Patent Application
20150050214
The present invention describes a novel composition of a three dimensional (3D) polymer, method of making the polymer and using the polymer for radiation treatment planning. More specifically it relates to radiation-induced polymerization of N-(Isobutoxymethyl) acrylamide normoxic 3D polymer gel dosimeters for planning of radiation treatment.
Over the past decade there has been a growing interest in the development 3D gel dosimeters to aid in the evaluation of the distribution and magnitude of absorbed dose in clinical radiation therapy. The most widely used dosimeter for verification of spatial dose distributions is the polyacrylamide gel (PAG) dosimeter (Fuxman A M, et al. 2005).
Schreiner et al. (2010) introduced polymer gels that are used as chemical dosimeters based on dose dependent radiation-induced polymerization and cross-linking of monomers in an irradiated volume. The changes were spatially localized in the volume by incorporating the initial monomers in an aqueous gel matrix in the dosimeter and can be probed by various imaging techniques such as magnetic resonance imaging (MRI), x-ray computed tomography (CT), and optical CT. As they are chemical dosimeters, polymer gels are sensitive to preparation conditions. The three dimensional dose readout is sensitive to the imaging modality and also to the technical conditions in use during specific scans.
Polymer gel dosimeters offer a wide range of potential applications in the three-dimensional verification of complex dose distribution such as in intensity-modulated radiotherapy (IMRT). However, polymer gel dosimeters have not been widely used in the clinic. One of the reasons is that they are difficult to manufacture. As the polymerization in polymer gels is inhibited by oxygen, all free oxygen has to be removed from the gels. For several years this was achieved by bubbling nitrogen through the gel solutions and by filling the phantoms in a glove box that is perfused with nitrogen. Recently another gel formulation was proposed in which oxygen is bound in a metallo-organic complex, thus removing the problem of oxygen inhibition. The proposed gel consists of methacrylic acid, gelatin, ascorbic acid, hydroquinone and copper (II)sulphate and is given the acronym MAGIC gel dosimeter. These gels are fabricated under normal atmospheric conditions and are therefore called ‘normoxic’ gel dosimeters. A chemical analysis on the MAGIC gel was performed by Deene and YD (2002). The composition of the gel was varied and its radiation response was evaluated. The role of different chemicals and the reaction kinetics were discussed. It was found that ascorbic acid alone was able to bind the oxygen and can thus be used as an anti-oxidant in a polymer gel dosimeter. It was also found that the anti-oxidants N-acetyl-cysteine and tetrakis(hydroxymethyl)phosphonium were effective in scavenging the oxygen. However, the rate of oxygen scavenging is dependent on the anti-oxidant and its concentration with tetrakis(hydroxymethyl)phosphonium being the most reactive anti-oxidant. Potentiometric oxygen measurements in solution provide an easy way to get a first impression on the rate of oxygen scavenging. It is shown that copper (II) sulphate operates as a catalyst in the oxidation of ascorbic acid; therefore the study proposes some new normoxic gel formulations that have a less complicated chemical formulation than the MAGIC gel. The important factor that can limit the wider use of MAGIC gel dosimeter is temperature, as gel melting can destroy 3D information.
The intra- and inter-batch accuracy and precision of MRI (polyacrylamide gelatin gel fabricated at atmospheric conditions)(PAGAT) polymer gel dosimeters was assessed in full 3D by Jan Vandecasteele et al. (2013). The intra-batch study showed high dosimetric precision (3.1%) notwithstanding poor accuracy (mean dose discrepancies up to 13.0%). In the inter-batch study, a similar dosimetric precision (4.3%) and accuracy (mean dose discrepancies up to 13.7%) were found. The poor dosimetric accuracy was attributed to a systematic fault that was related to the calibration method. Therefore, the dose maps were renormalized using an independent ion chamber dose measurement. It is illustrated that with this renormalization, excellent agreement between the gel measured and TPS calculated 3D dose maps is achievable: 97% and 99% of the pixels meet the 3%/3 mm criteria for the intra- and inter-batch experiments, respectively.
