Treatment Verification System Research Articles

A phamtom study: In vivo rectal dosimetry of high dose rate brachytherapy in cervical cancer

The purpose of this study was to perform in-vivo dosimetry using a diode rectal dosimeter in phantom and compare the dose delivered to the rectum between the dose measured by the diode dosimeter and the dose calculated by the treatment planning system in cervical cancer. The PTW T9112 diode detector calibrations were performed to find the correction factor. Then the calibrated diode detector was used to measure the radiation dose received in the rectum area in the in-house pelvic phantom. An Iridium-192 source was loaded into the phantom with 7 Gy, the measurements were 3 times per treatment plan, with 15 total plans studied. The average cumulative charge (nC) of each plan was converted to the absorbed dose (mGy) for comparison with the treatment planning system. Finally, to test the hypothesis that an absorbed dose from the detector and the treatment planning system were not significantly different, dependent t–test statistical analysis was applied with p-value <0.05. For distance and direction correction factors, we found that the factors were approximately 1 at 5 cm and 180°. The percentage differences of radiation dose between the diode dosimeter and the treatment planning system were between −3.3 and 4.1%. Statistical analysis revealed that the doses from the detector and the treatment planning system were not statistically significant different. The comparison showed that the percent difference between diode dosimeter and treatment planning system was acceptable to perform the in vivo dosimetry in brachytherapy. Therefore, the diode detector may be a suitable candidate for a treatment verification system in cervical cancer brachytherapy to prevent the dose delivery errors that directly affect the prognosis and may cause complications for the patient.

Combining a Customized Immobilization System with an Innovative Use of the ExacTrac System for Precise Volumetric Modulated Arc Therapy of Challenging Forearm Sarcomas

High-precision image-guided radiation therapy (RT) for tumors abutting the appendicular skeleton may mean technical difficulties and concerns among practitioners. This technical note addresses the specific challenge for normofractionated image-guided RT of a tumor target in a forearm through an unconventional use of a treatment verification system usually devoted to stereotactic RT.

A high-Z inorganic scintillator-based detector for time-resolved in vivo dosimetry during brachytherapy.

High-dose rate (HDR) and pulsed-dose rate (PDR) brachytherapy would benefit from an independent treatment verification system to monitor treatment delivery and to detect errors in real time. This paper characterizes and provides an uncertainty budget for a detector based on a fiber-coupled high-Z inorganic scintillator capable of performing time-resolved in vivo dosimetry during HDR and PDR brachytherapy. The detector was composed of a detector probe and an optical reader. The detector probe consisted of either a 0.5× 0.4 × 0.4 mm3 (HDR) or a 1.0 × 0.4 × 0.4 mm3 (PDR) cuboid ZnSe:O crystal glued onto an optical-fiber cable. The outer diameter of the detector probes was 1mm, and fit inside standard brachytherapy catheters. The signal from the detector probe was read out at 20Hz by a photodiode and a data acquisition device inside the optical reader. In order to construct an uncertainty budget for the detector, six characteristics were determined: (1) temperature dependence of the detector probe, (2) energy dependence as a function of the probe-to-source position in 2D (determined with 2 mm resolution using a robotic arm), (3) the signal-to-noise ratio (SNR), (4) short-term stability over 8h, and (5) long-term stability of three optical readers and four probes used for in vivo monitoring in HDR and PDR treatments over 21 months (196 treatments and 189 detector calibrations, and (6) dose-rate dependence. The total uncertainty of the detector at a 20 mm probe-to-source distance was<5.1% and<5.8% for the HDR and PDR versions, respectively. Regarding the above characteristics, (1) the sensitivity of the detector decreased by an average of 1.4%/°C for detector probe temperatures varying from 22 to 37°C; (2) the energy dependence of the detector was nonlinear and depended on both probe-to-source distance and the angle between the probe and the brachytherapy source; (3) the median SNRs were 187 and 34 at a 20 mm probe-to-source distance for the HDR and PDR versions, respectively (corresponding median source activities of 4.8 and 0.56Ci, respectively); (4) the detector response varied by 0.6% in 11 identical irradiations over 8h; (5) the sensitivity of the four detector probes decreased systematically by 0-1.2%/100Gy of dose delivered to the probes, and random fluctuations of 4.8% in the sensitivity were observed for the three probes used in PDR and 1.9% for the probe used in HDR; and (6) the detector response was linear with dose rate. ZnSe:O detectors can be used effectively for in vivo dosimetry and with high accuracy for HDR and PDR brachytherapy applications.

