Image-guided cervix high-dose-rate brachytherapy treatment planning: Does custom computed tomography planning for each insertion provide better conformal avoidance of organs at risk?

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.

Reporting of Inter Fraction Dose Variations of Organs at Risk in Computed Tomography-Guided High Dose Rate Intracavitary Brachytherapy in Carcinoma Cervix

Assess the interfraction dose variations of the organs at risk (OARs) in carcinoma cervix high dose rate (HDR) computed tomography (CT)-guided intra cavitary brachytherapy (ICBT). 120 CT scans of 40 patients who had undergone three fractions of ICBT (7 Gy/fr) were analyzed. Dose to Point A and the minimum doses to the volumes of 2, 1, and 0.1cc of bladder, rectum and sigmoid colon were recorded. Revised plans were generated in 20 patients. Paired t-test was used to compare the difference in the means. Point "A" mean dose difference was statistically significant between the treated and revised plans. For bladder, the difference in means of dosage to all volumes, whilst for the rectum and sigmoid colon, the low volume dosage (0.1cc) was statistically significant. Absence of individualized planning would have resulted in underdosage of tumor and increased dosage of up to 30% to OARs. CT-guided ICBT should be implemented for each HDR fraction treatment.

Automatic tandem and ring reconstruction using MRI for cervical cancer brachytherapy

PURPOSE

The MRI-guided cervical cancer brachytherapy provides unparalleled soft-tissue contrast for target and normal tissue contouring, but eliminates the ability to use conventional metallic fiducials for radiation source path reconstruction as required for treatment planning. Instead, the source path is reconstructed by manually aligning a library model to the signal void produced by the applicator, which takes time intraoperatively and precludes fully automated treatment planning. The purpose of this study is to present and validate an algorithm to automatically reconstruct tandem and ring applicators using MRI for cervical cancer brachytherapy treatment planning.

METHODS

Applicators were reconstructed using T2-weighted MR images acquired at 1.5 T from 33 brachytherapy fractions including 10 patients using a model-to-image registration algorithm. The algorithm involves (a) image filtering and maximum intensity projection to highlight the applicator, (b) ring center identification using the circular Hough transform, and (c) three-dimensional surface model registration, optimized by maximizing the image intensity gradient normal to the model surface. Two independent observers manually reconstructed all applicators, enabling the calculation of interobserver variability and establishing a ground truth. Algorithm variability was calculated by comparing algorithm results to each individual observer, and algorithm accuracy was calculated by comparing algorithm results to the ground truth. The algorithm variability and accuracy were compared to the interobserver variability using paired t-tests.

RESULTS

Mean ± SD interobserver variability was 0.83 ± 0.31 mm and 0.78 ± 0.29 mm for the ring and tandem, respectively. The algorithm had mean ± SD variability and accuracy of 0.72 ± 0.32 mm (P = 0.02) and 0.60 ± 0.24 mm (P = 0.0005) for the ring, and 0.70 ± 0.29 mm (P = 0.11) and 0.58 ± 0.24 mm (P = 0.004) for the tandem, respectively.

CONCLUSIONS

The algorithm variability and accuracy were within the interobserver variability measured in this study. The algorithm accuracy and mean execution time of 10.0 s are sufficient for clinical tandem and ring reconstruction, and are a step toward fully automated tandem and ring brachytherapy treatment planning.

Interfraction Variations in Organ Filling and Their Impact on Dosimetry in CT Image Based HDR Intracavitary Brachytherapy

Aim:

Since anatomical and geometric variations occur with every fraction, planning, and dose optimization is necessary for every fraction of high-dose rate intracavitary brachytherapy of carcinoma cervix. In this study, we have tried to quantify the differences in doses to organs at risk (OAR) for each fraction of brachytherapy.

Methods and Materials:

One hundred and seventy computed tomography datasets of cervical cancer patients receiving intracavitary brachytherapy at our institution between January and April 2015 were analyzed. The volumes of the high-risk clinical target volume and OAR contoured were recorded for every insertion. Dose-volume histograms were generated and D90 and D100CTV and D0.1, D1, and D2cc were recorded for bladder, rectum, and sigmoid for each insertion.

