Toxicity and Dosimetric Analysis of Early Breast Cancer (EBC) Patients Treated with Ultra-Hypofractionated Weekly Radiotherapy (RT) and Simultaneous Integrated Tumor Bed Boost

Abstract

EBC patients with advanced age, severe comorbidities/ logistic issues precluding daily treatment were offered ultra-hypofractionated once-weekly RT. For those women requiring additional tumor bed (TB) boost, a simultaneous integrated boost (SIB) was delivered to further reduce the number of hospital visits. We report feasibility and safety of this regimen in EBC patients. Thirty-seven patients of early breast cancer (T1N0: n = 17; T2N0: n = 20) treated from Dec 2018 -Feb 2020 at our institute with breast conservation were included in this study. They received 28.5Gy in 5 weekly fractions to entire breast and a SIB to the TB of 31.5-33Gy using VMAT technique along with image guidance in each fraction. Vacuum bag immobilization and volumetric image guidance with every fraction ensured accurate treatment delivery. The median age was 53 years (IQR: 50 - 61 years) where 19 patients (51%) had left breast cancer. Twenty-one patients (56.7%) had received adjuvant chemotherapy and 28 (75.7%) received concurrent hormonal therapy with RT. TB boost was recommended in view of grade III disease (n = 27), close/involved margins (n = 4), mucinous histology (n = 2) and young age (n = 4). Seven patients (19%) received a SIB doses of 32.5Gy and 27 (73%) received 33Gy. Dosimetric details are shown in table 1. At RT completion out of 30 patients 6, 23 and 1 patient showed RTOG Grade 0, I and II skin reaction respectively. The grade II skin reaction was seen in the axillary fold region within 4 fractions and was treated with the 5th fraction after replanning to underdose the area with skin fold. Once weekly whole breast RT with SIB to TB up to 33Gy in EBC appears to be a safe and feasible. Late toxicity of this regimen needs to be prospectively evaluated.Abstract 2126; TableDosimetric parametersParametersMean ValuesStandard DeviationInter-quartile rangePTV BreastVolume in cc898314.6650 – 1107V 95%96.9%1.5495.8- 98.4%PTV Tumor bedVolume in cc1105870.9 – 128.3V95%98.3%1.7997.3-99.5%Ipsilateral LungMean5.7Gy1.344.9- 6.3GyV5Gy35.7%10.1728.95- 42.1%V20Gy4.7%2.62.7-6.2 %Contralateral LungMean2.1Gy0.751.6- 2.5GyV5Gy5.4%5.10.99- 8.09%HeartMeanLeft -3.09Gy0.812.5-3.6GyRight-2.67Gy1.41.42-3.15GyV5GyLeft-15.3%9.069.4-18.4%Right-12.3%16.71.89-17.65%Left Anterior Descending ArteryMax dose (0.03cc)Left 11.1Gy1.999.3-12.8GyRight 3.8Gy1.492.5-5.1GyBrachial plexusMax dose9.29Gy7.361.6-15.4GyContralateral BreastMean2.4Gy0.811.6- 3.06GyConformity index tumor bedMedian1.080.251.03-1.12 Open table in a new tab