ElectroMagnetic-guided Interstitial Catheter Navigation for Gynecological brachyTherapy: A Phase I Trial

Cervical cancer poses a significant local and global health problem. In 2017 over 1,500 Canadian women were predicted to develop cervical cancer, and another 400 were approximated to die from the disease. Cervical cancer rates have steadily decreased in developed nations largely due to regular gynaecological screening and public human papillomavirus vaccination programs; however, the disease accounts for up to 12% of all female cancer diagnoses in developing nations, and poses a disproportionate burden on aboriginal women across Canada. Much work needs to be done to address disparities in care and treatment for cervical cancer, both in Canada and worldwide.

FIGO stage IA - IB1 is considered localized disease and treated primarily with surgery. In contrast to early stage disease, tumours that extend greater than 4 cm and beyond the cervix are considered locally advanced. The standard of care for locally advanced cervical cancer defined as FIGO stages IB2 - IVA is external beam radiation therapy with concurrent chemotherapy followed by brachytherapy.

Brachytherapy is a crucial component of therapeutic management that has been shown to be associated with improved local control. High dose rate brachytherapy involves the treatment of local bulky disease using a remotely loaded Iridium-192 source. Brachytherapy delivery exploits rapid dose fall off, allowing for the central pelvis to receive a very high dose while sparing the bladder, rectum, sigmoid and small bowel. This dose escalation is beyond what is conventionally achievable using external radiation therapy methods. More specifically, image guided adaptive brachytherapy employing intracavitary applicators allows for dose optimization and improves target dose coverage for limited size tumours.

Intracavitary applicators have been shown to be adequate from covering symmetric small tumours less than 30 cc. However, for large or complex asymmetric tumours with/without vaginal involvement they are not sufficient to cover the target while respecting normal tissue tolerances. To compensate for these limitations, improvements in local control have been achieved using a combined interstitial and intracavitary technique for larger tumours. Combined intracavitary - interstitial applicators have been designed to target tumours that are not adequately covered by intracavitary applicators alone. The addition of the interstitial technique involves the insertion of catheters into the tumour enabling higher dose conformity and normal tissue sparing. This combined technique has been shown in large tumours with extensive parametrial involvement as well as in cases with unfavourable topography to be effective. Employing this combined technique, perineal-based interstitial image guided adaptive brachytherapy makes it possible to deliver higher doses to the high risk clinical target volume without increasing dose to the bladder, rectum or sigmoid.

The combined interstitial and intracavitary brachytherapy workflow for locally advanced cervical cancer at the Odette Cancer Centre typically consists of four treatment fractions. The workflow begins with a pre-brachytherapy assessment MRI that is taken before brachytherapy treatment to assist in preplanning of catheter depth and location. At the time of this MRI the patient will have a vaginal cylinder in place. 1-2 weeks after the MRI, the implant and treatment is performed. Prior to the implantation procedure, the patient is given light sedation and a spinal anesthetic, subsequently a vaginal cylinder (Best Medical Systems, Inc, Springfield VA) is inserted into the patient. A perineal template that contains a central opening is fit on the vaginal cylinder. The template is then advanced until it is appositional on the perineum of the patient. Plastic catheters (6F 24 cm) containing metal stylets are inserted through the template and along the grooves of the vaginal cylinder thereby penetrating the perineum and the vagina, respectively. The number, position and depth of the catheters that are used are based on the pre-brachytherapy assessment MRI. After the implantation procedure the template is sutured to the patient and the patient is transferred to an MRI suite where an image of her anatomy is acquired with the catheters and applicators in place. The patient is then sent for a CT scan that is to be used for treatment planning.