Radiation Protection Dosimetry (2014), Vol. 162, No. 1–2, pp. 167 –170 Advance Access publication 27 July 2014
doi:10.1093/rpd/ncu252
ABSORBING MATERIALS WITH APPLICATIONS IN RADIOTHERAPY AND RADIOPROTECTION M. Spunei1,2, I. Malaescu1, M. Mihai3 and C. N. Marin1,* 1 Department of Physics, West University of Timisoara, Bd. V. Parvan No. 4, 300223 Timisoara, Romania 2 High Energy Radiotherapy Center, Str. Ghe. Dima No. 5, 300079 Timisoara, Romania 3 Emergency County Hospital Craiova, Str. Tabaci No. 1, 200642 Craiova, Romania
The radiotherapy centres are using linear accelerators equipped with multi-leaf collimators (MLCs) for treatments of various types of cancer. For superficial cancers located at a maximum depth of 3 cm high-energy electrons are often used, but MLC cannot be used together with electron applicators. Due to the fact that the tumour shape is not square (as electron applicators), searching for different materials that can be used as absorbents or shields for the protection of adjacent organs is of paramount importance. This study presents an experimental study regarding the transmitted dose through some laboratory-made materials when subjected to electron beams of various energies (ranging from 6 to 15 MeV). The investigated samples were composite materials consisting of silicon rubber and micrometre aluminium particles with different thicknesses and various mass fraction of aluminium. The measurements were performed at a source surface distance of 100 cm in the acrylic phantom. The experimental results show that the transmitted dose through tested samples is ranging between ∼1.8 and 90 %, depending on the electron beam energy, sample thickness and sample composition. These preliminary results suggest that the analysed materials can be used as absorbers or shields in different applications in radiotherapy and radioprotection.
INTRODUCTION Radiation oncology uses various ionising radiation techniques(1). One of the treatment technique is the external beam radiotherapy(2 – 6) and for superficial cancers, located at a maximum depth of 3 cm, high energy electron beams are used(7, 8). To spare organs located near tumour, multi-leaf collimators (MLCs) are used in photon beam radiotherapy techniques, but in high-energy electron beam techniques such MLC cannot be used(9). In order to protect adjacent organs, in electron beam technique for cancer treatment, finding of new electron absorbent materials is always a demand. Because the tumour shape is not square (as electron applicators), searching for different absorbent materials that could be cut into different shapes and are flexible is of paramount importance(10, 11). The basic conditions of these new materials, besides the mandatory radiation protection are: lower production costs; easy to produce and easy to design in the geometry of individual treatment; flexible and nontoxic. Aluminium is an example of electron absorber(12, 13) but in practice flexible and moldable protecting materials were needed. Starting from this idea, the authors tried to combine the flexibility and the ability to mold silicon rubber with the absorbing properties of aluminium. In this study an experimental study regarding the transmitted dose through some composite materials containing aluminium particles when subjected to
electron beams of various energies (ranging from 6 to 15 MeV) was presented The purpose of this study is finding of materials that can be used for individual protection in external radiotherapy with electron beams. MATERIALS AND METHODS For measurements three samples denoted A, B and C were made. Sample A was a moldable silicon rubber (with the commercial name RTV-530 from Prochima) (http://www.prochima.it/pages/trv-530.htm14), which is a nontoxic material and does not irritate the skin. Sample B was a composite, consisting of silicon rubber (RTV-530) and micrometric aluminium (Al) particles (with the mass fraction of Al equal to 5.5 %). Sample C was also a composite, consisting of the same materials as in sample B, but with the mass fraction of Al particles of 10.4 %. All samples have the same dimensions (120 mm` 120 mm` 6 mm) and same mass (131.2 g). By combining the samples A, B and C another three samples (denoted by D, E and F) with the dimensions of 120 mm` 120 mm` 12 mm were obtained, namely: sample D consisted of sample A superposed to sample B; sample E consisted of sample A superposed to sample C and sample F consisted of sample B superposed to sample C. The dosimetric measurements were performed with a linear accelerator (VARIAN 2100SC) at the High Energy Radiotherapy Center Timisoara.
