Interobserver Variability in the Delineation of the Tumor Bed Using Seroma and Surgical Clips Based on 4DCT Scan for External Beam Partial-Breast Irradiation

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International Journal of Radiation Oncology  Biology  Physics

Results: A total of 53,431 articles were screened, with consensus from both investigators on the articles included. In total, 10 clinical studies met inclusion criteria, with 268 patients treated by ablative therapies for MBC. Fourteen patients were treated with metastasectomy, 82 with radioembolization with 90Yttrium-labelled microspheres, 48 with radiofrequency ablation, 89 with SRS/SBRT, and 35 with a combination of SRS/SBRT and metastasectomy. Median OS was 28 months (range 8.2-60) amongst the reported studies. In 2 studies, median OS was not reached. PFS was poorly reported, but varied from 26% to 80% at 4-5-years. Initial analysis demonstrated improved PFS and OS in patients with limited metastatic lesions, disease confined to a single organ, and management with localized therapies as opposed to systemic treatment alone. Conclusion: MBC patients treated with ablative therapies represent a heterogeneous population that can benefit from long term PFS and OS when presenting with limited disease burden. The best predictors of PFS and OS were the number of metastatic lesions and single organ involvement, encouraging the consideration of these variables in future studies. Comparison of survival estimates versus trials using systemic therapy alone is warranted in order to determine the minimal clinically important differences for future randomized trial design. Author Disclosure: M.J. Kucharczyk: None. A. Swaminath: None.

technique. APBI patients prioritized similar concerns as WBI patients when making RT decisions but were more eager to reduce the number of treatment visits. APBI patients reported lesser maximal skin reaction and lower regret about the decision to have RT. Author Disclosure: A. Sabolch: None. K.A. Griffith: Research Grant; Blue Cross Blues Shield of Michigan. Consultant; Multiple Myeloma Group at the University of Chicago. S. Katz: None. M. Morrow: None. R. Jagsi: Research Grant; AbbVie, Blue Cross Blue Shield of Michigan. Advisory Board; Eviti.

2039 Decisions Regarding Accelerated Partial-Breast Irradiation in a Population-Based Sample of Early-Stage Breast Cancer Patients A. Sabolch,1 K.A. Griffith,1 S. Katz,1 M. Morrow,2 and R. Jagsi1; 1 University of Michigan, Ann Arbor, MI, 2Memorial Sloan Kettering Cancer Center, New York, NY Purpose/Objective(s): Accelerated partial breast irradiation (APBI) is increasingly used outside of clinical protocols. We sought to examine decision-making and experiences with APBI from the patient perspective. Materials/Methods: In 2013-14, we surveyed breast cancer patients identified by SEER registries of Georgia and Los Angeles about 6 months after diagnosis (survey receipt continues, current response rate 68%). We limited our sample to those who received breast-conserving surgery for unilateral disease and had initiated radiation therapy (RT) (NZ794). We evaluated correlates of being offered APBI and receiving APBI in multivariable models including clinical and sociodemographic factors. Results: Of the sample, 79% had invasive disease (21% DCIS) and 87% were node negative. 82 patients (10%) received APBI and 712 (90%) whole breast irradiation (WBI). APBI was offered to 35% of women: 28% with DCIS, 37% with node(-) invasive disease, and 35% with node(+) disease. Of those offered APBI, 55% reported being told that it works as well as WBI, 16% that it is investigational, and 10% that it may lead to worse cosmesis. On multivariable analyses, being offered APBI was not significantly associated with any clinical or sociodemographic factors evaluated; receipt of APBI was more likely with older age (ORZ1.2, 95% CI: 1.0-1.3 pZ0.01 for +5 years) and node(-) invasive disease (ORZ4.0, 95% CI: 1.8-8.7 p<0.001). Of those who received APBI, 13% had DCIS, 83% had node(-) invasive disease, and 5% had node(+) disease. APBI was delivered using external-beam, intracavitary brachytherapy, or interstitial brachytherapy in 11%, 87%, and 5% of cases (total >100% because some pts indicated more than one technique). Among 634 women who completed RT at the time of survey, 10% of APBI versus 25% of WBI patients reported a severe maximal skin reaction (pZ0.004). When asked what concerns were important in making treatment decisions, APBI and WBI patients were similar in indicating desire to minimize worry about recurrence (87 v 79%, pZ0.12), avoid side effects (71 v 70%, pZ0.95), and avoid RT exposure (40 v 35%, pZ0.36). More APBI pts desired treatments that required fewer visits (54 v 33%, p<0.001). 92 and 86% (pZ0.18) of women receiving APBI and WBI, respectively, were satisfied with the decision to have RT; 98 versus 87% (pZ0.005) indicated no regret in their decision to have RT. Conclusion: In this sample of early-stage breast cancer patients from the general population, about a third were offered APBI; few were told it is investigational. Brachytherapy was the most commonly used APBI