PO-1050 A gynecological multichannel applicator including a real-time treatment verification system

PO-1050 A gynecological multichannel applicator including a real-time treatment verification system

OA190] Novel inorganic scintillation detector system for real-time treatment verification during brachytherapy

Purpose Afterloaded brachytherapy administers a sealed radioisotope that is guided inside pre-inserted catheters in the tumor volume. The goal with the treatment modality is to deliver high doses to the tumor with steep dose gradients to spare adjacent organs and normal tissue. Real-time treatment verification could have an important role during brachytherapy treatments to detect errors that can lead to harmful consequences for the patient. However, real-time treatment verification is presently not performed during brachytherapy, partially because commercial technology does not exhibit adequate signal intensities over the entire range of absorbed dose rates. The limited use of treatment verification is problematic because errors can occur unnoticed. The purpose of this study was to develop scintillation-based point detectors that could have an important role for real-time verification during brachytherapy to detect and prevent treatment errors. Methods A real-time treatment verification system based on miniature inorganic scintillation detectors (ISDs) was developed. The ISDs consisted of a 1 mm-size scintillator that was optically coupled to a 1 mm-diameter and 15 m-long fiber-optic cable. The ISDs were based on the scintillation materials Al2O3:Cr, Y2O3:Eu, YVO4:Eu, ZnSe:O or CsI:Tl. The fiber-optic cable transmitted the scintillation to the photodetector system which consisted of a charge-coupled device camera or a spectrometer spectrograph. We tested the ISDs under brachytherapy treatment irradiation conditions using an Ir-192 source, and compared their performance with organic scintillators BCF-12 and BCF-60 which are the current standard for scintillation detectors in radiotherapy. Results The ISDs exhibited scintillation intensities that were up to 3 orders of magnitude greater than the detectors based on the organic scintillators. The large intensities of the ZnSe:O and CsI:Tl materials made it possible to develop an in vivo dosimetry system based on low-cost photodetector and data acquisition components. The prototype in vivo dosimetry system measured dose rates with Conclusions High-intensity ISD materials make it possible to develop low-cost in vivo dosimetry systems that precisely can monitor brachytherapy treatments. Miniature ISDs can therefore facilitate dissemination of real-time treatment verification technology for brachytherapy.

An integrated system for clinical treatment verification of HDR prostate brachytherapy combining source tracking with pretreatment imaging

PurposeHigh-dose-rate (HDR) prostate brachytherapy treatment is usually delivered in one or a few large dose fractions. Poor execution of a planned treatment could have significant clinical impact, as high doses are delivered in seconds, and mistakes in an individual fraction cannot be easily rectified. Given that most potential errors in HDR brachytherapy ultimately lead to a geographical miss, a more direct approach to verification of correct treatment delivery is to directly monitor the position of the source throughout the treatment. In this work, we report on the clinical implementation of our treatment verification system that uniquely combines the 2D source-tracking capability with 2D pretreatment imaging, using a single flat panel detector (FPD). Methods and MaterialsThe clinical brachytherapy treatment couch was modified to allow integration of the FPD into the couch. This enabled the patient to be set up in the brachytherapy bunker in a position that closely matched that at treatment planning imaging. An anteroposterior image was acquired of the patient immediately before treatment delivery and was assessed by the Radiation Oncologist online, to reestablish the positions of the catheters relative to the prostate. Assessment of catheter positions was performed in the left-right and superior-inferior directions along the entire catheter length and throughout the treatment volume. Source tracking was then performed during treatment delivery, and the measured position of the source dwells were directly compared to the treatment plan for verification. ResultsThe treatment verification system was integrated into the clinical environment without significant change to workflow. Two patient cases are presented in this work to provide clinical examples of this system, which is now in routine use for all patient treatments in our clinic. The catheter positions were visualized relative to the prostate, immediately before treatment delivery. For one of the patient cases presented in this work, they agreed with the treatment plan on average by 1.5 mm and were identifiable as a predominantly inferior shift. The source tracking was performed during treatment delivery, and for the same case, the mean deviation from the planned dwell positions was 1.9 mm (max = 4.9 mm) for 280 positions across all catheters. ConclusionWe have implemented our noninvasive treatment verification system based on an FPD in the clinical environment. The device is integrated into a patient treatment couch, and the process is now included in the routine clinical treatment procedure with minor impact on workflow. The system which combines both 2D pretreatment imaging and HDR 2D source tracking provides a range of information that can be used for comprehensive treatment verification. The system has the potential to meaningfully improve safety standards by allowing widespread adoption of routine treatment verification in HDR brachytherapy.