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at The University of British Colombia Library on June 21, 2015
*Corresponding author: [email protected]
M. SPUNEI ET AL.
For each value of electron beam energy, the relative measurements for determination of percentage depth dose (PDD) were performed in MP3 water phantom according to TRS398(14). In the experimental set-up (Figure 1) a Semiflex ionisation chamber (type 31010) and a Markus chamber (type 23343) have been used, produced by PTW-Freiburg, Germany. For the experimental data analysis, the Mephysto software has been used. The measurements of transmission through samples were performed in acrylic phantom (2967 type from PTW-Freiburg, Germany). The acrylic phantom consists of different slabs with different thicknesses from 1 to 10 mm. Using different combination of slabs it is possible to vary the measuring depth in increments of 1 mm. The size of the phantom can be chosen from 1 mm` 30 cm` 30 cm to 30 cm` 30 cm` 30 cm. The Markus ionisation chamber (type 23343) was placed in the phantom at the maximum dose depth for each electron beam energy (Figure 2). The electric charge collected by the ionisation chamber was measured using an UNIDOS electrometer. All the measurements are performed at a standard source surface distance (SSD) of 100 cm, using an electron applicator of 10 cm by 10 cm.
Experimental plots of the PDD, at four electron beam energy values, in water phantom are presented in Figure 3. The dimensions of the electron applicator are 10 cm` 10 cm. As shown in Figure 3 the position of the maximum depth dose is changing by increasing the electron beam energy, and is located between 1.2 cm (for 6 MeV) to 3.2 cm (for 15 MeV). Due to the fact that samples are meant to be used on the skin and the experimental set-up for PDD measurements in water phantom does not allow such dosimetric measurements, the samples on acrylic phantom were analysed. In Figure 4 are presented point doses as measured in acrylic phantom and compared with measured PDD in water phantom for electron beam energy of 6 MeV. As can be observed from Figure 4 the PDD measured in water phantom and in acrylic phantom have similar dependence. Therefore, one can use the measurement of PDD in water phantom for the maximum point dose in the acrylic phantom. Transmission through the sample is obtained by measuring the dose (electric charge) in acrylic
Figure 1. Experimental set-up for PDD measurements in water phantom.
Figure 2. Experimental set-up for transmission measurements in acrylic phantom.
RESULTS
Downloaded from http://rpd.oxfordjournals.org/ at The University of British Colombia Library on June 21, 2015
168
ABSORBING MATERIALS WITH APPLICATIONS IN RADIOTHERAPY Table 1. Transmission measured at a maximum depth dose for samples A, B and C with a thickness of 6 mm. Transmission (%)/electron beam energy (MeV)
Sample A Sample B Sample C
6 MeV
9 MeV
12 MeV
15 MeV
57.1 50.17 49.75
74.7 69.5 69.15
82.46 79.6 78.9
91.74 89.6 89.2
Figure 3. PDD distribution for field size 10 cm` 10 cm and different electron beam energy.
Transmission (%)/electron energy
Sample D Sample E Sample F
Figure 4. Comparison of PDD distribution in water (line) and in acrylic phantom (dots) for 6-MeV electron beam and 10 cm` 10 cm field size.
