1992, The British Journal of Radiology, 65, 814—815
Technical notes
Technical notes An afterloading technique utilizing The Royal London Hospital caesium-137 brain needle in an oral obturator By A. M. Tierney, BSc, B. S. Mantell, FRCP, FRCR Departments of Medical Physics and Radiotherapy and Oncology, The Royal London Hospital, London E1 1BB, UK (Received 13 September 1991 and in revised form 3 January 1992, accepted 15 January 1992) Keywords: Brachytherapy, Oral cancer
The intended use of the brain needle (Fig. 1) is the irradiation of brain tumours using a stereotactic technique (Mantell et al, 1986). We have adapted the needle to suit another purpose. A patient with a mixed tumour of the right paranasal sinuses was treated by initial chemotherapy followed by maxillectomy, leaving a large cavity extending to the roof of the sphenoid sinus, where histology of the resected specimen showed residual squamous cell carcinoma. Post-operative external irradiation using 8 MV X rays was given to the entire operated volume as a dose of 5000 cGy in 24 fractions over 36 days. It was intended to boost the dose to the region of the sphenoid sinus to minimize the risk of recurrence at this site, while keeping the dose to the brain stem within tolerance. This was achieved by brachytherapy using precisely placed radiation sources (CD 12040 miniature cylindrical sources, Amersham International) in the brain needle. In order to treat the surface of the cavity a closely fitting obturator was constructed by the dental laboratory. The mould was marked via the right nostril to obtain the entry point for the needle. Simulator films were then taken with the patient wearing the obturator. Gastrografin was used to highlight the surfaces of the obturator and the cavity and showed that they matched well. Isodoses of a tandem of sources of combined active length 10 mm and total activity 3020 MBq (81.6 mCi), were obtained from the Philips oncology support system and confirmed by calculations. The isodoses were corrected for magnification and superimposed on the simulator films enabling the desired source position to be determined. A hole was drilled in the obturator from the marked entry point allowing the needle to be inserted through the right nostril to bring the sources to the desired position (Fig. 2). A final check was made to ensure that the obturator could still be worn comfortably and that the brain needle could locate, with ease, in the obturator. The needle stayed in position and did not slip even when the patient moved so it did not appear necessary to have a method of holding the needle in position. However, a suitable tie was attached for reassurance. Fig. 3 shows the patient wearing the obturator with the needle in position. The patient did not suffer any discomfort and 814
Figure 1. Brain source needle.
with supervision was able to insert and retract the needle himself. The doses was prescribed to the maximum dose-rate on the surface of the obturator, 200 cGy h"1 and a dose of 2250 cGy was given with the needle in place for 11 h 15 min over a period of 30 h. This is shown on Fig. 4 (sagittal) from which it was also possible to estimate the dose-rate to the brain stem at 8.5 cGy h"1. Fig. 5 (coronal) shows the estimated dose-rates to the sides of the obturator and that to the left eye at 23 cGy h"' which were considered acceptable.
Figure 2. Needle situated in the obturator. The British Journal of Radiology, September 1992
Technical notes
Figure 3. Patient wearing the obturator with the needle inserted and ties to ensure correct source position is maintained.
Figure 4. Isodose distribution around the sources indicating the dose-rates on the surface of the obturator.
Brachytherapy for cavities such as the nasopharynx has long been carried out using gynaecological sources such as a radium pack and more recently high dose-rate afterloading equipment has been available for this purpose. In the absence of such a facility this technique is advantageous for radiation protection, accuracy of dosimetry and a shorter treatment time. Acknowledgments The authors wish to thank Mr El Amin and Derek Crome at the dental clinic and Paul Smith, radioactive sealed sources custodian and mould room technician, for their technical contribution. Reference MANTELL, B. S., KLEVENHAGEN, S. C , AFSHAR, F., 1986. An
afterloaded applicator for the interstitial irradiation of brain tumours. Clinical Radiology, 37, 35-38.
l. 65, No. 777
Figure 5. The estimated doses on the sides of the obturator.
