Partial Breast Irradiation Research Articles

Abstract PO5-22-04: Genomic analysis of local recurrences following risk adapted breast radiotherapy in the IMPORT trials defines 'true recurrences' and 'new primaries'

Abstract Background: Most ipsilateral breast tumor recurrences (IBTR) following breast conserving surgery occur near the tumor bed (Veronisi et al, Ann Oncol 2001) and are considered to represent ‘true recurrence’ (derived from residual malignant cells of the index cancer). A smaller number occur elsewhere in the breast and are thought to be ‘new primaries’ (independently occurring cancer). The IMPORT LOW (Coles et al, The Lancet 2017) and IMPORT HIGH (Coles et al, The Lancet 2023) trials investigated adaptation of radiotherapy dose-volume to this spatially varying risk, testing partial breast irradiation and simultaneous integrated boost in patients with tumors at low and high risk of IBTR respectively. We analysed genomic relationships between index cancers and recurrences in these trials, to ascertain the frequency of true recurrences and unrelated new primaries, and their spatial distribution. Methodology: FFPE blocks were obtained from 137 patients who developed subsequent ipsi- or contralateral breast cancer: 66 from IMPORT HIGH and 71 from IMPORT LOW (4 with bilateral second cancers). DNA extracted from index and subsequent cancers underwent shallow whole genome sequencing (sWGS) using the Illumina NovaSeq 6000 system. Copy number profiles were derived from sWGS data using the R package QDNAseq(Scheinin et al, Genome Res 2014); those that failed QC criteria were removed. Relatedness of tumor pairs was determined using the R package Breakclone (Lips et al, Nat Genet 2022). This approach uses individual copy number aberration breakpoint position rather than events at chromosomal arm level. The p value cutoff for relatedness was 0.01; values between 0.01 and 0.05 were considered ambiguous. Researchers were blinded to clinical information prior to results. Results: In 80/137 tumor pairs both copy number profiles met QC criteria and clonal relationship could be ascertained. In total 26/80 were considered related, 20/80 ambiguous and 34/40 non-related (Table 1). 16/26 ipsilateral subsequent cancers in IMPORT HIGH were clonally related to the primary tumor and could be considered true recurrences. In 5/26 it was impossible to accurately call clonality as pairs shared only common copy number changes such as 1q or 8q gain and 16q loss. 5/26 were considered new primaries. In the lower risk IMPORT LOW cohort, subsequent cancers appear to have similar chances of being related or independent. As expected, most contralateral tumors in IMPORT LOW showed no evidence of a clonal relationship to the index tumors. In both trials an ambiguous subgroup of pairs shared some common copy number changes suggesting similar phenotype.5/14 contralateral tumors in IMPORT HIGH, in which some women were also at high risk of systemic relapse, shared very similar copy number profiles to the index tumor and may be metastases rather than new primaries. Discussion: A considerable number of tumors classed as IBTR appear genomically unrelated to the index cancer particularly in low risk cancer; this biology is relevant to clinical management both initially and at ‘recurrence’. The finding that 5/14 contralateral cancers in the high risk group appear to be clonally related suggests that some may be metastases. Results are being confirmed by targeted sequencing and will be correlated with recorded spatial and clinicopathological data and patient outcome. Future work will analyse spatial relationships more precisely using deformable image registration. *From the 77 patients with baseline circulating tumor DNA samples, 2 patients were excluded because their samples failed during assay quality control. Table. PIK3CA and ESR1 alterations detected in circulating tumor DNA at baseline and post abemaciclib treatment Citation Format: Sara Lightowlers, Maria Roman-Escorza, Elena Provenzano, Judith Bliss, Jason Carroll, H Y Charlie Chan, Clare Griffin, Joanne Haviland, Monica Jefford, Anna Kirby, Navita Somaiah, Mark Sydenham, Jenny Titley, John Yarnold, Charlotte Coles, Elinor Sawyer. Genomic analysis of local recurrences following risk adapted breast radiotherapy in the IMPORT trials defines 'true recurrences' and 'new primaries' [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-22-04.

