A comparison of tandem ring and tandem ovoid treatment as a curative brachytherapy component for cervical cancer

Fletcher suit or ring: A comparison of Fletcher suit and ring applicators for retroverted uteri

Purpose

Approximately 20% of women worldwide have a retroverted uterus. A retroverted uterus is closer to the rectum and may cause toxicity during brachytherapy. Upon manipulation, a small percentage turn anteverted. Conventional brachytherapy applicators are designed for an anteverted uterus and can pose issues during insertion. Modified Fletcher suit and ring applicators have major differences in their geometry to achieve similar target coverage, and were analyzed in this study with respect to immediate adverse events and dosimetry.

Material and methods

Three hundred seventy-four consecutive applications performed over a 20-month period were studied retrospectively to identify intra-cavitary applications (ICAs) in retroverted uteri. Cases were divided into 2 groups: modified Fletcher suit applicator with hemi-ovoids (group A) and ring applicator (group B). D2cc for bladder and rectum were noted, and acute adverse events were recorded.

Results

Seventy-five applications were identified, out of which 47 cases used Fletcher suit applicator, and 28 cases used ring applicator. The median bladder D2cc for group A and B were 5.98 Gy and 6.3 Gy, respectively, and the median rectum D2cc was 5.27 Gy and 3.68 Gy, respectively; the median dose prescribed to point A was 6 Gy (range, 5.5-9.0 Gy). All patients had a point A coverage between 97% and 102%. Eighteen cases in both groups complained of pain requiring analgesics. Twenty-five cases (53.2%) and 20 cases (71.4%) in group A and B, respectively, required dose optimization, which was statistically insignificant (p > 0.11). A significant difference was identified (p < 0.00001) in rectal doses. A higher reported pain was noted in ring applicator group (p < 0.03). No patient experienced a profuse bleeding.

Conclusions

In most parameters, the two applicators demonstrated comparable results. The control of rectal dosage is superior in the ring applicator at the cost of higher pain incidence. Patient's comfort and rectal dose in EBRT should be taken into consideration, with preference given to the ring applicator.

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

Purpose

Rectal complications in radiotherapy for cervical cancer can highly affect quality of life and correlate with rectal dose. Vaginal gauze packing (VP) and rectal retraction (RR) are widely used for rectal dose reduction in high-dose-rate brachytherapy. We aimed to perform a dosimetric comparison of these two methods for three-dimensional image-guided adaptive brachytherapy.

Material and methods

We retrospectively examined 50 patients with cervical cancer treated with definitive radiotherapy, including intra-cavitary brachytherapy, performed with VP and RR. We extracted two fractions for each patient: one fraction with VP and the next fraction with RR, and then compared dose-volume parameters. In total, 50 fractions each were analyzed in VP and RR groups. Dose to 90% (D90) of high-risk clinical target volume (HR-CTV), and minimum dose to most exposed 2.0 cm3 of other organs at risk (D2cm3) for the rectum and bladder were determined from planning computed tomography.

Results

There were no significant differences between VP and RR in D90 of HR-CTV (mean: 7.479 Gy and 7.652 Gy, respectively, p = 0.172). The D2cm3 values for the rectum (mean: 4.234 Gy vs. 4.627 Gy, p = 0.008) and bladder (mean: 5.959 Gy vs. 6.690 Gy, p < 0.001) were significantly lower with VP compared with RR.

Conclusions

VP reduced the dose to the rectum and bladder when compared with RR without impairing the dose to CTV.

Commissioning and Dosimetric Results of an Indigenously Developed Intra-Vaginal Template for Interstitial Plus Intracavitary High dose Rate Image-Guided Brachytherapy of Advanced Cervix Cancer

Aim

The goal of this study is to discuss the commissioning and dosimetric parameters achieved during the clinical implementation of an indigenously developed intracavitary (IC) plus interstitial (IS) template for high dose rate (HDR) image-guided brachytherapy (IGBT) in cancer (Ca) cervix. We want to discuss our achieved values of cumulative equi-effective doses (EQD2) for high-risk clinical target volume (HRCTV) and organ at risk (OAR) and compare it with available published results.

Materials and Methods

Medanta anterior oblique/lateral oblique template has a total of 19 needles including the central tandem. For commissioning the template with needles, the indigenously made acrylic phantom was used. Oblique and straight needles were placed inside the acrylic phantom and a computed tomography (CT) scan was performed. Sixteen patients were treated in HDR IGBT using this template after external-beam radiotherapy. The IGBT plans were evaluated based on EQD2 of target coverage i.e., dose received by 98% (D98%_HRCTV), 90% (D90%_HRCTV), and 50% (D50%_HRCTV) volume of HRCTV, and dose received by 2 cc (D2cc) and 0.1 cc (D0.1cc) of OAR using linear quadratic (LQ) radiobiological model.