815
Technical notes
Technical notes An afterloading technique utilizing The Royal London Hospital caesium-137 brain needle in an oral obturator By A. M. Tierney, BSc, B. S. Mantell, FRCP, FRCR Departments of Medical Physics and Radiotherapy and Oncology, The Royal London Hospital, London E1 1BB, UK (Received 13 September 1991 and in revised form 3 January 1992, accepted 15 January 1992) Keywords: Brachytherapy, Oral cancer
The intended use of the brain needle (Fig. 1) is the irradiation of brain tumours using a stereotactic technique (Mantell et al, 1986). We have adapted the needle to suit another purpose. A patient with a mixed tumour of the right paranasal sinuses was treated by initial chemotherapy followed by maxillectomy, leaving a large cavity extending to the roof of the sphenoid sinus, where histology of the resected specimen showed residual squamous cell carcinoma. Post-operative external irradiation using 8 MV X rays was given to the entire operated volume as a dose of 5000 cGy in 24 fractions over 36 days. It was intended to boost the dose to the region of the sphenoid sinus to minimize the risk of recurrence at this site, while keeping the dose to the brain stem within tolerance. This was achieved by brachytherapy using precisely placed radiation sources (CD 12040 miniature cylindrical sources, Amersham International) in the brain needle. In order to treat the surface of the cavity a closely fitting obturator was constructed by the dental laboratory. The mould was marked via the right nostril to obtain the entry point for the needle. Simulator films were then taken with the patient wearing the obturator. Gastrografin was used to highlight the surfaces of the obturator and the cavity and showed that they matched well. Isodoses of a tandem of sources of combined active length 10 mm and total activity 3020 MBq (81.6 mCi), were obtained from the Philips oncology support system and confirmed by calculations. The isodoses were corrected for magnification and superimposed on the simulator films enabling the desired source position to be determined. A hole was drilled in the obturator from the marked entry point allowing the needle to be inserted through the right nostril to bring the sources to the desired position (Fig. 2). A final check was made to ensure that the obturator could still be worn comfortably and that the brain needle could locate, with ease, in the obturator. The needle stayed in position and did not slip even when the patient moved so it did not appear necessary to have a method of holding the needle in position. However, a suitable tie was attached for reassurance. Fig. 3 shows the patient wearing the obturator with the needle in position. The patient did not suffer any discomfort and 814
Figure 1. Brain source needle.
with supervision was able to insert and retract the needle himself. The doses was prescribed to the maximum dose-rate on the surface of the obturator, 200 cGy h"1 and a dose of 2250 cGy was given with the needle in place for 11 h 15 min over a period of 30 h. This is shown on Fig. 4 (sagittal) from which it was also possible to estimate the dose-rate to the brain stem at 8.5 cGy h"1. Fig. 5 (coronal) shows the estimated dose-rates to the sides of the obturator and that to the left eye at 23 cGy h"' which were considered acceptable.
Figure 2. Needle situated in the obturator. The British Journal of Radiology, September 1992
Technical notes
Figure 3. Patient wearing the obturator with the needle inserted and ties to ensure correct source position is maintained.
Figure 4. Isodose distribution around the sources indicating the dose-rates on the surface of the obturator.
Brachytherapy for cavities such as the nasopharynx has long been carried out using gynaecological sources such as a radium pack and more recently high dose-rate afterloading equipment has been available for this purpose. In the absence of such a facility this technique is advantageous for radiation protection, accuracy of dosimetry and a shorter treatment time. Acknowledgments The authors wish to thank Mr El Amin and Derek Crome at the dental clinic and Paul Smith, radioactive sealed sources custodian and mould room technician, for their technical contribution. Reference MANTELL, B. S., KLEVENHAGEN, S. C , AFSHAR, F., 1986. An
afterloaded applicator for the interstitial irradiation of brain tumours. Clinical Radiology, 37, 35-38.
l. 65, No. 777
Figure 5. The estimated doses on the sides of the obturator.
815
