British Journal of Neurosurgery (1992) 6 , 543-548
ORIGINAL ARTICLE
Br J Neurosurg Downloaded from informahealthcare.com by Flinders University of South Australia on 01/08/15 For personal use only.
Stereotactic brachytherapy for malignant glioma using a relocatable frame AJIT SOFAT, STEPHEN HUGHES, JAMES BRIGGS, RONALD P. BEANEY & DAVID G. T. THOMAS
The National Hospital for Neurology and Neurosurgery, Queen Square, London; and Department of Medical Physics, Maxillo-facial Surgery and Radiotherapy, St Thomas' Hospital, London
Abstract Interstitial brachytherapy for recurrent gliomas normally necessitates the rnvasive application of a stereotactic frame by screw-fixation which must be kept on for several hours. The use of a relocatable stereotactic frame offers many advantages over conventional systems. We present our experience in 18 patients and verify that the frame used is accurate, comfortable, well tolerated and associated with no major disadvantages.
Key words: Brachytherapy, computer planning, iodine-125, recurrent glioma, relocatable fiame.
nique carry out a stereotactic CT scan with the base ring of the stereotactic frame attached to Malignant gliomas grow rapidly and comprise the patient's head with screw-pin fixa40% of all central nervous system tum0urs.I Despite improvements in treatment they con- tion.7,15-17A repeat fixation kit such as that tinue to be a major problem and the median available for the Brown-Roberts-Wells survival time in most series is consistently (BRW) stereotactic system (Radionics Inc, reported at around 9 months with less than Burlington, MA, USA) may be used but this 10% of patients surviving 2 years2 The pattern still involves making screw holes in the outer of the skull.6%'sThus, normally the CT of failure is usually local tumour r e c u ~ r e n c e . ~ ,table ~ scan, radiotherapy planning and operation Interstitial brachytherapy allows a tumouricimust be carried out on the same day. This not dal radiation dose to be delivered to a localized only is inconvenient and possibly uncomforarea while minimizing the risk of irreversible table for the patient but also creates a certain radiation damage to surrounding normal brain degree of time pressure for the completion of tis~ue.~-'~ the planning, which may take several hours. A Our strategy in planning the interstitial further problem is that the stereotactic frame is brachytherapy of patients harbouring recurrent prevented from any other use for the duration malignant gliomas has been to use the minimum number of catheters, into which I2%odine of the whole procedure. A possible solution to seeds are after-loaded, to achieve a smooth this is to use a relocatable stereotactic sysdose distribution to the surface of the tu- tem.19-21This allows accurate re-application m o ~ r . " - ~Most ~ centres utilizing this tech- of a stereotactic frame so that procedures
Introduction
543
544
Ajit Sofut et al.
dependent on the frame can be carried out at different times.
Materials and methods
Br J Neurosurg Downloaded from informahealthcare.com by Flinders University of South Australia on 01/08/15 For personal use only.
Stereotactic frame The BRW stereotactic system and Gill Thomas Locator (GTL; Radionics Inc) were used in our s t ~ d y . ' The ~ . ~latter ~ consists of a noninvasive frame made of an anodized aluminium alloy. It is mounted onto the patient's head by temporary fixation to the maxillary teeth using a dental splint. The frame is further secured by two sets of vertical straps and an occipital back plate (Fig. 1). Normally the dental splint can be made within a few minutes by taking a dental impression using diethyl methylmethacrylate or UV-A cured dental impression material in a standard dental tray. Our approach was to adapt the frame slightly so that a purpose-made dental splint could be fixed directly onto it. The G T L is compatible with both the BRW and CRW systems.
sion. Dental plaster was poured into the impression which hardened to produce a positive model of the standing teeth. T h e gingival margins of the teeth were slightly deepened with a sharp instrument keeping in line with the curvature of each individual tooth. This model was duplicated using hard stone. A 3 mm sheet of dental modelling wax was then adapted over the teeth and trimmed around the gingival margins. T h e wax splint was invested with plaster of Paris. When this had hardened the wax was removed thus leaving an exact mould into which dental acrylic (methyl methacrylate) could be packed. When this had hardened the splint was removed and trimmed. The completed appliance could then be fitted to the duplicate model preventing any unnecessary easing before it was fitted onto the teeth. Small holes were made in the transparent acrylic splint so that once in place in the patient's mouth, apposition to the occlusal surface of the teeth could easily be ascertained.
Accuracy check The accuracy of the relocatability of the frame is dependent on the quality of the dental splint. This was evaluated in two ways. T h e frame was applied together with the BRW arc with a metal probe so positioned that it pointed to a position on the scalp. This was marked. The frame was removed and reapplied. The proximity of the probe to the point previously marked was noted. This was done in five patients (Table I). TABLE I. Proximity of the probe to the point previously marked
I . Gill Thomas Locator fitted onto a patient with BRW base and C T localizer ring. FIG.