Abstract PO4-09-12: Academic-community partnership bridges disparities in African American patient representation in accelerated partial breast irradiation clinical trials

Abstract Purpose/Objectives: Clinical outcomes in African American (AA) patients diagnosed with breast cancer continue to lag behind other racial groups. Thus, AA women are 41% more likely to die from breast cancer than White women despite lower incidence of breast cancer in AA women. Some of these disparities are related to barriers in access to standard-of-care treatments such as radiation therapy (RT). The prolonged nature of radiation treatments confers disproportionate higher burden (due to lost wages, transportation costs etc.) on economically disadvantaged groups such as AA women. Accelerated partial breast irradiation (ABPI), which dramatically reduces treatment time in appropriately selected patients, has the potential to mitigate financial toxicity, and improve access and treatment compliance for AA. However, underrepresentation of AA patients in APBI trials may pose a barrier to wide adoption of APBI treatments in this patient population. At our institution, we have established a unique partnership between our University Hospital and a county hospital that serves as a safety-net hospital for many economically disadvantaged groups and treats a large proportion of AA patients. The goal of this study is to determine if our unique academic-community partnership improves disparities in representation of AA patients in APBI trials. Methods: We performed a PUBMED search to identify 197 clinical trials involving ABPI. After excluding international trials and multiple reports from the same trials, we identified 80 unique studies that were based in the United States. A total of 20 studies investigating APBI provided demographics data, comprising 1735 total patients. AA enrollment rate in these trials was compared to APBI trials completed at our institution in partnership with our county hospital partner. Results: Out of 1785 patients enrolled in APBI trials in the United States where demographic information was available, 1488 patients were White (85.7%), 124 were Black (7.1%), 67 were Hispanic (3.9%), and 46 were Asian (2.7%), and 10 patients were classified as multiple or unknown (0.6%). We compared these results to two APBI trials conducted at our institution investigating 5-fraction and single fraction APBI regimens. Out of a total of 104 patients treated, 17 patients (16.3%) were Black. This difference in proportion of AA patient enrollment between our institution (16.3%) versus those reported in APBI trials across the United States (7.1%) was statistically significant (p < 0.05). Conclusion: Reporting and representation of AA patients in APBI trials remains low, which may lead to lower adoption of APBI treatments in AA patients. This may lead to underutilization of APBI, a convenient treatment with lower financial toxicity, among AA patients. Our study shows that effective academic-community partnerships can bridge such disparities in AA patient representation in APBI trials. Expansion of such academic-community partnerships across the country may bridge systemic disparities in AA patient representation in oncology clinical trials. Future studies are needed to determine if improved access to novel and convenient treatments such APBI will bridge existing disparities in clinical outcomes in patients diagnosed with breast cancer. Citation Format: Ev Kakadiaris, Brian Lue, Young Suk Kwon, Prasanna Alluri, D Nathan Kim, Ann Sprangler, Mona Arbab, Robert Timmerman, Asal Rahimi. Academic-community partnership bridges disparities in African American patient representation in accelerated partial breast irradiation clinical trials [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-09-12.

Abstract PO4-07-01: Deep learning guided radiation therapy machine selection via a multi-headed dose prediction model

Abstract Background: Accelerated Partial Breast Irradiation (APBI) is gaining popularity for the treatment of appropriately selected breast cancer patients in lieu of whole breast irradiation regimens due to its comparable clinical outcomes and improved patient convenience and quality-of-life. Currently, several machines for delivery of APBI are available such as CyberKnife, Elekta Unity, Varian Ethos and Varian TrueBeam. Each treatment machine yields a unique distribution of radiation dose, so a given modality may afford particular advantages or liabilities based on a patient’s anatomy. Existing methods for identification of an ideal modality that best suits a patient’s unique anatomical features are generally lacking, manual, and resource intensive. To overcome this limitation and personalize modality selection, we propose a deep learning (DL) based multi-modality dose prediction model. The model takes a patient’s computed tomography (CT) scan, segmented planning target volumes (PTVs) and segmented organs at risk (OARs) as input, and outputs predicted dose distributions for all trained modalities. Differences may then be evaluated between each radiation treatment modality’s corresponding dose distribution and dose volumetric histograms (DVH) to select the optimal modality for each patient. Methods: Our dataset contains 16 partial breast patients, each with 4 unique treatment plans generated for 4 distinct modalities – CyberKnife, Elekta Unity, Varian Ethos and Varian Truebeam. 10, 2, and 4 patients were dedicated to the train, validation and test datasets respectively. Our model’s architecture is a U-net with a shared encoder and 4 independent dose decoders, in which each decoder predicts dose for one modality. Each training patient’s CT scan, PTVs, OARs, and a PTV distance map are input to the model during training, and the shared encoder shares the input data’s latent representations with each of the 4 decoders. The 4 distinct dose distributions from each training patient are used as labels for the 4 corresponding decoders to supervise model training. The mean squared error, mean squared log error, and DVH losses are minimized during model training. The model trained until validation loss converged. The 4 dose distributions were predicted in ~ 1 minute per test patient, yielding 16 dose distributions in the test dataset. Model performance across the test dataset was evaluated by calculation of the mean absolute percent error (MAPE) of dose differences within the patient’s body between the model’s predicted doses and label doses, relative to patient prescription dose. Results: The performance of the multi-modal dose prediction model was evaluated in terms of dose differences throughout each patient’s body across the 16 test dose distributions as compared to the actual planned doses. The average MAPE of the multi-modal dose predictions was 1.27 ± 0.38% of a patient’s prescription dose as compared to the actual planned dose across the test dataset. For a prescription dose of 3000 cGy, that corresponds to an average MAPE of 38.1 ± 11.4 cGy. Conclusion: Our multi-modality dose prediction model’s novelty lies in its rapid provision and comparison of accurate and detailed dosimetric data for each treatment modality. This model can empower treating radiation oncologists to make informed decisions in radiation therapy machine selection on a patient-by-patient basis, potentially optimizing radiation treatment plans by reduction of delivered dose to organs at risk. Table. Citation Format: Austen Maniscalco, Ezek Mathew, David Parsons, Asal Rahimi, Mona Arbab, Prasanna Alluri, Xingzhe Li, Mu-Han Lin, Steve Jiang, Dan Nguyen. Deep learning guided radiation therapy machine selection via a multi-headed dose prediction model [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-07-01.

