Water equivalent path length measurement in proton radiotherapy using time resolved diode dosimetry

Gottschalk, B.; Tang, Shuli; Bentefour, El Hassane; Cascio, E; Prieels, D.; Lu, Hsiao‐Ming

doi:10.1118/1.3567498

Cited by 32 publications

(47 citation statements)

References 3 publications

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“…By comparing the WEPL from the actual treatment session to the WEPL from the first day of treatment one can verify if the total cumulated WEPL changes during the course of the treatment have become unacceptable for continuing use of the same treatment plan. The effectiveness of this approach should be first validated against an independent technique for range verification such as prompt gamma camera measurement, 19 , 20 the PET method, (7 – 9) proton radiography, (10) or the in vivo time resolved dose rate method 11 , 12 , 13 , 14 , 15 …”

Section: Discussionmentioning

confidence: 99%

“…It is obvious that using CBCT for detecting any relative changes in patient WEPL along the treatment beam path does not enable direct verification of the proton beam range; however, it can be used to indirectly derive the beam range correction for this particular treatment session. That is because one can quantify the needed range correction by relating the measured relative changes in the WEPL computed using CBCT data to the already base‐lined WEPL from previous treatment sessions where the beam range was actually verified by the PET method 7 , 9 or other in vivo range verification techniques like time resolved dosimetry 12 , 13 , 14 , 15 …”

Section: Introductionmentioning

confidence: 99%

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Using CBCT for pretreatment range check in proton therapy: a phantom study for prostate treatment by anterior–posterior beam

Bentefour

Both

Tang

et al. 2015

J Applied Clin Med Phys

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This study explores the potential of cone‐beam computed tomography (CBCT) for monitoring relative beam range variations due to daily changes in patient anatomy for prostate treatment by anterior proton beams. CBCT was used to image an anthropomorphic pelvic phantom, in eight sessions on eight different days. In each session, the phantom was scanned twice, first at a standard position as determined by the room lasers, and then after it was shifted by 10 mm translation randomly along one of the X, Y, or Z directions. The filling of the phantom bladder with water was not refreshed from day to day, inducing gradual change of the water‐equivalent path length (WEPL) across the bladder. MIMvista (MIM) software was used to perform image registration and re‐alignment of all the scans with the scan from the first session. The XiO treatment planning system was used to perform data analysis. It was found that, although the Hounsfield unit numbers in CBCT have substantially larger fluctuations than those in diagnostic CT, CBCT datasets taken for daily patient positioning could potentially be used to monitor changes in patient anatomy. The reproducibility of the WEPL, computed using CBCT along anterior–posterior (AP) paths across and around the phantom prostate, over a volume of 360 cc, is sufficient for detecting daily WEPL variations that are equal to or larger than 3 mm. This result also applies to CBCT scans of the phantom after it is randomly shifted from the treatment position by 10 mm. limiting the interest to WEPL variation over a specific path within the same CBCT slice, one can detect WEPL variation smaller than 1 mm. That is the case when using CBCT for tracking daily change of the WEPL across the phantom bladder that was induced by spontaneous change in the bladder filling due to evaporation. In summary, the phantom study suggests that CBCT can be used for monitoring day to day WEPL variations in a patient. The method can detect WEPL variation equal to or greater than 3 mm. The study calls for further investigation using the CBCT data from real patients. If confirmed with real patients' data, CBCT could become, in addition to patient setup, a standard tool for proton therapy pretreatment beam range check.PACS number: 87.55.Tm

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Using CBCT for pretreatment range check in proton therapy: a phantom study for prostate treatment by anterior–posterior beam

Bentefour

Both

Tang

et al. 2015

J Applied Clin Med Phys

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“…As shown previously, a statistical approach for analysis can be applied to correlate the dose rate profile per RMW cycle to WEPL 6. The root‐mean‐square (rms) width of each dose rate profile was computed for each detector positional depth, and a relationship between the rms width of the time the diode reads signal and WEPL was established.…”

Section: Methodsmentioning

confidence: 99%

“…Because the detector response is beam‐specific, experimental measurements in homogeneous media have been employed to establish a calibration curve of the response of the detector to WEPL for every SOBP that may be delivered for each given clinical case 4, 5, 6, 7, 8, 9, 10. This process is both tedious, as it necessitates a separate set of measurements for every new ‘scout’ beam (a 1 cm overshoot of the predicted detector depth with a dose of 4 cGy), as well as inconvenient due to the time constraints for access to the clinical beamline.…”

Section: Introductionmentioning

confidence: 99%

Time‐resolved diode dosimetry calibration through Monte Carlo modeling for in vivo passive scattered proton therapy range verification

