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Sensitivity optimization of PRESAGE polyurethane based dosimeter
Radiation Measurements 45 (2010) 89–91
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Sensitivity optimization of PRESAGE polyurethane based dosimeter Z. Sanjabi Eznaveh a, *, M.H. Zahamtkesh b, A.R. Kamali Asl a, S. Bagheri b a b
Shahid Beheshti University, Tehran, Iran Novin Radiomedicine Institute, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 July 2008 Received in revised form 10 August 2009 Accepted 10 August 2009
A new class of three-dimensional dosimeter (PRESAGE) has recently emerged, that consists of an optically clear polyurethane matrix containing a leuco dye and a free radical initiator. The dye exhibits a radiochromic response when exposed to ionizing radiation, changing color in proportion to the radiation dose. In this work we investigate and characterize the sensitivity of this new dosimeter by changing the portion of these two materials in the feature. Our results show considerable improvement in both dosimeter sensitivity and dose response stability by changing the percents of leuco dye and free radical initiator to approach to an optimum value. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Dosimeter Free radical initiator Leuco dye Polyurethane Radiochromic
1. Introduction Over the past 45 years, the ideal physical composition sought from a three-dimensional dosimeter was that it should be a transparent plastic that is firm in structure, and tissue equivalent (Potsaid and Irie, 1961). A 3D dosimetry material that exhibits optical-contrast through light-absorbance rather than light-scattering would have a clear advantage as it would negate the scattering artifacts (Oldham, 2006). Since the introduction of the non-scattering FBX gel-dosimeter, other absorbing gels have been reported but none has so far fully solved the issue of radiochromic diffusion (Oldham, 2006). Polyurethanes are one of the most versatile man-made synthetic polymers (Szycher, 1999). They are used in medical devices, coatings, adhesives, sealants, and as elastomers used on floors and tomotitve interiors (Adamovics and Maryanski, 2004). The solid PRESAGE dosimeter is formulated with free radical initiator and a leuco dye and it dose not require a container to maintain its shape. The polyurethane matrix is tissue equivalent prevents the diffusion of the dose distribution image. The response of the dosimeter is evaluated through optical computed tomographic (OCT) imaging and spectrophotometer system (Oldham, 2006). These two method promise to give threedimensional dose distributions without the cost attached to another system such as MRI. * Corresponding author. E-mail address: [email protected] (Z.S. Eznaveh). 1350-4487/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2009.08.005
Detailed analysis of the radiochromic response of PRESAGE has confirmed exceptional potential for 3D dosimetry (Guo et al., 2006a,b). Since then Particular emphasis has been put on this dosimeter that change its optical properties in proportion to the absorbed dose (Adamovics and Maryanski, 2006). 2. Materials and methods 2.1. Polyurethane formulation The polymeric matrix is formed in two steps. In the first step, a prepolymer, referred to as ‘Part A’, is formed by reacting a molar equivalent of commercially available polyol with two molar equivalents of a diisocyanate as shown below in Step 1. The resulting ‘Part A’ prepolymer contains 1–15% unreacted isocyanate and can be stored at room temperature for long periods of time (Adamovics and Maryanski, 2004). The second step consists of mixing the leuco dye, a free radical initiator, and a catalyst with ‘Part B’ (a commercially available polyol) then blending with Part A in equal proportions, placing the blended material in the appropriate mold, and incubating at an optimal temperature under a pressure of 60 psi to minimise outgassing. The reaction scheme is shown in the two step equation below (Adamovics and Maryanski, 2004). Step 1 HOeR1eOHðPolyolÞ D 2OCNeR2eNCOðDiisocyanateÞ / OCNe R2e½eNHeCð]OÞeOeR1eOeCð]OÞeNHeR2ene
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Z.S. Eznaveh et al. / Radiation Measurements 45 (2010) 89–91
Fig. 1. Variation of sensitivity with differing value of LMG (y1, y2, y3, normal, 4% and 6% increase respectively).