Results

The autoradiographic in radiochromic film shows that the distance between the needle tip and the middle of the source position is 6 mm. The mean D98%_HRCTV and D90%_HRCTV was 76.8 Gy (range: 70-87.7 Gy, P < 0.01) and 84.49 Gy (range: 76.6-96.7 Gy, P < 0.01), respectively. Mean EQD2 of D2cc of the bladder, rectum, and sigmoid was 85.6 Gy (range: 77.5-99.6 Gy, P < 0.03), 74.3 Gy (range: 70.9-76.7 Gy, P < 0.05), and 58.3 Gy (range: 50.6-67.9 Gy, P = 0.01), respectively. The mean total reference air kerma at a 1 m distance is 0.489cGy (range: 0.391-0.681cGy).

Conclusions

The indigenously developed template could attain satisfactory standards in terms of set parameters for commissioning and acceptable dose volume relations in our clinical use for treating the advanced Ca cervix patients who need IC + IS type of HDR IGBT. The comparative analysis with contemporary applicators was acceptable.

Evaluation of dose differences between intracavitary applicators for cervical brachytherapy using knowledge-based models

PURPOSE

Currently, there is a lack of patient-specific tools to guide brachytherapy planning and applicator choice for cervical cancer. The purpose of this study is to evaluate the accuracy of organ-at-risk (OAR) dose predictions using knowledge-based intracavitary models, and the use of these models and clinical data to determine the dosimetric differences of tandem-and-ring (T&R) and tandem-and-ovoids (T&O) applicators.

MATERIALS AND METHODS

Knowledge-based models, which predict organ D_2cc, were trained on 77/75 cases and validated on 32/38 for T&R/T&O applicators. Model performance was quantified using ΔD_2cc=D_2cc,actual-D_{2cc,predicted}, with standard deviation (σ(ΔD_2cc)) representing precision. Model-predicted applicator dose differences were determined by applying T&O models to T&R cases, and vice versa, and compared to clinically-achieved D_2cc differences. Applicator differences were assessed using a Student's t-test (p < 0.05 significant).

RESULTS

Validation T&O/T&R model precision was 0.65/0.55 Gy, 0.55/0.38 Gy, and 0.43/0.60 Gy for bladder, rectum and sigmoid, respectively, and similar to training. When applying T&O/T&R models to T&R/T&O cases, bladder, rectum and sigmoid D_2cc values in EQD2 were on average 5.69/2.62 Gy, 7.31/6.15 Gy and 3.65/0.69 Gy lower for T&R, with similar HRCTV volume and coverage. Clinical data also showed lower T&R OAR doses, with mean EQD2 D_2cc deviations of 0.61 Gy, 7.96 Gy (p < 0.01) and 5.86 Gy (p < 0.01) for bladder, rectum and sigmoid.

CONCLUSIONS

Accurate knowledge-based dose prediction models were developed for two common intracavitary applicators. These models could be beneficial for standardizing and improving the quality of brachytherapy plans. Both models and clinical data suggest that significant OAR sparing can be achieved with T&R over T&O applicators, particularly for the rectum.

Reproducibility of vaginal immobilization balloons in situ overnight for cervical cancer brachytherapy

Purpose

The use of vaginal immobilization balloons placed into the vagina for immobilization of tandem and ovoid (T+O) applicator during high-dose-rate (HDR) brachytherapy delivery has been used at our institution, and seems to have improved our patient comfort, decreased procedure time, and minimized applicator misplacement. We aimed to show that these balloons, while originally marketed for single-day use, are safe and maintain applicator positioning/dosimetry when left in situ overnight for treatment delivery on sequential days.

Material and methods

Forty-two paired computed tomography (CT) scans from thirteen patients who underwent T+O HDR treatments on sequential days with vaginal immobilization balloons in situ overnight were retrospectively compared to calculate mean change of balloon volumes and balloon/T+O distance to bony landmarks. Dosimetric planning was retroactively performed on day 2 using CT scan of each pair, and the change in estimated radiation delivery to the bladder and rectum was compared.

Results

No statistically significant overnight changes were found in balloon volumes or anterior balloon positioning. The posterior balloon shifted -0.29 ±0.46 cm (p = 0.03) to the anterior public symphysis and 0.32 ±0.50 cm (p = 0.01) to the right femoral head. The tandem shifted 0.37 ±0.39 cm (p = 0.002) to the pubic symphysis. There was no significant difference found in radiation delivered to the bladder or rectum between the paired scans.

Conclusions

This study showed minimal change in balloon volumes, balloons/T+O positioning, or in radiation dose to bladder and rectum when the applicator remained overnight. These findings support that inflatable vaginal immobilization balloons remaining in situ overnight for additional HDR T+O treatments on sequential days, is safe and provides stable dosimetry.