Treatment plan comparison for irradiation of multiple brain metastases with hippocampal avoidance whole brain radiotherapy and simultaneous integrated boost using the Varian Halcyon and the Elekta Synergy platforms

Excerpt

Around 20–40% of all cancer patients develop brain metastases during their course of disease which is associated with significant morbidity and mortality [1]. Brain metastases mostly occur in patients with lung cancer, breast cancer and melanoma [2]. The incidence generally slightly increased over the last years and especially the number of patients with multiple brain metastases is increasing [3]. The treatment of limited brain metastases is well defined in clinical guidelines and comprises upfront radiosurgery, resection followed by adjuvant radiosurgery/fractionated stereotactic radiotherapy or systemic therapy in cancer with a targetable driver mutation or excellent response to immunotherapy such as melanoma [4]. In contrast, the treatment of patients with multiple brain metastases is more challenging and a clear recommendation is not given within the guidelines [3]. There are two competing major radiotherapy policies for the treatment of multiple brain metastases—whole brain irradiation (WBRT) on the one hand and radiosurgery (SRS) on the other hand. Stereotactic radiotherapy or radiosurgery approaches apply a high dose to the tumor with a steep dose fall off to the surrounding tissue to spare as much as possible healthy brain tissue. Nevertheless, microscopic tumor spread within the brain is more likely with multiple brain metastases which can be drawn from a higher risk of loco-regional (distant brain) failure with SRS in multiple brain metastases [5, 6]. Whole-brain radiotherapy concepts have not been displaced by stereotactic radiotherapy in multiple brain metastases and yield the benefit of treating microscopic metastatic spread. However, the irradiation of the whole brain comes along with a detrimental neurocognitive decline with damaged neural stem cells within the hippocampal being the most relevant cause [7, 8]. Therefore hippocampal radiotherapy techniques have been introduced to spare the stem cells within the hippocampal area [9]. Hippocampus avoidance whole-brain irradiation (HA-WBRT) with simultaneous integrated boost (SIB) is the most sophisticated concept within whole-brain irradiation concepts, where in addition to hippocampal sparing and prophylactic dose to the healthy brain, dose escalation in the gross tumor volume is pursued to improve local control [10]. …