Abstract PO2-22-04: Median Five-Year Follow-Up Results from the Multi-Institution Trial for the Treatment of Early-Stage Breast Cancer Using Intra-Operative Electronic Brachytherapy

Abstract Background: An IRB-approved single arm prospective multi-institution trial was designed to determine the efficacy and outcome of single fraction 20 Gy intra-operative radiation therapy (IORT) using disposable balloon electronic brachytherapy at the time of breast conserving surgery for early-stage breast cancer (women at least 40 years old, infiltrating ductal carcinoma [IDC] or ductal carcinoma in situ [DCIS], single lesion no larger than 3 cm, pN0). Ipsilateral breast tumor recurrences (IBTR) at median 5-year follow-up, the primary protocol endpoint of the trial, would be analyzed with outcomes compared to reported whole breast radiation therapy (WBRT) results. Methods: Between May 2012–July 2018,1199 enrolled breast cancer patients at twenty-six national and international institutions were successfully treated per protocol with lumpectomy plus single 20 Gy fraction IORT using disposable balloon electronic brachytherapy. Data collection and retrospective chart review included demographics, treatment, histopathology, toxicity, IBTR (defined as recurrence in the lumpectomy cavity/index quadrant), and survival. Results: All subjects were successfully treated with a single 20 Gy fraction of IORT. IORT cohort characteristics of the treated subjects are summarized in Table 1. Sixty-six (5.5%) patients received subsequent unplanned risk-adjusted WBRT. At median 5.0-year follow-up (range 0.5 – 9 years), there were 42 (3.50%) IBTR. The original mean tumor size of patients with IBTR was 13.6mm (range 0.03 - 30mm). The mean time to IBTR was 47.6 months (range 12 – 98 months). There were 30 IBTR in patients originally diagnosed with IDC, and 12 IBTR among patients originally diagnosed with DCIS. Three patients originally diagnosed with IDC recurred as DCIS, while 4 patients with DCIS recurred as IDC. The remainder recurred with the same pathology as their original diagnoses. Sorting by 2017 ASTRO accelerated partial breast irradiation (APBI) criteria, there were 25 IBTR in patients categorized immediately following lumpectomy plus IORT as Suitable, 12 IBTR among patients categorized immediately following lumpectomy plus IORT as Cautionary, and 5 IBTR in patients categorized immediately following lumpectomy plus IORT as Unsuitable. Nine (0.75%) patients experienced new ipsilateral primary breast cancers, with 8 classified as Suitable and one as Cautionary using post-lumpectomy plus IORT ASTRO APBI criteria. Seventeen (1.4%) patients experienced acute serious adverse events (SAEs). These included 5 wound infections, 4 hematomas, 2 skin ulcerations, 2 cellulitis, 2 seromas, 1 skin necrosis, and 1 wound dehiscence. All SAEs resolved within 6 months of IORT. One patient died of breast cancer metastases at 3-year follow-up. One patient who was diagnosed with IBTR at 3-year follow-up died 3 years later from dementia. There were 45 unrelated patient deaths. Conclusions: At median 5.0-year follow-up, the 1199 early-stage breast cancer patients successfully treated in this multi-institution trial with a single 20 Gy fraction of IORT to the lumpectomy cavity at the time of partial mastectomy experienced an IBTR of 3.50%. This recurrence rate is acceptable when compared to the 0.9% - 2.5% IBTR reported for WBRT, given the benefits of IORT (convenience, decreased exposure to XRT, better cosmetic outcome, patient preference). Table 1. IORT cohort characteristics Citation Format: Barbara Schwartzberg, AM Nisar Syed, Ajay Bhatnagar, Sophia Rahman, Veronica Jones, Albert Chang, Todd Cockerham, Virginia Osborn, Robert Cohen, Charles Hodge, Christina Lopez-Penalver, Bapsi Chakravarthy, William Dooley, Chika Madu, Atsuko Okabe, Maen Farha, Andrea Madrigrano, Christopher Morrison, Geoffrey Neuner, Craig Wengler, Steven David, Katayoon Toosie, Bryon Stephens. Median Five-Year Follow-Up Results from the Multi-Institution Trial for the Treatment of Early-Stage Breast Cancer Using Intra-Operative Electronic Brachytherapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-22-04.

