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The use of an advanced composite material as an alternative to carbon fibre in radiotherapy
Radiography 18 (2012) 74e77
Contents lists available at SciVerse ScienceDirect
Radiography journal homepage: www.elsevier.com/locate/radi
The use of an advanced composite material as an alternative to carbon fibre in radiotherapy K.A. Langmack* Radiotherapy Physics, Nottingham City Hospital Campus, Nottingham University Hospital, Hucknall Road, Nottingham NG5 1PB, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 November 2011 Received in revised form 31 January 2012 Accepted 3 February 2012 Available online 24 February 2012
Carbon fibre has become the material of choice for many radiotherapy accessories, as it is lightweight, radio-translucent and rigid. Unfortunately specialised equipment is required to manufacture devices from it and hence these tend to be expensive. Also carbon fibre is conducting which limits its compatibility with MRI. Other composite materials have now become available that are rigid and lightweight and may be equally radio-translucent. Here we describe the use, in radiotherapy, of such a composite made of polypropylene and fibre glass (PFGC) that is MRI compatible. We measured the 6 MV x-ray transmission and build-up properties of 2.5 cm thick panels made of either carbon fibre or PFGC. They are found to have equivalent x-ray transmission properties, varying from about 0.98 at perpendicular incidence to about 0.96 at 60 oblique incidence. The build-up dose was found to be approximately 82% of the maximum dose. We also demonstrate the use of PFGC as a flat couch top for MRI scanners and as a head board for shell immobilisation devices. Ó 2012 The College of Radiographers. Published by Elsevier Ltd. All rights reserved.
Keywords: MRI Transmission
Introduction Carbon fibre was first suggested as an ideal material for radiotherapy by de Mooy due to its strength, rigidity and low density.1 For radiotherapy applications it has been shown to have low attenuation, but a significant effect on skin dose.2,3 More recently the attenuating effect of oblique incidence through carbon fibre tabletops due to the increased radiation path length has been recognised.4 However there are some disadvantages to the use of carbon fibre in radiotherapy. Specialised equipment is required to produce devices from carbon fibre.1 So carbon fibre accessories tend to be expensive and many departments do not have facilities to manufacture these in-house. Also, as magnetic resonance imaging (MRI) becomes an important imaging modality in radiotherapy treatment planning,5e7 MRI compatible accessories and flat couches are required for treatment simulation. Carbon fibre is conducting so can heat and produce image artefacts in MRI scanners.8 Also the construction material for an MR-compatible incubator had to be changed from carbon fibre to high tensile polyester as the conducting nature of carbon fibre produced RF shadowing artefacts.9 Hence it is not the ideal construction material for accessories that are required to be used with patients requiring MRI planning scans. * Tel.: þ44 (0)115 969116; fax: þ44 (0)115 9627994. E-mail address: [email protected].
Other composite materials have now become available that are rigid and lightweight and potentially are equally radio-translucent as carbon fibre. As fibre glass and carbon fibre have similar tensile strengths (3.45 GPa v 3.53 GPa typically), composite materials based on fibre glass can be as strong as those based on carbon fibre. Many such materials are produced on a commercial scale and can be fashioned in a reasonably well-equipped workshop. These materials could provide a cost-effective alternative to carbon fibre for some radiotherapy applications. Also these materials are nonconducting, so could be used to manufacture MRI-compatible radiotherapy couch tops and accessories. One such material is a composite of fibre glass and polypropylene, PFGC (Medibord Ltd, Nottingham, UK). This material comes as a thermoplastic sandwich panel, consisting of a polypropylene honeycomb with a glass fibre reinforced polypropylene face sheet joined to the honeycomb by a lamination process. Similar materials have a number of applications in the construction of commercial vehicles, portable buildings and logistic containers. It is possible to work this material in a reasonably well-equipped mechanical workshop and is manufacture from insulting materials making it MRI compatible. Here we compare the radiation transmission and build-up properties of this PFGC with a traditional carbon fibre panel from a radiotherapy couch top (Civco Medical Solutions, Kalona, Iowa, USA). We also describe the use of PFGC to fabricate a flat couch top for an MRI scanner and a shell head board for radiotherapy treatment planning purposes.