Toltz

Hoesl

Schuemann

et al. 2017

J Applied Clin Med Phys

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PurposeOur group previously introduced an in vivo proton range verification methodology in which a silicon diode array system is used to correlate the dose rate profile per range modulation wheel cycle of the detector signal to the water‐equivalent path length (WEPL) for passively scattered proton beam delivery. The implementation of this system requires a set of calibration data to establish a beam‐specific response to WEPL fit for the selected ‘scout’ beam (a 1 cm overshoot of the predicted detector depth with a dose of 4 cGy) in water‐equivalent plastic. This necessitates a separate set of measurements for every ‘scout’ beam that may be appropriate to the clinical case. The current study demonstrates the use of Monte Carlo simulations for calibration of the time‐resolved diode dosimetry technique.MethodsMeasurements for three ‘scout’ beams were compared against simulated detector response with Monte Carlo methods using the Tool for Particle Simulation (TOPAS). The ‘scout’ beams were then applied in the simulation environment to simulated water‐equivalent plastic, a CT of water‐equivalent plastic, and a patient CT data set to assess uncertainty.ResultsSimulated detector response in water‐equivalent plastic was validated against measurements for ‘scout’ spread out Bragg peaks of range 10 cm, 15 cm, and 21 cm (168 MeV, 177 MeV, and 210 MeV) to within 3.4 mm for all beams, and to within 1 mm in the region where the detector is expected to lie.ConclusionFeasibility has been shown for performing the calibration of the detector response for three ‘scout’ beams through simulation for the time‐resolved diode dosimetry technique in passive scattered proton delivery.

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“…3,17,35 The measurement of dose offers a simple approach to proton radiography. A range of such techniques have been tested, including using pairs of sloped spread-out Bragg peaks (SOBPs), 36,37 measuring the time-resolved dose from a proton beam passively scattered by a range modulator wheel, 10,38,39 and by measuring the ratio of doses of two pristine Bragg peaks, 40 which is the subject of this work. The technique works as follows: (1) measure depth dose curves in water for two pristine Bragg peaks; (2) determine the "dose ratio curve" for the energy pair by dividing the lower energy by the higher energy; (3) record the dose map beyond an object of unknown thickness/material for each of the two energies and calculate the dose ratio map; and (4) convert to a WET using the dose ratio curve.…”

Section: Introductionmentioning

confidence: 99%

Dose ratio proton radiography using the proximal side of the Bragg peak

et al. 2015

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Purpose: In recent years, there has been a movement toward single-detector proton radiography, due to its potential ease of implementation within the clinical environment. One such single-detector technique is the dose ratio method in which the dose maps from two pristine Bragg peaks are recorded beyond the patient. To date, this has only been investigated on the distal side of the lower energy Bragg peak, due to the sharp falloff. The authors investigate the limits and applicability of the dose ratio method on the proximal side of the lower energy Bragg peak, which has the potential to allow a much wider range of water-equivalent thicknesses (WET) to be imaged. Comparisons are made with the use of the distal side of the Bragg peak. Methods: Using the analytical approximation for the Bragg peak, the authors generated theoretical dose ratio curves for a range of energy pairs, and then determined how an uncertainty in the dose ratio would translate to a spread in the WET estimate. By defining this spread as the accuracy one could achieve in the WET estimate, the authors were able to generate lookup graphs of the range on the proximal side of the Bragg peak that one could reliably use. These were dependent on the energy pair, noise level in the dose ratio image and the required accuracy in the WET. Using these lookup graphs, the authors investigated the applicability of the technique for a range of patient treatment sites. The authors validated the theoretical approach with experimental measurements using a complementary metal oxide semiconductor active pixel sensor (CMOS APS), by imaging a small sapphire sphere in a high energy proton beam. Results: Provided the noise level in the dose ratio image was 1% or less, a larger spread of WETs could be imaged using the proximal side of the Bragg peak (max 5.31 cm) compared to the distal side (max 2.42 cm). In simulation, it was found that, for a pediatric brain, it is possible to use the technique to image a region with a square field equivalent size of 7.6 cm 2 , for a required accuracy in the WET of 3 mm and a 1% noise level in the dose ratio image. The technique showed limited applicability for other patient sites. The CMOS APS demonstrated a good accuracy, with a root-mean-square-error of 1.6 mm WET. The noise in the measured images was found to be σ = 1.2% (standard deviation) and theoretical predictions with a 1.96σ noise level showed good agreement with the measured errors. Conclusions: After validating the theoretical approach with measurements, the authors have shown that the use of the proximal side of the Bragg peak when performing dose ratio imaging is feasible, and allows for a wider dynamic range than when using the distal side. The dynamic range available increases as the demand on the accuracy of the WET decreases. The technique can only be applied to clinical sites with small maximum WETs such as for pediatric brains. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License...

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Water equivalent path length measurement in proton radiotherapy using time resolved diode dosimetry

Cited by 32 publications

References 3 publications

Using CBCT for pretreatment range check in proton therapy: a phantom study for prostate treatment by anterior–posterior beam

Using CBCT for pretreatment range check in proton therapy: a phantom study for prostate treatment by anterior–posterior beam

Time‐resolved diode dosimetry calibration through Monte Carlo modeling for in vivo passive scattered proton therapy range verification

Dose ratio proton radiography using the proximal side of the Bragg peak

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