested it to find out the minimal required pre-irradiation dose, the dose linearity, dose rate dependency and the angular response as well as usability in the small animal radiation research platform, SARRP (Xstrahl Ltd., Camberley, UK).For a stable signal in the range of energies used in the study, we found a required pre-irradiation dose of 10Gy. The dose linearity and dose rate dependence measurements showed a very good performance of the microDiamond detector. Regarding the effect of angular dependency, the variation of the response signal is less than 0.5% within the first 15° of the polar angle. In the azimuthal angle, however, there are differences in detector response up to 20%, depending on the range of energies used in the study. In addition, we compared the detector to a radiosensitive film for a profile measurement of a 5×5mm2 irradiation field. Both methods showed a good accordance with the field size, however, the film has a steeper dose gradient in the penumbra region but also a higher noise than the microDiamond detector.We demonstrated that the microDiamond detector is a useful measurement tool for small animal RT research due to its small size. Nevertheless, it seems to be very important to verify the response of the detector in the given set-up and energy range.

Suitability of microDiamond detectors for the determination of absorbed dose to water around high-dose-rate 192 Ir brachytherapy sources.

Experimental dosimetry of high-dose-rate (HDR) 192 Ir brachytherapy (BT) sources is complicated due to high dose and dose-rate gradients, and softening of photon energy spectrum with depth. A single crystal synthetic diamond detector microDiamond (PTW 60019, Freiburg, Germany) has a small active volume, high sensitivity, direct readout, and nearly water-equivalent active volume. The purpose of this study was to evaluate the suitability of microDiamond detectors for the determination of absorbed dose to water around HDR 192 Ir BT sources. Three microDiamond detectors were used, allowing for the comparison of their properties. In-phantom measurements were performed using microSelectron and VariSource iX HDR 192 Ir BT treatment units. Their treatment planning systems (TPSs), Oncentra (v. 4.3) and BrachyVision (v. 13.6), respectively, were used to create irradiation plans for a cubic PMMA phantom with the microDiamond positioned at one of three source-to-detector distances (SDDs) (1.5, 2.5, and 5.5cm) at a time. The source was stepped in increments of 0.5cm over a total length of 6cm to yield absorbed dose of 2Gy at the nominal reference-point of the detector. Detectors were calibrated in 60 Co beam in terms of absorbed dose to water, and Monte Carlo (MC) calculated beam quality correction factors were applied to account for absorbed-dose energy dependence. Phantom correction factors were applied to account for differences in dimensions between the measurement phantom and a water phantom used for absorbed dose calculations made with a TPS. The same measurements were made with all three of the detectors. Additionally, dose-rate dependence and stability of the detectors were evaluated in 60 Co beam. The percentage differences between experimentally determined and TPS-calculated absorbed doses to water were from -1.3% to +2.9%. The values agreed to within experimental uncertainties, which were from 1.9% to 4.3% (k=2) depending on the detector, SDD and treatment delivery unit. No dose-rate or intrinsic energy dependence corrections were applied. All microDiamonds were comparable in terms of preirradiation dose, stability of the readings and energy response, and showed a good agreement. The results indicate that the microDiamond is potentially suitable for the determination of absorbed dose to water around HDR 192 Ir BT sources and may be used for independent verification of TPS's calculations, as well as for QA measurements of HDR 192 Ir BT treatment delivery units at clinical sites.

Dosimetric characteristics of four PTW microDiamond detectors in high-energy proton beams

Small diamond detectors are useful for the dosimetry of high-energy proton beams. However, linear energy transfer (LET) dependence has been observed in the literature with such solid state detectors. A novel synthetic diamond detector has recently become commercially available from the manufacturer PTW-Freiburg (PTW microDiamond type 60019). This study was designed to thoroughly characterize four microDiamond detectors in clinical proton beams, in order to investigate their response and their reproducibility in high LET regions. Very good dosimetric characteristics were observed for two of them, with good stability of their response (deviation less than 0.4% after a pre-irradiation dose of approximately 12 Gy), good repeatability (coefficient of variation of 0.06%) and a sensitivity of approximately 0.85 nC Gy−1. A negligible dose rate dependence was also observed for these two microDiamonds with a deviation of the sensitivity less than 0.7% with respect to the one measured at the reference dose rate of 2.17 Gy min−1, in the investigated dose rate range from 1.01 Gy min−1 to 5.52 Gy min−1. Lateral dose profile measurements showed the high spatial resolution of the microDiamond oriented with its stem perpendicular to the beam axis and with its small sensitive thickness of about 1 μm in the scanning profile direction. Finally, no significant LET dependence was found with these two diamond dosimeters in comparison to a reference ionization chamber (model IBA PPC05). These good results were in accordance to the literature. However, this study showed also a non reproducibility between the devices in terms of stability, sensitivity and LET dependence, since the two other microDiamonds characterized in this work showed different dosimetric characteristics making them not suitable for proton beam dosimetry with a maximum difference of the peak-to-plateau ratio of 6.7% relative to the reference ionization chamber in a clinical 138 MeV proton beam.

