Abstract
BackgroundNavigated transcranial magnetic stimulation (nTMS) of the motor cortex has been successfully implemented into radiotherapy planning by a number of studies. Furthermore, the hippocampus has been identified as a radiation-sensitive structure meriting particular sparing in radiotherapy. This study assesses the joint protection of these two eloquent brain regions for the treatment of glioblastoma (GBM), with particular emphasis on the use of automatic planning.Patients and MethodsPatients with motor-eloquent brain glioblastoma who underwent surgical resection after nTMS mapping of the motor cortex and adjuvant radiotherapy were retrospectively evaluated. The radiotherapy treatment plans were retrieved, and the nTMS-defined motor cortex and hippocampus contours were added. Four additional treatment plans were created for each patient: two manual plans aimed to reduce the dose to the motor cortex and hippocampus by manual inverse planning. The second pair of re-optimized plans was created by the Auto-Planning algorithm. The optimized plans were compared with the “Original” plan regarding plan quality, planning target volume (PTV) coverage, and sparing of organs at risk (OAR).ResultsA total of 50 plans were analyzed. All plans were clinically acceptable with no differences in the PTV coverage and plan quality metrics. The OARs were preserved in all plans; however, overall the sparing was significantly improved by Auto-Planning. Motor cortex protection was feasible and significant, amounting to a reduction in the mean dose by >6 Gy. The dose to the motor cortex outside the PTV was reduced by >12 Gy (mean dose) and >5 Gy (maximum dose). The hippocampi were significantly improved (reduction in mean dose: ipsilateral >6 Gy, contralateral >4.6 Gy; reduction in maximum dose: ipsilateral >5 Gy, contralateral >5 Gy). While the dose reduction using Auto-Planning was generally better than by manual optimization, the radiated total monitor units were significantly increased.ConclusionConsiderable dose sparing of the nTMS-motor cortex and hippocampus could be achieved with no disadvantages in plan quality. Auto-Planning could further contribute to better protection of OAR. Whether the improved dosimetric protection of functional areas can translate into improved quality of life and motor or cognitive performance of the patients can only be decided by future studies.
Highlights
While it has long been observed that brain radiotherapy can cause neurocognitive sequelae [1,2,3,4,5], only recently have technological advances, such as image-guided radiotherapy, intensity- and volumetric-modulated therapy, and improved treatment planning algorithms, i.e., automatic inverse optimization, allowed selective protection of critical brain structures
The aim of our study is to further investigate the possibilities of motor cortex sparing in the treatment of high-grade gliomas
This study could show that combined sparing of the Navigated transcranial magnetic stimulation (nTMS)-defined motor cortex and the hippocampus is feasible in the radiotherapeutic treatment of patients with GBM without compromising target coverage, plan quality metrics, or sparing of traditional organs at risk (OAR), even in a collective of patients where the motor cortex was partially included in the planning target volume (PTV)
Summary
While it has long been observed that brain radiotherapy can cause neurocognitive sequelae [1,2,3,4,5], only recently have technological advances, such as image-guided radiotherapy, intensity- and volumetric-modulated therapy, and improved treatment planning algorithms, i.e., automatic inverse optimization, allowed selective protection of critical brain structures. Increasing focus is being placed on identifying structures vulnerable to radiation-induced deficits and protecting them by selective dose-shaping. Most research in this area has focused on the hippocampus, whose dentate gyrus presents a neuronal progenitor cell niche in the adult brain, meriting particular dose sparing in radiotherapy [6]. Related to cognitive effects, a dose-dependent volume loss has been observed for a variety of cortical and subcortical regions [14,15,16,17]. This study assesses the joint protection of these two eloquent brain regions for the treatment of glioblastoma (GBM), with particular emphasis on the use of automatic planning
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