Results:

Sixty-one percent had a decrease in bladder volume in the second fraction, 35% had an increase in bladder volume and 4% had no change in bladder volume. There was a strong positive correlation between increase in volume and dose (D2cc), which was statistically significant, r_s = 0.441, P = 0.013. Nearly 49.4% of patients had an increase in rectal volume during the second fraction. 45.9% had decrease in rectal volume during the second fraction. There was a positive correlation between the increase in volume and dose (D2cc), which was statistically significant, r_s = 0.393, P = 0.010. About 63.5% of the patients had a decrease in sigmoid volume during the second fraction, whereas 30.6% had an increase in volume and 5.9% had no change in volume.

Conclusion:

First, this study emphasizes the importance of imaging and planning for every fraction of brachytherapy to quantify the exact doses to the target and OAR s. Second, it is important to follow a uniform bladder protocol for every fraction, and adequate bowel preparation is needed for every fraction to minimize the interfraction variations. Finally, it also opens the realm of an adaptive planning strategy in cervical cancers which are known for rapid tumor regression during radiotherapy.

Benefit of adaptive CT-based treatment planning in high-dose-rate endorectal brachytherapy for rectal cancer

PURPOSE

In this planning study, we investigated the dosimetric benefit of repeat CT-based treatment planning at each fraction vs. the use of a single CT-based treatment plan for all fractions for high-dose-rate endorectal brachytherapy (HDREBT) for rectal cancer.

METHODS AND MATERIALS

We included 11 patients that received a CT scan with applicator in situ for all three fractions. The treatment plan of the first fraction was projected on the repeat CT scans to simulate the use of a single treatment plan. In addition, replanning was performed on the repeat CT scans, and these were compared to the corresponding projected treatment plans.

RESULTS

Repeat CT-based treatment planning resulted on average in a 21% higher (p = 0.01) conformity index compared to single CT-based treatment planning. Projecting the initial treatment plan to the repeat CT scans of fraction two and three, 12/22 fractions reached a CTV D98 of 85% of the prescribed dose of 7 Gy, which increased to 14/22 using replanning. For the remaining fractions, median CTV D98 was 4.2 Gy, and an intervention would be necessary to correct applicator balloon setup or to remove remaining air and/or feces between the CTV and the applicator.

CONCLUSIONS

Using a single CT-based treatment plan for all fractions may result in a suboptimal treatment at later fractions. Therefore, repeat CT imaging should be the minimal standard practice in HDREBT for rectal cancer to determine whether an intervention would be necessary. Replanning based on repeat CT imaging resulted in more conformal treatment plans and is therefore recommended.

American Brachytherapy Task Group Report: A pooled analysis of clinical outcomes for high-dose-rate brachytherapy for cervical cancer

PURPOSE

Advanced imaging used in combination with brachytherapy (BT) has revolutionized the treatment of patients with cervical cancer. We present a comprehensive review of the literature for definitive radiation with high-dose-rate (HDR) BT. In addition, we investigate potential outcome improvement with image-based brachytherapy (IBBT) compared to studies using traditional Point A dosing. This review extensively investigates acute and late toxicities.

METHODS AND MATERIALS

This study reviews the literature from 2000 to 2015 with an emphasis on modern approaches including concurrent chemotherapy (chemoRT), radiation, and HDR BT and IBBT. Descriptive statistics and pelvic control (PC), disease-free survival (DFS), and overall survival (OS) outcomes were calculated using weighted means to report pooled analysis of outcomes.

RESULTS

Literature search yielded 16 prospective, 51 retrospective studies that reported survival outcomes, and 13 retrospective studies that focused on acute and late toxicity outcomes regardless of applicator type. There are 57 studies that report Point A dose specification with 33 having chemoRT, and 10 studies that use IBBT, 8 with chemoRT. Patients receiving radiation and chemoRT with HDR BT in the prospective studies, with >24 months followup, rates of PC were: for RT: 73%, SD: 11; CRT: 82%, SD: 8; DFS-RT: 55%, SD: 10; CRT: 65%, SD: 7; OS-RT: 66%, SD: 7; CRT: 70%, SD: 11. In the retrospective studies, the PC rates (weighted means) for the radiation and chemoradiation outcomes are 75% vs. 80%, and for DFS, the values were 55% vs. 63%, respectively. Comparing patients receiving chemoRT and IBBT to traditional Point A dose specification, there is a significant improvement in PC (p < 0.01) and DFS (p < 0.01) with IBBT. The range of genitourinary late toxicity reported for radiation was Grade 3: 1-6% and for chemoRT 2-20%. The range of late gastrointestinal toxicity for radiation was Grade 3: 4-11% and for chemoRT, 1-11%. For the late gynecologic toxicity, only 1 of the 16 prospective trials report a Grade 1-2 of 17% for radiation and 9% for chemoRT effects.

