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Radiation exposure to family and household members after prostate brachytherapy
Int. J. Radiation Oncology Biol. Phys., Vol. 56, No. 3, pp. 764 –768, 2003 Copyright © 2003 Elsevier Inc. Printed in the USA. All rights reserved 0360-3016/03/$–see front matter
doi:10.1016/S0360-3016(03)00002-6
CLINICAL INVESTIGATION
Prostate
RADIATION EXPOSURE TO FAMILY AND HOUSEHOLD MEMBERS AFTER PROSTATE BRACHYTHERAPY JEFF MICHALSKI, M.D.,* SASA MUTIC, M.S.,* JOHN EICHLING, PH.D.,*
AND
S. NISAR AHMED, M.D.†
*Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO; †University of Witswatersrand, Johannesburg, South Africa Purpose: Patients with localized prostate cancer frequently seek alternatives to radical surgery and external beam radiation therapy. Permanent prostate brachytherapy is an acceptable option. However, fears of radiation exposure to family members may deter some individuals from choosing this treatment option. A direct measurement was performed to determine the expected lifetime exposure from the patient with a brachytherapy prostate implant to family members and the household. Methods and Materials: After a permanent brachytherapy implant with 125I or 103Pd, patients and their family members were provided radiation monitors to measure direct radiation exposure at home. Each patient was given two monitors to wear, and each member of the household, including the spouse, children, and pets, was given a single monitor. In addition, four rooms in the house frequently occupied by the patient were monitored. Based on the reading from the dosimeters measured at the first follow-up visit, the lifetime exposure to each individual or room was calculated. Forty-four patients, along with their families, agreed to participate and complied with the use of the dosimeters. Twenty-nine patients received a 125I implant and 15 a 103Pd implant. Assays were obtained on 272 monitors: 78 worn by patients, 52 worn by household members, and 142 posted in rooms. Results: Exposures measured by patient dosimeters were within the expected range for the type of implant received. Exposures to family members were low. Based on dosimeter readings, the calculated mean lifetime dose to a spouse from her husband was 0.1 (range: 0.04 – 0.55) mSv for a 125I implant and 0.02 (range: 0.015– 0.074) mSv for a 103Pd implant. Other family or household members had 0.07 (range: 0.04 – 0.32) mSv or 0.02 (range: 0.015– 0.044) mSv for 125I and 103Pd implants, respectively. The calculated lifetime exposure did not exceed the annual limit set by the U.S. Nuclear Regulatory Commission in any of the cases. The majority of room dosimeters (94%) had no detectable radiation exposure. Conclusions: Radiation exposure to family members from a patient receiving a permanent prostate brachytherapy implant with radioactive 125I or 103Pd is very low and well below the limits recommended by the U.S. Nuclear Regulatory Commission. Radiation exposure to members of a patient’s family or to the public should not be a deterrent to undergoing this procedure. © 2003 Elsevier Inc. Prostate, Brachytherapy, Radiation exposure,
125
I,
103
Pd.
INTRODUCTION Transrectal ultrasound– guided prostate brachytherapy has gained increasing acceptance as an alternative to radical prostatectomy or external beam radiation therapy for the management of localized prostate cancer. Cancer control and survival rates for appropriately selected patients seem to be equivalent to surgery or radiation therapy (1–3). The selection of treatment options for any individual patient must consider overall patient health, side effects and risks, and treatment cost. According to the Centers for Medicare and Medicaid Services, permanent prostate brachytherapy
was performed on approximately 19,200 men in the year 2000. One concern that has been expressed regarding brachytherapy is the incidental exposure of family members to radiation. Some patients may be inclined to reject radioactive seed implantation with either 103Pd or 125I because of concerns of unnecessarily high radiation exposure to family members. In our practice, a majority of men express some concern about radiation exposure to their families, especially grandchildren. We performed a study of patients who underwent permanent prostate brachytherapy to measure radiation exposure to household members, including pets.
