Evaluation of Dosimetric Consequences of Seroma Contour Variability in Accelerated Partial Breast Irradiation Using a Constructed Representative Seroma Contour

Feasibility study of adaptive radiotherapy with Ethos for breast cancer

Purpose

The aim of this study was to assess the feasibility of online adaptive radiotherapy with Ethos for breast cancer.

Materials and methods

This retrospective study included 20 breast cancer patients previously treated with TrueBeam. All had undergone breast surgery for different indications (right/left, lumpectomy/mastectomy) and were evenly divided between these four cases, with five extended cone beam computed tomography (CBCT) scans per patient. The dataset was used in an Ethos emulator to test the full adaptive workflow. The contours generated by artificial intelligence (AI) for the influencers (left and right breasts and lungs, heart) and elastic or rigid propagation for the target volumes (internal mammary chain (IMC) and clavicular lymph nodes (CLNs)) were compared to the initial contours delineated by the physician using two metrics: Dice similarity coefficient (DICE) and Hausdorff 95% distance (HD95). The repeatability of influencer generation was investigated. The times taken by the emulator to generate contours, optimize plans, and calculate doses were recorded. The quality of the scheduled and adapted plans generated by Ethos was assessed using planning target volume (PTV) coverage, homogeneity indices (HIs), and doses to organs at risk (OARs) via dose-volume histogram (DVH) metrics. Quality assurance (QA) of the treatment plans was performed using an independent portal dosimetry tool (EpiQA) and gamma index.

Results

On average, the DICE for the influencers was greater than 0.9. Contours resulting from rigid propagation had a higher DICE and a lower HD95 than those resulting from elastic deformation but remained below the values obtained for the influencers: DICE values were 0.79 ± 0.11 and 0.46 ± 0.17 for the CLN and IMC, respectively. Regarding the repeatability of the influencer segmentation, the DICE was close to 1, and the mean HD95 was strictly less than 0.15 mm. The mean time was 73 ± 4 s for contour generation per AI and 80 ± 9 s for propagations. The average time was 53 ± 3 s for dose calculation and 125 ± 9 s for plan optimization. A dosimetric comparison of scheduled and adapted plans showed a significant difference in PTV coverage: dose received by 95% of the volume (D95%) values were higher and closer to the prescribed doses for adapted plans. Doses to organs at risk were similar. The average gamma index for quality assurance of adapted plans was 99.93 ± 0.38 for a 3%/3mm criterion.

Conclusion

This study comprehensively evaluated the Ethos® adaptive workflow for breast cancer and its potential technical limitations. Although the results demonstrated the high accuracy of AI segmentation and the superiority of adapted plans in terms of target volume coverage, a medical assessment is still required.

Special issue. De-escalation of loco-regional treatment in breast cancer: Time to find the balance? Partial breast irradiation

Breast cancer is the most common cancer in women worldwide. Over the past few decades, remarkable progress has been made in understanding the biology and pathology of breast cancer. A personalized conservative approach has been currently adopted addressing the patient's individual risk of relapse. After postoperative whole breast irradiation for early-stage breast cancer, a rate of recurrences outside the initial tumour bed lower than 4% was observed. Thus, the highest benefits of breast irradiation seem to result from the dose delivered to the tissue neighbouring the tumour bed. Nonetheless, reducing treatment morbidity while maintaining radiation therapy's ability to decrease local recurrences is an important challenge in treating patients with radiation therapy. In this regard, strategies such as partial-breast irradiation have been developed to reduce toxicity without compromising oncologic outcomes. According to the national and international published guidelines, clinical oncologists can refer to specific dose/fractionation schedules and eligible criteria. However, there are still some areas of open questions. Breast cancer represents a multidisciplinary paradigm; it should be considered a heterogeneous disease where a "one-treatment-fits-all" approach cannot be considered an appropriate option. This is a wide overview on the main partial breast irradiation advantages, risks, timings, techniques, and available recommendations. We aim to provide practical findings to support clinical decision-making, exploring future perspectives, towards a balance for optimisation of breast cancer.

Automated Contouring and Planning in Radiation Therapy: What Is 'Clinically Acceptable'?

