0360-3016/91 $3.00 t .oO Copyright Q 1991 Pelgamon Press PIG
In, J Radialron Oncology RIO/. Phys.. Vol. 20. PD. 621425 Printed in the U.S.A. All rights reServd.
0 Technical Innovations and Notes A NEW DEVICE FOR INTERSTITIAL ‘*‘IODINE SEED IMPLANTATION ROBERT HAWLICZEK, M.D.,’ JOSEPH NEUBAUER, B.SC.,~ WERNER F. 0. SCHMIDT, PH.D.,’ PETER GRUNERT, M.D.3 AND LAWRENCE R. COIA, M.D.4 ‘Clinic of Radiotherapy and Radiobiology, University of Vienna; 2Center of Nuclear Investigation, Seibersdoti, 3Clinic of Neurosurgery, University of Vienna, Austria; and 4Department of Radiation Oncology-School of Medicine, University of Pennsylvania, The Fox Chase Cancer Center, Philadelphia, USA seeds is presented. The technical details and function of the system A new device for interstitial implantation of 112’ are described and compared with well-known commercial systems. Its unique design allows for simple, fast, and safe treatment of most tumor sites including stereotactic implantation of brain. Radiation measurements indicate low exposure to both patients and personnel during implantation. Iodine seeds, Interstitial implant, Technique.
of the carrier. The stylet passes through the rear hole and introduces seeds or spacers through the front hole into the carrier during the loading process. The disk is rotated to the next position and this process is repeated until the linear array of sources and spacers in the carrier has the prescribed length. The loading cone (Fig. 1) is used for filling the magazine, alternating seeds with spacers. It is put in a holder at the front plate of the magazine and directs the seed or spacer into its hole in the disk. This is the only working process involving unshielded seeds and can be done in a protected working place near the radioactive source safe. After loading, the disk is locked in position 0 for security. This position ensures that no seed can get lost during magazine transport. The loading device (Fig. 2, 3) is used for loading seeds and spacers into the carrier. The carrier is docked to the holder of the magazine so that the seeds can be pushed by a stylet from the magazine into the carrier. A small handle which rides on a track over the stylet allows this to be accomplished. The disk of the magazine is rotated from one position to the next, until the prescribed number of seeds and spacers is in the carrier. The carrier (Fig. 2, 4) is used to preform and subsequently carry the requisite linear array of seeds and spacers. The carrier attaches to the holder on the front plate of the magazine just as does the loading cone. The carrier consists of an inner glass tube and surrounding two slitted steel cylinders. By rotating the outer steel cylinder, the slits can be positioned above each other so that one may
INTRODUCIION The success of interstitial brachytherapy of malignant tumors is dependent on optimal source distribution. 112’ seed* (6) implantation requires especially high precision because of the low photon-energy (28 keV) and the steep dose fall off. Commercial applicators for Ii2’ seeds often have disadvantages in obtainable seed distributions and radiation protection or safety in handling. To overcome these problems we have developed a new high precision device for permanent Ii” implantation based on the work of De Ginder and Mistry (2) Scott (8, 9, 10) and Henschke et al. (4). This device is particularly useful for stereotactic procedures in the brain or for endoscopic use in head and neck regions, though it may be used in other regions of the body as well. METHODS
AND MATERIALS
The parts of‘the system The magazine (Fig. 1, 2) consists of a rotatable disk with 29 holes for spacers and seeds. Every hole has an engraved position number. At position 0 there is no hole and in this position the disk can be fixed by a screw for secure transportation. Both sides of the disk are covered by a plate. The front plate has a hole which can be traversed by seeds and spacers, the rear has one which can be traversed only by a thin stylet. The front hole is used for loading the magazine and the carrier and has a holder which fits to the loading cone as well as to the entrance
Reprint requests to: Robert Hawliczek, M.D., Clinic of Radiotherapy and Radiobiology, A- 1090, Vienna, Austria.
University
Accepted for publication * 3-M Corporation.
of Vienna, Alserstr. 4,
621
12 September
1990.
622
I. J. Radiation
Oncology
DISC WITH DRILLING
0 Biology 0 Physics
March 1991. Volume 20. Number
3
FOR SEEDS AND SPACERS
FRONT WINDOW
WITH POSlTlON
PLATE
NUMBER+
HOCDER FOR LOADING CONE
-
AND CARRIER
-6cm
1.8cm
-
VERTICAL SECTION .
