Tumor Bed Delineation Research Articles

Histological Assessment and Interobserver Agreement in Major Pathologic Response for Non-Small Cell Lung Cancer with Neoadjuvant Therapy.

Major pathologic response (MPR), defined as ≤10% of residual viable tumor (VT), is a prognostic factor in non-small cell lung cancer (NSCLC) after neoadjuvant therapy. This study evaluated interobserver reproducibility in assessing MPR, compared area-weighted and unweighted VT (%) calculation, and determined optimal VT (%) cutoffs across histologic subtypes for survival prediction. This retrospective study included 108 patients with NSCLC who underwent surgical resection after neoadjuvant chemotherapy or chemoradiation at Seoul National University Bundang Hospital between 2009-2018. Three observers with varying expertise independently assessed tumor bed and VT (%) based on digital whole-slide images. Reproducibility in tumor bed delineation was reduced in squamous cell carcinoma (SqCC) with smaller tumor bed, although overall concordance was high (Dice coefficient, 0.96; IoU score, 0.92). Excellent agreement was achieved for VT (%) (ICC=0.959) and MPR using 10% cutoff (Fleiss' kappa=0.911). Shifting between area-weighted and unweighted VT (%) showed only one case differing in MPR status out of 81 cases. The optimal cutoff was 10% for both adenocarcinoma (ADC) and SqCC. MPR+ was observed in 18 patients (17%), with SqCC showing higher MPR+ rates (p=0.044), lower VT (%) (p<0.001), and better event-free survival (p=0.015) than ADC. MPR+ significantly improved overall survival (p=0.023), event-free survival (p=0.001), and lung cancer-specific survival (p=0.012). While MPR assessment demonstrated robust reproducibility with minimal impact from the tumor bed, attention is warranted when evaluating smaller tumor beds in SqCC. A 10% cutoff reliably predicted survival across histologic subtypes with higher interobserver reproducibility.

Non-Animal Stabilized Hyaluronic Acid (NASHA) Gel Marker vs. Surgical Clips for Tumor Bed Delineation in Breast Cancer Using MR-Simulation

Consistent delineation of the tumor bed (TB) after breast conserving surgery (BCS) is critical and remains a challenge with increasing prevalence of oncoplastic surgeries. Clips are generally used to help TB identification on CT-simulation but they are not well identified on MR-simulation. The aim of this study is to assess whether the use of NASHA gel with MR-simulation yields similar interobserver variability (inter-OV) compared to clips with CT-simulation. This prospective single arm feasibility study included patients eligible for BCS. After lumpectomy, the surgeon placed both clips (>5) and NASHA gel drops as markers to define the TB. Patients underwent CT and MRI simulation scans. Five radiation oncologists and one radiologist delineated the TB aided by clips on CT, and gel on MRI. The observers also assessed the visibility and utility of the gel (scale from 1 to 10), as well as the cavity visualization score (CVS, scale from 1 to 5). The primary endpoint was the inter-OV of the delineated TB using the overlap difference of contours using clips and CT versus gel and MRI, with the conformity index measured according to the pair definition of the Dice Similarity Coefficient (DSC). Of the 35 patients recruited, 30 were eligible for inter-OV analysis of TB delineation and 5 patients required further breast surgery for positive margins. One third of the eligible patients underwent an oncoplastic procedure. There were no significant differences between inter-OV of delineated TB using clips and CT versus gel and T2-weighted MRI with the mean DSC (0.60 vs 0.62, p = 0.364). The observers reported higher usefulness of gel in patients with an oncoplastic procedure than not (median US 8.2 vs 6.6, p = 0.024), and higher visibility of gel in patients who had their scans within 6 weeks than beyond post-op (median VS 8.1 vs 6.1, p = 0.013). When the CVS was higher (3-5), the median US of gel was lower (5.9 vs 7.8, p = 0.004), and the conformity index of clip and CT delineated TB was higher (median DSC 0.72 vs 0.53, p <0.001). Interestingly, a higher CVS did not lead to significantly higher conformity index of gel and T2-weighted MR delineated TB (mean DSC 0.67 vs 0.58, p = 0.073). NASHA gel injection added a median of 3 minutes to the operating theatre (OT) time and was rated as 'easy' in 89% of cases by surgeons. There were no immediate adverse events (AE) in OT, while 2 of 35 patients later experienced a grade 3 AE - hematoma which required evacuation in OT day 1 post-BCS, and infected seroma which required drainage and washout in OT 2 months post-BCS and axillary dissection. These reflect common risks with standard BCS and are not clearly attributed to gel injection alone. Use of NASHA gel leads to similar inter-OV of BC TB delineation compared to >5 clips. NASHA gel is hence a reliable alternative to clips when MR-simulation is used.

