1976, British Journal of Radiology, 49, 963-965
NOVEMBER 1976
Technical note The Edinburgh afterloading technique for carcinoma of the uterine cervix By A. T. Redpath, B.Sc, Ph.D., M. A. J. T. Douglas, M. D., F.R.C.R., and J. A. Orr, F.R.C.S.E., F.R.C.R. Departments of Medical Physics and Radiotherapy, Western General Hospital, Edinburgh EH4 2XU {Received February, 1976 and in revised form July, 1976)
A partially afterloaded line source system was developed in Edinburgh and put into use in 1960 (Campbell and Douglas, 1966). In this system the intra-uterine source was preloaded and only the vaginal component afterloaded. With the availability of small caesium sources a modification has been made to allow full but manual afterloading. The sources manufactured by the Radiochemical Centre at Amersham, are 5 mm in length and 2 mm in diameter. The treatment regime is very similar to that described by Campbell and Douglas (1966).
applicators is possible. The caesium loading is uniform and varies from 20 to 70 mg radium equivalent according to the length of the holder (from two to 11 individual sources). The vaginal portion of the source holder is a rigid steel tube again 2.5 mm in diameter, and may contain from 25 to 70 mg radium equivalent (two to six sources). Loading is again
DESIGN OF THE CAESIUM APPLICATORS
A new flexible intra-uterine applicator has replaced the straight tube used in the earlier system, and the construction of the complete applicator is shown in Fig. 1. The external appearance of the vaginal applicator has not changed and still consists of Perspex bobbins and a perineal bar threaded over a stainless steel tube. Lead shielding is used posteriorly, and the applicators are available from 2 cm to 4 cm in diameter. The length of the intravaginal portion can be varied by altering the position of the perineal bar, and a screw locking nut at the lower end keeps the component parts firmly in place. The main difference between the present applicator and the previous one is that the central steel tube is not sealed at the proximal end. This allows the extrusion of a flexible Portex tube into the uterus after passage through the central steel tube of the vaginal applicator. This Portex tube (shown again in Fig. 2B) ultimately accommodates the caesium source holder (Fig. 2c), and is 4 mm in diameter and of varying length corresponding to the source holder. A small metal collar denotes the level of the external os, and is therefore the lower limit of the intra-uterine sources. The vaginal applicator (Fig. 2D) can slide over the Portex tube as far as this metal collar. The intra-uterine source holder is made of flexible steel mesh 2.5 mm external diameter and is available in varying lengths to accommodate a uterine cavity 3, 5, 6, 7 or 9 cm long. This holder is sealed at both ends and screws into the vaginal source holder (Fig. 2c) and therefore complete interchangeability of both
FIG. 1. The Complete Applicator A—Intra-uterine applicator B—Lead Shielding c—Perineal bar D—Perspex bobbins E—Locking nut
963
D FIG. 2. -Introducer -Source holder, Portex tube attached to stainless steel tube -Intra-uterine and vaginal source train -Central steel tube of the vaginal applicator
VOL.