Radiation induced emulsion graft polymerization of 4-vinylpyridine onto PE/PP nonwoven fabric for As(V) adsorption

A novel nonwoven fabric adsorbent having 4-vinylpyridine functional groups was prepared by using radiation-induced emulsion graft polymerization method and grafting 4-vinylpyridine monomer onto a polyethylene-coated polypropylene nonwoven fabric (NWF) in aqueous emulsion solution. The grafting conditions of the 4-vinylpyridine monomer onto the NWF were optimised and 150% Dg VP-g-NWF was prepared using 30 kGy pre-irradiation dose, 5% VP monomer concentration and 0.5% (w/w) Tween 20 in aqueous emulsion. Grafted 4-vinylpyridine chains on the NWF were then quaternized for the preparation of QVP-g-NWF adsorbent. All fabric structures were characterized by using Fourier-transform infrared spectrometer, x-ray photoelectron spectrometer and scanning electron microscope. QVP-g-NWF adsorbent was used in batch adsorption experiments for As(V) ions by studying the pH, contact time, and initial As(V) ion concentration parameters. Results showed that QVP-g-NWF adsorbent has significant As(V) adsorption and experimental As(V) adsorption capacity was 98.04mg As(V)/g polymer from 500mg/L initial As(V) concentration at pH 7.00.

Synthesis and characterization of stimuli-responsive polypropylene containing N-vinylcaprolactam and N-vinylimidazole obtained by ionizing radiation

Polypropylene films were grafted with thermo-responsive N-vinylcaprolactam and pH-responsive N-vinylimidazole polymers by means of gamma radiation using pre-irradiation and direct methods, in order to functionalize the films with thermo- and/or pH-responsiveness. The dependence of grafting yield on parameters such as co-monomer concentration, pre-irradiation dose, temperature, and reaction time was evaluated. The samples were characterized by Fourier transform infrared and X-ray photoelectron spectroscopies, differential scanning calorimetry, thermogravimetric analysis, swelling studies in different solvents, and water contact angle. The grafted copolymers presented thermo- and pH-sensitiveness, highlighting their potential as advanced biomaterials, capable of providing adequate environment for hosting and sustained release of antimicrobial drugs bearing cationic moieties, such as groups of diclofenac, while still exhibiting good cytocompatibility.

New approach for a reliable in vitro sun protection factor method - Part II: Practical aspects and implementations.

Our previous paper (Part I: Principle and mathematical aspects) presented a new reliable in vitro sun protection factor (SPF) method and demonstrated it to be reproducible and correlated with the in vivo method. Nevertheless, the relevance of an international method should to be adaptable to all products on the market and demonstrated with a blind test. Thus, the aim of this second article was to focus on the practical aspects and implementation (Part II) of a large population of different commercially available sunscreen formulations to obtain similar in vivo SPF results for the purpose of labelling. The method uses the spectroradiometric measurement of residual ultraviolet (UV) through the sample that was applied on a substrate with a robotic appliance. The method has been demonstrated to be highly reliable, and it is based on a multisubstrate solution with a single UV pre-irradiation dose. Furthermore, different categories of the product were studied to identify a reliable and universal in vitro SPF method. Based on different sunscreens products classified into 5 different groups (emulsion, oil, alcohol, stick and powder), it was demonstrated that our method has good reproducibility and accuracy compared with the clinical SPF method. Indeed, the mean coefficient of variation (CV%) was approximately 7%, and the coefficient of correlation reached approximately 0.8-1.0 for different types of tested products. Our second paper concludes that the new in vitro SPF method (based on 113 sunscreen products from the Parts I and II) is clearly adaptable for the SPF labelling purpose on any product type because it is non-invasive, less expensive, more practical and more reliable if performed under strict conditions.

