Guided Patient Setup Research Articles

Proton Therapy for Prostate Cancer: Challenges and Opportunities.

Simple SummaryReported clinical outcomes of proton therapy (PT) for localized prostate cancer are similar to photon-based external beam radiotherapy. Apparently, the dosimetric advantages of PT have yet to be translated to clinical benefits. The suboptimal clinical outcomes of PT might be attributable to inadequate dose prescription, as indicated by the ASCENDE-RT trial. Moreover, uncertainties involved in the treatment planning and delivery processes, as well as technological limitations in PT treatment systems, may lead to discrepancies between planned doses and actual doses delivered to patients. In this article, we reviewed the current status of PT for prostate cancer and discussed different clinical implementations that could potentially improve the clinical outcome of PT for prostate cancer. Various technological advancements under which uncertainties in dose calculations can be minimized, including MRI-guided PT, dual-energy photon-counting CT and high-resolution Monte Carlo-based treatment planning systems, are highlighted.The dosimetric advantages of proton therapy (PT) treatment plans are demonstrably superior to photon-based external beam radiotherapy (EBRT) for localized prostate cancer, but the reported clinical outcomes are similar. This may be due to inadequate dose prescription, especially in high-risk disease, as indicated by the ASCENDE-RT trial. Alternatively, the lack of clinical benefits with PT may be attributable to improper dose delivery, mainly due to geometric and dosimetric uncertainties during treatment planning, as well as delivery procedures that compromise the dose conformity of treatments. Advanced high-precision PT technologies, and treatment planning and beam delivery techniques are being developed to address these uncertainties. For instance, external magnetic resonance imaging (MRI)-guided patient setup rooms are being developed to improve the accuracy of patient positioning for treatment. In-room MRI-guided patient positioning systems are also being investigated to improve the geometric accuracy of PT. Soon, high-dose rate beam delivery systems will shorten beam delivery time to within one breath hold, minimizing the effects of organ motion and patient movements. Dual-energy photon-counting computed tomography and high-resolution Monte Carlo-based treatment planning systems are available to minimize uncertainties in dose planning calculations. Advanced in-room treatment verification tools such as prompt gamma detector systems will be used to verify the depth of PT. Clinical implementation of these new technologies is expected to improve the accuracy and dose conformity of PT in the treatment of localized prostate cancers, and lead to better clinical outcomes. Improvement in dose conformity may also facilitate dose escalation, improving local control and implementation of hypofractionation treatment schemes to improve patient throughput and make PT more cost effective.

Validating robotic couch isocentricity with 3D surface imaging.

BackgroundA proton therapy system with 190° gantries uses robotic couch rotations to change the treatment beam laterality. Couch rotations are typically validated clinically with post‐rotation radiographic imaging.AimsThis study assesses the specificity and sensitivity of a commercial 3D surface imaging system, AlignRT (Vision RT, London UK) for validating couch rotations.Materials & MethodsIn clinical operation, a reference surface image of the patient is acquired after radiographic setup with couch at 270°, perpendicular to the gantry axis of rotation. The couch is then rotated ±90° to a typical treatment angle, and AlignRT reports a 3D displacement vector. Patient motion, changes in patient surface, non‐coincidence between AlignRT and couch isocenter, and mechanical couch run‐out all contribute to the 3D vector magnitude. To assess AlignRT sensitivity in detecting couch run‐out, volunteers were positioned orthogonal to the proton gantry and reference surface images were captured without x‐ray localization. Subjects were repeatedly rotated ±90⁰ to typical treatment angles and displacement vectors were recorded. Additionally, measurements were performed in which intentional translations of 2, 4, 6, and 8 mm were combined with the intended isocentric rotations. Data sets were collected using a phantom; subjects with a thoracic isocenter and no immobilization; and subjects with a cranial isocenter and thermoplastic immobilization. A total of 300 rotations were measured.ResultsDuring isocentric rotations, the mean AlignRT displacement vectors for the phantom, immobilized, and non‐immobilized volunteers were 0.1 ± 0.1 mm, 0.8 ± 0.1 mm, and 1.1 ± 0.2 mm respectively. 95% of the AlignRT measurements for the immobilized and non‐immobilized subjects were within 1 mm and 2 mm of the actual displacement respectively.DiscussionAfter characterizing the accuracy using phantoms and volunteers, we have shown that a three‐pod surface imaging system can be used to identify gross non‐isocentric patient rotations. Significant positional deviations, either due to improper couch rotation or patient motion, should be followed by radiographic imaging and repositioning.ConculsionAlignRT can be used to verify patient positioning following couch rotations that are applied after the initial x‐ray guided patient setup. Using a three‐pod AlignRt system, positional deviations exceeding 4 mm were flagged with sensitivity and specificity of 90% and 100% respectively.