Abstract PD3-06: Robotic Stereotactic APBI for Early-Stage Breast Cancer: 2-year Outcomes of a Prospective Multi-Institutional Trial

Abstract Purpose: Outcomes following adjuvant accelerated partial breast irradiation (APBI) in select women with early-stage breast cancer are comparable to whole breast irradiation. Robotic stereotactic accelerated partial breast irradiation (RSAPBI) with fiducial tracking is an attractive treatment option, but limited outcomes data are available for this approach. We report 2-year outcomes for a prospective multi-institutional trial treating select women with RSAPBI. Materials and Methods: Post-menopausal women with DCIS and Stage IA breast cancer were treated over a five-year period extending from November 2015 to November 2020 and were followed for a minimum of 18 months. Treatments were delivered with a robotic radiosurgery system. Four gold fiducials were implanted around the lumpectomy cavity prior to the start of treatment for tumor bed delineation and target tracking. The CTV was defined as the lumpectomy cavity with a uniform 5-15 mm expansion confined to the breast tissue and the PTV was defined as the CTV with a 0-5 mm uniform expansion. The PTV was prescribed 30 Gy in 5 fractions. Disease status assessments were completed at 4 weeks, 3 months, 6 months, 12 months, 18 months, 24 months and yearly intervals thereafter for five years. Results: Eighty-one patients (median age 68 years) with hormone receptor-positive tumors were treated over a median 9 days (range, 5-15). Sixty-eight women had invasive ductal carcinoma (84%) and thirteen had DCIS (16%). The median treated PTV was 108 cm3 (IQR 66-156) and the median prescription isodose line was 81% (IQR 79-83). The median CTV expansion was 10 mm (range 5-10) and the median PTV expansion was 3 mm (range 0-5). At a median follow up of 2 years there was one new ipsilateral breast tumor diagnosed. There were no local, regional, or distant treatment failures. Conclusions: Two-year results suggest that RSAPBI with fiducial tracking is an effective technique for the adjuvant treatment of post-menopausal women with hormone receptor-positive early-stage breast cancer. Additional follow-up is planned to confirm this preliminary finding. Citation Format: Jonathan M. Cantalino, David D’Ambrosio, Arica Hirsch, Brian Collins, Malika Danner, Dawn Matsanka, Sonali Rudra, Simeng Suy, Sean Collins, Monica Pernia Marin, Michael Good, Jing Feng, John Lamond, Deborah Markiewicz, Rachelle Lanciano, Olusola Obayomi-Davies. Robotic Stereotactic APBI for Early-Stage Breast Cancer: 2-year Outcomes of a Prospective Multi-Institutional Trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD3-06.

The application of multiple metrics in deformable image registration for target volume delineation of breast tumor bed.

For postoperative breast cancer patients, deformable image registration (DIR) is challenged due to the large deformations and non-correspondence caused by tumor resection and clip insertion. To deal with it, three metrics (fiducial-, region-, and intensity-based) were jointly used in DIR algorithm for improved accuracy. Three types of metrics were combined to form a single-objective function in DIR algorithm. Fiducial-based metric was used to minimize the distance between the corresponding point sets of two images. Region-based metric was used to improve the overlap between the corresponding areas of two images. Intensity-based metric was used to maximize the correlation between the corresponding voxel intensities of two images. The two CT images, one before surgery and the other after surgery, were acquired from the same patient in the same radiotherapy treatment position. Twenty patients who underwent breast-conserving surgery and postoperative radiotherapy were enrolled in this study. For target registration error, the difference between the proposed and the conventional registration methods was statistically significant for soft tissue (2.06 vs. 7.82, p=0.00024<0.05) and body boundary (3.70 vs. 6.93, p=0.021<0.05). For visual assessment, the proposed method achieved better matching result for soft tissue and body boundary. Comparing to the conventional method, the registration accuracy of the proposed method was significantly improved. This method provided a feasible way for target volume delineation of tumor bed in postoperative radiotherapy of breast cancer patients.