Three new polymer gel dosimeter recipes were investigated by R. J. Senden Pdjkbmaljs (2006). These may be more suitable for widespread applications than polyacrylamide gel dosimeters, since the extremely toxic acrylamide was replaced with the less harmful monomers including N-isopropylacrylamide (NIPAM), diacetone acrylamide and N-vinylformamide. The new gel dosimeters contained gelatin (5 wt %), monomer (3 wt %), N,N′-methylene-bis-acrylamide crosslinker (3 wt %) and tetrakis(hydroxymethyl)phosphonium chloride as antioxidant (10 mM). The NMR response (R2) of the dosimeters was analyzed for conditions of varying doses, dose rate, time post-irradiation, and temperature during irradiation and scanning. It was shown that the dose-response behavior of the NIPAM/Bis gel dosimeter is comparable to that of normoxic polyacrylamide gel (PAGAT) in terms of high dose-sensitivity and low dependence on dose rate and irradiation temperature, within the ranges considered. The dose-response (R2) of NIPAM/Bis appears to be linear over a greater dose range (up to 15 Gy) than the PAGAT gel dosimeter. The effects of time post-irradiation (temporal instability) and temperature during NMR scanning on the R2 response were more significant for NIPAM/Bis dosimeters.
Radiation sensitive gels have been used as dosimeters for clinical dose verification of different radiation therapy modalities. However, the use of gels is not widespread, because careful techniques are required to achieve the dose precision and accuracy aimed for in clinical dose verification. Crescentira et. al. (2007) introduces a gel dosimetry in a clinical environment is described, including the whole chain of customizations and preparations required to introduce magnetic resonance (MR) based gel dosimetry into clinical routine. In order to standardize gel dosimetry in dose verifications for radiosurgery and intensity modulated radiotherapy (IMRT), customization of the gel composition and the MR imaging parameters to increase its precision was addressed. The relative amount of the components of the normoxic, methacrylic acid based gel (MAGIC) was changed to obtain linear and steep dose response relationship. MR imaging parameters were customized for the different dose ranges used in order to lower the relative standard deviation of the measured transversal relaxation rate (R2). An optimization parameter was introduced to quantify the change in the relative standard deviation of R2 (σR2,rel) taking the increase in MR time into account. A 9% methacrylic acid gel customized for radiosurgery was found to give a linear dose response up to 40 Gy with a slope of 0.94 Gy−1 s−1, while a 6% methacrylic acid gel customized for IMRT had a linear range up to 3 Gy with a slope of 1.86 Gy−1 s−1. With the help of an introduced optimization parameter, the mean σR2, really was improved by 13% for the high doses and by 55% for low doses, without increasing MR time to unacceptable values. A mean dose resolution of less than 0.13 Gy has been achieved with the gel and imaging parameters customized for IMRT and a dose resolution from 0.97 Gy (at 5 Gy) to 2.15 Gy(at 40 Gy) for the radiosurgery dose range. While high dose precision was achieved, further work is required to achieve clinically acceptable dose accuracy.
Vandecasteele et. al. (2013) quantified some major physico-chemical factors that influence the validity of MRI (PAGAT) polymer gel dosimetry: temperature history (pre-, during and post-irradiation), oxygen exposure (post-irradiation) and volumetric effects (experiment with phantom in which a small test tube is inserted). Results confirm the effects of thermal history prior to irradiation. By exposing a polymer gel sample to a linear temperature gradient of ˜2.8° C. cm−1 and following the dose deviation as a function of post-irradiation time new insights into temporal variations were added. A clear influence of the temperature treatment on the measured dose distribution is seen during the first hours post-irradiation (resulting in dose deviations up to 12%). This effect diminishes to 5% after 54 hours post-irradiation. Imposing a temperature offset (maximum 6° C. for 3 hours) during and following irradiation on a series of calibration phantoms results in only a small dose deviation of maximum 4%. Surprisingly, oxygen diffusing in a gel dosimeter up to 48 hours post-irradiation was shown to have no effect. However, it is concluded that these physico-chemical effects are important factors that should be addressed to further improve the dosimetric accuracy of 3D MRI polymer gel dosimetry.
A major source of dosimetric inaccuracy in normoxic polymer gel dosimeters has local variations in the concentration of oxygen scavenger. Currently, a phosphorus compound, tetrakis(hydroxymethyl)phosphonium chloride (THPC) as an oxygen scavenger of choice is used in most polymer gel dosimetry studies conducted by Mahbod et. al. (2012). Reactions of THPC in a gel dosimeter are not limited to oxygen. It can possibly be consumed in reacting with gelling agent, water free-radicals and polymer radicals before, during and after irradiation, hence affecting the dose response of the dosimeter in several ways. These reactions are not fully known or understood. Experiments were conducted in an anoxic acrylamide-based gel dosimeter. Scanning electron microscopy results indicate gelatin pores decreasing from 40 to 70 μm and a very different radiation-induced polymer structure in samples containing THPC; Fourier-transform Raman spectroscopy shows a twofold reduction in the dose constants of monomer consumption; however, a significant change in the relative dose constants of monomer consumption as a function of dose could not be detected.
