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Title: In vivo dosimetry for gynaecological brachytherapy using a novel position sensitive radiation detector: Feasibility study

Abstract

Purpose: In gynecological radiotherapy with high dose rate (HDR){sup 192}Ir brachytherapy, the treatment complexity has increased due to improved optimization techniques and dose constraints. As a consequence, it has become more important to verify the dose delivery to the target and also to the organs at risk (e.g., the bladder). In vivo dosimetry, where dosimeters are placed in or on the patient, is one way of verifying the dose but until recently this was hampered by motion of the radiation detectors with respect to the source. The authors present a novel dosimetry method using a position sensitive radiation detector. Methods: The prototype RADPOS system (Best Medical Canada) consists of a metal oxide field effect transistor (MOSFET) dosimeter coupled to a position-sensor, which deduces its 3D position in a magnetic field. To assess the feasibility of in vivo dosimetry based on the RADPOS system, different characteristics of the detector need to be investigated. Using a PMMA phantom, the positioning accuracy of the RADPOS system was quantified by comparing position readouts with the known position of the detector along the x and y-axes. RADPOS dose measurements were performed at various distances from a Nucletron{sup 192}Ir source in a PMMA phantom to evaluatemore » the energy dependence of the MOSFET. A sensitivity analysis was performed by calculating the dose after varying (1) the position of the RADPOS detector to simulate organ motion and (2) the position of the first dwell position to simulate errors in delivery. The authors also performed an uncertainty analysis to determine the action level (AL) that should be used during in vivo dosimetry. Results: Positioning accuracy is found to be within 1 mm in the 1-10 cm range from the origin along the x-axis (away from the transmitter), meeting the requirements for in vivo dosimetry. Similar results are obtained for the other axes. The ALs are chosen to take into account the total uncertainty on the measurements. As a consequence for in vivo dosimetry, it is determined that the RADPOS sensor, if placed, for example, in the bladder Foley balloon, would detect a 2 mm motion of the bladder, at a 5% chance of a false positive, with an AL limit of 9% of the dose delivered. The authors found that source position errors, caused by, e.g., a wrong first dwell position, are more difficult to detect; indeed, with our single RADPOS detector, positioned in the bladder, dwell position errors below 5 mm and resulting in a dose error within 10%, could be detected in the tandem but not in the colpostats. A possible solution to improve error detection is to use multiple MOSFETs to obtain multiple dose values. Conclusions: In this study, the authors proposed a dosimetry procedure, based on the novel RADPOS system, to accurately determine the position of the radiation dosimeter with respect to the applicator. The authors found that it is possible to monitor the delivered dose in a point and compare it to the predetermined dose. This allows in principle the detection of problems such as bladder motion/filling or source mispositioning. Further clinical investigation is warranted.« less

Authors:
; ; ; ;  [1]
  1. Department of Radiation Oncology (MAASTRO), GROW-School for Oncology and Developmental Biology, Maastricht University Medical Center, Maastricht 6229 ET (Netherlands)
Publication Date:
OSTI Identifier:
22098808
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 39; Journal Issue: 4; Other Information: (c) 2012 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 62 RADIOLOGY AND NUCLEAR MEDICINE; ACCURACY; BRACHYTHERAPY; DETECTION; DOSE RATES; DOSEMETERS; DOSIMETRY; ENERGY DEPENDENCE; ERRORS; GYNECOLOGY; IRIDIUM 192; MAGNETIC FIELDS; MOSFET; PATIENTS; PHANTOMS; POSITION SENSITIVE DETECTORS; RADIATION DOSES; READOUT SYSTEMS; SENSITIVITY ANALYSIS; SENSORS