A Prospective Study of a Resorbable Intravesical Fiducial Marker for Bladder Cancer Radiation Therapy

PurposeWe conducted a prospective pilot study to evaluate safety and feasibility of TraceIT, a resorbable radiopaque hydrogel, to improve image guidance for bladder cancer radiation therapy (RT). Methods and MaterialsPatients with muscle invasive bladder cancer receiving definitive RT were eligible. TraceIT was injected intravesically around the tumor bed during maximal transurethral resection of bladder tumor. The primary endpoint was the difference between radiation treatment planning margin on daily cone beam computed tomography based on alignment to TraceIT versus standard-of-care pelvic bone anatomy. The Van Herk margin formula was used to determine the optimal planning target volume margin. TraceIT visibility, recurrence rates, and survival were estimated by Kaplan-Meier method. Toxicity was measured by Common Terminology Criteria for Adverse Events version 4.03. ResultsThe trial was fully accrued and 15 patients were analyzed. TraceIT was injected in 4 sites/patient (range, 4-6). Overall, 94% (95% confidence interval [CI], 90%-98%) of injection sites were radiographically visible at RT initiation versus 71% (95% CI, 62%-81%) at RT completion. The median duration of radiographic visibility for injection sites was 106 days (95% CI, 104-113). Most patients were treated with a standard split-course approach with initial pelvic radiation fields, then midcourse repeat transurethral resection of bladder tumor followed by bladder tumor bed boost fields, and 14/15 received concurrent chemotherapy. Alignment to fiducials could allow for reduced planning target volume margins (0.67 vs 1.56 cm) for the initial phase of RT, but not for the boost (1.01 vs 0.96 cm). This allowed for improved target coverage (D95% 80%-83% to 91%-94%) for 2 patients retrospectively planned with both volumetric-modulated arc therapy and 3-dimensional conformal RT. At median follow-up of 22 months, no acute or late complications attributable to TraceIT placement occurred. No patients required salvage cystectomy. ConclusionsTraceIT intravesical fiducial placement is safe and feasible and may facilitate tumor bed delineation and targeting in patients undergoing RT for localized muscle invasive bladder cancer. Improved image guided treatment may facilitate strategies to improve local control and minimize toxicity.

Comparison of Tumor Bed Delineation Using a Novel Radiopaque Filament Marker vs. Surgical Clips for Targeting Breast Cancer Radiotherapy

<h3>Purpose/Objective(s)</h3> The accuracy of tumor bed (TB) delineation is essential for targeting boost dose or partial breast irradiation. Surgical clip markers (CM) are standardly used. However, despite using CM, multiple studies have shown high interobserver variability in TB delineation. We hypothesize that a radiopaque filament marker (FM) woven along the TB at the time of lumpectomy will improve accuracy of TB delineation. <h3>Materials/Methods</h3> An FDA-approved radiopaque filament was intraoperatively used to outline the tumor bed of patients undergoing lumpectomy. Between January 2020 and September 2020, 10 consecutive patients with the FM and 10 consecutive patients with the standard CM were identified for comparison. Five "experts," defined as board-certified radiation oncologists specializing in breast cancer, independently contoured all 20 tumor beds. Dice coefficients were then calculated for each patient by comparing the intersection and aggregate of each expert's contours with that of the other experts individually. An intersection and aggregate of the contours of all 5 experts was also analyzed for each patient. Dice coefficient of 1 represents perfect contour agreement, and 0 represents no agreement. Two-tailed paired samples t-tests were performed to compare dice coefficients between FM and CM cohorts. Furthermore, the center of mass (COM) coordinates were calculated to analyze the distance of the COM of each expert's contour to that of the aggregate of the other experts' contours for each patient. Two-tailed unpaired samples t-tests were performed to compare COM distances between FM and CM cohorts. <h3>Results</h3> For FM, mean dice coefficient and standard deviation for each expert was: 0.61 ± 0.09, 0.60 ± 0.10, 0.60 ± 0.10, 0.60 ± 0.09, and 0.55 ± 0.11, respectively. By comparison, for CM, mean dice coefficient and standard deviation for each expert was: 0.48 ± 0.22, 0.42 ± 0.25, 0.47 ± 0.21, 0.47 ± 0.22, and 0.40 ± 0.22, respectively. Thus, TB delineation agreement was significantly improved with FM (<i>P</i> = 0.0013, <i>P</i> = 0.0001, <i>P</i> = 0.0013, <i>P</i> = 0.0006, and <i>P</i> = 0.0008, respectively). Furthermore, the COM distance of each expert's contour to that of the aggregate of all experts' contours was significantly reduced (<i>P</i> < 0.001) from a mean of 0.96 cm ± 0.89 cm for CM to 0.25 cm ± 0.19 cm for FM. <h3>Conclusion</h3> Radiopaque filament resulted in significantly improved interobserver variability in tumor bed delineation compared with standard surgical clips. This difference was clinically meaningful with a reduction in mean COM contour disagreement from almost 1cm to 2.5mm, and suggests marked superiority of the radiopaque filament in targeting boost dose and/or partial breast irradiation.

