External Beam Partial Breast Irradiation Research Articles

Accelerated Partial Breast Irradiation for HER2-Positive Early-Stage Breast Cancer

HER2-positive (HER2+) breast cancer historically exhibited the most adverse local outcomes and, consequently, has had limited representation among trials of partial breast irradiation (PBI). We hypothesized that with contemporary HER2-targeted agents, patients may now exhibit excellent disease control outcomes after adjuvant PBI. Using a prospectively maintained institutional database, we identified patients with HER2+ breast cancer treated with breast conserving surgery (BCS) and PBI from 2000 to 2022. Salient clinicopathologic and treatment parameters were collected. All patients received external beam PBI to 40 Gy in 10 daily fractions. Cumulative incidence functions were calculated to estimate the incidence of local recurrence (LR) with the competing risk of death. We identified 1248 patients who underwent PBI at our institution, of whom the study cohort comprised 52 (4%) with HER2+ breast cancer (median age, 64 years; range, 44-87). Nearly all had T1 tumors (98%; median size, 12 mm [range, 1-21 mm]). Most had estrogen receptor positive disease (88%), and all patients had negative surgical margins. Nearly all underwent sentinel node biopsy (94%), with the remainder undergoing no surgical axillary evaluation. Forty-two (81%) received chemotherapy; 40 (77%), hormone therapy; and 42 (81%), HER2-directed therapy, most commonly trastuzumab. At 143.8 person-years of follow-up (range, 7-226 months for each patient), we observed 2 LR events at 14 and 26 months, respectively, yielding a 2-year LR rate of 3.8%. No regional or distant recurrences were observed, nor were any breast-specific mortality events. Two deaths were observed, both without evidence of disease. Among a cohort of patients with HER2+ early-stage breast cancer managed with BCS and PBI, we observed a 2-year LR rate of 3.8%, with no regional or distant recurrences and excellent overall survival. These findings require confirmation with longer follow-up among larger cohorts but appear consistent with the excellent results of contemporary randomized trials of PBI unselected for HER2 status.

One-week external beam partial breast irradiation: survival and toxicity outcomes.

According to ASTRO and ESTRO guidelines, external beam Partial Breast Irradiation (PBI) is a valid option for early-stage breast cancer patients. Nevertheless, there is lack of consensus about the best treatment schedule. We retrospectively analysed data of female patients treated at our institution from 2013 to 2022 with adjuvant "one-week" partial breast irradiation. Clinical Target Volume (CTV) was an isotropic expansion of 15mm from the tumour bed (identified as the breast tissue between surgical clips). The treatment schedule was 30Gy delivered with Volumetric Modulated Arc Therapy in 5 daily fractions. The primary endpoint was Local Control (LC). Disease-Free Survival (DFS), Overall Survival (OS) and safety were secondary endpoints. Three hundred and forty-four patients with a median age of 69 (33-87) years were included in the study.After a median follow-up of 34 (7-105) months, 7 patients (2.0%) developed a local recurrence. Three-year LC, DFS and OS actuarial rates were 97.5% (95% CI 96.2%-98.8%), 95.7% (95% CI 94.2%-97.2%), and 96.9% (95% CI 95.7%-98.1%), respectively. Ten (2.9%) patients experienced grade 2 late toxicities. Five (1.5%) patients reported late cardiac major events. Three (0.9%) late pulmonary toxicities were detected. One hundred and five (30.5%) patients reported fat necrosis. Good or excellent cosmetic evaluation following the Harvard Scale was reported in 252 (96.9%) cases by the physicians, while in 241 (89.2%) cases by the patients. "One-week" PBI is effective and safe, and this schedule is a valid option for highly selected early breast cancer patients.

PD-0233 One-Week External Beam Partial Breast Irradiation: Survival and Toxicity Outcomes

PD-0233 One-Week External Beam Partial Breast Irradiation: Survival and Toxicity Outcomes

Special Techniques of Adjuvant Breast Carcinoma Radiotherapy.

Modern radiotherapy techniques are designed to permit reduced irradiation of healthy tissue, resulting in a diminished risk of adverse effects and shortened recovery times. Several randomized studies have demonstrated the benefits of increased dosage to the tumor bed area in combination with whole breast irradiation (WBI). Conventional WBI treatment following breast-conserving procedures, which required 5-7 weeks of daily treatments, has been reduced to 3-4 weeks when using hyperfractionated regimens. The dosage administration improves local control, albeit with poorer cosmesis. The method of accelerated partial breast irradiation (APBI) shortens the treatment period whilst reducing the irradiated volume. APBI can be delivered using intraoperative radiation, brachytherapy, or external beam radiotherapy. Currently available data support the use of external beam partial breast irradiation in selected patients. Modern radiotherapy techniques make it possible to achieve favorable cosmesis in most patients undergoing immediate breast reconstruction surgery, and studies confirm that current methods of external beam radiation allow an acceptable coverage of target volumes both in the reconstructed breast and in the regional lymphatic nodes.

