Assessing protection against radiation exposure after prostate 125I brachytherapy

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.

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.

A novel radiation-shielding undergarment using tungsten functional paper for patients with permanent prostate brachytherapy

Tungsten functional paper (TFP) is a paper-based radiation-shielding material, which is lead-free and easy to cut. We developed a radiation protection undergarment using TFP for prostate cancer patients treated with permanent 125I seed implantation (PSI). The aim of this study was to evaluate the shielding ability of the undergarment with respect to household contacts and members of the public. Between October 2016 and April 2017, a total of 10 prostate cancer patients treated with PSI were enrolled in this prospective study. The external radiation exposure from each patient 1 day after PSI was measured with and without the undergarment. Measurements were performed using a survey meter at 100 cm from the surface of the patient's body. The exposure rates were measured from five directions: anterior, anteriorly oblique, lateral, posteriorly oblique, and posterior. The measured radiation exposure rates without the undergarment, expressed as mean ± standard deviation, from the anterior, anteriorly oblique, lateral, posteriorly oblique, and posterior directions were 1.28 ± 0.43 μSv/h, 0.70 ± 0.34 μSv/h, 0.21 ± 0.062 μSv/h, 0.65 ± 0.33 μSv/h and 1.24 ± 0.41 μSv/h, respectively. The undergarment was found to have (mean ± standard deviation) shielding abilities of 88.7 ± 5.8%, 44.0 ± 42.1%, 50.6 ± 15.9%, 72.9 ± 27.0% and 90.4 ± 10.7% from the anterior, anteriorly oblique, lateral, posteriorly oblique, and posterior directions, respectively. In conclusion, this shielding undergarment is a useful device that has the potential to reduce radiation exposure for the general public and the patient's family.

Do androgen deprivation and the biologically equivalent dose matter in low-dose-rate brachytherapy for intermediate-risk prostate cancer?

The objective of this study was to investigate the impact of the biologically equivalent dose (BED) on treatment outcomes after iodine‐125 low‐dose‐rate brachytherapy (LDR‐BT) with or without supplemental external beam radiotherapy (EBRT) and androgen deprivation therapy (ADT) for intermediate‐risk prostate cancer (PCa). We retrospectively evaluated 292 Japanese patients. The impact of the BED and ADT on treatment outcomes was investigated. Cox proportional hazard models were used for univariate and multivariate analysis with biological progression‐free survival (bPFS) and clinical progression‐free survival (cPFS) as the primary outcome measures. The median follow‐up was 66 months. The bPFS and cPFS rates at 5‐/7‐years were 91.6/87.7% and 95.9/94.0%, respectively. When stratified by BED levels, the bPFS rates at 5‐/7‐years were 92.1/89.3% for <178.0 Gy_2, and 91.2/86.0% for ≥178.0 Gy₂, respectively (P > 0.05). Based on ADT duration, the bPFS rates at 5‐/7‐years were 89.8/83.5%, 89.7/89.7%, and 97.5/97.5% for none, 1–3 months, and 4–12 months, respectively (P = 0.03). For the univariate analysis, the use of ADT and its duration were significant predictors for bPFS, whereas BED was not significant. A multivariate analysis did not indicate the use of ADT itself was significant, however, when covariates were accounted for by the duration of ADT, the longer use of ADT was found to significantly improve bPFS. Although cPFS was associated neither with the BED levels nor ADT duration (P > 0.05), ADT duration had a trend of improving cPFS (P = 0.053). The higher levels of BED did not significantly impact bPFS for intermediate‐risk PCa after LDR‐BT with or without supplemental EBRT and ADT. The longer duration of ADT could provide an additional benefit in the context of high‐dose irradiation generated by LDR‐BT.

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.

Predictive factors for urinary toxicity after iodine-125 prostate brachytherapy with or without supplemental external beam radiotherapy

PURPOSE

We examined the factors associated with urinary toxicities because of brachytherapy with iodine-125 with or without supplemental external beam radiotherapy (EBRT) for prostate cancer.

METHODS AND MATERIALS

We investigated 1313 patients with localized prostate cancer treated with iodine-125 brachytherapy with or without supplemental EBRT between 2003 and 2009. The International Prostate Symptom Score (IPSS) and Common Terminology Criteria for Adverse Events data were prospectively determined. Patients, treatment, and implant factors were investigated for their association with urinary toxicity or symptoms.

RESULTS

IPSS resolution was not associated with biologically effective dose (BED). Baseline IPSS, total needles, and the minimal dose received by 30% of the urethra had the greatest effect according to multivariate analysis (MVA). Urinary symptom flare was associated with baseline IPSS, age, BED, and EBRT on MVA. Urinary symptom flare and urinary Grade 2 or higher (G2+) toxicity occurred in 51%, 58%, and 67% (p = 0.025) and 16%, 22%, and 20% (p = 0.497) of the <180, 180-220, and >220 Gy BED groups, respectively. Urinary G2+ toxicity was associated with baseline IPSS, neoadjuvant androgen deprivation therapy (NADT), and seed density on MVA. When we divided patients into four groups according to prostate volume (<30 cc or ≥30 cc) and NADT use, urinary G2+ toxicity was most commonly observed in those patients with larger prostates who received NADT, and least in the patients with smaller prostates and no NADT.

CONCLUSIONS

NADT was associated with urinary G2+ toxicity. Higher dose and supplemental EBRT did not appear to increase moderate to severe urinary toxicities or time to IPSS resolution; however, it influenced urinary symptom flare.

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.