In vitro hemocompatibility of sulfonated polypropylene non-woven fabric prepared via a facile γ-ray pre-irradiation grafting method

Sulfonated polypropylene non-woven fabric (PPNWF) was successfully prepared via γ-ray pre-irradiation-induced graft polymerization of sodium styrenesulfonate (SSS) and acrylamide (AAm). The effect of pre-irradiation dose, reaction temperature, reaction time and concentration of binary monomer on the degree of grafting (DG) was studied. The chemical structure of the original and modified PPNWF materials were investigated by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to confirm the successful introduction of sulfonated (SO3−) group. The wettability was examined via measurement of de-ionized water adsorption percentage, which demonstrated that the hydrophilicity of PPNWF was greatly enhanced after graft modification. A little amount of bovine serum albumin (BSA) adsorption and nearly no platelet adhesion on the surface of modified PPNWF and low hemolytic ratio of the modified PPNWF revealed that the sulfonated PPNWF exhibited good hemocompatibility. Besides, blood clotting time measurement indicated that the anticoagulant property of PPNWF was effectively enhanced via SSS modification. Consequently, the hydrophilicity, in vitro hemocompatibility and anticoagulant effect of PPNWF were significantly improved by γ-ray pre-irradiation-induced graft polymerization of SSS.

Singly and binary grafted poly(vinyl chloride) urinary catheters that elute ciprofloxacin and prevent bacteria adhesion

Acrylic acid (AAc) and poly(ethylene glycol) methacrylate (PEGMA) were singly and dually grafted onto poly(vinyl chloride) (PVC) urinary catheters with the aim of preventing biofouling by endowing the catheters with the ability to load and release antimicrobial agents and to avoid bacteria adhesion. The polymers were grafted applying an oxidative pre-irradiation (60Co source) method in two steps. Grafting percentage and kinetics were evaluated by varying the absorbed pre-irradiation dose, reaction time, monomer concentration, and reaction temperature. Catheters with grafting percentages ranging from 8 to 207% were characterized regarding thermal stability, surface hydrophilicity, mechanical properties, swelling, and lubricity. The modified catheters proved to have better compatibility with fibroblast cells than PVC after long exposure times. Furthermore, grafted catheters were able to load ciprofloxacin and sustained its release in urine medium for several hours. Ciprofloxacin-loaded catheters inhibited the growth of Escherichia coli and Staphylococcus aureus in the catheter surroundings and prevented bacteria adhesion.

Grafting of N‐vinyl caprolactam and methacrylic acid onto silicone rubber films for drug‐eluting products

ABSTRACTSilicone rubber (SR), a material widely used in the biomedical field, was modified with stimuli‐responsive poly(N‐vinyl caprolactam) (PVCL) and poly(methacrylic acid) (PMAA) with the aim of improving its ability to host drug molecules. The grafting of PVCL and PMAA onto SR was carried out by means of a γ‐ray preirradiation method, and the dependence of the grafting yield on the comonomer concentration, preirradiation dose, temperature, and reaction time was evaluated. Modified SR films were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and swelling studies to confirm the grafting of the copolymer. The SR‐g‐[vinyl caprolactam (VCL)/methacrylic acid (MAA)] copolymers showed a sensitivity to the temperature and pH, high hemocompatibility, and low affinity to bovine serum albumin and fibrinogen proteins. Moreover, the SR‐g‐(VCL/MAA) copolymers were able to host some nonsteroidal anti‐inflammatory drugs, such as diclofenac and ibuprofen, and the antifungal agent nystatin. The graft copolymer was shown to be useful for providing sustained release for several hours; this indicates that the modified SR is a promising material for drug‐eluting medical devices. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41855.

Radiation induced synthesis of (gelatin-co-PVA)-g-poly (AAc) copolymer as wound dressing material

Copolymers of gelatin and poly (vinyl alcohol), (PVA) grafted by acrylic acid (AAc) with excellent water absorption and retention abilities under neutral conditions were successfully synthesized using <TEX>$^{60}Co$</TEX> gamma radiations in presence of ammonium persulphate (APS), as water soluble initiator and sodium bicarbonate (<TEX>$NaHCO_3$</TEX>) as foaming agent. The optimum synthesis conditions pertaining to maximum swelling percentage were evaluated as a function of gelatin/PVA ratio, amount of water, concentration of APS, <TEX>$NaHCO_3$</TEX>, monomer concentration and total irradiation dose. Maximum percent swelling (1694.59%) of the copolymer, gelatin-co-PVA, was obtained at optimum <TEX>$[APS]=2.92{\times}10^{-1}mol/L$</TEX>, <TEX>$[NaHCO_3]=7.94{\times}10^{-2}mol/L$</TEX> and 1.5 mL of water at total dose of 31.104 kGy while in case of grafted copolymer, (gelatin-co-PVA)-g-poly(AAc), maximum percent swelling (560.86%) was obtained using <TEX>$8.014{\times}10^{-1}mol/L$</TEX> of AAc in 9 mL water with 31.104 kGy preirradiation dose. The pristine and grafted copolymers were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Scanning electron Microscopy (SEM), Thermal gravimetric analysis (TGA) and X-Ray Diffraction (XRD) methods. The copolymers loaded with an antiseptic, Povidone, were used as wound dressing materials for wounded gastrocnemius muscle of mice and the results exhibit that (gelatin-co-PVA)-g-poly (AAc) copolymer is a potent wound dressing material as compared to the copolymer.

