Abstract
BackgroundFeasibility testing of a simultaneous sparing approach of hippocampus, hypothalamus and pituitary gland in patients undergoing whole-brain radiotherapy (WBRT) with and without a concomitant boost to metastatic sites.IntroductionCognitive impairment and hormonal dysfunction are common side effects of cranial radiotherapy. A reduced dose application to the patho-physiologically involved functional brain areas, i.e. hippocampus, hypothalamus and pituitary gland, could reduce these common side effects. While hippocampal sparing is already a common practice to improve cognitive outcome, technical experience of additional combined sparing of the hypothalamus/pituitary gland (HT-P) is insufficient.MethodsTwenty patients were included in the planning study. In 11 patients, a total dose of 36 Gy of WBRT (2 Gy per fraction) plus a simultaneous integrated boost (SIB) of 9 Gy (0.5 Gy per fraction, total dose: 45 Gy) to the brain metastases was applied. In 9 patients, prophylactic cranial irradiation (PCI) was simulated with a total dose of 30 Gy (2 Gy per fraction). In both patient cohorts, a sparing approach of the hippocampus and the HT-P area was simulated during WBRT. For all treatment plans, volumetric modulated arc therapy (VMAT) was used. Quality assurance included assessment of homogeneity, conformality and target coverage.ResultsThe mean dose to the hippocampus and HT-P region was limited to less than 50% of the prescribed dose to the planning target volume (PTV) in all treatment plans. Dose homogeneity (HI) of the target volume was satisfying (median HI = 0.16 for WBRT+SIB and 0.1 for PCI) and target coverage (conformation number, CN) was not compromised (median CN = 0.82 for SIB and 0.86 for PCI).ConclusionSimultaneous dose reduction to the hippocampus and the HT-P area did not compromise the PTV coverage in patients undergoing WBRT+SIB or PCI using VMAT. While the feasibility of the presented approach is promising, prospective neurologic, endocrine outcome and safety studies are required.
Highlights
Cognitive impairment and hormonal dysfunction are common side effects of cranial radiotherapy
The mean dose to the hippocampus and hypothalamus/pituitary gland (HT-P) region was limited to less than 50% of the prescribed dose to the planning target volume (PTV) in all treatment plans
In line with this finding, Gondi et al were able to show that conformal avoidance of the hippocampus during whole-brain radiotherapy (WBRT) was associated with preservation of memory function and quality of life (QoL), as compared to a non-sparing historical series [9]
Summary
Cognitive impairment and hormonal dysfunction are common side effects of cranial radiotherapy. A reduced dose application to the patho-physiologically involved functional brain areas, i.e. hippocampus, hypothalamus and pituitary gland, could reduce these common side effects. Apart from neurocognitive decline, another common sequela of cranial radiation therapy is functional endocrine impairment due to critical doses to the hypothalamus and the pituitary gland. It has been shown that hormonal changes can occur after applied doses as low as 18 Gy in patients with radiotherapy to head and neck cancers and brain tumors [13]. This dichotomy led us to investigate a combined sparing approach involving both the hippocampal and the hypothalamus/pituitary gland (HT-P) area during WBRT. In our planning study we examined the feasibility of such an approach using volumetric modulated arc therapy (VMAT)
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