phantom, with and without the sample in the same geometry (SSD ¼ 100 cm) and using the equation: Transmissionsample ð%Þ ¼ 100
Dosesample Doseopenfield
ð1Þ
The transmission through investigated samples is measured at a maximum depth dose for the available electron beams energies in acrylic phantom. The values obtained for transmission are shown in Table 1 (for samples A, B and C) and in Table 2 (for samples D, E and F). As can be seen in Table 1 and Table 2, the transmission through each sample increases with the increase of electron beam energy. Addition of aluminium (Al)
6 MeV
9 MeV
12 MeV
15 MeV
2.95 2.4 1.76
20.01 19.53 15.62
41.3 40.8 38.14
67 66.5 64.35
particles in samples leads to a decrease in transmission, the more concentrated the aluminium, the less the transmission. From Table 2 one can observe that increasing the thickness of samples and concentration of aluminium particles (by combining samples A, B and C) the transmission decreased to 1.76 % (for sample F at an electron beam energy of 6 MeV). However, samples D, E and F can be used in clinical practice as shields, for electron beam energy of 6 MeV, because the transmission is ,3 %. In clinical practice the tumour tissue is not located only on the skin surface, it has a three-dimensional irregular shape. Consequently, for an efficient distribution of dose into the tumour volume, a combination of shields and attenuators is necessary. Therefore, as can be observed from Tables 1 and 2, all investigated samples may be used as attenuators for different electron beam energies. For instance, if the applied dose is 50 Gy the adjacent organs will receive 10 Gy in case of using sample D as attenuator with an electron beam energy of 9 MeV.
CONCLUSIONS Different laboratory made materials with absorbent properties have been identified for use in electron beam radiotherapy. The analysed samples were composite materials obtained by mixing micrometre aluminium particles with moldable silicon rubber. Samples had different
169
Downloaded from http://rpd.oxfordjournals.org/ at The University of British Colombia Library on June 21, 2015
Table 2. Transmission measured at a maximum depth dose for samples D, E and F with a thickness of 12 mm.
M. SPUNEI ET AL.
2. 3. 4. 5. 6.
7.
8. 9. 10.
ACKNOWLEDGEMENTS The authors are deeply grateful to Dr S. Dema, head of Radiotherapy Department for his cooperation during this study.
11.
FUNDING
12.
This work was supported by the strategic grant POSDRU/DMI1.5, Project ID137750 (2013), cofinanced by the European Social Fund within the Sectorial Operational Program Human Resources Development 2007 –2013.
13.
REFERENCES
14.
1. Thariat, J., Hannoun-Levi, J. M., Myint, A. S., Vuong, T. and Ge´rard, J. P. Past, present, and future of
170
radiotherapy for the benefit of patients. Nat. Rev. Clin. Oncol. 10, 52– 60 (2013). Johns, H., Bates, I. and Watson, T. 1000 Curie cobalt units for radiation therapy. I. The Saskatchewan cobalt 60 unit. Br. J. Radiol. 25, 296– 302 (1952). Fry, D. W., Harvie, R. B., Mullett, L. B. and Walkinshaw, W. A travelling wave linear accelerator for 4 MeV electrons. Nature 162, 859– 861 (1948). Johns, H. E. and Cunningham, J. R. In: The Physics of Radiology, fourth edn. Thomas, Charles C., Ed. Springfield (1983). Catterall, M. Neutron therapy at Hammersmith Hospital 1970 to 1985. A reexamination of results. Strahlenther. Onkol. 165, 298– 301 (1989). Suit, H. D., Goitein, M., Munzenrider, J., Verhey, L., Urie, M., Gragoudas, E., Koehler, A., Gottschalk, B., Sisterson, J. and Tatsuzaki, H. Increased efficacy of radiation therapy by use of proton beam. Strahlenther. Onkol. 166, 40– 44 (1990). Laramore, G. E., Griffin, T. W., Parker, R. G. and Gerdes, A. J. The use of electron beams in treating local recurrence of breast cancer in previously irradiated fields. Cancer 41, 991 –995 (1978). Tapley, N. V. Clinical Applications of the Electron Beam. John Wiley & Sons, Inc. (1976). Podgorsak, E. B. Radiation Oncology Physics: A Handbook for Teachers and Students, 289–292. IAEA (2005). Paliwal, B. R., Rommelfanger, S. and Das, R. K. Attenuation characteristics of a new compensator material: thermo-shield for high energy electron and photon beams. Med. Phys. 25 (4), 484– 487 (1998). Kudchadker, R. J., Antolak, J. A., Morrison, W. H., Wong, P. F. and Hogstrom, K. R. Utilization of custom electron bolus in head and neck radiotherapy. J. Appl. Clin. Med. Phys. 4 (4), 321–333 (2003). Weaver, R. D., Gerbi, B. J. and Dusenbery, K. E. Evaluation of eye shields made of tungsten and aluminum in high-energy electron beams. Int. J. Radiat. Oncol. Biol. Phys. 41, 233–237 (1998). Kinhikar, R. A., Tambe, C. M., Upreti, R. R., Patkar, S., Patil, K. and Deshpande, D. D. Phantom dosimetric study of nondivergent aluminum tissue compensator using ion chamber, TLD, and gafchromic film. Med. Dosim. 33(4), 286–292 (2008). IAEA. Absorbed dose determination in external beam radiotherapy: an international code of practice for dosimetry based on standards dose to water. IAEA (2000) ISSN: 1011-4289.
