Proton Beam Delivery Research Articles

TH‐AB‐BRD‐02: Proton Treatment Planning

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.

TH‐AB‐BRD‐03: Radiation Dosimetry for Proton Therapy

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.

SU‐E‐T‐649: Quality Assurances for Proton Therapy Delivery Equipment

Purpose:The number of proton therapy centers has increased dramatically over the past decade. Currently, there is no comprehensive set of guidelines that addresses quality assurance (QA) procedures for the different technologies used for proton therapy. The AAPM has charged task group 224 (TG‐224) to provide recommendations for QA required for accurate and safe dose delivery, using existing and next generation proton therapy delivery equipment.Methods:A database comprised of QA procedures and tolerance limits was generated from many existing proton therapy centers in and outside of the US. These consist of proton therapy centers that possessed double scattering, uniform scanning, and pencil beams delivery systems. The diversity in beam delivery systems as well as the existing devices to perform QA checks for different beam parameters is the main subject of TG‐224. Based on current practice at the clinically active proton centers participating in this task group, consensus QA recommendations were developed. The methodologies and requirements of the parameters that must be verified for consistency of the performance of the proton beam delivery systems are discussed.Results:TG‐224 provides procedures and QA checks for mechanical, imaging, safety and dosimetry requirements for different proton equipment. These procedures are categorized based on their importance and their required frequencies in order to deliver a safe and consistent dose. The task group provides daily, weekly, monthly, and annual QA check procedures with their tolerance limits.Conclusions:The procedures outlined in this protocol provide sufficient information to qualified medical physicists to perform QA checks for any proton delivery system. Execution of these procedures should provide confidence that proton therapy equipment is functioning as commissioned for patient treatment and delivers dose safely and accurately within the established tolerance limits. The report will be published in late 2015.

SU‐E‐T‐08: A Beam Source Model for Monte Carlo Simulations of a Double‐Scattering Proton Beam Delivery System Using Beam Current Modulation

Purpose:To reconstruct phase‐space information upstream of patient specific collimators for Monte Carlo simulations using only radiotherapy planning system data.Methods:The proton energies are calculated based on residual ranges, e.g., sum of prescribed ranges in a patient and SSD. The Kapchinskij and Vladimirskij (KV) distribution was applied to sample proton's x‐y positions and momentum direction and the beam shape was assumed to be a circle. Free parameters, e.g., the initial energy spread and the emittance of KV distribution were estimated from the benchmarking with commissioning data in a commercial treatment planning system for an operational proton therapy center. The number of histories, which defines the height of individual pristine Bragg peaks (BP) of Spread‐out Bragg peak (SOBP), are weighted based on beam current modulation and a correction factor is applied to take into account the fluence reduction as the residual range decreases due to the rotation of the range modulator wheel. The timedependent behaviors, e.g., the changes of the residual range and histories per a pristine BP, are realized by utilizing TOPAS (Tool for Particle Simulation).Results:Benchmarking simulations for selected SOBPs ranging 7.5 cm to 15.5 cm matched within 2 mm in range and up to 5 mm in SOBP width against measurement data in water phantom. We found this model tends to underestimate entrance dose by about 5 % in comparison to measurement. This was attributed to the situation that the energy distribution used in the model was limited in its granularity at the limit of single energy spectrum for the narrow angle modulator steps used in the proximal pull back region of the SOBPs.Conclusion:Within these limitations the source modeling method proved itself an acceptable alternative of a full treatment head simulation when the machine geometry and materials information are not available.

MO‐D‐BRB‐02: Pediatric Treatment Planning II: Applications of Proton Beams for Pediatric Treatment