1078-8174/$ e see front matter Ó 2012 The College of Radiographers. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.radi.2012.02.001
K.A. Langmack / Radiography 18 (2012) 74e77
Direct radiation transmission A 0.6 cc thimble ionisation chamber (NE2571A, QADOS, Berkshire, UK) connected to an NE 2620 electrometer (QADOS, Berkshire, UK) was placed 5 cm deep in a block of solid water (WT1 manufactured by Barts NHS Trust, Tissue Equivalent Section, London, UK). The surface of the block was placed at 100 cm from the focus of an Elekta Precise linac (Elekta, Crawley, England). Three readings were taken using 400 MU with a 10 cm 10 cm square field and 6 MV x-ray beam. These readings were repeated with either a 2.5 cm thick carbon fibre panel or a 2.5 cm thick PFGC panel placed on top of the block. The ratio of the mean readings with and without the panels was used to calculate the transmission factors of the panels. Effect of gantry angle on x-ray transmission The x-ray transmission of such panels can be significantly affected by oblique incidence increasing the path length of radiation passing through the panel.4 So the method of McCormack, Diffey and Morgan4 was adapted to determine this effect with these carbon fibre and PFGC panels. Briefly, a 16 cm diameter Perspex cylinder was placed on top of the linac couch that had either the carbon fibre or PFGC panel inserted. A 0.6 cc thimble ionisation chamber was placed at the centre of the cylinder and the cylinder was centred at the isocentre of the linac. A 5 cm wide by 10 cm long field was used to irradiate the cylinder with 400 MU of 6 MV x-rays at a range of gantry angles between 180 and 90 . Three readings were taken per gantry angle. Unlike McCormack, Diffey and Morgan,4 the couch did not have a mylar cover able to support the cylinder in the absence of the panel, so we estimated the withoutpanel readings by taking readings at a variety of gantry angles where the panel did not intercept the beam. We used the variation in these reading to estimate the uncertainty caused by the slight variation of linac output with gantry angle that is generally observed. The ratio of the without-panel reading to with-panel reading was plotted as a function of gantry angel to demonstrate the variation of correction factor with gantry angle for the two panels. Measurement of build-up due to the panels
treatment position. This is required for accurate image registration with planning CT scans and allows image fusion using our virtual simulation package (ProSoma, MedCom, Germany). A 25 mm thick PFGC sheet was used to manufacture a shell head board to enable some of our head and neck cancer patients to be MRI scanned in the treatment position, again to enable accurate image registration with CT planning scans. Such fused multimodality imaging has been shown to improve accuracy in tumour delineation in head and neck cancer.6,7 Results Direct radiation transmission The 6 MV transmission factor for the carbon fibre panel was measured to be 0.984 0.002, and that for the PFGC panel was found to be 0.986 0.002. This demonstrates that the PFGC panel has a very similar direct 6 MV x-ray transmission value to the carbon fibre panel of the same thickness. Effect of gantry angle on x-ray transmission The variation of correction factor with gantry angle is shown in Fig. 1. The uncertainty due to the variation of linac output with gantry angle was found to be 0.5%. As can be seen from this figure the PFGC panel has a very similar variation in x-ray transmission with gantry angle as the traditional carbon fibre panel. The direct correction factor is about 1.018, increasing to 1.041 at 60 to the normal where the beam passes through the maximum thickness of the material. This is less that that in McCormack, Diffey and Morgan,4 but the direct transmission value is in agreement in other publications.2,3 It is noted by McCormack, Diffey and Morgan4 that these factors need to be measured locally due to differences caused by variations in panel construction. Build-up measurements The build-up curve is shown in Fig. 2. The carbon fibre panel was found to produce a skin dose of 83.1% of Dmax (4.6 mm of water equivalent thickness), and that of the PFGC panel was 81.5% of Dmax (4.4 mm of water equivalent thickness). Hence in this property the PFGC panel is also equivalent to the traditional carbon fibre panel.