Quality assurance program and early toxicities in the phase III BONBIS randomized trial evaluating the role of a localized radiation boost in ductal carcinoma in situ

PurposeTo describe the quality assurance (QA) program and early toxicities in the phase III randomized trial BONBIS (NCT00907868) on the role of a localized radiation boost in ductal carcinoma in situ (DCIS). Materials and methodsFrom November 2008 to July 2014, 2004 patients were randomized in arm A (only whole breast radiotherapy, WBRT) and arm B (WBRT + boost). The QA program involved 44 participant centers that performed the dummy run (DR). Compliance and uniformity of clinical target volume (CTV) delineations, and dose prescription and delivery according to the BONBIS trial radiotherapy guidelines were analyzed. Acute toxicities (during and up to 3 months after radiotherapy completion, NCI-CTCAE v3.0 classification) were evaluated in 1929 patients. ResultsThe differences in whole breast CTV (CTV1) and planning target volume (PTV1) were ≤10%, and the differences in boost CTV (CTV2) and PTV (PTV2) were ≥20% compared with the reference DR values; 95% of the prescribed dose encompassed 98.7% and 100% of the median CTV1 and CTV2. Grade ≥2 breast erythema (38.3% vs. 22.4% of grade 2 and 5.4% vs. 2.1% of grade 3, p < 0.001), grade ≥2 dermatitis (2.8% vs. 0.7%, p < 0.001), and grade 2 hyperpigmentation (6.9% vs. 3.6%, p = 0.005) were more frequent in arm B than arm A. No acute lung or cardiac toxicity was observed. Smoking history, large breast size, and large breast CTV were strong predictive factors of grade ≥2 acute skin toxicities. ConclusionsThe QA program showed deviations in breast and tumor bed delineation. The boost significantly increased acute skin toxicities.

Inter-observer variations of the tumor bed delineation for patients after breast conserving surgery in preoperative magnetic resonance and computed tomography scan fusion