Abstract PO1-22-02: Optimal intra-fraction PTV margins for patients receiving stereotactic partial breast radiation (SPBI) using cone beam adaptive radiation therapy

Abstract Objectives To quantify the intra-fraction tumor bed motion using image guidance and fiducial markers to determine optimal PTV margins in early-stage breast cancer patients receiving adaptive radiation therapy SPBI after partial mastectomy. Methods A retrospective cohort of five patients with pT1a-pT2N0, grade 1-2, ER+/PR+ early-stage invasive ductal carcinoma of either the right breast or left breast underwent partial mastectomy and adjuvant five-fraction SPBI using cone beam based online adaptation. A total of 62 CBCTs and 22 total fractions were analyzed after post-processing with an average time span of 39.1±8.9 minutes. Two methods were utilized to determine optimal CTV to PTV margins: one contouring-based and another fiducial-based. Our contouring-based method involved independently contouring on each fraction’s CBCTs including pre-treatment CBCT, intra-treatment CBCT, and post-treatment CBCT. After image registration with the original simulation CT image, these contours were propagated to and combined to create a new union CTV. Using the original CTV on the simulation CT, optimal PTV margin was determined to achieve 95% overlap of the union CTV created from fractionated CBCTs. In addition to the contouring-based method, our fiducial-based method utilized an in-house script to calculate the centroid of all fiducials per CBCT. The average and maximum anterior-posterior, medial-lateral, superior-inferior shifts of fiducials between intra-fraction CBCTs were recorded. Results Using our contouring-based method, we calculated and determined that a uniform 3.5 mm expansion around the original CT simulation CTV is needed to achieve 95% PTV overlap encompassing the pre-treatment, intra-treatment, and post-treatment union CTV. Furthermore, with our fiducial-based method, we calculated average centroid anterior-posterior, medial-lateral and superior-inferior shifts to be the following: 1.51±0.79mm, 1.04±0.55 mm, 1.78±0.94 mm respectively. Average maximum shifts were determined to be 2.13±1.18mm anterior-posterior, 1.45±0.76mm medial-lateral and 2.47±1.40mm superior-inferior shifts. Conclusion With our contouring-based analysis, this preliminarily study suggests CTV to PTV margin of 3.5mm is adequate. On the other hand, our fiducial-based method suggests decreased movement and smaller asymmetric margin. Further CBCT adaptation images will be analyzed. In conjunction with these two methods, we currently recommend utilizing a 3.5mm uniform margin for intrafraction motion and to assess adequate coverage with image guidance during daily adaptation for patients with early-stage breast cancer receiving SPBI. Citation Format: Meng-Lun Hsieh, Justin Visak, Sean Domal, Gabrielle Gard, Steven Montalvo, Liyuan Chen, Xinran Zhong, Zohaib Iqbal, Tingliang Zhuang, Bin Cai, Heejung Kim, Mona Arbab, Prasanna Alluri, Nathan Kim, Mu-Han Lin, David Parsons, Asal Rahimi. Optimal intra-fraction PTV margins for patients receiving stereotactic partial breast radiation (SPBI) using cone beam adaptive radiation therapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-22-02.