2040 Planning Considerations for Skin Dose Reduction in Proton Beam Accelerated Partial-Breast Irradiation S.E. James,1 N. Remmes,2 L. Brown,2 C. Beltran,1 S.S. Park,1 and R.W. Mutter1; 1Mayo Clinic, Rochester, MN, 2Mayo Clinic, Rochester, MN Purpose/Objective(s): Accelerated partial breast irradiation (APBI) lowers local recurrence in appropriately selected patients on multiple prospective clinical trials. APBI is a convenient adjuvant option given the reduction in treatment time and normal tissue dose. Proton therapy is an attractive modality for APBI given the dose reduction to organs at risk when compared to 3DCRT and superior dose homogeneity when compared to brachytherapy techniques. Long term outcomes of patients treated with passive scatter proton therapy (PSPT) revealed a high incidence of skin toxicity. This planning study aims to evaluate the potential reduction in skin dose achievable with scanning beam proton therapy (SBPT). Materials/Methods: SBPT plans were created for eight consecutive patients treated with 3DCRT APBI on the NSABP B-39/ RTOG 0413 trial. SBPT plans were generated using a commercially available treatment planning system. As per protocol, the CTV was restricted to be within 5mm of the skin surface. Skin constraints were optimized until coverage was impacted. All SBPT plans were normalized for 100% of the CTV to receive at least 98% of the prescription dose. Planned dose was 38.5 Gy in ten fractions. Robustness analysis was performed with +/- 3% range uncertainty and +/- 5mm position uncertainty in each direction. Two-field single (SFO) and multi-field optimization (MFO) was also performed for each plan. Results: Mean maximum skin dose for all SBPT plans was 100.3% (98.6100.6%) compared to 112.5% (102.2-110.7%) for photon plans. Mean skin D0.05cc was 38.2 Gy (37.2-40.2 Gy) for SBPT plans compared to 42.9 Gy (38.7-56.5 Gy) for the corresponding photon plans, demonstrating a 10.9% reduction with SBPT. Even in the worst case robustness, skin dose was no worse than 98.6% of the max skin dose in photon plans. Mean ipsilateral breast V50% was 438.5cc (202.7-773.6cc) for SBPT plans and 906.34cc (549.8-1411.8cc) for 3DCRT plans. Ipsilateral lung V20 Gy was also minimized with a mean of 0.3% (0-1.9%) for SBPT plans and 2.5% (0.64.6%) for associated photon plans. Two-field SFO provided robust CTV 95% coverage when compared to MFO plans. Conclusion: SBPT is capable of delivering APBI with robust CTV coverage while reducing maximum skin dose. Two-field SFO with small angle separation provides an acceptable compromise between skin sparing and robust CTV coverage. Author Disclosure: S.E. James: None. N. Remmes: None. L. Brown: None. C. Beltran: None. S.S. Park: None. R.W. Mutter: None.