PurposeTumor bed (TB) delineation based on preoperative magnetic resonance imaging (pre-MRI) fused with postoperative computed tomography (post-CT) were compared to post-CT only to define pre-MRI may aid in improving the accuracy of delineation.Methods and materialsThe pre-MRI imaging of 10 patients underwent radiotherapy (RT) after breast conserving surgery (BCS) were reviewed. Post-CT scans were acquired in the same prone position as pre-MRI. Pre-MRI and post-CT automatically match and then manual alignment was given to enhance fusion consistency. Three radiation oncologists and 2 radiologists delineated the clinical target volume (CTV) for CT-based. The gross target volume (GTV) of pre-MRI-based was determined by the volume of tumor acquired with 6 sequences: T1, T2, T2W-SPAIR, DWI, dyn-eTHRIVE and sdyn-eTHRIVE, expended 10 mm to form the CTV-pre-MRI. Planning target volume (PTV) for each sequence was determined by CTV extended 15 mm, trimmed to 3 mm from skin and the breast-chest wall interface. The variability of the TB delineation were developed as follows: the mean volume, conformity index (CI) and dice coefficient (DC).ResultsThe mean volumes of CTV and PTV delineated with CT were all larger than those with pre-MRI. The lower inter-observer variability was observed from PTV, especially in sdyn-eTHRIVE in all sequences. For each sequence of pre-MRI, all DCs were larger than post-CT, and the largest DC was observed by sdyn-eTHRIVE sequence fusion to post-CT. The overlap for PTV was significantly improved in the pre-MRI-based compared with the CT-based.ConclusionsTB volumes based on pre-MRI were smaller than post-CT with CVS increased. Pre-MRI provided a more precise definition of the TB with observers performed a smaller inter-observer variability than CT. Pre-MRI, especially in sdyn-eTHRIVE sequence, should help in reducing treatment volumes with the improved accuracy of TB delineation of adjuvant RT of breast cancer.

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

PurposeOur 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 MaterialsForty-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). ResultsThe 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). ConclusionsT1fs 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.

Partial Breast Irradiation and Surgical Clip Usage for Tumor Bed Delineation After Breast-Conserving Surgery in Canada: A Radiation Oncology Perspective

PurposeOur purpose was to evaluate the usage and perceived benefit of surgical clips for breast radiation therapy planning in Canada, focusing on partial breast irradiation (PBI) after breast-conserving surgery. Methods and MaterialsA retrospective institutional review identified patients eligible for PBI based on clinicopathologic criteria, and tumor bed visualization was determined from computed tomography-planning scans. An online survey was subsequently distributed to Canadian radiation oncologists addressing the usage and added value of surgical clips for breast radiation therapy planning purposes. The survey also evaluated PBI usage and regimens. Responses were collected over a 4-week period. PBI regimen usage at our institution was also reviewed from May 1 to December 18, 2020. ResultsBased on clinicopathologic criteria, 306 patients were identified between 2013 and 2018 who were eligible for PBI. However, only 24% (72/306) of cases were noted to have surgical clips, of which over 50% did not assist in tumor bed localization due to inconsistent clip positioning. Similarly, nearly two-thirds (28/43) of survey respondents indicated that surgical clips are placed in the tumor bed in less than 50% of cases. Almost all respondents (42/43) indicated that surgical clips facilitate breast radiation therapy planning and favor the development of guidelines to increase the consistent placement of surgical clips in the tumor bed after breast-conserving surgery. Approximately two-thirds of respondents (28/43) offer PBI to eligible patients as routine treatment, with moderate hypofractionated regimens most commonly recommended. However, the 1-week daily regimen of 26 Gy in 5 fractions is now offered to the majority (77%) of patients at our institution. ConclusionsThere was strong agreement among Canadian radiation oncologists that surgical clip placement facilitates breast radiation therapy planning, and most favor the development of surgical guidelines for the consistent placement of surgical clips in this setting. With the growing use of PBI, accurate localization of the tumor bed is extremely important.

Finding an Alternative for the Surgical Clips-based Delineation of Tumor Bed Boost Volume for Radiotherapy after Breast Conserving Surgery: A Prospective Comparative Study

Background: Radiotherapy after breast conserving surgery includes irradiation of whole breast and regional lymphatic areas which is followed by a boost to the tumor bed. Several different techniques have been proposed for delineation of tumor bed for boost. The purpose of the study was to identify the best method for localizing the tumor bed. Methods: 21 patients with histologically proven stage I and II infiltating ductal carcinoma of breast who underwent breast conserving surgery were included in the study. We delineated the boost volumes using five different techniques viz., patients’ self-localization, surgeon’s localization, pre-op CT based, scar-based and surgical clips based. The surgical clips-based volume is taken as a standard volume and the other volumes were compared with it. The outcome measures studied were the mean overlap volumes, the mean volume of surgical clips based volume missed by the other PTVs, the mean volumes of breast tissue outside the clips based PTV that could have been irradiated by the other PTVs. Results: None of the PTV volumes had good concordance with the surgical clips-based volume (PTV1). The best volume overlap was with patient’s self-localization (PTV3) albeit only being 34%. The scar-based localization volume had the least overlap with PTV1 (23%). The patients’ self-localization volume (PTV3) had the highest amount of breast tissue included outside PTV1 (64cc) and preop CT based volume (PTV4) included the least (42cc). Conclusion: Delineation of boost volume using surgical clips augmented by the simulation CT should be the standard technique for boost bed irradiation.