According to Steven Babic (2008), the RPC head phantom and optical CT-scanned FX gels can be used for accurate intensity-modulated radiation therapy dose verification in three dimensions. Radiochromic micelle gel dosimeters seem promising for three-dimensional (3D) radiation dosimetry because they can be read out by optical CT techniques and they have superior spatial stability compared to polymer and Fricke gel dosimeters according to Toljsakbm (2013). However, these are transparent gels and did not change color to indicate the effective treatment dose. Only turbid gels and emulsions with precipitated particles responded to radiation. Their results indicate that the color change was due to the oligomerization within precipitated PCDA crystals, and that liquid-phase emulsified PCDA did not undergo oligomerization. As a result, PCDA is not suitable for use in micelle gel dosimeters, and other radiochromic reporter molecules need to be identified. Unfortunately, all phantoms that were used experienced a color change were turbid and would be unsuitable for 3D dosimetry.
However, none of the above-discussed references discloses or suggests a relatively inexpensive but highly effective 3D polymer composition for dosimetric use. Accordingly, there exists a need in the art to overcome the deficiencies and limitations described herein above.
The present invention relates to normoxic polymer gel dosimeters containing N-(Isobutoxymethyl) (NIBMA) to make and use as a 3D gel dosimeter and to be used for radiation therapy planning.
In one embodiment, a 3D polymer gel composition comprises of Gelatin is between 2-5 g w/w % by weight; N-(Isobutoxymethyl)acrylamide (NIBMA) is between 1-2 w/w % by weight; N,N-methylene-bis-acrylamide (BIS) is between 1-4 w/w % by weight; glycerol as co-solvent is between 0-29 w/w % by weight; Trakis (hydroxymethyl)phosphonium chloride (THPC) concentration is between 1-20 mM and an Ultra-pure de-ionized water as a solvent and at least one of a glycerol, acetone and methanol as co-solvent to make a 3D gel dosimeter for planning a radiation treatment.
In another embodiment, the Trakis (hydroxymethyl)phosphonium chloride (THPC) concentration is 5 mM, gelatin is 4 g w/w % by weight, N,N-methylene-bis-acrylamide (BIS) 3 w/w % by weight, N-(Isobutoxymethyl)acrylamide (NIBMA) is 1.8 w/w % by weight.
In one embodiment, N-(iso-butoxymethyl) acrylamide (NIBMA), a homolog of N-methylolacrylamide (NMA), is the isobutyl ether of NMA. It contains a readily polymerizable vinyl group as well as a crosslinkable iso-butoxymethyl group.
In another embodiment, a method of making a normoxic 3D polymer gel (NIBMAGAT) using a combination of chemicals at a certain weight and a ratio and pouring the NIBMAGAT into tubes; storing NIBMAGAT in refrigerator at 10° C. before use; and irradiating them using a linear accelerator at a specific absorbed dose to observe the dose response and plan radiation treatment for clinical use. In another embodiment, combination of chemicals is a gelatin, a N-(Isobutoxymethyl)acrylamide (NIBMA), a N,N-methylene-bis-acrylamide (BIS), a tetrakis (hydroxymethyl)phosphonium chloride (THPC) and a glycerol. In another embodiment, certain weight and the ratio is the gelatin is between 2-5 g w/w % by weight; the N-(Isobutoxymethyl) acrylamide (NIBMA) is between 1-2 w/w % by weight; the N,N-methylene-bis-acrylamide (BIS) is between 1-4 w/w % by weight; the Trakis (hydroxymethyl)phosphonium chloride (THPC) concentration is between 1-20 mM and the glycerol as co-solvent is between 0-29 w/w % by weight. In another embodiment, gelatin is 4 wt/wt % by weight, the N,N-methylene-bis-acrylamide (BIS) is 4 wt/wt % by weight, the N-(Isobutoxymethyl)acrylamide (NIBMA) is 1 wt/wt % by weight, the Trakis (hydroxymethyl)phosphonium chloride (THPC) is 5 mM and the glycerol is 17 wt/wt % by weight and the absorbed dose is between 0-20 Gy.
