Quality Assurance In Proton Therapy Research Articles

Application of Six Sigma Approach to Improve the Efficiency of Patient-Specific Quality Assurance in Proton Therapy

Application of Six Sigma Approach to Improve the Efficiency of Patient-Specific Quality Assurance in Proton Therapy

SP-0007: Patient specific quality assurance in proton therapy

SP-0007: Patient specific quality assurance in proton therapy

SU‐E‐T‐75: A Simple Technique for Proton Beam Range Verification

Purpose:To develop a measurement‐based technique to verify the range of proton beams for quality assurance (QA).Methods:We developed a simple technique to verify the proton beam range with in‐house fabricated devices. Two separate devices were fabricated; a clear acrylic rectangular cuboid and a solid polyvinyl chloride (PVC) step wedge. For efficiency in our clinic, we used the rectangular cuboid for double scattering (DS) beams and the step wedge for pencil beam scanning (PBS) beams. These devices were added to our QA phantom to measure dose points along the distal fall‐off region (between 80% and 20%) in addition to dose at mid‐SOBP (spread out Bragg peak) using a two‐dimensional parallel plate chamber array (MatriXX™, IBA Dosimetry, Schwarzenbruck, Germany). This method relies on the fact that the slope of the distal fall‐off is linear and does not vary with small changes in energy. Using a multi‐layer ionization chamber (Zebra™, IBA Dosimetry), percent depth dose (PDD) curves were measured for our standard daily QA beams. The range (energy) for each beam was then varied (i.e. ±2mm and ±5mm) and additional PDD curves were measured. The distal fall‐off of all PDD curves was fit to a linear equation. The distal fall‐off measured dose for a particular beam was used in our linear equation to determine the beam range.Results:The linear fit of the fall‐off region for the PDD curves, when varying the range by a few millimeters for a specific QA beam, yielded identical slopes. The calculated range based on measured point dose(s) in the fall‐off region using the slope resulted in agreement of ±1mm of the expected beam range.Conclusion:We developed a simple technique for accurately verifying the beam range for proton therapy QA programs.

Technology for bolus verification in proton therapy

To ensure the conformal depth-dose distribution of a proton beam within a target volume, complex shaped range shifters (so-called boluses), which account for the heterogeneous structure of patient tissue and organs in the beam path, were calculated and manufactured. The precise manufacturing of proton compensators used for patient treatment is a vital step in quality assurance in proton therapy. In this work a software-hardware complex that verifies the quality and precision of bolus manufacturing at the Medico-Technical Complex (MTC) was developed. The boluses consisted of a positioning system with two photoelectric biosensors. We evaluated 20 boluses used in proton therapy of five patients. A total number of 2562 experimental points were measured, of which only two points had values that differed from the calculated value by more than 0.5 mm. The other data points displayed a deviation within ±0.5 mm from the calculated value. The technology for bolus verification developed in this work can be used for the high precision testing of geometrical parameters of proton compensators in radiotherapy.

Daily QA in proton therapy using a single commercially available detector.

We present here a novel method for using a single device in the daily quality assurance (QA) of pencil beam scanning (PBS) proton beams and an improved method for uniform scanning (US). The device can be used to measure the spot position, spot sigma, range, output, collinearity of the X‐ray system and proton beam, and to QA the first scatterers and a number of other imaging and mechanical checks. We have performed the daily QA according to this procedure for more than six months in both a PBS gantry and a US gantry. All of the tests were found to be sensitive and accurate enough to determine if the property being tested is within the tolerance. The output has remained within the ±2% tolerance, with the majority of measurements within ±1%, and the range was within ±0.5mm. The collinearity of the proton beam in both gantries is within the ±1mm tolerance in both X and Y directions for all measurements. A novel procedure to measure the functionality of the first scatterers in the US gantry is included in the QA procedure. It was found to be sensitive enough to pick up the thinnest scatterer of 0.6 mm in both possible failure methods — when it always remains in the beam or in the case when it never goes into the beam. The daily QA procedure presented here can be implemented at PBS or US proton therapy centers with a minimal outlay for equipment and setup time. The procedure can be performed in less than 30 min, and has been found to be accurate and reliable enough for the QA of a proton therapy gantry before patient treatment every day.PACS number: 87.55.Qr

MO‐A‐18C‐01: Proton Therapy I: Basics of Proton Therapy

The goal of this session is to introduce the audience to the physics, dosimetry and treatment planning procedures used in proton therapy. The course material covers the basic physics of proton interaction with matter and physical characteristics of clinical proton beams. It will provide information on proton delivery systems and beam delivery techniques for scattered and scanning proton beams. It will include the requirements for dosimetry measurements and present the equipment needed for commissioning of proton beams for clinical use and quality assurance checks as well as methods used for proton beam calibration and dose verification of patient treatment fields. The session covers the treatment planning strategies for various anatomical sites, methods to address uncertainties in proton therapy and uncertainty mitigation to generate robust treatment plans. Challenges involved in the motion management in proton therapy will also be discussed.Learning Objectives: Gain knowledge on physics, dosimetry, treatment planning and quality assurance for proton therapy. Understand the uncertainties associated with proton therapy and currently used strategies for their mitigation in treatment planning.