O4. Monte Carlo modelling of a prototype beam delivery check system for intensity modulated radiation therapy plan

Introduction Monte Carlo (MC) simulation techniques can accurately solve complex radiation transport challenges. This study applied the BEAMnrc Monte Carlo code technique to model an online dose monitoring system, the Integral Quality Monitoring (IQM) device (iRT Systems GmbH, Koblenz, Germany) and study the signal response of an IMRT treatment plan using the IQM model. IMRT treatments have generated complexities in their pretreatment quality assurance (QA) and there is huge curiosity to verify the treatment plan data during the real-time treatment. The Integral Quality Monitor (IQM) is an independent real-time treatment verification system which verifies the integrity and validates the accuracy of the treatment plan data. The IQM also functions as a pretreatment quality assurance tool for radiotherapy. Materials and methods The EGSnrc/BEAMnrc MC codes were utilized to model the Elekta Synergy linac equipped with Agility 160-leaf MLC as well as a MC model of the IQM. Full clinical IMRT plans were extracted from a DICOM plan file to create input files for the MC simulations. The simulated output signals from the IQM model were generated. Results IQM model was successfully developed and the Monte Carlo calculated IMRT signals show a good response from one segment to another of maximum IMRT plan signal. Conclusion Application of MC techniques to online dose monitoring is authentic. It demonstrates that MC radiation transport method is virtually unlimited when it comes to solving radiation transport and dose calculation challenges.

MO-FG-202-01: A Fast Yet Sensitive EPID-Based Real-Time Treatment Verification System

Purpose: To create a real-time EPID-based treatment verification system which robustly detects treatment delivery and patient attenuation variations. Methods: Treatment plan DICOM files sent to the record-and-verify system are captured and utilized to predict EPID images for each planned control point using a modified GPU-based digitally reconstructed radiograph algorithm which accounts for the patient attenuation, source energy fluence, source size effects, and MLC attenuation. The DICOM and predicted images are utilized by our C++ treatment verification software which compares EPID acquired 1024×768 resolution frames acquired at ∼8.5hz from Varian Truebeam™ system. To maximize detection sensitivity, image comparisons determine (1) if radiation exists outside of the desired treatment field; (2) if radiation is lacking inside the treatment field; (3) if translations, rotations, and magnifications of the image are within tolerance. Acquisition was tested with known test fields and prior patient fields. Error detection was tested in real-time and utilizing images acquired during treatment with another system. Results: The computational time of the prediction algorithms, for a patient plan with 350 control points and 60×60×42cm^3 CT volume, is 2–3minutes on CPU and <27 seconds on GPU for 1024×768 images. The verification software requires a maximum of ∼9ms and ∼19ms for 512×384 and 1024×768 resolution images, respectively, to perform image analysis and dosimetric validations. Typical variations in geometric parameters between reference and the measured images are 0.32°for gantry rotation, 1.006 for scaling factor, and 0.67mm for translation. For excess out-of-field/missing in-field fluence, with masks extending 1mm (at isocenter) from the detected aperture edge, the average total in-field area missing EPID fluence was 1.5mm2 the out-of-field excess EPID fluence was 8mm^2, both below error tolerances. Conclusion: A real-time verification software, with EPID images prediction algorithm, was developed. The system is capable of performing verifications between frames acquisitions and identifying source(s) of any out-of-tolerance variations. This work was supported in part by Varian Medical Systems.

