Abstract
Aim: This study aims to evaluate the difference between depth data from an intraoral cone and a conventional irradiation tube calculated using a treatment planning system (TPS), and that measured using an intraoral cone for electron radiotherapy. Background: A TPS is only compatible with conventional irradiation tubes. However, such systems are not suitable for determining dose distributions when a special cone is employed. Materials and Methods: Dose distributions were calculated using the beam data for mounted intraoral cones using a TPS. Then, the dose distribution by field size was calculated for a low-melting-point lead alloy using the beam data for a mounted conventional tube. The calculated data were evaluated against the measured intraoral-cone depth data based on the dose and depth differences. Results: The calculated data for the intraoral cone case did not match the measured data. However, the depth data obtained considering the field size determined for the lead alloy using the conventional tube were close to the measured values for the intraoral cone case. The difference in the depth at which the absorbed dose was 50% of the maximum value of the percentage depth dose was less than ±4 mm for the generalized Gaussian pencil beam convolution algorithm and less than ±1 mm for the electron Monte Carlo algorithm. Conclusion: It was found that the measured and calculated dose distributions were in agreement, especially when then electron Monte Carlo algorithm was used. Thus, the TPS can be employed to determine dose distributions for intraoral cone applications.
Highlights
In external electron radiotherapy, conventional irradiation tubes and metallic cones are employed according to the application requirements, via attachment to the medical linear accelerator outlet
Aim: This study aims to evaluate the difference between depth data from an intraoral cone and a conventional irradiation tube calculated using a treatment planning system (TPS), and that measured using an intraoral cone for electron radiotherapy
The goal of this study is to evaluate the differences between the depth doses calculated from the beam data obtained using an intraoral cone, along with those calculated from the radiation field determined by a low-melting-point lead alloy (LMA) using the TPS applicator beam data, through comparison with the measured depth doses for an intraoral cone, considering electron beams with energies higher than 6 MeV
Summary
Conventional irradiation tubes (applicators) and metallic cones (used in intracavitary [1] and intraoperative [2] irradiation) are employed according to the application requirements, via attachment to the medical linear accelerator (linac) outlet. A TPS is only compatible with applicators added to the linac, and cannot be used to determine the dose distribution when a special cone, such as an intraoral cone, is employed [4]. Slyk and Litoborski [3] have reported that the dose distribution calculated using the generalized Gaussian pencil beam (GGPB) electron algorithm installed in a commercial Eclipse TPS (Varian Medical Systems, Palo Alto, CA, USA) does not correspond to the measured data when an intraoperative metallic cone is used. A commercial implementation based on the macro Monte Carlo (MC) method [5] has been developed and has been made available as the electron MC (eMC) dose calculation algorithm in Eclipse. The eMC implementation yields an extremely large improvement when compared with the commonly used pencil beam convolution algorithm, there are some limitations for electron beam energies ≤ 6 MeV [4] [6] [7]
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