Can we rely on surgical clips placed during oncoplastic breast surgery to accurately delineate the tumor bedfor targeted breast radiotherapy?

Oncoplastic breast surgery (OBS) is gaining popularity among surgeons for breast-conserving surgery treatments. OBS relies on complex relocation and deformation of breast tissue involving the tumor bed (TB). In this study, we investigate the validity of using surgical clips with OBS for accurate TB delineation in adjuvant, targeted breastradiotherapy. Different OBS techniques were simulated on realistic breast phantoms. Surgical clips were used to demarcate the TB. Following tumor resection and closure, the true TB (TBTrue) was extracted. Each phantom was CT imaged at several phases of surgery in order to record pre- and post-OBS closure surgical clip displacements. Two senior radiation oncologists (ROs) were asked to delineate TBs on CTs by relying on surgical clips placedas per standard protocol, and by referring to operative notes. Their original contours, as well as those expanded using 5-15 mm margins, were compared with the accurate TBTrue using the dice similarity coefficient (DSC), Hausdorff Distance (HD), and over- and under-contoured volumes. Inter- and intra-RO contour agreements were also evaluated. Post-OBS surgical clips were significantly displaced outside the original breast quadrant. Inter- and Intra-RO TB contours were consistent, yet systematically differed from TBTrue (DSC values range = 0.38 to 0.69, and maximum HD range = 17.8 mm to 38.0mm). Using expansion margins did not improve contour congruence and caused significant over-contoured volumes. Following OBS, surgical clips alone are not reliable radiographic surrogates of TB locations and accurate TB delineation is challenging. For complex OBS cases, indication of any type of partial breast irradiation is very questionable.

The Location of Implantable Bioabsorable Tissue Marker in Relation to Preoperative Tumor Location and Postoperative Seroma: Implications for Target Delineation

In breast radiotherapy, delineation of tumor bed (TB) is critical for boost volumes and in partial breast irradiation (PBI). With growing use of 3-dimensional implantable bioabsorbable tissue markers (BZ), it is unclear how to incorporate BZ into delineation of TB. We sought to understand the location of BZ in relation to preoperative (preop) tumor location and postoperative seromas (SE), and what affects SE formation. Using retrospective chart review, we identified 35 women with breast cancer who had lumpectomy and BZ. Patients were stage Tis-T2, Nx-N1, M0. 14% had oncoplastic surgery. 23 patients (66%) were treated with whole breast radiation (65% with boost); 12 patients (34%) were treated with PBI (30Gy/5 fx, 24Gy/3 fx, and or 45Gy/30 fx bid). 31 patients were treated prone (89%). BZ and SE were contoured on CT-simulation (CT-sim) and the overlap between the structures measured. No overlap was defined as <5%, partial overlap 5-95%, and full overlap >95%. Distances between the center of BZ and SE and the minimum distance between non-overlapping areas were recorded. 16 patients had preop cross-sectional imaging (CI) (15 MRIs, 1 CT). The position (prone vs. supine) of the preop CI and the CT-sim was concordant in 81%. The breast was divided into tertiles in the medial/lateral (M/L) and the anterior/posterior (A/P) dimensions on preop CI and CT-sim. The tumor and TB were classified into tertiles on the CI and CT-sim respectively and concordance determined. For sensitivity analysis, this was repeated by dividing the breast into halves. Twenty-eight patients (80%) had SE on CT-sim. SE was not associated with diabetes, BMI, T-stage, infection, age, or menopausal status. SE was less likely in patients who had oncoplastic surgery (p=0.04). Among the patients with SE, overlap between SE and BZ was: 21% no overlap, 39% partial overlap, and 39% complete overlap, with center-to-center distances of 34±9.7 mm, 24±15.7 mm, and 19±8.3 mm, respectively. In cases of no overlap, the average distance between the structures was 8.9 mm. Of the 16 patients with preop CI, there was discordance between tumor location and BZ among 63% (A/P) and 38% (M/L) when using tertiles. With halves, the discordance was reduced to 37% A/P and 6% M/L. The BZ was posterior to the preop tumor whether dividing the breast into tertiles or halves. Of these, 40% were initially anteriorly located with tertiles. The majority of patients had SE which was inversely associated with oncoplastic surgery. There was a high discordance between BZ and preop tumor location, particularly in the anterior/posterior dimension with the BZ always located more posterior to the tumor in discordant cases. In cases where pre-operative CI imaging is not available, a more generous anterior margin on the BZ may be needed to account for pre-op tumor location, particularly in PBI.