Reprint requests to: Jeff M. Michalski, M.D., Department of Radiation Oncology, Washington University School of Medicine, 4921 Parkview Place, Box 8224, St. Louis, MO 63110. Tel: (314) 362-8566; Fax: (314) 362-8521; E-mail: michalski@radonc. wustl.edu This work is supported by an unrestricted research grant from Nycomed-Amersham. No commercial products are described or
endorsed by the authors. The authors have no relationship with organizations that would influence the results reported in this manuscript. Dr. Ahmed’s participation was supported by a grant from the International Atomic Energy Commission. Received Aug 27, 2002, and in revised form Dec 17, 2002. Accepted for publication Dec 26, 2002. 764
Radiation exposure after brachytherapy
The U.S. Nuclear Regulatory Commission (NRC) (4) regulations (10 CFR 35.75) require that patients undergoing permanent brachytherapy receive instructions regarding precautions against unnecessary exposure to others. The published data describing radiation exposure rates from patients who have undergone prostate brachytherapy are scarce. Instantaneous exposure rates from the patient’s surface have been measured and used to calculate the contact time necessary to meet NRC annual limits (4). Continuous direct patient contact, even in families, does not actually occur, as such an assumption would imply. Personal radiation dosimeters sensitive to 0.01 mSv (1 mrem) have become available at reasonable cost. These dosimeters can detect radiation exposures within the range of limits mandated by the Nuclear Regulatory Commission. We elected to conduct a study that would measure radiation exposure to household members from patients undergoing permanent prostate brachytherapy. The methodology of this study is comparable to one conducted at our institution involving patients treated for thyroid cancer with radioactive iodine (131I) (5). In that study, patients were provided with optically stimulated luminescence dosimeters to be worn by household members or household pets or to be placed in each of four rooms in their houses. In both of these studies, exposure to household members was recorded as the effective deep dose equivalent as defined by the International Commission on Radiologic Protection (6 –9). This quantity is routinely used to report personnel doses, and it is a reasonable measure of doses received by members of households of prostate implant patients. METHODS AND MATERIALS Sixty patients, along with their household members, were recruited to participate in this prospective measurement of radiation exposure after radioactive seed implantation. This research project was reviewed and approved by the Washington University Institutional Review Board. All patients provided signed, informed consent expressing their willingness to participate in the trial. Each patient underwent a permanent radioactive seed implant with either 125I or 103 Pd. The choice of the radioactive isotope was made by the radiation oncologist. At the time of the study, it was our preference to use 125I for low or moderately differentiated tumors and 103Pd for poorly differentiated tumors. Eleven participants were excluded from the final analysis, because they failed to return at least half of the dosimeters provided. Another 5 patients were excluded because analysis of the dosimeters indicated that the patient did not comply with the study instructions. For example, if the patient’s collar and waist dosimeters had no exposure, the implication was that they were not worn. Including these patients’ and their family members’ dosimeter readings would have falsely lowered the mean exposure from the compliant study subjects. The remaining 44 patients are the focus of this analysis. The details of their treatment are
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765
Table 1. Patient treatment characteristics Isotope used 125
I
103
Pd
Number of patients 28 1 11 4
Brachytherapy prescription* 145 109 115 90
Gy Gy Gy Gy
Mean activity (mCi) implanted (range) 37.9 (29.6–47.1) 30.1 (na) 135.6 (96.4–186.3) 117.7 (86.4–128.7)
* Brachytherapy monotherapy prescription was 145 Gy (125I) or 115 Gy (103Pd). When combined with prior 45 Gy external beam, the prescription was 109 Gy (125I) or 90 Gy (103Pd).
presented in Table 1. Twenty-nine patients received a 125I implant, and the other 15 received a 103Pd implant. Five patients received external beam irradiation in addition to the brachytherapy. The total implanted activity was related to brachytherapy prescription and prostate gland volume. There was no significant difference in implanted activity in patients who received an implant alone vs. those receiving it after external radiation therapy. Therefore, patients’ data are analyzed only by isotope and not by whether the implant was a boost or sole therapy. To be eligible for the study, patients were required to have at least one household member living with them who was willing to be monitored. Each patient wore two dosimeters. One was at his collar and the other at the waist. These dosimeters were used to estimate compliance with the study. In most circumstances, the spouse was the only other household member. Some men had children at home in addition to their spouse. Starting on the day of the implant, all study participants were asked to wear the dosimeters continuously, 24 h a day, except when bathing, for the 3-week duration of the study. During the study period, no patient or family member traveled by air—an activity that would account for radiation exposure above background. Patients have occasionally expressed concern about radiation exposure to pets. When present, house pets were included as household members if they could wear the radiation dosimeter on a collar. Four rooms were monitored for exposure: the bedroom, bathroom, kitchen, and family/living rooms. Patients were instructed to place the radiation dosimeters adjacent to where they would normally sit or sleep in these rooms. Generally, this was on a nightstand, end table, or kitchen table less than 1 meter away. Dosimeters were returned 3 weeks after the brachytherapy implant procedure when the patient returned for a follow-up visit. Landauer Luxel radiation dosimeters (Landauer, Inc., Glenwood, IL) were distributed to each patient to begin wearing the day of the implant. Luxel’s optically stimulated luminescence dosimeter measures radiation exposure due to X-ray, beta, and gamma radiation through a thin layer of aluminum oxide. These dosimeters are sensitive to radiation energies from 5 KeV to 40 MeV. The radiation energies from both 125I and 103Pd (28 KeV and 21 KeV, respectively) are within the sensitive range of these dosimeters. The exposure measurable range is 0.01 mSv to 10 Sv for X-ray and gamma radiation for these dosimeters.
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Volume 56, Number 3, 2003
Table 2. Lifetime effective dose equivalent predicted from radiation monitors Patient Waist dose (mSv)
Isotope
Patient Collar dose (mSv)
Mean effective dose equivalent (entire study population) 125 6.47 1.10 I (n ⫽ 29) 103 3.33 0.30 Pd (n ⫽ 15) Mean effective dose equivalent (worst cases, ⬎75%ile) 125 14.04 3.27 I 103 6.39 0.80 Pd
Lifetime exposures to family members and rooms were calculated assuming the monitors were exposed for a time equal from the day they were provided on the day of the implant to the day they were returned approximately 3 weeks later. For a naturally decaying isotope, the exposure measured at time T is a function of the isotope’s half-life • and the initial dose rate, D (0), at the time of the implant.
