226
TECHNICAL NOTES
•
October1975
• Gonadal Shield 1 James A. Purdy, Ph.D., Ron D. SIReler, B.S., Glenn P. Glasgow, Ph.D. and William B. Mill, M.D.
A secondary gonadal shield for use in the pelvic irradiation of males was designed and built using material and apparatus available with the Cerrobend blocking system. The gonadal dose was reduced to approximately 1.5 to 2.5 % of the given dose. INDEX TERMS:
Fig. 1.
Side view of gonadal shield.
Gonads. Radiations, protective and therapeutic agents and
devices Radiology 117:226, October 1975
•
•
In the treatment of Hodgkin's disease and other malignant lymphomas, the inguinal and femoral lymph nodes are frequently irradiated. The gonadal region normally is shielded with field-shaping blocks of five half-value layers supported on a blocking tray located above the patient. Blocks of double this thickness are sometimes used, but this may require a special support due to the extra height of the blocks. However, regardless of how well the primary beam is attenuated, the absorbed dose in the testicular region, due to scatter radiation from the lower abdomen and thighs, may be of the order of 5 to 10% of the midline dose, depending on radiation quality and geometrical considerations. In an effort to reduce the gonadal dose, a secondary shield for use with the primary block was developed at this Institute. Various shield designs initially were tested by measuring the dose absorbed in the simulated testicles of a clay phantom man. The shields were made using materials and equipment available with the field shaping system described by Powers et a/. (1), that is, the shields are cast using a lowmelting-point alloy, Cerrobend.f in a Styrofoam mold which was cut using a hot wire device. Measurements were made with a Farmer 0.6 ml ion chamber and a 602 Keithley electrometer. The wall thickness of the shield, selected for clinical use, is one centimeter, but this could be increased with no difficulty. As shown in Figure 1, one end of the shield is shaped to fit snugly to the perineum. The shield is mounted on a clay pedestal of sufficient height with the top properly angled to elevate the penis and testicles above the thighs and abdomen (Fig. 2). For the sake of hygiene, the penis and testicles are wrapped in a disposable tissue. Measurements are reported here for the following conditions: (a) a five half-value layer Cerrobend primary block; (b) the primary block plus 1.0 em Cerrobend side blocks as described by Jackson et a/. (2); and (e) the primary blocks plus the gonadal shield described in this article. The gonadal dose for (a) was between 4 and 6 % of the given dose while (b) and (e) effectively reduced the gonadal dose to between 1.5 and 2.5% of the given dose. These results are similar to
Fig. 2.
Gonadal shield in treatment position.
those obtained by Jackson et al. (2) and Glenn et et. (3). Measurements also were made with the side blocks tilted slightly so that they were struck by the primary beam. Experience has shown this is a frequent error and the measurements indicated that this results in a significant increase in the gonadal dose. There are three primary advantages of this shield. It is easily fabricated and can be custom designed for individual patients. The shield can be readily modified. For example, the thickness of the anterior side can be increased if added thickness blocks cannot be positioned on the conventional blocking tray. The clay pedestal with angled top supports the shield and effectively elevates the gonads above the thighs and abdomen. REFERENCES 1. Powers WE, Kinzie JJ, Demidecki AJ, et al: A new system of field shaping for external-beam radiation therapy. Radiology 108: 407-411, Aug 1973 2. Jackson HL, Hass AC, Sooby 0, et al: The gonadal exposure of boys and young men treated with inverted "V" fields: its reduction and genetic significance. Radiology96:181-186, Jul1970 3. Glenn OW, Johnson RE: Male gonadal shielding during cobalt teletherapy. Radiology 104:214, Jul 1972 1 From the Division of Radiation Oncology, Washington University School of Medicine, Mallinckrodt Institute of Radiology, 510 South Kingshighway, St. Louis, Mo. 63110. Accepted for publication in May 1975. 2 A trademark of CERRO Corporation. dk
TECHNICAL NOTES
•
October1975
• Gonadal Shield 1 James A. Purdy, Ph.D., Ron D. SIReler, B.S., Glenn P. Glasgow, Ph.D. and William B. Mill, M.D.
