The significance of free-hand needles in cervical cancer brachytherapy

Modern applicators in cervical cancer brachytherapy (BT) have an integrated option for using interstitial needles. Even though this allows improved dose coverage in large tumors, there are cases where pre-positioned needle arrangements within applicator are not optimal. In such cases, free-hand needles (FHNs) can be inserted into tumor without using applicator's positions. However, this requires a skilled professional, because the depth of tissue must be estimated without any help of needle insertion tools, and the angle of needle is critical. Improved dose coverage of the tumor and the effect on critical organ doses are yet to be estimated, if they constitute the time used and possible additional complication risk using FHNs.

In this work, clinical brachytherapy treatment plans using FHNs were compared with hypothetical plans, in which the best possible effort was applied to produce acceptable treatment plans without FHNs. Twenty-four cervix cancer patients with FHNs were re-planned without FHNs. Biological total doses were calculated for target volumes (high-risk clinical target volume [HR-CTV], gross tumor volume [GTV], and intermediate-risk clinical target volume [IR-CTV]) and organs at risk. External beam radiation therapy (EBRT) dose distributions were summed to brachytherapy plans, and total doses were compared.

The statistically significant differences favoring FHNs usage were observed, with HR-CTV D₉₀ (p = 0.043), bladder (D_2cc) (p = 0.017), rectum (D_2cc) (p = 0.022), and sigmoid (D_2cc) (p = 0.065). The average 2 Gy equivalent total doses and p-values, without/with FHNs were respectively: HR-CTV D₉₀ = 88.8/91.5 (p = 0.043); bladder (D_2cc) = 87.5/86.2 (p = 0.017); rectum (D_2cc) = 70.2/69.2 (p = 0.022); sigmoid (D_2cc) = 70.1/69.3 (p = 0.065) (α/β = 10 Gy for targets and α/β = 3 Gy for OARs, respectively).

The utilization of FHNs resulted in higher dose coverage to HR-CTV, and lower doses to bladder and rectum. There was no difference in GTV, bowel, or vaginal point doses.