ESTRO 2022 - Abstract Book

S821

Abstract book

ESTRO 2022

1. Chiesa S, Hohaus S, Falcinelli L et al. Chemoradiotherapy with temozolomide after high-dose methotrexate for primary CNS lymphoma: a multicenter phase I study of a response-adapted strategy. Ann Hematol. 2020 Oct;99(10):2367- 2375. doi: 10.1007/s00277-020-04220-1. 2. Houillier C, et al Management and outcome of primary CNS lymphoma in the modern era: An LOC network study. Neurology. 2020 Mar10;94(10):e1027-e1039. doi: 10.1212/WNL.0000000000008900. Epub 2020 Jan 6. PMID: 31907289; PMCID: PMC7238921.

Proffered Papers: Breast

OC-0930 Breast induration versus irradiated breast volume in the randomized phase III DBCG PBI trial

M.S. Thomsen 1 , J. Alsner 2 , M. Berg 3 , I. Jensen 4 , M. Josipovic 5 , E.L. Lorenzen 6 , E. Yates 1 , H.M. Nielsen 7 , E.H. Jakobsen 8 , L. Stenbygaard 9 , A.N. Pedersen 5 , M.H. Nielsen 10 , M.R. Jensen 11 , J. Overgaard 2 , B.V. Offersen 12 1 Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark; 2 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark; 3 Lillebaelt Hospital, Department of Medical Physics, Vejle, Denmark; 4 Aalborg University Hospital, Department of Medical Physics, Aalborg, Denmark; 5 Copenhagen University Hospital, Rigshospitalet, Department of Oncology, Copenhagen, Denmark; 6 Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark; 7 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 8 Lillebaelt Hospital, Department of Oncology, Vejle, Denmark; 9 Aalborg University Hospital, Department of Oncology, Aalborg, Denmark; 10 Odense University Hospital, Department of Oncology, Odense, Denmark; 11 Copenhagen University Hospital, Rigshospitalet, Danish Breast Cancer Group, Copenhagen, Denmark; 12 Aarhus University Hospital, Department of Experimental Clinical Oncology and Department of Oncology, Aarhus, Denmark Purpose or Objective The phase III randomized Danish Breast Cancer Group (DBCG) Partial Breast Irradiation (PBI) trial randomized relatively low-risk breast cancer patients (pts) ≥ 60 years (yrs) to PBI versus whole breast irradiation (WBI) with 40Gy in 15 fractions. The primary endpoint was 3-year grade 2/3 induration. Here, we investigate the relation between frequency of breast induration grade 2/3 at 3 yrs after radiation therapy (RT) and irradiated breast volume. Materials and Methods During the accrual period 2009-16, RT plans for the pts were stored in the Danish national RT data bank (DcmCollab). Information about treatment arm and induration 3 yrs after RT was obtained from the DBCG database. Dose-volume histograms and volumes of the delineated structures were collected from DcmCollab. The volume of the whole breast covered with various dose levels was determined for both PBI and WBI pts. For the analysis of frequency of breast induration versus volume of breast irradiated to a certain dose a logistic regression was performed on all patients. Furthermore, the patients in both arms were separated into irradiated breast volume quartiles and the frequency of induration grade 2/3 in each group was determined. Results 865 pts (431 PBI, 434 WBI) with a median age of 66 yrs were included from five Danish centers. RT plans from 820 pts (414 PBI, 406 WBI) were available for analysis. No statistically significant difference (p=0.99) was found for the whole breast volume in the two treatment arms with median and interquartile ranges (IQR) of 711mL (IQR:468-969mL) (PBI) and 665mL (IQR:432-996mL) (WBI). The median dose to the irradiated breast was 25.8Gy (IQR: 22.3-29.2Gy) (PBI) and 40.0Gy (IQR: 40.0-40.1Gy) (WBI). The median breast volume covered with D ≥ 38Gy (V 38Gy ) was 49.2% (IQR: 40.0-57.9%) (PBI) and 96.4% (IQR: 94.9-97.6%) (WBI). The corresponding figures for V 40Gy were 25.0% (IQR: 18.8-32.2%) and 57.8% (53.2-65.8%). The distribution of volume of breast irradiated to D ≥ 40 Gy is shown in fig. 1. The maximum breast dose exceeded 105% of the prescription dose in 36% (PBI) and 58% (WBI) of the pts, however, V 42Gy was less than 2% in 97.6% (PBI) and 91.4% (WBI) of the pts. Breast induration scores 3 yrs after RT were available for 706 pts (353 PBI, 353 WBI) of which 17 PBI and 37 WBI pts had a grade 2/3 induration. Fig. 2 shows the frequency of grade 2/3 induration versus breast volume irradiated to D ≥ 40Gy, demonstrating an increasing frequency of induration with V 40Gy . According to the model, a 5% and 10% frequency of induration is found for V 40Gy = 79.2mL (98.1-260.3mL; 95% CI) and 410.9mL (279.5-542.2mL; 95% CI), respectively.