gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

Dosimetric characteristics of the OneDose MOSFET decector for in-vivo dosimetry in proton beam therapy (PBT)

Meeting Abstract

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  • M. Wolanski - Midwest Proton Radiotherapy Institute, Bloomington, USA
  • C.-W. Cheng - Midwest Proton Radiotherapy Institute, Bloomington, USA
  • A. Gautam - Midwest Proton Radiotherapy Institute, Bloomington, USA
  • I. Das - Radiation Oncology, Indiana University, Indianapolis, USA

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog224

DOI: 10.3205/09ptcog224, URN: urn:nbn:de:0183-09ptcog2245

Published: September 24, 2009

© 2009 Wolanski et al.
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Outline

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Introduction: PBT is a precise radiotherapy modality due to its unique characteristic. However, in-vivo dosimetry, which is a standard of practice for treatment QA in external beams, is rarely performed in PBT. The single use OneDose MOSFET detector, with 1mm diameter and flexible design has gained popularity in in-vivo dosimetry in external beams. In this study, we investigate the dosimetric characteristics of OneDose for similar application in PBT.

Materials and methods: The dosimetric characteristics of the MOSFET detector are investigated in a solid water (or polystyrene) phantom: reproducibility, inter and intra batch variation, consistency, linearity with dose and dose rate, energy dependence, angular dependence, field size dependence and linear energy transfer (LET) dE/dx of the medium. Response of the OneDose results are compared with ion chamber (IC) measurements under identical conditions.

Results: For 10 repeated measurements, the dose variation is within ±0.5% of the averaged value indicating high manufacturing quality. Analysis of the data showed that OneDose is linear with dose in the range 25-500 MU and independent of the dose rate (50–400 cGy/min). The dose measured in air with OneDose and also at both the entrance and exit surface of a polystyrene phantom normalized to the corresponding IC measurements produced the same result (±2.0%), indicating that OneDose does not depend on the medium. The slight energy dependence of OneDose (Figure 1 [Fig. 1]) could be accounted for with a regression technique. The detector exhibits an angluar dependence within ±2.0% (Figure 2 [Fig. 2]). This could be due to the output variation of the proton beam with gantry angle and an inherent characteristic of the solid state detector. There is also an anisotropic dose response of detector orientation relative to the incident beam (Figure 3 [Fig. 3]). The dose response variation with dE/dx (Figure 4 [Fig. 4]) indicates that OneDose is best suited for surface dose measurements and at shallow depths at which the variation is modest.

Conclusion: The OneDose detector exhibits dosimetric characteristics suitable for in-vivo patient dosimetry in PBT. The detector should be calibrated to allow correction for energy and angular variation in its clinical application. The small detector size and its relatively flexible design allow dose measurement to be performed on a curved surface or in small cavities, which would be otherwise difficult with the conventional radiation detectors.

Acknowledgement: The authors would like to thank Secil Technologies for supplying the detectors for the study.