Abstract PO3-20-10: Case Series: Invasive Secretory Carcinoma

Abstract Secretory variant invasive ductal carcinoma is not well described in the literature but is defined by its unique histopathology. These tumors stain positive for S100 and are typically triple negative hormonal cancers with an overall good prognosis. There is speculation that secretory carcinoma in adults is more aggressive with a greater likelihood for tumor recurrence. We present two case studies of this rare histopathologic diagnosis. First, a 76-year-old female with a recurrent secretory variant, invasive ductal carcinoma of the left breast. Second, a 68-year-old male who presented with invasive and in situ secretory carcinoma. A thorough chart review of all available institutional and outside institution records was performed from initial diagnosis to current treatment. Background information and de-identified patient information was summarized for this case series. This is a 76-year-old female who presented to her physician in 2011 with a palpable left breast and axillary mass. Her workup demonstrated ER+/PR+/HER2- invasive ductal carcinoma with lobular features of the left breast measuring 2.3 cm, along with a 1.5 cm malignant axillary lymph node. She underwent a left breast lumpectomy with axillary dissection. She underwent adjuvant whole breast radiation, axillary nodal radiation, and was placed on anastrozole therapy for 5 years. Seven years later a recurrence was noted in the superior aspect of the left breast. MRI guided biopsy revealed recurrent left breast cancer with pathology of invasive ductal carcinoma, secretory variant. She elected to undergo lumpectomy alone. Final pathology demonstrated invasive ductal carcinoma, secretory variant, ER negative (0%), PR negative (0%), HER2 negative (0%), pT1bNx. She underwent accelerated adjuvant partial breast radiation. Follow up and surveillance with bilateral breast MRI two years later demonstrated a new left breast mass, found to be triple negative, recurrent secretory variant invasive ductal carcinoma. She underwent definitive treatment with a left skin sparing mastectomy, right sentinel lymph node biopsy, and a latissimus dorsi flap with implant placement. Final pathology demonstrated multifocal recurrent secretory carcinoma, two foci measuring 6 and 11 mm. Our second patient was a 68-year-old male who initially presented to the clinic for evaluation of a ventral incisional hernia. During his initial assessment, a palpable retro-areolar nodule was noted on physical exam. Subsequent mammography demonstrated a hypoechoic mass with irregular margins measuring 2.8 x 2.3 x 1.7 cm along with increased vascularity and calcifications. An ultrasound guided biopsy demonstrated invasive secretory carcinoma. Initial pathologic testing of the tumor demonstrated ER positive (5%), PR positive (1%), and HER2 negative. The patient was taken to the operating room for a total mastectomy with sentinel lymph node biopsy. His postoperative pathology demonstrated negative margins, and invasive secretory carcinoma with lymph nodes negative for metastatic disease. Secretory variant of invasive ductal carcinoma is rare and is determined by its unique immunohistochemical features. We present two cases of secretory carcinoma at our institution. Data suggests that local recurrence is common in patients with secretory breast cancer, occurring in 33-44% of cases. Ki-67 index has been used as a prognostic indicator for metastases and recurrence of disease. Current treatment regimens are diverse; however, surgery is favored as the primary method. This report shows that although indolent, multifocality and recurrence is plausible. Given the limited data on this subset of carcinoma, more investigation is warranted to describe the effectiveness of adjuvant treatment options. Case 1 –insert figure image– Histopathologic examination at 200x shows invasive carcinoma with dense eosinophilic secretory material. By immunohistochemistry, the cells are negative for ER (0%) and PR (0%) with a HER2Neu score of 0, supporting the diagnosis of invasive secretory carcinoma. Case 2 –insert figure image– Histopathologic examination at 200x shows invasive carcinoma with dense eosinophilic secretory material. The tumor cells are positive for CK5/6 (patchy), CD117, ER (focal and weakly), and S100; negative for p63 and calponin, supporting the diagnosis of invasive secretory carcinoma. NTRK3 gene rearrangement was detected on fluorescence in situ hybridization (FISH). Citation Format: Lauren Geisel, Hemanth Venkatesh, Alyssa Obermiller, Quyen Chu, Jessica Gielow, Danielle Henry. Case Series: Invasive Secretory Carcinoma [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-20-10.

3200: Ultra versus moderate-hypofractionation in Partial Breast Irradiation.

3200: Ultra versus moderate-hypofractionation in Partial Breast Irradiation.