Five Fraction External Beam Partial Breast Irradiation: A User's Guide.

Mature follow up from multiple randomized trials have demonstrated the safety and efficacy of external beam partial breast irradiation (PBI) for appropriately selected patients with early stage breast cancer. Despite this evidence, external beam PBI remains underutilized. In this user guide we outline patient selection, workflow, and address possible challenges to aid in implementation of evidence-based external beam PBI. Review of the current guidelines for PBI suitability, surgical considerations, treatment technique, simulation, contouring, and treatment planning, citing the latest published literature to support PBI utilization. Prospective data supports the use of 30 Gy in 5 fractions delivered with intensity modulated radiation therapy on a daily or every other day basis for a significant proportion of early stage breast cancer patients. The surgical cavity must be clearly visualized on treatment planning scan, recommend 3-5 weeks post-operatively, and the recommended clinical target volume expansion on the surgical cavity is 0.5-1.0 cm. A planning target volume expansion, based on motion management and image guidance, of 0.5-1.0 cm should be used. Organ at risk dose constraints of heart V3Gy ≤10% and contralateral breast Dmax ≤1 Gy are often achievable. Five fraction external beam PBI is a highly effective treatment with very limited toxicity for patients with early stage breast cancer following breast conserving surgery. Commonly utilized intensity modulated treatment planning techniques with plan delivery on standard linear accelerators results significant normal tissue sparing and makes implementation feasible at most radiation oncology centers.

Optimizing Preventive Adjuvant Linac-Based (OPAL) Radiation: A Phase 2 Trial of Daily Partial Breast Irradiation

Evidence supports use of partial-breast irradiation (PBI) in the management of early breast cancer, but the optimal dose-fractionation remains unsettled. We conducted a phase 2 clinical trial (OPAL trial) to evaluate a novel PBI dosing schedule of 35 Gy in 10 daily fractions. Patients with close (<2 mm) margins also received a boost of 9 Gy in 3 fractions. Eligible patients underwent margin-negative lumpectomy for ductal carcinoma in situ or estrogen receptor-positive invasive breast cancer, up to 3 cm, pTis-T2 N0. The primary outcome was any grade ≥2 toxic effect occurring from the start of radiation through 6 months of follow-up. Secondary outcomes included patient-reported cosmesis, breast pain, and functional status, measured using the Breast Cancer Treatment Outcomes Scale, and physician-reported cosmesis, measured using the Radiation Therapy and Oncology Group scale. The Cochran-Armitage trend test and multivariable mixed-effects longitudinal growth curve models compared outcomes for the OPAL study population with those for a control group of similar patients treated with whole-breast irradiation (WBI) plus boost. All 149 patients enrolled on the OPAL trial received the prescribed dose, and 17.4% received boost. The median age was 64 years; 83.2% were White, and 73.8% were overweight or obese. With median follow-up of 2.0 years, 1 patient (0.7%) experienced in-breast recurrence. Prevalence of the primary toxicity outcome was 17.4% (26 of 149 patients) in the OPAL trial compared with 72.7% (128 of 176 patients) in the control WBI-plus-boost cohort (P < .001). In longitudinal multivariable analysis, treatment on the OPAL trial was associated with improved patient-reported cosmesis (P < .001), functional status (P=.004), breast pain (P=.004), and physician-reported cosmesis (P < .001). Treatment with daily PBI was associated with substantial reduction in early toxicity and improved patient- and physician-reported outcomes compared with WBI plus boost. Daily external-beam partial-breast irradiation with 13 or fewer fractions merits further prospective evaluation.

Partial Breast Irradiation Versus Whole Breast Irradiation for Early Breast Cancer Patients in a Randomized Phase III Trial: The Danish Breast Cancer Group Partial Breast Irradiation Trial.

