ESTRO 2024 - Abstract Book

S724

Clinical - Breast

ESTRO 2024

Therapy Oncology Group (RTOG) scale. Statistical analysis was performed with IBM SPSS Statistics version 29 using Mann-Whitney and Chi-Square tests, accordingly. A significance level of 0.05 was considered.

Results:

A total of 101 patients were considered, 54 patients followed 40Gy in 15 fractions schedule and 47 patients 26Gy in 5 fractions. Both groups were homogeneous in their sociodemographic variables. Mean age was 64,9 years old. Carcinoma of the right breast was observed in 53 patients (52,5%) and 48 patients (47,5%) in left breast. NST-type carcinoma was found in 59 patients, 3 with DCIS and 39 patients NST-type carcinoma with associated DCIS. Most patients were T1 stage (83,2 %) with all patients being stage N0M0 at diagnose. The mean tumor size was 12,2 mm with a standard deviation of 8,3; the median closest margin was 5 mm. Forty-four patients had Grade 1, 46 patients Grade 2 and 6 patients had Grade 3 concerning tumor grade. All patients were ER positive, 91 patients were PR positive and 29 HER2 positive. Ninety-seven patients underwent radiotherapy plus hormone therapy with 4 patients having chemotherapy too. The 40Gy in 15 fractions group had a median follow-up of 7,9 years and the 26Gy in 5 fractions group 1 year (11,9 months). There was a statistically significant difference (p=0,03) regarding the laterality of breast cancer, were in the 40Gy in 15 fractions scheme, 57,4% of women had cancer in the right breast while 42,6% had cancer in the left breast, compared to 32,6% and 63,8%, respectively, in the 26Gy in 5 fractions scheme. Patients with a positive HER2 result were more present in the group that received 26Gy in 5 fractions (44,7%) versus 15,1% in the group that received 40Gy in 15 fractions (p=0,001). Concerning acute toxicity in the 40Gy in 15 fractions regiment, 86,5% of patients suffered from G1 erythema, 9,6% from G2 erythema, 9,6% from G1 pigmentation and no patient had breast edema. One patient developed a periareolar fistula. On the other hand, in the 26Gy in 5 fractions regimen, 90% of patients had G1 erythema, 3,3% G2 erythema, 13,3% breast edema and no patient had pigmentation. A patient suffered a worsening of her mastitis after starting radiotherapy, with the need to temporarily suspend treatment. Comparing groups, edema was more present in patients who underwent the 26Gy in 5 fractions (p=0,01). Subacute toxicity to radiotherapy treatment was 13,5% in the 40Gy in 15 fractions scheme. and 6,4% in 26Gy/5 fractions, mainly breast pain and pigmentation. No cardiac or pulmonary toxicity was found. From the 40Gy in 15 fractions regimen one patient revealed distance recurrence (liver metastasis) leading to death through hepatic failure. Two patients died due to unknown cause. One patient was lost to follow-up. Between groups no cases of loco-regional relapse were observed.

Conclusion:

Ultra-hypofractionated partial breast RT seems feasible. Acute adverse effects seen were substantially mild, resolving afterwards, revealing non-inferiority when compared to the standard schedule. The 26 Gy dose level is similar to 40 Gy in 15 fractions in terms of patient-assessed normal tissue effects and clinician-assessed normal