3D source tracking and error detection in HDR using two independent scintillator dosimetry systems

Rosales, Haydee M. Linares; Johansen, Jacob; Kertzscher, Gustavo; Tanderup, Kari; Beaulieu, Luc; Beddar, Sam

doi:10.1002/mp.14607

Cited by 17 publications

(25 citation statements)

References 29 publications

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“…The energy dependence of the detector can be expressed as the absorbed dose rate sensitivity given in Equation (6).…”

Section: Energy Dependence Of the Detector Responsementioning

confidence: 99%

“…1 This has led to the development of complex real-time error-detection and treatment-verification algorithms. 2,3 Furthermore, time-resolved IVD has made it possible to perform source tracking [4][5][6][7] and dwell-time verification 7,8 during treatment. For these reasons, timeresolved IVD has great potential for providing clinical staff with valuable information during or after BT treatment.…”

Section: Introductionmentioning

confidence: 99%

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A high‐Z inorganic scintillator–based detector for time‐resolved in vivo dosimetry during brachytherapy

et al. 2021

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Purpose High‐dose rate (HDR) and pulsed‐dose rate (PDR) brachytherapy would benefit from an independent treatment verification system to monitor treatment delivery and to detect errors in real time. This paper characterizes and provides an uncertainty budget for a detector based on a fiber‐coupled high‐Z inorganic scintillator capable of performing time‐resolved in vivo dosimetry during HDR and PDR brachytherapy. Method The detector was composed of a detector probe and an optical reader. The detector probe consisted of either a 0.5 × 0.4 × 0.4 mm3 (HDR) or a 1.0 × 0.4 × 0.4 mm3 (PDR) cuboid ZnSe:O crystal glued onto an optical‐fiber cable. The outer diameter of the detector probes was 1 mm, and fit inside standard brachytherapy catheters. The signal from the detector probe was read out at 20 Hz by a photodiode and a data acquisition device inside the optical reader. In order to construct an uncertainty budget for the detector, six characteristics were determined: (1) temperature dependence of the detector probe, (2) energy dependence as a function of the probe‐to‐source position in 2D (determined with 2 mm resolution using a robotic arm), (3) the signal‐to‐noise ratio (SNR), (4) short‐term stability over 8 h, and (5) long‐term stability of three optical readers and four probes used for in vivo monitoring in HDR and PDR treatments over 21 months (196 treatments and 189 detector calibrations, and (6) dose‐rate dependence. Results The total uncertainty of the detector at a 20 mm probe‐to‐source distance was < 5.1% and < 5.8% for the HDR and PDR versions, respectively. Regarding the above characteristics, (1) the sensitivity of the detector decreased by an average of 1.4%/°C for detector probe temperatures varying from 22 to 37°C; (2) the energy dependence of the detector was nonlinear and depended on both probe‐to‐source distance and the angle between the probe and the brachytherapy source; (3) the median SNRs were 187 and 34 at a 20 mm probe‐to‐source distance for the HDR and PDR versions, respectively (corresponding median source activities of 4.8 and 0.56 Ci, respectively); (4) the detector response varied by 0.6% in 11 identical irradiations over 8 h; (5) the sensitivity of the four detector probes decreased systematically by 0–1.2%/100 Gy of dose delivered to the probes, and random fluctuations of 4.8% in the sensitivity were observed for the three probes used in PDR and 1.9% for the probe used in HDR; and (6) the detector response was linear with dose rate. Conclusion ZnSe:O detectors can be used effectively for in vivo dosimetry and with high accuracy for HDR and PDR brachytherapy applications.

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“…The energy dependence of the detector can be expressed as the absorbed dose rate sensitivity given in Equation (6).…”

Section: Energy Dependence Of the Detector Responsementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A high‐Z inorganic scintillator–based detector for time‐resolved in vivo dosimetry during brachytherapy

et al. 2021

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“…One way to overcome this is to add one or more additional detectors as studied by Lineares Rosales. 30 The choice of alarm threshold could potentially depend on: (a) the positional uncertainty of the ST detection method used, (b) priority between false negatives and false positives, (c) the clinical impact of the detected shifts, and (d) how frequent the shifts of different magnitude happen in patients. This subject of alarm thresholds has recently been discussed by G. Fonseca and J. Johansen et al 5 The presented IVD-based ST method requires the insertion of an additional needle into the patient.…”