Dosimetric characterization of a synthetic single crystal diamond detector in a clinical 62 MeV ocular therapy proton beam

A synthetic single crystal diamond based Schottky photodiode was tested at INFN-LNS on the proton beam line (62MeV) dedicated to the radiation treatment of ocular disease. The diamond detector response was studied in terms of pre-irradiation dose, linearity with dose and dose rate, and angular dependence. Depth dose curves were measured for the 62MeV pristine proton beam and for three unmodulated range-shifted proton beams; furthermore, the spread-out Bragg peak was measured for a modulated therapeutic proton beam. Beam parameters, recommended by the ICRU report 78, were evaluated to analyze depth-dose curves from diamond detector. Measured dose distributions were compared with the corresponding dose distributions acquired with reference plane-parallel ionization chambers. Field size dependence of the output factor (dose per monitor unit) in a therapeutic modulated proton beam was measured with the diamond detector over the range of ocular proton therapy collimator diameters (5–30mm). Output factors measured with the diamond detector were compared to the ones by a Markus ionization chamber, a Scanditronix Hi-p Si stereotactic diode and a radiochromic EBT2 film. Signal stability within 0.5% was demonstrated for the diamond detector with no need of any pre-irradiation dose. Dose and dose rate dependence of the diamond response was measured: deviations from linearity resulted to be within ±0.5% over the investigated ranges of 0.5–40.0Gy and 0.3–30.0Gy/min respectively. Output factors from diamond detector measured with the smallest collimator (5mm in diameter) showed a maximum deviation of about 3% with respect to the high resolution radiochromic EBT2 film. Depth-dose curves measured by diamond for unmodulated and modulated beams were in good agreement with those from the reference plane-parallel Markus chamber, with relative differences lower than ±1% in peak-to-plateau ratios, well within experimental uncertainties. A 2.5% variation in diamond detector response was observed in angular dependence measurements carried-out by varying the proton beam incidence angle in the polar direction. The dosimetric characterization of the tested synthetic single crystal diamond detector clearly indicates its suitability for relative dosimetry in ocular therapy proton beams, with no need of any correction factors accounting for dose rate and linear energy transfer dependence.

γ-Ray Pre-Irradiated Grafting of Polytetrafluoroethylene Film Membrane

The changes induced by γ-ray pre-irradiated grafting of polytetrafluoroethylene (PTFE) with alkalo-amines such as Monoethanolamine (MEA), Diethanolamine (DEA) and Methyldiethanolamine (MDEA) solvents were investigated. Samples of the commercially available fluoropolymer, i.e. PTFE film membranes were irradiated with 60Co source γ-radiation with absorbed doses of 30 to 90 kGy. Effects of the grafting conditions of the amines onto the pre-irradiated PTFE, such as grafting time, reaction temperature and pre-irradiation doses on the resulting grafting yield are reported. The grafted PTFE was characterized by the FT-IR spectroscopy and FESEM.The gravimeteric analysis showed that the maximum grafting yield obtained is 2.9% for the 30 kGy irradiated MDEA grafted PTFE (MDEA-g-PTFE) at 10 min grafting time. However, at 60 min grafting time the maximum grafting yield reduced to 1.05% for the same sample. Consequently, therefore, for the low dose γ-ray pre-irradiated samples, the effects of applied dose and grafting time were found to be remarkably insignificant.

Radiochemical Graft Copolymerization and Characterization of Acrylate Monomers on to Polyethylene Film

Functionalization of polyethylene (PE) film by radiation-induced graft copolymerization of ethyl acrylate (EA) and ethyl methacrylate (EMA) has been carried out using a preirradiation technique to develop materials with different degrees of grafting for use in ion separation processes. The influence of reaction conditions such as preirradiation dose, monomer concentration, reaction time and amount of solvent on percentage of grafting (Pg) has been studied and maximum Pg values of EA (144.97%) and EMA (142.35%) were respectively obtained at [EA] = 0.92 mol/L, [EMA] = 0.80 mol/L, total dose = 14.4 kGy and 17.28 kGy at 100 °C in 120 and 180 min. The effect of different monohydric alcohols of varying chain lengths on Pg has also been studied. The modified films have been characterized by FTIR, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. Some selective properties of pristine and grafted PE film such as swelling and ion uptake studies have also been investigated. The grafted films showed better swelling and ion uptake capacity in comparison to the pristine film.