Improving internal radiation treatment of cervical cancer with 3D imaging
In 2020, 1350 Canadian women were diagnosed with cervical cancer, accounting for 1.3% of all female cancers and 1.1% of female cancer-related deaths. For the women diagnosed with cervical cancer, various treatment options are available depending on the type, stage, and extent of the disease. The three main types of treatment for cervical cancer include surgery, radiation therapy (radiotherapy) and chemotherapy.
Most early-stage cervical cancer treatments involve hysterectomy, which can be classified as either total or radical hysterectomy. Total hysterectomy involves the complete surgical removal of the entire uterus and cervix, with radical hysterectomy including the removal of surrounding organs such as the ovaries, fallopian tubes, and parts of the vagina as well. Although hysterectomy for cervical cancer may completely remove any tumours present, there is a high risk for complications after surgery. Additionally, despite surgical removal, some patients may experience cancer recurrence due to the spread of abnormal cells to small regions outside the cervix. Because of this, radiotherapy or chemotherapy is often recommended to increase the likelihood of successful cancer treatment.
The most common radiotherapy treatment technique is known as external beam radiotherapy. External beam radiotherapy involves the use of a specialized machine called a linear accelerator (LINAC) to generate beams of high-energy x-rays, which are directed outside the body toward a tumour to destroy cancer cells. External beam radiotherapy can be combined with another radiotherapy technique known as internal radiotherapy to improve treatment outcomes. Internal radiotherapy involves implanting radioactive materials inside the body, directly into the tumour, around the tumour, or in the area in which the tumour was previously removed. This special internal radiotherapy is also known as brachytherapy. These radioactive materials can be implanted in several ways, including temporary insertion into a body cavity, called intracavitary brachytherapy, or insertion directly into the tissue using specialized hollow needles, called interstitial brachytherapy.
High-dose-rate (HDR) interstitial brachytherapy is particularly useful for early-stage and locally advanced or recurrent cancers, as it allows for a high dose of radiation to be delivered to a precise location over a short amount of time. This therapy requires the precise placement of multiple hollow needles into the tumour and surrounding tissues. This must be done while avoiding healthy tissues and nearby organs at risk (OAR) such as the bladder and rectum. Despite the need for highly accurate needle placement, there is still no clinical standard to guide or visualize these needles during the brachytherapy procedure or intraoperatively.
Research led by Dr. Jessica Rodgers and Dr. Aaron Fenster in the Translational Ultrasound Technology (TRUST) lab at the Robarts Research Institute and Western University, in collaboration with the London Regional Cancer Program and London Health Sciences Centre, presented novel technology to improve HDR brachytherapy needle placement using three-dimensional (3D) ultrasound imaging.
This technology uses a commercial endocavity ultrasound probe, commonly used in the clinic, which is placed directly in the vagina for imaging (known as transvaginal ultrasound). This allows physicians to image brachytherapy needles and critical surrounding anatomy including the pelvis, vaginal wall, bladder, urethra, and rectum in most cases. Recently in 2019, work published by this research group has extended the standard transvaginal ultrasound imaging to a full 3D ultrasound visualization with a 360° image acquisition.
In the proposed imaging system, the commercial ultrasound probe is supported by a counter-balanced stabilizer, which provides the device a weightless feel for physicians, allowing for easy positioning of the probe within the vagina. When the probe is in position, it can be mechanically rotated through a full 360° arc over 20 seconds. During rotation, standard two-dimensional (2D) ultrasound images are collected and combined using custom software, resulting in a donut-shaped 3D image with the ultrasound probe at the center. This image provides a unique perspective for the physician, as they can now see the anatomy and inserted needles in 3D and on all sides of the vagina in a single image!
The system was first tested using phantoms, which are specially manufactured objects designed to simulate human body parts or tissue. Dr. Rodgers developed a female pelvis phantom containing a specialized agar-based mixture to mimic the appearance of human tissue when imaged with ultrasound. By fabricating a complete female pelvis, the authors could simulate a brachytherapy procedure, including needle insertion and imaging. Results of the phantom study demonstrated the effectiveness and safety of the imaging system, which could be translated from the bench-to-bedside in patients without additional risk.
Building on the successful phantom experiment, a small patient study was completed that included 6 patients who underwent HDR interstitial brachytherapy for vaginal tumours at the London Health Sciences Centre. Following the insertion of all needles, a 3D transvaginal ultrasound image was captured. Across these patients, the 3D transvaginal ultrasound images provided clear visualization of all inserted needles and the surrounding organs, including the rectum, the pubis, the bladder, the vaginal wall, and even the catheter in the urethra. In comparison to standard-of-care computed tomography (CT) imaging, the needle visualization accuracy was very similar while being much quicker. This work demonstrates the potential benefit of 3D ultrasound as an intraoperative tool in gynecological brachytherapy.
Now that you have seen the potential of 3D ultrasound imaging in gynecologic brachytherapy, you might be wondering – why would we want to use ultrasound imaging in the first place? Although competing imaging modalities such as CT and magnetic resonance imaging (MRI) can provide high-resolution 3D images, they still suffer from limitations, including long scan times, low availability, and high cost. Ultrasound, on the other hand, is a safe, inexpensive, and real-time imaging modality. The main limitation is its 2D nature, making it highly dependent on physician skill and experience. The TRUST lab’s 3D ultrasound imaging technology utilizes the same commercial 2D ultrasound probes to generate a high-resolution 3D image, providing a safe and highly accessible imaging modality.
This research presents the first step toward improving radiotherapy options for gynecological cancer patients in Canada and beyond. Although the potential utility of 3D ultrasound imaging in gynecological brachytherapy is clear, continued clinical trials using this novel technology are needed to demonstrate its effectiveness for women with cervical cancer. Interestingly, this technology can also be used in the treatment of other gynecological cancers in the female pelvis, such as mid and upper vaginal tumors, providing exciting future research directions. Furthermore, this new inexpensive ultrasound-based technology provides the potential to increase accessibility to high-quality imaging and radiation treatment intervention for women with limited access to care, including those in rural areas.
Original Article: Rodgers JR, Bax J, Surry K, Velker V, Leung E, D’Souza D, Fenster A (2019) Intraoperative 360-deg three-dimensional transvaginal ultrasound during needle insertions for high-dose-rate transperineal interstitial gynecologic brachytherapy of vaginal tumors. J Med Imaging (Bellingham). 2019 Apr;6(2):025001. https://doi.org/10.1117/1.JMI.6.2.025001