WE‐D‐17A‐06: Optically Stimulated Luminescence Detectors as ‘LET‐Meters’ in Proton Beams

Purpose:To demonstrate and evaluate the potential of optically stimulated luminescence (OSL) detectors (OSLDs) for measurements of linear energy transfer (LET) in therapeutic proton beams.Methods:Batches of Al2O2:C OSLDs were irradiated with an absorbed dose of 0.2 Gy in un‐modulated proton beams of varying LET (0.67 keV/μm to 2.58 keV/μm). The OSLDs were read using continuous wave (CW‐OSL) and pulsed (P‐OSL) stimulation modes. We parameterized and calibrated three characteristics of the OSL signals as functions of LET: CW‐OSL curve shape, P‐OSL curve shape and the ratio of the two OSL emission band intensities (ultraviolet/blue ratio). Calibration curves were created for each of these characteristics to describe their behaviors as functions of LET. The true LET values were determined using a validated Monte Carlo model of the proton therapy nozzle used to irradiate the OSLDs. We then irradiated batches of OSLDs with an absorbed dose of 0.2 Gy at various depths in two modulated proton beams (140 MeV, 4 cm wide spread‐out Bragg peak (SOBP) and 250 MeV, 10 cm wide SOBP). The LET values were calculated using the OSL response and the calibration curves. Finally, measured LET values were compared to the true values determined using Monte Carlo simulations.Results:The CW‐OSL curve shape, P‐OSL curve shape and the ultraviolet/blue‐ratio provided proton LET estimates within 12.4%, 5.7% and 30.9% of the true values, respectively.Conclusion:We have demonstrated that LET can be measured within 5.7% using Al2O3:C OSLDs in the therapeutic proton beams used in this investigation. From a single OSLD readout, it is possible to measure both the absorbed dose and LET. This has potential future applications in proton therapy quality assurance, particularly for treatment plans based on optimization of LET distributions.This research was partially supported by the Natural Sciences and Engineering Research Council of Canada.

55: TOF-PET scanner configurations for quality assurance in proton therapy: a patient case study

In order to determine the clinical benefit of positron emission tomography (PET) for dose delivery verification in proton therapy, we performed a patient case study comparing in-situ with in-room time-of-flight (TOF) PET. For the in-situ option, we consider both a (limited-angle) clinical scanner and a dual-head scanner placed close to the patient.

Experimental validation of the TOPAS Monte Carlo system for passive scattering proton therapy

TOPAS (TOol for PArticle Simulation) is a particle simulation code recently developed with the specific aim of making Monte Carlo simulations user-friendly for research and clinical physicists in the particle therapy community. The authors present a thorough and extensive experimental validation of Monte Carlo simulations performed with TOPAS in a variety of setups relevant for proton therapy applications. The set of validation measurements performed in this work represents an overall end-to-end testing strategy recommended for all clinical centers planning to rely on TOPAS for quality assurance or patient dose calculation and, more generally, for all the institutions using passive-scattering proton therapy systems. The authors systematically compared TOPAS simulations with measurements that are performed routinely within the quality assurance (QA) program in our institution as well as experiments specifically designed for this validation study. First, the authors compared TOPAS simulations with measurements of depth-dose curves for spread-out Bragg peak (SOBP) fields. Second, absolute dosimetry simulations were benchmarked against measured machine output factors (OFs). Third, the authors simulated and measured 2D dose profiles and analyzed the differences in terms of field flatness and symmetry and usable field size. Fourth, the authors designed a simple experiment using a half-beam shifter to assess the effects of multiple Coulomb scattering, beam divergence, and inverse square attenuation on lateral and longitudinal dose profiles measured and simulated in a water phantom. Fifth, TOPAS' capabilities to simulate time dependent beam delivery was benchmarked against dose rate functions (i.e., dose per unit time vs time) measured at different depths inside an SOBP field. Sixth, simulations of the charge deposited by protons fully stopping in two different types of multilayer Faraday cups (MLFCs) were compared with measurements to benchmark the nuclear interaction models used in the simulations. SOBPs' range and modulation width were reproduced, on average, with an accuracy of +1, -2 and ±3 mm, respectively. OF simulations reproduced measured data within ±3%. Simulated 2D dose-profiles show field flatness and average field radius within ±3% of measured profiles. The field symmetry resulted, on average in ±3% agreement with commissioned profiles. TOPAS accuracy in reproducing measured dose profiles downstream the half beam shifter is better than 2%. Dose rate function simulation reproduced the measurements within ∼2% showing that the four-dimensional modeling of the passively modulation system was implement correctly and millimeter accuracy can be achieved in reproducing measured data. For MLFCs simulations, 2% agreement was found between TOPAS and both sets of experimental measurements. The overall results show that TOPAS simulations are within the clinical accepted tolerances for all QA measurements performed at our institution. Our Monte Carlo simulations reproduced accurately the experimental data acquired through all the measurements performed in this study. Thus, TOPAS can reliably be applied to quality assurance for proton therapy and also as an input for commissioning of commercial treatment planning systems. This work also provides the basis for routine clinical dose calculations in patients for all passive scattering proton therapy centers using TOPAS.

