Monte Carlo systems used for treatment planning and dose verification

General-purpose radiation transport Monte Carlo codes have been used for estimation of the absorbed dose distribution in external photon and electron beam radiotherapy patients since several decades. Results obtained with these codes are usually more accurate than those provided by treatment planning systems based on non-stochastic methods. Traditionally, absorbed dose computations based on general-purpose Monte Carlo codes have been used only for research, owing to the difficulties associated with setting up a simulation and the long computation time required. To take advantage of radiation transport Monte Carlo codes applied to routine clinical practice, researchers and private companies have developed treatment planning and dose verification systems that are partly or fully based on fast Monte Carlo algorithms. This review presents a comprehensive list of the currently existing Monte Carlo systems that can be used to calculate or verify an external photon and electron beam radiotherapy treatment plan. Particular attention is given to those systems that are distributed, either freely or commercially, and that do not require programming tasks from the end user. These systems are compared in terms of features and the simulation time required to compute a set of benchmark calculations.     

BNCT dose distribution in liver with epithermal D-D and D-T fusion-based neutron beams.

Recently, a new application of boron neutron capture therapy (BNCT) treatment has been introduced. Results have indicated that liver tumors can be treated by BNCT after removal of the liver from the body. At Lawrence Berkeley National Laboratory, compact neutron generators based on (2)H(d,n)(3)He (D-D) or (3)H(t,n)(4)He (D-T) fusion reactions are being developed. Preliminary simulations of the applicability of 2.45 MeV D-D fusion and 14.1 MeV D-T fusion neutrons for in vivo liver tumor BNCT, without removing the liver from the body, have been carried out. MCNP simulations were performed in order to find a moderator configuration for creating a neutron beam of optimal neutron energy and to create a source model for dose calculations with the simulation environment for radiotherapy applications (SERA) treatment planning program. SERA dose calculations were performed in a patient model based on CT scans of the body. The BNCT dose distribution in liver and surrounding healthy organs was calculated with rectangular beam aperture sizes of 20 cm x 20 cm and 25 cm x 25 cm. Collimator thicknesses of 10 and 15 cm were used. The beam strength to obtain a practical treatment time was studied. In this paper, the beam shaping assemblies for D-D and D-T neutron generators and dose calculation results are presented.     

Synchronous bilateral squamous cell carcinoma of the lung successfully treated using intensity-modulated radiotherapy

We present a case of synchronous bilateral inoperable lung cancer which required treatment with external beam radiotherapy to a radical dose. Intensity-modulated radiotherapy (IMRT) was used. More conformal dose distribution within the planning target volume was obtained using IMRT than the conventional technique. Dose-volume constraints defined for the lungs were met. Treatment was subsequently delivered using a seven-field IMRT plan. The patient remains alive and disease-free 48 months after the completion of radiotherapy. IMRT can be considered an effective treatment for synchronous bilateral lung cancer.     

A policy for radiotherapy in patients with implanted pacemakers.

As the prevalence of implanted pacemakers increases, the likelihood that cancer requiring radiotherapy will develop in pacemaker-bearing patients increases proportionately. A management policy for pacemaker-dependent patients who require radiotherapy helps assure that they will be safely and efficiently treated with external beam radiation. Guidelines for external beam treatment have been set forth in the ASTRO Newsletter. These guidelines are the basis of the specific policy that was developed and implemented. This policy (1) requires a cardiology consultation and discussion with the manufacturer before treatment, (2) prohibits the use of a betatron, (3) suggests that attempts be made to limit the dose received by the pacemaker to 2-Gy, (4) requires that pacemaker dose be calculated, measured, and recorded in the patient chart, (5) requires cardiac monitoring in accordance with the degree of patient pacemaker dependence, and (6) requires a follow-up cardiology consultation after the patient's final treatment. Adherence to this policy is assured by use of a worksheet that is included in each pacemaker patient's chart.     

3D treatment planning system—Pinnacle system

The treatment planning system is key for the success of external beam radiotherapy, directly impacting the quality of treatment plans and accuracy of dose calculation in the plans. In this article, we provided an overview of the Pinnacle treatment planning system for external beam planning, including 3-dimensional (3D) conformal plans, step-shoot intensity modulated radiotherapy (IMRT) plans, and volumetric modulated arc therapy (VMAT) plans. We discussed dose calculation algorithm and other utilities, including image fusion, plan documentation, and adaptive planning. Based on our many years of clinical experience with the system, the aim of this article is to provide readers with a summary of this particular planning system.     

