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The Kelowna GYN template (Varian Medical Systems; Palo Alto, CA) is a perineal template for interstitial GYN brachytherapy designed for compatibility with a single channel vaginal cylinder as the vaginal obturator. We present the first reported series of patients treated with this system and an additional 3D printed modification for utilization of this template with an intrauterine tandem for treatment of locally advanced cervical cancer. Indications included bulky cervical tumor that responds poorly to external beam radiotherapy and/or vaginal involvement (tumor thickness greater than 0.5 cm), or for bladder invasion, and primary vaginal carcinomas and recurrent endometrial carcinomas with depth of invasion >0.5cm per GEC-ESTRO and ABS guidelines.

The Kelowna template allows placement of titanium or plastic interstitial needles with straight angled holes to provide coverage of the craniocaudal and lateral extension up to 3 cm from the vaginal cylinder. A modified applicator system using a custom 3D printed adaptor piece allows secure attachment of the tandem to the template for patients with an intact uterus (Figure 1d). Transabdominal ultrasound was utilized to guide needle placement. CT treatment planning with stepwise dwell weight adaptation and needle loading to achieve optimal dose coverage and sparing of organs at risk (OARs). Dose constraints were applied for dose-volume histogram parameters per ABS guidelines for HDR brachytherapy. Dosimetric data was evaluated including the D90 and D98 of high risk-clinical target volume (HR-CTV) with total EQD2 including whole pelvis radiotherapy (biologically equivalent to 2 Gy fractionation, alpha/beta = 10). D2cc (Dose to 2cc) of OARs were recorded.

Between October 2018 and June 2019, eleven patients with GYN malignancies were treated using the Kelowna template. Patients with cervical cancer had median HR-CTV volumes of 46 cm3. Mean number of needles utilized was 11 (range 5 to 17). Treatments consisted of 3 or 4 fractions on consecutive days (BID). Dosing was 21 Gy in 3 fractions (n=9), 24 Gy in 4 fx (n=1) and 28 Gy in 1 fx (n=1). For cervical tumors, the median D90 was 81.9 Gy (range 80.3 - 92.6). For vaginal and recurrent endometrial, the median D90 was 83.1Gy (range 75.8 - 91.1). Individual dosimetric data is displayed in Table 1. Interstitial needles allowed dose coverage of heterogenous asymmetric HR-CTV volumes as demonstrated in Figure 1. The median dose to OARs was within standard limits for intracavitary brachytherapy alone (EQD2cc for bladder of 72.3 Gy (IQR 67.2 - 77.5 Gy) and rectum of 61.6 Gy (IQR 58.7 - 62.7)). No patients needed adjustment in needle position between treatments. No patients had grade 3 acute toxicities. No patients had recurrence on follow-up.

The Kelowna template allows for customized safe, robust, and reproducible implants with combined interstitial-intracavitary applicator for selected cases of bulky, asymmetric cervical, vaginal, and recurrent endometrial cancer.