Intensity modulated proton arc therapy via geometry-based energy selection for ependymoma
Cao Wen-huaYupeng LiXiaodong ZhangFalk PoenischPablo YepesNarayan SahooDavid R. GrosshansSusan L. McGovernG. Brandon GunnSteven J. FrankXiaorong Zhu
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We developed a novel method of creating intensity modulated proton arc therapy (IMPAT) plans that uses computing resources efficiently and may offer a dosimetric benefit for patients with ependymoma or similar tumor geometries. Our IMPAT planning method consists of a geometry-based energy selection step with major scanning spot contributions as inputs computed using ray-tracing and single-Gaussian approximation of lateral spot profiles. Based on the geometric relation of scanning spots and dose voxels, our energy selection module selects a minimum set of energy layers at each gantry angle such that each target voxel is covered by sufficient scanning spots as specified by the planner, with dose contributions above the specified threshold. Finally, IMPAT plans are generated by robustly optimizing scanning spots of the selected energy layers using a commercial proton treatment planning system. The IMPAT plan quality was assessed for four ependymoma patients. Reference three-field IMPT plans were created with similar planning objective functions and compared with the IMPAT plans. In all plans, the prescribed dose covered 95% of the clinical target volume (CTV) while maintaining similar maximum doses for the brainstem. While IMPAT and IMPT achieved comparable plan robustness, the IMPAT plans achieved better homogeneity and conformity than the IMPT plans. The IMPAT plans also exhibited higher relative biological effectiveness (RBE) enhancement than did the corresponding reference IMPT plans for the CTV in all four patients and brainstem in three of them. The proposed method demonstrated potential as an efficient technique for IMPAT planning and may offer a dosimetric benefit for patients with ependymoma or tumors in close proximity to critical organs. IMPAT plans created using this method had elevated RBE enhancement associated with increased linear energy transfer.Abstract Introduction: In the recent years, some publications (mainly from one group of authors) have dealt with the effectiveness of proton–boron fusion therapy (PBFT). This theory is based on the Q-value of three produced α particles in the reaction of protons with boron ( 11 B). They claim that this reaction significantly increases the absorbed dose in the target volume. However, the current study would re-evaluate their method to show if PBFT is really effective. Methods and materials: A parallel 80-MeV proton beam was irradiated on a water medium in a cubic boron uptake region (BUR). The two-dimensional dose distribution and percentage depth dose of protons, alphas and all particles were calculated using tally F6 and mesh-tallies by Monte Carlo N Particle Transport code. Results: The results not only showed that the dose enhancement in BUR is neglectable but also the higher density of BUR in comparison with water led to decrement of dose in this region. Because of low cross section of boron for proton beam (<100 mb), the α particles’ dose is 1,000 times lower than the proton dose. Conclusions: The physical aspects and the simulation results did not show any effectiveness of the PBFT for proton therapy dose enhancement.
Particle Therapy
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Protons deposit the majority of their energy at the end of their lifetimes, characterized by a Bragg peak. This makes proton therapy a viable way to target cancerous tissue while minimizing damage to surrounding healthy tissue. However, in order to utilize this high precision treatment, greater accuracy in tumor imaging is needed. An approximate uncertainty of ±3% exists in the current practice of proton therapy due to conversions between x-ray and proton stopping power. An imaging system utilizing protons has the potential to eliminate that inaccuracy. This study focuses on developing a proof of concept proton-imaging detector built with a high-density glass scintillator.
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Proton treatment planning involves many issues that affect the accuracy and robustness of treatment planning and delivery. Some issues such as patient setup uncertainty and CT number calibration are common with photon planning but have potentially greater effects on the treatment plan simulation and delivery for proton. Other issues such as range uncertainty and LET and RBE variations are unique to particle therapy. The complications of proton treatment planning have been well documented in the literature but there are multiple planning methods developed by clinics to reduce or avoid proton dosimetry errors in treatment delivery. Additionally, error reduction methods are dependent upon the delivery Method: scattering or scanning, single-field optimization or multi-field optimization. This educational session will discuss the documented proton treatment planning issues and the methods developed in three different clinical centers to minimize or eliminate the errors associated with the issues for various treatment sites and proton treatment modalities.1. Understand the issues associated with proton treatment planning and the effects of range uncertainty, LET variations, and setup uncertainties. 2. Understand the differences of photon and proton treatment planning issues. 3. Understand the methods developed to reduce errors in proton treatment planning and delivery at three different centers.
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This study presents the clinical experiences of the New York Proton Center in employing proton pencil beam scanning (PBS) for the treatment of lung stereotactic body radiation therapy. It encompasses a comprehensive examination of multiple facets, including patient simulation, delineation of target volumes and organs at risk, treatment planning, plan evaluation, quality assurance, and motion management strategies. By sharing the approaches of the New York Proton Center and providing recommendations across simulation, treatment planning, and treatment delivery, it is anticipated that the valuable experience will be provided to a broader proton therapy community, serving as a useful reference for future clinical practice and research endeavors in the field of stereotactic body proton therapy for lung tumors.