On the basis of low risk of local recurrence in elderly patients with breast cancer after conservative surgery followed by whole breast irradiation (WBI), the Danish Breast Cancer Group initiated the noninferiority external-beam partial breast irradiation (PBI) trial (ClinicalTrials.gov identifier: NCT00892814). We hypothesized that PBI was noninferior to WBI regarding breast induration. Patients operated with breast conservation for relatively low-risk breast cancer were randomly assigned to WBI versus PBI, and all had 40 Gy/15 fractions. The primary end point was 3-year grade 2-3 breast induration. In total, 865 evaluable patients (434 WBI and 431 PBI) were enrolled between 2009 and 2016. Median follow-up was 5.0 years (morbidity) and 7.6 years (locoregional recurrence). The 3-year rate of induration was 9.7% for WBI and 5.1% for PBI (P = .014). Large breast size was significantly associated with induration with a 3-year incidence of 13% (WBI) and 6% (PBI) for large-breasted patients versus 6% (WBI) and 5% (PBI) for small-breasted patients. PBI showed no increased risk of dyspigmentation, telangiectasia, edema, or pain, and patient satisfaction was high. Letrozole and smoking did not increase the risk of radiation-associated morbidity. Sixteen patients had a locoregional recurrence (six WBI and 10 PBI; P = .28), 20 patients had a contralateral breast cancer, and eight patients had distant failure (five WBI and three PBI). A nonbreast second cancer was detected in 73 patients (8.4%), and there was no difference between groups. External-beam PBI for patients with low-risk breast cancer was noninferior to WBI in terms of breast induration. Large breast size was a risk factor for radiation-associated induration. Few recurrences were detected and unrelated to PBI.

Impact of the Delineation Accuracy of Lumpectomy Cavity on Planning Target Volume in Partial-Breast Irradiation Using Brachytherapy and External-Beam Radiotherapy

Background: In partial-breast irradiation (PBI), the accurate target volume delineation based on the lumpectomy cavity (LC) remained difficult due to uncertain LC identification. However, the impact of accurate LC delineation on the planning target volume (PTV) has not been investigated. Materials and Methods: Between September 2018 and April 2020, 159 patients receiving perioperative PBI with multicather-interstitial brachytherapy have been evaluated. While LC delineated using implanted catheters as fiducial markers was used as a reference, conventional LC was virtually delineated on computed tomography with clips. PTV1-cm margin and PTV2-cm margin, which means 1cm and 2cm expansion from LC, were developed and assumed for brachytherapy and external-beam PBI, respectively. The target accuracy and the impact of the delineation accuracy of LC on PTVs were evaluated. The geographic miss index (GMI) and normal tissue index (NTI) were used as accuracy indices and were defined as the percentage of under- and overestimating volume, respectively. Results: The PTV1-cm margin and PTV2-cm margin were significantly larger than the reference volume, 57.9cm3 vs. 37.9cm3 (P&lt;0.001) and 113.2cm3 vs. 93.8cm3 (P&lt;0.001), respectively. The GMI and NTI of LC were 27.3% and 41.2%, respectively. Although the GMI in the PTV1-cm margin and PTV2-cm margin was significantly reduced to 9.8% (P&lt;0.0001) and 9.9% (P&lt;0.0001), respectively, the NTI was not significantly improved in the PTV1-cm margin, which was 41.8% (P=0.60) but was improved in PTV2-cm margin, which was 23.1% (P&lt;0.0001). Conclusion: The GMI in PTV1-cm margin was reduced to be as low as PTV2-cm margin. Although PTV2-cm margin was associated with lower NTI, the absolute volume was almost double with PTV1-cm margin. Although further research was required, brachytherapy-based PBI may be a reasonable option to achieve tumor control and cosmesis using conventional delineation method.

Optimizing Preventive Adjuvant LINAC (OPAL) Radiation: A Phase II Trial of Daily Partial Breast Irradiation