Spouse dose (mSv)
Other family dose (mSv)
Any room dose (mSv)
0.10 0.02
0.07 0.02
0.05 0.02
0.21 0.03
0.07 0.02
0.07 0.02
implant would predict for a cumulative lifetime exposure of 0.092 mSv with all but 0.1–1.5% given in the year after the implant. A Student’s t test was done to detect differences between two types of implants. In the 44 patients who returned their dosimeters, we assayed 38 patient waists, 40 patient collars, 52 household members (including 7 pets), and 142 room dosimeters.
•
D共T兲 ⫽ 1.443 ⫻ t 1/ 2D 共0兲 ⫻ 关1 ⫺ e ⫺T⫻0.693/t1/ 2兴 RESULTS The lifetime exposure at an infinite time point is also a function of the initial dose rate and the isotope’s half-life: •
D共⬁兲 ⫽ 1.443 ⫻ t 1/ 2 ⫻ D 共0兲 Combining these equations allows one to calculate the lifetime exposure, D(⬁), based on the measured exposure, D(T), at time T: D共⬁兲 ⫽
D共T兲 关1 ⫺ e ⫺T⫻0.693/t1/ 2兴
Dosimeters were returned to the manufacturer for exposure assay. Control dosimeters, held by our radiation safety office, were used to measure background exposures during the study period. Background exposure was subtracted from each dosimeter to estimate actual radiation exposure contribution from the patient’s implant. The annual exposure to each individual or room monitor was calculated based on the 3-week dosimeter reading. We assumed that the patient would not change his living habits over the next year, and the 3-week measurement could be used to calculate an approximate lifetime exposure. The half-life of each isotope was used to calculate the expected lifetime exposure. 125I with a half-life of 60 days delivers 98% of its lifetime dose in the first year. 103Pd with a half-life of 17 days delivers 99.9% of its lifetime dose in the first year. In many circumstances, the dosimeters had no exposure exceeding background. In those circumstances, we assumed the exposure was equal to the threshold of the dosimeter, 1 mrem. This assumption would tend to overestimate the actual household member exposure. As an example, a dosimeter returned with an exposure reading of 0.02 mSv after 21 days of exposure to an iodine
Table 2 summarizes the mean effective dose equivalent that each patient, spouse, or other family member received after the implant. As expected, the patient dosimeter readings were the highest with values remarkably consistent with previously reported exposure rates, which indicates good compliance with wearing the dosimeter (10). These values do not truly reflect patient dose, given the dosimeters were designed to detect external radiation exposure, not internal implant dose. Iodine gave consistently higher exposure readings than palladium, because of its higher photon energy. The majority of patients’ spouses and other family members demonstrated very little radiation exposure. The calculated lifetime radiation doses were not normally distributed with the data skewed toward no measurable dose detected above background. The mean (range) effective dose equivalent for the spouses (assuming that a dosimeter with no exposure above background gave at least 0.01 mSv) was 0.10 (range: 0.04 – 0.55) mSv for an iodine implant and 0.02 (range: 0.015– 0.074) mSv for a palladium implant. Other family members and pets had a mean effective dose equivalent of 0.07 (range: 0.04 – 0.32) mSv for iodine implants and 0.02 (range: 0.015– 0.044) mSv for palladium implants. The majority (94%) of the room monitors had no detectable exposure above background. To estimate the “worst case,” the highest quartile of each set of exposure readings was selected (Table 3). In this quartile with the highest exposures, the spouse mean effective dose equivalent was 0.21 (range: 0.04 – 0.55) mSv for iodine and 0.03 (range: 0.015– 0.074) mSv for palladium. The highest exposures to any individual family members were to spouses with 0.55 mSv after iodine implants and 0.074 mSv after palladium implants. Spouses received significantly less radiation from the 103Pd implants than the 125I
Radiation exposure after brachytherapy
Table 3. Events, activities, or environments that contribute to average effective dose-equivalent exposures Source
Estimate exposure
Chest X-ray Daily salt substitute (KCl) use for 1 year Air travel (round trip NYC to SF) Air travel (round trip LA to Tokyo) Average internal source (40K, 16C, 87Rb) Average background exposure, U.S. citizen (all sources) Additional environmental and cosmic exposure, Denver vs. St. Louis Lifetime exposure from patient with 125 I prostate implant
0.02 mSv/procedure 0.10 mSv/year 0.12 mSv/trip 0.20 mSv/trip 0.25–0.35 mSv/year 3.60 mSv/year ⬎1.20 mSv/year 0.10 (0.04–0.55) mSv
implants (p ⬍ 0.05). All exposures were below limits set by the U.S. Nuclear Regulatory Commission for both isotopes. DISCUSSION In compliance with 10 CFR 35.75(a), the U.S. Nuclear Regulatory Commission (4) allows patient discharge to home if no more than 9 mCi (0.34 GBq) 125I or 40 mCi (1.5 GBq) 103Pd was implanted. Not surprisingly, all the implants in this study exceeded this limit. However, because of internal absorption of radiation by the patient, very little radiation is emitted, and alternative regulations allow discharge if the exposure rate at 1 meter is at or below 0.01 mSv/h for 125I and 0.03 mSv/h for 103Pd. It is estimated that these dose rates keep exposure to an individual to less than 5 mSv total effective dose. Smathers et al. (10) reported that the exposure rates from patients with permanent brachytherapy implants are below these limits. Immediately after the brachytherapy procedure, exposures from patients treated at our institution are surveyed at 1 meter. In more than 300 consecutive prostate brachytherapy implants, we have never measured an exposure rate that exceeded the NRC guidelines. The lifetime exposures calculated based on direct readings from our patients’ household and family member dosimeters are well below the annual limit set by the NRC and other regulatory agencies. Even the highest exposures received by the patients’ spouses are barely half the annual limit for members of the general public. The less intimate household readings of children, pets, and environment suggest that unusually high exposures are unlikely to be achieved through typical contact with the patient at home.
