Radiation Exposure after Neurosurgical Resection and Permanent Intraoperative Cesium-131 Radio-isotope Brachytherapy in Patients with Brain Tumors

PurposeCs-131 post-resection permanent brachytherapy has been shown to be a safe, well tolerated, and convenient for patients. The results of our prospective study demonstrated excellent control and minimal toxicity (Wernicke et al). However, limited information is available regarding the radiation exposure after Cs-131 intracranial brachytherapy. In this study we prospectively analyzed radiation exposure data after Cs-131 brachytherapy in patients with resected brain tumors.Materials and MethodsBetween September 2010 and September 2011, 20 patients with newly diagnosed brain tumors were treated with resection and implant of permanent intra-operative Cs-131 brachytherapy seeds on the prospective IRB approved clinical trial. The prescription dose was 80 Gy to a 5 mm depth from the surface of resection cavity wall. In the operating room, after the implant procedure was completed, radiation exposure measurements were taken at the surface of the patient, as well as at 100 cm and 35 cm distances using Keithley 36100 dose rate meter calibrated annually at an accredited calibration center. Using the t1/2 of Cs-131 (9.69 days) we were able to extrapolate the exposure at these distances over an extended period of time (t=30 days), considering that 90% of the intended dose is delivered within the first 33 days. Additionally, dosimetry badges worn on the leaded aprons and rings worn under the leaded gloves were worn by both the surgeon and radiation oncologist throughout the procedure. These badges measure radiation exposure at the levels of "eye" (ocular lens), "shallow" (hands/skin), and "deep" (whole-body).ResultsThe median number of seeds was 12 (range, 4-50) and the median seeds activity was 3.85 mCi (range, 3.31-4.84mCi). The median exposure was 24.75 mRem/hr (range, 6.8-125 mRem/hr), 1.0 mRem/hr (range, 0.1-12 mRem/hr), and 0.1 mRem/hr (range, 0.1-1.9 mRem/hr) at the surface, 35 cm and 100 cm respectively. When extrapolated out to 30 days post-implant the median exposure was 2.98 mRem/hr (range, 0.80-14.63 mRem/hr), 0.12 mRem/hr (range, 0.01-1.4 mRem/hr), and 0.01 mRem/hr (range, 0.01-0.22 mRem/hr) at the surface, 35 cm and 100 cm respectively. All of the badges and rings measured minimal levels of exposure which correspond close to 0 mRem/hr. These levels of exposure compare favorably to the NCRP dose limit recommendation of 100 mRem for the general public from continuous or frequent exposure, and 500 mRem from infrequent exposure.ConclusionsOur data show that there is a low level of exposure at the surface, and even lower 35 cm and 100 cm away at the time of implantation and 1 month after brachytherapy. With the NCRP guidelines in mind, we can state conclusively that exposure from permanent Cs-131 brachytherapy for the treatment of brain tumors is limited, and it maintains safe levels of exposure to family and medical personnel. PurposeCs-131 post-resection permanent brachytherapy has been shown to be a safe, well tolerated, and convenient for patients. The results of our prospective study demonstrated excellent control and minimal toxicity (Wernicke et al). However, limited information is available regarding the radiation exposure after Cs-131 intracranial brachytherapy. In this study we prospectively analyzed radiation exposure data after Cs-131 brachytherapy in patients with resected brain tumors. Cs-131 post-resection permanent brachytherapy has been shown to be a safe, well tolerated, and convenient for patients. The results of our prospective study demonstrated excellent control and minimal toxicity (Wernicke et al). However, limited information is available regarding the radiation exposure after Cs-131 intracranial brachytherapy. In this study we prospectively analyzed radiation exposure data after Cs-131 brachytherapy in patients with resected brain tumors. Materials and MethodsBetween September 2010 and September 2011, 20 patients with newly diagnosed brain tumors were treated with resection and implant of permanent intra-operative Cs-131 brachytherapy seeds on the prospective IRB approved clinical trial. The prescription dose was 80 Gy to a 5 mm depth from the surface of resection cavity wall. In the operating room, after the implant