Less-restrictive, patient-specific radiation safety precautions can be safely prescribed after permanent seed implantation

Radiation Safety Assessment in Prostate Cancer Treatment: A Predictive Approach for I-125 Brachytherapy

This study uses Monte Carlo simulation and experimental measurements to develop a predictive model for estimating the external dose rate associated with permanent radioactive source implantation in prostate cancer patients. The objective is to estimate the accuracy of the patient's external dose rate measurement. First, I-125 radioactive sources were implanted into Mylar window water phantoms to simulate the permanent implantation of these sources in patients. Water phantom experimental measurement was combined with Monte Carlo simulation to develop predictive equations, whose performance was verified against external clinical data. The model's accuracy in predicting the external dose rate in patients with permanently implanted I-125 radioactive sources was high (R2 = 0.999). A comparative analysis of the experimental measurements and the Monte Carlo simulations revealed that the maximum discrepancy between the measured and calculated values for the water phantom was less than 5.00%. The model is practical for radiation safety assessments, enabling the evaluation of radiation exposure risks to individuals around patients with permanently implanted I-125 radioactive sources.

Patient‐specific radiological protection precautions following Cs collagen embedded Cs‐131 implantation in the brain

Objective

Cesium‐131 brachytherapy is an adjunct for brain tumor treatment, offering potential clinical and radiation protection advantages over other isotopes including iodine‐125. We present evidence‐based radiation safety recommendations from an initial experience with Cs‐131 brachytherapy in the resection cavities of recurrent, previously irradiated brain metastases.

Methods

Twenty‐two recurrent brain metastases in 18 patients were resected and treated with permanent Cs‐131 brachytherapy implantation using commercially procured seed‐impregnated collagen tiles (GammaTile, GT Medical Technologies). Exposure to intraoperative staff was monitored with NVLAP‐accredited ring dosimeters. For patient release considerations, NCRP guidelines were used to develop an algorithm for modeling lifetime exposure to family and ancillary staff caring for patients based on measured dose rates.

Results

A median of 16 Cs‐131 seeds were implanted (range 6–46) with median cumulative strength of 58.72U (20.64‐150.42). Resulting dose rates were 1.19 mSv/h (0.28–3.3) on contact, 0.08 mSv/h (0.01–0.35) at 30 cm, and 0.01 mSv/h (0.001–0.03) at 100 cm from the patient. Modeled total caregiver exposure was 0.91 mSv (0.16–3.26), and occupational exposure was 0.06 mSv (0.02–0.23) accounting for patient self‐shielding via skull and soft tissue attenuation. Real‐time dose rate measurements were grouped into brackets to provide close contact precautions for caregivers ranging from 1–3 weeks for adults and longer for pregnant women and children, including cases with multiple implantations.

Conclusions

Radiological protection precautions were developed based on patient‐specific emissions and accounted for multiple implantations of Cs‐131, to maintain exposure to staff and the public in accordance with relevant regulatory dose constraints.

Recommendations for intraoperative mesh brachytherapy: Report of AAPM Task Group No. 222

Mesh brachytherapy is a special type of a permanent brachytherapy implant: it uses low-energy radioactive seeds in an absorbable mesh that is sutured onto the tumor bed immediately after a surgical resection. This treatment offers low additional risk to the patient as the implant procedure is carried out as part of the tumor resection surgery. Mesh brachytherapy utilizes identification of the tumor bed through direct visual evaluation during surgery or medical imaging following surgery through radiographic imaging of radio-opaque markers within the sources located on the tumor bed. Thus, mesh brachytherapy is customizable for individual patients. Mesh brachytherapy is an intraoperative procedure involving mesh implantation and potentially real-time treatment planning while the patient is under general anesthesia. The procedure is multidisciplinary and requires the complex coordination of multiple medical specialties. The preimplant dosimetry calculation can be performed days beforehand or expediently in the operating room with the use of lookup tables. In this report, the guidelines of American Association of Physicists in Medicine (AAPM) are presented on the physics aspects of mesh brachytherapy. It describes the selection of radioactive sources, design and preparation of the mesh, preimplant treatment planning using a Task Group (TG) 43-based lookup table, and postimplant dosimetric evaluation using the TG-43 formalism or advanced algorithms. It introduces quality metrics for the mesh implant and presents an example of a risk analysis based on the AAPM TG-100 report. Recommendations include that the preimplant treatment plan be based upon the TG-43 dose calculation formalism with the point source approximation, and the postimplant dosimetric evaluation be performed by using either the TG-43 approach, or preferably the newer model-based algorithms (viz., TG-186 report) if available to account for effects of material heterogeneities. To comply with the written directive and regulations governing the medical use of radionuclides, this report recommends that the prescription and written directive be based upon the implanted source strength, not target-volume dose coverage. The dose delivered by mesh implants can vary and depends upon multiple factors, such as postsurgery recovery and distortions in the implant shape over time. For the sake of consistency necessary for outcome analysis, prescriptions based on the lookup table (with selection of the intended dose, depth, and treatment area) are recommended, but the use of more advanced techniques that can account for real situations, such as material heterogeneities, implant geometric perturbations, and changes in source orientations, is encouraged in the dosimetric evaluation. The clinical workflow, logistics, and precautions are also presented.