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The average effective dose equivalent received from all sources by a member of the U.S. population is 3.6 mSv per year (11). In the year after a prostate brachytherapy implant, a spouse would add 0.20 mSv to her cumulative annual dose. In that year, a spouse would receive no more than 5% of her total annual radiation exposure from her husband’s implant. Of course, patients receive only a single implant, and for all other years before and after the implant, the spouse would not be exposed to this source of radiation. To put the findings of this study into a perspective that patients and the general public may understand, Table 3 lists radiation exposures that individuals may receive performing everyday activities or living in other metropolitan areas (7). The annual radiation exposure difference that a Denver citizen receives compared to a St. Louisan is nearly 5-fold greater than the lifetime exposure received by living with a man who had a radioactive 125I implant. The magnitude of radiation exposure to family members from patients undergoing prostate brachytherapy is no worse than that from events most people take for granted every day. It is important to stress that there may be no “safe” thresholds for radiation exposure. The National Council on Radiation Protection and Measurement encourages the concept of “As Low As Reasonably Achievable” (12). The ALARA principle still applies in the context of the patient’s home. Patients should do simple things to minimize exposure to family members, especially children and pregnant women, who may be more sensitive to radiation. Minimizing direct contact for prolonged periods of time, especially for the first few weeks or months after an implant, should be practiced. An implant patient can hold a child, but he should restrict activities such as allowing the child to sit in his lap for many hours on multiple occasions. Wearable lead shields that minimize radiation exposure seem entirely unnecessary. In those uncommon situations where a patient is at home with a pregnant spouse or family member, the choice of 103Pd will reduce the expected radiation exposure to the woman and fetus. CONCLUSION Radiation exposure to family and household members from a patient receiving a radioactive prostate brachytherapy implant is very low and should be a minor factor in the decision making process for his primary therapy. This study demonstrates that the lifetime exposure to household members is below the limit set by the NRC for members of the lay public.
REFERENCES 1. Ragde H, Elgamal AA, Snow PB, et al. Ten-year disease free survival after transperineal sonography-guided iodine-125 brachytherapy with or without 45-Gray external beam irradiation in the treatment of patients with clinically localized, low to high Gleason grade prostate carcinoma. Cancer 1998;83: 989–1001.
2. Beyer DC, Priestley JB, Jr. Biochemical disease-free survival following 125I prostate implantation. Int J Radiat Oncol Biol Phys 1997;37:559–563. 3. Wallner K, Roy J, Harrison L. Tumor control and morbidity following transperineal iodine 125 implantation for stage T1/T2 prostatic carcinoma. J Clin Oncol 1996;14:449–453.
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4. Nuclear Regulatory Commission. Regulatory Guide 8.39: Release of patients administered radioactive materials. NRC 1997;8.39-1– 8.39-19. 5. Grigsby PW, Siegel BA, Baker S, Eichling JO. Radiation exposure from outpatient radioactive Iodine (131I) therapy for thyroid carcinoma. JAMA 2000;283:2272–2274. 6. International Commission on Radiological Protection. Recommendations of the International Commission on Radiological Protection, ICRP Publication 26, Annals of the ICRP 1 (Pergamon Press, Elmsford, New York), 1977. 7. International Commission on Radiation Units and Measurements. Measurement of Dose Equivalents from External Radiation Sources-Part 2, ICRU Report No. 47, Annals of the ICRP 1 (International Commission on Radiation Units and Measurements, Bethesda, Maryland), 1992. 8. National Council on Radiation Protection and Measurements. Use of Personal Monitors to Estimate Effective Dose Equiv-
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9.