Inter-Observer Variations of the Tumor Bed Delineation for Patients after Breast-Conserving Surgery in Preoperative Magnetic Resonance and Computed Tomography Scan Fusion

Inter-Observer Variations of the Tumor Bed Delineation for Patients after Breast-Conserving Surgery in Preoperative Magnetic Resonance and Computed Tomography Scan Fusion

How Does 0.35T Magnetic Resonance Imaging Compare with Computed Tomography for Post-Lumpectomy Tumor Bed Delineation in Breast Cancer?

How Does 0.35T Magnetic Resonance Imaging Compare with Computed Tomography for Post-Lumpectomy Tumor Bed Delineation in Breast Cancer?

Segmentation of MR Breast Cancer Images based on DWT and K-means algorithm

Breast-conserving surgery followed by radiotherapy to the whole breast and boost irradiation to the lumpectomy cavity (LC) is the standard strategy for the early stage breast cancer patients. Accurate segmentation of the target volume is a prerequisite for accurate radiotherapy, which directly affects the success or failure of tumor treatment. The current delineation of target is mainly done by manual drawing, which is time-consuming, laborious and easy to be affected by subjective factors. To solve this problem, we enhance the MR breast images using DWT (discrete wavelet transform) to get more detail of MR image feature firstly. Secondly, we use K-means algorithm to classify the feature vectors and establish the image segmentation model. Finally, compared with the traditional threshold segmentation method, the model is most suitable for automatic delineation of radiotherapy target area and the setting of optimal parameters are obtained. This method can realize the accurate automatic delineation of target area basically, and solve the problem of lack of accuracy and standardization in current tumor bed delineation.

External partial breast irradiation in prone position: how to improve accuracy?

Introduction: In view of the limited incremental benefit between whole breast irradiation (WBI), accelerated partial breast irradiation (APBI) and omission of radiotherapy in favorable early-stage breast cancer (ESBC), APBI can only be justified if it combines adequate target coverage with the lowest achievable toxicity. Interobserver exercises demonstrated the difficulty of precise target delineation, especially in prone position; information on accuracy is even scarcer. We tested the impact of inserting an additional indicator clip, marking the depth of the tumor in the breast, and the added value of a preoperative CT in treatment position on precision and accuracy.Material and methods: In 12 patients, tumor bed delineation was performed by four radiation oncologists, with CTVstandard (clinical target volume) based on standard delineation guidelines, CTVclip resulting from a 1–2-cm symmetrical expansion with the indicator clip as center and CTVclip_CT expanding from the midpoint between the indicator clip and preoperative gross tumor volume (GTV) as center. Precision was measured as the mean pairwise Jaccard index (JIpairs) between observers, accuracy as the mean overlap between GTV and respective CTVs.Results: JIpairs was 0.38 for CTVstandard, 0.75 for CTVclip and 0.59 for CTVclip_CT. Overlap rate of GTV with CTVs was respectively 0.48, 0.67 and improved further to 0.88 for CTVclip_CT. High-dose coverage of GTV (D95 and D90) improved with an indicator clip, but the most optimal result was reached when preoperative CT was added.Conclusions: If EB-APBI in prone position is aimed for, an indicator clip intended to mark the depth of the tumor increases the probability of accurate target coverage, but cannot entirely replace the added value of a preoperative CT in treatment position. Avoiding the cost and effort of such CT implies a risk of missing the target, especially when small volumes are aimed for. Increasing target volumes to reduces this risk, questions the concept of APBI.