Radiation dose rate variations in different measurement scenarios after prostate 125I brachytherapy

PURPOSE

This study aimed to directly compare different measurement scenarios using a supplemental radiation exposure measurement data set.

MATERIALS AND METHODS

Two sets of measurement scenarios comparing different body postures, such as standing and chair sitting positions, and different measurement directions, such as anterior and posterior directions, were assessed for radiation dose rate variations in this study at the Tokyo Medical Center, Japan. The estimated precaution time for holding children in the spoon position while sitting was also calculated.

RESULTS

Different radiation dose rate measurement scenarios showed different variation tendencies. Radiation dose rate measurement showed higher mean values of measured radiation dose tendency in the standing position than in the sitting positions. The measurement from the anterior direction showed a slightly lower tendency than that from the posterior direction. Assuming a dose limit of 1 mSv, the precaution time calculated for children being held in the spoon position for a certain duration every day was 51.5 (range, 12.5-152.2) minutes.

CONCLUSIONS

Our study presented a supplemental radiation exposure measurement data set and directly compared different measurement scenarios. Several trends in radiation exposure variations were found in the measurement scenarios at different body postures and different measurement directions. Our study data set could be a useful source of concrete information regarding radiation safety and contribute to the review and revision of public guidance in the future.

Brachytherapy: Increased Use in Patients With Intermediate- and High-Risk Prostate Cancers

BACKGROUND

Brachytherapy is a well-established and effective primary treatment modality for low- and favorable intermediate-risk prostate cancers. Although the benefits of brachytherapy in unfavorable intermediate- and high-risk prostate cancers have not been as clear, research suggests that brachytherapy boost may improve biochemical progression-free survival in these patients.

OBJECTIVES

This article aims to discuss evidence for the revival of brachytherapy use in unfavorable intermediate- and high-risk prostate cancers and specific nursing implications in the management of these patients.

METHODS

The literature on brachytherapy and its use to treat localized prostate cancers was reviewed.

FINDINGS

Nurses should be knowledgeable about the indications for brachytherapy, patient eligibility, anticipated side effects, and symptom management.

Radiation protection and dosimetry issues for patients with prostate cancer after I-125 low-dose-rate brachytherapy permanent implant

PURPOSE

The aim of this work was to analyze the exposure rates measured in the proximity of patients who underwent prostate low-dose-rate brachytherapy with I-125 implant. Effective doses to relatives and to population were computed to estimate the time to reach radioprotection dose constraints.

METHODS AND MATERIALS

Measurements were obtained from 180 patients, whereas the body mass index was calculated and reported for 77 patients. The day after the implant, K˙ measurements were conducted at various skin distances and positions and converted to effective doses. A theoretical model was developed to estimate effective doses from total implanted activity. The latter was approximated with a 10-mL vial inside the patient.

RESULTS

The K˙ measurements showed a low correlation with the total implanted activity, albeit an increasing trend of K˙ was observed on increasing the activity. A stronger correlation was found between body mass index and K˙ measurements. The effective dose to population is in general lower than dose constraints as well as the effective doses to relatives, with the exception of children and pregnant women, who command special precautions. We report differences between the experimental model- and theoretical model-based dose evaluation together with their comparison with previous studies found in literature.

CONCLUSIONS

Based on the K˙ measurements and the results of the present analysis, it is possible to provide the patient with radiation safety instructions specifically tailored to his relatives' habits and working environment.

Prospective study of direct radiation exposure measurements for family members living with patients with prostate (125)I seed implantation: Evidence of radiation safety

PURPOSE

To broaden the current understanding of radiation exposure and risk and to provide concrete evidence of radiation safety related to (125)I seed implantation.

METHODS AND MATERIALS

Direct radiation exposure measurements were obtained from dosimeters provided to 25 patients who underwent (125)I seed implantation, along with their family members. The estimated lifetime exposure dose and the precaution time for holding children near the patient's chest were calculated in two study periods.

RESULTS

During the first and second study period, the mean estimated lifetime exposure doses were, respectively, 7.61 (range: 0.45, 20.21) mSv and 6.84 (range: 0.41, 19.20) mSv for patients, and 0.19 (range: 0.02, 0.54) mSv and 0.25 (range: 0.04, 1.00) mSv for family members. The mean ratios of first and second period measurements were 1.05 (range: 0.44, 3.18) for patients and 1.82 (range: 0.21, 7.04) for family members. The corresponding absolute differences between first and second period measurements were -0.77 (range: -11.40, 7.63) mSv and 0.06 (range: -0.26, 0.79) mSv, respectively. Assuming a dose limit of 1 mSv, the precaution times for holding a child every day of the first and second periods were 250.9 (range: 71.3, 849.4) min and 275.2 (range: 75.0, 883.4) min, respectively. Assuming a dose limit of 0.5 mSv, the corresponding precaution times were 179.0 (range: 35.6, 811.5) min and 178.9 (range: 37.5, 1131.8) min, respectively.

