Planning and delivery of whole brain radiation therapy with simultaneous integrated boost to brain metastases and synchronous limited-field thoracic radiotherapy using helical tomotherapy: a preliminary experience

Lung cancer is the commonest source of brain metastases, which has been traditionally treated with Whole Brain Radiation Therapy (WBRT) with or without focal boost. We herein report our preliminary experience of the planning and delivery of WBRT with Simultaneous Integrated Boost (SIB) to brain metastases along with synchronous limited-field thoracic radiotherapy using Helical TomoTherapy in four patients with lung cancer. All plans were iteratively optimized for maximal target volume coverage and organ-at-risk (OAR) sparing. Standardized dose metrics were used for plan evaluation. All treated regions were imaged with a megavoltage computed tomography (CT) prior to treatment and co-registered with planning CT for image-guidance. Helical TomoTherapy was able to achieve highly conformal and homogeneous dose distributions with excellent OAR sparing both in the brain and the chest. The mean (standard deviation) Dose Homogeneity Index (DHI) and Conformity Index (CI) was 0.06 (0.01) & 0.79 (0.07); 0.04 (0.02) & 0.57 (0.22); and 0.03 (0.02) & 0.77 (0.06) for whole brain, brain metastases, and chest, respectively. The mean monitor units (MU) per fraction and time taken for delivery were 8595 and 9898 MU and 9.8 and 11.3 minutes for the brain and chest plans, respectively. Although the dosimetric equivalence of SIB to a single fraction radiosurgery might still be questionable, our preliminary experience of WBRT with SIB to individual brain metastases using Helical TomoTherapy has been encouraging. In addition, it allows synchronous irradiation of other involved primary or metastatic sites for palliative effect.