An NACP2 chamber (QADOS, Berkshire, UK) was placed with its front face flush to the surface of a block of WT1 solid water. The surface of the chamber was place on the central axis of a 10 cm by 10 cm square field at 100 cm from the radiation focus of an Elekta Precise linac using 400 MU of a 6 MV x-ray beam. A build-up curve was obtained by placing increasing thicknesses of solid water on top of the chamber and block. This was done until the depth of maximum dose (Dmax) had been exceeded. Two readings were taken per thickness. The additional solid water on top of the block was then removed and replace by either the carbon fibre or PFGC panel. The ratio of the mean with-panel readings to the mean readings at Dmax was used to calculate the percentage build-up due the panels. The build-up curve was used to estimate the water equivalent thickness of the panels.
1.05 Carbon fibre
1.04
PGFC 1.03
1.02
Clinical examples e MRI compatible couch top and shell head board A flat sheet of 15 mm thick PFGC was manufactured by our workshop to fit the hospital’s MRI scanner couch (Signa Excite 1.5T, GE, UK). This provided a flat couch top similar to those found in radiotherapy so that MRI could be used to scan patients in the
Correction Factor
Materials and methods
75
1.01 190
170
150
130
110
90
Gantry Angle Figure 1. Variation of correction factor with gantry angle. Error bars indicate data range.
76
K.A. Langmack / Radiography 18 (2012) 74e77
120.0
Percent of Dmax
100.0 80.0 60.0
Build-up curve Carbon fibre
40.0
PGFC 20.0 0.0 0
5
10
15
20
25
Added Build-up (mm) Figure 2. Build-up curve. Error bars are too small to show.
Clinical examples e MRI compatible couch top and shell head board A pelvic MRI with the PFGC couch top present is shown in Fig. 3. We have used this couch top to MRI simulate the majority of our prostate cancer patients since 2008 (approximately 400 patients). We have not observed any image quality issues with these scans. An MRI with the PFGC head board present is shown in Fig. 4. This head board can be used during radiotherapy treatments as well as for scanning purposes. It has only recently been introduced into clinical use, but is proving very successful with over 20 patients being treated using it. Discussion In this study the PFGC panel was found to have very similar x-ray transmission and build-up properties to a traditional carbon fibre panel in routine use in radiotherapy. So PFGC has the potential to provide an alternative to carbon fibre in the construction of radiotherapy accessories if it proves to be as light and mechanically
Figure 4. An axial T1 weighted MRI scan of a subject immobilised with a shell. The shell head board is made of 25 mm thick PFGC.
rigid as carbon fibre. Medibord produces PFGC panels in several thicknesses (15e50 mm). The 25 mm panel used in this study had an area density of 4.4 kgm2, while the carbon fibre panel of the same thickness had an area density of 5.5 kgm2. So there is a weight advantage in favour of PFGC over carbon fibre for the same size of panel. As for strength, PFGC can be used as a building material. Qualitatively the PFGC panels we have seem as rigid as carbon fibre panels. It is possible to shape PFGC during manufacture, and put various fastenings into the material. Hence it is possible to fabricate radiotherapy accessories from this material. One interesting difference between PFGC and carbon fibre is its compatibility with MRI scanners. As carbon fibre conducts electricity, when it is placed in an MRI scanner eddy currents can be produced. These currents can lead to heating of the material and image artefacts. PFGC does not conduct electricity so does not display these effects. We have successfully constructed a flat table top insert for an MRI scanner and an MRI compatible shell head board from panels of this material. These are in routine clinical use at our hospital for carrying out planning MRI scans for radiotherapy treatment planning. The shell head board is also being used during radiotherapy treatments. Conclusions PFGC has very similar 6 MV radiation transmission properties to carbon fibre. It can be used as an alternative material to carbon fibre in the construction of accessories for radiotherapy applications, especially where MRI compatibility is required. References
Figure 3. An axial T2 weighted MRI scan of a pelvis. The subject is lying on a flat couch top made from a 15 mm thick PFGC panel.