<h3>Purpose/Objective(s)</h3> Twice daily accelerated partial breast irradiation (APBI) may confer worse long-term cosmetic outcome than daily whole breast irradiation (WBI). We hypothesized that daily partial breast irradiation would yield improved cosmetic outcomes without compromising tumor control. To test this hypothesis, we conducted a phase II trial to evaluate a ten-fraction regimen of daily PBI (OPAL regimen). <h3>Materials/Methods</h3> From 2017-2018, 149 women aged ≥ 50 with DCIS or early invasive, ER+ breast cancer were enrolled into a multi-institutional phase II trial that treated the partial breast to 35 Gy in 10 daily fractions. Patients with close margins (< 2 mm) also received a boost of 9 Gy in 3 daily fractions. Toxicities were evaluated using CTCAE v4.0 and physician-reported cosmesis was assessed using the RTOG scale. The Breast Cancer Treatment Outcomes Scale (BCTOS) assessed patient-reported cosmesis, breast pain, and functional status. Outcomes were assessed at baseline, 6 months, 1 year, and annually thereafter. The primary outcome was incidence of grade ≥ 2 toxicity within 6 months of PBI initiation. To facilitate a comparison of the OPAL regimen to WBI, we identified 176 patients with similar clinical-pathologic features from our prior trial of WBI+boost in which toxicities were also prospectively collected. Differences in cross-sectional outcomes between the OPAL trial and historical WBI+boost cohort were tested using chi-square test. Mixed effect growth curve models evaluated outcomes over time adjusting for relevant covariates. <h3>Results</h3> Median age was 64 years and median follow-up was 2 years. All 149 patients received 35 Gy in 10 daily fractions and 26 received a boost. One patient developed an in-field DCIS recurrence. For the primary outcome, grade ≥ 2 toxicity within 6 months of PBI initiation was 14.1% with OPAL compared to 71% in the WBI+boost cohort (<i>P</i> < 0.001). At two years post-radiation, fatigue (8% vs 16%), hyperpigmentation (18% vs 30%), breast edema (0% vs 9%), superficial fibrosis (18% vs 31%), deep fibrosis (6% vs 13%), nipple areolar changes (6% vs 17%), and breast atrophy (19% vs 35%) were less prevalent in patients treated with OPAL (all <i>P</i> < 0.05). At two years, 93% of patients treated with OPAL had excellent/good cosmetic outcome compared to 77% of patients treated with WBI+boost (<i>P</i> < 0.001). In multivariable longitudinal analysis, treatment with OPAL was associated with improved patient-reported cosmetic outcome (<i>P</i> < 0.001), functional status (<i>P</i> = 0.02), breast pain (<i>P</i> = 0.003) and physician-reported cosmetic outcome (<i>P</i> < 0.001). <h3>Conclusion</h3> Treatment with this novel daily PBI regimen of 35 Gy in 10 daily fractions with selective boost yielded better cosmetic and functional outcomes and less breast pain and toxicity than WBI+boost with median follow up of 2 years. Daily external beam partial breast irradiation with 10 or fewer fractions merits further prospective evaluation.

The Acute and Late Toxicities of MRI-Guided External Beam Partial Breast Irradiation Delivered Using a Once-per-Day Regimen

<h3>Purpose/Objective(s)</h3> The use of external beam accelerated partial breast irradiation (APBI) using a twice-per-day regimen has raised concerns about increase rates of late toxicities. We compared toxicity outcomes of external beam APBI using a once-per-day regimen and accelerated hypofractionated whole breast irradiation (AWBI) in patients with early-stage breast cancer. <h3>Materials/Methods</h3> This was a single-institution, retrospective cohort study. Patients aged ≥50 years with pTisN0 or pT1N0 breast cancer who underwent breast-conserving surgery and adjuvant radiotherapy were included. APBI was delivered at 38.5 Gy in 10 fractions once daily using magnetic resonance imaging (MRI)-guided radiotherapy only to patients who were strictly "suitable", according to the ASTRO-APBI guidelines. AWBI was delivered at 40.5–43.2 Gy in 15 or 16 fractions with or without a boost. <h3>Results</h3> Between October 2015 and December 2018, 173 and 300 patients underwent APBI and AWBI, respectively. At a median follow-up of 34.9 months (range 7.1 to 55.4 months), the 3-year recurrence-free survival rates of the APBI and AWBI groups were both 99.2% (<i>P</i> = 0.63). Acute toxicities were less frequent in the APBI than AWBI group (grade 1: 95 [54.9%] vs. 233 [77.7%] patients; grade 2: 7 [4.0%] vs. 44 [14.7%] patients; no grade ≥3 toxicities were observed in either group, <i>P</i> < 0.001). Late toxicities were less common in the APBI than AWBI group (grade 1: 112 [64.7%] vs. 197 [65.7%] patients; grade 2: 9 [5.2%] vs. 64 [21.3%] patients; grade 3: 0 vs. 5 [1.7%] patients, <i>P</i> < 0.001). Multivariate analysis showed that APBI was significantly associated with fewer late toxicities of grade ≥2 compared with AWBI (odds ratio 4.17, <i>P</i> = 0.006). <h3>Conclusion</h3> Once-per-day APBI using MRI-guided radiotherapy afforded excellent locoregional control and fewer toxicities compared with AWBI. This scheme could be an attractive alternative to AWBI in patients who meet the ASTRO-APBI guidelines.