SEED
SIDE VIEW +
Fig. 1. Magazine for 1”‘-seeds and PDS-spacers. radiation measurements as shown by symbols.
TLD I
The position
observe the sources and spacers inside the inner glass tube. positions, the seeds are shielded completely. Loss of seeds is prevented at both entrance and exit of the carrier during movement. The exit is supplied with a luer-lock connection which attaches to the needle. The needles (Fig. 4) (1.2 mm diameter 0.1 mm wall thickness) are used with a matching stylet and luer-lock high precision cone. They are available for any required length. The stylet is used to introduce the seeds and spacers from the carrier into the needle and tumor. It is a stainless steel wire with a diameter of 0.7 mm. The stylet holder used is similar to that used by De Ginder (2) and Scott (8) and is shown in Figure 5. It stops the stylet to avoid active movement of the linear array of seeds and spacers into the tissue distal the needle. The requirements for the spacers are to be absorbable, non-toxic, and able to traverse the different tube connections without obstruction or physical breakdown. We met these requirements by use of a Polydioxanone (PDS) rod of 0.8 mm diameter. Chemically, PDS is a synthetic aliphatic polyester available in 5 cm length rods, which are cut to the desired length and loaded into the magazines under sterile conditions before implantation. Without the use of such spacers with high mechanical quality, the applicator does not function properly. If the slits are in different
Implantation procedure The basis of the application consists of positioning linear arrays of seeds and PDS-spacers (3).+ These absorbable spacers were invented and first used by the author because of the poor mechanical quality of catgut (2, 8) which is traditionally used. For fast and precise manual cutting of spacers we use a simple selfmade cutter, but a calibrated
+ Ethicon,
PDS-rod,
0.8 mm diameter.
IONISATION
CHAMBER
of sources, TLD’s and ionisation
chambers
used for
cutter is commercially available.’ The magazines are prefilled with seeds, sterilized (one or two seeds per hole), and a PDS spacer of adjustable length to 11 mm is placed between the seeds under sterile condition in the operating room by use of the revolverlike mechanism of the magazine. described in more detail above. The requisite number of seeds and spacers for each needle is loaded in a carrier comprised of a glass tube surrounded by a double cylinder of steel. Visual control of the correct number of sources in the glass tube is possible by the use of slits in the steel cylinder. The carrier containing the radioactive sources is attached to the luer-lock cone of the hollow
Fig. 2. Loading position.
device with magazine
t Scott Applicator
and carrier
Kit, 3-M Corporation.
in working
Iodine- I25 seed implantation 0
R.
HAWLICZEK
HANDLE
LOADING
623
el a/
STYLET /
FOR LOADING
STYLET
h
K-
CLAMP FOR CARRIER
/
I
\
/
I
/
BASEPLATE
HOLDING
FIXATION
DEVICE FOR MAG.
I
SCREW
22 CM
I
Fig. 3. Device for loading the carrier with 112’ -seeds and spacers
implantation needle. For correct adjustment of the stylet, the distance of the skin (template) surface to tumor surface as well as tumor diameter has to be known for each needle. The active length of seeds and spacers must be identical to the tumor diameter along the path of the needle. The stylet is inserted in the open end of the carrier and the linear array of seeds and spacers pushed into the needle. When the foot of the stylet holder touches the skin (template) surface, the tip of the stylet will be at the tumor surface in the needle and distal seed will be at the tip of the needle. The stylet holder is held in this position while the carrier and needle are retracted together off of the stylet. In that way the linear array of seeds and spacers stays exactly in the former position of the needle. There is no active movement of a seed into the tissue. This results in a perfectly parallel and colinear placement and no further trauma by seeds or stylet. After removal of carrier and needle, the system is free of activity and all seeds are in correct position.
(side view).
distances from the magazine. The magazine was loaded with 4 seeds of total activity of 17.8 mCi. We did not choose lower activity seeds (e.g., 0.55 mCi/seed) because we thought it more interesting to test seeds with high activity as used in brain implants. The total activity of 17.8 cCi also approximates the total activity of a typical implant for prostate (e.g., 30 seeds at 0.55 mCi/seed). Therefore this loading of the magazine provides a rough estimate of the radiation exposure in either brain or prostate implants. At the surface of the magazine thermoluminescent dosimeters (TLD’s)§ were placed at 13 points (3 TLD’s per
RESULTS The prototype was used for stereotactic brain-implant, transperineal prostate implantation, percutaneous implantation in the retrobulbar region of the eye, and for intraoperative applications and head and neck sites. The time needed to load one needle depends on the experience of the user. In our hands about 2 to 3 minutes are required from measurement and calculation of active length to removal of the carrier and needle. Time spent cutting the spacers and leading them into the magazine is not included. The ability to control the correct number of sources in the carrier afforded by this system has proven to be a very useful advantage over other applicators. For estimation of radiation exposure of the user in a clinical situation, measurements around the magazine and carrier were performed at the surface as well as at various
p TLD- 100, Harshaw.
