Clinical and cosmetic results of breast boost radiotherapy in early breast cancer: a randomized study between electron and photon.

INTRODUCTION: Breast-conserving surgery followed by radiation therapy (RT) to the intact breast is now clearly established as the most acceptable strategy for women with early-stage invasive breast cancer. Recommended techniques for radiotherapy is whole breast irradiation (WBI) followed by boost to the tumor bed.

AIMS: The aim of this study is to compare the modalities of three-dimensional conformal RT (3DCRT) and electron beam therapy as boost in post-lumpectomy patients of early stage breast cancer, following WBI.

MATERIALS AND METHODS: The study comprised of selecting 50 patients of early-stage post-lumpectomy breast cancer. Each patient was initially treated by WBI (40 Gy in 16 fractions) and then followed by tumor bed boost (16 Gy in 8 fractions) with either electron beam therapy or with photon (3DCRT), 25 patients in each arm. Patients were evaluated regularly for acute and chronic radiation toxicities, cosmesis, and pattern of failure. Dosimetric comparison of the plans was also done.

RESULTS: Median age of the patients was 42 years with 66% being premenopausal. Median duration of follow-up was 23 months. In arm A (electrons), two patients had grade III-IV reactions at treatment completion with one patient required RT interruption. Whereas, in arm B (3DCRT), five patients had grade III-IV reactions at treatment completion with three patients required RT interruption. At 6 months and 2 years follow-up, both the arms had almost similar skin, subcutaneous toxicity, and cosmetic score. At the end of 2 years, there were totally four failures among 50 patients, with one locoregional failure in both arms (4%). Dosimetric analysis revealed that conformality (radiation conformity index (RCI)), dose homogeneity index (DHI) and planning target volume (PTV) coverage was significantly better in 3DCRT boost plans. Organs at risk (OAR) dosimetry also revealed significant decrease in ipsilateral lung and heart doses with 3DCRT plans in which tangential or oblique fields were used; and whereas in electron beam, only single direct fields were used.

CONCLUSIONS: Both electrons and 3DCRT can be used for boost planning to the tumor bed in post-lumpectomy patients. Though there was slightly increased acute skin toxicity with 3DCRT photon which led to interruption of therapy, overall cosmesis at 2 years is similar in both modalities. 3DCRT boost is a better option than electrons dosimetrically, considering the fact that conformality; PTV coverage and OAR dosimetry were superior with photons. Thus in centers where electron beam therapy is not available, 3DCRT photon can be used effectively for tumor bed boost.