Effect of arc length on skin dose from hypofractionated volumetric modulated arc radiotherapy treatments of the lung and spine

Due to large doses per fraction, stereotactic ablative radiotherapy of lung or spine can lead to skin tissue toxicity, the amount of which depends on a variety of factors such as target location, beam geometry, and immobilization. The effect of arc length on spreading out entrance and exit doses and the corresponding predictions of skin reactions has not yet been studied for stereotactic body radiotherapy volumetric modulated arc therapy (VMAT) treatments. 58 clinically relevant VMAT stereotactic body radiotherapy spine and lung plans were created for an anthropomorphic phantom utilizing a range of target locations, beam geometries and arc lengths. Skin dose was assessed by considering the National Cancer Institute skin reaction grades adjusted for 3 fraction treatments. While the skin volumes predicted to exhibit low grade reactions decreased with arc length, high grade reactions were found to increase at smaller arcs as well as at full arcs where a superposition of entrance and exit doses would occur. It is possible for skin dose to be effectively optimized by choice of arc length (within clinically relevant boundaries) and thus minimize the skin reaction. High skin doses are often attributed to effects arising from the distance between the planning target volume and patient surface but this study has demonstrated that VMAT arc length is of equal importance. Understanding this relationship will assist in minimizing skin reactions through modification of plan parameters and will provide clinicians more information for patient selection.     

Monte Carlo simulation for MLC-based intensity-modulated radiotherapy.

This article describes photon beam Monte Carlo simulation for multi leaf collimator (MLC)-based intensity-modulated radiotherapy (IMRT). We present the general aspects of the Monte Carlo method for the non-Monte Carloist with an emphasis given to patient-specific radiotherapy application. Patient-specific application of the Monte Carlo method can be used for IMRT dose verification, inverse planning, and forward planning in conventional conformal radiotherapy. Because it is difficult to measure IMRT dose distributions in heterogeneous phantoms that approximate a patient, Monte Carlo methods can be used to verify IMRT dose distributions that are calculated using conventional methods. Furthermore, using Monte Carlo as the dose calculation method for inverse planning results in better-optimized treatment plans. We describe both aspects and present our recent results to illustrate the discussion. Finally, we present current issues related to clinical implementation of Monte Carlo dose calculation. Monte Carlo is the most recent, and most accurate, method of radiotherapy dose calculation. It is currently in the process of being implemented by various treatment planning vendors and will be available for clinical use in the immediate future.     

宫颈癌多模态融合图像引导近距离放射治疗发展现状

以顺铂为基础的全身化疗联合外照射序贯腔内近距离放射治疗(ICBT)已成为局部晚期宫颈癌的标准治疗模式。得益于医学影像设备成像精度的提高和图像融合技术的发展,ICBT已向图像引导的近距离治疗(IGBT)发展,并已走出了仅仅依赖单一影像引导的模式。如何选择适合的影像采集技术、优化多模态成像融合策略以降低IGBT的剂量偏差等因素是决定宫颈癌治疗成败的关键,也是困扰放疗实践的重要因素。基于深度学习的人工智能技术在智能放疗平台搭建及解决方案中崭露头角,已成为解决多模态融合宫颈癌IGBT关键问题的重要抓手,同时也为提升宫颈癌区域整体诊疗水平、减轻医师工作负担、向基层单位推广放疗经验提供一条新途径。     

Radiation transport calculations in treatment planning

This article reviews the role of radiation transport calculations in radiotherapy dose computation. The physical and mathematical principles underlying transport theory, as applied to electrons and photons, are discussed. Practical methods of solving the transport equation, with emphasis on Monte Carlo techniques, are reviewed. The contribution of analytic and Monte Carlo transport calculations to electron beam, photon beam, and brachytherapy treatment planning dosimetry is assessed. Currently, the most important roles of transport theory include using approximate solutions of the transport equation as theoretical foundations of dose computation algorithms, and using Monte Carlo simulation to calculate basic treatment planning data, characteristic of the treatment modality, which can serve as input to a dose computation algorithm.     

Dynamic targeting image-guided radiotherapy.

Volumetric imaging and planning for 3-dimensional (3D) conformal radiotherapy and intensity-modulated radiotherapy (IMRT) have highlighted the need to the oncology community to better understand the geometric uncertainties inherent in the radiotherapy delivery process, including setup error (interfraction) as well as organ motion during treatment (intrafraction). This has ushered in the development of emerging technologies and clinical processes, collectively referred to as image-guided radiotherapy (IGRT). The goal of IGRT is to provide the tools needed to manage both inter- and intrafraction motion to improve the accuracy of treatment delivery. Like IMRT, IGRT is a process involving all steps in the radiotherapy treatment process, including patient immobilization, computed tomography (CT) simulation, treatment planning, plan verification, patient setup verification and correction, delivery, and quality assurance. The technology and capability of the Dynamic Targeting IGRT system developed by Varian Medical Systems is presented. The core of this system is a Clinac or Trilogy accelerator equipped with a gantry-mounted imaging system known as the On-Board Imager (OBI). This includes a kilovoltage (kV) x-ray source, an amorphous silicon kV digital image detector, and 2 robotic arms that independently position the kV source and imager orthogonal to the treatment beam. A similar robotic arm positions the PortalVision megavoltage (MV) portal digital image detector, allowing both to be used in concert. The system is designed to support a variety of imaging modalities. The following applications and how they fit in the overall clinical process are described: kV and MV planar radiographic imaging for patient repositioning, kV volumetric cone beam CT imaging for patient repositioning, and kV planar fluoroscopic imaging for gating verification. Achieving image-guided motion management throughout the radiation oncology process requires not just a single product, but a suite of integrated products to manipulate all patient data, including images, efficiently and effectively.     