49, No. 587 Technical note
uniform except in the 70 mg holder where the source strength is slightly reduced at the end of the source train. The lower end of the holder has a screw thread and also bears a figure denoting the mg radium equivalent of the caesium. In order to obtain the correct overall length of the source trains, spacers are inserted between the active sources. These spacers are 2 mm long in the intrauterine holder and 4 mm long in the vaginal holder. A dummy source holder is initially inserted until a radiological check has verified the correct position of the applicator. METHOD OF INSERTION OF THE APPLICATOR
Silver seeds are inserted into the cervix as radiological markers at a preliminary staging examination carried out under anaesthesia. In the assembly of the applicator, it is usual to place two Perspex bobbins containing lead protection posteriorly at the upper end, but this may be altered according to the length of the vagina or the extension of the tumour down the vagina. In an unusually narrow vagina, smaller diameter bobbins 2.5 or 3 cm in diameter are used without lead protection. The cervix is then dilated to No. 6, and the uterocervical canal is measured. A source holder of suitable length is chosen and inserted into the uterus. The steel collar at the lower end of the intra-uterine portion should be visible at the os. A catheter must be inserted into the bladder at this time through the aperture in the perineal bar. The applicator is then threaded over the Portex source holder until the lower metal tab of the introducer (Fig. 2A) projects through the lower end of the steel rod. The introducer is then removed. A double-threaded locking nut is now screwed into the lower end of the source holder, thus completing assembly. It only remains to pack carbonet and gauze around the vulva. It is important to keep the perineal bar in close opposition with the vulva during this operation. Tapes are then passed from the back of an abdominal belt through the posterior and anterior holes of the perineal bar and secured to the front of the belt. This method has proved to be extremely simple in use and the position of the caesium is virtually guaranteed. DOSAGE MEASUREMENT AND CALCULATION
The dose distribution around individual caesium sources was measured in a water bath by two independent methods: (1) a PTW micro-ionization chamber, and (2) a needle geiger tube. Both methods showed that the exposure rate obeyed inverse square law at distances between 1.5 cm and
FIG. 3. Antero-posterior radiograph (dose rates in rad/hr)
10 cm from the source and the error introduced by an assumption of spherical isodoses around the source was small enough to be ignored. Absolute measurement of the absorbed dose rate around an individual source was obtained by the use of lithium fluoride. Uniform exposure of the entire sample was obtained by correct positioning, and dose values were calculated by comparison with standards irradiated to a known dose on a 4 MV linear accelerator. This procedure was carried out for a number of sources, and the results when used in conjunction with the Amersham test reports gave an effective value for the K-factor. An estimation was also made of the attenuation in the steel walls of the vaginal applicator at the point where the dose to the patient would be specified. These results compared satisfactorily with those calculated by summation of the contribution from each individual source. Figure 3 is an antero-posterior radiograph of a dummy source holder in position within a patient, and also shows the dose distribution obtained for that particular insertion.
964
Technical note TABLE I AVERAGE YEARLY EXPOSURES IN MR IN THE YEAR PRECEDING AND FOLLOWING THE INTRODUCTION OF THE FULLY AFTERLOADED SYSTEM
Theatre Staff Radiotherapist Diagnostic Radiographer Senior Ward Nursing Staff
1971
1973
770 360 800 470
100 40 60 250
with the technique. Approximately 200 insertions a year were performed. As shown, a very significant reduction in dose to the staff has been achieved. A lead screen also provides radiation protection around the patient's pelvis during the time of the caesium insertion, and as expected the reduction in exposure to ward nursing staff is not so marked. ACKNOWLEDGMENT
We wish to thank other members of the Medical Physics Department, both past and present, who have collaborated in the development and production of this system. RADIATION PROTECTION RESULTS
The full afterloading system was introduced in 1972, and Table I shows the average yearly exposure in mR for the year preceding and the year following this introduction for the staff most closely concerned
REFERENCES CAMPBELL, Elisabeth M., and DOUGLAS, Mary, 1966. The
treatment of carcinoma of the uterine cervix using a linear vaginal source and 4 MeV X-rays. British Journal of Radiology, 39, 537-546.
Book review Natural Background Radiation in the United States. N.C.R.P. Report No. 45, pp. xi + 163, 1975 (Washington, N.C.R.P. Publications). This report runs to some 130 pages and contains 57 tables of data. In compiling it, the authors have drawn on vast quantities of recorded measurements and have included extensive calculations and estimates. Cosmic radiation, cosmic ray produced radioactivity, terrestial radionuclides and the effects of radionuclides both in the soil and in the air are all dealt with. A considerable amount of space is devoted to the calculation of dose levels received by man. Although many of the data relate directly to measurements made in the United States and to dose calculations in that country, much of the report deals with the subject on a global basis. In an appendix, data are presented
on the fall-out from nuclear tests together with calculations on human body dose and dose commitments resulting from the tests. One section deals with measurements of cosmic radiation and associated absorbed dose rates, and gives the results of observations made in the upper atmosphere extending to heights of 25 kilometres above ground level. Following from this, estimates are given of the dose rates to which aircraft passengers are exposed. The summary of the report contains a table giving average values of dose equivalent rates from various sources of natural background radiation, under the headings gonads, lung, bone and G.I. tract. It is an excellent report.