CONCLUSIONS

We present concise outcomes of PC, DFS, OS, and toxicity for cervical cancer patients treated with chemoradiation and HDR BT. Our data suggest an improvement in outcomes with the use of IBBT compared with traditional Point A dose prescriptions. In conclusion, HDR BT is a safe, effective modality when combined with IBBT.

Improving the efficiency of image guided brachytherapy in cervical cancer

Brachytherapy is an essential component of the treatment of locally advanced cervical cancers. It enables the dose to the tumor to be boosted whilst allowing relative sparing of the normal tissues. Traditionally, cervical brachytherapy was prescribed to point A but since the GEC-ESTRO guidelines were published in 2005, there has been a move towards prescribing the dose to a 3D volume. Image guided brachytherapy has been shown to reduce local recurrence, and improve survival and is optimally predicated on magnetic resonance imaging. Radiological studies, patient workflow, operative parameters, and intensive therapy planning can represent a challenge to clinical resources. This article explores the ways, in which 3D conformal brachytherapy can be implemented and draws findings from recent literature and a well-developed hospital practice in order to suggest ways to improve the efficiency and efficacy of a brachytherapy service. Finally, we discuss relatively underexploited translational research opportunities.

A comprehensive evaluation of adaptive daily planning for cervical cancer HDR brachytherapy

The purpose of this study was to evaluate adaptive daily planning for cervical cancer patients who underwent high‐dose‐rate intracavitary brachytherapy (HDR‐BT) using comprehensive interfractional organ motion measurements. This study included 22 cervical cancer patients who underwent 5 fractions of HDR‐BT. Regions of interest (ROIs) including high‐risk clinical tumor volume (HR‐CTV) and organs at risk (OARs) were manually contoured on daily CT images. All patients were clinically treated with adaptive daily plans (ADP), which involved ROI delineation and dose optimization at each treatment fraction. Single treatment plans (SP) were retrospectively generated by applying the first treatment fraction's dwell times adjusted for decay and dwell positions of the applicator to subsequent treatment fractions. Various existing similarity metrics were calculated for the ROIs to quantify interfractional organ variations. A novel similarity (JRARM) score was established, which combined both volumetric overlap metrics (DSC, JSC, and RVD) and distance metrics (ASD, MSD, and RMSD). Linear regression was performed to determine a relationship between interfractional organ variations of various similarity metrics and D2cc variations from both plans. Wilcoxon signed‐rank tests were used to assess ADP and SP by comparing EQD2D2cc(α/β=3) for OARs. For interfractional organ variations, the sigmoid demonstrated the greatest variations based on the JRARM, DSC, and RMSD metrics. Comparisons between paired ROIs showed differences in metrics at each treatment fraction. RVD, MSD, and RMSD were found to be significantly correlated to D2cc variations for bladder and sigmoid. The comparison between plans found ADP provided lower EQD2 D2cc of OARs than SP. Specifically, the sigmoid demonstrated statistically significant dose variations (p=0.015). Substantial interfractional organ motion occurs during HDR‐BT based on comprehensive measurements and may significantly affect D2cc of OARs. Adaptive daily planning provides improved dose sparing for OARs compared to single planning with the extent of sparing being different among OARs.

PACS number(s): 87.55.D, 87.55.de, 87.55.kh, 87.57.nj

Redesign of process map to increase efficiency: Reducing procedure time in cervical cancer brachytherapy

PURPOSE

To increase intraprocedural efficiency in the use of clinical resources and to decrease planning time for cervical cancer brachytherapy treatments through redesign of the procedure's process map.

METHODS AND MATERIALS

A multidisciplinary team identified all tasks and associated resources involved in cervical cancer brachytherapy in our institution and arranged them in a process map. A redesign of the treatment planning component of the process map was conducted with the goal of minimizing planning time. Planning time was measured on 20 consecutive insertions, of which 10 were performed with standard procedures and 10 with the redesigned process map, and results were compared. Statistical significance (p < 0.05) was measured with a two-tailed t test.

