Dose measurement for medical staff with glass dosemeters and thermoluminescence dosemeters during 125I brachytherapy for prostate cancer

Evaluation of a new acrylic-lead shielding device for peripheral dose reduction during cone-beam computed tomography

Objective

To clarify the peripheral dose changes, especially in the eye lens and thyroid gland regions, using an acrylic-lead shield in cone-beam computed tomography (CBCT).

Methods

The acrylic-lead shield consists of system walls and a system mat. The radiophotoluminescence glass dosemeter was set on the eye lens and thyroid gland regions on the RANDO phantom. The system mat was laid under the RANDO phantom ranging from the top of the head to the shoulders, and then, the system walls shielded the phantom's head. Additionally, the phantom was covered anteriorly with a band that had the same shielding ability as the system mat to cover the thyroid gland region. Protocols for CBCT imaging of the thoracic or pelvic region in clinical practice were used. The measurement was performed with and without the acrylic-lead shield.

Results

The dose to the eye lens region was reduced by 45% using the system wall. Conversely, the dose to the thyroid gland was unchanged. The use of the system mat reduced the dose to the thyroid gland region by 47%, and the dose to the eye lens was reduced by 22%. The dose to the eye lens region decreased to the background level using the system walls and mat.

Conclusion

The newly proposed device using an acrylic-lead shield reduced the peripheral dose in CBCT imaging.

Advances in knowledge

Attention is focused on managing peripheral dose in image-guided radiation therapy. The peripheral dose reduction using the acrylic-lead shield is a new proposal in radiotherapy that has never been studied.

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.

Evaluation of physician eye lens doses during permanent seed implant brachytherapy for prostate cancer

Treatment of low grade prostate cancer with permanent implant of radioactive seeds has become one of the most common brachytherapy procedures in use today. The implant procedure is usually performed with fluoroscopy image guidance to ensure that the seeds are deployed in the planned locations. In this situation the physician performing the transperineal implant is required to be close to the fluoroscopy unit and dose to the eye lens may be of concern. In 1991 the International Commission on Radiological Protection (ICRP) provided a recommended dose limit of 150 mSv yr(-1) for occupational exposures to the lens of the eye. With more long term follow-up data, this limit was revised in 2011 to 20 mSv yr(-1). With this revised limit in mind, we have investigated the dose to the lens of the eye received by physicians during prostate brachytherapy seed implantation. By making an approximation of annual workload, we have related the dose received to the annual background dose. Through clinical and phantom measurements with thermoluminescent dosimeters, it was found that the excess dose to the physician's eye lens received for a conservative estimate of annual workload was never greater than 100% of the annual background dose.