965
N. W. RAMSEY.
NOVEMBER 1976
Technical note The Edinburgh afterloading technique for carcinoma of the uterine cervix By A. T. Redpath, B.Sc, Ph.D., M. A. J. T. Douglas, M. D., F.R.C.R., and J. A. Orr, F.R.C.S.E., F.R.C.R. Departments of Medical Physics and Radiotherapy, Western General Hospital, Edinburgh EH4 2XU {Received February, 1976 and in revised form July, 1976)
A partially afterloaded line source system was developed in Edinburgh and put into use in 1960 (Campbell and Douglas, 1966). In this system the intra-uterine source was preloaded and only the vaginal component afterloaded. With the availability of small caesium sources a modification has been made to allow full but manual afterloading. The sources manufactured by the Radiochemical Centre at Amersham, are 5 mm in length and 2 mm in diameter. The treatment regime is very similar to that described by Campbell and Douglas (1966).
applicators is possible. The caesium loading is uniform and varies from 20 to 70 mg radium equivalent according to the length of the holder (from two to 11 individual sources). The vaginal portion of the source holder is a rigid steel tube again 2.5 mm in diameter, and may contain from 25 to 70 mg radium equivalent (two to six sources). Loading is again
DESIGN OF THE CAESIUM APPLICATORS
A new flexible intra-uterine applicator has replaced the straight tube used in the earlier system, and the construction of the complete applicator is shown in Fig. 1. The external appearance of the vaginal applicator has not changed and still consists of Perspex bobbins and a perineal bar threaded over a stainless steel tube. Lead shielding is used posteriorly, and the applicators are available from 2 cm to 4 cm in diameter. The length of the intravaginal portion can be varied by altering the position of the perineal bar, and a screw locking nut at the lower end keeps the component parts firmly in place. The main difference between the present applicator and the previous one is that the central steel tube is not sealed at the proximal end. This allows the extrusion of a flexible Portex tube into the uterus after passage through the central steel tube of the vaginal applicator. This Portex tube (shown again in Fig. 2B) ultimately accommodates the caesium source holder (Fig. 2c), and is 4 mm in diameter and of varying length corresponding to the source holder. A small metal collar denotes the level of the external os, and is therefore the lower limit of the intra-uterine sources. The vaginal applicator (Fig. 2D) can slide over the Portex tube as far as this metal collar. The intra-uterine source holder is made of flexible steel mesh 2.5 mm external diameter and is available in varying lengths to accommodate a uterine cavity 3, 5, 6, 7 or 9 cm long. This holder is sealed at both ends and screws into the vaginal source holder (Fig. 2c) and therefore complete interchangeability of both
FIG. 1. The Complete Applicator A—Intra-uterine applicator B—Lead Shielding c—Perineal bar D—Perspex bobbins E—Locking nut
963
D FIG. 2. -Introducer -Source holder, Portex tube attached to stainless steel tube -Intra-uterine and vaginal source train -Central steel tube of the vaginal applicator
VOL.