NCOðprepolymer; PART AÞ Step 2 PART A D HO R3eOHðPART BÞ D leuco dye D free radical initiator D catalyst / e½ðCð]OÞeNHeR2eNHeCð]OÞeOeR1eO Cð [ OÞeNHeR2ÞneNHeCð]OÞeOeR3eOem D leuco dye D free radical initiator D catalyst
2.2. Fabrication process 3D dosimetry materials do exist but improvements would be valuable especially with regards to stability, uniformity, ease of handling and re-usability. There are many choices to select free radical initiator and Leuco dye. Some of these are introduced in a patent published at 2004 (Adamovics, 2006). The Leuco dye used in this study was Leuco Malachite Green (LMG, Sigma Aldrich) and the free radical initiators used was carbon tetrachloride (CCl4, Fluka). The portions of LMG and CCl4 at the first compound are 2% and 28% respectively. We investigated the improvement of dose response sensitivity in two steps. At first we tried to get the best sensitivity with changing the percent of LMG in the dosimeter formulation and after that we changed the percent of CCl4 in this compound with obtained optimum percent of LMG. Different samples of the transparent solid plastic dosimeter PRESAGE were prepared in the 5 1 1 cm3 Perspex cuvettes. These were irradiated with 60Co photon beam at the different doses from 10–40 Gy. Field size was set to 20 20 cm2 and 80 cm SSD from the dosimeter surface. Samples were immersed 5 cm in a water tank in order to receiving the maximum dose possible. The absorbance was measured using a spectrophotometer (Visible-UV EZ210 Lambda) just after the radiation.
Fig. 3. Post-irradiation stability for different dose level (y1, y2, y3, y4, the same day, three, six and nine days post irradiation).
3. Results The polymer formulation hardens in 18–24 h at an optimal temperature under a pressure of 60 psi to minimize outgassing. After radiolytic oxidation the leuco malachite green has a visible absorbance maximum at 633 nm, though the color development of the exposed portions in a dosimeter is not detectable unless there is a radical initiator in the formulation that produces radicals during the irradiation (Adamovics and Maryanski, 2004). The obtained results by changing the percent of both LMG and CCl4 have been shown in Figs. 1 and 2. Fig. 1 indicates that by increasing the percent of LMG by 4% in the first step, one can reach an optimum sensitivity, the slop of absorption vs. dose diagram, from 0.0099 at the first compound to 0.0128 arb unit/Gy using the spectrophotometer. Additional increase over 6% causes decrease in the sensitivity (Fig. 1, y3). At the second step we changed the percent of CCl4 in the optimum achieved compound from the first step. Fig. 2 shows the results from increasing this blend by 4%, 6% and 8% (y1, y2, y3 respectively). One can show easily that the best sensitivity is obtained by 6% increase in CCl4 then by additional increasing, sensitivity diminishes quickly. With these results we can get the best feature for dosimeter compound that is 4% and 6% increase in portion of LMG and CCl4 respectively which result in the amount of 6% and 32% as the total percent of these two materials in the final compound. In order to investigate the dose response stability of the dosimeter, the absorbance was also measured several days just after radiation. Some of the achieved Results are plotted as a diagram of absorption vs. dose (Fig. 3). This diagram shows that the dose response is with good estimation stable during 9 days post irradiation (the same day, three, six and nine days after radiation). The slop of the curves defines the sensitivity of the dosimeter which is 0.102 approximately. 4. Conclusions In this work the optimum sensitivity of a new radiochromic polyurethane based dosimeter PRESAGE, was obtained by changing the LMG and CCl4 percents in the total composition of the dosimeter. A good value for dose response stability during 9 days post irradiation was gained as well, confirming that this parameter can be considered stable after this time. In future one can continue this examination during further post irradiation time to approach the final acceptable value. Acknowledgement
Fig. 2. Variation of sensitivity with differing percent of CCl4 in dosimeter formulation (y1, y2, y3, 4%, 6% and 8% increase respectively).
The authors would like to thank Mr. Shiraseb and the Head of Novin Radiation Medicine Institution for beneficial and helpful advice and their support.
Z.S. Eznaveh et al. / Radiation Measurements 45 (2010) 89–91
References Adamovics, John A., 2006. Three-dimensional Dosimeter for Penetrating Radiation and Method of Use. United States Patent: 7098463. Adamovics, J., Maryanski, M.J., 2004. A new approach to radiochromic threedimensional dosimetry-polyurethane. J. Phys. Conf. Ser. 3, 172–175. Adamovics, J., Maryanski, M.J., 2006. Characterisation of presage: a new 3-D radiochromic solid polymer dosimeter for ionising radiation. Radiat. Prot. Dosimetry 120 (1–4), 107–112.
91
Guo, P., Adamovics, J., Oldham, M., 2006a. Characterization of a new radiochromic three-dimensional dosimeter. Med. Phys. 33, 1338–1345. Guo, P., Adamovics, J., Oldham, M., 2006b. A practical three-dimensional dosimetry system for radiation therapy. Med. Phys.. Oldham, Mark, 2006. 3D dosimetry by optical-CT scanning. J. Phys. 56, 58–71. Potsaid, M.S., Irie, G., 1961. Paraffin base halogenated hydrocarbon chemical dosimeters. Radiology 77, 61–65. Szycher, M., 1999. Handbook of Polyurethanes. CRC Press, Boca Raton, Florida.