2041 Interobserver Variability in the Delineation of the Tumor Bed Using Seroma and Surgical Clips Based on 4DCT Scan for External Beam Partial-Breast Irradiation B. Guo,1 J. Li,2 W. Wang,3 M. Xu,2 Q. Shao,3 Y. Zhang,4 C. Liang,4 and Y. Guo4; 1Shandong Cancer Hospital & Institute, Jinan, China, 2Shan Dong Cancer Hospital, Jinan, China, 3Shan dong Cancer Hospital, Jinan, China, 4Shandong Cancer Hospital, Jinan, China Purpose/Objective(s): To explore the interobserver variability in the delineation of the tumor bed using seroma and surgical clips based on the

Volume 93  Number 3S  Supplement 2015 four-dimensional computed tomography (4DCT) scan for external-beam partial breast irradiation (EB-PBI) during free breathing. Materials/Methods: Patients with a seroma clarity score (SCS) 3w5 and 5 surgical clips in the lumpectomy cavity after breast-conserving surgery who were recruited for EB-PBI underwent 4DCT simulation. Based on the ten sets of 4DCT images acquired, the tumor bed formed using the clips, the seroma, and both the clips and seroma (defined as TBC, TBS and TBC+S, respectively) were delineated by five radiation oncologists using specific guidelines. The following parameters were calculated to analyze interobserver variability: volume of the tumor bed (TBC, TBS, TBC+S), coefficient of variation (COVC, COVS, COVC+S), and matching degree (MDC, MDS, MDC+S). Results: The interobserver variability for TBC and TBC+S and for COVC and COVC+S were statistically significant (pZ0.021, 0.008, 0.002, 0.015). No significant difference was observed for TBS and COVS (pZ0.867, 0.061). Significant differences in interobserver variability were observed for MDC vs MDS, MDC vs MDC+S, MDS vs MDC+S (pZ0.000, 0.032, 0.008), the interobserver variability of MDS was smaller than that of MDC and MDC+S (MDS>MDC+S>MDC). Conclusion: When the SCS was 3w5 points and the number of surgical clips was 5, interobserver variability was minimal for the delineation of the tumor bed based on seroma. Author Disclosure: B. Guo: None. J. Li: None. W. Wang: None. M. Xu: None. Q. Shao: None. Y. Zhang: None. C. Liang: None. Y. Guo: None.

2042 Utilization of Radiation Therapy in Elderly Patients With Triple Negative Breast Cancer: A National Cancer Database Study O. Algan, Y.D. Zhao, and T.S. Herman; University of Oklahoma Health Sciences Center, Oklahoma City, OK Purpose/Objective(s): Triple negative breast cancer (TNBC) occurs in approximately 15% of all breast cancer patients and portends a worse outcome. The purpose of this study was to evaluate the use of RT in older patients with TNBC. Materials/Methods: The NCDB is a comprehensive national database that captures approximately 70% of newly diagnosed cancer patients in the US. Data for patients meeting the criteria of TNBC were extracted including patient demographics, tumor characteristics, treatment modalities used, and overall survival (OS). Trends in RT utilization with year-of-diagnosis were evaluated with Cochran-Armitage trend test. The association between RT use and covariates was assessed using univariate chi-square test and multiple logistic regressions. Overall survival curves were estimated using Kaplan-Meier method and compared between age groups using the logrank test. Results: 63,841 patients (Median Age 58) diagnosed between 1998 and 2012 with TNBC were identified. Of these, 29,368 underwent mastectomy and 29,267 underwent breast conserving surgery (BCS). Of the mastectomy patients, 9684 had locally advanced disease (T3-4, N1-3, M0) with indications for post mastectomy RT (PMRT), and 5275 (54.5%) received PMRT. 23,916 (81.7%) patients received RT after BCS. Of the 29 variables evaluated, 26 were significant for RT utilization on univariate analysis. These included demographic parameters (facility location, crow fly distance), patient characteristics (age, race, morbidity score), tumor factors (histology, size, presence of LN’s, and analytic stage), and socioeconomic factors (insurance status, education and income level). On multivariate analysis, factors that remained significant included Facility location, age, CDCC, year-of-diagnosis, and tumor characteristics (grade, primary site, lymph node status, pathologic T/N stages, and use of systemic chemotherapy). Age was significant on both univariate and multivariate analysis for RT use, with older patients being less likely to receive RT. Treatment outcomes are shown below. On multivariate analysis, RT was associated with improved survival rates when compared to patients receiving no RT. This was true for patients < 70 years as well as for older patients. Conclusion: In this group of high risk patients, there was decreased use of RT in older patients. In our study of a large patient population with TNBC,

