ESTRO 2024 - Abstract Book

S700

Clinical - Breast

ESTRO 2024

Results:

Twenty patients were analysed. Results show : mean age 55.7years, T stage (T1 n =11, T2 n=7, Tis n=2), N stage (N0 n=11, N1 n=7, Nx n=2), grade ( 1 n=2, 2 n=10, 3 n=5, unknown n=2) , LVI (positive n=7, negative n=13), histology (invasive ductal carcinoma +/- DCIS n=15 , lobular +/- LCIS 1, DCIS only n= 2, other n=2), hormone receptor positive (n=14), triple negative (n=3) , chemotherapy n=11, sentinel lymph node biopsy (n=15), axillary lymph node dissection n=2. PTV volumes as per various delineation methods were as shown in table below;

Delineation protocol

Minimum volume (cm3 )

Maximum volume (cm3 )

Mean (cm3 ) 52.335

volume

Import High Trial;

14.3

167.7

(Clips + seroma) = CTV + 5mm = PTV 2

NRG Trial;

90.6

450.6

203.21

(Clips + seroma) + 1cm= CTV +7mm = PTV 3

Current institutional guidelines

40.2

273.4

104.725

(Clips + seroma) + 5mm = CTV +5mm = PTV

Alternative institutional guidelines

49.1

313.1

125.66

(Clips + seroma) + 5mm = CTV + 7mm = PTV

Correlation with published evidence 4 would suggest long-term risk of fibrosis to vary between approximately 1.5% and 4.5% from varying boost delineation methods.

Conclusion:

Comparison of boost volume delineation methods show significant variation in the volume of breast tissue irradiated. Delineation methods used in published trials produce a four-fold variation in boost PTV volumes. An increase in PTV margin from 5mm to 7mm in institutional protocols resulted in a 20% increase in mean PTV volume. Greater boost volume may increase late toxicity. In addition to choice of delineation protocol, IGRT protocols should be designed to allow minimisation of PTV margin.

Keywords: boost, volume, delineation

References:

1. Bartelink, H. (2015) ‘European Organisation for Research and Treatment of Cancer Radiation Oncology and Breast Cancer Groups. Whole-breast irradiation with or without a boost for patients treated with breast-conserving surgery for early breast cancer: 20-year follow- up of a randomised phase 3 trial.’ Lancet Oncol. 2015 Jan;16(1):47 -56. doi: 10.1016/S1470-2045(14)71156-8. Epub 2014 Dec 9. Erratum in: Lancet Oncol. 2015 Jan;16(1):e6. PMID: 25500422.