Preliminary results of modified interstitial MIAMI brachytherapy applicator for treatment of upper and apical vaginal tumors

Abstract

Purpose: Intracavitary vaginal brachytherapy (VBT) cylinders are limited in treating upper/apical vaginal disease due to the distance between the target and radiation source positions. Interstitial brachytherapy devices directly expose the vaginal mucosa to radiation sources, increasing morbidity. To target apical disease while limiting excessive treatment to the vaginal mucosa and organs at risk, we modified the commercially available multichannel MIAMI applicator, allowing the direct extension of needles into the apex with the protection of cylinder.

Material and methods: The device has one central plastic core with six peripheral channels. The modified device permits titanium needles to surpass the apical surface into vaginal tissue. A retrospective analysis on thirteen patients treated with this device was conducted. Patient demographics, gross tumor volume (GTV)/clinical target volume (CTV), initial diagnosis and management, toxicity data, and EQD₂ data for the bladder and rectum were obtained.

Results: There were ten patients with vaginal recurrences and three with primary vaginal/cervical cancers. Mean dosage of VBT treatment was 25.5 Gy in 3-5 fractions. Mean dosage of external beam radiation therapy (EBRT) treatment was 44 Gy. Common acute toxicities included diarrhea, fatigue, cystitis, and nausea. Common chronic toxicities were pelvic pain, vaginal stenosis, and skin telangiectasia. Mean EQD₂ dose for bladder and rectum were 72.3 Gy and 62.3 Gy, respectively. Ten patients had no evidence of relapse, two suffered from distant metastases, and one patient with stage IIIA cervical adenocarcinoma had loco-regional recurrence seventeen months after radiation treatment.

Conclusions: Our data suggests that the custom applicator is associated with robust dosimetric coverage, good loco-regional control, acceptable toxicity, and reduced tissue trauma. This device allows treatment of apically located vaginal tumors without significant damage to the vaginal vault and organs at risk. Additionally, it provides the flexibility to treat multiple patients with variable vaginal diameters and sizes/depths of apical tumors using a single device.

Keywords: apical tumor; endometrial cancer; multichannel; vaginal brachytherapy; vaginal cuff.

Fig. 1

Cross-sectional graphical representation of multi- channel applicator

Fig. 2

Interstitial MIAMI applicator set. A) The applicator set consists of an applicator core, cylinder sleeves (diameters of 3.0, 3.5, 4.0 cm) to accommodate a central tandem or needle, ring clamps, straight and 45-degree tandems, and 17 g needles. B) Top view of the applicator sleeves. Holes were drilled through the apex of the sleeves to allow for penetration of 17 g needles. C) A 17 g needle is shown exiting apically through the sleeves with a tandem (top image) and with a needle (bottom image)

Fig. 3

Measurement of high-risk clinical target volume (HR-CTV) tumor dimensions outlined in red. The sagittal view (A) showing measurement of maximum (1.73 cm) and minimum (0.58 cm) distance from the apex of cylinder to the HR-CTV, and the axial view (B) showing measurement of maximum (0.66 cm) and minimum (0.41 cm) distance laterally from the cylinder to the HR-CTV

Fig. 4

Sagittal (A), axial (B), and coronal (C) views of a brachytherapy plan using CT-based planning with the modified MIAMI interstitial applicator for apical recurrence of stage IB endometrial adenocarcinoma. Image shows controlled extension of peripheral needles through the channel into the apical tissue. The pink-shaded region represents the high-risk clinical target volume (HR-CTV). The 150% isodose line is in red, 100% in white, 90% in blue, 75% in green, and 50% in yellow

Fig. 5

Intact cervix example: visual representation of benefits of interstitial MIAMI applicator with axial and sagittal views. The pink outline is the high-risk clinical target volume, the yellow outline is the bladder, and the orange outline is the rectum. A) Axial 90% isodose showing an asymmetric dose distribution avoiding organs at risk. B) Axial 200% isodose showing interstitial needles (white arrows) contained within the multi-channel cylinder, minimizing high-dose to vaginal wall. C) Sagittal 90% isodose showing ability to treat the tumor in the cervix as well as the upper vagina, with > 90% of tumor receiving 90%+ of dose. D) Sagittal 200% isodose showing controlled placement of needles (white arrows) extending into apical tissue and 200% isodose away from the vaginal mucosa

Fig. 6

Apical disease example: visual representation of benefits of interstitial MIAMI applicator with axial and sagittal views. The pink outline is the high-risk clinical target volume, the yellow outline is the bladder, and the orange outline is the rectum. A) Axial 90% isodose showing asymmetric dose distribution avoiding organs-at-risk. B) Axial 200% isodose showing interstitial needles (white arrows) contained within the multi-channel cylinder, minimizing high-dose to vaginal wall. C) Sagittal 90% isodose showing ability to treat the tumor deep in the apex of vagina, with > 90% of tumor receiving 90%+ of dose. D) Sagittal 200% isodose showing controlled placement of needles (white arrows) extending into apical tissue and 200% isodose away from the vaginal mucosa