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Sensitivity optimization of PRESAGE polyurethane based dosimeter Z. Sanjabi Eznaveh a, *, M.H. Zahamtkesh b, A.R. Kamali Asl a, S. Bagheri b a b
Shahid Beheshti University, Tehran, Iran Novin Radiomedicine Institute, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 July 2008 Received in revised form 10 August 2009 Accepted 10 August 2009
A new class of three-dimensional dosimeter (PRESAGE) has recently emerged, that consists of an optically clear polyurethane matrix containing a leuco dye and a free radical initiator. The dye exhibits a radiochromic response when exposed to ionizing radiation, changing color in proportion to the radiation dose. In this work we investigate and characterize the sensitivity of this new dosimeter by changing the portion of these two materials in the feature. Our results show considerable improvement in both dosimeter sensitivity and dose response stability by changing the percents of leuco dye and free radical initiator to approach to an optimum value. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Dosimeter Free radical initiator Leuco dye Polyurethane Radiochromic
1. Introduction Over the past 45 years, the ideal physical composition sought from a three-dimensional dosimeter was that it should be a transparent plastic that is firm in structure, and tissue equivalent (Potsaid and Irie, 1961). A 3D dosimetry material that exhibits optical-contrast through light-absorbance rather than light-scattering would have a clear advantage as it would negate the scattering artifacts (Oldham, 2006). Since the introduction of the non-scattering FBX gel-dosimeter, other absorbing gels have been reported but none has so far fully solved the issue of radiochromic diffusion (Oldham, 2006). Polyurethanes are one of the most versatile man-made synthetic polymers (Szycher, 1999). They are used in medical devices, coatings, adhesives, sealants, and as elastomers used on floors and tomotitve interiors (Adamovics and Maryanski, 2004). The solid PRESAGE dosimeter is formulated with free radical initiator and a leuco dye and it dose not require a container to maintain its shape. The polyurethane matrix is tissue equivalent prevents the diffusion of the dose distribution image. The response of the dosimeter is evaluated through optical computed tomographic (OCT) imaging and spectrophotometer system (Oldham, 2006). These two method promise to give threedimensional dose distributions without the cost attached to another system such as MRI. * Corresponding author. E-mail address: [email protected] (Z.S. Eznaveh). 1350-4487/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2009.08.005
Detailed analysis of the radiochromic response of PRESAGE has confirmed exceptional potential for 3D dosimetry (Guo et al., 2006a,b). Since then Particular emphasis has been put on this dosimeter that change its optical properties in proportion to the absorbed dose (Adamovics and Maryanski, 2006). 2. Materials and methods 2.1. Polyurethane formulation The polymeric matrix is formed in two steps. In the first step, a prepolymer, referred to as ‘Part A’, is formed by reacting a molar equivalent of commercially available polyol with two molar equivalents of a diisocyanate as shown below in Step 1. The resulting ‘Part A’ prepolymer contains 1–15% unreacted isocyanate and can be stored at room temperature for long periods of time (Adamovics and Maryanski, 2004). The second step consists of mixing the leuco dye, a free radical initiator, and a catalyst with ‘Part B’ (a commercially available polyol) then blending with Part A in equal proportions, placing the blended material in the appropriate mold, and incubating at an optimal temperature under a pressure of 60 psi to minimise outgassing. The reaction scheme is shown in the two step equation below (Adamovics and Maryanski, 2004). Step 1 HOeR1eOHðPolyolÞ D 2OCNeR2eNCOðDiisocyanateÞ / OCNe R2e½eNHeCð]OÞeOeR1eOeCð]OÞeNHeR2ene
90
Z.S. Eznaveh et al. / Radiation Measurements 45 (2010) 89–91
Fig. 1. Variation of sensitivity with differing value of LMG (y1, y2, y3, normal, 4% and 6% increase respectively).