Downloaded from http://rpd.oxfordjournals.org/ at The University of British Colombia Library on June 21, 2015
thickness and different mass fraction of aluminium particles. Dosimetric measurements have been performed both in water phantom and in acrylic phantom and allowed the determination of the maximum point dose. The transmission through samples has been evaluated at the maximum dose point for different electron beam energies within the 6–14 MeV. The experimental results showed that the transmission through samples increases with the electron beam energy increase. For a given value of the electron beam energy the transmission decreases by addition of aluminium particles, the larger the particle concentration, the smaller the electron transmission. Also increasing the sample thickness led to the decrease in electron transmission. Taking into account the measured transmission all the investigated samples may be used as electron absorbents. In addition, samples D, E and F can be used as shields for an electron beam energy of 6 MeV, as the transmission through the samples is ,3 %. As in radiotherapy practice, both shields and attenuators are useful, this preliminary result recommends the investigated samples in clinical situation.
doi:10.1093/rpd/ncu252
ABSORBING MATERIALS WITH APPLICATIONS IN RADIOTHERAPY AND RADIOPROTECTION M. Spunei1,2, I. Malaescu1, M. Mihai3 and C. N. Marin1,* 1 Department of Physics, West University of Timisoara, Bd. V. Parvan No. 4, 300223 Timisoara, Romania 2 High Energy Radiotherapy Center, Str. Ghe. Dima No. 5, 300079 Timisoara, Romania 3 Emergency County Hospital Craiova, Str. Tabaci No. 1, 200642 Craiova, Romania
The radiotherapy centres are using linear accelerators equipped with multi-leaf collimators (MLCs) for treatments of various types of cancer. For superficial cancers located at a maximum depth of 3 cm high-energy electrons are often used, but MLC cannot be used together with electron applicators. Due to the fact that the tumour shape is not square (as electron applicators), searching for different materials that can be used as absorbents or shields for the protection of adjacent organs is of paramount importance. This study presents an experimental study regarding the transmitted dose through some laboratory-made materials when subjected to electron beams of various energies (ranging from 6 to 15 MeV). The investigated samples were composite materials consisting of silicon rubber and micrometre aluminium particles with different thicknesses and various mass fraction of aluminium. The measurements were performed at a source surface distance of 100 cm in the acrylic phantom. The experimental results show that the transmitted dose through tested samples is ranging between ∼1.8 and 90 %, depending on the electron beam energy, sample thickness and sample composition. These preliminary results suggest that the analysed materials can be used as absorbers or shields in different applications in radiotherapy and radioprotection.
