Retrospective analysis of dosimetry on hippocampal-avoidance whole-brain radiotherapy in a regional hospital

Background: Hippocampal-avoidance whole-brain radiotherapy presents a significant technical challenge in terms of treatment planning in order to spare the hippocampus. To ensure dose homogeneity and precision, the Radiation Therapy Oncology Group (RTOG) 0933 recommends strict dose criteria. To balance the clinical workload with these time-consuming treatments is a challenge. Noncompliance adversely might affect clinical outcomes in cancer patients with brain metastasis. We intend to retrospectively evaluate the quality and dosimetry differences in delivering hippocampal-avoidance whole-brain radiotherapy in a regional hospital. Methods: We retrospectively analyzed cancer patients with brain metastases who were diagnosed between January 2014 and December 2020. Dosimetry parameters were compared in terms of deviation from the RTOG 0933 protocol. Results: We identified 21 eligible cancer patients with brain metastasis who underwent hippocampal-avoidance whole-brain radiotherapy. The patients’ ages ranged from 36 to 81 years (median, 58 years). Sixteen patients (76%) received linear accelerator-based treatment, while five received TomoTherapy. The maximal dose to bilateral hippocampi ranged from 9.2 to 25.8 Gy, with a median of 14.4 Gy. In our cross-modality analysis of the planning target volume (PTV) coverage, linear accelerator planning was comparable to TomoTherapy (P=0.29), and both treatments met the RTOG 0933 criteria in (D_2% ≤37.5 Gy) hotspot evaluation. TomoTherapy was statistically superior to linear accelerator in the minimum PTV dose criteria (D_98% >25 Gy) (P=0.03). Regarding the constraint dose of hippocampi, TomoTherapy tend to outperform linear accelerator treatment (P=0.1). The TomoTherapy technique had the longest delivery time (median: 437 sec), compared to 364 sec for the linear accelerator, with statistical significance (P=0.03). Conclusions: In this study, we presented a dosimetry analysis of hippocampal-avoidance whole-brain radiotherapy in clinical settings. The dilemma does exist in balancing clinical workload with the time-consuming planning, so daily treatment may come at the expense of noncompliance and non-conformity on planning targets. In determining the final plan, the choice of the physician should depend on patient’s clinical situation and institutional facility.