1. de Mooy LG. The use of carbon fibres in radiotherapy. Radiother Oncol 1991;22:140e2. 2. De Ost B, Vanregemorter J, Schaeken B, Van den Weyngaert D. The effect of carbon fibre inserts on the build-up and attenuation of high energy photon beams. Radiother Oncol 1997;45:275e7.
K.A. Langmack / Radiography 18 (2012) 74e77 3. Meara SJ, Langmack KA. An investigation into the use of carbon fibre for megavoltage radiotherapy applications. Phys Med Biol 1998;43:1359e66. 4. McCormack S, Diffey J, Morgan A. The effect of gantry angle on megavoltage photon beam attenuation by a carbon fiber couch insert. Med Phys 2005;32:483e7. 5. The Royal College of Radiologists. Imaging for oncology: collaboration between clinical radiologists and clinical oncologists in diagnosis, staging and radiotherapy planning. Board of the Faculty of Clinical Oncology; 2004. 6. Ahmed M, Schmidt M, Sohaib A, Kong C, Burke K, Richardson C, et al. The value of magnetic resonance imaging in target volume delineation of base of tongue tumours e A study using flexible surface coils. Radioth Oncol 2010;94:161e7.
77
7. Verduijn GM, Bartels LW, Raaijmakers CPJ, Terhaard CHJ, Pameijer FA, Van Den Berg CAT. Magnetic resonance imaging protocol optimization for delineation of gross tumor volume in hypopharyngeal and laryngeal tumors. Int J Radiat Oncol Biol Phys 2009;74:630e6. 8. Ernstberger T, Buchhorn G, Baums MH, Heidrich G. In-vitro MRI detectability of interbody test spacers made of carbon fibre-reinforced polymers, titanium and titanium-coated carbon fibre-reinforced polymers. Acta Orthop Belg 2007;73: 244e9. 9. Paley MNJ, Hart AR, Lait M, Griffiths PD. An MR-compatible neonatal incubator. Br J Radiol December 13, 2011. doi:10.1259/bjr/30017508.
Contents lists available at SciVerse ScienceDirect
Radiography journal homepage: www.elsevier.com/locate/radi
The use of an advanced composite material as an alternative to carbon fibre in radiotherapy K.A. Langmack* Radiotherapy Physics, Nottingham City Hospital Campus, Nottingham University Hospital, Hucknall Road, Nottingham NG5 1PB, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 November 2011 Received in revised form 31 January 2012 Accepted 3 February 2012 Available online 24 February 2012
Carbon fibre has become the material of choice for many radiotherapy accessories, as it is lightweight, radio-translucent and rigid. Unfortunately specialised equipment is required to manufacture devices from it and hence these tend to be expensive. Also carbon fibre is conducting which limits its compatibility with MRI. Other composite materials have now become available that are rigid and lightweight and may be equally radio-translucent. Here we describe the use, in radiotherapy, of such a composite made of polypropylene and fibre glass (PFGC) that is MRI compatible. We measured the 6 MV x-ray transmission and build-up properties of 2.5 cm thick panels made of either carbon fibre or PFGC. They are found to have equivalent x-ray transmission properties, varying from about 0.98 at perpendicular incidence to about 0.96 at 60 oblique incidence. The build-up dose was found to be approximately 82% of the maximum dose. We also demonstrate the use of PFGC as a flat couch top for MRI scanners and as a head board for shell immobilisation devices. Ó 2012 The College of Radiographers. Published by Elsevier Ltd. All rights reserved.