49, No. 587 Technical note
uniform except in the 70 mg holder where the source strength is slightly reduced at the end of the source train. The lower end of the holder has a screw thread and also bears a figure denoting the mg radium equivalent of the caesium. In order to obtain the correct overall length of the source trains, spacers are inserted between the active sources. These spacers are 2 mm long in the intrauterine holder and 4 mm long in the vaginal holder. A dummy source holder is initially inserted until a radiological check has verified the correct position of the applicator. METHOD OF INSERTION OF THE APPLICATOR
Silver seeds are inserted into the cervix as radiological markers at a preliminary staging examination carried out under anaesthesia. In the assembly of the applicator, it is usual to place two Perspex bobbins containing lead protection posteriorly at the upper end, but this may be altered according to the length of the vagina or the extension of the tumour down the vagina. In an unusually narrow vagina, smaller diameter bobbins 2.5 or 3 cm in diameter are used without lead protection. The cervix is then dilated to No. 6, and the uterocervical canal is measured. A source holder of suitable length is chosen and inserted into the uterus. The steel collar at the lower end of the intra-uterine portion should be visible at the os. A catheter must be inserted into the bladder at this time through the aperture in the perineal bar. The applicator is then threaded over the Portex source holder until the lower metal tab of the introducer (Fig. 2A) projects through the lower end of the steel rod. The introducer is then removed. A double-threaded locking nut is now screwed into the lower end of the source holder, thus completing assembly. It only remains to pack carbonet and gauze around the vulva. It is important to keep the perineal bar in close opposition with the vulva during this operation. Tapes are then passed from the back of an abdominal belt through the posterior and anterior holes of the perineal bar and secured to the front of the belt. This method has proved to be extremely simple in use and the position of the caesium is virtually guaranteed. DOSAGE MEASUREMENT AND CALCULATION
The dose distribution around individual caesium sources was measured in a water bath by two independent methods: (1) a PTW micro-ionization chamber, and (2) a needle geiger tube. Both methods showed that the exposure rate obeyed inverse square law at distances between 1.5 cm and
FIG. 3. Antero-posterior radiograph (dose rates in rad/hr)
10 cm from the source and the error introduced by an assumption of spherical isodoses around the source was small enough to be ignored. Absolute measurement of the absorbed dose rate around an individual source was obtained by the use of lithium fluoride. Uniform exposure of the entire sample was obtained by correct positioning, and dose values were calculated by comparison with standards irradiated to a known dose on a 4 MV linear accelerator. This procedure was carried out for a number of sources, and the results when used in conjunction with the Amersham test reports gave an effective value for the K-factor. An estimation was also made of the attenuation in the steel walls of the vaginal applicator at the point where the dose to the patient would be specified. These results compared satisfactorily with those calculated by summation of the contribution from each individual source. Figure 3 is an antero-posterior radiograph of a dummy source holder in position within a patient, and also shows the dose distribution obtained for that particular insertion.
964
Technical note TABLE I AVERAGE YEARLY EXPOSURES IN MR IN THE YEAR PRECEDING AND FOLLOWING THE INTRODUCTION OF THE FULLY AFTERLOADED SYSTEM
Theatre Staff Radiotherapist Diagnostic Radiographer Senior Ward Nursing Staff
1971
1973
770 360 800 470
100 40 60 250
with the technique. Approximately 200 insertions a year were performed. As shown, a very significant reduction in dose to the staff has been achieved. A lead screen also provides radiation protection around the patient's pelvis during the time of the caesium insertion, and as expected the reduction in exposure to ward nursing staff is not so marked. ACKNOWLEDGMENT
We wish to thank other members of the Medical Physics Department, both past and present, who have collaborated in the development and production of this system. RADIATION PROTECTION RESULTS
The full afterloading system was introduced in 1972, and Table I shows the average yearly exposure in mR for the year preceding and the year following this introduction for the staff most closely concerned
REFERENCES CAMPBELL, Elisabeth M., and DOUGLAS, Mary, 1966. The
treatment of carcinoma of the uterine cervix using a linear vaginal source and 4 MeV X-rays. British Journal of Radiology, 39, 537-546.
Book review Natural Background Radiation in the United States. N.C.R.P. Report No. 45, pp. xi + 163, 1975 (Washington, N.C.R.P. Publications). This report runs to some 130 pages and contains 57 tables of data. In compiling it, the authors have drawn on vast quantities of recorded measurements and have included extensive calculations and estimates. Cosmic radiation, cosmic ray produced radioactivity, terrestial radionuclides and the effects of radionuclides both in the soil and in the air are all dealt with. A considerable amount of space is devoted to the calculation of dose levels received by man. Although many of the data relate directly to measurements made in the United States and to dose calculations in that country, much of the report deals with the subject on a global basis. In an appendix, data are presented
on the fall-out from nuclear tests together with calculations on human body dose and dose commitments resulting from the tests. One section deals with measurements of cosmic radiation and associated absorbed dose rates, and gives the results of observations made in the upper atmosphere extending to heights of 25 kilometres above ground level. Following from this, estimates are given of the dose rates to which aircraft passengers are exposed. The summary of the report contains a table giving average values of dose equivalent rates from various sources of natural background radiation, under the headings gonads, lung, bone and G.I. tract. It is an excellent report.
965
N. W. RAMSEY.