The Acute and Late Toxicities of MRI-Guided External Beam Partial Breast Irradiation Delivered Using a Once-Per-Day Regimen.

Background and PurposeThe use of external beam accelerated partial breast irradiation (APBI) using a twice-per-day regimen has raised concerns about increase rates of late toxicities. We compared toxicity outcomes of external beam APBI using a once-per-day regimen and accelerated hypofractionated whole breast irradiation (AWBI) in patients with early-stage breast cancer.Materials and MethodsThis was a single-institution, retrospective cohort study. Patients aged ≥50 years with pTisN0 or pT1N0 breast cancer who underwent breast-conserving surgery and adjuvant radiotherapy were included. APBI was delivered at 38.5 Gy in 10 fractions once daily using magnetic resonance imaging (MRI)-guided radiotherapy only to patients who were strictly “suitable”, according to the ASTRO-APBI guidelines. AWBI was delivered at 40.5–43.2 Gy in 15 or 16 fractions with or without a boost.ResultsBetween October 2015 and December 2018, 173 and 300 patients underwent APBI and AWBI, respectively. At a median follow-up of 34.9 months (range 7.1 to 55.4 months), the 3-year recurrence-free survival rates of the APBI and AWBI groups were both 99.2% (p=0.63). Acute toxicities were less frequent in the APBI than AWBI group (grade 1: 95 [54.9%] vs. 233 [77.7%] patients; grade 2: 7 [4.0%] vs. 44 [14.7%] patients; no grade ≥3 toxicities were observed in either group, p<0.001). Late toxicities were less common in the APBI than AWBI group (grade 1: 112 [64.7%] vs. 197 [65.7%] patients; grade 2: 9 [5.2%] vs. 64 [21.3%] patients; grade 3: 0 vs. 5 [1.7%] patients, p<0.001). Multivariate analysis showed that APBI was significantly associated with fewer late toxicities of grade ≥2 compared with AWBI (odds ratio 4.17, p=0.006).ConclusionOnce-per-day APBI afforded excellent locoregional control and fewer toxicities compared with AWBI. This scheme could be an attractive alternative to AWBI in patients who meet the ASTRO-APBI guidelines.

Outcomes and Toxicities with Partial Breast Irradiation vs. Whole Breast Irradiation: A Meta-Analysis

Whole breast irradiation (WBI) has traditionally been considered the primary adjuvant radiation therapy technique after breast conserving surgery. However, over the past two decades, partial breast irradiation (PBI) has emerged as an alternative to WBI, offering the potential for shorter courses of radiation and improved toxicity profiles. Several randomized trials using different PBI techniques have recently been published. We therefore performed a meta-analysis to compare outcomes between WBI and PBI as well as compare outcomes with various PBI techniques. For this analysis, seven randomized trials were included (National Institute of Oncology, GEC-ESTRO, University of Florence, Barcelona, RAPID, IMPORT-LOW, and NSABP B39). Older trials evaluating PBI were excluded as they were performed prior to the 3-dimensional treatment era and were not consistent with modern PBI techniques. Randomized trials evaluating intraoperative radiation therapy were excluded due to differences in technique as compared to traditional PBI techniques. PBI trials were divided into external beam (3D-CRT/IMRT; University of Florence, Barcelona, RAPID, IMPORT-LOW, and NSABP B39) and brachytherapy (National Institute of Oncology, GEC-ESTRO). As the majority of patients in NSABP B39 were treated with 3D-CRT (73%, n = 1536), this was considered an external beam PBI trial in this analysis. Outcomes evaluated included ipsilateral breast tumor recurrence (IBTR) at 5 years as well as acute (RAPID, University of Florence and Barcelona trials) and late toxicities (RAPID, University of Florence, Barcelona; GEC-ESTRO, IMPORT LOW trials provided Grade 2+ toxicities). A Bayesian logistic regression model evaluated the risk of above outcomes for evidence of deviation by WBI and PBI techniques. Statistical estimation reports risk of rate by posterior median and 95% highest posterior density (HPD) interval. A total of 9,758 patients were included with 4,840 receiving WBI and 4,918 PBI. At 5 years, no difference in IBTR was noted between PBI (1.8%, 95% CI 0.68%-3.2%) and WBI (1.7%, 95% CI 0.92%-2.4%). By PBI technique, the 5-year IBTR rate for 3DCRT/IMRT was 1.7%, and 2.2% for brachytherapy. With respect to acute toxicities, grade 2/3 rates were 7.1%/0% with PBI as compared to 40.0%/3.6% with WBI. For late toxicities, grade 2/3 rates were 0%/0% with PBI as compared to 1.0%/0% with WBI and for grade 2+ were 1.2% with PBI versus 3.6% with WBI. IBTR rates were similar between PBI and WBI with no differences noted by PBI technique. Acute and late toxicities were lower with PBI as compared to WBI. Additional data from randomized trials is needed to compare toxicity profiles between various PBI techniques.