Keywords: MRI Transmission
Introduction Carbon fibre was first suggested as an ideal material for radiotherapy by de Mooy due to its strength, rigidity and low density.1 For radiotherapy applications it has been shown to have low attenuation, but a significant effect on skin dose.2,3 More recently the attenuating effect of oblique incidence through carbon fibre tabletops due to the increased radiation path length has been recognised.4 However there are some disadvantages to the use of carbon fibre in radiotherapy. Specialised equipment is required to produce devices from carbon fibre.1 So carbon fibre accessories tend to be expensive and many departments do not have facilities to manufacture these in-house. Also, as magnetic resonance imaging (MRI) becomes an important imaging modality in radiotherapy treatment planning,5e7 MRI compatible accessories and flat couches are required for treatment simulation. Carbon fibre is conducting so can heat and produce image artefacts in MRI scanners.8 Also the construction material for an MR-compatible incubator had to be changed from carbon fibre to high tensile polyester as the conducting nature of carbon fibre produced RF shadowing artefacts.9 Hence it is not the ideal construction material for accessories that are required to be used with patients requiring MRI planning scans. * Tel.: þ44 (0)115 969116; fax: þ44 (0)115 9627994. E-mail address: [email protected].
Other composite materials have now become available that are rigid and lightweight and potentially are equally radio-translucent as carbon fibre. As fibre glass and carbon fibre have similar tensile strengths (3.45 GPa v 3.53 GPa typically), composite materials based on fibre glass can be as strong as those based on carbon fibre. Many such materials are produced on a commercial scale and can be fashioned in a reasonably well-equipped workshop. These materials could provide a cost-effective alternative to carbon fibre for some radiotherapy applications. Also these materials are nonconducting, so could be used to manufacture MRI-compatible radiotherapy couch tops and accessories. One such material is a composite of fibre glass and polypropylene, PFGC (Medibord Ltd, Nottingham, UK). This material comes as a thermoplastic sandwich panel, consisting of a polypropylene honeycomb with a glass fibre reinforced polypropylene face sheet joined to the honeycomb by a lamination process. Similar materials have a number of applications in the construction of commercial vehicles, portable buildings and logistic containers. It is possible to work this material in a reasonably well-equipped mechanical workshop and is manufacture from insulting materials making it MRI compatible. Here we compare the radiation transmission and build-up properties of this PFGC with a traditional carbon fibre panel from a radiotherapy couch top (Civco Medical Solutions, Kalona, Iowa, USA). We also describe the use of PFGC to fabricate a flat couch top for an MRI scanner and a shell head board for radiotherapy treatment planning purposes.
1078-8174/$ e see front matter Ó 2012 The College of Radiographers. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.radi.2012.02.001
K.A. Langmack / Radiography 18 (2012) 74e77
Direct radiation transmission A 0.6 cc thimble ionisation chamber (NE2571A, QADOS, Berkshire, UK) connected to an NE 2620 electrometer (QADOS, Berkshire, UK) was placed 5 cm deep in a block of solid water (WT1 manufactured by Barts NHS Trust, Tissue Equivalent Section, London, UK). The surface of the block was placed at 100 cm from the focus of an Elekta Precise linac (Elekta, Crawley, England). Three readings were taken using 400 MU with a 10 cm 10 cm square field and 6 MV x-ray beam. These readings were repeated with either a 2.5 cm thick carbon fibre panel or a 2.5 cm thick PFGC panel placed on top of the block. The ratio of the mean readings with and without the panels was used to calculate the transmission factors of the panels. Effect of gantry angle on x-ray transmission The x-ray transmission of such panels can be significantly affected by oblique incidence increasing the path length of radiation passing through the panel.4 So the method of McCormack, Diffey and Morgan4 was adapted to determine this effect with these carbon fibre and PFGC panels. Briefly, a 16 cm diameter Perspex cylinder was placed on top of the linac couch that had either the carbon fibre or PFGC panel inserted. A 0.6 cc thimble ionisation chamber was placed at the centre of the cylinder and the cylinder was