Dirk Wagenaar1, Roel G J Kierkels2, Jeffrey Free2, Johannes A Langendijk2, Stefan Both2, Erik W Korevaar2. 1. Department of Radiation Oncology, University Medical Center Groningen, University of Groningen, the Netherlands. Electronic address: ir.d.wagenaar@gmail.com. 2. Department of Radiation Oncology, University Medical Center Groningen, University of Groningen, the Netherlands.
Abstract
BACKGROUND AND PURPOSE: To assess the potential of composite minimax robust optimization (CMRO) compared to planning target volume (PTV)-based optimization for head and neck cancer (HNC) patients treated with volumetric modulated arc therapy (VMAT). MATERIALS AND METHODS: Ten HNC patients previously treated with a PTV-based VMAT plan were studied. In addition to the PTV-plan a VMAT plan was created with CMRO. For both plans an adapted planning strategy was also investigated, including a plan adaptation during the third week of treatment. The PTV-plans and CMRO-plans (adapted and non-adapted) were evaluated by means of the estimated actually given dose (EAGD). Therefore, the dose was calculated on daily acquired CBCTs, mapped onto the planning CT and accumulated. The plans were compared by dosimetric parameters and normal tissue complication probabilities (NTCPs) for tube feeding dependence, grade 2-4 dysphagia and xerostomia. The accuracy of CBCT-based dose accumulation was further quantified by comparisons of dose accumulation on weekly verification CTs. RESULTS: On average, CMRO significantly increased (1.5 Gy) the D98% of the EAGD to the clinical target volume and significantly decreased the mean dose of the ipsilateral parotid (2.8 Gy), inferior pharynx constrictor muscle (0.7 Gy) and the oral cavity (0.8 Gy). This translated into significantly reduced NTCP of tube feeding dependence (0.9%) and xerostomia (2.8%). The differences in EAGD derived from evaluation CTs or CBCTs were minimal. CONCLUSION: Minimax robust optimization led to improved target coverage and dose reduction in organs at risk in HNC patients treated with VMAT.
BACKGROUND AND PURPOSE: To assess the potential of composite minimax robust optimization (CMRO) compared to planning target volume (PTV)-based optimization for head and neck cancer (HNC) patients treated with volumetric modulated arc therapy (VMAT). MATERIALS AND METHODS: Ten HNC patients previously treated with a PTV-based VMAT plan were studied. In addition to the PTV-plan a VMAT plan was created with CMRO. For both plans an adapted planning strategy was also investigated, including a plan adaptation during the third week of treatment. The PTV-plans and CMRO-plans (adapted and non-adapted) were evaluated by means of the estimated actually given dose (EAGD). Therefore, the dose was calculated on daily acquired CBCTs, mapped onto the planning CT and accumulated. The plans were compared by dosimetric parameters and normal tissue complication probabilities (NTCPs) for tube feeding dependence, grade 2-4 dysphagia and xerostomia. The accuracy of CBCT-based dose accumulation was further quantified by comparisons of dose accumulation on weekly verification CTs. RESULTS: On average, CMRO significantly increased (1.5 Gy) the D98% of the EAGD to the clinical target volume and significantly decreased the mean dose of the ipsilateral parotid (2.8 Gy), inferior pharynx constrictor muscle (0.7 Gy) and the oral cavity (0.8 Gy). This translated into significantly reduced NTCP of tube feeding dependence (0.9%) and xerostomia (2.8%). The differences in EAGD derived from evaluation CTs or CBCTs were minimal. CONCLUSION: Minimax robust optimization led to improved target coverage and dose reduction in organs at risk in HNC patients treated with VMAT.
Authors: A Gutierrez; V Rompokos; K Li; C Gillies; D D'Souza; F Solda; N Fersht; Y-C Chang; G Royle; R A Amos; T Underwood Journal: Acta Oncol Date: 2019-08-20 Impact factor: 4.089