Efficacy of medial needles in mitigating dose deficits from sub-optimally inserted tandems in cervical interstitial brachytherapy

Purpose:
In cervical interstitial brachytherapy, sub-optimal tandem insertion can lead to inadequate dose coverage of clinical target volume (CTV). This study aimed to evaluate the effectiveness of medial interstitial needles in optimizing dose to CTV, while minimizing toxicity to organs at risk (OARs), such as bladder, rectum, and sigmoid colon.

Material and methods:
The study included 25 brachytherapy plans in seven subjects with locally advanced cervical cancer, who had sub-optimal tandem insertions during cervical interstitial brachytherapy, for which 1 or more medial needle was inserted via Utrecht applicator. For each plan, a test plan was created after inactivating medial needles. Doses to 90% of high-risk (HR) CTV (D9₀) and OARs (D_2cc bladder, rectum, and sigmoid) were evaluated and compared using Wilcoxon signed rank test in SPSS v. 21.0.

Results:
Compared with plans without medial needles (x‾ = 5.22 ±1.60 Gy, median = 5.68 Gy), the plans with medial needles activated (x‾ = 6.59 ±1.55 Gy, median = 7.08 Gy) achieved 26.2% and 24.6% improvement (p = 0.001) in CTV D90 mean and median, respectively. The mean total dose per patient in the medial needle activated group (x‾ = 82.84 ±6.32 Gy) was significantly greater (p = 0.018), with a mean difference of 8.48 Gy from the medial needle inactivated group. No significant dose difference was observed across OARs. Fifty-two needles were inserted in total, out of which, 39 had more than 2 cm depth. Complete response was seen in all subjects.

Conclusions:
In patients with sub-optimal tandem insertion, the placement of medial needles can compensate dose deficit, while keeping OARs doses within acceptable constraints. Further studies among larger cohorts are warranted to optimize treatment protocol.