Radiotherapy Planning in Synchronous Bilateral Breast Cancer Irradiation: A Dosimetric Study

Abstract

Background: The large radiation field and surrounding normal structures make treatment planning and dose delivery of synchronous bilateral breast cancer (SBBC) much more difficult than it is for unilateral breast cancer. Intensity-modulated radiation therapy (IMRT) or volumetric-modulated arc therapy (VMAT) can produce acceptable normal tissue sparing while improving target dose coverage compared to 3D-CRT. With this context in mind, we carried out a study to examine the dosimetric variations of IMRT and VMAT techniques using a single isocenter for planning cases of SBBC. Patients and methods: Five patients were considered for this study. All the patients had undergone bilateral mastectomy. Dose prescribed was 50 Gy in 25 fractions. VMAT and IMRT plans were created for each patient. All the plans made were mono-isocentric. Dosimetric data of the target and organs at risk (OAR) were compared. Results: There is a trend towards better PTV coverage using VMAT compared to IMRT (V95 IMRT=94.8720, V95 VMAT=95.8740; P=0.316). VMAT plans significantly improved the dose homogeneity as V105% decreased from 2.886% to 0.312% using VMAT plans (P=0.001). IMRT plans showed trend towards higher lung Dmean and V20Gy than VMAT plans. The irradiation dose to the heart was significantly higher in the IMRT plan than VMAT plan, resulting in Dmean of 15.836 Gy vs 13.580 Gy (P=0.026), V25Gy of 16.498% vs 13.832% (P=0.046) and V30 Gy of 9.774% vs 7.022% (P= 0.043). Conclusion: The single isocentric VMAT technique can be performed conveniently in SBBC. It improves target volume coverage with optimal normal tissue sparing. It is a feasible approach while planning synchronous bilateral breast irradiation.