EP-1169: Preoperative CT scan in tumor bed delineation after breast conserving surgery and oncoplasty

EP-1169: Preoperative CT scan in tumor bed delineation after breast conserving surgery and oncoplasty

A topology-based method to mitigate the dosimetric uncertainty caused by the positional variation of the boost volume in breast conservative radiotherapy

BackgroundTo improve local control rate in patients with breast cancer receiving adjuvant radiotherapy after breast conservative surgery, additional boost dose to the tumor bed could be delivered simultaneously via the simultaneous integrated boost (SIB) modulated technique. However, the position of tumor bed kept changing during the treatment course as the treatment position was aligned to bony anatomy. This study aimed to analyze the positional uncertainties between bony anatomy and tumor bed, and a topology-based approach was derived to stratify patients with high variation in tumor bed localization.MethodsSixty patients with early-stage breast cancer or ductal carcinoma in situ were enrolled. All received adjuvant whole breast radiotherapy with or without local boost via SIB technique. The delineation of tumor bed was defined by incorporating the anatomy of seroma, adjacent surgical clips, and any architectural distortion on computed tomography simulation. A total of 1740 on-board images were retrospectively analyzed. Positional uncertainty of tumor bed was assessed by four components: namely systematic error (SE), and random error (RE), through anterior-posterior (AP), cranial-caudal (CC), left-right (LR) directions and couch rotation (CR). Age, tumor location, and body-mass factors including volume of breast, volume of tumor bed, breast thickness, and body mass index (BMI) were analyzed for their predictive role. The appropriate margin to accommodate the positional uncertainty of the boost volume was assessed, and the new plans with this margin for the tumor bed was designed as the high risk planning target volume (PTV-H) were created retrospectively to evaluate the impact on organs at risk.ResultsIn univariate analysis, a larger breast thickness, larger breast volume, higher BMI, and different tumor locations correlated with a greater positional uncertainty of tumor bed. However, BMI was the only factor associated with displacements of surgical clips in the multivariate analysis and patients with higher BMI were stratified as high variation group. When image guidance was aligned to bony structures, the SE and RE of clip displacement were consistently larger in the high variation group. The corresponding PTV-H margins for the high- and low-variation groups were 7, 10, 10 mm and 4, 9, 6 mm in AP, CC, LR directions, respectively. The heart dose between the two plans was not significantly different, whereas the dosimetric parameters for the ipsilateral lung were generally higher in the new plans.ConclusionsIn patients with breast cancer receiving adjuvant radiotherapy, a higher BMI is associated with a greater positional uncertainty of the boost tumor volume. More generous margin should be considered and it can be safely applied through proper design of beam arrangement with advanced treatment techniques.

RESULTS OF EARLY-STAGE BREAST CANCER PATIENTS’ TREATMENT USING ACCELERATED PARTIAL BREAST IRRADIATION TECHNIQUE AFTER BREAST-CONSERVING SURGERY. EXPERIENCE OF N.N. BLOKHIN NATIONAL MEDICAL RESEARCH CENTER OF ONCOLOGY

Objective: to analyze the results of early-stage breast cancer patients’ treatment using accelerated partial breast irradiation technique after breast-conserving surgery. Materials and methods. The study enrolled 100 patients with histologically proven breast cancer pT1–2N0–micM0 who were treated in N.N. Blokhin National Medical Research Center of Oncology in 2008–2017. Median age – 65 years, median of follow-up – 36 months. All patients underwent breast-conserving surgical treatment (radical resection), radiation therapy and hormonal therapy if needed. Radiation therapy was performed in accelerated partial breast irradiation technique. All patients corresponded strict selection bias. For proper visualization and accurate delineation of tumor bed 94 % underwent clipping with radiopaque metal clips. All patients were treated with 3D-conformal radiation therapy in 2.5 Gy per fraction twice a day, overall dose 40 Gy (in 16 fractions). Results. Median follow-up was 36 months. No locoregional recurrences or distant metastases were observed. Excellent and good cosmetic results were observed in 96 % patients. Conclusions. Accelerated partial breast irradiation in very selected patients after breast-conserving surgery gives excellent clinical results, quite similar with those after whole breast irradiation.