Fig. 4. Carrier, needle and a row of PDS-Spacers carrier is opened and the glass tube removed).
and seeds (the
624
I. J. Radiation Oncology 0 Biology 0 Physics
Fig. 5. Stylet holder for correct adjustment
point) and exposed for 66 hours. The positions of seeds and TLD’s are illustrated in Figure 1. Calibration of TLD’s was done with a well defined dose of 6oCo radiation from a therapy unit. The oversensitivity of the TLD’s used is less than 30% for 30 KeV photons (1). Additional influences on dose measured arise from scattering processes in the magazine as well as in the TLD itself but are not regarded to be important for this estimation. For calculation of dose-equivalent (Sv), a quality-factor of 1 was assumed (5). The mean dose-rate at the front plate of the magazine (holder for the carrier) was 30 &/h, and at the back plate 150 pSv/h (4 points each). The difference is simply due to the seeds being closer to the back plate because during loading they drop (by gravity) to the back plate. The mean dose-rate at the surface of the rotatable disc was determined to be 450 pSv/h (5 points). the higher values can be explained by geometrical considerations. Additional measurements were performed along the axis (Fig. 1) of the rotatable disk as well as perpendicular to it at distances up to 100 cm by two different ionisation chambers.** The mean dose-rate was 100 $Sv/h at 10 cm and 0.7 @v/h at 100 cm respectively. Measurements with the different chambers agreed with 15%. For estimation of the dose-rate at the carrier’s surface, it was loaded with 5 seeds of total activity 5 mCi. With the slit closed, a surface dose rate of 30 &v/h was determined. During implantation procedures, radiation exposure of users was monitored by pocket dosimeterstt positioned at the anterior chest wall outside the lead apron. After typical prostate implants (e.g., 50 seeds a at 0.55 mCi/ seed) the measured dose never exceeded 20 &v (minimum detectable dose), mainly because of the short times
** LB- 133; Berthold:
TOL E. Berthold.
March 1991. Volume 20. Number 3
of the stylet length to the tumor surface.
required in handling the device. Furthermore, it should be remarked that the prototype of our system is made of duraluminium. The use of stainless steel of same thickness would reduce radiation exposure to less than 5% of the values measured above.
DISCUSSION Our new device for permanent 1’25 seed implantation combines the advantages of the systems by Henschke et al. (4), Schulz and Bush (7). and by Scott (8, 9, 10). The use of a carrier for preformed linear arrays of seeds and spacers was developed by De Ginder and Mistry (2) but their system did not work properly in our hands, mostly because of the poor quality of catgut spacers and the complicated application procedure. Compared to our system, the Mick-applicator has the potential disadvantages of less precise spacing along the needle track and seeds are pushed actively into the tissue so that their position is often not colinear. During stepwise retraction of the needle for placement of each seed, the rigid tissue of the tumor or the tumor-bearing organ (e.g., prostate) is moved unpredictably so that the step length of retraction measured at the surface is often not the same as in the tumor. In our procedure one single retraction is needed per needle and seedspacing is not influenced by the possible changes in the position of the tumor. Also, with the Mick applicator the seed sometimes adheres to the stylet and may be retracted back into the needle. The retracted seed is then incorrectly replaced together with the next seed by the next step of application or stays in the removed needle. With our device, seed retraction is possible only
++FR 39R5 (14 KaV-3MeV):
Frieseke and Hoepfner.
Iodine-135 seed implan station 0
with the last seed of each linear array. Such a retraction has never occurred, perhaps because of the smooth fit of seeds into the needle. Also, in comparison to our applicator, the Mick system is long and heavy, thus requiring more room during use, and it can act like a lever to the implanted needle. The Scott system has disadvantages in radiation protection because it uses loose unshielded seeds in the operating room. Furthermore, the loading procedure is relatively slow and the implantation process re-
R. HAWLICZEK et d.
625
quires significantly longer time than our device, thus increasing exposure to the operating team. Our new device is potentially useful in nearly all body sites. However, because of its compactness and its precise atraumatic delivery of seeds, it is particularly useful in stereotactic brain implantation. The handling is simple and fast and radiation exposure minimal. The seeds are placed precisely and atraumatically. In our opinion it is a superior alternative to the available systems as described.