INTRODUCTION Radiation oncology uses various ionising radiation techniques(1). One of the treatment technique is the external beam radiotherapy(2 – 6) and for superficial cancers, located at a maximum depth of 3 cm, high energy electron beams are used(7, 8). To spare organs located near tumour, multi-leaf collimators (MLCs) are used in photon beam radiotherapy techniques, but in high-energy electron beam techniques such MLC cannot be used(9). In order to protect adjacent organs, in electron beam technique for cancer treatment, finding of new electron absorbent materials is always a demand. Because the tumour shape is not square (as electron applicators), searching for different absorbent materials that could be cut into different shapes and are flexible is of paramount importance(10, 11). The basic conditions of these new materials, besides the mandatory radiation protection are: lower production costs; easy to produce and easy to design in the geometry of individual treatment; flexible and nontoxic. Aluminium is an example of electron absorber(12, 13) but in practice flexible and moldable protecting materials were needed. Starting from this idea, the authors tried to combine the flexibility and the ability to mold silicon rubber with the absorbing properties of aluminium. In this study an experimental study regarding the transmitted dose through some composite materials containing aluminium particles when subjected to
electron beams of various energies (ranging from 6 to 15 MeV) was presented The purpose of this study is finding of materials that can be used for individual protection in external radiotherapy with electron beams. MATERIALS AND METHODS For measurements three samples denoted A, B and C were made. Sample A was a moldable silicon rubber (with the commercial name RTV-530 from Prochima) (http://www.prochima.it/pages/trv-530.htm14), which is a nontoxic material and does not irritate the skin. Sample B was a composite, consisting of silicon rubber (RTV-530) and micrometric aluminium (Al) particles (with the mass fraction of Al equal to 5.5 %). Sample C was also a composite, consisting of the same materials as in sample B, but with the mass fraction of Al particles of 10.4 %. All samples have the same dimensions (120 mm` 120 mm` 6 mm) and same mass (131.2 g). By combining the samples A, B and C another three samples (denoted by D, E and F) with the dimensions of 120 mm` 120 mm` 12 mm were obtained, namely: sample D consisted of sample A superposed to sample B; sample E consisted of sample A superposed to sample C and sample F consisted of sample B superposed to sample C. The dosimetric measurements were performed with a linear accelerator (VARIAN 2100SC) at the High Energy Radiotherapy Center Timisoara.
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at The University of British Colombia Library on June 21, 2015
*Corresponding author: [email protected]
M. SPUNEI ET AL.
For each value of electron beam energy, the relative measurements for determination of percentage depth dose (PDD) were performed in MP3 water phantom according to TRS398(14). In the experimental set-up (Figure 1) a Semiflex ionisation chamber (type 31010) and a Markus chamber (type 23343) have been used, produced by PTW-Freiburg, Germany. For the experimental data analysis, the Mephysto software has been used. The measurements of transmission through samples were performed in acrylic phantom (2967 type from PTW-Freiburg, Germany). The acrylic phantom consists of different slabs with different thicknesses from 1 to 10 mm. Using different combination of slabs it is possible to vary the measuring depth in increments of 1 mm. The size of the phantom can be chosen from 1 mm` 30 cm` 30 cm to 30 cm` 30 cm` 30 cm. The Markus ionisation chamber (type 23343) was placed in the phantom at the maximum dose depth for each electron beam energy (Figure 2). The electric charge collected by the ionisation chamber was measured using an UNIDOS electrometer. All the measurements are performed at a standard source surface distance (SSD) of 100 cm, using an electron applicator of 10 cm by 10 cm.
Experimental plots of the PDD, at four electron beam energy values, in water phantom are presented in Figure 3. The dimensions of the electron applicator are 10 cm` 10 cm. As shown in Figure 3 the position of the maximum depth dose is changing by increasing the electron beam energy, and is located between 1.2 cm (for 6 MeV) to 3.2 cm (for 15 MeV). Due to the fact that samples are meant to be used on the skin and the experimental set-up for PDD measurements in water phantom does not allow such dosimetric measurements, the samples on acrylic phantom were analysed. In Figure 4 are presented point doses as measured in acrylic phantom and compared with measured PDD in water phantom for electron beam energy of 6 MeV. As can be observed from Figure 4 the PDD measured in water phantom and in acrylic phantom have similar dependence. Therefore, one can use the measurement of PDD in water phantom for the maximum point dose in the acrylic phantom. Transmission through the sample is obtained by measuring the dose (electric charge) in acrylic
Figure 1. Experimental set-up for PDD measurements in water phantom.