10. 11. 12.
alent and Effective Dose to Workers for External Exposure to Low-LET Radiation, NCRP Report No. 122 (National Council on Radiation Protection and Measurements, Bethesda, Maryland), 1995. U.S. Nuclear Regulatory Commission. Standards for protection against radiation, page 23390 in Code of Federal Regulations 10CFR20 Federal Register 56 (U.S. Government Printing Office, Washington). 1991;9. Smathers S, Wallner K, Korssjoen T, et al. Radiation safety parameters following prostate brachytherapy. Int J Radiat Oncol Biol Phys 1999;45(2):397–399. National Council on Radiation Protection and Measurements. Limitation of exposure to ionizing radiation. NCRP 1987; Report No. 93. National Council on Radiation Protection and Measurements. Limitation of exposure to ionizing radiation. NCRP 1993; Report No. 116.
doi:10.1016/S0360-3016(03)00002-6
CLINICAL INVESTIGATION
Prostate
RADIATION EXPOSURE TO FAMILY AND HOUSEHOLD MEMBERS AFTER PROSTATE BRACHYTHERAPY JEFF MICHALSKI, M.D.,* SASA MUTIC, M.S.,* JOHN EICHLING, PH.D.,*
AND
S. NISAR AHMED, M.D.†
*Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO; †University of Witswatersrand, Johannesburg, South Africa Purpose: Patients with localized prostate cancer frequently seek alternatives to radical surgery and external beam radiation therapy. Permanent prostate brachytherapy is an acceptable option. However, fears of radiation exposure to family members may deter some individuals from choosing this treatment option. A direct measurement was performed to determine the expected lifetime exposure from the patient with a brachytherapy prostate implant to family members and the household. Methods and Materials: After a permanent brachytherapy implant with 125I or 103Pd, patients and their family members were provided radiation monitors to measure direct radiation exposure at home. Each patient was given two monitors to wear, and each member of the household, including the spouse, children, and pets, was given a single monitor. In addition, four rooms in the house frequently occupied by the patient were monitored. Based on the reading from the dosimeters measured at the first follow-up visit, the lifetime exposure to each individual or room was calculated. Forty-four patients, along with their families, agreed to participate and complied with the use of the dosimeters. Twenty-nine patients received a 125I implant and 15 a 103Pd implant. Assays were obtained on 272 monitors: 78 worn by patients, 52 worn by household members, and 142 posted in rooms. Results: Exposures measured by patient dosimeters were within the expected range for the type of implant received. Exposures to family members were low. Based on dosimeter readings, the calculated mean lifetime dose to a spouse from her husband was 0.1 (range: 0.04 – 0.55) mSv for a 125I implant and 0.02 (range: 0.015– 0.074) mSv for a 103Pd implant. Other family or household members had 0.07 (range: 0.04 – 0.32) mSv or 0.02 (range: 0.015– 0.044) mSv for 125I and 103Pd implants, respectively. The calculated lifetime exposure did not exceed the annual limit set by the U.S. Nuclear Regulatory Commission in any of the cases. The majority of room dosimeters (94%) had no detectable radiation exposure. Conclusions: Radiation exposure to family members from a patient receiving a permanent prostate brachytherapy implant with radioactive 125I or 103Pd is very low and well below the limits recommended by the U.S. Nuclear Regulatory Commission. Radiation exposure to members of a patient’s family or to the public should not be a deterrent to undergoing this procedure. © 2003 Elsevier Inc. Prostate, Brachytherapy, Radiation exposure,
125
I,
103
Pd.
INTRODUCTION Transrectal ultrasound– guided prostate brachytherapy has gained increasing acceptance as an alternative to radical prostatectomy or external beam radiation therapy for the management of localized prostate cancer. Cancer control and survival rates for appropriately selected patients seem to be equivalent to surgery or radiation therapy (1–3). The selection of treatment options for any individual patient must consider overall patient health, side effects and risks, and treatment cost. According to the Centers for Medicare and Medicaid Services, permanent prostate brachytherapy
was performed on approximately 19,200 men in the year 2000. One concern that has been expressed regarding brachytherapy is the incidental exposure of family members to radiation. Some patients may be inclined to reject radioactive seed implantation with either 103Pd or 125I because of concerns of unnecessarily high radiation exposure to family members. In our practice, a majority of men express some concern about radiation exposure to their families, especially grandchildren. We performed a study of patients who underwent permanent prostate brachytherapy to measure radiation exposure to household members, including pets.