Evaluation of daily quality assurance for proton therapy at National Cancer Center Hospital East.

It is very important for proton therapy to make and carry out a quality assurance (QA) program. Operators and medical personnel have to avoid any trouble during treatment and provide patients with high quality and reliable treatment. A proton therapy machine consists of an accelerator, gantry and various beam modifying devices. Although QA for proton therapy is complicated and difficult, we tried to realize daily QA for proton therapy. Two main purposes in daily QA are stable operation of the accelerator and reliable control of the irradiation system. In order to determine the daily QA issues, past problems were considered. We made a daily QA program and used it for one year. In this paper, we show the daily QA program and report our results. The daily QA was clearly effective for stable operation of the accelerator and for controlling quality of the irradiation system.

SU-E-T-202: Comprehensive Quality Assurance Procedures for Uniform Scanning Proton Therapy Machines.

Quality assurance (QA) is essential in safe and accurate delivery of radiation therapy. However, QA in proton therapy is challenging due to complicated and often facility-specific beam delivery systems and limited beam time for QA. The purpose of this study is to develop an efficient and comprehensive QA procedure for a multi-room proton therapy center using uniform scanning beams. Our proton therapy center is comprised of a 230 MeV cyclotron, one fixed beam room, two inclined beam rooms, and one gantry room. Uniform scanning is employed exclusively in all treatment rooms. A rfDaily QA3 (Sun Nuclear Inc., Melbourne, Florida) together with home-made devices is used for daily QA. Parallel plane chambers, a multi-layer ionization chamber array (Zebra, IBA dosimetry, Schwarzenbruck, German), and an IC profiler (Sun Nuclear Inc., Melbourne, Florida) are used to QA the characteristics of the uniform scanning beams, including output, range, modulation width, flatness, symmetry, and penumbra, for both monthly and annual QA. QA procedures and acceptance criteria were developed, taking into account the likelihood and potential risk of failure, as well as the available equipment, personnel and other resources. QA procedures and tolerances were developed for daily, monthly and annual QA at our proton therapy center. Daily QA is performed by radiation therapists, and can be completed within 30 minutes for all rooms. Monthly QA and annual QA are performed by physicists, taking about 4 hours and a weekend respectively. Trend analysis was performed for various machine characteristics, such as machine output, range, flatness, and symmetry. QA standards are desired in Radiation Oncology, but not many standards are developed and available for proton therapy. In the mean time, facility-specific QA procedures should be developed based on the equipment failure modes and available resources.

SU-E-T-491: Accuracy of Dose Calculation in Inhomogeneity Region for Proton Radiotherapy

Purpose: The purpose of this study was to evaluate the accuracy of dose calculation in inhomogeneity region provided with Eclipse treatment planning system for proton therapy using the head and neck phantom. Method and Materials: The inhomogenous head and neck phantom for proton therapy quality assurance (QA) was housed in a custom-designed package for efficient evaluation of the measured doses using the different materials and various dosimeters (pinpoint type ionization chamber, TLD- 100, glass dosimeter). All measurements were performed in clinical proton beam at National Cancer Center in Korea. The accuracy of proton therapy dose calculations with pencil-beam algorithms (Varian Eclipse) were also investigated with respect to measurements used in head and neck phantom in the presence of inhomogeneity region (PMMA, air, bony structure). Results: The differences for pencil-beam dose calculation algorithm and measured dose with dosimeters were 3.0% in average target doses (PMMA region). However, the measured results with dosimeters were approximately 7.0% higher than the calculated dose by Eclipse in air region. Conclusion: Our results show that accurate measurements of the inhomogeneity region improve the accuracy of the dose calculation algorithms predicted by the treatment planning system.