Figure 2. Experimental set-up for transmission measurements in acrylic phantom.
RESULTS
Downloaded from http://rpd.oxfordjournals.org/ at The University of British Colombia Library on June 21, 2015
168
ABSORBING MATERIALS WITH APPLICATIONS IN RADIOTHERAPY Table 1. Transmission measured at a maximum depth dose for samples A, B and C with a thickness of 6 mm. Transmission (%)/electron beam energy (MeV)
Sample A Sample B Sample C
6 MeV
9 MeV
12 MeV
15 MeV
57.1 50.17 49.75
74.7 69.5 69.15
82.46 79.6 78.9
91.74 89.6 89.2
Figure 3. PDD distribution for field size 10 cm` 10 cm and different electron beam energy.
Transmission (%)/electron energy
Sample D Sample E Sample F
Figure 4. Comparison of PDD distribution in water (line) and in acrylic phantom (dots) for 6-MeV electron beam and 10 cm` 10 cm field size.
phantom, with and without the sample in the same geometry (SSD ¼ 100 cm) and using the equation: Transmissionsample ð%Þ ¼ 100
Dosesample Doseopenfield
ð1Þ
The transmission through investigated samples is measured at a maximum depth dose for the available electron beams energies in acrylic phantom. The values obtained for transmission are shown in Table 1 (for samples A, B and C) and in Table 2 (for samples D, E and F). As can be seen in Table 1 and Table 2, the transmission through each sample increases with the increase of electron beam energy. Addition of aluminium (Al)
6 MeV
9 MeV
12 MeV
15 MeV
2.95 2.4 1.76
20.01 19.53 15.62
41.3 40.8 38.14
67 66.5 64.35
particles in samples leads to a decrease in transmission, the more concentrated the aluminium, the less the transmission. From Table 2 one can observe that increasing the thickness of samples and concentration of aluminium particles (by combining samples A, B and C) the transmission decreased to 1.76 % (for sample F at an electron beam energy of 6 MeV). However, samples D, E and F can be used in clinical practice as shields, for electron beam energy of 6 MeV, because the transmission is ,3 %. In clinical practice the tumour tissue is not located only on the skin surface, it has a three-dimensional irregular shape. Consequently, for an efficient distribution of dose into the tumour volume, a combination of shields and attenuators is necessary. Therefore, as can be observed from Tables 1 and 2, all investigated samples may be used as attenuators for different electron beam energies. For instance, if the applied dose is 50 Gy the adjacent organs will receive 10 Gy in case of using sample D as attenuator with an electron beam energy of 9 MeV.
CONCLUSIONS Different laboratory made materials with absorbent properties have been identified for use in electron beam radiotherapy. The analysed samples were composite materials obtained by mixing micrometre aluminium particles with moldable silicon rubber. Samples had different
169
Downloaded from http://rpd.oxfordjournals.org/ at The University of British Colombia Library on June 21, 2015
Table 2. Transmission measured at a maximum depth dose for samples D, E and F with a thickness of 12 mm.
M. SPUNEI ET AL.
2. 3. 4. 5. 6.
7.
8. 9. 10.
ACKNOWLEDGEMENTS The authors are deeply grateful to Dr S. Dema, head of Radiotherapy Department for his cooperation during this study.
11.
FUNDING
12.
This work was supported by the strategic grant POSDRU/DMI1.5, Project ID137750 (2013), cofinanced by the European Social Fund within the Sectorial Operational Program Human Resources Development 2007 –2013.
13.
REFERENCES
14.