Reprint requests to: Jeff M. Michalski, M.D., Department of Radiation Oncology, Washington University School of Medicine, 4921 Parkview Place, Box 8224, St. Louis, MO 63110. Tel: (314) 362-8566; Fax: (314) 362-8521; E-mail: michalski@radonc. wustl.edu This work is supported by an unrestricted research grant from Nycomed-Amersham. No commercial products are described or
endorsed by the authors. The authors have no relationship with organizations that would influence the results reported in this manuscript. Dr. Ahmed’s participation was supported by a grant from the International Atomic Energy Commission. Received Aug 27, 2002, and in revised form Dec 17, 2002. Accepted for publication Dec 26, 2002. 764
Radiation exposure after brachytherapy
The U.S. Nuclear Regulatory Commission (NRC) (4) regulations (10 CFR 35.75) require that patients undergoing permanent brachytherapy receive instructions regarding precautions against unnecessary exposure to others. The published data describing radiation exposure rates from patients who have undergone prostate brachytherapy are scarce. Instantaneous exposure rates from the patient’s surface have been measured and used to calculate the contact time necessary to meet NRC annual limits (4). Continuous direct patient contact, even in families, does not actually occur, as such an assumption would imply. Personal radiation dosimeters sensitive to 0.01 mSv (1 mrem) have become available at reasonable cost. These dosimeters can detect radiation exposures within the range of limits mandated by the Nuclear Regulatory Commission. We elected to conduct a study that would measure radiation exposure to household members from patients undergoing permanent prostate brachytherapy. The methodology of this study is comparable to one conducted at our institution involving patients treated for thyroid cancer with radioactive iodine (131I) (5). In that study, patients were provided with optically stimulated luminescence dosimeters to be worn by household members or household pets or to be placed in each of four rooms in their houses. In both of these studies, exposure to household members was recorded as the effective deep dose equivalent as defined by the International Commission on Radiologic Protection (6 –9). This quantity is routinely used to report personnel doses, and it is a reasonable measure of doses received by members of households of prostate implant patients. METHODS AND MATERIALS Sixty patients, along with their household members, were recruited to participate in this prospective measurement of radiation exposure after radioactive seed implantation. This research project was reviewed and approved by the Washington University Institutional Review Board. All patients provided signed, informed consent expressing their willingness to participate in the trial. Each patient underwent a permanent radioactive seed implant with either 125I or 103 Pd. The choice of the radioactive isotope was made by the radiation oncologist. At the time of the study, it was our preference to use 125I for low or moderately differentiated tumors and 103Pd for poorly differentiated tumors. Eleven participants were excluded from the final analysis, because they failed to return at least half of the dosimeters provided. Another 5 patients were excluded because analysis of the dosimeters indicated that the patient did not comply with the study instructions. For example, if the patient’s collar and waist dosimeters had no exposure, the implication was that they were not worn. Including these patients’ and their family members’ dosimeter readings would have falsely lowered the mean exposure from the compliant study subjects. The remaining 44 patients are the focus of this analysis. The details of their treatment are
● J. MICHALSKI et al.
765
Table 1. Patient treatment characteristics Isotope used 125
I
103
Pd
Number of patients 28 1 11 4
Brachytherapy prescription* 145 109 115 90
Gy Gy Gy Gy
Mean activity (mCi) implanted (range) 37.9 (29.6–47.1) 30.1 (na) 135.6 (96.4–186.3) 117.7 (86.4–128.7)
* Brachytherapy monotherapy prescription was 145 Gy (125I) or 115 Gy (103Pd). When combined with prior 45 Gy external beam, the prescription was 109 Gy (125I) or 90 Gy (103Pd).
presented in Table 1. Twenty-nine patients received a 125I implant, and the other 15 received a 103Pd implant. Five patients received external beam irradiation in addition to the brachytherapy. The total implanted activity was related to brachytherapy prescription and prostate gland volume. There was no significant difference in implanted activity in patients who received an implant alone vs. those receiving it after external radiation therapy. Therefore, patients’ data are analyzed only by isotope and not by whether the implant was a boost or sole therapy. To be eligible for the study, patients were required to have at least one household member living with them who was willing to be monitored. Each patient wore two dosimeters. One was at his collar and the other at the waist. These dosimeters were used to estimate compliance with the study. In most circumstances, the spouse was the only other household member. Some men had children at home in addition to their spouse. Starting on the day of the implant, all study participants were asked to wear the dosimeters continuously, 24 h a day, except when bathing, for the 3-week duration of the study. During the study period, no patient or family member traveled by air—an activity that would account for radiation exposure above background. Patients have occasionally expressed concern about radiation exposure to pets. When present, house pets were included as household members if they could wear the radiation dosimeter on a collar. Four rooms were monitored for exposure: the bedroom, bathroom, kitchen, and family/living rooms. Patients were instructed to place the radiation dosimeters adjacent to where they would normally sit or sleep in these rooms. Generally, this was on a nightstand, end table, or kitchen table less than 1 meter away. Dosimeters were returned 3 weeks after the brachytherapy implant procedure when the patient returned for a follow-up visit. Landauer Luxel radiation dosimeters (Landauer, Inc., Glenwood, IL) were distributed to each patient to begin wearing the day of the implant. Luxel’s optically stimulated luminescence dosimeter measures radiation exposure due to X-ray, beta, and gamma radiation through a thin layer of aluminum oxide. These dosimeters are sensitive to radiation energies from 5 KeV to 40 MeV. The radiation energies from both 125I and 103Pd (28 KeV and 21 KeV, respectively) are within the sensitive range of these dosimeters. The exposure measurable range is 0.01 mSv to 10 Sv for X-ray and gamma radiation for these dosimeters.