RESULTS

Twelve tasks involved in cervical cancer brachytherapy treatments were identified. The process map showed that in standard procedures, the treatment planning tasks were performed sequentially. The process map was redesigned to specify that contouring and some planning tasks are performed concomitantly. Some quality assurance tasks were reorganized to minimize adverse effects of a possible error on procedure time. Test dry runs followed by live implementation confirmed the applicability of the new process map to clinical conditions. A 29% reduction in planning time (p < 0.01) was observed with the introduction of the redesigned process map.

CONCLUSIONS

A process map for cervical cancer brachytherapy was generated. The treatment planning component of the process map was redesigned, resulting in a 29% decrease in planning time and a streamlining of the quality assurance process.

Magnitude and Implications of Interfraction Variations in Organ Doses during High Dose Rate Brachytherapy of Cervix Cancer: A CT Based Planning Study

Background. Quantifying the interfraction dose variations in the organs at risk (OAR) in HDR intracavitary brachytherapy (HDR ICBT). Methods. Rectum and bladder were contoured in 44 patients of cervical carcinoma on CT after each fraction of HDR ICBT (9 Gy/2 fractions). Interfraction dose variations (VAR_act) were calculated. Rigid image registration of consecutive fraction images allowed quantification of the hypothetical variation in dose (VAR_hypo) arising exclusively due to changes in applicator placement and geometry. VAR_hypo was regressed against the VAR_act to find out to what extent the applicator variation could explain the VAR_act in the OAR. The rest of the variation was assumed to be due to organ deformation. Results. The VAR_act in the dose to 2 cc of bladder and rectum were 1.46 and 1.16 Gy, respectively. Increased dose was seen in 16 and 23 patients in the subsequent fraction for bladder and rectum, respectively. Doses to OAR would have exceeded constraints in 16% patients if second fraction was not imaged. VAR_hypo explained 19% and 47% of the VAR_act observed for the bladder and rectum respectively. Conclusions. Significant interfraction variations in OAR doses can occur in HDR ICBT. Organ deformations are mostly responsible for this variation.

Better survival with three-dimensional conformal radiotherapy than with conventional radiotherapy for cervical cancer: a population-based study

Three-dimensional conformal radiation therapy (3DCRT) has emerged as a preferred treatment for gynecologic malignancies. Yet its superiority to conventional radiotherapy (2-dimensional radiotherapy (2DRT)) for gynecologic malignancies has not been well established. Data from the 2005 to 2010 National Health Insurance Research Database (NHIRD) provided by the National Research Institutes in Taiwan were analyzed to address this issue. Patients were initially diagnosed as having cervical cancer according to the International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM) code 180, and this clinical diagnosis was confirmed histopathologically or cytologically. Kaplan-Meier method and Cox proportional hazards regression were used to analyze the reported data. Between January 2005 and December 2010, there were 776 patients with newly diagnosed cervical cancer without metastasis, local recurrence, or surgical treatment before RT and 132 and 644 patients, respectively, who received 2DRT and 3DCRT. After adjustment for age, diabetes mellitus, hypertension, coronary heart disease, hyperlipidemia, side effects, urbanization level, geographic region, and enrollee category in the 5-year follow-up period, the HR was 1.82 (95% CI, 1.16–2.85, P = 0.009). The 5-year survival rate in the 2DRT and 3DCRT groups was 73.0% and 82.3%, P = 0.007, respectively. Cervical cancer patients treated with 3DCRT had better overall survival.

Three-dimensional image-based planning for cervix brachytherapy with bilateral hip prostheses: a solution using MVCT with helical tomotherapy

PURPOSE

We present a method of three-dimensional image-based planning for cervix high-dose-rate (HDR) brachytherapy for patients with bilateral metal hip prostheses using megavoltage computed tomography (MVCT) imaging.

METHODS AND MATERIALS

Two patients with bilateral metal hip prostheses were treated with our standard HDR brachytherapy fractionation and critical structure tolerance limits for cervical cancer. MVCT imaging was used for treatment planning because of artifacts present in kilovoltage computed tomography (kVCT), which did not allow visualization of the organs of interest.

