Abstract
Background and purposeRe-irradiation may be used for recurrent glioblastoma (GBM) patients. In some cases Planning Target Volume (PTV) under-coverage is necessary to meet organ at risk (OAR) constraints. This study aimed to develop a Volumetric Modulated Arc Therapy planning solution for GBM re-irradiation including a means of assessing if target coverage would be achievable and how much PTV ‘cropping’ would be required to meet OAR constraints, based on PTV volume and OAR proximity.Materials and methodsFor 10 PTVs, 360°, 180°, two coplanar 180° and 180° + non-coplanar 45° arc arrangements were compared using 35 Gy in 10 fractions. Using the preferred arrangement, dose fall-off was modelled to determine the separation required between PTV and OAR to ensure OAR dose constraints were met, with data presented graphically. To evaluate the graph as an aid to planning, seven cases with overlap were replanned in two treatment planning systems (TPSs).ResultsThere were no significant dosimetric differences between arc arrangements. 180° was preferred due to shorter treatment times. The graph, which indicated if 95% PTV coverage would be achievable based on PTV volume and OAR proximity, was employed in seven cases to guide planning in two TPSs. Plans were deliverable.ConclusionsRe-irradiation treatment planning can be challenging, especially when PTV under-coverage is necessary. 180° was considered optimal. To assist in the planning process, graphical guidance was produced to inform planners whether PTV under-coverage would be necessary and how much PTV ’cropping’ would be required to meet constraints during optimisation.
Highlights
Glioblastoma (GBM) is the most common brain tumour in adults
Re-irradiation may be employed at recurrence, practice varies in terms of uptake, dose and fractionation and organ at risk (OAR) constraints
There was no significant difference between arc arrangements (Fig. 2) except for estimated delivery time (EDT), which was significantly lower for 1PA (p = 0.005; SM, table E)
Summary
Glioblastoma (GBM) is the most common brain tumour in adults. Following initial treatment, most tumours recur after a median of seven months [1]. Re-irradiation may be employed at recurrence, practice varies in terms of uptake, dose and fractionation and organ at risk (OAR) constraints. To date there has been little published regarding Volumetric Modulated Arc Therapy (VMAT) planning solutions for recurrent GBM. In some cases Planning Target Volume (PTV) under-coverage is necessary to meet organ at risk (OAR) constraints. This study aimed to develop a Volumetric Modulated Arc Therapy planning solution for GBM re-irradiation including a means of assessing if target coverage would be achievable and how much PTV ‘cropping’ would be required to meet OAR constraints, based on PTV volume and OAR proximity. The graph, which indicated if 95% PTV coverage would be achievable based on PTV volume and OAR proximity, was employed in seven cases to guide planning in two TPSs. Plans were deliverable. To assist in the planning process, graphical guidance was produced to inform planners whether PTV under-coverage would be necessary and how much PTV ’cropping’ would be required to meet constraints during optimisation
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