ESTRO 2024 - Abstract Book

S611

Clinical - Breast

ESTRO 2024

Patients’ characteristics are shown in Table 1. Group A median age was 69 years (range: 46 – 87) VS 71 years (range: 46 – 84) for Group B (p = 0.16); five PBI (5.6%) and 4 (4.5%) WBI patients had diabetes (p = 0.73); T-stage was 1 for every patient. The most striking difference was the median follow-up: 37 (5 – 109) VS 67 (53 – 155) months for Groups A and B, respectively (p < 0.0001). Radiologically detected fat necrosis occurred in 29 (33.0%) PBI patients, with a median time interval from RT end to fat necrosis diagnosis of 8 months (range: 3 – 31). In the WBI group, fat necrosis rate was 28/88 (31.8%), with a median time of insurgence of 24 months (range: 5 – 66) after the end of RT. Kaplan-Meyers curves for the actuarial rates of fat necrosis after PBI vs WBI are shown in Fig.1. The chi-squared test proved no significant difference between the two groups regarding crude rates of fat necrosis (p = 0.87). The Cox regression resulted in a Hazard Ratio (HR) of 1.5 [95% Confidence Interval: 0.86 to 2.5, p = 0.16] for the fat necrosis rate for PBI vs WBI. The present population of 176 patients does not have the statistical power to detect HRs<2.6 as significant. The results from Cox regression remain inconclusive and a larger population size is needed to clarify the issue ( ∼ 800 patients).

Table 1. Patients Characteristics PBI

WBI

p-value

Total patients

88

88

Age

69 (46 – 87)

71 (46 – 84)

0.16 0.73 0.36

Diabetes

5 (5.6%)

4 (4.5%)

Hypertension

43 (48.9%)

37 (42.0%)

T-stage = 1

88 (100%)

88 (100%)

Hormonal Therapy

66 (75.0%)

77 (87.5%)

0.03

Median Follow-up

37 (5 – 109) months

67 (53 – 155) months

< 0.0001

RT technique

VMAT (100%)

3D (100%)

Fat Necrosis 0.87 PBI: Partial Breast Irradiation; WBI: Whole Breast Irradiation; RT: Radiation Therapy; VMAT: Volumetric Modulated Arc Therapy. 29 (33.0%) 28 (31.8%)