International Commission on Radiological Protection. Radiation safety aspects of brachytherapy for prostate cancer using permanently implanted sources. A report of ICRP Publication 98

Incidence of subsequent primary cancers and radiation-induced subsequent primary cancers after low dose-rate brachytherapy monotherapy for prostate cancer in long-term follow-up

BACKGROUND

As aging is the most significant risk factor for cancer development, long-term prostate cancer (PCa) survivors have an evident risk of developing subsequent primary cancers (SPCs). Radiotherapy itself is an additional risk factor for cancer development and the SPCs appearing beyond 5 years after radiotherapy in the original treatment field can be considered as radiation-induced subsequent primary cancers (RISPCs).

METHODS

During the years 1999-2008, 241 patients with localized PCa who underwent low dose-rate brachytherapy (LDR-BT) with I125 and were followed-up in Kuopio University Hospital, were included in this study. In this study the incidences and types of SPCs and RISPCs with a very long follow-up time after LDR-BT were evaluated.

RESULTS

During the median follow-up time of 11.4 years, a total of 34 (14.1%) patients developed a metachronous SPC. The most abundant SPCs were lung and colorectal cancers, each diagnosed in six patients (16.7% out of all SPCs). The crude incidence rate of RISPC was 1.7% (n = 4). Half of the SPC cases (50%) were diagnosed during the latter half of the follow-up time as the risk to develop an SPC continued throughout the whole follow-up time with the actuarial 10-year SPC rate of 7.0%. The crude death rates due to metachronous out-of-field SPCs and RISPCs were 50 and 50%, respectively.

CONCLUSION

The crude rate of SPC was in line with previously published data and the incidence of RISPC was very low. These results support the role of LDR-BT as a safe treatment option for patients with localized PCa.

Comparison of 125 Iodine Seed-Loaded Stents with Different Diameters in Esophageal Cancer: A Multicenter Retrospective Cohort Study

Currently, there are no recommendations or guidelines concerning the preferred diameter of esophageal stents for palliative treatment, owing to the lack of adequate evidence. We therefore conducted a retrospective cohort study to evaluate whether 18 mm stents would achieve a similar function of dysphagia relief with fewer complications and longer survival compared to 20 mm stents. Esophageal cancer patients who underwent 125 iodine seed-loaded stent placement with a diameter of either 18 mm (n = 103) or 20 mm (n = 54) were included at five hospitals in China. The stabilized inverse probability of treatment weighting (IPTW) was used to control potential confounding factors and bias that are inherent in a retrospective study. The primary endpoint was dysphagia relief. Stent-related complications and overall survival were assessed as the secondary endpoints. In the IPTW-adjusted analysis, no significant difference was found in the dysphagia score between the two groups either at 1 week after stent placement or at the last week before death. Despite a comparable rate of overall complications, there was a significantly lower incidence of severe retrosternal pain (15.4% vs. 32.7%, p = 0.013) and a trend toward longer survival (median survival, 176 days [95% confidence interval (CI) 144 to 209] vs. 109 days [92 to 126], p = 0.057) in the 18 mm group. An irradiated stent with a diameter of 18 mm showed a similar outcome of dysphagia relief to that achieved with a 20 mm diameter stent, but halved the incidence of retrosternal pain after stent placement.

Radiomics Facilitates Candidate Selection for Irradiation Stents Among Patients With Unresectable Pancreatic Cancer

Purpose: To develop a model to select appropriate candidates for irradiation stent placement among patients with unresectable pancreatic cancer with malignant biliary obstruction (UPC-MBO). Methods: This retrospective study included 106 patients treated with an irradiation stent for UPC-MBO. These patients were randomly divided into a training group (74 patients) and a validation group (32 patients). A clinical model for predicting restenosis-free survival (RFS) was developed with clinical predictors selected by univariate and multivariate analyses. After integrating the radiomics signature, a combined model was constructed to predict RFS. The predictive performance was evaluated with the concordance index (C-index) in both the training and validation groups. The median risk score of progression in the training group was used to divide patients into high- and low-risk subgroups. Results: Radiomics features were integrated with clinical predictors to develop a combined model. The predictive performance was better in the combined model (C-index, 0.791 and 0.779 in the training and validation groups, respectively) than in the clinical model (C-index, 0.673 and 0.667 in the training and validation groups, respectively). According to the median risk score of 1.264, the RFS was significantly different between the high- and low-risk groups (p < 0.001 for the training group, and p = 0.016 for the validation group). Conclusions: The radiomics-based model had good performance for RFS prediction in patients with UPC-MBO who received an irradiation stent. Patients with slow progression should consider undergoing irradiation stent placement for a longer RFS.

Efficacy and dosimetry analysis of image-guided radioactive ¹²⁵I seed implantation as salvage treatment for pelvic recurrent cervical cancer after external beam radiotherapy

Objective

To investigate the efficacy of image-guided radioactive ¹²⁵I seed (IGRIS) implantation for pelvic recurrent cervical cancer (PRCC) after external beam radiotherapy (EBRT), and analyze the influence of clinical and dosimetric factors on efficacy.

Methods

From July 2005 to October 2015, 36 patients with PRCC received IGRIS. We evaluated local progression-free survival (LPFS) and overall survival (OS).