REFERENCES I.
3.
3 _
4.
5.
Becker, K. Solid state dosimetry. Cleveland. Ohio: CRC Press: 1973. De Ginder, W. L.; Mistry. V. D. Novel and inexpensive system for interstitial “510dine seed implants. Int. J. Radiat. Oncol. Biol. Phys. 4:745-747; 1978. Hammer, J.; Hawliczek. R.: Karcher, K. H.: Riccabona. M. A new spacing material for interstitial implantation of radioactive seeds. Int. J. Radiat. Oncol. Biol. Phys. 16:259260: 1989. Henschke. U. K.: Hilaris. B. S.: Mahan. G. D. Afterloading in interstitial and intracavitary radiation therapy. Am. J. Roentgenol. 90:386-395: 1963. ICRU 40: The quality factor in radiation protection. Report of a Joint Task Group of the ICRP and ICRU. Bethesda, Maryland: ICRU Publications: 1986.
D.: 6. Ling, C. C.; Yorke, E. D.; Spiro. 1. S.; Kubiatowicz, Bennett, D. Physical dosimetry of I2S-Iodine seeds of a new design for interstitial implant. Int. J. Radiat. Oncol. Biol. Phys. 9:1747-1752: 1983. Schulz, V.: Busch. M. Ein neuer Applikator Therapie mit Au-198 and I-125 Seeds. 157(2):104-105; 1981.
zur interstitiellen Strahlentherapie
Scott, W. P. Rapid injector for permanent radioactive plantation. Radiology 105(2):454-455: 1972.
im-
Scott. W. P. A spacer injector needle for I-“5 and other radioactive sources in permanent seed implants. Radiology 122(3):832-834; 1977. IO. Scott, W. P. lmplanter for radioactive sources. Int. J. Radiat. Oncol. Biol. Phys. 7:263-266; I98 I.
In, J Radialron Oncology RIO/. Phys.. Vol. 20. PD. 621425 Printed in the U.S.A. All rights reServd.
0 Technical Innovations and Notes A NEW DEVICE FOR INTERSTITIAL ‘*‘IODINE SEED IMPLANTATION ROBERT HAWLICZEK, M.D.,’ JOSEPH NEUBAUER, B.SC.,~ WERNER F. 0. SCHMIDT, PH.D.,’ PETER GRUNERT, M.D.3 AND LAWRENCE R. COIA, M.D.4 ‘Clinic of Radiotherapy and Radiobiology, University of Vienna; 2Center of Nuclear Investigation, Seibersdoti, 3Clinic of Neurosurgery, University of Vienna, Austria; and 4Department of Radiation Oncology-School of Medicine, University of Pennsylvania, The Fox Chase Cancer Center, Philadelphia, USA seeds is presented. The technical details and function of the system A new device for interstitial implantation of 112’ are described and compared with well-known commercial systems. Its unique design allows for simple, fast, and safe treatment of most tumor sites including stereotactic implantation of brain. Radiation measurements indicate low exposure to both patients and personnel during implantation. Iodine seeds, Interstitial implant, Technique.