centred at the isocentre of the linac. A 5 cm wide by 10 cm long field was used to irradiate the cylinder with 400 MU of 6 MV x-rays at a range of gantry angles between 180 and 90 . Three readings were taken per gantry angle. Unlike McCormack, Diffey and Morgan,4 the couch did not have a mylar cover able to support the cylinder in the absence of the panel, so we estimated the withoutpanel readings by taking readings at a variety of gantry angles where the panel did not intercept the beam. We used the variation in these reading to estimate the uncertainty caused by the slight variation of linac output with gantry angle that is generally observed. The ratio of the without-panel reading to with-panel reading was plotted as a function of gantry angel to demonstrate the variation of correction factor with gantry angle for the two panels. Measurement of build-up due to the panels
treatment position. This is required for accurate image registration with planning CT scans and allows image fusion using our virtual simulation package (ProSoma, MedCom, Germany). A 25 mm thick PFGC sheet was used to manufacture a shell head board to enable some of our head and neck cancer patients to be MRI scanned in the treatment position, again to enable accurate image registration with CT planning scans. Such fused multimodality imaging has been shown to improve accuracy in tumour delineation in head and neck cancer.6,7 Results Direct radiation transmission The 6 MV transmission factor for the carbon fibre panel was measured to be 0.984 0.002, and that for the PFGC panel was found to be 0.986 0.002. This demonstrates that the PFGC panel has a very similar direct 6 MV x-ray transmission value to the carbon fibre panel of the same thickness. Effect of gantry angle on x-ray transmission The variation of correction factor with gantry angle is shown in Fig. 1. The uncertainty due to the variation of linac output with gantry angle was found to be 0.5%. As can be seen from this figure the PFGC panel has a very similar variation in x-ray transmission with gantry angle as the traditional carbon fibre panel. The direct correction factor is about 1.018, increasing to 1.041 at 60 to the normal where the beam passes through the maximum thickness of the material. This is less that that in McCormack, Diffey and Morgan,4 but the direct transmission value is in agreement in other publications.2,3 It is noted by McCormack, Diffey and Morgan4 that these factors need to be measured locally due to differences caused by variations in panel construction. Build-up measurements The build-up curve is shown in Fig. 2. The carbon fibre panel was found to produce a skin dose of 83.1% of Dmax (4.6 mm of water equivalent thickness), and that of the PFGC panel was 81.5% of Dmax (4.4 mm of water equivalent thickness). Hence in this property the PFGC panel is also equivalent to the traditional carbon fibre panel.
An NACP2 chamber (QADOS, Berkshire, UK) was placed with its front face flush to the surface of a block of WT1 solid water. The surface of the chamber was place on the central axis of a 10 cm by 10 cm square field at 100 cm from the radiation focus of an Elekta Precise linac using 400 MU of a 6 MV x-ray beam. A build-up curve was obtained by placing increasing thicknesses of solid water on top of the chamber and block. This was done until the depth of maximum dose (Dmax) had been exceeded. Two readings were taken per thickness. The additional solid water on top of the block was then removed and replace by either the carbon fibre or PFGC panel. The ratio of the mean with-panel readings to the mean readings at Dmax was used to calculate the percentage build-up due the panels. The build-up curve was used to estimate the water equivalent thickness of the panels.
1.05 Carbon fibre
1.04
PGFC 1.03
1.02
Clinical examples e MRI compatible couch top and shell head board A flat sheet of 15 mm thick PFGC was manufactured by our workshop to fit the hospital’s MRI scanner couch (Signa Excite 1.5T, GE, UK). This provided a flat couch top similar to those found in radiotherapy so that MRI could be used to scan patients in the
Correction Factor
Materials and methods
75
1.01 190
170
150
130
110
90
Gantry Angle Figure 1. Variation of correction factor with gantry angle. Error bars indicate data range.
76
K.A. Langmack / Radiography 18 (2012) 74e77
120.0
Percent of Dmax
100.0 80.0 60.0
Build-up curve Carbon fibre
40.0
PGFC 20.0 0.0 0
5
10
15
20
25
Added Build-up (mm) Figure 2. Build-up curve. Error bars are too small to show.
