Dysphagia Optimized Head and Neck Volumetric Modulated Arc Therapy

Abstract

Purpose/Objective(s)Recently, several reports have demonstrated that certain swallowing structures may be inadvertently damaged during IMRT radiotherapy for head-and-neck (H&N) cancer. Dysphagia optimized IMRT plans have been created with the goal of sparing these swallowing structures. These plans often employ more fields, and require an increased number of monitor units. Recently, linear accelerator control systems have become available that are capable of delivering volumetric modulated arc therapy (VMAT), an arc-based approach to the delivery of IMRT. In this study, we compared dysphagia-optimized VMAT and fixed-field IMRT treatment plans in terms of plan quality and delivery efficiency.Materials/MethodsFive complex head and neck cases involving multiple targets and multiple prescription levels were selected for this study. Fixed-field IMRT treatment plans were generated using the Pinnacle3 planning system. VMAT plans were created using Pinnacle3 in conjunction with our in-house arc-sequencing algorithm that converts optimized intensity maps into deliverable VMAT arcs. The algorithm uses simulated annealing to minimize the discrepancies between the planned and sequenced intensity maps while simultaneously ensuring that the plan does not violate any of the MLC delivery constraints required for VMAT delivery. For each case, plan verifications were performed on an Elekta linear accelerator in our clinic using the Precise Beam Infinity™ control system. Film and ion chamber measurements were obtained to verify the accuracy of the deliveries.ResultsVMAT and 9-field IMRT are each capable of providing highly uniform target doses. On average, 98.9% and 98.8% of the target volumes (PTV1, PTV2, and PTV3) were covered with 95% of the prescribed dose for the fixed field and VMAT plans, respectively. VMAT, however, was able to provide improved critical structure sparing. For example, in the dysphagia optimized plans, VMAT was able to reduce the mean dose to the larynx from 38.9 to 35.9 Gy and the V50 was reduced from 7.0 to 2.1%. With VMAT, the mean dose to the pharyngeal constrictors was reduced from 42.6 to 39.5 Gy and the V50 was reduced from 31.3% to 21.9%. VMAT also provided dose reductions for the parotid glands with the mean dose reduced on average from 15.7 to 13.1 Gy. In terms of delivery efficiency, VMAT reduced the average total monitor units from 1083 to 536. The average delivery time using VMAT was 6.4 minutes as compared with 14.5 minutes for fixed field IMRT.ConclusionsBy utilizing the dosimetric advantages of rotational IMRT, VMAT provides improved dosimetric sparing of the critical structures including the pharyngeal constrictors and larynx while maintaining highly uniform target doses. VMAT also provides significant improvement in the delivery time for these complex treatment plans. Purpose/Objective(s)Recently, several reports have demonstrated that certain swallowing structures may be inadvertently damaged during IMRT radiotherapy for head-and-neck (H&N) cancer. Dysphagia optimized IMRT plans have been created with the goal of sparing these swallowing structures. These plans often employ more fields, and require an increased number of monitor units. Recently, linear accelerator control systems have become available that are capable of delivering volumetric modulated arc therapy (VMAT), an arc-based approach to the delivery of IMRT. In this study, we compared dysphagia-optimized VMAT and fixed-field IMRT treatment plans in terms of plan quality and delivery efficiency. Recently, several reports have demonstrated that certain swallowing structures may be inadvertently damaged during IMRT radiotherapy for head-and-neck (H&N) cancer. Dysphagia optimized IMRT plans have been created with the goal of sparing these swallowing structures. These plans often employ more fields, and require an increased number of monitor units. Recently, linear accelerator control systems have become available that are capable of delivering volumetric modulated arc therapy (VMAT), an arc-based approach to the delivery of IMRT. In this study, we compared dysphagia-optimized VMAT and fixed-field IMRT treatment plans in terms of plan quality and delivery efficiency. Materials/MethodsFive complex head and neck cases involving multiple targets and multiple prescription levels were selected for this study. Fixed-field IMRT treatment plans were generated using the Pinnacle3 planning system. VMAT plans were created using Pinnacle3 in conjunction with our in-house arc-sequencing algorithm that converts optimized intensity maps into deliverable VMAT arcs. The algorithm uses simulated annealing to minimize the discrepancies between the planned and sequenced intensity maps while simultaneously ensuring that the plan does not violate any of the MLC delivery constraints required for VMAT delivery. For each case, plan verifications were performed on an Elekta linear accelerator in our clinic using the Precise Beam Infinity™ control system. Film and ion chamber measurements were obtained to verify the accuracy of the deliveries. Five complex head and neck cases involving multiple targets and multiple prescription levels were selected for this study. Fixed-field IMRT treatment plans were generated using the Pinnacle3 planning system. VMAT plans were created using Pinnacle3 in conjunction with our in-house arc-sequencing algorithm that converts optimized intensity maps into deliverable VMAT arcs. The algorithm uses simulated annealing to minimize the discrepancies between the planned and sequenced intensity maps while simultaneously ensuring that the plan does not violate any of the MLC delivery constraints required for VMAT delivery. For each case, plan verifications were performed on an Elekta linear accelerator in our clinic using the Precise Beam Infinity™ control system. Film and ion chamber measurements were obtained to verify the accuracy of the deliveries. ResultsVMAT and 9-field IMRT are each capable of providing highly uniform target doses. On average, 98.9% and 98.8% of the target volumes (PTV1, PTV2, and PTV3) were covered with 95% of the prescribed dose for the fixed field and VMAT plans, respectively. VMAT, however, was able to provide improved critical structure sparing. For example, in the dysphagia optimized plans, VMAT was able to reduce the mean dose to the larynx from 38.9 to 35.9 Gy and the V50 was reduced from 7.0 to 2.1%. With VMAT, the mean dose to the pharyngeal constrictors was reduced from 42.6 to 39.5 Gy and the V50 was reduced from 31.3% to 21.9%. VMAT also provided dose reductions for the parotid glands with the mean dose reduced on average from 15.7 to 13.1 Gy. In terms of delivery efficiency, VMAT reduced the average total monitor units from 1083 to 536. The average delivery time using VMAT was 6.4 minutes as compared with 14.5 minutes for fixed field IMRT. VMAT and 9-field IMRT are each capable of providing highly uniform target doses. On average, 98.9% and 98.8% of the target volumes (PTV1, PTV2, and PTV3) were covered with 95% of the prescribed dose for the fixed field and VMAT plans, respectively. VMAT, however, was able to provide improved critical structure sparing. For example, in the dysphagia optimized plans, VMAT was able to reduce the mean dose to the larynx from 38.9 to 35.9 Gy and the V50 was reduced from 7.0 to 2.1%. With VMAT, the mean dose to the pharyngeal constrictors was reduced from 42.6 to 39.5 Gy and the V50 was reduced from 31.3% to 21.9%. VMAT also provided dose reductions for the parotid glands with the mean dose reduced on average from 15.7 to 13.1 Gy. In terms of delivery efficiency, VMAT reduced the average total monitor units from 1083 to 536. The average delivery time using VMAT was 6.4 minutes as compared with 14.5 minutes for fixed field IMRT. ConclusionsBy utilizing the dosimetric advantages of rotational IMRT, VMAT provides improved dosimetric sparing of the critical structures including the pharyngeal constrictors and larynx while maintaining highly uniform target doses. VMAT also provides significant improvement in the delivery time for these complex treatment plans. By utilizing the dosimetric advantages of rotational IMRT, VMAT provides improved dosimetric sparing of the critical structures including the pharyngeal constrictors and larynx while maintaining highly uniform target doses. VMAT also provides significant improvement in the delivery time for these complex treatment plans.