Most Medical Physicists working in radiotherapy departments see few pediatric patients. This is because, fortunately, children get cancer at a rate nearly 100 times lower than adults. Children have not smoked, abused alcohol, or been exposed to environmental carcinogens for decades, and of course, have not fallen victim to the aging process. Children get very different cancers than adults. Breast or prostate cancers, typical in adults, are rarely seen in children but instead a variety of tumors occur in children that are rarely seen in adults; examples are germinomas, ependymomas and primitive neuroectodermal tumors, which require treatment of the child's brain or neuroblastoma, requiring treatment in the abdomen. The treatment of children with cancer using radiation therapy is one of the most challenging planning and delivery problems facing the physicist. This is because bones, brain, breast tissue, and other organs are more sensitive to radiation in children than in adults. Because most therapy departments treat mostly adults, when the rare 8 year‐old patient comes to the department for treatment, the physicist may not understand the clinical issues of his disease which drive the planning and delivery decisions. Additionally, children are more prone than adults to developing secondary cancers after radiation. For bilateral retinoblastoma for example, an irradiated child has a 40% chance of developing a second cancer by age 50. The dosimetric tradeoffs made during the planning process are complex and require careful consideration for children treated with radiotherapy.In the first presentation, an overview of childhood cancers and their corresponding treatment techniques will be given. These can be some of the most complex treatments that are delivered in the radiation therapy department. These cancers include leukemia treated with total body irradiation, medulloblastoma, treated with craniospinal irradiation plus a conformal boost to the posterior fossa, neuroblastoma, requiring focal abdominal irradiation to avoid kidney, liver, and vertebral body damage, retinoblastoma, requiring treatment to an eye while minimizing dose to surrounding tissues, and a variety of other tumors which occur anywhere in the body. Case studies will be presented showing the treatment technique and resulting dosimetry, highlighting the objectives for tumor coverage and organ‐at‐risk sparing. Practical issues that have to be faced when treating children will also be discussed such as daily sedation and immobilization. Late effects based on the current understanding of dose‐volume response in normal tissues will be discussed.In the second presentation, specific focus will be on pediatric proton therapy. We will review literature publications on dosimetric comparison of proton versus photon plans, common pediatric tumors treated with protons, and available clinical outcomes. We will describe simulation technique, treatment planning, image guidance for setup verification, and proton beam delivery unique to pediatric and adolescent patients. Finally, we will discuss desired improvements, outlook, and opportunities for medical physicists in pediatric proton therapy.Learning Objectives: Improve understanding about childhood cancer and treatment with radiation Understand treatment planning and delivery issues and associated late effects specific to children Become aware of specific treatment methods for the most challenging pediatric cancers Know the current status, techniques, and desired improvements for pediatric proton therapy

MO‐D‐BRB‐00: Pediatric Radiation Therapy Planning, Treatment, and Late Effects

Most Medical Physicists working in radiotherapy departments see few pediatric patients. This is because, fortunately, children get cancer at a rate nearly 100 times lower than adults. Children have not smoked, abused alcohol, or been exposed to environmental carcinogens for decades, and of course, have not fallen victim to the aging process. Children get very different cancers than adults. Breast or prostate cancers, typical in adults, are rarely seen in children but instead a variety of tumors occur in children that are rarely seen in adults; examples are germinomas, ependymomas and primitive neuroectodermal tumors, which require treatment of the child's brain or neuroblastoma, requiring treatment in the abdomen. The treatment of children with cancer using radiation therapy is one of the most challenging planning and delivery problems facing the physicist. This is because bones, brain, breast tissue, and other organs are more sensitive to radiation in children than in adults. Because most therapy departments treat mostly adults, when the rare 8 year‐old patient comes to the department for treatment, the physicist may not understand the clinical issues of his disease which drive the planning and delivery decisions. Additionally, children are more prone than adults to developing secondary cancers after radiation. For bilateral retinoblastoma for example, an irradiated child has a 40% chance of developing a second cancer by age 50. The dosimetric tradeoffs made during the planning process are complex and require careful consideration for children treated with radiotherapy.In the first presentation, an overview of childhood cancers and their corresponding treatment techniques will be given. These can be some of the most complex treatments that are delivered in the radiation therapy department. These cancers include leukemia treated with total body irradiation, medulloblastoma, treated with craniospinal irradiation plus a conformal boost to the posterior fossa, neuroblastoma, requiring focal abdominal irradiation to avoid kidney, liver, and vertebral body damage, retinoblastoma, requiring treatment to an eye while minimizing dose to surrounding tissues, and a variety of other tumors which occur anywhere in the body. Case studies will be presented showing the treatment technique and resulting dosimetry, highlighting the objectives for tumor coverage and organ‐at‐risk sparing. Practical issues that have to be faced when treating children will also be discussed such as daily sedation and immobilization. Late effects based on the current understanding of dose‐volume response in normal tissues will be discussed.In the second presentation, specific focus will be on pediatric proton therapy. We will review literature publications on dosimetric comparison of proton versus photon plans, common pediatric tumors treated with protons, and available clinical outcomes. We will describe simulation technique, treatment planning, image guidance for setup verification, and proton beam delivery unique to pediatric and adolescent patients. Finally, we will discuss desired improvements, outlook, and opportunities for medical physicists in pediatric proton therapy.Learning Objectives: Improve understanding about childhood cancer and treatment with radiation Understand treatment planning and delivery issues and associated late effects specific to children Become aware of specific treatment methods for the most challenging pediatric cancers Know the current status, techniques, and desired improvements for pediatric proton therapy