Developers and users of artificial-intelligence-based tools for automatic contouring and treatment planning in radiotherapy are expected to assess clinical acceptability of these tools. However, what is 'clinical acceptability'? Quantitative and qualitative approaches have been used to assess this ill-defined concept, all of which have advantages and disadvantages or limitations. The approach chosen may depend on the goal of the study as well as on available resources. In this paper, we discuss various aspects of 'clinical acceptability' and how they can move us toward a standard for defining clinical acceptability of new autocontouring and planning tools.

Magnetic Resonance Imaging for Breast Tumor Bed Delineation: Computed Tomography Comparison and Sequence Variation

Purpose

Our purpose was to investigate the interobserver variability in breast tumor bed delineation using magnetic resonance (MR) compared with computed tomography (CT) at baseline and to quantify the change in tumor bed volume between pretreatment and end-of-treatment MR for patients undergoing whole breast radiation therapy.

Methods and Materials

Forty-eight patients with breast cancer planned for whole breast radiation therapy underwent CT and MR (T1, T1 fat-suppression [T1fs], and T2) simulation in the supine treatment position before radiation therapy and MR (T1, T1fs, and T2) at the end of treatment in the same position. Two observers delineated 50 tumor beds on the CT and all MR sequences and assigned cavity visualization scores to the images. The primary endpoint was interobserver variability, measured using the conformity index (CI).

Results

The mean cavity visualization scores at baseline were 3.14 (CT), 3.26 (T1), 3.41 (T1fs), and 3.58 (T2). The mean CIs were 0.65, 0.65, 0.72, and 0.68, respectively. T1fs significantly improved interobserver variability compared with CT, T1, or T2 (P < .001, P < .001, and P = .011, respectively). The CI for T1fs was significantly higher than T1 and T2 at the end of treatment (mean 0.72, 0.64, and 0.66, respectively; P < .001). The mean tumor bed volume on the T1fs sequence decreased from 18 cm³ at baseline to 13 cm³ at the end of treatment (P < .01).

Conclusions

T1fs reduced interobserver variability on both pre- and end-of-treatment scans and measured a reduction in tumor bed volume during whole breast radiation therapy. This rapid sequence could be easily used for adaptive boost or partial breast irradiation, especially on MR linear accelerators.

A rapid review of influential factors and appraised solutions on organ delineation uncertainties reduction in radiotherapy

Background and purpose.Accurate volume delineation plays an essential role in radiotherapy. Contouring is a potential source of uncertainties in radiotherapy treatment planning that could affect treatment outcomes. Therefore, reducing the degree of contouring uncertainties is crucial. The role of utilized imaging modality in the organ delineation uncertainties has been investigated. This systematic review explores the influential factors on inter-and intra-observer uncertainties of target volume and organs at risk (OARs) delineation focusing on the used imaging modality for these uncertainties reduction and the reported subsequent histopathology and follow-up assessment.Methods and materials.An inclusive search strategy has been conducted to query the available online databases (Scopus, Google Scholar, PubMed, and Medline). 'Organ at risk', 'target', 'delineation', 'uncertainties', 'radiotherapy' and their relevant terms were utilized using every database searching syntax. Final article extraction was performed following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. Included studies were limited to the ones published in English between 1995 and 2020 and that just deal with computed tomography (CT) and magnetic resonance imaging (MRI) modalities.Results.A total of 923 studies were screened and 78 were included of which 31 related to the prostate 20 to the breast, 18 to the head and neck, and 9 to the brain tumor site. 98% of the extracted studies performed volumetric analysis. Only 24% of the publications reported the dose deviations resulted from variation in volume delineation Also, heterogeneity in studied populations and reported geometric and volumetric parameters were identified such that quantitative synthesis was not appropriate.Conclusion.This review highlightes the inter- and intra-observer variations that could lead to contouring uncertainties and impede tumor control in radiotherapy. For improving volume delineation and reducing inter-observer variability, the implementation of well structured training programs, homogeneity in following consensus and guidelines, reliable ground truth selection, and proper imaging modality utilization could be clinically beneficial.

Geometric contour variation in clinical target volume of axillary lymph nodes in breast cancer radiotherapy: an AIRO multi-institutional study

OBJECTIVES

To determine interobserver variability in axillary nodal contouring in breast cancer (BC) radiotherapy (RT) by comparing the clinical target volume of participating single centres (SC-CTV) with a gold-standard CTV (GS-CTV).