Poster Viewing Session

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RT was associated with increased OS rates, and should be strongly considered, when indicated, in triple negative patients. Poster Viewing Abstracts 2042; Table 1

All Age < 70 Age >/Z 70

RT No RT RT No RT RT No RT

Median (mo)

25 Quartile (Mo)

10 yr OS (%)

NR 109.1 NR NR 92.8 47.1

50.8 33.2 61.7 43.6 39.2 20.0

64 49 66% 56% 44 29

p-value < 0.001 < 0.001 < 0.001

Author Disclosure: O. Algan: None. Y.D. Zhao: None. T.S. Herman: None.

2043 Weekly Concomitant Boost During Whole-Breast Hypofractionated Radiation Therapy: A Feasibility and Toxicity Study A. Hosni, E. Awad, B. Refky, and G. Ezzat Eladawei; Mansoura University, Mansoura, Egypt Purpose/Objective(s): A prospective cohort study was conducted to evaluate the feasibility, acute and late toxicity of a hypofractionated three weeks whole breast irradiation schedule with concomitant boost to the tumor bed once- a- week, in patients with early stage breast cancer. Correlation between acute and late skin toxicity with patient and treatment characteristics was also analyzed. Materials/Methods: Sixty seven women with early stage invasive breast cancer underwent conservative surgery were enrolled in this study. All patients were treated with a hypofractionated forward planned tangential IMRT. The basic course for whole breast irradiation consisted of 40 Gy in 15 fractions, 5 times a week, for 3 weeks plus a concomitant weekly boost dose to lumpectomy area of 3 Gy in 3 fractions. Acute skin toxicity was graded based on the RTOG acute toxicity scale. Late skin toxicity was assessed at 6 months from the end of radiation therapy and thereafter and was scored with RTOG/EORTC scale. Results: In our population study, the median follow up was 25 months (range, 11-34); median age was 49 years (range, 31 e 69); 19 T1 (28%) and 48 T2 (72%); 59 histological grade 2/3 (88%); 20 ER/PR negative (30%), 10 HER2 positive (15%), all patients with negative surgical margin (at least 2 mm) and 6 had diabetes mellitus (9%). Adjuvant chemotherapy consisted of 5-fluorouracil, epirubicin and cyclophosphamide; 43 (64%) before and 24 (36%) after radiation therapy; while 47 patients received adjuvant hormonal therapy (33 tamoxifen and 14 aromatase inhibitor). The median contoured clinical target volume (CTV) of breast and boost were 1593 cc and 250 cc; respectively. At last follow up, all patients were alive without locoregional recurrence or distant metastasis. Acute skin toxicity was: G1 (nZ47, 70.1%), G2 (nZ9, 13.4%) and G3 (nZ1, 1.5%). On multivariate analysis (MVA), diabetes mellitus was the only significant variable to predict acute toxicity (pZ 0.003). Late G1 skin toxicity was observed in 13 patients (19.4%). No late toxicity more than G1 was observed. In MVA, age (pZ0.029) and diabetes mellitus (pZ 0.013) correlated with late radiation toxicity. Conclusion: The proposed whole breast irradiation with concomitant weekly boost appears to be feasible and safe. Further research is required to prove the efficacy of this schedule as an alternative option to standard sequential boost technique. Author Disclosure: A. Hosni: None. E. Awad: None. B. Refky: None. G. Ezzat Eladawei: None.

2044 Practice Patterns of Radiation Field Design for Sentinel Lymph Node Positive Early-Stage Breast Cancer S. Azghadi,1 M.E. Daly,2 and J.S. Mayadev3; 1University of California, Davis School of Medicine, Sacramento, CA, 2University of California, Davis Cancer Center, Sacramento, CA, 3University of California, Davis, Sacramento, CA