Presentation Evaluation of scanned beam accuracy using a verification tool of 2D fluence distribution

Tansho, Ryohei  ,  Furukawa, Takuji  ,  Hara, Yousuke  ,  Mizushima, Kota  ,  Saotome, Naoya  ,  Saraya, Yuichi  ,  Shirai, Toshiyuki  ,  Noda, Koji

We have developed a verification tool of a 2D fluence distribution for evaluation of scanned beam accuracy. The 2D fluence distributions of all slices are measured and recorded with a beam position monitor using a multi-wire proportional chamber during irradiation. Using a beam irradiation pattern file, the verification tool calculates the 2D fluence distributions on the plane that the beam position monitor is located. Moreover, the tool evaluates the effect of the accuracy of scanned beam delivery on the 2D fluence distributions by comparing the measured fluence distributions with calculated ones. Fig. 1 shows an example result of the 2D fluence based verification. For the patient-specific QA of this irradiation, it was difficult to evaluate the dose distribution measured by the conventional method using a 2D ionization chamber and a water phantom, since the number of evaluated point was less than 10. We tried to apply the 2D fluence based verification as additional check of scanned beam delivery. The γ-analysis of the 2D fluence distribution of each slice passed the acceptable pass rate of 90% and the result helped us to confirm the beam irradiation accuracy for this patient. The verification tool of 2D fluence distribution is a useful to ensure accurate beam delivery for pencil beam scanning. We will present the method for utilization of this tool in more detail, which includes the calculation method using a pencil beam profile measured with the beam position monitor and the verification method of the measured fluence distribution accuracy.
The 55th Annual Conference of the Particle Therapy Co-operative Group (PTCOG55)

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