1. Thariat, J., Hannoun-Levi, J. M., Myint, A. S., Vuong, T. and Ge´rard, J. P. Past, present, and future of
170
radiotherapy for the benefit of patients. Nat. Rev. Clin. Oncol. 10, 52– 60 (2013). Johns, H., Bates, I. and Watson, T. 1000 Curie cobalt units for radiation therapy. I. The Saskatchewan cobalt 60 unit. Br. J. Radiol. 25, 296– 302 (1952). Fry, D. W., Harvie, R. B., Mullett, L. B. and Walkinshaw, W. A travelling wave linear accelerator for 4 MeV electrons. Nature 162, 859– 861 (1948). Johns, H. E. and Cunningham, J. R. In: The Physics of Radiology, fourth edn. Thomas, Charles C., Ed. Springfield (1983). Catterall, M. Neutron therapy at Hammersmith Hospital 1970 to 1985. A reexamination of results. Strahlenther. Onkol. 165, 298– 301 (1989). Suit, H. D., Goitein, M., Munzenrider, J., Verhey, L., Urie, M., Gragoudas, E., Koehler, A., Gottschalk, B., Sisterson, J. and Tatsuzaki, H. Increased efficacy of radiation therapy by use of proton beam. Strahlenther. Onkol. 166, 40– 44 (1990). Laramore, G. E., Griffin, T. W., Parker, R. G. and Gerdes, A. J. The use of electron beams in treating local recurrence of breast cancer in previously irradiated fields. Cancer 41, 991 –995 (1978). Tapley, N. V. Clinical Applications of the Electron Beam. John Wiley & Sons, Inc. (1976). Podgorsak, E. B. Radiation Oncology Physics: A Handbook for Teachers and Students, 289–292. IAEA (2005). Paliwal, B. R., Rommelfanger, S. and Das, R. K. Attenuation characteristics of a new compensator material: thermo-shield for high energy electron and photon beams. Med. Phys. 25 (4), 484– 487 (1998). Kudchadker, R. J., Antolak, J. A., Morrison, W. H., Wong, P. F. and Hogstrom, K. R. Utilization of custom electron bolus in head and neck radiotherapy. J. Appl. Clin. Med. Phys. 4 (4), 321–333 (2003). Weaver, R. D., Gerbi, B. J. and Dusenbery, K. E. Evaluation of eye shields made of tungsten and aluminum in high-energy electron beams. Int. J. Radiat. Oncol. Biol. Phys. 41, 233–237 (1998). Kinhikar, R. A., Tambe, C. M., Upreti, R. R., Patkar, S., Patil, K. and Deshpande, D. D. Phantom dosimetric study of nondivergent aluminum tissue compensator using ion chamber, TLD, and gafchromic film. Med. Dosim. 33(4), 286–292 (2008). IAEA. Absorbed dose determination in external beam radiotherapy: an international code of practice for dosimetry based on standards dose to water. IAEA (2000) ISSN: 1011-4289.
Downloaded from http://rpd.oxfordjournals.org/ at The University of British Colombia Library on June 21, 2015
thickness and different mass fraction of aluminium particles. Dosimetric measurements have been performed both in water phantom and in acrylic phantom and allowed the determination of the maximum point dose. The transmission through samples has been evaluated at the maximum dose point for different electron beam energies within the 6–14 MeV. The experimental results showed that the transmission through samples increases with the electron beam energy increase. For a given value of the electron beam energy the transmission decreases by addition of aluminium particles, the larger the particle concentration, the smaller the electron transmission. Also increasing the sample thickness led to the decrease in electron transmission. Taking into account the measured transmission all the investigated samples may be used as electron absorbents. In addition, samples D, E and F can be used as shields for an electron beam energy of 6 MeV, as the transmission through the samples is ,3 %. As in radiotherapy practice, both shields and attenuators are useful, this preliminary result recommends the investigated samples in clinical situation.