procedure was completed, radiation exposure measurements were taken at the surface of the patient, as well as at 100 cm and 35 cm distances using Keithley 36100 dose rate meter calibrated annually at an accredited calibration center. Using the t1/2 of Cs-131 (9.69 days) we were able to extrapolate the exposure at these distances over an extended period of time (t=30 days), considering that 90% of the intended dose is delivered within the first 33 days. Additionally, dosimetry badges worn on the leaded aprons and rings worn under the leaded gloves were worn by both the surgeon and radiation oncologist throughout the procedure. These badges measure radiation exposure at the levels of "eye" (ocular lens), "shallow" (hands/skin), and "deep" (whole-body). Between September 2010 and September 2011, 20 patients with newly diagnosed brain tumors were treated with resection and implant of permanent intra-operative Cs-131 brachytherapy seeds on the prospective IRB approved clinical trial. The prescription dose was 80 Gy to a 5 mm depth from the surface of resection cavity wall. In the operating room, after the implant procedure was completed, radiation exposure measurements were taken at the surface of the patient, as well as at 100 cm and 35 cm distances using Keithley 36100 dose rate meter calibrated annually at an accredited calibration center. Using the t1/2 of Cs-131 (9.69 days) we were able to extrapolate the exposure at these distances over an extended period of time (t=30 days), considering that 90% of the intended dose is delivered within the first 33 days. Additionally, dosimetry badges worn on the leaded aprons and rings worn under the leaded gloves were worn by both the surgeon and radiation oncologist throughout the procedure. These badges measure radiation exposure at the levels of "eye" (ocular lens), "shallow" (hands/skin), and "deep" (whole-body). ResultsThe median number of seeds was 12 (range, 4-50) and the median seeds activity was 3.85 mCi (range, 3.31-4.84mCi). The median exposure was 24.75 mRem/hr (range, 6.8-125 mRem/hr), 1.0 mRem/hr (range, 0.1-12 mRem/hr), and 0.1 mRem/hr (range, 0.1-1.9 mRem/hr) at the surface, 35 cm and 100 cm respectively. When extrapolated out to 30 days post-implant the median exposure was 2.98 mRem/hr (range, 0.80-14.63 mRem/hr), 0.12 mRem/hr (range, 0.01-1.4 mRem/hr), and 0.01 mRem/hr (range, 0.01-0.22 mRem/hr) at the surface, 35 cm and 100 cm respectively. All of the badges and rings measured minimal levels of exposure which correspond close to 0 mRem/hr. These levels of exposure compare favorably to the NCRP dose limit recommendation of 100 mRem for the general public from continuous or frequent exposure, and 500 mRem from infrequent exposure. The median number of seeds was 12 (range, 4-50) and the median seeds activity was 3.85 mCi (range, 3.31-4.84mCi). The median exposure was 24.75 mRem/hr (range, 6.8-125 mRem/hr), 1.0 mRem/hr (range, 0.1-12 mRem/hr), and 0.1 mRem/hr (range, 0.1-1.9 mRem/hr) at the surface, 35 cm and 100 cm respectively. When extrapolated out to 30 days post-implant the median exposure was 2.98 mRem/hr (range, 0.80-14.63 mRem/hr), 0.12 mRem/hr (range, 0.01-1.4 mRem/hr), and 0.01 mRem/hr (range, 0.01-0.22 mRem/hr) at the surface, 35 cm and 100 cm respectively. All of the badges and rings measured minimal levels of exposure which correspond close to 0 mRem/hr. These levels of exposure compare favorably to the NCRP dose limit recommendation of 100 mRem for the general public from continuous or frequent exposure, and 500 mRem from infrequent exposure. ConclusionsOur data show that there is a low level of exposure at the surface, and even lower 35 cm and 100 cm away at the time of implantation and 1 month after brachytherapy. With the NCRP guidelines in mind, we can state conclusively that exposure from permanent Cs-131 brachytherapy for the treatment of brain tumors is limited, and it maintains safe levels of exposure to family and medical personnel. Our data show that there is a low level of exposure at the surface, and even lower 35 cm and 100 cm away at the time of implantation and 1 month after brachytherapy. With the NCRP guidelines in mind, we can state conclusively that exposure from permanent Cs-131 brachytherapy for the treatment of brain tumors is limited, and it maintains safe levels of exposure to family and medical personnel.