A method for verification of treatment delivery in HDR prostate brachytherapy using a flat panel detector for both imaging and source tracking.

Verification of high dose rate (HDR) brachytherapy treatment delivery is an important step, but is generally difficult to achieve. A technique is required to monitor the treatment as it is delivered, allowing comparison with the treatment plan and error detection. In this work, we demonstrate a method for monitoring the treatment as it is delivered and directly comparing the delivered treatment with the treatment plan in the clinical workspace. This treatment verification system is based on a flat panel detector (FPD) used for both pre-treatment imaging and source tracking. A phantom study was conducted to establish the resolution and precision of the system. A pretreatment radiograph of a phantom containing brachytherapy catheters is acquired and registration between the measurement and treatment planning system (TPS) is performed using implanted fiducial markers. The measured catheter paths immediately prior to treatment were then compared with the plan. During treatment delivery, the position of the (192)Ir source is determined at each dwell position by measuring the exit radiation with the FPD and directly compared to the planned source dwell positions. The registration between the two corresponding sets of fiducial markers in the TPS and radiograph yielded a registration error (residual) of 1.0 mm. The measured catheter paths agreed with the planned catheter paths on average to within 0.5 mm. The source positions measured with the FPD matched the planned source positions for all dwells on average within 0.6 mm (s.d. 0.3, min. 0.1, max. 1.4 mm). We have demonstrated a method for directly comparing the treatment plan with the delivered treatment that can be easily implemented in the clinical workspace. Pretreatment imaging was performed, enabling visualization of the implant before treatment delivery and identification of possible catheter displacement. Treatment delivery verification was performed by measuring the source position as each dwell was delivered. This approach using a FPD for imaging and source tracking provides a noninvasive method of acquiring extensive information for verification in HDR prostate brachytherapy.

Implementation of an intraoperative electron radiotherapy in vivo dosimetry program.

BackgroundIntraoperative electron radiotherapy (IOERT) is a highly selective radiotherapy technique which aims to treat restricted anatomic volumes during oncological surgery and is now the subject of intense re-evaluation. In vivo dosimetry has been recommended for IOERT and has been identified as a risk-reduction intervention in the context of an IOERT risk analysis. Despite reports of fruitful experiences, information about in vivo dosimetry in intraoperative radiotherapy is somewhat scarce. Therefore, the aim of this paper is to report our experience in developing a program of in vivo dosimetry for IOERT, from both multidisciplinary and practical approaches, in a consistent patient series. We also report several current weaknesses.MethodsReinforced TN-502RDM-H mobile metal oxide semiconductor field effect transistors (MOSFETs) and Gafchromic MD-55-2 films were used as a redundant in vivo treatment verification system with an Elekta Precise fixed linear accelerator for calibrations and treatments. In vivo dosimetry was performed in 45 patients in cases involving primary tumors or relapses. The most frequent primary tumors were breast (37 %) and colorectal (29 %), and local recurrences among relapses was 83 %. We made 50 attempts to measure with MOSFETs and 48 attempts to measure with films in the treatment zones. The surgical team placed both detectors with supervision from the radiation oncologist and following their instructions.ResultsThe program was considered an overall success by the different professionals involved. The absorbed doses measured with MOSFETs and films were 93.8 ± 6.7 % and 97.9 ± 9.0 % (mean ± SD) respectively using a scale in which 90 % is the prescribed dose and 100 % is the maximum absorbed dose delivered by the beam. However, in 10 % of cases we experienced dosimetric problems due to detector misalignment, a situation which might be avoided with additional checks. The useful MOSFET lifetime length and the film sterilization procedure should also be controlled.ConclusionsIt is feasible to establish an in vivo dosimetry program for a wide set of locations treated with IOERT using a multidisciplinary approach according to the skills of the professionals present and the detectors used; oncological surgeons’ commitment is key to success in this context. Films are more unstable and show higher uncertainty than MOSFETs but are cheaper and are useful and convenient if real-time treatment monitoring is not necessary.