RESULTS

The MVCT images provided adequate contrast to allow the contouring of organs at risk and the digitization of HDR applicators. HDR brachytherapy treatment planning was successfully accomplished based on MVCT images for 2 patients with bilateral metal hip prostheses.

CONCLUSIONS

Using MVCT imaging eliminated streak artifacts, which improved the image quality for treatment planning. MVCT offers an option for three-dimensional planning for cervix brachytherapy in patients with bilateral hip prostheses.

Factors for predicting rectal dose of high-dose-rate intracavitary brachytherapy after pelvic irradiation in patients with cervical cancer: a retrospective study with radiography-based dosimetry

PURPOSE

To evaluate the predictive factors for rectal dose of the first fraction of high-dose-rate intracavitary brachytherapy (HDR-ICBT) in patients with cervical cancer.

METHODS AND MATERIALS

From March 1993 through February 2008, 946 patients undergoing pelvic irradiation and HDR-ICBT were analyzed. Examination under anesthesia (EUA) at the first implantation of the applicator was usually performed in the early period. Rectal point was determined radiographically according to the 38th Report of the International Commission of Radiation Units and Measurements (ICRU). The ICRU rectal dose (PRD) as a percentage of point A dose was calculated; multiple linear regression models were used to predict PRD.

RESULTS

Factors influencing successful rectal dose calculation were EUA (p < 0.001) and absence of diabetes (p = 0.047). Age (p < 0.001), body weight (p = 0.002), diabetes (p = 0.020), and EUA (p < 0.001) were independent factors for the PRD. The predictive equation derived from the regression model was PRD (%) = 57.002 + 0.443 x age (years) - 0.257 x body weight (kg) + 6.028 x diabetes (no: 0; yes: 1) - 8.325 x EUA (no: 0; yes: 1)

CONCLUSION

Rectal dose at the first fraction of HDR-ICBT is positively influenced by age and diabetes, and negatively correlated with EUA and body weight. A small fraction size at point A may be considered in patients with a potentially high rectal dose to reduce the biologically effective dose if the ICRU rectal dose has not been immediately obtained in the first fraction of HDR-ICBT.

Present status and future of high-precision image guided adaptive brachytherapy for cervix carcinoma

INTRODUCTION

Image guided adaptive brachytherapy (IGABT) for cervical cancer, using mainly MRI, is an evolving method, increasingly replacing the 2D approach based on conventional radiography. During the complex 4D chain of this procedure image-assistance is provided for disease assessment, provisional treatment planning ("pre-planning"), applicator placement and reconstruction, as well as for contouring, definitive treatment planning and quality control of dose delivery. With IGABT changes of topography adjacent to the applicator, caused by tumour regression, oedema, organ changes and dilation are identified. Thus, the CTV for IGABT is primarily based on the tumour volume at the time of BT and takes into account both time and spatial domains. IGABT requires systematic concepts for target, OAR, biological modelling, DVH analysis, and dose-volume-adaptation.

METHODS AND RESULTS

This report focuses on the advantages and uncertainties, dose-effect relations and clinical results of the IGABT procedure addressing the current status and future perspectives. Uncertainties during the 4D chain of IGABT are mainly related to target contouring, applicator reconstruction, as well as to inter-fraction, intra-fraction and inter-application variability, as caused by tumour response and organ changes. Different from EBRT where set-up uncertainties are compensated by adding a margin to the CTV, no margins to the lateral and anterior-posterior directions can be used for IGABT.

DISCUSSION

By 3D treatment planning for IGABT significant improvement of the DVH parameters is achieved compared to 2D library plans. In small tumours the benefit is primarily obtained by a decrease of dose to nearby OAR while in large tumours the use of supplementary interstitial techniques and optimization may double the target volume that can be treated at a therapeutic dose level. The clinical impact of IGABT could recently be demonstrated by the establishment of some correlations between target- and organ-related DVH parameters versus disease control and side effects, which need further clarification. Overall, a very high local control rate can be achieved with minor treatment related morbidity. This favourable therapeutic ratio seems to be now reproducible under different conditions at various treatment centres. These results have to be validated within the upcoming multi-centre prospective IntErnational study on MRI-guided brachytherapy in locally advanced cervical cancer (EMBRACE).