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Workflow of the in Vivo Range Verification in Proton Therapy

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D Samuel

D Samuel1*, M Testa2, J Lee1, E Cascio2, J Orban de Xivry1, B Gottschalk3, E Bentefour4, H Lu2, (1) Universite catholique de Louvain, Louvain-la-neuve, Belgium, (2) Massachussetts General Hospital, Boston, MA, (3) Harvard University, Cambridge, MA, (4) Ion Beam Applications S.A, Louvain-la-Neuve, Belgium.

TH-C-144-9 Thursday 10:30AM - 12:30PM Room: 144

Purpose:
A practical and effective range verification technique for proton treatments is the current need to harness the entire benefits of proton therapy. We developed a new technique to compute the proton beam range in the double scattering mode using the unique time-dose patterns produced by the steps in the range modulator wheel.
We present the integration of the range verification system for treatments of prostate cancer in the AP field configuration with the standard proton therapy workflow. We also present the status of the latest detector design, the various steps of the clinical workflow and the integration of the logical modules for a safe and effective range guided treatment of prostate cancer with AP field.

Methods:
The method uses a matrix of diodes as dosimeters designed to be inserted in the rectum using a rectal balloon. The diodes measure the time-dose patterns for a range-check beam. An analysis routine calculates the WEPL at each diode position and evaluates if the signals are range mixed. The obtained WEPL values are compared with treatment planning for beam range verification and correction and the treatment proceeds. During the treatment, the same detectors are used to monitor the dose to the rectum. The standard workflow for proton therapy is modified to adapt for this range verification procedure by adding the above processes.

Results:
The validation study on a pelvic phantom proved that the range could be verified with an accuracy of 2 mm with just 0.2 % of the fractionated dose. This workflow enables treatment of prostate cancer albeit sparing the rectum.

Conclusion:
The range verification system will improve treatment quality for prostate cancers using AP fields. With the results from clinical trials, we hope this simple method will find uses in other proton treatments where a range verification system would be advantageous.

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