Patient-Specific QA of Spot-Scanning Proton Beams Using Radiochromic Film

Chan, Maria F.; Chen, Chin-Cheng; Shi, Chengyu; Li, Jingdong; Tang, Xiaoli; Li, Xiang; Mah, Dennis

doi:10.4236/ijmpcero.2017.62011

Cited by 16 publications

(14 citation statements)

References 39 publications

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“…For intensity-modulated proton therapy (IMPT), several studies have investigated the use of these 2D detector arrays, especially the MatriXX PT detector array (IBA dosimetry, Schwarzenbruck, Germany). [15][16][17][18][19] These studies mainly deal with the general applicability of the detectors for plan verification measurements. A detailed analysis of the applicability of these arrays in IMPT by studying their signal theoretical properties has not been performed so far.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of the applicability of two‐dimensional detector arrays in terms of sampling rate and detector size to verify scanned intensity‐modulated proton therapy plans

et al. 2020

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The introduction of advanced treatment techniques in proton therapy, such as intensitymodulated proton therapy, leads to an increased need for patient-specific quality assurance, especially an accurate treatment plan verification becomes inevitable. In this study, signal theoretical analysis of dose distributions in scanned proton therapy is performed to investigate the feasibility and limits of two-dimensional (2D) detector arrays for treatment plan verification. Methods: 2D detector arrays are characterized by two main aspects: the distance between the single detectors on the array or the sampling frequency; and the lateral response functions of a single detector. The analysis is based on single spots, reference fields and on measured and calculated dose distributions of typical intensity-modulated proton therapy treatment plans with and without range shifter. Measurements were performed with Gafchromic EBT3 films (Ashland Speciality Ingredients G.P., Bridgewater, NJ, USA), the MatriXX PT detector array (IBA Dosimetry, Schwarzenbruck, Germany) and the OCTAVIUS detector array 1500XDR (PTW-Freiburg, Germany) at an IBA Proteus PLUS proton therapy system (Ion Beam Applications, Louvain-la-Neuve, Belgium). Dose calculations were performed with the treatment planning system RayStation 6 or 8 (RaySearch Laboratories, Sweden). Results: The Fourier analysis of the data of the treatment planning system and film measurements show maximum frequencies of 0.06/mm for the plan with range shifter and 0.083/mm for the plan without range shifter. According to the Nyquist theorem, this corresponds to minimum required sampling distances of 8.3 and 6 mm, respectively. By comparison, the sampling distances of the arrays of 7.6 mm (MatriXX PT) and 7.1 mm (OD1500XDR) are sufficient to reconstruct the dose distributions adequately from measurements if range shifters are used, whereas some fields of the plans without range shifter violated the Nyquist requirement. The lateral dose response functions of the single detectors within the arrays have clearly higher frequencies than the treatment plans and thus the volume effect only slightly influences the measurements. Consequently, the array measurements show high gamma passing rates with at least 96 % and a good agreement between the investigated line profiles. Conclusion: The results indicate that the detector dimensions and sampling distances of the arrays are in most studied cases adequate not to substantially influence the measurement process when they are used for analyzing typical intensity-modulated proton therapy treatment plans. Nevertheless, clinical conditions have been identified, for instance treatment plans without range shifter, under which the Nyquist theorem is violated such that a full representation of the dose distributions with the measurements is not feasible. In these cases, analysis of measurements is limited to pointwise comparisons.

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Section: Introductionmentioning

confidence: 99%

“…For intensity‐modulated proton therapy (IMPT), several studies have investigated the use of these 2D detector arrays, especially the MatriXX PT detector array (IBA dosimetry, Schwarzenbruck, Germany) 15–19 . These studies mainly deal with the general applicability of the detectors for plan verification measurements.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the applicability of two‐dimensional detector arrays in terms of sampling rate and detector size to verify scanned intensity‐modulated proton therapy plans

et al. 2020

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“…For the case of single‐field uniform dose deliveries, the dose distribution is optimized to be uniform throughout the planning treatment volume (PTV) resembling a spread out BP along a ray projected normally through the beam's eye view plane. A similar idea was investigated by Chan et al., who proposed a one‐scan protocol with a proton step‐wedge for EBT3 film calibration to be used with patient‐specific QA of spot‐scanning proton beams . However, this study had a limited scope of only investigating a single set of proton range modulations, neglected the intra‐ and interfilm variability, and does not include any investigation into the uncertainty as it reflects upon the final measured dose.…”

Section: Introductionmentioning

confidence: 99%

“…A similar idea was investigated by Chan et al, who proposed a one-scan protocol with a proton step-wedge for EBT3 film calibration to be used with patient-specific QA of spot-scanning proton beams. 27 However, this study had a limited scope of only investigating a single set of proton range modulations, neglected the intra-and interfilm variability, and does not include any investigation into the uncertainty as it reflects upon the final measured dose. There is still currently a need to investigate the calibration of film response in proton beams.…”