Interobserver Variability of Target Volumes Delineated in the Supine and Prone Positions Based on Computed Tomography Images for External-Beam Partial Breast Irradiation after Breast-Conserving Surgery: A Comparative Study

Interobserver Variability of Target Volumes Delineated in the Supine and Prone Positions Based on Computed Tomography Images for External-Beam Partial Breast Irradiation after Breast-Conserving Surgery: A Comparative Study

Interobserver Variability of Target Volumes Delineated in the Supine and Prone Positions Based on Computed Tomography Images for External-Beam Partial Breast Irradiation After Breast-Conserving Surgery: A Comparative Study.

Background: Although the supine position remains the dominant position for external-beam partial breast irradiation (EB-PBI), the advantages of administering EB-PBI in the prone position have been recognized. The interobserver variability between target volumes delineated in the different positions for EB-PBI after breast-conserving surgery needs to be investigated.Methods: Twenty-seven patients suitable for EB-PBI were enrolled from July 2016 to April 2017. Supine and prone simulation CT images were sequentially acquired for all enrolled patients during free breathing. Five experienced radiotherapists delineated the target volumes for all patients on supine and prone simulation CT images. The selected parameters, including target volumes, the coefficient of variation (COV), the matching degree (MD), and so on, were calculated to analyze the interobserver variability.Results: Regardless of the patient position, the interobserver variability between tumor bed (TB) and clinical target volume (CTV) measurements in supine and prone positions were statistically significant (F = 31.34, 19.467; 44.000, 41.985; P = 0.000, 0.001; 0.000, 0.001). The interobserver variability of COVCTV was significantly greater in the supine position than in the prone position (T = 2.64, P = 0.014). Furthermore, the interobserver variabilities of MDTB and MDCTV were statistically lower in the supine position than in the prone position (Z = −3.460, −3.195, P = 0.000, 0.001).Conclusion: When delineating the target volume for EB-PBI, the interobserver variability in the prone position was lower than that in the supine position. Hence, the administration of EB-PBI in the prone position during free breathing is a reasonable option.

Abstract P4-12-24: Evaluation of partial breast irradiation suitability in early stage breast cancer patients