Development of an automated ballast water treatment verification system utilizing fluorescein diacetate hydrolysis as a measure of treatment efficacy

Methods for verifying ballast water treatments in foreign vessels are needed to protect the Great Lakes from the discharge of live non-native organisms or pathogens. A prototype automated viability test system using fluorescein diacetate (FDA), a membrane permeable fluorogen, to differentiate live from dead bacteria and algae is described. The automated fluorescence intensity detection device (AFIDD) captures cultured algae or organisms in Detroit River water (simulated ballast water) on 0.2 μm filters, backwashes them from the filter into a cuvette with buffer and FDA for subsequent fluorescence intensity measurements, and washes the filters with sterile water for serial automated reuse. Preliminary manual versions of these procedures were also tested. Tests of various buffers determined N,N-Bis(2-hydroxyethyl)-2-aminoethanesulfonic acid, N,N-Bis(2-hydroxyethyl)taurine (BES) and 3-(N-morpholino)propanesulfonic acid (MOPS) at pH 7.0 to be the best buffers, causing the least spontaneous FDA breakdown without inhibiting enzymatic activity. Fluorescence in the presence of live organisms increased linearly over time, and the rate of increase was dependent on the sample concentration. Following simulated ballast water treatments with heat or chlorine, the fluorescence produced by Detroit River samples decreased to near control (sterile water) levels. Automated measurements of FDA hydrolysis with a reusable filter backwash system should be applicable to near real-time remote-controlled monitoring of live organisms in ballast water.

SU‐C‐16A‐01: In Vivo Source Position Verification in High Dose Rate (HDR) Prostate Brachytherapy Using a Flat Panel Imager: Initial Clinical Experience

Purpose:We report our initial clinical experience with a novel position‐sensitive source‐tracking system based on a flat panel imager. The system has been trialled with 4 prostate HDR brachytherapy patients (8 treatment fractions) in this initial study.Methods:The flat panel imaging system was mounted under a customised carbon fibre couch top assembly (Figure 1). Three gold fiducial markers were implanted into the prostate of each patient at the time of catheter placement. X‐ray dwell position markers were inserted into three catheters and a radiograph acquired to locate the implant relative to the imaging device. During treatment, as the HDR source dwells were delivered, images were acquired and processed to determine the position of the source in the patient. Source positions measured by the imaging device were compared to the treatment plan for verification of treatment delivery.Results:Measured dwell positions provided verification of relative dwell spacing within and between catheters, in the coronal plane. Measurements were typically within 2.0mm (0.2mm – 3.3mm, s.d. 0.8mm) of the planned positions over 60 dwells (Figure 2). Discrimination between larger dwell intervals and catheter differentiation were clear. This confirms important delivery attributes such as correct transfer tube connection, source step size, relative catheter positions and therefore overall correct plan selection and delivery. The fiducial markers, visible on the radiograph, provided verification of treatment delivery to the correct anatomical location. The absolute position of the dwells was determined by comparing the measured dwell positions with the x‐ray markers from the radiograph, validating the programmed treatment indexer length. The total impact on procedure time was less than 5 minutes.Conclusion:The novel, noninvasive HDR brachytherapy treatment verification system was used clinically with minor impact on workflow. The system allows verification of correct treatment delivery, free of most potential human related errors identified in ICRP 97.This research is supported by funding from the Australian Government Department of Health through Cancer Australia grant no. 616614.

SU-E-T-721: Validation of a 3D Treatment Verification System Based On AAPM TG-119 Recommendations