Section: Introductionmentioning

confidence: 99%

LET response variability of Gafchromic EBT3 film from a Co calibration in clinical proton beam qualities

et al. 2019

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Purpose To establish a method of accurate dosimetry required to quantify the expected linear energy transfer (LET) quenching effect of EBT3 film used to benchmark the dose distribution for a given treatment field and specified measurement depth. In order to facilitate this technique, a full analysis of film calibration which considers LET variability at the plane of measurement and as a function of proton beam quality is demonstrated. Additionally, the corresponding uncertainty from the process was quantified for several measurement scenarios. Materials and methods The net change in optical density (OD) from a single version of GafchromicTM EBT3 film was measured using an Epson flatbed scanner and NIST‐traceable OD filters. Film OD response was characterized with respect to the known dose to water at the point of measurement for both a NIST‐traceable 60Co beam at the UWADCL and several clinical single‐energy and spread‐out Bragg peak (SOBP) proton beam qualities at the Northwestern Medicine Chicago Proton Center. Increasing proton LET environments were acquired by placing film at increasing depths of Gammex HE Solid Water® whose water‐equivalent thickness was characterized prior to measurement. Results A strong LET dependence was observed near the Bragg peak (BP) consistent with previous studies performed with earlier versions of EBT3 film. The influence of range straggling on the film's LET response appears to have a uniform effect toward the BP regardless of the nominal beam energy. Proximal to this depth, the film's response decreased with decreasing energy at the same dose‐average LET. The opposite trend was observed for depths past the BP. Changes in the SOBP energy modulation showed a linear relationship between the film's relative response and dose‐averaged LET. Relative effectiveness factors (RE) were observed to range between 2%–7% depending on the width of the SOBP and depth of the film. Using the field‐specific calibration technique, a total k = 1 uncertainty in the absorbed dose to water was estimated to range from 4.68%–5.21%. Conclusion While EBT3 film's strong LET dependence is a common problem in proton beam dosimetry, this work has shown that the LET dependence can be taken into account by carefully considering the depth and energy modulation across the film using field‐specific corrections. RE factors were determined with a combined k = 1 uncertainty of 3.57% for SOBP environments and between 3.17%–4.69% for uniform, monoenergetic fields proximal to the distal 80% of the BP.

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“…The EBT3 film was calibrated by a step‐wedge in six‐dose level ranging from 65 cGy (relative biological effectiveness) to 250 cGy (relative biological effectiveness,) at depths of 18, 20, and 24 cm in the Plastic Water. Detailed information on the film calibration was documented in our earlier study …”

Section: Methodsmentioning

confidence: 99%

Monte Carlo calculation of the mass stopping power of EBT3 and EBT‐XD films for protons for energy ranges of 50–400 MeV

Shi

Chen

Mah

et al. 2018

Precision Radiation Oncology

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Objective: The goal of the present study was to calculate the continuous slowing down approximation (CDSA) ranges and derive mass stopping power for EBT3 and EBT-XD films for therapeutic protons energy ranges of 50–400 MeV. Methods: The MCNPX and TRansport of Ions in Matter (TRIM) Monte Carlo codes were used in this study. Utilizing the published International Commission on Radiation Units and Measurement 49 data for the water mass stopping power and CSDA ranges, the mass stopping powers of EBT3 and EBT-XD films were derived using the approximation proposed by Newhauser and Zhang in 2009. Results: The calculated CSDA ranges by MCNPX and TRIM in water were first benchmarked to International Commission on Radiation Units and Measurement 49 published data for water, and found to be within 1% with a 1.4-mm maximum difference. The calculated CSDA values in EBT3 film, compared with the measured CSDA ranges in the EBT3 film, were within 2% of the calculated values with a 3-mm maximum difference. The MCNPX and TRIM results for CSDA ranges agreed with each other to within 2.7% for EBT3 film and 4.4% for EBT-XD film. The overall uncertainties of the MCNPX and TRIM-derived CSDA ranges were 3% and 1.3%, respectively. Conclusion: The mass stopping powers for Gafchromic EBT3 and EBT-XD films were derived.

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Patient-Specific QA of Spot-Scanning Proton Beams Using Radiochromic Film

Cited by 16 publications

References 39 publications

Analysis of the applicability of two‐dimensional detector arrays in terms of sampling rate and detector size to verify scanned intensity‐modulated proton therapy plans

Analysis of the applicability of two‐dimensional detector arrays in terms of sampling rate and detector size to verify scanned intensity‐modulated proton therapy plans

LET response variability of Gafchromic EBT3 film from a Co calibration in clinical proton beam qualities

Monte Carlo calculation of the mass stopping power of EBT3 and EBT‐XD films for protons for energy ranges of 50–400 MeV

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