1014: Dosimetric evaluation of accelerated partial breast irradiation using VMAT technique

1014: Dosimetric evaluation of accelerated partial breast irradiation using VMAT technique

727: Stereotactic Partial Breast Irradiation: 4-year Clinical Results and Cosmetic Outcomes

727: Stereotactic Partial Breast Irradiation: 4-year Clinical Results and Cosmetic Outcomes

1095: Whole Breast versus Partial Breast Irradiation for early-stage breast cancer: the HYPAB trial

1095: Whole Breast versus Partial Breast Irradiation for early-stage breast cancer: the HYPAB trial

2246: Five-year results of Very Accelerated Partial Breast Irradiation VAPBI phase I-II GEC-ESTRO trial

2246: Five-year results of Very Accelerated Partial Breast Irradiation VAPBI phase I-II GEC-ESTRO trial

Targeted Intraoperative Radiotherapy (TARGIT-IORT) in Breast Cancer Surgery

According to the WHO, breast cancer (BC) has become the largest increase cancer in the world. The vast majority of cancers require radiotherapy and it is the mainstream treatment modality. Although there are numerous treatments, it still does not have a suitable one because of the side effects of radiotherapy. To reduce the harm to the body, people are attending to find a fewer side-effect one. Nowadays, the intraoperative radiation therapy（IORT）is starting to come into its own. TARGIT-IORT is a type of accelerated partial breast irradiation (APBI). The differences between TARGIT-IORT and traditional radiation are the localized radiating space and radiotherapy can be administered during surgery. Researchers have now found that it has a precise radiation range and can be performed simultaneously during surgery. Besides, it performs even better than traditional radiation therapy in various aspects. This is certainly a new trend in breast cancer treatment. TARGIT-IORT is expected to be the next trend in the treatment of BC.

Partial-accelerated irradiation with stereotactic radiotherapy at a dose of 30Gy in 5fractions in early breast cancer.

To evaluate feasibility of accelerated partial breast irradiation (APBI) using stereotactic radiotherapy (SBRT) Thirty Gy delivered in 5 fractions for patients with early breast cancer. Between January 1st, 2018, and December 31s, 2022, we conducted 117 treatments for patients with early-stage breast cancer. All patients underwent conservative surgery followed by APBI using stereotactic external beam radiotherapy. We analyzed local, regional, distant control, overall survival, toxicity, and cosmetic outcomes. The average age was 62years. 21.3% ductal and 78.7% invasive carcinomas. Regarding the PTV volume, the median was 198.8 cc (38-794cc). Treatments were completed in all cases. The median follow-up period was of 21months (1-62 months). Regarding acute toxicity, no Grade 3-4 toxicities were recorded. One patient experienced Grade 2 neuropathic pain. One patient developed subacute fibrosis and two patients developed telangiectasia as subacute and chronic toxicity. Cosmetic results were "good" or "very good" in 96.3% of cases. None of the patients relapsed at any level (local, regional, or distant) and overall survival during follow.up was 100%. APBI with SBRT 30Gy in 5 fractions in early-stage breast cancer is a feasible technique, very-well tolerated and has excellent oncologic and cosmetic outcome during our follow-up period.

Ten-Year Results of Accelerated Partial-Breast Irradiation with Interstitial Multicatheter Brachytherapy after Breast-Conserving Surgery for Low-Risk Early Breast Cancer.

Patients with an early carcinoma of the breast are commonly treated by breast-conserving surgery (BCS) and postoperative radiotherapy. Partial-breast irradiation has gained acceptance in the last few years. Between December 2008 and December 2017, 182 low-risk breast cancer patients treated by BCS in the four university hospitals of the province of Las Palmas and treated with APBI using interstitial multicatheter brachytherapy were included in this study. After a mean follow-up for survivors of 10 years, the treatment was shown to be safe, as no severe acute/late toxicity (grade ≥ 3) was observed. The 10-year IBTR was 1.7% (95%CI: 0.7-2.7%), and the cause-specific survival was 94.9% (95%CI: 93.2-96.6%). We suggest that multicatheter brachytherapy after BCS is safe and effective in early breast cancer patients.

