Abstract
P0306: Analysis of Treatment Planning Techniques in Commercially Available Interstitial Vaginal Template-Based Hybrid Applicator
Brachytherapy, v 24(4), pp S72-S72
Jul 2025
Abstract
Hybrid interstitial gynecological applicators have become more popular in patients with locally advanced cervical cancer due to ability to improve HR-CTV coverage and/or decrease dose to organs at risk (OAR). The Varian Aarhus hybrid interstitial vaginal template lacks a true ring channel, which presents knowledge gap about appropriate dwell position weighting within the ring. Our institution employs a standard loading technique (SLT) treating the ring-shaped template as a ring with dwell positions weighted at 60/30/10 for the tandem, ring, and needles, respectively as a starting point with subsequent manual optimization. An alternative planning approach, tandem and needle technique (TNT) is to optimize the weighting of the tandem and needles without adjusting needle dwell weights at ring irrespective of the ring. This study investigates the dosimetric differences between treatment plans using SLT planning versus TNT planning.
A total of 23 fractions using the Varian Aarhus hybrid interstitial applicator were initially planned by adapting the SLT as per institutional protocol to achieve HRCTV coverage and meet OAR constraints. These fractions were retrospectively replanned using Brachyvision 16.1 treatment planning system. Tandem weighting was locked to match the clinical plan, and the VEGO-TG43 Volume Optimizer was used to load the needles based on objectives created from the constraints on the HRCTV and OARs, irrespective of the ring placement. The coverage was given the maximum priority and set to D90%=clinical D90%. Fractions included a sample of tandem sizes from 3cm to 8cm, ring template diameters of 32mm and 36mm, and prescribed doses of 24-28Gy in 4 fractions. The number of needles used in the fractions ranged from 3 to 12, strategically placed based on estimated HRCTV volumes from a prior MRI.
On initial planning with SLT, the median dwell weighting inside the ring of the hybrid applicator was 23.75% (Interquartile Range [IQR], 21.49 - 32.93) of the total treatment time and the final treated SLT plan ring weighting decreased to a median of 10.4% (IQR, 7.2 - 16.27) after optimization of HRCTV coverage and OAR sparing. The TNT replans without considering the ring dwells within the template had a median ring weighting of 6.71% (IQR, 2.95 - 13.26). The treated SLT plans gave a median ICRU recto-vaginal point dose of 468.3cGy (IQR, 410.7 - 575.0), while the TNT plans gave a median of 460.4cGy (IQR, 371 - 555.2). Bladder point dose median for the SLT plans was 447.7cGy (IQR, 388.7 - 532.6) while the TNT plan median was 494.3cGy (IQR, 387.9 - 574.9) The D2cc for bladder and rectum, per fraction, increased by 10cGy and 27cGy on average, respectively for TNT plans. With TNT, the V150% and V200% of prescription dose increased on average 3.04% (p = 0.3931) and 4.6% (p = 0.106), respectively. Total reference air kerma (TRAK) between SLT and TNT plans did not differ. There is no statistically significant difference between doses to HRCTV, OARs and/or volume receiving V150/V200 when comparing SLT versus TNT treatment planning approaches.
The hybrid vaginal template interstitial applicator resembles a standard intercavitary design but incorporates needles advanced through a ring-like template directly into patient disease. This study demonstrates no difference in OAR sparing, V150% and V200% with similar HRCTV coverage and TRAK between planning methods. Treating these applicators as a tandem and needle template alone simplifies planning while preserving plan quality, target coverage and OAR sparing.
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Details
- Title
- P0306: Analysis of Treatment Planning Techniques in Commercially Available Interstitial Vaginal Template-Based Hybrid Applicator
- Creators
- April Shorthouse - West Virginia UniversityCody R. Kilar - West Virginia UniversityBrooke Maxwell - West Virginia UniversityJ. Christopher Knoth - West Virginia UniversityJoshua Hack - West Virginia UniversitySushil Beriwal - Allegheny Health NetworkPhillip M. Pifer - West Virginia University
- Publication Details
- Brachytherapy, v 24(4), pp S72-S72
- Publisher
- Elsevier Inc
- Resource Type
- Abstract
- Language
- English
- Academic Unit
- Radiation Oncology (and Nuclear Medicine)
- Other Identifier
- 991022084855904721