Patient
2 3
Dental splint T o manufacture a dental splint a negative likeness of the patient's upper teeth was obtained by taking a routine alginate impres-
Application 1 Application 2 (mm) (mm)
4
ORIGINAL ARTICLE
Br J Neurosurg Downloaded from informahealthcare.com by Flinders University of South Australia on 01/08/15 For personal use only.
Stereotactic brachytherapy for malignant glioma using a relocatable frame AJIT SOFAT, STEPHEN HUGHES, JAMES BRIGGS, RONALD P. BEANEY & DAVID G. T. THOMAS
The National Hospital for Neurology and Neurosurgery, Queen Square, London; and Department of Medical Physics, Maxillo-facial Surgery and Radiotherapy, St Thomas' Hospital, London
Abstract Interstitial brachytherapy for recurrent gliomas normally necessitates the rnvasive application of a stereotactic frame by screw-fixation which must be kept on for several hours. The use of a relocatable stereotactic frame offers many advantages over conventional systems. We present our experience in 18 patients and verify that the frame used is accurate, comfortable, well tolerated and associated with no major disadvantages.
Key words: Brachytherapy, computer planning, iodine-125, recurrent glioma, relocatable fiame.
nique carry out a stereotactic CT scan with the base ring of the stereotactic frame attached to Malignant gliomas grow rapidly and comprise the patient's head with screw-pin fixa40% of all central nervous system tum0urs.I Despite improvements in treatment they con- tion.7,15-17A repeat fixation kit such as that tinue to be a major problem and the median available for the Brown-Roberts-Wells survival time in most series is consistently (BRW) stereotactic system (Radionics Inc, reported at around 9 months with less than Burlington, MA, USA) may be used but this 10% of patients surviving 2 years2 The pattern still involves making screw holes in the outer of the skull.6%'sThus, normally the CT of failure is usually local tumour r e c u ~ r e n c e . ~ ,table ~ scan, radiotherapy planning and operation Interstitial brachytherapy allows a tumouricimust be carried out on the same day. This not dal radiation dose to be delivered to a localized only is inconvenient and possibly uncomforarea while minimizing the risk of irreversible table for the patient but also creates a certain radiation damage to surrounding normal brain degree of time pressure for the completion of tis~ue.~-'~ the planning, which may take several hours. A Our strategy in planning the interstitial further problem is that the stereotactic frame is brachytherapy of patients harbouring recurrent prevented from any other use for the duration malignant gliomas has been to use the minimum number of catheters, into which I2%odine of the whole procedure. A possible solution to seeds are after-loaded, to achieve a smooth this is to use a relocatable stereotactic sysdose distribution to the surface of the tu- tem.19-21This allows accurate re-application m o ~ r . " - ~Most ~ centres utilizing this tech- of a stereotactic frame so that procedures
Introduction
543
544
Ajit Sofut et al.
dependent on the frame can be carried out at different times.
Materials and methods
Br J Neurosurg Downloaded from informahealthcare.com by Flinders University of South Australia on 01/08/15 For personal use only.
Stereotactic frame The BRW stereotactic system and Gill Thomas Locator (GTL; Radionics Inc) were used in our s t ~ d y . ' The ~ . ~latter ~ consists of a noninvasive frame made of an anodized aluminium alloy. It is mounted onto the patient's head by temporary fixation to the maxillary teeth using a dental splint. The frame is further secured by two sets of vertical straps and an occipital back plate (Fig. 1). Normally the dental splint can be made within a few minutes by taking a dental impression using diethyl methylmethacrylate or UV-A cured dental impression material in a standard dental tray. Our approach was to adapt the frame slightly so that a purpose-made dental splint could be fixed directly onto it. The G T L is compatible with both the BRW and CRW systems.
sion. Dental plaster was poured into the impression which hardened to produce a positive model of the standing teeth. T h e gingival margins of the teeth were slightly deepened with a sharp instrument keeping in line with the curvature of each individual tooth. This model was duplicated using hard stone. A 3 mm sheet of dental modelling wax was then adapted over the teeth and trimmed around the gingival margins. T h e wax splint was invested with plaster of Paris. When this had hardened the wax was removed thus leaving an exact mould into which dental acrylic (methyl methacrylate) could be packed. When this had hardened the splint was removed and trimmed. The completed appliance could then be fitted to the duplicate model preventing any unnecessary easing before it was fitted onto the teeth. Small holes were made in the transparent acrylic splint so that once in place in the patient's mouth, apposition to the occlusal surface of the teeth could easily be ascertained.
Accuracy check The accuracy of the relocatability of the frame is dependent on the quality of the dental splint. This was evaluated in two ways. T h e frame was applied together with the BRW arc with a metal probe so positioned that it pointed to a position on the scalp. This was marked. The frame was removed and reapplied. The proximity of the probe to the point previously marked was noted. This was done in five patients (Table I). TABLE I. Proximity of the probe to the point previously marked
I . Gill Thomas Locator fitted onto a patient with BRW base and C T localizer ring. FIG.
Patient
2 3
Dental splint T o manufacture a dental splint a negative likeness of the patient's upper teeth was obtained by taking a routine alginate impres-
Application 1 Application 2 (mm) (mm)
4