Very accelerated partial breast irradiation in 1 or 2 days: Late toxicity and early oncological outcome of the GEC-ESTRO VAPBI cohort

PurposeTo analyze late toxicity after very accelerated partial breast irradiation (VAPBI) for low-risk breast cancer. MaterialsMethods: In this retrospective, observational, international multicenter study (HDH F20220713143949), patients with low-risk breast cancer underwent lumpectomy + vAPBI (high-dose rate multicatheter interstitial brachytherapy-MIBT). VAPBI was performed with 4(4x6.2 Gy/2d), 3(3x7.45 Gy/2d) or 1 fraction (1x16Gy or 1x18Gy/1d). Primary endpoint was late toxicity. Secondary endpoints were cumulative incidence of breast cancer local relapse (LR) and distant metastatic relapse (DMR) and specific (SS) and overall (OS) survivals. Prognostic factors for late toxicity were analyzed. ResultsFrom 01/2012 to 06/2022, 516 pts with early breast cancer were enrolled. Median follow-up was 44 months [95 %CI 39–46]. Median age was 71 years [40–100]. Median tumor size was 12 mm [1–35]. VAPBI delivered 1, 3 and 4 fractions for 205pts (39.7 %), 167pts (32.4 %) and 144pts (28 %) respectively. 221 late toxicity events were observed in 168pts (32.6 %) (Fibrosis, dyschromia, pain and telangiectasia). Grade 2 and 3 late toxicities were observed in 7.2 and 0.6 % respectively (no G4) with no difference between 1 and ≥ 2 treatment days. CTV > 50 cc (p = 0.007) and V150 > 40 % (p = 0.027) were prognostic factors for G ≥ 2 late toxicity. Four-year cumulative incidence rates of LR and DMR were 2 % [95 %CI 0–3] and 1 % [95 %CI 0–2] respectively. ConclusionsVAPBI based on 1 or ≥ 2 days of MIBT represents an attractive de-escalation of irradiation approach for low-risk breast cancer. Late toxicity profile appears acceptable while early oncological outcome shows encouraging local control. Longer follow-up is warranted in order to confirm these preliminary results.

Benefit of respiratory gating in the Danish Breast Cancer Group partial breast irradiation trial

Background and purposePartial breast irradiation (PBI)has beenthe Danish Breast Cancer Group(DBCG) standard for selected breast cancer patients since 2016 based onearlyresults from the DBCG PBI trial.During trial accrual, respiratory-gated radiotherapy was introduced in Denmark. This study aims to investigate the effect of respiratory-gating on mean heart dose (MHD). Patients and methodsFrom 2009 to 2016 the DBCG PBI trial included 230 patientswith left-sided breast cancer receiving external beam PBI, 40 Gy/15 fractions/3 weeks.Localization of the tumor bed on the planning CT scan, the use of respiratory-gating, coverage of the clinical target volume (CTV), and doses to organs at risk were collected. ResultsRespiratory-gating was used in 123 patients (53 %). In 176 patients (77 %) the tumor bed was in the upper and in 54 patients (23 %) in the lower breast quadrants. The median MHD was 0.37 Gy (interquartile range 0.26–0.57 Gy), 0.33 Gy (0.23–0.49 Gy) for respiratory-gating, and 0.49 Gy (0.31–0.70 Gy) for free breathing, p < 0.0001. MHD was < 1 Gy in 206 patients (90 %) and < 2 Gy in 221 patients (96 %).Respiratory-gating led to significantly lower MHD for upper-located, but not for lower-located tumor beds, however, all MHD were low irrespective of respiratory-gating. Respiratory-gating did not improve CTV coverage or lower lung doses. ConclusionsPBI ensured a low MHD for most patients. Adding respiratory-gating further reduced MHD for upper-located but not for lower-located tumor beds but did not influence target coverage or lung doses. Respiratory-gating is no longer DBCG standard for left-sided PBI.

Long-term results of intraoperative multicatheter breast implant (IOMBI) for accelerated partial breast irradiation (APBI) on early breast cancer patients

