Computed tomography-based treatment planning for high-dose-rate brachytherapy using the tandem and ring applicator: influence of applicator choice on organ dose and inter-fraction adaptive planning

Method to assess the need for re-planning HDR brachytherapy tandem and ring treatments

High dose rate (HDR) brachytherapy procedures for cervical cancer require multiple applicator insertions for multiple (typically 5) fractions of a single plan, which carries a risk for variability in applicator position between fractions. Due to applicator displacement relative to patient anatomy, the dose to nearby organs-at-risk (OARs) may vary significantly from one fraction to the next. The purpose of this study was to evaluate the effect of changes in HDR tandem and ring (T&R) applicator position on doses to nearby OARs and to present a quick and simple method to estimate doses to OARs inter-fractionally without having to perform a re-plan. Ninety CT image sets for 20 patients, ages 44 to 86, undergoing T&R-based HDR for cervical cancer were used retrospectively for this study. Measures of applicator positional and angular changes relative to the bony anatomy were obtained using image fusion in MIM software, between the planning CT (plan CT) and the CT on the treatment day (CT-TX). Dosimetric data were determined, also using MIM software, using the original (first fraction) dose distribution applied to organs at risk (rectum and bladder), transferred via rigid registration from the plan CT to each CT-TX. Bladder and rectum contours were also transferred from each plan CT to each CT-TX and were tweaked manually to match anatomy on each CT-TX and examined visually for appropriateness. Differences in translation and rotation of the T&R applicator between the planning CT and subsequent individual fractions were recorded and plotted against dose differences between each fraction of treatment and the original (first) fraction. Absolute dose (D2cc) and volume (V50) differences vs positional shifts were calculated and plotted, and the Pearson Product-Moment correlation coefficient between dose parameters and measured positional shifts was determined. Average dosimetric differences between planned dose and subsequent fractional doses obtained through rigid registration were 1.48 ± 1.92 Gy, 14.91 ± 11.92 cm3, 0.56 ± 0.93 Gy, and 1.77 ± 2.18 cm3 for Bladder D2cc, Bladder V50, Rectum D2cc, and Rectum V50, respectively. Correlation between Bladder V50 and sagittal plane rotation gave an r2 of 0.4, showing the most correlation of all parameters studied. Bladder dose and volume increased by a maximum of about 2.7 Gy and 50 cm3 overall for Bladder D2cc and Bladder V50, respectively. Bladder V50 was most sensitive to T&R applicator displacements. We have quantified the effects of applicator positional changes on dose changes for the bladder and rectum. Even large changes in applicator position between fractions did not result in significant changes in dose to these normal tissues, indicating that adaptive re-planning is not necessary.

Single- versus Multi-computed Tomography Simulation for High-dose-rate Postoperative Gynecological Intracavitary Brachytherapy

Introduction

This study aimed to investigate whether there is a dosimetric difference of implementing single instead of multi-computed tomography (CT) simulation treatment planning for high-dose-rate postoperative gynecological intracavitary brachytherapy (BT).

Materials and Methods

Eighty patients were registered in the study. They received three BT fractions of 7 Gy/week (three CTs, three original plans). The organs at risk (OAR), the rectal wall, and the clinical target volume (CTV) were delineated. The delivered doses for the 2cc of OARs (D2cc), 1cc of rectal wall (D1cc), as well as for the 90% and 100% of CTV volume (DCTV90%, DCTV100%) were evaluated. To evaluate the values of the above parameters if the single-CT-simulation method has been chosen, the time of the first treatment plan was corrected for the decay and applied as the second and third CT, retrospectively, creating the next fractions (two revised plans).

Results

No statistically significant (P > 0.05) differences were found between the original and revised plans for the OARs and CTV. However, for the single-CT-simulation method, it was noted that the dose constraints for the total rectal dose were exceeded in some cases (36.3%).

Conclusion

The fact that rectal dose constraints were exceeded in 1/3 of patients with the single-CT-simulation method is dosimetrically significant.

The influence of the used applicators on organ and target doses for cervical cancer patients treated with HDR brachytherapy

Introduction: The aim of this work was to study the influence of the applicators used for cervical cancer patients treated with high dose-rate brachytherapy (HDR-BT) in the Maria Sklodowska-Curie National Research Institute of Oncology in Warsaw, Poland on doses in the tumour volumes and organs at risk.

Material and methods: The treatment was carried out using Iridium-192 in 4 fractions (7.5 Gy each) given in weekly intervals. Two types of applicators were used for comparison: fletcher and ring. The standard dose distribution parameters, read from the system Oncentra Brachy (version 4.5, Elekta), for bladder, rectum, and sigmoid (D2 cc) and tumour (HRCTV D100, D98, D90) were studied. Patients were divided into two groups (240 treatment plans) depending on the type of applicator used and into four groups according to the tumour volumes (HR-CTV < 25 cm3 or HR-CTV ≥ 25 cm3). The collected data were analysed using the PQStatSoftware (version 1.8.2).

