How does knowledge of three-dimensional excision margins following breast conservation surgery impact upon clinical target volume definition for partial-breast radiotherapy?

Kirby, Anna M.; Evans, Philip M.; Nerurkar, Ashutosh Y.; Desai, Saral S.; Krupa, Jaroslaw; Devalia, Haresh; Rovere, Guidubaldo Querci della; Harris, Emma J.; Kyriakidou, Julia; Yarnold, John R.

doi:10.1016/j.radonc.2009.11.002

« Previous Next »Radiotherapy & Oncology
Volume 94, Issue 3 , Pages 292-299, March 2010

How does knowledge of three-dimensional excision margins following breast conservation surgery impact upon clinical target volume definition for partial-breast radiotherapy?

Anna M. Kirby
- Department of Academic Radiotherapy, Royal Marsden NHS Foundation Trust, Sutton, UK
- Corresponding author. Address: Department of Academic Radiotherapy, Royal Marsden NHS Foundation Trust, Downs Road, Sutton, Surrey SM2 5PT, UK.
Philip M. Evans
- Joint Department of Radiotherapy and Physics, Institute of Cancer Research, Sutton, UK
Ashutosh Y. Nerurkar
- Department of Histopathology; and
Saral S. Desai
- Department of Histopathology; and
Jaroslaw Krupa
- Department of Surgery, Royal Marsden NHS Foundation Trust, Sutton, UK
Haresh Devalia
- Department of Surgery, Royal Marsden NHS Foundation Trust, Sutton, UK
Guidubaldo Querci della Rovere
- Department of Surgery, Royal Marsden NHS Foundation Trust, Sutton, UK
- Mr Guidubaldo (Uccio) Querci della Rovere died peacefully in July 2009 after a long illness. The colleagues and friends with whom he collaborated wish to dedicate this manuscript to his memory.
Emma J. Harris
- Joint Department of Radiotherapy and Physics, Institute of Cancer Research, Sutton, UK
Julia Kyriakidou
- Joint Department of Radiotherapy and Physics, Institute of Cancer Research, Sutton, UK
John R. Yarnold
- Department of Academic Radiotherapy, Royal Marsden NHS Foundation Trust, Sutton, UK
- Joint Department of Radiotherapy and Physics, Institute of Cancer Research, Sutton, UK

Received 11 September 2009; received in revised form 5 November 2009; accepted 10 November 2009. published online 07 December 2009.

Abstract

Background and purpose

To compare partial-breast clinical target volumes generated using a standard 15mm margin (CTV_standard) with those generated using three-dimensional surgical excision margins (CTV_tailored30) in women who have undergone wide local excision (WLE) for breast cancer.

Material and methods

Thirty-five women underwent WLE with placement of clips in the anterior, deep and coronal excision cavity walls. Distances from tumour to each of six margins were measured microscopically. Tumour bed was defined on kV-CT images using clips. CTV_standard was generated by adding a uniform three-dimensional 15mm margin, and CTV_tailored30 was generated by adding 30mm minus the excision margin in three-dimensions. Concordance between CTV_standard and CTV_tailored30 was quantified using conformity (CoI), geographical-miss (GMI) and normal-tissue (NTI) indices. An external-beam partial-breast irradiation (PBI) plan was generated to cover 95% of CTV_standard with the 95% isodose. Percentage-volume coverage of CTV_tailored30 by the 95% isodose was measured.

Results

Median (range) coronal, superficial and deep excision margins were 15.0 (0.5–76.0)mm, 4.0 (0.0–60.0)mm and 4.0 (0.5–35.0)mm, respectively. Median CoI, GMI and NTI were 0.62, 0.16 and 0.20, respectively. Median coverage of CTV_tailored30 by the PBI-plan was 97.7% (range 84.9–100.0%). CTV_tailored30 was inadequately covered by the 95% isodose in 4/29 cases. In three cases, the excision margin in the direction of inadequate coverage was ⩽2mm.

Conclusions

CTVs based on 3D excision margin data are discordant with those defined using a standard uniform 15mm TB–CTV margin. In women with narrow excision margins, the standard TB–CTV margin could result in a geographical miss. Therefore, wider TB–CTV margins should be considered where re-excision does not occur.

Keywords: Breast cancer, Partial-breast radiotherapy, Target volume delineation, Histopathological excision margins