Investigation of electron boost radiotherapy in patients with breast cancer: Is a direct electron field optimal?

Historically, electron boost dose mainly was delivered by a direct field in adjuvant radiotherapy of breast cancer. In this prospective study, we investigated direct electron field, in terms of optimal coverage of tumour bed volume following localization using ultrasound and surgical clips.

First, for all 24 patients, a breast sonographer drew perimeter of tumour bed on the breast skin. Then an electron boost field was outlined on the demarcated territory, and a lead wire marker compatible with CT scan was placed on the field borders by a 2cm margin. After CT scan simulation, all patients underwent adjuvant whole breast irradiation with 3D-conformal radiotherapy to 50Gy in 25 fractions. Then for boost radiotherapy, lead wire in CT images was countoured as electron boost field. Also, the tumour bed was contoured based on surgical clips (true clinical target volume and true planning target volume). Electron treatment planning was done for electron boost field. Finally isodose coverages for true planning target volume investigated.

On average, 16.68% of clips planning target volume (true planning target volume; range: 0.00 to 95%) received 90% oor more of the prescribed dose when the electron treatment plan was made. Isodose curves does not provide adequate coverage on the tumour bed (clips planning target volume) when electron boost treatment planning was generated for electron boost field (en face electron field). In fact, a part of target (planning target volume-c) is missed and more doses is absorbed in normal tissue.

Electron boost treatment planning (an en face electron field) following tumour bed localization using ultrasonography does not provide an optimized coverage of tumour bed volume.