SU-GG-T-456: Dosimetric Evaluation of Heterogeneity Correction Algorithm for Proton Therapy

Purpose: The purpose of this study was to evaluate the accuracy of heterogeneity correction algorithm provided with Eclipse treatment planning system for proton therapy using the head and neck phantom. Method and Materials: The heterogeneity head and neck phantom for proton therapyquality assurance (QA) was housed in a custom‐designed package for efficient evaluation of the measured doses using the different materials and various dosimeters (pinpoint type ionization chamber, TLD‐100, glass dosimeter). Before the measurement, we performed a dosimetric test of the glass dosimeter with respect to reproducibility, linearity, fading, angular dependence and dose‐distribution (Bragg peak curve, Spread‐out Bragg curve) for proton therapy beam. All measurements were performed in clinical proton beam at National Cancer Center in Korea. The accuracy of proton therapy dose calculations with pencil‐beam algorithms (Varian Eclipse) were also investigated with respect to measurements used in head and neck phantom in the presence of heterogeneities. Results: The differences for pencil‐beam dose calculation algorithm and measured dose with glass dosimeter was 7.0% in average target doses. Ionization chamber experiments showed approximately 5.0% better agreement than the glass dosimeter. The results of glass dosimeter were substantially higher than the TLD result. Conclusion: Our results show that accurate measurements of the heterogeneity region improve the accuracy of the dose calculation algorithms predicted by the treatment planning system. We also investigate that the glass dosimeter has considerable potential to be used for protondosimetry.

Proton radiography for clinical applications

Proton imaging is not yet applied as a clinical routine, although its advantages have been demonstrated. In the context of quality assurance in proton therapy, proton images can be used to verify the correct positioning of the patient and to control the range of protons. Proton computed tomography (pCT) is a 3D imaging method appropriate for planning and verification of proton radiation treatments, because it allows evaluating the distributions of proton stopping power within the tissues and can be directly utilized when the patient is in the actual treatment position. The aim of the PRoton IMAging experiment, supported by INFN, and the PRIN 2006 project, supported by MIUR, is to realize a proton computed radiography (pCR) prototype for reconstruction of proton images from a single projection in order to validate the technique with pre-clinical studies and, eventually, to conceive the configuration of a complete pCT system. A preliminary experiment performed at the 250 MeV proton synchrotron of Loma Linda University Medical Center (LLUMC) allowed acquisition of experimental data before the completion of PRIMA project's prototype. In this paper, the results of the LLUMC experiment are reported and the reconstruction of proton images of two phantoms is discussed.

An overview of the comprehensive proton therapy machine quality assurance procedures implemented at The University of Texas M. D. Anderson Cancer Center Proton Therapy Center–Houston

The number of proton and carbon ion therapy centers is increasing; however, since the publication of the International Commission on Radiation Units and Measurements report, there has been no dedicated report dealing with proton therapy quality assurance. The purpose of this article is to describe the quality assurance procedures performed on the passively scattered proton therapy beams at The University of Texas M. D. Anderson Cancer Center Proton Therapy Center in Houston. The majorities of these procedures are either adopted from procedures outlined in the American Association of Physicists in Medical Task Group (TG) 40 report or are a modified version of the TG 40 procedures. In addition, new procedures, which were designed specifically to be applicable to the synchrotron at the author's center, have been implemented. The authors' procedures were developed and customized to ensure patient safety and accurate operation of synchrotron to within explicit limits. This article describes these procedures and can be used by others as a guideline for developing QA procedures based on particle accelerator specific parameters and local regulations pertinent to any new facility.

Use of a two‐dimensional ionization chamber array for proton therapy beam quality assurance

Two-dimensional ion chamber arrays are primarily used for conventional and intensity modulated radiotherapy quality assurance. There is no commercial device of such type available on the market that is offered for proton therapy quality assurance. We have investigated suitability of the MatriXX, a commercial two-dimensional ion chamber array detector for proton therapy QA. This device is designed to be used for photon and electron therapy QA. The device is equipped with 32 x 32 parallel plate ion chambers, each with 4.5 mm diam and 7.62 mm center-to-center separation. A 250 MeV proton beam was used to calibrate the dose measured by this device. The water equivalent thickness of the buildup material was determined to be 3.9 mm using a 160 MeV proton beam. Proton beams of different energies were used to measure the reproducibility of dose output and to evaluate the consistency in the beam flatness and symmetry measured by MatriXX. The output measurement results were compared with the clinical commissioning beam data that were obtained using a 0.6 cc Farmer chamber. The agreement was consistently found to be within 1%. The profiles were compared with film dosimetry and also with ion chamber data in water with an excellent agreement. The device is found to be well suited for quality assurance of proton therapy beams. It provides fast two-dimensional dose distribution information in real time with the accuracy comparable to that of ion chamber measurements and film dosimetry.