TH-CD-BRA-09: Quality Assurance of Scanned Proton Beams with a Volumetric Liquid Scintillator Detector

Purpose: To develop a volumetric scintillation detector capable of quickly and accurately measuring the range, lateral profile, and lateral position of scanned proton beams. Methods: A volumetric scintillation detector was constructed, consisting of a tank of liquid scintillator imaged on two sides by CCD cameras. The cameras measured orthogonal projections of the emitted light in cine mode at frame rates of 1 frame/s or 37 frames/s, depending on the proton beam delivery rate. Proton beams with 60 energies ranging from 72.5 to 168.8 MeV were measured in a single delivery sequence, requiring less than 3 minutes of beam time to measure the range and lateral profile. The measured range and lateral profile width were compared with the nominal beam ranges and the lateral profiles measured with an ionization chamber. A 3×3 grid of proton beams with 5 cm spacing at 5 different energies was also measured, and the lateral position of each beam was compared with its nominal position. Results: The mean difference between the measured and nominal beam ranges was 0.1 mm (σ=0.1 mm), with a maximum difference of 0.3 mm. The differences between the measured and nominal lateral beam positions ranged from 0.22 mm to 2.64 mm, with the errors increasing with distance from the center of the detector. The lateral beam profile widths were systematically 1 mm narrower than reference measurements using an ionization chamber. Conclusion: The detector described in this study can provide fast, high-resolution measurements of the range, lateral profile, and lateral position for scanned proton beams. The ability of the detector to rapidly measure proton beam characteristics at multiple energies makes it particularly promising as a tool for scanned proton beam quality assurance.

MO‐D‐BRB‐01: Pediatric Treatment Planning I: Overview of Planning Strategies and Challenges

Most Medical Physicists working in radiotherapy departments see few pediatric patients. This is because, fortunately, children get cancer at a rate nearly 100 times lower than adults. Children have not smoked, abused alcohol, or been exposed to environmental carcinogens for decades, and of course, have not fallen victim to the aging process. Children get very different cancers than adults. Breast or prostate cancers, typical in adults, are rarely seen in children but instead a variety of tumors occur in children that are rarely seen in adults; examples are germinomas, ependymomas and primitive neuroectodermal tumors, which require treatment of the child's brain or neuroblastoma, requiring treatment in the abdomen. The treatment of children with cancer using radiation therapy is one of the most challenging planning and delivery problems facing the physicist. This is because bones, brain, breast tissue, and other organs are more sensitive to radiation in children than in adults. Because most therapy departments treat mostly adults, when the rare 8 year‐old patient comes to the department for treatment, the physicist may not understand the clinical issues of his disease which drive the planning and delivery decisions. Additionally, children are more prone than adults to developing secondary cancers after radiation. For bilateral retinoblastoma for example, an irradiated child has a 40% chance of developing a second cancer by age 50. The dosimetric tradeoffs made during the planning process are complex and require careful consideration for children treated with radiotherapy.In the first presentation, an overview of childhood cancers and their corresponding treatment techniques will be given. These can be some of the most complex treatments that are delivered in the radiation therapy department. These cancers include leukemia treated with total body irradiation, medulloblastoma, treated with craniospinal irradiation plus a conformal boost to the posterior fossa, neuroblastoma, requiring focal abdominal irradiation to avoid kidney, liver, and vertebral body damage, retinoblastoma, requiring treatment to an eye while minimizing dose to surrounding tissues, and a variety of other tumors which occur anywhere in the body. Case studies will be presented showing the treatment technique and resulting dosimetry, highlighting the objectives for tumor coverage and organ‐at‐risk sparing. Practical issues that have to be faced when treating children will also be discussed such as daily sedation and immobilization. Late effects based on the current understanding of dose‐volume response in normal tissues will be discussed.In the second presentation, specific focus will be on pediatric proton therapy. We will review literature publications on dosimetric comparison of proton versus photon plans, common pediatric tumors treated with protons, and available clinical outcomes. We will describe simulation technique, treatment planning, image guidance for setup verification, and proton beam delivery unique to pediatric and adolescent patients. Finally, we will discuss desired improvements, outlook, and opportunities for medical physicists in pediatric proton therapy.Learning Objectives: Improve understanding about childhood cancer and treatment with radiation Understand treatment planning and delivery issues and associated late effects specific to children Become aware of specific treatment methods for the most challenging pediatric cancers Know the current status, techniques, and desired improvements for pediatric proton therapy