METHODS

The GS-CTV of three patients (P1, P2, P3) with increasing complexity was created in DICOM format from the median contour of axillary CTVs drawn by BC experts, validated using the simultaneous truth and performance-level estimation and peer-reviewed. GS-CTVs were compared with the correspondent SC-CTVs drawn by radiation oncologists, using validated metrics and a total score (TS) integrating all of them.

RESULTS

Eighteen RT centres participated in the study. Comparative analyses revealed that, on average, the SC-CTVs were smaller than GS-CTV for P1 and P2 (by -29.25% and -27.83%, respectively) and larger for P3 (by +12.53%). The mean Jaccard index was greater for P1 and P2 compared to P3, but the overlap extent value was around 0.50 or less. Regarding nodal levels, L4 showed the highest concordance with the GS. In the intra-patient comparison, L2 and L3 achieved lower TS than L4. Nodal levels showed discrepancy with GS, which was not statistically significant for P1, and negligible for P2, while P3 had the worst agreement. DICE similarity coefficient did not exceed the minimum threshold for agreement of 0.70 in all the measurements.

CONCLUSIONS

Substantial differences were observed between SC- and GS-CTV, especially for P3 with altered arm setup. L2 and L3 were the most critical levels. The study highlighted these key points to address.

ADVANCES IN KNOWLEDGE

The present study compares, by means of validated geometric indexes, manual segmentations of axillary lymph nodes in breast cancer from different observers and different institutions made on radiotherapy planning CT images. Assessing such variability is of paramount importance, as geometric uncertainties might lead to incorrect dosimetry and compromise oncological outcome.

Characterization and registration of 3D ultrasound for use in permanent breast seed implant brachytherapy treatment planning

PURPOSE

Permanent breast seed implant (PBSI) brachytherapy is a novel technique for early-stage breast cancer. Computed tomography (CT) images are used for treatment planning and freehand 2D ultrasound for implant guidance. The multimodality imaging approach leads to discrepancies in target identification. To address this, a prototype 3D ultrasound (3DUS) system was recently developed for PBSI. In this study, we characterize the 3DUS system performance, establish QA baselines, and develop and test a method to register 3DUS images to CT images for PBSI planning.

METHODS AND MATERIALS

3DUS system performance was characterized by testing distance and volume measurement accuracy, and needle template alignment accuracy. 3DUS-CT registration was achieved through point-based registration using a 3D-printed model designed and constructed to provide visible landmarks on both images and tested on an in-house made gel breast phantom.

RESULTS

The 3DUS system mean distance measurement accuracy was within 1% in axial, lateral, and elevational directions. A volumetric error of 3% was observed. The mean needle template alignment error was 1.0° ± 0.3 ° and 1.3 ± 0.5 mm. The mean 3DUS-CT registration error was within 3 mm when imaging at the breast centre or across all breast quadrants.

CONCLUSIONS

This study provided baseline data to characterize the performance of a prototype 3DUS system for PBSI planning and developed and tested a method to obtain accurate 3DUS-CT image registration for PBSI planning. Future work will focus on system validation and characterization in a clinical context as well as the assessment of impact on treatment plans.

The use of hyaluronic acid hydrogel as a tumour bed marker in breast-conserving therapy

PURPOSE

To evaluate usefulness of hyaluronic acid (HA) hydrogel as a tumour bed marker in breast conserving therapy (BCT). To analyze inter- (Inter-OV) and intraobserver (Intra-OV) variability of contouring boost target volume (CTV_boost) in external beam radiotherapy (EBRT).

MATERIALS AND METHODS

Thirty-two patients in the HA group and 30 patients in the control group with an early stage breast cancer were included in the study. During the surgery 1-3 ml of HA hydrogel was injected into breast to mark the tumour bed for every patient in the HA group. Moreover, surgical clips were placed underneath the lumpectomy cavity. Patients in the control group were marked only by metal markers. Three radiation oncologists delineated CTV_boost twice for every patient. Three parameters were calculated to quantify contouring variability: coefficient of variation for volumes (COV_V), center of mass displacement (CoMd) and conformity index (CI).