The composition and methods disclosed herein may be implemented in any means for achieving various aspects, and may be executed manually or automated using a computer. Other features will be apparent from the accompanying figures and from the detailed description that follows.
Example embodiments are illustrated by way of example in the accompanying figures in which:
Other features of the present embodiments will be apparent from the detailed description and claims that follows.
Several embodiments for 3D polymer gel composition, method of making and the 3D polymer gel to be used in radiation treatment planning are disclosed. Although the present embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the various embodiments.
The materials Gelatin (Type A, bloom 300), N-(Isobutoxymethyl)acrylamide (NIBMA), N,N-methylene-bis-acrylamide (BIS), tetrakis(hydroxymethyl)phosphonium chloride (THPC) and Glycerol from Sigma Chemical Co. (St. Louis, Mo., USA). The N-(Isobutoxymethyl) acrylamide polymer gels were synthesized under a fume hood in normal atmospheric condition. The NIBMAGAT dosimeters were composed of N-(Isobutoxymethyl)acrylamide (NIBMA) monomer, N,N-methylene-bis-acrylamide (BIS) cross-linker, gelatin (Type A, bloom 300), glycerol and tetrakis(hydroxymethyl)phosphonium chloride (THPC). N-(iso-butoxymethyl) acrylamide (NIBMA), a homolog of N-methylolacrylamide (NMA), is the isobutyl ether of NMA. It contains a readily polymerizable vinyl group as well as a crosslinkable iso-butoxymethyl group. The isobutyl group imparts organic solubility to NIBMA permitting the preparation of three general classes of polymers:
a. Organic solvent soluble or solvent based polymers which, on application can be thermoset or crosslinked through either self or external cros slinking mechanisms.
b. Water based or emulsion polymers which, can also be either self or externally crosslinked at the point of application.
c. In radiation curing systems, NIBMA can be used as a reactive diluent. All of the components present in IBMA with the exception of a small amount of isobutanol are radiation polymerizable through the vinyl double bond. Upon further heating of the NIBMA-containing radiation-cured polymer, additional crosslinking can take place through the iso-butoxymethyl group. The presence of the iso-butoxymethyl group offers several advantages in emulsion polymers. The organic solubility of NIBMA enhances its compatibility with other vinyl monomers permitting the incorporation of larger quantities into the polymer backbone relative to NMA. The alkyl ether stabilizes the methylol group, thus providing greater resistance to premature crosslinking. The iso-butoxymethyl group in IBMA provides a more controllable cure rate, thus minimizing cracking and checking of the final thermoset polymers. The major polymer properties imparted by NIBMA, but not limited to, include: improved water and solvent resistance, improved adhesion, improved tensile strength, higher impact resistance, flexibility, resistance to blocking and good handing properties.
Method of making the 3D polymer gel is performed by soaking a gelatin between 2-5 g w/w % by weight for 10 minutes in the ultra-pure deionized water to make a mixture of the gelatin and deionized water; heating the mixture of the gelatin and the deionized water for 1 hour at 50° C. to make a gelatin solution; cooling the gelatin solution to 40° C.; adding a N, N-methylene-bis-acrylamide (BIS) is between 1-4 w/w % by weight and a N-(Isobutoxymethyl) acrylamide (NIBMA) between 1-2 w/w % by weight and a glycerol as co-solvents is between 0-29 w/w % by weight to the gelatin solution and mixing to make a second solution; cooling the second solution to 35° C.; and adding a Trakis (hydroxymethyl)phosphonium chloride (THPC) between 1-20 mM to the second solution and forming a N-(Isobutoxymethyl)acrylamide (NIBMAGAT) polymer gel and stored at 10° C. in a refrigerator until further used for planning of radiation treatment. In order to perform characterization study the polymer gels were filled into 10 mm NMR tube (Wilmad glass, Buena, N.J., USA) and sealed. All gels were stored in a refrigerator (10° C.) overnight prior to irradiation or until further use.
The irradiation of polymer gels were performed using a 6 MV photon beam of a medical linear accelerator (Varian medical systems, USA) with dose rate of 600 cGy/minute calibrated using ionization chamber. Each sample was filled with gel and was placed in a 30×30×30 cm3 cubic water phantom. The samples were then irradiated in a beam field of size 10×10 cm2 with different doses at 5 cm depth and 100 cm (SSD). The sample was transferred back to the refrigerator and kept for about 24 hours before NMR measurements. The dosimeters were irradiated with linear accelerator at absorbed doses up to 30 Gy.