of the carrier. The stylet passes through the rear hole and introduces seeds or spacers through the front hole into the carrier during the loading process. The disk is rotated to the next position and this process is repeated until the linear array of sources and spacers in the carrier has the prescribed length. The loading cone (Fig. 1) is used for filling the magazine, alternating seeds with spacers. It is put in a holder at the front plate of the magazine and directs the seed or spacer into its hole in the disk. This is the only working process involving unshielded seeds and can be done in a protected working place near the radioactive source safe. After loading, the disk is locked in position 0 for security. This position ensures that no seed can get lost during magazine transport. The loading device (Fig. 2, 3) is used for loading seeds and spacers into the carrier. The carrier is docked to the holder of the magazine so that the seeds can be pushed by a stylet from the magazine into the carrier. A small handle which rides on a track over the stylet allows this to be accomplished. The disk of the magazine is rotated from one position to the next, until the prescribed number of seeds and spacers is in the carrier. The carrier (Fig. 2, 4) is used to preform and subsequently carry the requisite linear array of seeds and spacers. The carrier attaches to the holder on the front plate of the magazine just as does the loading cone. The carrier consists of an inner glass tube and surrounding two slitted steel cylinders. By rotating the outer steel cylinder, the slits can be positioned above each other so that one may
INTRODUCIION The success of interstitial brachytherapy of malignant tumors is dependent on optimal source distribution. 112’ seed* (6) implantation requires especially high precision because of the low photon-energy (28 keV) and the steep dose fall off. Commercial applicators for Ii2’ seeds often have disadvantages in obtainable seed distributions and radiation protection or safety in handling. To overcome these problems we have developed a new high precision device for permanent Ii” implantation based on the work of De Ginder and Mistry (2) Scott (8, 9, 10) and Henschke et al. (4). This device is particularly useful for stereotactic procedures in the brain or for endoscopic use in head and neck regions, though it may be used in other regions of the body as well. METHODS
AND MATERIALS
The parts of‘the system The magazine (Fig. 1, 2) consists of a rotatable disk with 29 holes for spacers and seeds. Every hole has an engraved position number. At position 0 there is no hole and in this position the disk can be fixed by a screw for secure transportation. Both sides of the disk are covered by a plate. The front plate has a hole which can be traversed by seeds and spacers, the rear has one which can be traversed only by a thin stylet. The front hole is used for loading the magazine and the carrier and has a holder which fits to the loading cone as well as to the entrance
Reprint requests to: Robert Hawliczek, M.D., Clinic of Radiotherapy and Radiobiology, A- 1090, Vienna, Austria.
University
Accepted for publication * 3-M Corporation.
of Vienna, Alserstr. 4,
621
12 September
1990.
622
I. J. Radiation
Oncology
DISC WITH DRILLING
0 Biology 0 Physics
March 1991. Volume 20. Number
3
FOR SEEDS AND SPACERS
FRONT WINDOW
WITH POSlTlON
PLATE
NUMBER+
HOCDER FOR LOADING CONE
-
AND CARRIER
-6cm
1.8cm
-
VERTICAL SECTION .
SEED
SIDE VIEW +
Fig. 1. Magazine for 1”‘-seeds and PDS-spacers. radiation measurements as shown by symbols.
TLD I
The position
observe the sources and spacers inside the inner glass tube. positions, the seeds are shielded completely. Loss of seeds is prevented at both entrance and exit of the carrier during movement. The exit is supplied with a luer-lock connection which attaches to the needle. The needles (Fig. 4) (1.2 mm diameter 0.1 mm wall thickness) are used with a matching stylet and luer-lock high precision cone. They are available for any required length. The stylet is used to introduce the seeds and spacers from the carrier into the needle and tumor. It is a stainless steel wire with a diameter of 0.7 mm. The stylet holder used is similar to that used by De Ginder (2) and Scott (8) and is shown in Figure 5. It stops the stylet to avoid active movement of the linear array of seeds and spacers into the tissue distal the needle. The requirements for the spacers are to be absorbable, non-toxic, and able to traverse the different tube connections without obstruction or physical breakdown. We met these requirements by use of a Polydioxanone (PDS) rod of 0.8 mm diameter. Chemically, PDS is a synthetic aliphatic polyester available in 5 cm length rods, which are cut to the desired length and loaded into the magazines under sterile conditions before implantation. Without the use of such spacers with high mechanical quality, the applicator does not function properly. If the slits are in different
Implantation procedure The basis of the application consists of positioning linear arrays of seeds and PDS-spacers (3).+ These absorbable spacers were invented and first used by the author because of the poor mechanical quality of catgut (2, 8) which is traditionally used. For fast and precise manual cutting of spacers we use a simple selfmade cutter, but a calibrated
+ Ethicon,
PDS-rod,
0.8 mm diameter.
IONISATION
CHAMBER
of sources, TLD’s and ionisation
chambers
used for
cutter is commercially available.’ The magazines are prefilled with seeds, sterilized (one or two seeds per hole), and a PDS spacer of adjustable length to 11 mm is placed between the seeds under sterile condition in the operating room by use of the revolverlike mechanism of the magazine. described in more detail above. The requisite number of seeds and spacers for each needle is loaded in a carrier comprised of a glass tube surrounded by a double cylinder of steel. Visual control of the correct number of sources in the glass tube is possible by the use of slits in the steel cylinder. The carrier containing the radioactive sources is attached to the luer-lock cone of the hollow
Fig. 2. Loading position.
device with magazine
t Scott Applicator
and carrier
Kit, 3-M Corporation.
in working
Iodine- I25 seed implantation 0
R.
