ESTRO 2022 - Abstract Book

S1041

Abstract book

ESTRO 2022

while 4 patients (14.8%) had adjuvant chemotherapy only. Most of the patients [24 patients (88.9%)] developed LM during the follow-up of initial treatment, while only 3 patients (11.1%) had LM at the time of first diagnosis. At the last visit, 16 patients (59.3%) had disease recurrence median 11 months (range 3 – 43 months) after completion of lung SBRT. Median OS and PFS were 32.1 months [95% confidence interval (CI) 17.3– 46.8 months]) and 11 months (95% CI; 4.7 – 17.3 months), respectively. The 1-year PFS and OS rates were 47% and 62%, respectively. Seven patients (25.9%) had local recurrences. None of the patients experienced grade ≥ 3 acute or late toxicities. Conclusion This study is the first to evaluate the feasibility of SBRT to BCLM patients in a relatively larger patient cohort. Our findings support that the lung SBRT is a feasible and safe method for BCLM with acceptable LC and toxicities. Future prospective studies are warranted to observe the effect on survival in breast cancer patients.

PO-1233 Late Hepatic Toxicities after Breast Cancer Irradiation with Helicoidal Tomotherapy

K. QUINTIN 1

1 Curie Paris, Radiothérapie, Paris, France

Purpose or Objective Helical tomotherapy (HT) is a rotational intensity modulated radiation therapy (IMRT) technique, which allows conformal target irradiation and efficient cardiac sparing in case of complex target volumes and of specific anatomic considerations. However, HT increases low-dose bath to non-target volumes (such as the lungs, the contralateral breast or the liver), which late consequences are still poorly known. The aim of this study was to analyze late hepatic toxicities after irradiation of non-metastatic breast cancer with HT. Materials and Methods This single center retrospective study included all non-metastatic breast cancer patients treated with tomotherapy between 01/10 and 01/21 at the IC (Paris, France), with a biological hepatic function considered as normal before irradiation and re-assessed after more than 1 year without metastatic disease at this reevaluation time point, and for whom the dosimetric parameters to the whole liver were assessable. Biological hepatic function evaluation included γ GT, ALT, AST, total bilirubin and LDH. Mean and maximum dose to the liver were retrieved from DVH. A logistic regression analysis was carried out with cancer laterality, obesity, chemotherapy, hormonotherapy, trastuzumab, mean and maximum dose as explanatory variables for late biological hepatic toxicity perturbation. The selected covariates for the multivariate analysis were those with a p-value less or equal to 0.20 in the univariate analysis. Significance level was 0.05. Results Forty-nine patients were included in this study; 15 patients (31%) received neoadjuvant chemotherapy, 28 patients (57%) adjuvant chemotherapy, 11 patients (22%) Trastuzumab for 1 year for HER2-expression tumors, and 38 patients (78%) hormonotherapy; 27 patients (55%) were irradiated for a right breast cancer; 43 patients (88%) received lymph node irradiation and 41 patients (84%) a tumor bed boost. Median total prescription dose was 63.8 Gy [40-66]. Median mean and maximum dose to the liver were 2.8 Gy [0.3-16.6] and 26.9 Gy [0.7-51.7], respectively. At a median follow-up of 56 months, 11 patients (22%) developed low grade late biological hepatic perturbation: all patients had late grade 1 hepatic toxicities predominating on γ GT (5 patients) and ALT (3 patients); 3 patients (6%) had additional late grade 2 hepatic toxicities ( γ GT, ALT and total bilirubin increase). There was no grade ≥ 3 toxicity. Univariate and multivariate analysis, Trastuzumab was a significant predictor variable of late biological hepatic toxicity (OR=4.4 [1.01-20.18], p=0.04). No other variable was significant. Conclusion Late hepatic toxicity was negligible after multimodal management of non-metastatic breast cancer including tomotherapy irradiation and was not influenced by irradiation side or radiation doses delivered to the liver, which were usually low. Consequently, liver may not be a relevant organ-at-risk when planning breast cancer tomotherapy.

PO-1234 Physical result of Phase II Clinical Trial of 24 Gy Single Fraction SBRT of stage 1-2 breast cancer

S. Velázquez 1 , N. López-Martín 1 , M. González-Vizuete 1 , D. Muñoz-Carmona 2 , F.J. Luis Simón 1

1 Virgen del Rocío University Hospitals, Department of Medical Physics, Seville, Spain; 2 Virgen del Rocío University Hospitals, Department of Radiotherapy, Seville, Spain Purpose or Objective To investigate the feasibility of 28 stereotactic single-dose radiation treatments for breast tumor in our institution. In elderly patients with localized breast cancer who refuse surgery, or for whom surgery is not indicated, SBRT could more effectively control local disease. Materials and Methods Between May 2017 and July 2021, 28 early-stage breast cancer patients were indicated for SABR treatment with MRI contraindication. We used a breast stereotactic prototype with ribs dampening (BSRD), developed and patented in our hospital.