The relaxation Rate (R2) measurements were performed using 0.5 Tesla NMR (Bruker, Germany). The main components of a magnetic module are permanent magnetic, correction loop of magnetic field, a magnetic temperature control circuit and a probe and receiver of radio frequency (RF) which consists of an amplifier, magnetic, emitter, filter, preamplifier, receiver, detector and output amplifier. The magnet has 0.5 Tesla of strength. The control module contained three main parts, radio frequency wave transmitter (frequency circuit), and source energy and microprocessor unit. The control module operates by computer control. A standard malti-Spin-Echo Carr Purcell Meiboom Gill (CPMG) sequence was used to measure relaxation time (T2). The irradiated polymer gel sample was put in NMR tube (1 cm diameter and 20 cm height) and lowered into magnetic box (probe head). The 90° pulse was first applied to the spin system that rotates the magnetization down into the x′y′ plane. The transverse magnetization begins to diphase. At some point in time after the pulse 90° pulses, a 180° pulse was applied. This pulse rotates the magnetization by 180° about the x-axis. The 180° pulse causes the magnetization to at least partially rephrase and to produce a signal call an echo. The Experiment Supervisor program was chosen to determine T2. The values of relaxation rate (R2=1/T2) can be obtained directly from the computer screen. The temperature during measurements was 22±0.5° C. The nuclear magnetic resonance (NMR) spin-spin relaxation rate (relaxation rate for short form) (R2) for water proton surrounding polymer formulation was used to investigate the degree of polymerization of NIBMAGAT gels. The change in R2 corresponding to the degree of polymerization in NIBMAGAT gel increases gradually with absorbed dose up to 20 Gy. Dose response of both gel dosimeters increases with increase of monomer concentration.
The absorption spectra of irradiated 3D polymer gel samples in the wavelength range from 350-650 nm were measured using UV/VIS spectrophotometer, model Lambda 850, from Perkin-Elmer, USA. A zero Gy vial was inserted in the spectrophotometer prior to every light absorption measurement. Three samples at each absorbed dose were measured, but no significant differences in their characteristics were found during measurements. UV/Vis spectrophotometer was used to investigate the degree of whiteness of irradiated samples of NIBMAGAT which is associated with the degree of polymerization of polymer gel dosimeters. The absorbance increases with absorbed dose for all gel dosimeters in the dose range between 0 and 30 Gy. The absorbance of NIBMAGAT gel significantly increases with increase of THPC concentration, while R2 of NIBMAGAT gel is slightly affected by increase of THPC concentration, indicating that NMR method is more sensitive to radiation-induced polymerization than UV/Vis spectrophotometer method. It was found that there is no effect of dose rate and radiation energy on NIBMAGAT polymer gel dosimeters. The stability of NIBMAGAT dosimeters after irradiation was up to 8 days.
The instant disclosure presents NIBMAGAT polymer gel as a novel normoxic polymer gel dosimeters for radiation therapy with low toxicity, low cost and high dose response. These gels are fabricated under normal atmospheric conditions and are therefore called ‘normoxic’ gel dosimeters. The effect of anti-oxidant (THPC) concentrations on the response of the NIBMAGAT dosimeter was investigated by preparing different compositions of gel dosimeters as listed in Table 1.
The effect of NIBMA concentrations on the response of the NIBMAGAT dosimeter was investigated by preparing different compositions of gel dosimeters as listed in Table 3. The selected THPC concentration is 5 mM. Instant invention we introduced a monomer N-(Isobutoxymethyl) acrylamide (NIBMA) with minimum effective concentration and in normoxic condition when compared to Mahbod et. al (2012).
The sensitivity of polymer gel dosimeters to radiation is directly related to % T, the total weight percent of monomer and THPC concentration in the system.
The effect of bis-acrylamide (BISAAm) concentration on the dose response of the NIBMAGAT dosimeter was investigated by preparing different compositions of gel dosimeters as listed in Table 6.
The effect of gelatin concentration on the response of the NIBMAGAT dosimeter was investigated by preparing different compositions of gel dosimeters as listed in Table 8. It may be concluded that THPC not only scavenges radical species but also modifies the morphology of the gelatin network and of the polymer, possibly by intervening in the polymerization of monomers.