HAWLICZEK
HANDLE
LOADING
623
el a/
STYLET /
FOR LOADING
STYLET
h
K-
CLAMP FOR CARRIER
/
I
\
/
I
/
BASEPLATE
HOLDING
FIXATION
DEVICE FOR MAG.
I
SCREW
22 CM
I
Fig. 3. Device for loading the carrier with 112’ -seeds and spacers
implantation needle. For correct adjustment of the stylet, the distance of the skin (template) surface to tumor surface as well as tumor diameter has to be known for each needle. The active length of seeds and spacers must be identical to the tumor diameter along the path of the needle. The stylet is inserted in the open end of the carrier and the linear array of seeds and spacers pushed into the needle. When the foot of the stylet holder touches the skin (template) surface, the tip of the stylet will be at the tumor surface in the needle and distal seed will be at the tip of the needle. The stylet holder is held in this position while the carrier and needle are retracted together off of the stylet. In that way the linear array of seeds and spacers stays exactly in the former position of the needle. There is no active movement of a seed into the tissue. This results in a perfectly parallel and colinear placement and no further trauma by seeds or stylet. After removal of carrier and needle, the system is free of activity and all seeds are in correct position.
(side view).
distances from the magazine. The magazine was loaded with 4 seeds of total activity of 17.8 mCi. We did not choose lower activity seeds (e.g., 0.55 mCi/seed) because we thought it more interesting to test seeds with high activity as used in brain implants. The total activity of 17.8 cCi also approximates the total activity of a typical implant for prostate (e.g., 30 seeds at 0.55 mCi/seed). Therefore this loading of the magazine provides a rough estimate of the radiation exposure in either brain or prostate implants. At the surface of the magazine thermoluminescent dosimeters (TLD’s)§ were placed at 13 points (3 TLD’s per
RESULTS The prototype was used for stereotactic brain-implant, transperineal prostate implantation, percutaneous implantation in the retrobulbar region of the eye, and for intraoperative applications and head and neck sites. The time needed to load one needle depends on the experience of the user. In our hands about 2 to 3 minutes are required from measurement and calculation of active length to removal of the carrier and needle. Time spent cutting the spacers and leading them into the magazine is not included. The ability to control the correct number of sources in the carrier afforded by this system has proven to be a very useful advantage over other applicators. For estimation of radiation exposure of the user in a clinical situation, measurements around the magazine and carrier were performed at the surface as well as at various
p TLD- 100, Harshaw.
Fig. 4. Carrier, needle and a row of PDS-Spacers carrier is opened and the glass tube removed).
and seeds (the
624
I. J. Radiation Oncology 0 Biology 0 Physics
Fig. 5. Stylet holder for correct adjustment
point) and exposed for 66 hours. The positions of seeds and TLD’s are illustrated in Figure 1. Calibration of TLD’s was done with a well defined dose of 6oCo radiation from a therapy unit. The oversensitivity of the TLD’s used is less than 30% for 30 KeV photons (1). Additional influences on dose measured arise from scattering processes in the magazine as well as in the TLD itself but are not regarded to be important for this estimation. For calculation of dose-equivalent (Sv), a quality-factor of 1 was assumed (5). The mean dose-rate at the front plate of the magazine (holder for the carrier) was 30 &/h, and at the back plate 150 pSv/h (4 points each). The difference is simply due to the seeds being closer to the back plate because during loading they drop (by gravity) to the back plate. The mean dose-rate at the surface of the rotatable disc was determined to be 450 pSv/h (5 points). the higher values can be explained by geometrical considerations. Additional measurements were performed along the axis (Fig. 1) of the rotatable disk as well as perpendicular to it at distances up to 100 cm by two different ionisation chambers.** The mean dose-rate was 100 $Sv/h at 10 cm and 0.7 @v/h at 100 cm respectively. Measurements with the different chambers agreed with 15%. For estimation of the dose-rate at the carrier’s surface, it was loaded with 5 seeds of total activity 5 mCi. With the slit closed, a surface dose rate of 30 &v/h was determined. During implantation procedures, radiation exposure of users was monitored by pocket dosimeterstt positioned at the anterior chest wall outside the lead apron. After typical prostate implants (e.g., 50 seeds a at 0.55 mCi/ seed) the measured dose never exceeded 20 &v (minimum detectable dose), mainly because of the short times
** LB- 133; Berthold:
TOL E. Berthold.