SU‐E‐T‐638: Proton Beam Delivery to a Moving Lung Tumor and Monte Carlo Simulation with TOPAS

Purpose:To estimate the dose delivered to a moving lung tumor by proton therapy beams of different modulation types, and compare with Monte Carlo predictions.Methods:A radiology support devices (RSD) phantom was irradiated with therapeutic proton radiation beams using two different types of modulation: uniform scanning (US) and double scattered (DS). The Eclipse© dose plan was designed to deliver 1.00Gy to the isocenter of a static ∼3×3×3cm (27cc) tumor in the phantom with 100% coverage. The peak to peak amplitude of tumor motion varied from 0.0 to 2.5cm. The radiation dose was measured with an ion‐chamber (CC‐13) located within the tumor. The time required to deliver the radiation dose varied from an average of 65s for the DS beams to an average of 95s for the US beams.Results:The amount of radiation dose varied from 100% (both US and DS) to the static tumor down to approximately 92% for the moving tumor. The ratio of US dose to DS dose ranged from approximately 1.01 for the static tumor, down to 0.99 for the 2.5cm moving tumor. A Monte Carlo simulation using TOPAS included a lung tumor with 4.0cm of peak to peak motion. In this simulation, the dose received by the tumor varied by ∼40% as the period of this motion varied from 1s to 4s.Conclusion:The radiation dose deposited to a moving tumor was less than for a static tumor, as expected. At large (2.5cm) amplitudes, the DS proton beams gave a dose closer to the desired dose than the US beams, but equal within experimental uncertainty. TOPAS Monte Carlo simulation can give insight into the moving tumor — dose relationship.This work was supported in part by the Philips corporation.

SP-0372: The delivery of proton beam

SP-0372: The delivery of proton beam

SP-0024: Current developments in proton and ion beam production and delivery

SP-0024: Current developments in proton and ion beam production and delivery

Radiation for Prostate Cancer: Intensity Modulated Radiation Therapy versus Proton Beam

To the Editor: This opposing views article highlights some of the fundamental differences in how radiation oncologists view the burgeoning (but not new) application of proton beam therapy (PBT) to treat prostate cancer. Hoppe et al articulate the respective arguments of the so-called proton and photon “camps” that have emerged within our specialty. These camps predictably fall along the lines of whether one practices at a center with PBT, and the financial differences between the 2 technologies are the key driver of the debate. Frankly none of us would be arguing against a product or device that delivers less unwanted radiation while maintaining (if not increasing) dose to the targetdif the cost is comparable to the alternatives. But it is different with prostate cancer. Excellent and affordable alternatives do exist, including brachytherapy, which is cheaper and more conformal than PBT and intensity modulated radiation therapy (IMRT). Those who use PBT should ask the important clinical questions, test them, and be given the time and resources to do so. Those who use only photon based techniques should, in turn, support these efforts, recognizing that IMRT was not held to the same standard when it was widely adopted over older and cheaper conventional techniques. Rather than recapitulating conflicting interpretations of the same methodologically flawed study, 1,2 as is done here, the radiation oncology community could look to patient level data on prospectively collected toxicity and quality of life outcomes for a disease as prevalent as prostate cancer. 3 In the spirit of incorporating patient reported outcomes Hoppe and Bryant suggest that the retrospectively observed 6% to 8% difference in bowel quality of life as measured by EPIC (Expanded Prostate Cancer Index Composite) is not only statistically significant, but also clinically relevant. 4 Sandler references the currently open randomized trial of IMRT vs proton therapy in prostate cancer, which has a primary end point of 2-year patient reported bowel quality of life (using EPIC). While this study will examine whether the retrospectively observed difference in bowel quality of life is statistically significant in a phase III setting, will it answer the question of whether it is clinically meaningful? If we do not see a difference for this specific end point, the trial will be negative. But will we truly feel that we answered the question of which is better? The media and payers certainly will, and frankly in many cases they have already decided that cheaper is better, period. The tide against PBT due to its generally greater costs is a foregone conclusion in many parts of the country but we have not afforded it the opportunity to prove itself. The institutional studies that have been reported to date generally all used passive scatter technique, an increasingly outdated and suboptimal form of proton beam delivery. We need to compare the “best” PBT techniques (ie pencil beam scanning) to the best IMRT. This comparison will require patience as centers work to responsibly deploy such capabilities. 5 While time is a rare luxury in the world of “do more with less,” it is necessary if we really want to test the various hypotheses described by the authors. Although there is multidirectional pressure to produce and report trial results quickly, doing so in prostate cancer can give a limited view of a disease with a long natural history involving patients who are at risk for late toxicities and relapses. As Sandler notes, the proton debate in prostate cancer carries great economic importance. But the comparative effectiveness challenges inherent to prostate cancer hopefully will not translate to a general disregard of PBT for other cancers. As a genitourinary radiation oncologist who uses PBT and photon based IMRT, I would like us to focus our efforts on investigating the promise of