Gelatin was added because, in addition to being soft-tissue equivalent it has low melting point. The low melting point helps prevents dissolved oxygen in the solution which occurs upon heating and enhances the performance. The dose response increases significantly with increase of gelatin concentration from 2 to 5% within gel dosimeters. The variation of absorbance versus absorbed dose for polymerization of NIBMAGAT having 2 to 5 wt % concentration of gelatin as shown in
Lower gelatin levels lead to higher optical dose sensitivity. Therefore, when using optical imaging, lowering the gelatin concentration is recommended (along with reduced % T) to produce gels with adequate sensitivity and less light scattering. The spectra of gels prepared with different gelatin concentrations showed little influence of gelatin concentration on dose sensitivity.
The effect of different co-solvents on the response of the NIBMAGAT dosimeter was investigated by preparing different compositions of gel dosimeters as listed in Table 10. As compared to R. J. Senden Pdjkbmaljs (2006). The instant NIBMAGAT dose-response (R2) appears to be linear over a greater dose range (up to 30 Gy).
The effect of glycerol concentration on the response of the NIBMAGAT dosimeter was investigated by preparing different compositions of gel dosimeters as listed in Table 12.
Addition of co-solvent increases the relative rate of consumption of bisacrylamide as well as being good solvent for NIBMA monomer, since NIBMA consumption rates remain unchanged with the addition of co-solvent. The results show that the solubility of NIBMA within NIBMAGAT polymer gels increases with increasing glycerol concentration. The results are also presented in table 13 for further clarifications.
The effect of dose rate on the response of NIBMAGAT polymer gel dosimeters which its compositions based on 4% gelatin, 1% NIBMA, 3% BisAAm, and 17% glycerol were investigated using 200, 400 and 600 cGy/minute under 10 MV radiation energy. The samples were irradiated for absorbed doses of 0, 2.5, 5, 10, 15, 20 and 30 Gy. Three dosimeters were irradiated at each dose point. A centigray (cGy) is a derived metric (SI) measurement unit of absorbed radiation dose of ionizing radiation, e.g. X-rays. The SI prefix centi stands for one hundredths. The centigray is equal to one hundredth of a gray (0.01 Gy), and the gray is defined as the absorption of one joule of ionizing radiation by one kilogram (1 J/kg) of matter, e.g. human tissue. It was found that there is no appreciable effect of dose rate on NIBMAGAT polymer gel dosimeters as shown in
The effect of radiation energy on the response of NIBMAGAT polymer gel dosimeters which its compositions based on 4% gelatin, 1% NIMA, 3% BisAAm, and 17% glycerol was investigated using 6, 10 and 18 MV at 600 Gy/minute dose rate. The samples were irradiated for absorbed doses of 0, 2.5, 5, 10, 15, 20 and 30 Gy. Three dosimeters were irradiated at each dose point. It was found that there is no appreciable effect of radiation energy on NIBMAGAT polymer gel dosimeters as shown in
The effect of scanning temperature of NMR on relaxation rate R2 of NIBMAGAT polymer gel dosimeters was investigated by irradiating samples of formulation based on 4% gelatin, 1% NIMA, 3% BisAAm, and 17% glycerol to 5, 10 and 20 Gy. A set of three samples was used for each temperate. The results show that R2 increases upon cooling the gel during the NMR measurement (
The stability of gel dosimeters was tested by irradiating NIBMAGAT dosimeters samples of formulations based on 4% gelatin, 1% NIMA, 3% BisAAm, and 17% glycerol to 5, 10 and 20 Gy and storing in a refrigerator (10° C.). A set of three samples was used for each dose. The change of the response of normoxic polymer gel was investigated with time after irradiation. The results (see
Dose response (R2) at 24 hours post-irradiation for the gel dosimeter was investigated by preparing NIBMAGAT dosimeters of formulations based on 4% gelatin, 1% NIMA, 3% BisAAm, and 17% glycerol irradiated up to 5 Gy by 0.5 Gy interval and storing in a refrigerator (10° C.). A set of three samples was used for each dose. The change in the proton relaxation rate R2 versus absorbed dose for polymerization of NIBMAGAT is shown in
A relationship between glycerol concentration in the NIBMAGAT gel dosimeters and dose sensitivity has been observed with MR scanning. The dose sensitivity was taken from the slope of linear plot of dose D versus R2 of
In addition, it will be appreciated that the novel 3D polymer for dosimetric use disclosed herein may be embodied using means for achieving better quality images for medical use and diagnosis. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.