CONCLUSIONS

Our study demonstrated low radiation exposures to family members of patients undergoing (125)I prostate implantation. It was clear that (125)I seed implantation did not pose a threat to the safety of family members.

Radiation safety of receptive anal intercourse with prostate cancer patients treated with low-dose-rate brachytherapy

PURPOSE

Prostate low-dose-rate (LDR) brachytherapy involves implantation of radioactive seeds permanently into the prostate gland. During receptive anal intercourse, the penis of the partner may come in close proximity to the implanted prostate gland. We estimate the potential intrarectal dose rates and suggest guidance on radiation precautions.

METHODS AND MATERIALS

One hundred two patients were included in the study. After implantation, with patients under anesthesia in the dorsal lithotomy position, a new set of ultrasound (US) images and a CT scan were obtained. The images were fused, radioactive seeds and US probe locations were determined on the CT, and prostate, bladder, and rectal contours were drawn on the US. Dose rates (cGy/h) were calculated for the portion of the US probe spanning the prostate for several dose-volume histogram parameters.

RESULTS

Twenty patients were treated with (125)I and 82 patients with (103)Pd. Average dose rates at Day 0 to the portion of the US probe spanning the prostate were 2.1 ± 1.3 cGy/h and 2.5 ± 0.8 cGy/h for patients treated with (125)I and (103)Pd, respectively. After 60 days, average calculated probe dose drops to 1.0 ± 0.6 cGy/h and 0.2 ± 0.1 cGy/h for (125)I and (103)Pd, respectively.

CONCLUSIONS

During the immediate weeks after prostate seed implant, the estimated intrarectal dose rates are higher in (103)Pd compared to (125)I. As (103)Pd decays faster than (125)I, 2 months after the implant, radiation exposure from (103)Pd becomes lower than (125)I. Receptive anal intercourse time should be kept as low as possible during 2 and 6 months after low-dose-rate brachytherapy of the prostate with (103)Pd and (125)I, respectively.

A novel perineal shield for low-dose-rate prostate brachytherapy

Purpose

To study the impact on radiation exposure to staff through the use of an original perineal shield during low-dose-rate prostate brachytherapy.

Material and methods

We designed a 1 mm thick stainless steel shield that duplicates and is able to slide directly over a standard commercialized prostate brachytherapy grid. We then analyzed the post-procedure exposure in 15 consecutive patients who underwent Iodine-125 seed placement. Measurements were performed with and without the shield in place at fixed locations relative to the grid template. Endpoints were analyzed using the paired two-sample t-test, with statistical significance defined as a p-value < 0.05.

Results

The exposure at the midline grid template ranged from 0.144-0.768 mSv/hr without the shield, and 0.038-0.144 mSv/hr with the shield (p < 0.0001). The exposure 10 cm left of the grid template was 0.134-0.576 mSv/hr without the shield, and 0.001-0.012 mSv/hr with the shield (p < 0.0001). The exposure 10 cm right of the grid template was 0.125-0.576 mSv/hr without the shield, and 0.001-0.012 mSv/hr with the shield (p < 0.0001). The median reduction of exposure at the grid was 76% midline, 98.5% left, and 99% right. Similarly, each individual dose rate was recorded at 25 cm from the perineum, both with and without shield. The median reduction of exposure 25 cm from the perineum was 73.7% midline, 77.7% left and 81.6% right (p < 0.0001).

Conclusions

Our novel shield took seconds to install and was non-restrictive during the procedure, and provided at least a four-fold reduction in radiation exposure to the brachytherapist.

Radioactive seed localization with 125I for nonpalpable lesions prior to breast lumpectomy and/or excisional biopsy: methodology, safety, and experience of initial year

The use of radioactive seed localization (RSL) as an alternative to wire localizations (WL) for nonpalpable breast lesions is rapidly gaining acceptance because of its advantages for both the patient and the surgical staff. This paper examines the initial experience with over 1,200 patients seen at a comprehensive cancer center. Radiation safety procedures for radiology, surgery, and pathology were implemented, and radioactive material inventory control was maintained using an intranet-based program. Surgical probes allowed for discrimination between 125I seed photon energies from 99mTc administered for sentinel node testing. A total of 1,127 patients (median age of 57.2 y) underwent RSL procedures with 1,223 seeds implanted. Implanted seed depth ranged from 10.3-107.8 mm. The median length of time from RSL implant to surgical excision was 2 d. The median 125I activity at time of implant was 3.1 MBq (1.9 to 4.6). The median dose rate from patients with a single seed was 9.5 µSv h-1 and 0.5 µSv h-1 at contact and 1 m, respectively. The maximum contact dose rate was 187 µSv h-1 from a superficially placed seed. RSL performed greater than 1 d before surgery is a viable alternative to WL, allowing flexibility in scheduling, minimizing day of surgery procedures, and improving workflow in breast imaging and surgery. RSL has been shown to be a safe and effective procedure for preoperative localization under mammographic and ultrasound guidance, which can be managed with the use of customized radiation protection controls.