Section: Discussionmentioning

confidence: 99%

Accuracy of an in vivo dosimetry‐based source tracking method for afterloading brachytherapy — A phantom study

et al. 2021

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To report on the accuracy of an in vivo dosimetry (IVD)-based source tracking (ST) method for high dose rate (HDR) prostate brachytherapy (BT). Methods: The ST was performed on a needle-by-needle basis. A least square fit of the expected to the measured dose rate was performed using the active dwell positions in the given needle. Two fitting parameters were used to determine the position of each needle relative to the IVD detector: radial (away or toward the detector) and longitudinal (along the axis of the treatment needle). The accuracy of the ST was assessed in a phantom where the geometries of five HDR prostate BT treatments previously treated at our clinic were reproduced. For each of the five treatment geometries, one irradiation was performed with the detector placed in the middle of the implant. Furthermore, four additional irradiations were performed for one of the geometries where the detector was retracted caudally in four steps of 10-15 mm and up to 12 mm inferior of the most inferior active dwell position, which represented the prostate apex. The time resolved dose measurements were retrieved at a rate of 20 Hz using a detector based on an Al 2 O 3 :C radioluminescence crystal, which was placed inside a standard BT needle. Individual calibrations of the detector were performed prior to each of the nine irradiations.Results: Source tracking could be applied in all needles across all nine irradiations. For irradiations with the detector located in the middle region of the implant (a total of 89 needles), the mean AE standard deviation (SD, k = 1) accuracy was −0.01 mm AE 0.38 mm and 0.30 mm AE 0.38 mm in the radial and longitudinal directions, respectively. Caudal retraction of the detector did not lead to reduced accuracy as long as the detector was located superior to the most inferior active dwell positions in all needles. However, reduced accuracy was observed for detector positions inferior to the most inferior active dwell positions which corresponded to detector positions in and inferior to the prostate apex region. Detector positions in the prostate apex and 12 mm inferior to the prostate resulted in mean AE SD (k = 1) ST accuracy of 0.7 mm AE 1 mm and 2.8 mm AE 1.6 mm, respectively, in radial direction, and −1.7 mm AE 1 mm and −2.1 mm AE 1.1 mm, respectively, in longitudinal direction. The largest deviations for the configurations with those detector positions were 2.6 and 5.4 mm, respectively, in the radial direction and −3.5 and −3.8 mm, respectively, in the longitudinal direction. Conclusion: This phantom study demonstrates that ST based on IVD during prostate BT is adequately accurate for clinical use. The ST yields submillimeter accuracy on needle positions as long as the IVD detector is positioned superior to at least one active dwell position in all needles. Locations of the detector inferior to the prostate apex result in decreased ST accuracy while detector locations in the apex region and above are advantageous for clinical applications.

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“…Several groups with well-developed IVD systems have recognised the value of source tracking, either by measuring the individual 3D source positions or by measuring implant movements relative to the in vivo dosimeter. [4][5][6][7][8] Other groups have performed source tracking via other methods of directly measuring the source position with detectors including fluoroscopy, pinhole cameras, magnetic resonance, or 2D arrays. [3,[9][10][11][12][13][14] Some of the source tracking approaches have been demonstrated clinically, [3,7,9,15] or in principle [5,6,8,[10][11][12][13]16].…”

Section: Introductionmentioning

confidence: 99%

MaxiCalc: A tool for online dosimetric evaluation of source-tracking based treatment verification in HDR brachytherapy

2022

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Source tracking is becoming a more widely used approach in HDR brachytherapy treatment verification. While it provides a sensitive method to detect deviations from the treatment plan during delivery, it does not show the clinical significance of any detected changes. By incorporating a tool that calculates volumetric doses and DVH indices from measurements, source tracking systems can be expanded to assess dosimetric significance of any deviations from the plan. Methods: The source tracking dose calculation tool, MaxiCalc, was developed in MATLAB. Validation was performed by comparing doses and DVH indices calculated in MaxiCalc to those calculated by the clinical TPS, for several test plans and 10 clinical plans. Clinical implementation was demonstrated by calculating volumetric doses from a clinical source tracking event.Results: MaxiCalc showed excellent agreement with the clinical TPS for point and volumetric doses (mean difference < 0.01% and 0.1% respectively). MaxiCalc calculates dosimetrically equivalent plans to the TPS with agreement < 0.3% for all DVH indices except PTV V200%. Small differences seen for the clinical source tracking event were consistent with the known tracking uncertainties enabling them to be quantified for clinical decision making. Calculations are fast, enabling real-time use. Conclusions: MaxiCalc is an independent tool that calculates doses and DVH indices from dwells measured with any clinical HDR brachytherapy source tracking system. This extends the capabilities of source tracking systems from determining discrepancies in positions or times during delivery to assessing the dosimetric impact of any detected deviations, allowing for more comprehensive treatment verification and evaluation.

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3D source tracking and error detection in HDR using two independent scintillator dosimetry systems

Cited by 17 publications

References 29 publications

A high‐Z inorganic scintillator–based detector for time‐resolved in vivo dosimetry during brachytherapy

A high‐Z inorganic scintillator–based detector for time‐resolved in vivo dosimetry during brachytherapy

Accuracy of an in vivo dosimetry‐based source tracking method for afterloading brachytherapy — A phantom study

MaxiCalc: A tool for online dosimetric evaluation of source-tracking based treatment verification in HDR brachytherapy

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