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The goal of this session is to introduce the audience to the physics, dosimetry, treatment planning techniques, and quality assurances (QA) procedures used in proton therapy. The course material covers the 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 double scattering (DS), uniform scanning (US), and pencil beam scanning (PBS). The session covers the treatment planning strategies used in DS, US, and PBS 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. It will also include the methodology for proton beam dosimetry for clinical commissioning, beam calibration, and quality assurance checks. Learning Objectives: Gain knowledge on physics, dosimetry, and treatment planning for proton therapy including intensity modulated proton therapy. Be acquainted with the procedures involved in machine and patient treatment field specific QA. Understand the uncertainties associated with proton therapy and currently used strategies for their mitigation in treatment planning.
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Proton therapy planning strategies differ in many aspects from traditional planning done for photon treatments. Both passive scattered and scanning proton treatment planning systems and protocols must account for proton specific uncertainties to deliver high fidelity plans to the patient. While many uncertainties have been discussed in the literature, clinical implementations of proton treatment planning systems require adequate procedures to address uncertainties. Some uncertainties are constant between passive scattered and scanning systems but other uncertainties, due to the differences in beam delivery methods, necessitate different approaches to accurately deliver the prescribed treatment. For example, range, LET, RBE, and patient position uncertainties are common to all particle therapies but the effects on the delivered treatment are dependent upon the delivery method. Passive scattered delivery techniques must account for field size effects, output factors, hardware uncertainties, air gaps and penumbras. Scanning beams encounter different uncertainties regarding spot size, scanning positional accuracy, beam spot dosimetry, and magnet calibration uncertainties. Learning Objectives: 1. To understand the fundamentals of treatment planning for passive and scanned proton therapy, including Intensity Modulated Proton Therapy 2. To understand the proton specific strategies in treatment planning for passive scattering and scanning 3. To understand uncertainties of proton therapy and their implications on proton treatment planning 4. To understand the limitations of current proton treatment planning techniques.
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Abstract Purpose. To develop a novel treatment planning process (TPP) with simultaneous optimization of modulated photon, electron and proton beams for improved treatment plan quality in radiotherapy. Methods. A framework for fluence map optimization of Monte Carlo (MC) calculated beamlet dose distributions is developed to generate treatment plans consisting of photon, electron and spot scanning proton fields. Initially, in-house intensity modulated proton therapy (IMPT) plans are compared to proton plans created by a commercial treatment planning system (TPS). A triple beam radiotherapy (TriB-RT) plan is generated for an exemplary academic case and the dose contributions of the three particle types are investigated. To investigate the dosimetric potential, a TriB-RT plan is compared to an in-house IMPT plan for two clinically motivated cases. Benefits of TriB-RT for a fixed proton beam line with a single proton field are investigated. Results. In-house optimized IMPT are of at least equal or better quality than TPS-generated proton plans, and MC-based optimization shows dosimetric advantages for inhomogeneous situations. Concerning TriB-RT, for the academic case, the resulting plan shows substantial contribution of all particle types. For the clinically motivated case, improved sparing of organs at risk close to the target volume is achieved compared to IMPT (e.g. myelon and brainstem D m a x −37%) at cost of an increased low dose bath (healthy tissue V 10% +22%). In the scenario of a fixed proton beam line, TriB-RT plans are able to compensate the loss in degrees of freedom to substantially improve plan quality compared to a single field proton plan. Conclusion. A novel TPP which simultaneously optimizes photon, electron and proton beams was successfully developed. TriB-RT shows the potential for improved treatment plan quality and is especially promising for cost-effective single-room proton solutions with a fixed beamline in combination with a conventional linac delivering photon and electron fields.
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One of the drawbacks of the Intensity Modulated Radiation Therapy (IMRT) technique is that the absorbed dose in healthy tissue is relatively high. Proton beam has characteristics that can compensate for these drawbacks. The Bragg peak characteristic of a proton beam allows the administration of high radiation doses to the target organ only. Non-Small Cell Lung Cancer (NSCLC) cases are located in the vicinity of many vital organs, so radiation doses that exceed a certain limit will have a significant impact on these organs. Proton is a heavy particle that exhibits interaction patterns with tissue heterogeneity that differ from that of photon. This study aims to determine the distribution of proton beam planning doses in the NSCLC cases with the Intensity Modulated Proton Therapy (IMPT) technique and compare its effectiveness with the IMRT technique. Treatment planning was done by using TPS Eclipse on the water phantom and on the in-house thorax dynamic phantom. The water phantom planning parameters used are one field at 0° and three fields at 45°, 135°, and 225°. In this study, a single, sum, and multiple field techniques on the in-house thorax dynamic phantom were used. The evaluation was performed by calculating Conformity Index (CI), Homogeneity Index (HI), and Gradient Index (GI) parameters for each treatment planning. As a result, a bit of difference in the CI the HI values are shown between IMPT and IMRT planning. The GI values of IMPT planning are in the range between 4.15-4.53, while the GI value of IMRT is 7.89. The histogram results of the planar dose distribution show that the IMPT treatment planning provides fewer off-target organ doses than the IMRT planning. Evaluation was also carried out on the IMPT treatment planning of target organs in five areas of interest and four OAR positions. The evaluation results were then compared with the IMRT measurement data. As a result, the value of the point doses at the target organ did not differ significantly. However, the absorbed dose with the IMPT technique at four OAR positions is nearly zero, which had a large difference compared to the IMRT technique.
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