Results: The treatment plans prepared with all types of applicators fulfil the dose distribution requirements, however, the dose delivered to the tumour using the ring applicator was found to be the highest. For the bladder and sigmoid the optimal dose distribution was obtained when using the fletcher applicator, while for the rectum the ring applicator gave the smallest dose value. The D2 cc parameter for sigmoid obtained for fletcher treatment has smaller values in the case of patients with small tumour volume and for this type of applicator was observed a statistically significant difference when compared with the ring.

Conclusions: The ring applicator gives the optimal parameters of the dose distribution independently on the tumour volume with respect to the fletcher applicator, which is however more often used in clinical practice.

Predictive value of Excel forms based on an automatic calculation of dose equivalent in 2 Gy per fraction in adaptive brachytherapy for cervical cancer

Purpose

External beam radiotherapy (EBRT) combined with brachytherapy (BT) is the standard mode of radical radiotherapy for locally advanced cervical cancer. The cumulative equivalent doses in 2 Gy per fraction (EQD₂) is an important basis for estimating the probability of local control of tumors and monitoring the occurrence of side effects in normal tissues. The purpose of this study was to explore the predictive value of Excel forms based on an automatic calculation in radical adaptive BT for cervical cancer.

Material and methods

A retrospective analysis of 119 patients suffering from cervical cancer, treated with radical radiotherapy. All patients were treated with EBRT and adaptive BT. EBRT prescribed dose was 42.0-50.4 Gy in 21-28 fractions. BT nominal prescribed dose was 28 Gy in 4 fractions, separated by one week. Total EQD₂ prediction at nth (n = 1-3) BT (TEPB_n) or actual cumulative EQD₂ (ACEQD₂) can be calculated automatically by inputting the physical dose based on an in-house designed application. The relationship between TEPB_n and ACEQD₂ was evaluated, and the predictive value of Excel forms based on the automatic calculation was analyzed.

Results

For the volume of high-risk clinical target, there was a significant decrease between BT1 and BT2. Similarly, for the volume of intermediate-risk clinical target, there was a significant decrease between BT2 and BT3. The sensitivity ranges of TEPB₁, TEPB₂, and TEPB₃ prediction were 74.5-91.3%, 83.7-95.7%, and 92.9-99.1%, respectively, and the specificity ranges were 46.7-80.0%, 53.3-90.5%, and 66.7-90.5%, respectively.

Conclusions

The in-house designed application has the function of quickly reading dose-volume histogram (DVH) parameters from the treatment planning system, which allows for balance between the total dose to target volumes and organs at risk (OARs). Excel forms based on EQD₂ automatic calculation presents high predictive accuracy.

Imaging-guided brachytherapy for locally advanced cervical cancer: the main process and common techniques

Brachytherapy (BT) delivers integrated boost doses to the central tumor while sparing the surrounding organs at risk (OARs) efficiently. It's a mandatory treatment component for locally advanced cervical cancer (LACC) because it results in excellent overall survival and local control compared with other dose boosting modalities. Currently, BT is undergoing a transition from 2-dimensional (2D) to 3-dimensional (3D) treatment planning. Imaging-guided BT (IGBT) employing computed tomography (CT) or magnetic resonance imaging (MRI) can provide exact individual delineation of target and OARs meanwhile prescribe the dose to the target volume instead of "point A" for X-ray-based BT. There are three main techniques for BT: intracavitary (IC), interstitial (IS), and intracavitary/interstitial (IC/IS) combination. The applicator choice depends on the specific tumor extension. The real-time transabdominal ultrasound (US)-guided applicator placement technique is strongly recommended to ensure ideal applicator positioning. MRI is the ideal standard imaging for BT owing to its superior soft tissue visualization than CT. However, CT-based BT is more often performed because of the availability. In developing countries, US-based BT can be adopted. For treatment planning, the applicator reconstruction is easier on CT than on MRI, because the applicator image is more clearly visible. Individual treatment planning should be performed for every single applicator insertion to ensure dose accuracy. In this review article, we explain the main clinical process and common techniques, including the applicator choice and placement, imaging techniques, target delineation, and treatment planning; asthose will help to improve the efficiency of 3D BT.