Study of the Angular Dependence of a Prompt Gamma Detector Response during Proton Radiation Therapy

Abstract Purpose: Several studies have recently shown that the characteristics of prompt gamma (PG) rays emitted during proton radiation therapy are beneficial for verifying proton beam range during treatment delivery. Since PG rays are produced instantaneously upon the proton beam delivery, the viability of in vivo beam range verification using PG rays depends greatly on the design optimization of not only intrinsically highly efficient detectors, but also detector location around the beam to maximize detection efficiency. The purpose of this study is to characterize angular dependence of the PG detection rates as a function of proton beam energy to help develop the design of clinically feasible detectors. Materials and Methods: In this study as a part of the long-term goal of developing a clinically feasible multistage Compton camera, we performed a Monte Carlo–based study of the detector response in a water phantom over the clinical range of beam energies, 50 to 200 MeV, and characterized PG emission s...

A Recommendation on How to Analyze In-Room PET for In Vivo Proton Range Verification Using a Distal PET Surface Method

We describe the rationale and implementation of a method for analyzing in-room positron emission tomography (PET) data to verify the proton beam range. The method is based on analyzing distal PET surfaces after passive scattering proton beam delivery. Typically in vivo range verification is done by comparing measured and predicted PET distribution for a single activity level at a selected activity line along the beam passage. In the method presented here, we suggest using a middle point method based on dual PET activity levels to minimize the uncertainty due to local variations in the PET activity. Furthermore, we introduce 2-dimensional (2D) PET activity level surfaces based on 3-dimensional maps of the PET activities along the beam passage. This allows determining not only average range differences but also range difference distributions as well as root mean square deviations (RMSDs) for a more comprehensive range analysis. The method is demonstrated using data from 8 patients who were scanned with an in-room PET scanner. For each of the 8 patients, the average range difference was less than 5 mm and the RMSD was 4 to 11 mm between the measured and simulated PET activity level surfaces for single-field treatments. An ongoing protocol at our institution allows the use of a single field for patients being imaged for the PET range verification study at 1 fraction during their treatment course. Visualizing the range difference distributions using the PET surfaces offers a convenient visual verification of range uncertainties in 2D. Using the distal activity level surfaces of simulated and measured PET distributions at the middle of 25% and 50% activity level is a robust method for in vivo range verification.

Proton beam monitor chamber calibration

The first goal of this paper is to clarify the reference conditions for the reference dosimetry of clinical proton beams. A clear distinction is made between proton beam delivery systems which should be calibrated with a spread-out Bragg peak field and those that should be calibrated with a (pseudo-)monoenergetic proton beam. For the latter, this paper also compares two independent dosimetry techniques to calibrate the beam monitor chambers: absolute dosimetry (of the number of protons exiting the nozzle) with a Faraday cup and reference dosimetry (i.e. determination of the absorbed dose to water under IAEA TRS-398 reference conditions) with an ionization chamber. To compare the two techniques, Monte Carlo simulations were performed to convert dose-to-water to proton fluence. A good agreement was found between the Faraday cup technique and the reference dosimetry with a plane-parallel ionization chamber. The differences—of the order of 3%—were found to be within the uncertainty of the comparison. For cylindrical ionization chambers, however, the agreement was only possible when positioning the effective point of measurement of the chamber at the reference measurement depth—i.e. not complying with IAEA TRS-398 recommendations. In conclusion, for cylindrical ionization chambers, IAEA TRS-398 reference conditions for monoenergetic proton beams led to a systematic error in the determination of the absorbed dose to water, especially relevant for low-energy proton beams. To overcome this problem, the effective point of measurement of cylindrical ionization chambers should be taken into account when positioning the reference point of the chamber. Within the current IAEA TRS-398 recommendations, it seems advisable to use plane-parallel ionization chambers—rather than cylindrical chambers—for the reference dosimetry of pseudo-monoenergetic proton beams.