RESULTS

There were no significant differences between mean values of COV_V for HA and control group, neither for Intra-OV (0.14 vs 0.13) nor Inter-OV (0.19 vs 0.18) calculations. The mean CoMd were 6.1 mm and 9.1 mm for Inter-OV calculations and 3.9 mm and 6.4 mm for Intra-OV in the HA and the control group respectively. The mean CI for Intra-OV improved from 0.61 to 0.65 and from 0.47 to 0.56 for Inter-OV in the control and HA group respectively.

CONCLUSION

HA hydrogel used as a tumour bed marker improves tumour bed visibility and reduces inter- and intraobserver variability of EBRT boost target volume delineations.

Coverage with dosimetric concordance index (CDCI): a tool for evaluating dosimetric impact of inter-observer target variability in brachytherapy

Purpose

The aim of this study was to propose an index for evaluating dosimetric impact of inter-observer target delineation variability in brachytherapy.

Material and methods

The coverage with dosimetric concordance index (CDCI) is expressed as CDCI_common and CDCI_pair. The CDCI_common is the mean coverage of target volume with common volume irradiated by prescription dose among all observers and represents the condition of worst target coverage. CDCI_pair is the generalized form of CDCI, which is mean target coverage with common prescription volume obtained between all possible pairs of observers and represents more realistic coverage of target with dosimetric concordance. The index was used to evaluate the dosimetric impact of target delineation variability in optimized conformal plans on target volumes of five radiation oncologists for twenty patients of multi-catheter interstitial partial breast brachytherapy.

Results

The mean decline of 5.6 ±3.2% and 11.3 ±5.7% in CDCI_pair and CDCI_common, respectively, was observed comparing to coverage index (CI) of target volume in all patients due to inter-observer target variability. CDCI_common and CDCI_pair were found to have significant linear correlation (r = 0.964, p < 0.000). The difference between CDC and CI increased with the mean relative target volume among observers. Significant correlation (r = 0.962, p < 0.000) was also noted for the difference (Δ) in CDCI_common and CDCI_pair with CI of target volume.

Conclusions

The recommended indices and difference between the dosimetric coverage of target volume (CI) with CDCI (ΔCDCI) can be used for evaluating dosimetric impact of the inter-observer target delineation variability.

Bridging the Gap in Global Advanced Radiation Oncology Training: Impact of a Web-Based Open-Access Interactive Three-Dimensional Contouring Atlas on Radiation Oncologist Practice in Russia

Radiation oncologists in Russia face a number of unique professional difficulties including lack of standardized training and continuing medical education. To combat this, under the auspices of the Russian Society of Clinical Oncology (RUSSCO), our group has developed a series of ongoing in-person interactive contouring workshops that are held during the major Russian oncology conferences in Moscow, Russia. Since November 2016 during each workshop, we utilized a web-based open-access interactive three-dimensional contouring atlas as part of our didactics. We sought to determine the impact of this resource on radiation oncology practice in Russia. We distributed an IRB-approved web-based survey to 172 practicing radiation oncologists in Russia. We inquired about practice demographics, RUSSCO contouring workshop attendance, and the clinical use of open-access English language interactive contouring atlas (eContour). The survey remained open for 2 months until November 2017. Eighty radiation oncologists completed the survey with a 46.5% response rate. Mean number of years in practice was 13.7. Sixty respondents (75%) attended at least one RUSSCO contouring workshop. Of those who were aware of eContour, 76% were introduced during a RUSSCO contouring workshop, and 81% continue to use it in their daily practice. The greatest obstacles to using the program were language barrier (51%) and internet access (38%). Nearly 90% reported their contouring practices changed since they started using the program, particularly for delineation of clinical target volumes (57%) and/or organs at risk (46%). More than 97% found the clinical pearls/links to cooperative group protocols in the software helpful in their daily practice. The majority used the contouring program several times per month (43%) or several times per week (41%). Face-to-face contouring instruction in combination with open-access web-based interactive contouring resource had a meaningful impact on perceived quality of radiation oncology contours among Russian practitioners and has the potential to have applications worldwide.