NCOðprepolymer; PART AÞ Step 2 PART A D HO R3eOHðPART BÞ D leuco dye D free radical initiator D catalyst / e½ðCð]OÞeNHeR2eNHeCð]OÞeOeR1eO Cð [ OÞeNHeR2ÞneNHeCð]OÞeOeR3eOem D leuco dye D free radical initiator D catalyst
2.2. Fabrication process 3D dosimetry materials do exist but improvements would be valuable especially with regards to stability, uniformity, ease of handling and re-usability. There are many choices to select free radical initiator and Leuco dye. Some of these are introduced in a patent published at 2004 (Adamovics, 2006). The Leuco dye used in this study was Leuco Malachite Green (LMG, Sigma Aldrich) and the free radical initiators used was carbon tetrachloride (CCl4, Fluka). The portions of LMG and CCl4 at the first compound are 2% and 28% respectively. We investigated the improvement of dose response sensitivity in two steps. At first we tried to get the best sensitivity with changing the percent of LMG in the dosimeter formulation and after that we changed the percent of CCl4 in this compound with obtained optimum percent of LMG. Different samples of the transparent solid plastic dosimeter PRESAGE were prepared in the 5 1 1 cm3 Perspex cuvettes. These were irradiated with 60Co photon beam at the different doses from 10–40 Gy. Field size was set to 20 20 cm2 and 80 cm SSD from the dosimeter surface. Samples were immersed 5 cm in a water tank in order to receiving the maximum dose possible. The absorbance was measured using a spectrophotometer (Visible-UV EZ210 Lambda) just after the radiation.
Fig. 3. Post-irradiation stability for different dose level (y1, y2, y3, y4, the same day, three, six and nine days post irradiation).
3. Results The polymer formulation hardens in 18–24 h at an optimal temperature under a pressure of 60 psi to minimize outgassing. After radiolytic oxidation the leuco malachite green has a visible absorbance maximum at 633 nm, though the color development of the exposed portions in a dosimeter is not detectable unless there is a radical initiator in the formulation that produces radicals during the irradiation (Adamovics and Maryanski, 2004). The obtained results by changing the percent of both LMG and CCl4 have been shown in Figs. 1 and 2. Fig. 1 indicates that by increasing the percent of LMG by 4% in the first step, one can reach an optimum sensitivity, the slop of absorption vs. dose diagram, from 0.0099 at the first compound to 0.0128 arb unit/Gy using the spectrophotometer. Additional increase over 6% causes decrease in the sensitivity (Fig. 1, y3). At the second step we changed the percent of CCl4 in the optimum achieved compound from the first step. Fig. 2 shows the results from increasing this blend by 4%, 6% and 8% (y1, y2, y3 respectively). One can show easily that the best sensitivity is obtained by 6% increase in CCl4 then by additional increasing, sensitivity diminishes quickly. With these results we can get the best feature for dosimeter compound that is 4% and 6% increase in portion of LMG and CCl4 respectively which result in the amount of 6% and 32% as the total percent of these two materials in the final compound. In order to investigate the dose response stability of the dosimeter, the absorbance was also measured several days just after radiation. Some of the achieved Results are plotted as a diagram of absorption vs. dose (Fig. 3). This diagram shows that the dose response is with good estimation stable during 9 days post irradiation (the same day, three, six and nine days after radiation). The slop of the curves defines the sensitivity of the dosimeter which is 0.102 approximately. 4. Conclusions In this work the optimum sensitivity of a new radiochromic polyurethane based dosimeter PRESAGE, was obtained by changing the LMG and CCl4 percents in the total composition of the dosimeter. A good value for dose response stability during 9 days post irradiation was gained as well, confirming that this parameter can be considered stable after this time. In future one can continue this examination during further post irradiation time to approach the final acceptable value. Acknowledgement
Fig. 2. Variation of sensitivity with differing percent of CCl4 in dosimeter formulation (y1, y2, y3, 4%, 6% and 8% increase respectively).
The authors would like to thank Mr. Shiraseb and the Head of Novin Radiation Medicine Institution for beneficial and helpful advice and their support.
Z.S. Eznaveh et al. / Radiation Measurements 45 (2010) 89–91
References Adamovics, John A., 2006. Three-dimensional Dosimeter for Penetrating Radiation and Method of Use. United States Patent: 7098463. Adamovics, J., Maryanski, M.J., 2004. A new approach to radiochromic threedimensional dosimetry-polyurethane. J. Phys. Conf. Ser. 3, 172–175. Adamovics, J., Maryanski, M.J., 2006. Characterisation of presage: a new 3-D radiochromic solid polymer dosimeter for ionising radiation. Radiat. Prot. Dosimetry 120 (1–4), 107–112.
91
Guo, P., Adamovics, J., Oldham, M., 2006a. Characterization of a new radiochromic three-dimensional dosimeter. Med. Phys. 33, 1338–1345. Guo, P., Adamovics, J., Oldham, M., 2006b. A practical three-dimensional dosimetry system for radiation therapy. Med. Phys.. Oldham, Mark, 2006. 3D dosimetry by optical-CT scanning. J. Phys. 56, 58–71. Potsaid, M.S., Irie, G., 1961. Paraffin base halogenated hydrocarbon chemical dosimeters. Radiology 77, 61–65. Szycher, M., 1999. Handbook of Polyurethanes. CRC Press, Boca Raton, Florida.