Multimaterial three-dimensional printing in brachytherapy: Prototyping teaching tools for interstitial and intracavitary procedures in cervical cancers

Purpose:

As the utilization of brachytherapy procedures continues to decline in clinics, a need for accessible training tools is required to help bridge the gap between resident comfort in brachytherapy training and clinical practice. To improve the quality of intracavitary and interstitial HDR brachytherapy education, a multi-material modular 3D printed pelvic phantom prototype simulating normal and cervix pathological conditions has been developed.

Methods and Materials:

Patient anatomy was derived from pelvic CT and MRI scans from 50 representative patients diagnosed with localized cervical cancer. Dimensions measured from patients’ uterine body and uterine canal sizes were used to construct a variety of uteri based off of the averages and standard deviations of the subjects in our study. Soft-tissue anatomy was 3D printed using Agilus blends (shore 30 and 70), and modular components in Vero (shore 85).

Results:

The kit consists of four uteri, a standard bladder, standard rectum, two embedded GTVs and four clip-on GTV attachments. The three anteverted uteri in the kit are based on the smallest, the average, and the largest dimensions from our patient set while the retroverted uterus assumes average dimensions.

Conclusions:

This educational HDR gynecological pelvic phantom is an accessible and cost-effective way to improve radiation oncology resident training in intracavitary/interstitial brachytherapy cases. Implementation of this phantom in resident education will allow for more thorough and comprehensive physician training through its ability to transform the patient scenario. It is expected that this tool will help improve confidence and efficiency when performing brachytherapy procedures in patients.

The impact of inter-fraction changes for perineal template-based interstitial gynecologic brachytherapy implants

Purpose

Perineal template-based interstitial gynecologic brachytherapy (ISBT) treatments are evaluated to determine whether adaptive inter-fraction re-planning is beneficial and necessary to meet the treatment aims of the American Brachytherapy Society (ABS) consensus guidelines for interstitial brachytherapy. Adherence to the EMBRACE II protocol is also assessed.

Material and methods

Ten patients receiving radical intent treatment for locally advanced or recurrent gynecologic malignancies underwent a three-fraction ISBT treatment with an ABS-recommended prescription regimen of 21 to 24 Gy. Clinical treatment plans were created according to a computed tomography (CT) acquired immediately post-implant. The first fraction was delivered on the same day as the implant (Day 1). The remaining two fractions were delivered on the next day (Day 2), at least six hours apart. Prior to treating on Day 2, a verification CT was acquired, permitting assessment of over-night changes. The Day 2 CT was used to evaluate deviations in 2-Gy-per-fraction equivalent dose (EQD₂) from the clinically intended dosimetry for clinical target volume (CTV), bladder, rectum, and sigmoid.

Results

For all patients, the median (range) difference between the intended and the delivered dosimetry for the CTV D90% was 1.4 Gy₁₀ (0.3-4.4 Gy₁₀). For all normal tissues, the median (range) difference from the intended normal tissue dose was 2.6 Gy₃ (0.1-15.5 Gy₃). In all cases, the deviation from clinically intended dosimetry did not lead to a violation of recommended normal tissue dose guidelines. For two of 10 patients with large normal tissue differences (> 10 Gy₃ from the intended dose), inter-fraction adaptive planning did improve the plan quality, but was not strictly required to meet the normal tissue dose planning aims.

Conclusions

The implementation of perineal template-based ISBT treatment without inter-fraction adaptive planning can be delivered to comply with the ABS normal tissue dose guidelines and EMBRACE II limits for prescribed dose.

Evaluation of offline adaptive planning techniques in image-guided brachytherapy of cervical cancer

Modern three‐dimensional image‐guided intracavitary high dose rate (HDR) brachytherapy is often used in combination with external beam radiotherapy (EBRT) to manage cervical cancer. Intrafraction motion of critical organs relative to the HDR applicator in the time between the planning CT and treatment delivery can cause marked deviations between the planned and delivered doses. This study examines offline adaptive planning techniques that may reduce intrafraction uncertainties by shortening the time between the planning CT and treatment delivery. Eight patients who received EBRT followed by HDR boosts were retrospectively reviewed. A CT scan was obtained for each insertion. Four strategies were simulated: (A) plans based on the current treatment day CT; (B) plans based on the first fraction CT; (C) plans based on the CT from the immediately preceding fraction; (D) plans based on the closest anatomically matched previous CT, using all prior plans as a library. Strategies B, C, and D allow plans to be created prior to the treatment day insertion, and then rapidly compared with the new CT. Equivalent doses in 2 Gy for combined EBRT and HDR were compared with online adaptive plans (strategy A) at D₉₀ and D₉₈ for the high‐risk CTV (HR‐CTV), and D_2 cc for the bladder, rectum, sigmoid, and bowel. Compared to strategy A, D₉₀ deviations for the HR‐CTV were −0.5 ± 2.8 Gy, −0.9 ± 1.0 Gy, and −0.7 ± 1.0 Gy for Strategies B, C, and D, respectively. D_2 cc changes for rectum were 2.7 ± 5.6 Gy, 0.6 ± 1.7 Gy, and 1.1 ± 2.4 Gy for Strategies B, C, and D. With the exception of one patient using strategy B, no notable variations for bladder, sigmoid, and bowel were found. Offline adaptive planning techniques can shorten time between CT and treatment delivery from hours to minutes, with minimal loss of dosimetric accuracy, greatly reducing the chance of intrafraction motion.