Project for the development of the linac based NCT facility in University of Tsukuba

A project team headed by University of Tsukuba launched the development of a new accelerator based BNCT facility. In the project, we have adopted Radio-Frequency Quadrupole (RFQ)+Drift Tube Linac (DTL) type linac as proton accelerators. Proton energy generated from the linac was set to 8 MeV and average current was 10 mA. The linac tube has been constructed by Mitsubishi Heavy Industry Co. For neutron generator device, beryllium is selected as neutron target material; high intensity neutrons are generated by the reaction with beryllium and the 80 kW proton beam.Our team chose beryllium as the neutron target material. At present beryllium target system is being designed with Monte-Carlo estimations and heat analysis with ANSYS. The neutron generator consists of moderator, collimator and shielding. It is being designed together with the beryllium target system. We also acquired a building in Tokai village; the building has been renovated for use as BNCT treatment facility. It is noteworthy that the linac tube had been installed in the facility in September 2012.In BNCT procedure, several medical devices are required for BNCT treatment such as treatment planning system, patient positioning device and radiation monitors. Thus these are being developed together with the linac based neutron source. For treatment planning system, we are now developing a new multi-modal Monte-Carlo treatment planning system based on JCDS. The system allows us to perform dose estimation for BNCT as well as particle radiotherapy and X-ray therapy. And the patient positioning device can navigate a patient to irradiation position quickly and properly. Furthermore the device is able to monitor movement of the patient׳s position during irradiation.     

Daily online adaptive magnetic resonance image (MRI) guided stereotactic body radiation therapy for primary renal cell cancer

Stereotactic body radiotherapy (SBRT) has demonstrated promising outcomes for patients with early-stage, medically inoperable, primary renal cell carcinoma (RCC) in large multi-institutional studies and prospective clinical trials. The traditional approach used in these studies consisted of a CT-based planning approach for target and organ-at-risk (OAR) volume delineation, treatment planning, and daily treatment delivery. Alternatively, MRI-based approaches using daily online adaptive radiotherapy have multiple advantages to improve treatment outcomes: (1) more accurate delineation of the target volume and OAR volumes with improved soft tissue visualization; (2) gated beam delivery with biofeedback from the patient; and (3) potential for daily plan adaptation due to changes in anatomy to improve target coverage, reduce dose to OARs, or both. The workflow, treatment planning principles, and aspects of treatment delivery specific to this technology are outlined using a case example of a patient with an early-stage RCC of the right kidney treated with MRI-guided SBRT using daily adaptive treatment to a dose of 42 Gy in 3 fractions.     

Intensity-modulated radiosurgery/radiotherapy using a micromultileaf collimator.

Intensity modulation with inverse treatment planning for 3 clinical stereotactic radiotherapy cases were directly compared against forward planning techniques using beam modification by enhanced dynamic wedge. Dose-volume histogram (DVH) analysis demonstrated that a significant reduction in dose to neighboring critical structures can-be achieved through intensity modulation patterns determined from inverse planning, while a marginal change is achieved in the target volume dose uniformity. This study also demonstrates that the intensity modulated dose patterns generated from inverse planning may differ significantly from the intuitive beam modified patterns developed in the forward planning model. These results suggest that one advantage of intensity modulated radiosurgery/radiotherapy with inverse planning is the significant reduction in dose to normal tissue and critical structures, with its coincident implications for dose escalation studies.     

Proton therapy at Harvard

Fractionated precision high-dose proton radiotherapy has been carried out at the Harvard Cyclotron Laboratory (HCL) since 1973, in a collaborative effort with the Radiation Medicine Department of Massachusetts General Hospital (MGH) and the Retina Service of the Massachusetts Eye and Ear Infirmary (MEEI). This paper will discuss proton treatment in general, treatment planning procedures, and results to date in major patient categories. 846 patients have been treated with fractionated proton therapy at the Harvard Cyclotron, with normal tissue and tumor responses consistent with an RBE of 1.1 for the proton beam. Proton beam therapy is the treatment of choice for patients with uveal melanomas, and chordomas and chondrosarcomas involving the skull base and cervical spine. Improved dose distribution possible with protons have allowed greater doses than are given conventionally to be delivered to patients with prostatic carcinoma, head and neck malignancies, ano-rectal cancers, and retroperitoneal tumors. Doses employed have been usually 10 to 20% greater than normally would be delivered in our department to such tumors. Generally, local control rates have been good.     

