Dosimetric comparison of two different applicators and rectal retraction methods used in inverse optimization-based intracavitary brachytherapy for cervical cancer

Abstract

Purpose: The purpose of this study was to evaluate the dosimetric differences between two different applicators and rectal-retraction methods used in image-guided brachytherapy (IGBT) for locally advanced cervical cancer (LACC). Material and methods: Ten patients with LACC treated with definitive chemoradiotherapy and inverse optimization-based IGBT were included in this study. In each patient, at least one fraction of IGBT was performed using tandem-ovoids (TO) with vaginal gauze packing (VGP) or tandem-ring (TR) with rectal-retractor (RR). High-risk clinical target volume (CTV HR) and intermediate-risk CTV (CTV IR) were defined as CTVs, and bladder, rectum, sigmoid, small bowel, urethra, and vaginal mucosa were defined as organs at risk (OARs). All patients received 50.4 Gy external beam radiotherapy (EBRT) in 28 fractions. After EBRT, 28 Gy high-dose-rate (HDR) IGBT in 4 fractions was delivered to central disease. A plan comparison was performed using dose-volume histogram (DVH) and treatment planning parameters for CTVs and OARs. Results: There were no significant differences in D 90 values of CTV HR. In terms of rectum dose, TR with RR was found to be significantly better than TO with VGP (p < 0.0001 for D 2cm3 and p < 0.013 for V 5Gy). Although, there were no statistically significant differences in D 2cm3 value of bladder, sigmoid, small bowel, upper vaginal mucosa, and urethra, mean value of D 2cm3 for all defined OARs were found lower in TR than in TO. Bladder V 7Gy , upper vaginal mucosa V 7Gy , middle and lower vaginal mucosa D 2cm3 values were all found to be significantly lower for TR than for TO (p < 0.035). CTV HR and CTV IR volumes contoured in TR were approximately 11% and 9% smaller than TO, respectively. Conclusions: The results showed that there were no statistically differences in D 90 value of CTV HR and CTV IR. However, all DVH parameters for OARs in TR with RR were found to be better than in TO with VGP.

Dosimetric comparison of rectal dose-reductive techniques in intra-cavitary brachytherapy for cervical cancer: A retrospective analysis

“…Several previous studies have demonstrated a better rectal dose reduction effect of RR than VP [15][16][17]. The present study appears to contradict these previous studies' findings.…”

“…The dose to the sigmoid colon tended to be lower in the VP group than in RR group, but the difference was not significant. The superiority of VP or RR in reducing dose to the sigmoid colon is not clear in previous studies on TR [ 15 - 17 ]. A earlier study comparing VP and balloon packing showed no significant results in the dose to the sigmoid [ 31 ].…”

“…Of these, RR and VP were the most prevalent. Several studies have shown that RR combined with tandem and ring applicator (TR) achieves a lower rectal dose than VP alone [15][16][17]. However, few studies have compared RR and VP in terms of tandem and ovoid applicator (TO) only.…”

A comparison of dosimetric parameters in high-dose-rate intracavitary brachytherapy using tandem and ring applicators: is the combination of a rectal retractor and radio-opaque vaginal packing better than rectal retractor alone for rectum sparing in cervical cancer?

“…T&O applicators with VP and T&R applicators with RR are the two most commonly used applicators for ICB in cervical cancer [ 15 , 16 ]. T&R applicators have recently become popular in image-guided BT (IGBT) for cervical cancer due to their reproducible geometry and ease of application compared to T&O applicators [ 17 , 18 ]. Studies have shown that in dosimetric comparisons between the two applicators, T&O applicators treat larger volumes than T&R applicators [ 19 , 20 ].…”

“…Studies have shown that in dosimetric comparisons between the two applicators, T&O applicators treat larger volumes than T&R applicators [ 19 , 20 ]. In terms of rectal dose, T&R applicators with an RR achieve significantly better rectum sparing than T&O applicators with VP when the reference doses were prescribed as per the Groupe Européen de Curiethérapie-European Society for Radiotherapy & Oncology (GEC-ESTRO) guidelines [ 17 ]. In the EMBRACE (European study on MRI-guided brachytherapy in locally advanced cervical cancer) 1 study, patients treated with T&R applicators showed a more favourable therapeutic ratio in the evaluation of target, bladder and rectum doses and V 85Gy [ 21 ].…”