Background and purposeMulticatheter breast brachytherapy is a standard technique for accelerated partial breast irradiation (APBI) in early breast cancer patients. Intraoperative multicatheter breast implant (IOMBI) followed by perioperative high-dose-rate brachytherapy (PHDRBT) offers a novel and advantageous approach. We present long-term oncological, toxicity, and cosmesis outcomes for a well-experienced single institution. Materials and methodsEligible women aged ≥ 40 years with clinically and radiologically confirmed unifocal invasive or in situ ≤ 3 cm breast tumors underwent IOMBI during breast-conserving surgery. Patients meeting APBI criteria by definitive pathologic results received 3.4 Gy × 10fx with PHDRBT. Patients not suitable for APBI received PHDRBT-boost followed by WBRT. ResultsA total of 171 patients underwent IOMBI during BCS, 120 patients (70.1 %) were suitable for APBI and 51 (29.8 %) for anticipated PHDRBT-boost. The median age was 61 years (range: 40–78), the median tumor size was 1.1 cm (range: 0.2–3.5), with a histological diagnosis of invasive ductal carcinoma in 78.9 % and ductal in situ in 21.1 %. A median of 9 catheters (range: 4–14) were used. For APBI, the median CTV and V100 were 40.8 cc (range: 8.6–99) and 35.4 cc (range: 7.2–94). The median of healthy breast tissue irradiated represents 7.2 % (range: 2.3–28 %) and the median local treatment duration was 10 days (range: 7–16). With a median follow-up of 8.8 years (range: 0.3–16.25), the 8-year local, locoregional, and distant control rates were 99 %, 98.1 %, and 100 %. G1-G2 late-toxicity rate was 53.4 %. Long-term cosmetic evaluation was excellent-good in 90.8 %. ConclusionIOMBI&PHDRBT program reports excellent long-term oncological outcomes, with a reduction from unnecessary irradiation exposure which translates into low long-term toxicity and good cosmesis outcomes, especially on well-selected APBI patients.

6 Mini Oral - Adjuvant Hypofractionated Whole Breast Irradiation (WBI) Versus Accelerated Partial Breast Irradiation (APBI) in Postmenopausal Women with Early Stage Breast Cancer: 5-Years Update of the HYPAB Trial

6 Mini Oral - Adjuvant Hypofractionated Whole Breast Irradiation (WBI) Versus Accelerated Partial Breast Irradiation (APBI) in Postmenopausal Women with Early Stage Breast Cancer: 5-Years Update of the HYPAB Trial

155 (PB-062) Poster - Utility of clinical-pathological parameters for exclusion of BRCA1/2 mutation carriers as candidates for partial breast irradiation

155 (PB-062) Poster - Utility of clinical-pathological parameters for exclusion of BRCA1/2 mutation carriers as candidates for partial breast irradiation

Differences in Patterns of Care and Referral Between Proton and Photon Therapy

PurposeTo report demographic and clinical characteristics of patients who were more likely to receive proton beam therapy (PBT) than photon therapy from facilities with access to proton centers. Materials and MethodsWe utilized the national cancer database to identify the facilities with access to PBT between 2004 and 2015 and compared the relative usage of photons and PBT for demographic and clinical scenarios in breast, prostate, and nonsmall cell cancer. ResultsIn total, 231 facilities with access to proton centers accounted for 168 323 breast, 39 975 lung, and 77 297 prostate cancer patients treated definitively. Proton beam therapy was used in 0.5%, 1.5%, and 8.9% of breast, lung, and prostate cases. Proton beam therapy was correlated with a farther distance traveled and longer start time from diagnosis for each site (P < .05).For breast, demographic correlates of PBT were treatment in the west coast (odds ratio [OR] = 4.81), age <60 (OR = 1.25), white race (OR = 1.94), and metropolitan area (OR = 1.58). Left-sided cancers (OR = 1.28), N2 (OR = 1.71), non-ER+/PR+/Her2Neu− cancers (OR = 1.24), accelerated partial breast irradiation (OR = 1.98), and hypofractionation (OR = 2.35) were predictors of PBT.For nonsmall cell cancer, demographic correlates of PBT were treatment in the south (OR = 2.6), metropolitan area (OR = 1.72), and Medicare insurance (OR = 1.64). Higher comorbid score (OR = 1.36), later year treated (OR = 3.16), and hypofractionation (not SBRT) (OR = 3.7) were predictors of PBT.For prostate, correlates of PBT were treatment in the west coast (OR = 2.48), age <70 (OR = 1.19), white race (OR = 1.41), metropolitan area (OR = 1.25), higher income/education (OR = 1.25), and treatment at an academic center (OR = 33.94). Lower comorbidity score (OR = 1.42), later year treated (OR = 1.37), low-risk disease (OR = 1.45), definitive compared to postoperative (OR = 6.10), and conventional fractionation (OR = 1.64) were predictors of PBT. ConclusionEven for facilities with established referrals to proton centers, PBT utilization was low; socioeconomic status was potentially a factor. Proton beam therapy was more often used with left-sided breast and low-risk prostate cancers, without a clear clinical pattern in lung cancer.