Improving Radiotherapy for Breast Cancer: Identification of the Tumour Bed and Characterisation of Target Volume Changes

Abstract

Improving Radiotherapy for Breast Cancer: Identification of the tumour bed and characterisation of target volume changes. Purpose: This project investigates improvements for breast radiotherapy (RT) by surgical clip insertion for clinical target volume (CTV) delineation, determination of the optimal time for the CT planning scan, and recommendations on the best method for breast imaging on the treatment machine. Methods and Materials: In this ethics approved study forty-two women with early stage breast cancer were split into two cohorts: those with a breast lumpectomy followed by RT and those with breast lumpectomy, then chemotherapy, followed by RT. Radio-opaque clips were surgically placed around the tumour bed to ensure consistent CTV delineation. The CTV volume was measured on serial CT data sets. A systematic review was carried out into on-board kV imaging for breast radiotherapy leading to recommendations on treatment verification imaging. Results: Radio-opaque surgical clips were placed satisfactorily around the tumour cavity using a standard surgical placement protocol. CT imaging demonstrated that the breast boost CTV reduced significantly (p=0.01) and that the initial defined CTV does not predict CTV reduction (p>0.05). CTV reduction correlates to time post-surgery and appears to be independent of treatment modality. For robust radiotherapy techniques such as the traditional tangential technique, megavoltage imaging is adequate. Volumetric kV CBCT is useful for complex breast treatment techniques to accommodate changing target volumes. Conclusion: This work has informed practice in the following areas: routine insertion of surgical clips at the time of lumpectomy, characterization of CTV change over time, recommendations on the optimum time for pre-treatment CT, and recommendations regarding routine on-treatment verification imaging. Keywords: Breast, Radiotherapy, Surgical clips, CTV changes, kV imaging