(S023) Ultrasound Tissue Characterization of Breast Fibrosis Following Hypofractionated Breast Radiotherapy

Xiaofeng Yang, Mylin Torres, MD, Simone Henry, Donna Mister, Tatiana Han, Walter Curran, Tian Liu; Emory University

PURPOSE: Hypofractionation whole-breast radiotherapy (RT) following conservation surgery has been used in many institutions for several decades. However, the hypofractionation regimen has not been widely accepted in the United States. Criticism has focused on concerns about late normal-tissue effects. The purpose of this study is to evaluate breast fibrosis in patients receiving hypofractionated RT using quantitative ultrasound tissue characterization.

MATERIALS AND METHODS: Twenty postlumpectomy women were enrolled in a prospective, longitudinal ultrasound imaging study to examine the development of RT-induced normal-tissue toxicity. Each received simultaneous integrated boost (SIB) RT (40 Gy plus simultaneous cavity boost to 48 Gy in 15 fractions). A baseline ultrasound scan was performed 1 week prior to RT, plus one scan during RT, followed by evaluation at the 1-year follow-up. Patients were imaged with 10-MHz ultrasonography at the 12, 3, 6, and 9 o’clock positions of the breast. To compensate for individual variation, scans taken on the untreated contralateral breast served as a control. Ultrasonography parameters, including skin thickness, Pearson coefficient, and midband fit, were calculated to quantify cutaneous and glandular tissue toxicity. Quantitative ultrasonography parameters were generated by normalizing to the corresponding contralateral breast. Ultrasonography findings were compared with clinical assessments based on the Radiation Therapy Oncology Group (RTOG) toxicity scheme.

RESULTS: Based on the ultrasonography measurements, 50% to 60% of patients developed mild to moderate late toxicity (fibrosis) 1-year post-RT. For the 20 patients, the average skin thickness ratios were 1.23 prior to RT, 1.33 during RT, and 1.37 at the 1-year follow-up. Prior to RT, the diseased breast experienced 23% greater skin thickening secondary to postsurgical changes. The midband fit ratios were 1.12 prior to RT, 1.70 during RT, and 2.45 1-year post-RT. The Pearson ratios were 0.92 prior to RT, 0.78 during RT, and 0.63 1-year post-RT. Increased skin thickness and midband fit values correlated with increased cutaneous toxicity assessed using RTOG scores (P < .05). The ultrasonography findings were consistent with the clinical assessments: 60% developed RTOG grade 1 toxicity, and 10% developed grade 2 toxicity at 1 year.

CONCLUSIONS: This is the first prospective imaging study to objectively document normal-tissue toxicity in patients treated with hypofractionation breast RT using ultrasonography tissue characterization. Contrary to the criticism, patients receiving hypofractionation RT recovered better and experienced less late toxicity at the 1-year follow-up. With this noninvasive ultrasonography technology, physicians can objectively compare the late effects of hypofractionation with the standard regimen and gain a better understanding of treatment responses in individual patients. 

Proceedings of the 97th Annual Meeting of the American Radium Society- americanradiumsociety.org