Abstract
In this study, we have characterized the efficiency of an Elekta linac in the delivery of gated radiotherapy. We have explored techniques to reduce the beam‐on delay and to improve the delivery efficiency, and have investigated the impact of frequent beam interruptions on the dosimetric accuracy of gated deliveries. A newly available gating interface was installed on an Elekta Synergy. Gating signals were generated using a surface mapping system in conjunction with a respiratory motion phantom. A series of gated deliveries were performed using volumetric modulated arc therapy (VMAT) treatment plans previously generated for lung cancer patients treated with stereotactic body radiotherapy. Baseline values were determined for the delivery times. The machine was then tuned in an effort to minimize beam‐on delays and improve delivery efficiency. After that process was completed, the dosimetric accuracy of the gated deliveries was evaluated by comparing the measured and the planned coronal dose distributions using gamma index analyses. Comparison of the gated and the non‐gated deliveries were also performed. The results demonstrated that, with the optimal machine settings, the average beam‐on delay was reduced to less than 0.22 s. High dosimetric accuracy was demonstrated with gamma index passing rates no lower than 99.0% for all tests (3%/3 mm criteria). Consequently, Elekta linacs can provide a practical solution for gated VMAT treatments with high dosimetric accuracy and only a moderate increase in the overall delivery time.PACS numbers: 87.56.bd, 87.55.de, 87.55.ne
Highlights
Complex radiotherapy delivery techniques, such as step-and-shoot intensity-modulated radiotherapy (IMRT) and respiratory gated treatments, incorporate numerous beam interruptions that can negatively impact the overall delivery efficiency
Linac performance using this gating interface has been reported in terms of basic dosimetric accuracy, flatness, and symmetry.[12] the beam-on delay associated with each beam interruption and its impact on the delivery efficiency, as well as the dosimetric accuracy, have not been addressed
Baseline values of delivery times and average beam-on delays Table 1 shows the baseline values of the delivery times and the average beam-on delays for three volumetric modulated arc therapy (VMAT) plan deliveries with the binned dose rate (BDR) and the default gun hold-on time of 1.38 s
Summary
Complex radiotherapy delivery techniques, such as step-and-shoot intensity-modulated radiotherapy (IMRT) and respiratory gated treatments, incorporate numerous beam interruptions that can negatively impact the overall delivery efficiency. The beam characteristics and dosimetric accuracy of gated beam delivery has been evaluated for Varian,(1,7) Siemens,(4,8) and Brainlab systems.[9,10] For Elekta linacs, gated delivery has focused on forced breath-hold with the Active Breathing Coordinator (ABC) system.[11] The first commercial gating interface for Elekta linacs has recently become available Linac performance using this gating interface has been reported in terms of basic dosimetric accuracy, flatness, and symmetry.[12] the beam-on delay associated with each beam interruption and its impact on the delivery efficiency, as well as the dosimetric accuracy, have not been addressed. These are critical components of gating an Elekta linac, where beam-on delays of up to 4 s have been previously reported.[13]
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