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‐03: Improvement of Accuracy of Spot‐Scanning Proton Beam Delivery for Liver Tumor by Real‐Time Tumor‐Monitoring and Gating System: A Simulation Study

Purpose:To improve the accuracy of spot‐scanning proton beam delivery for target in motion, a real‐time tumor‐monitoring and gating system using fluoroscopy images was developed. This study investigates the efficacy of this method for treatment of liver tumors using simulation.Methods:Three‐dimensional position of a fiducial marker inserted close to the tumor is calculated in real time and proton beam is gated according to the marker's distance from the planned position (Shirato, 2012). The efficient beam delivery is realized even for the irregular and sporadic motion signals, by employing the multiple‐gated irradiations per operation cycle (Umezawa, 2012). For each of two breath‐hold CTs (CTV=14.6cc, 63.1cc), dose distributions were calculated with internal margins corresponding to freebreathing (FB) and real‐time gating (RG) with a 2‐mm gating window. We applied 8 trajectories of liver tumor recorded during the treatment of RTRT in X‐ray therapy and 6 initial timings. Dmax/Dmin in CTV, mean liver dose (MLD), and irradiation time to administer 3 Gy (RBE) dose were estimated assuming rigid motion of targets by using in‐house simulation tools and VQA treatment planning system (Hitachi, Ltd., Tokyo).Results:Dmax/Dmin was degraded by less than 5% compared to the prescribed dose with all motion parameters for smaller CTV and less than 7% for larger CTV with one exception. Irradiation time showed only a modest increase if RG was used instead of FB; the average value over motion parameters was 113 (FB) and 138 s (RG) for smaller CTV and 120 (FB) and 207 s (RG) for larger CTV. In RG, it was within 5 min for all but one trajectory. MLD was markedly decreased by 14% and 5–6% for smaller and larger CTVs respectively, if RG was applied.Conclusions:Spot‐scanning proton beam was shown to be delivered successfully to liver tumor without much lengthening of treatment time.This research was supported by the Cabinet Office, Government of Japan and the Japan Society for the Promotion of Science (JSPS) through the Funding Program for World‐Leading Innovative R&D on Science and Technology (FIRST Program), initiated by the Council for Science and Technology Policy (CSTP).

WE‐E‐BRF‐01: The ESTRO‐AAPM Joint Symposium On Imaging for Proton Treatment Planning and Guidance

In this first inaugural joint ESTRO‐AAPM session we will attempt to provide some answers to the problems encountered in the clinical application of particle therapy.Indeed the main advantage is that the physical properties of ion beams offer high ballistic accuracy for tightly conformal irradiation of the tumour volume, with excellent sparing of surrounding healthy tissue and critical organs, This also its Achilles' heel calling for an increasing role of imaging to ensure safe application of the intended dose to the targeted area during the entire course of fractionated therapy.We have three distinguished speakers addressing possible solutions.Katia Parodi (Ludwig Maximilians University, Munich, Germany)To date, Positron Emission Tomography (PET) is the only technique which has been already clinically investigated for in‐vivo visualization of the beam range during or shortly after ion beam delivery. The method exploits the transient amount of β2‐activity induced in nuclear interactions between the primary beam and the irradiated tissue, depending on the ion beam species, the tissue elemental composition and physiological properties (in terms of biological clearance), as well as the time course of irradiation and imaging. This contribution will review initial results, ongoing methodological developments and remaining challenges related to the clinical usage of viable but often suboptimal instrumentation and workflows of PET‐based treatment verification. Moreover, it will present and discuss promising new detector developments towards next‐generation dedicated PET scanners relying on full‐ring or dual‐head designs for in‐beam quasi real‐time imaging.Denis Dauvergne (Institut de Physique Nucleaire de Lyon, Lyon, France) Prompt gamma radiation monitoring of hadron therapy presents the advantage of real time capability to measure the ion range. Both simulations and experiments show that millimetric verification of the range can be achieved at the pencil beam scale for active proton beam delivery in homogenous targets. The development of gamma cameras, that has been studied by several groups worldwide over the last years, now reaches – for some of them – the stage of being applicable in clinical conditions, with real size prototypes and count rate capability matching the therapeutic beam intensities. We will review the different concepts of gamma cameras, the advantages and limitations of this method, and the main challenges that should still be overcome before the widespread of prompt gamma quality assurance for proton and hadrontherapy.Jon Kruse (Mayo Clinic, Rochester, MN, USA)Treatment simulation images for proton therapy are used to determine proton stopping power and range in the patient. This talk will discuss the careful control of CT numbers and conversion of CT number to stopping power required in proton therapy. Imaging for treatment guidance of proton therapy also presents unique challenges which will be addressed. Among them are the enhanced relationship between internal anatomy changes and dosimetry, the need for imaging to support adaptive planning protocols, and high operational efficiency.Learning Objectives: To learn about the possibilities of using activation products to determine the range of particle beams in a patient treatment setting To be informed on an alternative methodology using prompt gamma detectors To understand the impact of the accuracy of the knowledge of the patient information with respect to the delivered treatment.