Results

The median follow up was 11.5 months. The 1- and 2-year LPFS rate was 34.9% and 20%, respectively. The multivariate analysis indicated recurrence site (central or pelvic wall) (hazard ratio [HR]=0.294; 95% confidence interval [CI]=0.121–0.718), lesion volume (HR=2.898; 95% CI=1.139–7.372), D₉₀ (HR=0.332; 95% CI=0.130–0.850) were the independent factors affecting LPFS. The 1- and 2-year OS rate was 52.0% and 19.6%, respectively. The multivariate analysis suggested pathological type (HR=9.713; 95% CI=2.136–44.176) and recurrence site (HR=0.358; 95% CI=0.136–0.940) were the independent factors affecting OS. The dosimetric parameters of 33 patients mainly included D₉₀ (128.5±47.4 Gy), D₁₀₀ (50.4±23.7 Gy) and V₁₀₀ (86.7%±12.9%). When D₉₀ ≥105 Gy or D₁₀₀ ≥55 Gy or V₁₀₀ ≥91%, LPFS was extended significantly, but no significant difference for OS. The 79.2% of 24 patients with local pain were suffering from pain downgraded after radioactive ¹²⁵I seed implantation.

Conclusion

IGRIS implantation could be a safe and effective salvage treatment for PRCC after EBRT, which could markedly release the pain. Recurrence site, tumor volume and dose were the main factors affected efficacy. Compared with central recurrence, it was more suitable for patients with pelvic wall recurrent cervical cancer after EBRT.

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.

Reducing radiation risks to staff for patients with permanently implanted radioactive sources requiring unrelated surgery

Permanent implant of sealed radioactive sources is an effective technique for treating cancer. Typically, the radioactive sources are implanted in and near the disease, depositing radiation absorbed dose locally over several months. There may be instances where these patients must undergo unrelated surgical procedures when the radioactive material remains active enough to pose risks. This work explores these risks, discusses strategies to mitigate those risks, and describes a case study for a permanent iodine‐125 (I‐125) prostate brachytherapy implant patient who developed colorectal cancer and required surgery six months after brachytherapy. The first consideration is identifying the radiological risk to the patient and staff before, during, and after the surgical procedure. The second is identifying the risk the surgical procedure may have on the efficacy of the brachytherapy implant. Finally, there are considerations for controlling the radioactive substances from a regulatory perspective. After these risks are defined, strategies to mitigate those risks are considered. We summarize this experience with some guidelines: If the surgical procedure is near (e.g., within 5–10 cm of) the implant; and, the surgical intervention may dislodge sources enough to compromise treatment or introduces radiation safety risks; and, the radioactivity has not sufficiently decayed to background levels; and, the surgery cannot be postponed, then a detailed analysis of risk is advised.

PACS numbers: 87.53Bn, 87.53Jw, 87.55.N, 87.56.bg

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.

Dosimetric audit in brachytherapy

Dosimetric audit is required for the improvement of patient safety in radiotherapy and to aid optimization of treatment. The reassurance that treatment is being delivered in line with accepted standards, that delivered doses are as prescribed and that quality improvement is enabled is as essential for brachytherapy as it is for the more commonly audited external beam radiotherapy. Dose measurement in brachytherapy is challenging owing to steep dose gradients and small scales, especially in the context of an audit. Several different approaches have been taken for audit measurement to date: thimble and well-type ionization chambers, thermoluminescent detectors, optically stimulated luminescence detectors, radiochromic film and alanine. In this work, we review all of the dosimetric brachytherapy audits that have been conducted in recent years, look at current audits in progress and propose required directions for brachytherapy dosimetric audit in the future. The concern over accurate source strength measurement may be essentially resolved with modern equipment and calibration methods, but brachytherapy is a rapidly developing field and dosimetric audit must keep pace.

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

PURPOSE

To use radiation exposure rate measurements to determine patient-specific radiation safety instructions with the aim of reducing unnecessary precaution times and to evaluate potential doses to members of the public.

METHODS AND MATERIALS

Radiation exposure rate measurements were obtained from 1279 patients with Stage T1-2 prostate cancer who underwent transperineal (125)I or (103)Pd seed implantation from January 1995 through July 2008. An algorithm was developed from these measurements to determine the required precaution times to maintain public effective doses below 50% of the limits for specific exposure situations.

RESULTS

The median air kerma rates at 30 cm from the anterior skin surface were 4.9 microGy/h (range: 0.1-31.5) for (125)I and 1.5 microGy/h (range: 0.02-14.9) for (103)Pd. The derived algorithms depended primarily on the half-life T(p), the measured exposure rate at 30 cm, and specific exposure situation factors. For the typical (103)Pd patient, no radiation safety precautions are required. For the typical (125)I patient, no precautions are required for coworkers, nonpregnant adults who do not sleep with the patient, or nonpregnant adults who sleep with the patient. Typical (125)I patients should only avoid sleeping in the "spoon" position (i.e., in contact) with pregnant adults and avoid holding a child for long periods of time in the lap for about 2 months.

CONCLUSIONS

The large number of cases available for this study permitted the development of an algorithm to simply determine patient-specific radiation safety instructions. The resulting precaution times are significantly less restrictive than those generally prescribed currently.