Impact of inter-observer variations in target volume delineation on dose volume indices for accelerated partial breast irradiation with multi-catheter interstitial brachytherapy

PURPOSE

To investigate dosimetric impact of inter-observer variation in clinical target volume(CTV) delineation for patients undergoing interstitial partial breast brachytherapy.

METHODS

Five radiation oncologists delineated CTV in twenty patients who underwent multi-catheter partial breast brachytherapy. Five treatment plans for each patient were graphically optimized for CTV of all observers and evaluated using coverage index(CI), external volume index(EI), overdose volume index(OI) and conformal index(COIN). In addition, volume enclosed by prescription isodose(V₁₀₀), its spatial concordance(CI_common), mean coverage of all CTVs with common volume of prescription dose(V_{100_common}) and mean CTV coverage for all pairs of observer with common prescription volume of respective pairs(V_{100_pair}) were also computed.

RESULTS

The mean ± standard deviation(SD) of CI and COIN ranged from 0.756 ± 0.076 to 0.840 ± 0.070 and 0.591 ± 0.090 to 0.673 ± 0.06 respectively. When a plan made for CTV of individual observer was evaluated on CTV of all observers, the maximum variations(ρ < 0.05) in the mean CI,COIN,OI and EI were 10.6%,11.4%,10.6% and 72.7% respectively. The observed mean ± SD of V₁₀₀, CI_common of V₁₀₀, CTV coverage with V_{100_common} and V_{100_pair} was 160.7 ± 52.1, 0.70 ± 0.09, 73.1 ± 8.1% and 77.9 ± 7.3% respectively.

CONCLUSION

Inter-observer variation in delineation of CTV showed significant dosimetric impact with mean CTV coverage of 73.1% and 77.9% by common and paired prescription dose volume respectively among all observers.

Interobserver variations of target volume delineation and its impact on irradiated volume in accelerated partial breast irradiation with intraoperative interstitial breast implant

Purpose

To investigate the interobserver variations in delineation of lumpectomy cavity (LC) and clinical target volume (CTV), and its impact on irradiated volume in accelerated partial breast irradiation using intraoperative multicatheter brachytherapy.

Material and methods

Delineation of LC and CTV was done by five radiation oncologists on planning computed tomography (CT) scans of 20 patients with intraoperative interstitial breast implant. Cavity visualization index (CVI), four-point index ranging from (0 = poor) to (3 = excellent) was created and assigned by observers for each patient. In total, 200 contours for all observers and 100 treatment plans were evaluated. Spatial concordance (conformity index, CI_common, and CI_gen), average shift in the center of mass (COM), and ratio of maximum and minimum volumes (V_max/V_min) of LC and CTV were quantified among all observers and statistically analyzed. Variation in active dwell positions (0.5 cm step) for each catheter, total reference air kerma (TRAK), volume enclosed by prescription isodose (V_100%) among observers and its spatial concordance were analyzed.

Results

The mean ± SD CI_common of LC and CTV was 0.54 ± 0.09, and 0.58 ± 0.08, respectively. Conformity index tends to increase, shift in COM and V_max/V_min decrease significantly (p < 0.05), as CVI increased. Out of total 309 catheters, 29.8% catheters had no change, 29.8% and 17.5% catheters had variations of 1 and 2 dwell positions (0.5 cm and 1 cm), respectively. 9.3% catheters shown variations ≥ 10 dwell positions (5 cm). The mean ± SD CI_common of V_100% was 0.75 ± 0.11. The mean observed V_max/V_min of prescription isodose and TRAK was 1.18 (range, 1.03 to 1.56) and 1.11 (range, 1.03 to 1.35), respectively.

Conclusions

Interobserver variability in delineation of target volume was found to be significantly related to CVI. Smaller variability was observed with excellent visualization of LC. Interobserver variations showed dosimetric impact on irradiation of breast tissue volume with prescription dose.

Uncertainties in volume delineation in radiation oncology: A systematic review and recommendations for future studies

BACKGROUND AND PURPOSE

Volume delineation is a well-recognised potential source of error in radiotherapy. Whilst it is important to quantify the degree of interobserver variability (IOV) in volume delineation, the resulting impact on dosimetry and clinical outcomes is a more relevant endpoint. We performed a literature review of studies evaluating IOV in target volume and organ-at-risk (OAR) delineation in order to analyse these with respect to the metrics used, reporting of dosimetric consequences, and use of statistical tests.