SU‐FF‐T‐435: Use of a Two‐Dimensional Ionization Chamber Array for Proton Therapy Quality Assurance Checks

Purpose: To investigate the characteristics and the suitability of a two‐dimensional ion chamber array detector for proton therapy quality assurance dosimetry measurements. Methods and Material: Matrixx (Scanditronix‐Wellhofer, Bartlett, TN) is equipped with 32 × 32 parallel plate ion chambers with 4.5 mm diameters and separation of 7.5 mm. The water equivalent thickness (WET) for buildup material was determined by measuring the shift of the location of 90% distal dose point measured using plastic water relative to the depth dose measurement in water tank using a Markus chamber. The measured WET of the build up material was found to be 3.9 ± 0.1 mm. The device was used to obtain the profiles and isodose distribution for the patient portals at different depths. The dose distribution calculated by the Eclipse Treatment Planning Systems (TPS) was imported to Matrixx for comparison purpose. The Matrixx was also used for the determination of absolute dose at a calibration point and the monitor units to be used for patient treatment. Results: The point dose measured by Matrixx was found to be within 1% of that measured by a Framer type chamber. However, the penumbra width for open field for 250 MeV measured with matrix was 1.58 cm as compare to 1.24 cm measured in the water tank using a PTW pinpoint chamber. This significant difference in penumbra width is mainly due to the large inter‐chamber separation in Matrixx. The measured 2‐D dose distribution by Matrixx agreed well with that from TPS. Most of the differences in the separation of a given isodose line were within 2mm. Conclusion: The device is found to be well suited for measurement and verification of proton therapy dose distribution of patient treatment fields. Measurements are in real time, which makes this device more convenient compare to film dosimetry.

BANG®-Polymergeldosimetrie in der Protonentherapie von Augentumoren

The use of polymer gel makes it possible to measure three-dimensional dose distributions of ionizing radiation. Phantoms with BANG-1 and BANG-3 gel were irradiated using a 68 MeV proton beam at the eye tumour therapy beam line of the Hahn Meitner Institute in Berlin. Up to twelve treatment fields could be applied to one gel phantom. The investigations consisted of mono-energetic Bragg curves, spread-out Bragg curves of circular fields (diameter 20 mm), and spread-out Bragg curves of patient fields. Magnetic resonance imaging was used to obtain the gel dose distributions. The results were compared to measurements of a water-phantom ionization chamber. The BANG polymer gels showed a significant quenching of Bragg peaks compared to ionization chamber measurements. The BANG-3 gel was found to be unsuitable for further investigations with 68 MeV protons. The use of BANG-1 allowed the verification of wedge slopes and irregular field forms. On the basis of our experience, polymer gels are well suited for quality assurance in proton therapy in principle.

Quality assurance in protontherapy: a systematic approach in progress at Orsay

The degree of accuracy and reliability required in proton therapy can only be guaranteed if a comprehensive quality assurance (QA) programme is established. Such a programme obviously has common features with general QA in radiotherapy, but some aspects are specific to the use of protons and particularly to the characteristics of each facility. A study is in progress at Orsay to convert a series of quality controls into a systematic quality assurance programme. It includes some basic steps on organisation, setting up a QA committee and QA task groups, organising meetings, policies, procedures, records, qualifications, and determining some examples of tolerance in controls. Among some critical and specific points identified in this process are the combined treatment with photons at different institutions, the specificity of a non-hospital-based and complex facility, the high degree of precision required for the patient setup, and the need to develop in-house basic tools such as the treatment planning system. The inclusion of all the patients in prospective well-defined clinical trials, the comparison with alternative techniques and the radiobiological studies are considered as fundamentals for the QA programme. Present dosimetric and radiobiological intercomparisons between protontherapy centres are considered as partial audits. A study is in progress to establish common dosimetric and clinical protocols, radiobiological models and dose and volume specifications. In spite of the differences between the existing facilities, it should also be possible to obtain international consensus on general guidelines for a QA programme in proton therapy.