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Copenhagen, Denmark
Onsite/Online

ESTRO 2022

Session Item

Monday
May 09
16:45 - 17:45
Room D4
Breast
John Maduro, The Netherlands;
Meriem Bohli, Tunisia
3470
Proffered Papers
Clinical
16:45 - 16:55
Breast induration versus irradiated breast volume in the randomized phase III DBCG PBI trial
Mette Skovhus Thomsen, Denmark
OC-0930

Abstract

Breast induration versus irradiated breast volume in the randomized phase III DBCG PBI trial
Authors:

Mette Skovhus Thomsen1, Jan Alsner2, Martin Berg3, Ingelise Jensen4, Mirjana Josipovic5, Ebbe Laugaard Lorenzen6, Esben Yates1, Hanne Melgaard Nielsen7, Erik Hugger Jakobsen8, Lars Stenbygaard9, Anders Navrsted Pedersen5, Mette Holck Nielsen10, Maj-Britt Raaby Jensen11, Jens Overgaard2, Birgitte Vrou Offersen12

1Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark; 2Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark; 3Lillebaelt Hospital, Department of Medical Physics, Vejle, Denmark; 4Aalborg University Hospital, Department of Medical Physics, Aalborg, Denmark; 5Copenhagen University Hospital, Rigshospitalet, Department of Oncology, Copenhagen, Denmark; 6Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark; 7Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 8Lillebaelt Hospital, Department of Oncology, Vejle, Denmark; 9Aalborg University Hospital, Department of Oncology, Aalborg, Denmark; 10Odense University Hospital, Department of Oncology, Odense, Denmark; 11Copenhagen University Hospital, Rigshospitalet, Danish Breast Cancer Group, Copenhagen, Denmark; 12Aarhus University Hospital, Department of Experimental Clinical Oncology and Department of Oncology, Aarhus, Denmark

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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.

Material 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 (V38Gy) was 49.2% (IQR: 40.0-57.9%) (PBI) and 96.4% (IQR: 94.9-97.6%) (WBI). The corresponding figures for V40Gy 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, V42Gy 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 V40Gy. According to the model, a 5% and 10% frequency of induration is found for V40Gy= 79.2mL (98.1-260.3mL; 95% CI) and 410.9mL (279.5-542.2mL; 95% CI), respectively. 

Conclusion

No difference in whole breast volume was observed between the pts in the two arms of the DBCG PBI trial, but the irradiated breast volume was significantly smaller with PBI. The frequency of breast induration grade 2/3 at 3 yrs after RT increased significantly with increasing irradiated breast volume, thus strongly favouring small volumes and PBI.