SU-E-T-586: Field Size Dependence of Output Factor for Uniform Scanning Proton Beams: A Comparison of TPS Calculation, Measurement and Monte Carlo Simulation

Purpose: Output dependence on field size for uniform scanning beams, and the accuracy of treatment planning system (TPS) calculation are not well studied. The purpose of this work is to investigate the dependence of output on field size for uniform scanning beams and compare it among TPS calculation, measurements and Monte Carlo simulations. Methods: Field size dependence was studied using various field sizes between 2.5 cm diameter to 10 cm diameter. The field size factor was studied for a number of proton range and modulation combinations based on output at the center of spread out Bragg peak normalized to a 10 cm diameter field. Three methods were used and compared in this study: 1) TPS calculation, 2) ionization chamber measurement, and 3) Monte Carlos simulation. The XiO TPS (Electa, St. Louis) was used to calculate the output factor using a pencil beam algorithm; a pinpoint ionization chamber was used for measurements; and the Fluka code was used for Monte Carlo simulations. Results: The field size factor varied with proton beam parameters, such as range, modulation, and calibration depth, and could decrease over 10% from a 10 cm to 3 cm diameter field for a large range proton beam. The XiO TPS predicted the field size factor relatively well at large field size, but could differ from measurements by 5% or more for small field and large range beams. Monte Carlo simulations predicted the field size factor within 1.5% of measurements. Conclusion: Output factor can vary largely with field size, and needs to be accounted for accurate proton beam delivery. This is especially important for small field beams such as in stereotactic proton therapy, where the field size dependence is large and TPS calculation is inaccurate. Measurements or Monte Carlo simulations are recommended for output determination for such cases.

WE‐D‐BRF‐03: Proton Beam Range Verification with a Single Prompt Gamma‐Ray Detector

Purpose:To present an experimental study of a novel range verification method for scanned and scattered proton beams.Methods:A detection system consisting of an actively shielded lanthanum(III)bromide scintillator and a one‐sided lead collimator was used to measure prompt gamma‐rays emitted during the delivery of proton beams to a water phantom and an anthropomorphic head phantom. The residual proton range at the collimator position was determined by comparing gamma‐ray intensities while the proton energy was modulated to the distal end of the target. We used a clinical field to deliver a 50 cGy dose to a 12 cm diameter target in the water phantom and to a 175 cc tumor‐shaped target in the head phantom. The detector signals were acquired with a custom data acquisition system enabling energy and time‐of‐flight discrimination of prompt gamma‐rays.Results:Range deviations were detected with a statistical accuracy of ± 0.2 mm and ± 1.4 mm at 90% confidence level, respectively for the water and head phantom. We obtained a time resolution of 1 ns FWHM and an energy resolution < 2% FWHM for the main gamma lines from proton‐induced nuclear reactions with carbon and oxygen. This allowed for an accurate separation of the prompt gamma‐rays from neutron‐induced background.Conclusion:Proton range deviations can be detected with millimeter accuracy using a single prompt gamma‐ray measurement point acquired during the delivery of a few proton energy layers to the distal part of the target. The method is also feasible in the presence of background radiation from passively scattered proton beam delivery.