METHODS AND MATERIALS

Medline and Pubmed databases were queried for relevant articles using keywords. We included studies published in English between 2000 and 2014 with more than two observers.

RESULTS

119 studies were identified covering all major tumour sites. CTV (n=47) and GTV (n=38) were most commonly contoured. Median number of participants and data sets were 7 (3-50) and 9 (1-132) respectively. There was considerable heterogeneity in the use of metrics and methods of analysis. Statistical analysis of results was reported in 68% (n=81) and dosimetric consequences in 21% (n=25) of studies.

CONCLUSION

There is a lack of consistency in conducting and reporting analyses from IOV studies. We suggest a framework to use for future studies evaluating IOV.

Comparison of Magnetic Resonance Imaging and Computed Tomography for Breast Target Volume Delineation in Prone and Supine Positions

PURPOSE

To determine whether T2-weighted MRI improves seroma cavity (SC) and whole breast (WB) interobserver conformity for radiation therapy purposes, compared with the gold standard of CT, both in the prone and supine positions.

METHODS AND MATERIALS

Eleven observers (2 radiologists and 9 radiation oncologists) delineated SC and WB clinical target volumes (CTVs) on T2-weighted MRI and CT supine and prone scans (4 scans per patient) for 33 patient datasets. Individual observer's volumes were compared using the Dice similarity coefficient, volume overlap index, center of mass shift, and Hausdorff distances. An average cavity visualization score was also determined.

RESULTS

Imaging modality did not affect interobserver variation for WB CTVs. Prone WB CTVs were larger in volume and more conformal than supine CTVs (on both MRI and CT). Seroma cavity volumes were larger on CT than on MRI. Seroma cavity volumes proved to be comparable in interobserver conformity in both modalities (volume overlap index of 0.57 (95% Confidence Interval (CI) 0.54-0.60) for CT supine and 0.52 (95% CI 0.48-0.56) for MRI supine, 0.56 (95% CI 0.53-0.59) for CT prone and 0.55 (95% CI 0.51-0.59) for MRI prone); however, after registering modalities together the intermodality variation (Dice similarity coefficient of 0.41 (95% CI 0.36-0.46) for supine and 0.38 (0.34-0.42) for prone) was larger than the interobserver variability for SC, despite the location typically remaining constant.

CONCLUSIONS

Magnetic resonance imaging interobserver variation was comparable to CT for the WB CTV and SC delineation, in both prone and supine positions. Although the cavity visualization score and interobserver concordance was not significantly higher for MRI than for CT, the SCs were smaller on MRI, potentially owing to clearer SC definition, especially on T2-weighted MR images.

Recommendations from GEC ESTRO Breast Cancer Working Group (II): Target definition and target delineation for accelerated or boost partial breast irradiation using multicatheter interstitial brachytherapy after breast conserving open cavity surgery

OBJECTIVE

To prepare guidelines for target definition and delineations after open cavity breast conserving surgery in accelerated partial breast irradiations or boost treatments using multicatheter interstitial brachytherapy based on the consensus of the Breast Working Group of GEC-ESTRO.

METHOD

Following a study on interobserver variations of target volume delineation in multicatheter breast brachytherapy after open cavity surgery and a number of discussions in consensus meetings these guidelines were worked out by experts on the field.

PROPOSED RECOMMENDATIONS

(1) Consistent windowing has to be used for proper cavity visualization. (2) The cavity visualization score has to be at least 3 in order to minimize the interobserver variations of target definition. (3) At delineation of surgical cavity only the homogeneous part of the postoperative seroma has to be included in the contours and protrusions or sharp irregularities have to be excluded. When surgical clips are present, they have to be surrounded by the contour with close contact. (4) CTV is created from the outlined surgical cavity with a nonisotropic geometrical extension. In each direction the safety margin is calculated by taking into account the size of the free resection margin. The total size of safety margin is always 20mm which is the sum of the surgical and added safety margins. CTV is limited to chest wall/pectoral muscles and 5mm below the skin surface.

CONCLUSION

Following these guidelines the target volume definition in breast brachytherapy after open cavity surgery is expected to be accomplished in more consistent way with low interobserver variations.