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Study of Basic Dosimetric Beam Characteristics of the New Tomotherapy Delivery System Radixact

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T Romaguera

T Romaguera1*, J Bennouna1 , U Robins1 , N Thakur2 , A Gutierrez1 , (1) Miami Cancer Institute, Miami, FL (2) Accuray, Madison, Wisconsin


SU-I-GPD-T-493 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Study of basic dosimetric beam’s characteristics of the new tomotherapy delivery system “Radixact” compared to its predecessor Tomotherapy H-series beam model.

Methods: “Radixact” has a new redesign LINAC, which allows an increase in its output. The system delivers 1000 cGy/min at isocenter. The beam model used in the twinning process for the Tomotherapy H-series machines was used for the Radixact model. The manufacturer uses solid water measurements during the twinning process. The recommended tests according to the TG-148 where performed during the commissioning process. As part of the commissioning, the beam quality, the output static, dynamic output, longitudinal and transverse profiles where measured for all field sizes. The agreement between the model and the actual beam was assessed using the gamma analysis.The stability of those parameters were followed for six months using the Total Quality Assurance (TQA) software provided by the manufacturer, which uses the on-board detectors to collect beam data. Other independent methods using ionization chambers, cheese phantom and diode arrays were used for comparison.

Results: The result of the water dosimetry done on site during the commissioning, called for an adjustment of 1% in the energy. The percentage depth dose curves (PDDs), the transverse and the longitudinal profiles measured in water show a good agreement with the beam model (gamma values < 0.8). The measurement of the beam quality index PDD (20/10) within the guidelines. The daily output within the tolerance limit of 2%.

Conclusion: This study indicates that the Radixact machine twinned using the actual gold model developed for the previous TomoTherapy H-series machines shows the expected dosimetric characteristics within the specifications.The daily output, beam quality and jaws setting met the TG-148 recommendations during the 6 months evaluation period.

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