Purpose: To use AAPM TG‐119 protocol to determine validity of a commercially available 3D treatment verification software system. The software determines dose in the patient CT dataset via a collapsed cone algorithm which is modeled on energy fluence of the linear accelerator. The software provides the user the ability to evaluate the dose difference and gamma factor relative to the treatment planning system (TPS). Methods: TG‐119 protocol structures were downloaded into a CT dataset of a plastic phantom which included an ion chamber planar array. The four central chambers were also contoured for dose statistics. IMRT plans were created in the TPS based on the protocol specifications. The plan parameters were transferred to the verification system for analysis via DICOM RT. Average dose and average gamma were determined for PTVs and OARs as well as the central chambers. V(100) was also determined for the PTVs. The ratio between the verification system and the TPS was tracked. Gamma analysis was based on 2%/2 mm deviation. Results: The normalized average dose (+/&−; 2σ) for PTVs, OARs, and centrally located chambers is 1.00 +/− 0.02, 0.95 +/− 0.10, and 0.98 +/− 0.08, respectively. The normalized V(100) for PTV is 0.98 +/− 0.08. The average gamma for PTVs, OARs and centrally located chambers is 0.27 +/− 0.26, 0.29 +/− 0.23, and 0.30 +/− 0.44, respectively. Conclusion: The TG‐119 protocol provides for an effective way to evaluate a 3D verification software system. It allows the user to ensure the system is functioning to institution specifications and also gives the user another method to assess quality of treatment plans.

SU‐E‐T‐340: Estimation of the Delivered Fractional and Accumulative Patient Dose in IMRT and VMAT

Purpose: To estimate the delivered dose after each fraction of treatment as well as the delivered accumulative dose distribution. The goal of this project is to develop an automatic verification system using daily images and machine log files. Methods: First, we perform deformable registration from CT to CBCT and correct CBCT artifacts and CT numbers. Due to the limitation of the current scanning protocol, CBCT may not cover the whole treatment region needed for dose reconstruction. In that case, we use deformed CT for dose calculation which has correct CT number as well as daily patient geometry within whole treatment region. With machine log files, we generate actually delivered fluence maps at all delivery angles for that fraction. Then a GPU‐based Monte Carlo dose calculation package, gDPM, is employed to get delivered fractional dose on deformed CT or corrected CBCT. To compare the planned dose with the delivered dose, the delivered dose on new daily image is transferred back to the original CT geometry using the deformation vector fields obtained in the first step. This procedure is employed for each fraction to get the accumulative dose on original CT. Results: We demonstrate this treatment verification system on VMAT patients. We plot the DVHs for delivered and planned dose distributions and summarize the absolute errors in dose matrix report. Conclusions: We have proposed a procedure to estimate the delivered fractional and accumulative patient doses in IMRT and VMAT. If big errors are observed in the dose matrix report, then a warning should be sent out to responsible personnel, so the error can be indentified and corrected promptly.

TH‐C‐BRB‐08: Treatment Verification Using Post‐Treatment PET Imaging and Monte Carlo Simulation

Purpose: Investigate the feasibility of using post proton therapy PET and Monte Carlo simulation as a treatment verification system for pediatric patients with localized brain tumors. Method: Under a prospective IRB approved protocol, twelve patients received proton therapy followed by a PET activation study. All patients were under the age of 3 and were under general anesthesia during treatment and post PET imaging. On the day of the PET evaluation, the patient was treated with a single beam corresponding to the activation beam under study. A separate plan was developed to ensure that using a single beam did not compromise the treatment plan. The duration between end of treatment and start of PET imaging for each of the single field treatments was recorded. The PET activation study was acquired for 30 minutes. The patient was fully immobilized for the PET in the same manner as during treatment. The Monte Carlo simulation utilized a previously verified proton dose distribution system modified to report a weighted count of positrons. Comparisons between the treatment planning dose and acquired PET image and between the acquired PET image and Monte Carlos simulated image were made. Results: On average, there were 3 treatment fields per plan and 2 per plan that met the criteria for the PET activation study. The average time between end of irradiation and start of PET acquisition was 14.5+/−1.3 minutes. Based on preliminary data, setup errors are detectable and, utilizing Monte Carlo, distal edge errors may be detectable. Conclusion: The potential exists to detect setup errors and it may be possible to determine if there is a discrepancy between the planned and delivered distal edge of a field. Out of room PET verification has limited clinical usefulness; however, in room PET may be of benefit.