Citation Formats

Reniers, B., Landry, G., Eichner, R., Hallil, A., Verhaegen, F., Best Medical Canada, Ottawa K2K 0E4, and Department of Radiation Oncology. In vivo dosimetry for gynaecological brachytherapy using a novel position sensitive radiation detector: Feasibility study. United States: N. p., 2012. Web. doi:10.1118/1.3693049.
Reniers, B., Landry, G., Eichner, R., Hallil, A., Verhaegen, F., Best Medical Canada, Ottawa K2K 0E4, & Department of Radiation Oncology. In vivo dosimetry for gynaecological brachytherapy using a novel position sensitive radiation detector: Feasibility study. United States. https://doi.org/10.1118/1.3693049
Reniers, B., Landry, G., Eichner, R., Hallil, A., Verhaegen, F., Best Medical Canada, Ottawa K2K 0E4, and Department of Radiation Oncology. 2012. "In vivo dosimetry for gynaecological brachytherapy using a novel position sensitive radiation detector: Feasibility study". United States. https://doi.org/10.1118/1.3693049.
@article{osti_22098808,
title = {In vivo dosimetry for gynaecological brachytherapy using a novel position sensitive radiation detector: Feasibility study},
author = {Reniers, B. and Landry, G. and Eichner, R. and Hallil, A. and Verhaegen, F. and Best Medical Canada, Ottawa K2K 0E4 and Department of Radiation Oncology},
abstractNote = {Purpose: In gynecological radiotherapy with high dose rate (HDR){sup 192}Ir brachytherapy, the treatment complexity has increased due to improved optimization techniques and dose constraints. As a consequence, it has become more important to verify the dose delivery to the target and also to the organs at risk (e.g., the bladder). In vivo dosimetry, where dosimeters are placed in or on the patient, is one way of verifying the dose but until recently this was hampered by motion of the radiation detectors with respect to the source. The authors present a novel dosimetry method using a position sensitive radiation detector. Methods: The prototype RADPOS system (Best Medical Canada) consists of a metal oxide field effect transistor (MOSFET) dosimeter coupled to a position-sensor, which deduces its 3D position in a magnetic field. To assess the feasibility of in vivo dosimetry based on the RADPOS system, different characteristics of the detector need to be investigated. Using a PMMA phantom, the positioning accuracy of the RADPOS system was quantified by comparing position readouts with the known position of the detector along the x and y-axes. RADPOS dose measurements were performed at various distances from a Nucletron{sup 192}Ir source in a PMMA phantom to evaluate the energy dependence of the MOSFET. A sensitivity analysis was performed by calculating the dose after varying (1) the position of the RADPOS detector to simulate organ motion and (2) the position of the first dwell position to simulate errors in delivery. The authors also performed an uncertainty analysis to determine the action level (AL) that should be used during in vivo dosimetry. Results: Positioning accuracy is found to be within 1 mm in the 1-10 cm range from the origin along the x-axis (away from the transmitter), meeting the requirements for in vivo dosimetry. Similar results are obtained for the other axes. The ALs are chosen to take into account the total uncertainty on the measurements. As a consequence for in vivo dosimetry, it is determined that the RADPOS sensor, if placed, for example, in the bladder Foley balloon, would detect a 2 mm motion of the bladder, at a 5% chance of a false positive, with an AL limit of 9% of the dose delivered. The authors found that source position errors, caused by, e.g., a wrong first dwell position, are more difficult to detect; indeed, with our single RADPOS detector, positioned in the bladder, dwell position errors below 5 mm and resulting in a dose error within 10%, could be detected in the tandem but not in the colpostats. A possible solution to improve error detection is to use multiple MOSFETs to obtain multiple dose values. Conclusions: In this study, the authors proposed a dosimetry procedure, based on the novel RADPOS system, to accurately determine the position of the radiation dosimeter with respect to the applicator. The authors found that it is possible to monitor the delivered dose in a point and compare it to the predetermined dose. This allows in principle the detection of problems such as bladder motion/filling or source mispositioning. Further clinical investigation is warranted.},
doi = {10.1118/1.3693049},
url = {https://www.osti.gov/biblio/22098808}, journal = {Medical Physics},
issn = {0094-2405},
number = 4,
volume = 39,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2012},
month = {Sun Apr 15 00:00:00 EDT 2012}
}