Modern techniques in the radiotherapy of prostate cancer. Non-surgical treatment options for localized stages

The implementation of computer-assisted three-dimensional radiotherapy treatment planning methods based on computed tomography together with sophisticated beam modeling with individual blocks and multi-leaf-collimators in the 90's enabled the creation of steep dose gradients between the target volume and surrounding radiosensitive normal tissue. For prostate cancer, a clear dose dependence between the treated radiation dose and the treatment success is proven, especially for patients with intermediate and unfavorable prognostic criteria. However, with conventional radiotherapy, rectum and urinary bladder are limiting the applicable dose. New technical methods allow a safe dose escalation without increasing of treatment-related toxicity. An improvement in terms of PSA remission and local control was yielded. This article presents the different established external beam and interstitial treatment techniques and their clinical results.     

Proton imaging for medical applications

In order to demonstrate the potential advantages of proton imaging for medical use, a 205-MeV proton beam was developed using the Argonne National Laboratory Booster I synchrotron. Data were taken using a narrow scanning beam and an electronic detector system. The dose reduction and an improved mass resulution over the radiographs. The images also show significant differences in the proton stopping power of different tissues, thus demonstrating considerable potential in soft-tissue imaging. The development of a proton tomographic scan system is also briefly discussed.     

Quality assurance procedures for the Peacock system.

The Peacock system is the product of technological innovations that are changing the practice of radiotherapy. It uses dynamic beam modulation technique and inverse planning algorithm, both of which are new methodologies, to perform intensity-modulation radiation therapy (IMRT). The quality assurance (QA) procedure established by Task Group No. 40 did not adequately consider these emerging modalities. A review of literature indicates that published articles on QA procedures concentrate primarily on the verification of dose delivered to phantom during commissioning of the system and dose delivered to phantom before treating patients. Absolute dose measurements using ion chambers and relative dose measurements using film dosimetry have been used to verify delivered doses. QA on equipment performance and equipment safety is limited. This paper will discuss QA on equipment performance, equipment safety, and patient setup reproducibility.     

The clinical implementation of respiratory-gated intensity-modulated radiotherapy.

The clinical use of respiratory-gated radiotherapy and the application of intensity-modulated radiotherapy (IMRT) are 2 relatively new innovations to the treatment of lung cancer. Respiratory gating can reduce the deleterious effects of intrafraction motion, and IMRT can concurrently increase tumor dose homogeneity and reduce dose to critical structures including the lungs, spinal cord, esophagus, and heart. The aim of this work is to describe the clinical implementation of respiratory-gated IMRT for the treatment of non-small cell lung cancer. Documented clinical procedures were developed to include a tumor motion study, gated CT imaging, IMRT treatment planning, and gated IMRT delivery. Treatment planning procedures for respiratory-gated IMRT including beam arrangements and dose-volume constraints were developed. Quality assurance procedures were designed to quantify both the dosimetric and positional accuracy of respiratory-gated IMRT, including film dosimetry dose measurements and Monte Carlo dose calculations for verification and validation of individual patient treatments. Respiratory-gated IMRT is accepted by both treatment staff and patients. The dosimetric and positional quality assurance test results indicate that respiratory-gated IMRT can be delivered accurately. If carefully implemented, respiratory-gated IMRT is a practical alternative to conventional thoracic radiotherapy. For mobile tumors, respiratory-gated radiotherapy is used as the standard of care at our institution. Due to the increased workload, the choice of IMRT is taken on a case-by-case basis, with approximately half of the non-small cell lung cancer patients receiving respiratory-gated IMRT. We are currently evaluating whether superior tumor coverage and limited normal tissue dosing will lead to improvements in local control and survival in non-small cell lung cancer.     

Bildgeführte Strahlentherapie

Radiotherapy technology has improved rapidly over the past two decades. New imaging modalities, such as positron emission (computed) tomography (PET, PET-CT) and high-resolution morphological and functional magnetic resonance imaging (MRI) have been introduced into the treatment planning process. Image-guided radiation therapy (IGRT) with 3D soft tissue depiction directly imaging target and normal structures, is currently replacing patient positioning based on patient surface markers, frame-based intracranial and extracranial stereotactic treatment and partially also 2D field verification methods. On-line 3D soft tissue-based position correction unlocked the full potential of new delivery techniques, such as intensity-modulated radiotherapy, by safely delivering highly conformal dose distributions that facilitate dose escalation and hypofractionation. These strategies have already resulted in better clinical outcomes, e.g. in prostate and lung cancer and are expected to further improve radiotherapy results.