Planning and verification in radiotherapy: our experience in a filmless hospital

Planning and verification in radiotherapy: our experience in a filmless hospital In our hospital we have recently installed a new radiotherapy treatment planning and verification system. Our system allows to follow the normal clinical workflow: from patient identification to follow-up through the treatment delivery with the study of the best irradiation geometry. We designed a new technical solutions relating to the use of four linear accelerators, a Record and Verify system, a Treatment Planning System (TPS) and a clinical folder, completely paperless. All the procedures for treatment planning, setup and verification are integrated in our digital imaging long-term archive. The integration is based on the existing HL7 and DICOM standard protocols described in the International Committee and IHE RO Technical Framework, which is able to support the workflow. All the images used for planning and setup are stored in the Oncentra DICOM archive server for short-term archiving and then are sent to the Agfa DICOM long-term archive for legal and scientific purposes.

SU‐FF‐J‐48: Developing In‐Line KV Fluoroscopic Verification for 4D Adaptive Radiotherapy

Purpose: To develop a system for on‐line real‐time treatment verification for 4D‐ART using in‐line kV fluoroscopy that will be included in a new generation of accelerator. Method and Materials: We have developed a software tool, as a component of the 4D‐ART verification system, to register fluoroscopic with dynamic (time‐sequenced) DRR (DDRR) images. The fluoroscopic images are obtained using kV x‐rays in‐line with the treatment‐beam direction. The DDRR images (DRRs at different phases during respiratory cycle) are generated from 4DCT. The image registration of DDRR and fluoroscopy is based on pre‐defined structures or points of interest and needs to be performed on‐line in real time, allowing the treatment parameters to be modified in real time if a discrepancy is observed. To approve the principle, we have employed a simulator (Siemens/Mevasim) to acquire the fluoroscopic images. Both hardware and software tools were developed to synchronize the acquisition of fluoroscopy with respiratory signal using a pressure sensor (Anzai). This synchronization, in turn, harmonizes fluoroscopic images with DDRR. The verification system was tested on a motion phantom and on lung cancer cases. Results: The system developed can effectively register respiration‐synchronized fluoroscopic and DDRR images for both phantom and patient data. The registration is able to detect discrepancies between planning images (DDRR) and verification images (in‐line fluoroscopy) for a 4D‐ART delivery. The system is found to be effective for validating respiratory gating. Conclusion: We have developed a treatment verification system for 4D‐ART. The system, employing in‐line kV fluoroscopy, may be used for validating respiratory gating and for 4D‐ART with the new generation of image‐guided delivery machine capable of in‐line dynamic imaging. The system can be also potentially useful for 4D real‐time tumor tracking based on fluoroscopy. Conflict of Interest: This work is supported in part by Siemens OCS.

Recomendações para se evitar grandes erros de dose em tratamentos radioterapêuticos

Erros humanos são uma importante fonte de falhas em todos os passos do planejamento e do tratamento radioterapêutico. Com o objetivo de reduzir este grau de incerteza, várias organizações especializadas recomendam minuciosos programas de garantia da qualidade. No Brasil, programas deste tipo vêm tendo sua exigência intensificada, e a maioria dos serviços de radioterapia vem se orientando neste sentido, tanto em relação aos equipamentos de radiação e dosimetria, quanto em relação à verificação dos cálculos de dose em pacientes e das revisões das fichas de planejamento. Como uma contribuição a este esforço de qualidade, apresentam-se algumas recomendações para se evitar falhas de tratamento devidas a erros na dose de radiação recebida pelo paciente, como redundância nas verificações dos cálculos feitos manualmente ou por computador, e, também, a verificação da dose acumulada para cada paciente sob tratamento, semanalmente, além de se evitar a possibilidade de acesso a qualquer sistema de segurança do equipamento ao pessoal técnico treinado para apenas o operar. Além disso, deve-se considerar a possibilidade de se empregar um sistema computadorizado de verificação e registro do tratamento, dessa maneira prevenindo-se erros durante a aplicação diária devidos à seleção indevida dos diferentes parâmetros do tratamento. Reportam-se quatro incidentes radioativos recentes ocorridos no mundo, com injúrias em pacientes, e algumas ocorrências de erros grandes de dose.

An on-line treatment verification system for dynamic IMRT techniques

An on-line treatment verification system for dynamic IMRT techniques

283. デジタルポータルイメージング装置を用いた治療照合システム(治療機器-2 照射位置の照合法及びシステム)

283. デジタルポータルイメージング装置を用いた治療照合システム(治療機器-2 照射位置の照合法及びシステム)