Pre-treatment quality assurance for stereotactic cranial plans

Abstract

Objective To report the Results of Quality Assurance (QA) dose planning for stereotactic cranial treatments delivered with Dynamic Conformal Arcs (DCA) or Volumetric Modulated Arc Therapy (VMAT) techniques. Material and methods A total of 26 dose plans, 19 patients with DCA from Iplan® (Brainlab) and 7 patients with VMAT from EclipseTM (Varian), were verified with different QA methods. Plans were delivered on a Novalis TX unit. Each treatment field was checked for absolute isocenter dose using a Lucy® 3D QA Phantom (Standard Imaging) and a Diamond chamber (PTW). GafchromicTM EBT3 film dosimetry (ISP) was selected to verify total dose plans in the 2D axial planes. A flatbed RGB scanner (Epson Expression 10,000 XL) was used to digitize the films and the RIT software to analyze the data (gamma criteria 1 mm and 3%). Relative dose analysis was performed normalized at isocenter. Same criteria were used for Portal dosimetry (PD) verifications of VMAT plans. Finally for DCA plans, manual independent Monitor Units Calculation (MUC) number was implemented. Results Absolute isocenter dose measurements: the mean dose ratio (measured/expected) was for DCA (total of 102 fields, dose range 0.3–6 Gy), and for VMAT treatments (a total of 22 treatment fields, and dose range 0.3–1.3 Gy) 1.014 (SD 0.017) and 1.034 (SD 0.031) respectively. Films: the mean gamma agreement index (GAI) was for DCA plans (3 patients) and VMAT plans (3 patients) 99.9% (SD 0.1%) and 93.0 (SD 3.9%) respectively. PD: for VMAT plans (22 fields) the mean GAI was 93.4% (SD 3.4%). MUC: the mean relative difference over 102 treatment fields was 0.02% (SD 1.64%). Conclusion DCA QA results were excellent. VMAT, chosen to better spare organ at risk with its modulation, showed worst results likely for this last feature. HybridArc will next be tested. To report the Results of Quality Assurance (QA) dose planning for stereotactic cranial treatments delivered with Dynamic Conformal Arcs (DCA) or Volumetric Modulated Arc Therapy (VMAT) techniques. A total of 26 dose plans, 19 patients with DCA from Iplan® (Brainlab) and 7 patients with VMAT from EclipseTM (Varian), were verified with different QA methods. Plans were delivered on a Novalis TX unit. Each treatment field was checked for absolute isocenter dose using a Lucy® 3D QA Phantom (Standard Imaging) and a Diamond chamber (PTW). GafchromicTM EBT3 film dosimetry (ISP) was selected to verify total dose plans in the 2D axial planes. A flatbed RGB scanner (Epson Expression 10,000 XL) was used to digitize the films and the RIT software to analyze the data (gamma criteria 1 mm and 3%). Relative dose analysis was performed normalized at isocenter. Same criteria were used for Portal dosimetry (PD) verifications of VMAT plans. Finally for DCA plans, manual independent Monitor Units Calculation (MUC) number was implemented. Absolute isocenter dose measurements: the mean dose ratio (measured/expected) was for DCA (total of 102 fields, dose range 0.3–6 Gy), and for VMAT treatments (a total of 22 treatment fields, and dose range 0.3–1.3 Gy) 1.014 (SD 0.017) and 1.034 (SD 0.031) respectively. Films: the mean gamma agreement index (GAI) was for DCA plans (3 patients) and VMAT plans (3 patients) 99.9% (SD 0.1%) and 93.0 (SD 3.9%) respectively. PD: for VMAT plans (22 fields) the mean GAI was 93.4% (SD 3.4%). MUC: the mean relative difference over 102 treatment fields was 0.02% (SD 1.64%). DCA QA results were excellent. VMAT, chosen to better spare organ at risk with its modulation, showed worst results likely for this last feature. HybridArc will next be tested.