Clinical examples e MRI compatible couch top and shell head board A pelvic MRI with the PFGC couch top present is shown in Fig. 3. We have used this couch top to MRI simulate the majority of our prostate cancer patients since 2008 (approximately 400 patients). We have not observed any image quality issues with these scans. An MRI with the PFGC head board present is shown in Fig. 4. This head board can be used during radiotherapy treatments as well as for scanning purposes. It has only recently been introduced into clinical use, but is proving very successful with over 20 patients being treated using it. Discussion In this study the PFGC panel was found to have very similar x-ray transmission and build-up properties to a traditional carbon fibre panel in routine use in radiotherapy. So PFGC has the potential to provide an alternative to carbon fibre in the construction of radiotherapy accessories if it proves to be as light and mechanically
Figure 4. An axial T1 weighted MRI scan of a subject immobilised with a shell. The shell head board is made of 25 mm thick PFGC.
rigid as carbon fibre. Medibord produces PFGC panels in several thicknesses (15e50 mm). The 25 mm panel used in this study had an area density of 4.4 kgm2, while the carbon fibre panel of the same thickness had an area density of 5.5 kgm2. So there is a weight advantage in favour of PFGC over carbon fibre for the same size of panel. As for strength, PFGC can be used as a building material. Qualitatively the PFGC panels we have seem as rigid as carbon fibre panels. It is possible to shape PFGC during manufacture, and put various fastenings into the material. Hence it is possible to fabricate radiotherapy accessories from this material. One interesting difference between PFGC and carbon fibre is its compatibility with MRI scanners. As carbon fibre conducts electricity, when it is placed in an MRI scanner eddy currents can be produced. These currents can lead to heating of the material and image artefacts. PFGC does not conduct electricity so does not display these effects. We have successfully constructed a flat table top insert for an MRI scanner and an MRI compatible shell head board from panels of this material. These are in routine clinical use at our hospital for carrying out planning MRI scans for radiotherapy treatment planning. The shell head board is also being used during radiotherapy treatments. Conclusions PFGC has very similar 6 MV radiation transmission properties to carbon fibre. It can be used as an alternative material to carbon fibre in the construction of accessories for radiotherapy applications, especially where MRI compatibility is required. References
Figure 3. An axial T2 weighted MRI scan of a pelvis. The subject is lying on a flat couch top made from a 15 mm thick PFGC panel.
1. de Mooy LG. The use of carbon fibres in radiotherapy. Radiother Oncol 1991;22:140e2. 2. De Ost B, Vanregemorter J, Schaeken B, Van den Weyngaert D. The effect of carbon fibre inserts on the build-up and attenuation of high energy photon beams. Radiother Oncol 1997;45:275e7.
K.A. Langmack / Radiography 18 (2012) 74e77 3. Meara SJ, Langmack KA. An investigation into the use of carbon fibre for megavoltage radiotherapy applications. Phys Med Biol 1998;43:1359e66. 4. McCormack S, Diffey J, Morgan A. The effect of gantry angle on megavoltage photon beam attenuation by a carbon fiber couch insert. Med Phys 2005;32:483e7. 5. The Royal College of Radiologists. Imaging for oncology: collaboration between clinical radiologists and clinical oncologists in diagnosis, staging and radiotherapy planning. Board of the Faculty of Clinical Oncology; 2004. 6. Ahmed M, Schmidt M, Sohaib A, Kong C, Burke K, Richardson C, et al. The value of magnetic resonance imaging in target volume delineation of base of tongue tumours e A study using flexible surface coils. Radioth Oncol 2010;94:161e7.
77
7. Verduijn GM, Bartels LW, Raaijmakers CPJ, Terhaard CHJ, Pameijer FA, Van Den Berg CAT. Magnetic resonance imaging protocol optimization for delineation of gross tumor volume in hypopharyngeal and laryngeal tumors. Int J Radiat Oncol Biol Phys 2009;74:630e6. 8. Ernstberger T, Buchhorn G, Baums MH, Heidrich G. In-vitro MRI detectability of interbody test spacers made of carbon fibre-reinforced polymers, titanium and titanium-coated carbon fibre-reinforced polymers. Acta Orthop Belg 2007;73: 244e9. 9. Paley MNJ, Hart AR, Lait M, Griffiths PD. An MR-compatible neonatal incubator. Br J Radiol December 13, 2011. doi:10.1259/bjr/30017508.