Abstract Purpose: Partial Breast Irradiation (PBI) treats the tumor bed plus a margin in low risk early stage breast cancers, reducing exposure to organs at risk. Randomized trials have shown that PBI with external beam radiotherapy is non-inferior to whole breast irradiation in terms of local control with fewer late normal tissue adverse events. We aimed to determine the proportion of women with early stage breast cancer suitable for external beam PBI at our institution using adapted ASTRO guidelines for accelerated PBI whereby both clinical-pathological factors and visualization of the tumor bed/cavity on planning scans were determined to quantify PBI eligibility. Methods: Patients were identified retrospectively from January 1, 2013 to November 1, 2018 based on age (≥55), tumor size (≤2cm invasive, ≤2.5cm DCIS), nodal negativity and grade (1 or 2). Cases identified were unifocal, lymphovascular invasion negative, ER positive, HER2 negative, with margins ≥2mm (invasive) and ≥3mm (DCIS), no chemotherapy, non-lobular, no extensive intraductal component, no previous/ bilateral cancers and endocrine therapy optional. Planning scans were reviewed to assess for presence of surgical clips and assigned cavity visualization scores (CVS); CVS 1=cavity not visualized, CVS 2=cavity visualized with indistinct margins, CVS 3=cavity visualised with some distinct margins and heterogeneous appearance, CVS 4= cavity visualised with mostly distinct margins and mildly heterogeneous appearance, CVS 5= all cavity margins clearly defined and homogeneous appearance. These features were used to determine if cases were considered radiologically suitable for PBI. Results: Thirty-seven percent (1051/2824) of cases identified were deemed eligible based on age, grade and T1N0/Tis. Of the 1051, 306 (29%) met all the pathologic criteria; the main reasons for exclusion were previous breast cancer, lobular histology, or multifocality. Median age of eligible cases was 65 years (range 55-88 years). The majority (254) had invasive disease (T1mi: 6, T1a: 17, T1b: 98, T1c: 133); 52 had DCIS. There were 169 right-sided and 137 left-sided cases. Endocrine therapy was documented in 55% of cases. CVS (1-5) were: 11%, 22%, 30%, 29%, 8%. Overall, 66% (201/306) of cases were considered radiologically suitable for PBI (of the 201 cases, 97% had CVS ≥3). Seventy-two cases (72/306; 24%) had tumor bed clips, of which, 34 were considered suitable for PBI (91% CVS ≥3; 9% CVS 2). Conclusions: Overall, a low proportion of all patients were eligible for PBI based on clinical features, but two-thirds of eligible cases were suitable for PBI based on CVS score alone. In contrast, the suitability for PBI within the cohort with surgical clip placement was low. Visualization of the tumor bed is essential to safely deliver PBI and is guided by identification of the cavity seroma and/or surgical clips. Development of standard practice guidelines for surgical clip positioning to identify the tumor bed will potentially assist in increasing the proportion of early stage breast cancer patients suitable to receive PBI, even if the CVS is less favorable. Citation Format: Christine Anne Koch, Gemma Corey, Kathy Han, Grace Lee, Tom Purdie, Chris McIntosh, Patricia Lindsay, Fei-Fei Liu, Anthony Fyles, Wilf Levin, Jennifer Croke, Aisling Barry, Danielle Rodin, Nhu Tram Nguyen, Tatiana Conrad. Evaluation of partial breast irradiation suitability in early stage breast cancer patients [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-12-24.

The Role of Partial Breast Radiation in the Previously Radiated Breast.

The aim of this study was to analyze breast cancer patients who previously had mantle-field or breast radiation (RT) followed by retreatment with external beam partial breast irradiation (EB PBI). We retrospectively reviewed all women with newly diagnosed early-stage breast cancer treated with lumpectomy and partial breast irradiation between 2007 and 2017 who had undergone prior chest or breast RT. Of 11 patients recorded, 8 (73%) had Hodgkin lymphoma, and 3 (27%) had ipsilateral breast cancer diagnosis. Median age at initial and second diagnosis was 28 and 48 years, respectively. The lymphoma patients received a dose of 35 Gy in 16 to 20 fractions to a classic mantle-upper abdomen field. Patients with an initial diagnosis of breast cancer received whole-breast RT (2 with 50 Gy/25 fractions, 1 with 40 Gy in 16 fractions). Median time from initial to second diagnosis was 22.6 years (range, 13.5 to 32.6 y). All had early-stage (I to II) invasive ductal carcinoma and were treated with lumpectomy or repeat lumpectomy and EB PBI. Four received a dose of 45 Gy/25 fractions, 4 to 50 Gy/25 fractions, and 3 to 42.4 Gy/16 fractions. All patients received adjuvant systemic treatment. Two patients had toxicity, 1 had grade 1 induration, and the other had grade 2 fat atrophy and grade 1 fibrosis. One patient developed a contralateral breast cancer. No locoregional recurrences were reported at the median follow-up of 4.6 years (range, 0.6 to 10.5 y). EB PBI after lumpectomy seems to be a safe and effective RT treatment option for selected patients with prior RT and localized early-stage breast cancer.

A comparative study based on deformable image registration of the target volumes for external-beam partial breast irradiation defined using preoperative prone magnetic resonance imaging and postoperative prone computed tomography imaging

BackgroundTo explore the differences and correlations between the target volumes defined using preoperative prone diagnostic magnetic resonance imaging (MRI) and postoperative prone computed tomography (CT) simulation imaging based on deformable image registration (DIR) for external-beam partial breast irradiation (EB-PBI) after breast-conserving surgery (BCS).MethodsEighteen breast cancer patients suitable for EB-PBI were enrolled. Preoperative prone diagnostic MRI and postoperative prone CT scan sets for all the patients were acquired during free breathing. Target volumes and ipsilateral breast were all contoured by the same radiation oncologist. The gross tumor volume (GTV) delineated on the preoperative MRI images was denoted as the GTVpreMR and the tumor bed (TB) delineated on the postoperative prone CT images was denoted as the GTVpostCT. The MIM software system was used to deformably register the MRI and CT images.ResultsWhen based on the coincidence of the compared target centers, there were statistically significant increases in the conformity index (CI) and degree of inclusion (DI) values for GTVpostCT-GTVpreMR, GTVpostCT-CTVpreMR + 10, CTVpostCT + 10-GTVpreMR, and CTVpostCT + 10-CTVpreMR + 10 when compared with those based on the DIR of the thorax (Z = − 3.724, − 3.724, − 2.591, − 3.593, all P < 0.05; Z = -3.724, − 3.724, − 3.201, − 3.724, all P < 0.05, respectively).ConclusionsAlthough based on DIR, there was relatively poor spatial overlap between the preoperative prone diagnostic MRI images and the postoperative prone CT simulation images for either the whole breast or the target volumes. Therefore, it is unreasonable to use preoperative prone diagnostic MRI images to guide postoperative target delineation for EB-PBI.