March 1991. Volume 20. Number 3
of the stylet length to the tumor surface.
required in handling the device. Furthermore, it should be remarked that the prototype of our system is made of duraluminium. The use of stainless steel of same thickness would reduce radiation exposure to less than 5% of the values measured above.
DISCUSSION Our new device for permanent 1’25 seed implantation combines the advantages of the systems by Henschke et al. (4), Schulz and Bush (7). and by Scott (8, 9, 10). The use of a carrier for preformed linear arrays of seeds and spacers was developed by De Ginder and Mistry (2) but their system did not work properly in our hands, mostly because of the poor quality of catgut spacers and the complicated application procedure. Compared to our system, the Mick-applicator has the potential disadvantages of less precise spacing along the needle track and seeds are pushed actively into the tissue so that their position is often not colinear. During stepwise retraction of the needle for placement of each seed, the rigid tissue of the tumor or the tumor-bearing organ (e.g., prostate) is moved unpredictably so that the step length of retraction measured at the surface is often not the same as in the tumor. In our procedure one single retraction is needed per needle and seedspacing is not influenced by the possible changes in the position of the tumor. Also, with the Mick applicator the seed sometimes adheres to the stylet and may be retracted back into the needle. The retracted seed is then incorrectly replaced together with the next seed by the next step of application or stays in the removed needle. With our device, seed retraction is possible only
++FR 39R5 (14 KaV-3MeV):
Frieseke and Hoepfner.
Iodine-135 seed implan station 0
with the last seed of each linear array. Such a retraction has never occurred, perhaps because of the smooth fit of seeds into the needle. Also, in comparison to our applicator, the Mick system is long and heavy, thus requiring more room during use, and it can act like a lever to the implanted needle. The Scott system has disadvantages in radiation protection because it uses loose unshielded seeds in the operating room. Furthermore, the loading procedure is relatively slow and the implantation process re-
R. HAWLICZEK et d.
625
quires significantly longer time than our device, thus increasing exposure to the operating team. Our new device is potentially useful in nearly all body sites. However, because of its compactness and its precise atraumatic delivery of seeds, it is particularly useful in stereotactic brain implantation. The handling is simple and fast and radiation exposure minimal. The seeds are placed precisely and atraumatically. In our opinion it is a superior alternative to the available systems as described.
REFERENCES I.
3.
3 _
4.
5.
Becker, K. Solid state dosimetry. Cleveland. Ohio: CRC Press: 1973. De Ginder, W. L.; Mistry. V. D. Novel and inexpensive system for interstitial “510dine seed implants. Int. J. Radiat. Oncol. Biol. Phys. 4:745-747; 1978. Hammer, J.; Hawliczek. R.: Karcher, K. H.: Riccabona. M. A new spacing material for interstitial implantation of radioactive seeds. Int. J. Radiat. Oncol. Biol. Phys. 16:259260: 1989. Henschke. U. K.: Hilaris. B. S.: Mahan. G. D. Afterloading in interstitial and intracavitary radiation therapy. Am. J. Roentgenol. 90:386-395: 1963. ICRU 40: The quality factor in radiation protection. Report of a Joint Task Group of the ICRP and ICRU. Bethesda, Maryland: ICRU Publications: 1986.
D.: 6. Ling, C. C.; Yorke, E. D.; Spiro. 1. S.; Kubiatowicz, Bennett, D. Physical dosimetry of I2S-Iodine seeds of a new design for interstitial implant. Int. J. Radiat. Oncol. Biol. Phys. 9:1747-1752: 1983. Schulz, V.: Busch. M. Ein neuer Applikator Therapie mit Au-198 and I-125 Seeds. 157(2):104-105; 1981.
zur interstitiellen Strahlentherapie
Scott, W. P. Rapid injector for permanent radioactive plantation. Radiology 105(2):454-455: 1972.
im-
Scott. W. P. A spacer injector needle for I-“5 and other radioactive sources in permanent seed implants. Radiology 122(3):832-834; 1977. IO. Scott, W. P. lmplanter for radioactive sources. Int. J. Radiat. Oncol. Biol. Phys. 7:263-266; I98 I.