A secondary gonadal shield for use in the pelvic irradiation of males was designed and built using material and apparatus available with the Cerrobend blocking system. The gonadal dose was reduced to approximately 1.5 to 2.5 % of the given dose. INDEX TERMS:
Fig. 1.
Side view of gonadal shield.
Gonads. Radiations, protective and therapeutic agents and
devices Radiology 117:226, October 1975
•
•
In the treatment of Hodgkin's disease and other malignant lymphomas, the inguinal and femoral lymph nodes are frequently irradiated. The gonadal region normally is shielded with field-shaping blocks of five half-value layers supported on a blocking tray located above the patient. Blocks of double this thickness are sometimes used, but this may require a special support due to the extra height of the blocks. However, regardless of how well the primary beam is attenuated, the absorbed dose in the testicular region, due to scatter radiation from the lower abdomen and thighs, may be of the order of 5 to 10% of the midline dose, depending on radiation quality and geometrical considerations. In an effort to reduce the gonadal dose, a secondary shield for use with the primary block was developed at this Institute. Various shield designs initially were tested by measuring the dose absorbed in the simulated testicles of a clay phantom man. The shields were made using materials and equipment available with the field shaping system described by Powers et a/. (1), that is, the shields are cast using a lowmelting-point alloy, Cerrobend.f in a Styrofoam mold which was cut using a hot wire device. Measurements were made with a Farmer 0.6 ml ion chamber and a 602 Keithley electrometer. The wall thickness of the shield, selected for clinical use, is one centimeter, but this could be increased with no difficulty. As shown in Figure 1, one end of the shield is shaped to fit snugly to the perineum. The shield is mounted on a clay pedestal of sufficient height with the top properly angled to elevate the penis and testicles above the thighs and abdomen (Fig. 2). For the sake of hygiene, the penis and testicles are wrapped in a disposable tissue. Measurements are reported here for the following conditions: (a) a five half-value layer Cerrobend primary block; (b) the primary block plus 1.0 em Cerrobend side blocks as described by Jackson et a/. (2); and (e) the primary blocks plus the gonadal shield described in this article. The gonadal dose for (a) was between 4 and 6 % of the given dose while (b) and (e) effectively reduced the gonadal dose to between 1.5 and 2.5% of the given dose. These results are similar to
Fig. 2.
Gonadal shield in treatment position.
those obtained by Jackson et al. (2) and Glenn et et. (3). Measurements also were made with the side blocks tilted slightly so that they were struck by the primary beam. Experience has shown this is a frequent error and the measurements indicated that this results in a significant increase in the gonadal dose. There are three primary advantages of this shield. It is easily fabricated and can be custom designed for individual patients. The shield can be readily modified. For example, the thickness of the anterior side can be increased if added thickness blocks cannot be positioned on the conventional blocking tray. The clay pedestal with angled top supports the shield and effectively elevates the gonads above the thighs and abdomen. REFERENCES 1. Powers WE, Kinzie JJ, Demidecki AJ, et al: A new system of field shaping for external-beam radiation therapy. Radiology 108: 407-411, Aug 1973 2. Jackson HL, Hass AC, Sooby 0, et al: The gonadal exposure of boys and young men treated with inverted "V" fields: its reduction and genetic significance. Radiology96:181-186, Jul1970 3. Glenn OW, Johnson RE: Male gonadal shielding during cobalt teletherapy. Radiology 104:214, Jul 1972 1 From the Division of Radiation Oncology, Washington University School of Medicine, Mallinckrodt Institute of Radiology, 510 South Kingshighway, St. Louis, Mo. 63110. Accepted for publication in May 1975. 2 A trademark of CERRO Corporation. dk