Dosimetric evaluation of Point A and volume-based high-dose-rate plans: a single institution study on adaptive brachytherapy planning for cervical cancer

Purpose

External beam radiation therapy (EBRT) and brachytherapy (BT) with concurrent cisplatin is the standard of care for locally advanced cervical cancer. The applicability of image-guided adaptive volume-based high-dose-rate (HDR) intracavitary brachytherapy planning is an active area of investigation. In this study, we examined whether volume-based HDR-BT (HDR_VOL) plans leads to more conformal plans compared to Point A (HDR_PointA)-based plans.

Material and methods

Two hundred and forty HDR_PointA plans from 48 cervical cancer patients treated with chemoradiotherapy were retrospectively collected. Point A plans were renormalized with respect to the high-risk clinical target volume (HR-CTV) for the HDR_VOL plans. The doses to organs at risk (OAR; rectum, sigmoid, and bladder), and HR-CTV and the conformal index were compared between HDR_PointA and HDR_VOL plans.

Results

HDR_VOL plans resulted in a 6-12% reduction in the total dose (EBRT + HDR-BT) to 0.1 cc, 1.0 cc, and 2.0 cc of the OAR as well as an 8-37% reduction in the dose to 2 cc of OAR per HDR-BT fraction compared to HDR_PointA plans. Differences in the conformal indexes between the two groups of plans showed an 18-31% relative increase per HDR-BT fraction for HDR_VOL plans. The D₉₀ of the HR-CTV was reduced by 11% by HDR_VOL planning and had a median dose of 86 Gy.

Conclusions

Our study reports the relative improvement in OAR doses per HDR-BT fraction by HDR_VOL planning compared to HDR_PointA planning and demonstrates the dosimetric advantages of volume-based HDR-BT planning in creating more conformal plans.

Reduction of applicator displacement in MR/CT-guided cervical cancer HDR brachytherapy by the use of patient hover transport system

Purpose

To quantify the reduction of relative displacement between the implanted intracavitary applicator and the patient bony anatomy, due to the use of a hover transport system during the patient transports between the imaging table and the treatment table.

Material and methods

The displacement of the applicator inside the patient was measured by comparing the distance between the tip of the tandem and the pubic bone on X-ray radiography images taken before and after moving a patient to magnetic resonance/computed tomography imaging. Displacements were evaluated for 27 fractions of treatment using hover transport and 185 fractions of treatment using manual transport.

Results

The use of hover transport system reduced the percentage of fractions with displacements greater than 5 mm from 22.7% to 7.4%. The reduction of applicator displacement using hover transport is statistically significant, compared to the manual transport method (p-value 0.0086; mean displacement 3.41 mm [95% CI: 2.96-3.97] for manual transport, and 2.27 mm [95% CI: 1.71-2.97] for hover transport fractions).

Conclusions

This study indicates that the hover transport system is effectively reducing displacement between tandem and patient bony anatomy during patient transports. The potential improvement in dosimetric accuracy due to this reduction warrants further study.

Locally advanced squamous cell cervical cancer in a patient with septate uterus

A 33-year-old premenopausal multiparous woman with the history of septate uterus was referred to the hospital with menorrhagia and inter-menstrual bleeding occurring for the last 6 months. Work-up revealed a stage IIB cervical cancer. The patient underwent curative chemo/radiotherapy. The patient’s septate uterus presented several difficulties during application. Brachytherapy was applied using standard computed tomography-compatible tandem and ovoids. The high-risk clinical target volume (HR-CTV), intermediate risk CTV, and organs at risk were contoured according to the Groupe Européen de Curiethérapie – European Society for Radiology and Oncology (GEC-ESTRO) guidelines. Treatment was performed via 3-dimensional high-dose-rate technique with ¹⁹²Ir, with brachytherapy dose of 28 Gy in 4 fractions/7 Gy each, prescribed to the HR-CTV. Treatment was well tolerated with manageable acute toxicities. To the best of our knowledge, the current case is the second case of septate uterus with locally advanced cervical carcinoma. Due to the lack of guidelines about brachytherapy applications in patients with uterine anomaly and owing to the anatomical anomaly, brachytherapy application is challenging in this patients population.