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Table 2. Lifetime effective dose equivalent predicted from radiation monitors Patient Waist dose (mSv)
Isotope
Patient Collar dose (mSv)
Mean effective dose equivalent (entire study population) 125 6.47 1.10 I (n ⫽ 29) 103 3.33 0.30 Pd (n ⫽ 15) Mean effective dose equivalent (worst cases, ⬎75%ile) 125 14.04 3.27 I 103 6.39 0.80 Pd
Lifetime exposures to family members and rooms were calculated assuming the monitors were exposed for a time equal from the day they were provided on the day of the implant to the day they were returned approximately 3 weeks later. For a naturally decaying isotope, the exposure measured at time T is a function of the isotope’s half-life • and the initial dose rate, D (0), at the time of the implant.
Spouse dose (mSv)
Other family dose (mSv)
Any room dose (mSv)
0.10 0.02
0.07 0.02
0.05 0.02
0.21 0.03
0.07 0.02
0.07 0.02
implant would predict for a cumulative lifetime exposure of 0.092 mSv with all but 0.1–1.5% given in the year after the implant. A Student’s t test was done to detect differences between two types of implants. In the 44 patients who returned their dosimeters, we assayed 38 patient waists, 40 patient collars, 52 household members (including 7 pets), and 142 room dosimeters.
•
D共T兲 ⫽ 1.443 ⫻ t 1/ 2D 共0兲 ⫻ 关1 ⫺ e ⫺T⫻0.693/t1/ 2兴 RESULTS The lifetime exposure at an infinite time point is also a function of the initial dose rate and the isotope’s half-life: •
D共⬁兲 ⫽ 1.443 ⫻ t 1/ 2 ⫻ D 共0兲 Combining these equations allows one to calculate the lifetime exposure, D(⬁), based on the measured exposure, D(T), at time T: D共⬁兲 ⫽
D共T兲 关1 ⫺ e ⫺T⫻0.693/t1/ 2兴
Dosimeters were returned to the manufacturer for exposure assay. Control dosimeters, held by our radiation safety office, were used to measure background exposures during the study period. Background exposure was subtracted from each dosimeter to estimate actual radiation exposure contribution from the patient’s implant. The annual exposure to each individual or room monitor was calculated based on the 3-week dosimeter reading. We assumed that the patient would not change his living habits over the next year, and the 3-week measurement could be used to calculate an approximate lifetime exposure. The half-life of each isotope was used to calculate the expected lifetime exposure. 125I with a half-life of 60 days delivers 98% of its lifetime dose in the first year. 103Pd with a half-life of 17 days delivers 99.9% of its lifetime dose in the first year. In many circumstances, the dosimeters had no exposure exceeding background. In those circumstances, we assumed the exposure was equal to the threshold of the dosimeter, 1 mrem. This assumption would tend to overestimate the actual household member exposure. As an example, a dosimeter returned with an exposure reading of 0.02 mSv after 21 days of exposure to an iodine
Table 2 summarizes the mean effective dose equivalent that each patient, spouse, or other family member received after the implant. As expected, the patient dosimeter readings were the highest with values remarkably consistent with previously reported exposure rates, which indicates good compliance with wearing the dosimeter (10). These values do not truly reflect patient dose, given the dosimeters were designed to detect external radiation exposure, not internal implant dose. Iodine gave consistently higher exposure readings than palladium, because of its higher photon energy. The majority of patients’ spouses and other family members demonstrated very little radiation exposure. The calculated lifetime radiation doses were not normally distributed with the data skewed toward no measurable dose detected above background. The mean (range) effective dose equivalent for the spouses (assuming that a dosimeter with no exposure above background gave at least 0.01 mSv) was 0.10 (range: 0.04 – 0.55) mSv for an iodine implant and 0.02 (range: 0.015– 0.074) mSv for a palladium implant. Other family members and pets had a mean effective dose equivalent of 0.07 (range: 0.04 – 0.32) mSv for iodine implants and 0.02 (range: 0.015– 0.044) mSv for palladium implants. The majority (94%) of the room monitors had no detectable exposure above background. To estimate the “worst case,” the highest quartile of each set of exposure readings was selected (Table 3). In this quartile with the highest exposures, the spouse mean effective dose equivalent was 0.21 (range: 0.04 – 0.55) mSv for iodine and 0.03 (range: 0.015– 0.074) mSv for palladium. The highest exposures to any individual family members were to spouses with 0.55 mSv after iodine implants and 0.074 mSv after palladium implants. Spouses received significantly less radiation from the 103Pd implants than the 125I
Radiation exposure after brachytherapy
Table 3. Events, activities, or environments that contribute to average effective dose-equivalent exposures Source
Estimate exposure
Chest X-ray Daily salt substitute (KCl) use for 1 year Air travel (round trip NYC to SF) Air travel (round trip LA to Tokyo) Average internal source (40K, 16C, 87Rb) Average background exposure, U.S. citizen (all sources) Additional environmental and cosmic exposure, Denver vs. St. Louis Lifetime exposure from patient with 125 I prostate implant
0.02 mSv/procedure 0.10 mSv/year 0.12 mSv/trip 0.20 mSv/trip 0.25–0.35 mSv/year 3.60 mSv/year ⬎1.20 mSv/year 0.10 (0.04–0.55) mSv
