ESTRO 2024 - Abstract Book

S152

Brachytherapy - Breast

ESTRO 2024

280

Proffered Paper

Salvage brachytherapy in second ipsilateral breast tumor event: Relating dosimetry with late toxicity

Mohammed Abdul-Latif 1 , Jocelyn Gal 2 , Renaud Schiappa 2 , Mathieu Gautier 3 , Yassine Rizzi 3 , Jean-Michel Hannoun Levi 3 1 Mount Vernon Cancer Centre, Department of Radiotherapy, Northwood, United Kingdom. 2 Antoine Lacassagne Cancer Center, Biostatistics Unit, Nice, France. 3 Antoine Lacassagne Cancer Center, Department of Radiotherapy, Nice, France

Purpose/Objective:

Conservative treatment (CT) involving wide local excision (WLE) and accelerated partial breast reirradiation (APBrI) for second ipsilateral breast tumour event (2 nd IBTE) is increasingly used as an alternative to mastectomy 1 . Data regarding late toxicity in this context is limited. This study investigates the impact of APBrI technique and dosimetry parameters on toxicity and survival in patients with 2 nd IBTE receiving CT.

Material/Methods:

Patients with 2 nd IBTE who underwent second CT were investigated. 2 nd IBTE was defined as a distinct presentation of breast cancer within the same breast as the 1 st IBTE, with a minimum interval of one year in between both events. Exclusion criteria included in-breast skin and distant metastatic disease, as well as clear indications for mastectomy. CT encompassed WLE with adequate surgical margins and use of clips, in addition to APBrI employing multicatheter interstitial high-dose rate brachytherapy (MIB). Clinical Target Volume (CTV) was delineated following GEC-ESTRO contouring guidelines. The standard prescribed dose was 32 Gy in 8 fractions over 4 days. Patients were followed up post-treatment, with clinical examinations and annual mammograms. The primary objective was 5-year cumulative incidence of late toxicity. Secondary objectives included oncological outcomes (5-year 3 rd IBTE, disease-free and overall survival). The optimal cut-point value of dosimetric constraints for CTV, V100 (cc), V150 (cc), V200 (cc) and Dose non-uniformity ratio (DNR = V150/V100) regarding late toxicity probability were identified using bootstrap method. Survival data was presented graphically as Kaplan Meier curves. Survival rates at various times, median survival and 95%CI of the study population were shown. The survival curves were compared by Log-Rank test.

Results:

Between July 2005 and July 2023, 201 patients received second CT (WLE and APBrI) for 2 nd IBTE. Median follow-up was 49.2 months [44.9 – 59.5]. Median age at 2 nd IBTE was 69 years, with a median time interval of 174 months [20 - 437] between first and second CT. The majority of patients had tumours less than 2 cm in size, were estrogen receptor positive, and classified as low or intermediate GEC-ESTRO APBI risk. Median radiotherapy doses for 1 st and 2 nd IBTE were 50 Gy and 32 Gy, respectively. Late toxicities were observed in 34.8% of patients, primarily grade 1 and grade 2, with low occurrences of grade 3 (5.8%) and grade 4 (1.2%). Cosmetic outcomes were rated as excellent (64.1%), good (27.6%), fair (7.3%), and poor (1%).

Patients with no late complications had on average more needles (p = 0.008), lower CTV (p = 0.003), lower V100 (p = 0.004), lower V150 (p = 0.001), and lower V200 (p < 0.001). DNR, although not significant (p = 0.099) was median