Setup Error Assessment and Correction in Planar kV Image- Versus Cone Beam CT Image-Guided Radiation Therapy: A Clinical Study of Early Breast Cancer Treated With External Beam Partial Breast Irradiation

Objective:To compare differences in setup error assessment and correction between planar kilovolt images and cone beam computed tomography images for external beam partial breast irradiation during free breathing.Methods:Nineteen patients who received external beam partial breast irradiation after breast-conserving surgery were recruited. Interfraction setup error was acquired using planar kilovolt images and cone beam computed tomography. After online setup correction, the residual error was calculated, and the setup error was compared. The residual error and setup margin were quantified for planar kilovolt and cone beam computed tomography images.Results:The largest setup error was observed in the anteroposterior direction for both cone beam computed tomography and planar kilovolt imaging (−1.45 mm, 1.74 mm). The cone beam computed tomography–based setup error (systematic error [Σ]) was less than the planar kilovolt images based on Σ in the anteroposterior direction (–1.2 mm vs 2.00 mm; P = .005), and no significant differences were observed for random error (σ) in 3 dimensions (P = .948, .376, .314). After online setup correction, cone beam computed tomography significantly reduced the residual setup error compared with planar kilovolt images in the anteroposterior direction (Σ: −0.20 mm vs 0.50 mm, P = .008; σ: 0.45 mm vs 1.34 mm, P = .002). The cone beam computed tomography–based setup margin was smaller than the planar kilovolt image-based setup margin in the anteroposterior direction (−1.39 mm vs 5.57 mm, P = .003; 0.00 mm vs 3.20 mm, P = .003).Conclusions:Discrepancy between the setup errors observed with planar kilovolt and cone beam computed tomography was obvious in the anteroposterior direction. Compared to cone beam computed tomography, the elapsed treatment time was smaller when the initial alignment used kilovolt planar imaging. Whether using planar kilovolt or cone beam computed tomography, residual errors can be reduced to 1.5 mm for external beam partial breast irradiation procedures.

A Comparative Study on the Target Volumes Defined Using Preoperative Prone Magnetic Resonance Image and Postoperative Prone Computed Tomography Image Based Deformable Image Registration for External-Beam Partial Breast Irradiation

A Comparative Study on the Target Volumes Defined Using Preoperative Prone Magnetic Resonance Image and Postoperative Prone Computed Tomography Image Based Deformable Image Registration for External-Beam Partial Breast Irradiation

External-beam partial breast irradiation in a supine versus prone position after breast-conserving surgery for Chinese breast cancer patients

To investigate the differences in target volumes and dosimetric parameters between the supine and prone positions for external-beam partial breast irradiation (EB-PBI) after breast-conserving surgery (BCS) for Chinese breast cancer patients, thirty breast cancer patients who underwent three-dimensional conformal radiation therapy (3DCRT) EB-PBI after BCS were enrolled. Supine and prone scan sets were acquired during free breathing for all patients. Target volumes and organs at risk (OARs) including the heart, ipsilateral lung and bilateral breast were contoured by the same radiation oncologist. For each patient, supine and prone EB-PBI plans were generated based on the same planning criteria. The clinical target volume (CTV) and planning target volume (PTV) in the prone position were significantly greater than those in the supine position (P = 0.003, 0.004, respectively). A 0.95 Gy reduction in the mean dose (Dmean) to the heart (P = 0.000) was apparent in the supine position compared to the prone position. The Dmean to the ipsilateral lung was significantly lower in the prone position than in the supine position (1.59 Gy vs. 1.72 Gy, P = 0.029). Therefore, for Chinese breast cancer patients, carrying out 3DCRT EB-PBI in the prone position during free breathing is feasible.