implants (p ⬍ 0.05). All exposures were below limits set by the U.S. Nuclear Regulatory Commission for both isotopes. DISCUSSION In compliance with 10 CFR 35.75(a), the U.S. Nuclear Regulatory Commission (4) allows patient discharge to home if no more than 9 mCi (0.34 GBq) 125I or 40 mCi (1.5 GBq) 103Pd was implanted. Not surprisingly, all the implants in this study exceeded this limit. However, because of internal absorption of radiation by the patient, very little radiation is emitted, and alternative regulations allow discharge if the exposure rate at 1 meter is at or below 0.01 mSv/h for 125I and 0.03 mSv/h for 103Pd. It is estimated that these dose rates keep exposure to an individual to less than 5 mSv total effective dose. Smathers et al. (10) reported that the exposure rates from patients with permanent brachytherapy implants are below these limits. Immediately after the brachytherapy procedure, exposures from patients treated at our institution are surveyed at 1 meter. In more than 300 consecutive prostate brachytherapy implants, we have never measured an exposure rate that exceeded the NRC guidelines. The lifetime exposures calculated based on direct readings from our patients’ household and family member dosimeters are well below the annual limit set by the NRC and other regulatory agencies. Even the highest exposures received by the patients’ spouses are barely half the annual limit for members of the general public. The less intimate household readings of children, pets, and environment suggest that unusually high exposures are unlikely to be achieved through typical contact with the patient at home.
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The average effective dose equivalent received from all sources by a member of the U.S. population is 3.6 mSv per year (11). In the year after a prostate brachytherapy implant, a spouse would add 0.20 mSv to her cumulative annual dose. In that year, a spouse would receive no more than 5% of her total annual radiation exposure from her husband’s implant. Of course, patients receive only a single implant, and for all other years before and after the implant, the spouse would not be exposed to this source of radiation. To put the findings of this study into a perspective that patients and the general public may understand, Table 3 lists radiation exposures that individuals may receive performing everyday activities or living in other metropolitan areas (7). The annual radiation exposure difference that a Denver citizen receives compared to a St. Louisan is nearly 5-fold greater than the lifetime exposure received by living with a man who had a radioactive 125I implant. The magnitude of radiation exposure to family members from patients undergoing prostate brachytherapy is no worse than that from events most people take for granted every day. It is important to stress that there may be no “safe” thresholds for radiation exposure. The National Council on Radiation Protection and Measurement encourages the concept of “As Low As Reasonably Achievable” (12). The ALARA principle still applies in the context of the patient’s home. Patients should do simple things to minimize exposure to family members, especially children and pregnant women, who may be more sensitive to radiation. Minimizing direct contact for prolonged periods of time, especially for the first few weeks or months after an implant, should be practiced. An implant patient can hold a child, but he should restrict activities such as allowing the child to sit in his lap for many hours on multiple occasions. Wearable lead shields that minimize radiation exposure seem entirely unnecessary. In those uncommon situations where a patient is at home with a pregnant spouse or family member, the choice of 103Pd will reduce the expected radiation exposure to the woman and fetus. CONCLUSION Radiation exposure to family and household members from a patient receiving a radioactive prostate brachytherapy implant is very low and should be a minor factor in the decision making process for his primary therapy. This study demonstrates that the lifetime exposure to household members is below the limit set by the NRC for members of the lay public.
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2. Beyer DC, Priestley JB, Jr. Biochemical disease-free survival following 125I prostate implantation. Int J Radiat Oncol Biol Phys 1997;37:559–563. 3. Wallner K, Roy J, Harrison L. Tumor control and morbidity following transperineal iodine 125 implantation for stage T1/T2 prostatic carcinoma. J Clin Oncol 1996;14:449–453.
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● Biology ● Physics
4. Nuclear Regulatory Commission. Regulatory Guide 8.39: Release of patients administered radioactive materials. NRC 1997;8.39-1– 8.39-19. 5. Grigsby PW, Siegel BA, Baker S, Eichling JO. Radiation exposure from outpatient radioactive Iodine (131I) therapy for thyroid carcinoma. JAMA 2000;283:2272–2274. 6. International Commission on Radiological Protection. Recommendations of the International Commission on Radiological Protection, ICRP Publication 26, Annals of the ICRP 1 (Pergamon Press, Elmsford, New York), 1977. 7. International Commission on Radiation Units and Measurements. Measurement of Dose Equivalents from External Radiation Sources-Part 2, ICRU Report No. 47, Annals of the ICRP 1 (International Commission on Radiation Units and Measurements, Bethesda, Maryland), 1992. 8. National Council on Radiation Protection and Measurements. Use of Personal Monitors to Estimate Effective Dose Equiv-
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