Therapeutic analysis of high-dose-rate (192)Ir vaginal cuff brachytherapy for endometrial cancer using a cylindrical target volume model and varied cancer cell distributions

A comparison between 2D and 3D planning of high-dose-rate vaginal cuff brachytherapy in patients with stage I-II endometrial cancer using cobalt-60

Purpose

Post-surgery radiation can reduce the risk of loco-regional relapse in high-intermediate-risk endometrial cancer. High-dose-rate vaginal cuff brachytherapy (HDR-BRT) is an acceptable method of radiation in majority of endometrial cancer cases. Although 2D planning is frequently used for treatment based on physical examination without any imaging, measurement of the dose received by organs-at-risk (OARs) is not possible. Therefore, the present study was the first to compare dose delivered to target and OARs in 2D vs. 3D planning in patients treated with cobalt-60 source.

Material and methods

In this study, organs including vagina wall, bladder, rectum, and sigmoid were contoured on computed tomography (CT) scan images of 37 endometrial cancer patients, and doses delivered to organs were recorded. Statistics, such as D₉₀, D₉₉, V₁₀₀, V₁₅₀, V₂₀₀, D_0.1cc, D_1cc, and D_2cc were determined.

Results

D₉₀ and D₉₉ were lower in 3D treatment planning in comparison with 2D. Although V₁₀₀ was more in 3D planning, V₁₅₀ and V₂₀₀ were less. Analyzing D_0.1cc, D_1cc, and D_2cc of OARs revealed that doses given to rectum, sigmoid, and bladder were less in 3D planning compared to 2D.

Conclusions

Comparison of 2D and 3D planning results showed that 3D planning could deliver an appropriate dose to the target while sparing more OARs.

3D printer-based novel intensity-modulated vaginal brachytherapy applicator: feasibility study

Purpose

To design a novel high-dose-rate intracavitary applicator which may lead to enhanced dose modulation in the brachytherapy of gynecological cancers.

Material and methods

A novel brachytherapy applicator, auxiliary equipment and quality control phantom were modeled in SketchUp Pro 2017 modeling software and printed out from a MakerBot Replicator Z18 three-dimensional printer. As a printing material polylactic acid (PLA) filament was used and compensator materials including aluminum, stainless-steel and Cerrobend alloy were selected according to their radiation attenuation properties. To evaluate the feasibility of the novel applicator, two sets of measurements were performed in a Varian GammaMed iX Plus high-dose rate iridium-192 (¹⁹²Ir) brachytherapy unit and all of the treatment plans were calculated in Varian BrachyVision treatment planning system v.8.9 with TG43-based formalism. In the first step, catheter and source-dwell positioning accuracy, reproducibility of catheter and source positions, linearity of relative dose with changing dwell times and compensator materials were tested to evaluate the mechanical stability of the designed applicator. In the second step, to validate the dosimetric accuracy of the novel applicator measured point dose and two-dimensional dose distributions in homogeneous medium were compared with calculated data in the treatment planning system using PTW VeriSoft v.5.1 software.

Results

In mechanical quality control tests source-dwell positioning accuracy and linearity of the designed applicator were measured as ≤ 0.5 mm and ≤ 1.5%, respectively. Reproducibility of the treatment planning was ≥ 97.7% for gamma evaluation criteria of 1 mm distance to agreement and 1% dose difference of local dose. In dosimetric quality control tests, maximum difference between measured and calculated point dose was found as 3.8% in homogeneous medium. In two-dimensional analysis, the number of passing points was greater than 90% for all measurements using gamma evaluation criteria of 3 mm distance to agreement and 3% dose difference of local dose.

Conclusions

The novel brachytherapy applicator met the necessary requirements in quality control tests.

Quality of life and oncological outcome in endometrial cancer patients after vaginal brachytherapy: comparison of two dosing schemes

PURPOSE

Vaginal brachytherapy reduces the risk of local recurrence and was shown to be equieffective in preventing vaginal vault recurrence, but less toxic compared to external-beam radiotherapy in a subset of high intermediate-risk endometrial cancer patients and is administered as single adjuvant treatment in those patients. Different radiotherapeutic approaches with various dosing schemes exist toward brachytherapy. The aim of this study was to compare the outcome and long-term quality of life after brachytherapy with two different high-dose-rate dosing schemes.

METHODS

Retrospective analysis was conducted of the recurrence and survival rates of 104 patients with endometrial cancer FIGO stage I-II that underwent adjuvant brachytherapy with three times 5 Gy or four times 5 Gy to the upper two-thirds of the vaginal vault in two different institutions between January 2010 and December 2013. Quality of life was assessed by EORTC QLQ-30 questionnaire and EN 24 module.

RESULTS

The vaginal vault recurrence rates were 4.9% and 5.0% for patients treated with 3 × 5 Gy and 4 × 5 Gy, respectively (p = 0.98). We did not observe a difference in pelvic recurrence (p = 0.96), overall survival (p = 0.33) or quality of life between the different radiotherapy regimens. Metastatic recurrence and the use of chemotherapy contribute to impairment on quality of life. Younger patients (< 70 years) reported worse emotional functioning (p = 0.02) and higher symptom scales of diarrhea (p = 0.01) and financial problems (p = 0.03). Sexual activity was lower in patients younger than 70 years (p = 0.05).

CONCLUSIONS

Further prospective studies are needed to evaluate the effect of dosing schemes on recurrence rates and quality of life. Younger patients (< 70 years) seem to experience greater reduction in quality of life due to endometrial cancer diagnosis.

Dosimetric impact of cylinder size in high-dose rate vaginal cuff brachytherapy (VCBT) for primary endometrial cancer

The purpose of this study was to evaluate the dosimetric impact of cylinder size in high‐dose‐rate (HDR) vaginal cuff brachytherapy (VCBT). Sample plans of HDR VCBT in a list of cylinders ranging from 2.5 to 4 cm in diameter at 0.5 cm increment were created and analyzed. The doses were prescribed either at the 0.5 cm depth with 5.5 Gy for 4 fractions or at the cylinder surface with 8.8 Gy for 4 fractions, in various treatment lengths. A 0.5 cm shell volume called PTV_Eval was contoured for each plan and served as the target volume for dosimetric evaluation. The cumulative and differential dose volume histograms (c‐DVH and d‐DVH), mean doses (D‐mean) and the doses covering 90% (D90), 10% (D10), and 5% (D5) of PTV_Eval were calculated. In the 0.5 cm depth regimen, the DVH curves were found to have shifted toward the lower dose zone when a larger cylinder was used, but in the surface regimen the DVH curves shifted toward the higher dose zone as the cylinder size increased. The D‐means of the both regimens were between 6.9 and 7.8 Gy and dependent on the cylinder size but independent of the treatment length. A 0.5 cm variation of diameter could result in a 4% change of D‐mean. Average D90s were 5.7 (ranging from 5.6 to 5.8 Gy) and 6.1 Gy (from 5.7 to 6.4 Gy), respectively, for the 0.5 cm and surface regimens. Average D10 and D5 were 9.2 and 11 Gy, respectively, for the 0.5 cm depth regimen, and 8.9 and 9.7 Gy, respectively, for the surface regimen. D‐mean, D90, D10, and D5 for other prescription doses could be calculated from the lookup tables of this study. Results indicated that the cylinder size has moderate dosimetric impact, and that both regimens are comparable in dosimetric quality.

PACS number(s): 87.61.‐c, 87.53.Jw, 87.19.xj