An Infrared Guided Patient Setup Method for Radiotherapy by Using a Modified Spirit Level

An Infrared Guided Patient Setup Method for Radiotherapy by Using a Modified Spirit Level

MO‐D‐BRB‐02: SBRT Treatment Planning and Delivery

Increased use of SBRT and hypofractionation in radiation oncology practice has posted a number of challenges to medical physicist, ranging from planning, image‐guided patient setup and on‐treatment monitoring, to quality assurance (QA) and dose delivery. This symposium is designed to provide current knowledge necessary for the safe and efficient implementation of SBRT in various linac platforms, including the emerging digital linacs equipped with high dose rate FFF beams. Issues related to 4D CT, PET and MRI simulations, 3D/4D CBCT guided patient setup, real‐time image guidance during SBRT dose delivery using gated/un‐gated VMAT/IMRT, and technical advancements in QA of SBRT (in particular, strategies dealing with high dose rate FFF beams) will be addressed. The symposium will help the attendees to gain a comprehensive understanding of the SBRT workflow and facilitate their clinical implementation of the state‐of‐art imaging and planning techniques. Learning Objectives: Present background knowledge of SBRT, describe essential requirements for safe implementation of SBRT, and discuss issues specific to SBRT treatment planning and QA. Update on the use of multi‐dimensional and multi‐modality imaging for reliable guidance of SBRT. Discuss treatment planning and QA issues specific to SBRT. Provide a comprehensive overview of emerging digital linacs and summarize the key geometric and dosimetric features of the new generation of linacs for substantially improved SBRT.NIH/NCI; Varian Medical Systems; F. Yin, Duke University has a research agreement with Varian Medical Systems. In addition to research grant, I had a technology license agreement with Varian Medical Systems

MO‐D‐BRB‐01: Fundamental Aspects of SBRT

Increased use of SBRT and hypofractionation in radiation oncology practice has posted a number of challenges to medical physicist, ranging from planning, image‐guided patient setup and on‐treatment monitoring, to quality assurance (QA) and dose delivery. This symposium is designed to provide current knowledge necessary for the safe and efficient implementation of SBRT in various linac platforms, including the emerging digital linacs equipped with high dose rate FFF beams. Issues related to 4D CT, PET and MRI simulations, 3D/4D CBCT guided patient setup, real‐time image guidance during SBRT dose delivery using gated/un‐gated VMAT/IMRT, and technical advancements in QA of SBRT (in particular, strategies dealing with high dose rate FFF beams) will be addressed. The symposium will help the attendees to gain a comprehensive understanding of the SBRT workflow and facilitate their clinical implementation of the state‐of‐art imaging and planning techniques. Learning Objectives: Present background knowledge of SBRT, describe essential requirements for safe implementation of SBRT, and discuss issues specific to SBRT treatment planning and QA. Update on the use of multi‐dimensional and multi‐modality imaging for reliable guidance of SBRT. Discuss treatment planning and QA issues specific to SBRT. Provide a comprehensive overview of emerging digital linacs and summarize the key geometric and dosimetric features of the new generation of linacs for substantially improved SBRT.NIH/NCI; Varian Medical Systems; F. Yin, Duke University has a research agreement with Varian Medical Systems. In addition to research grant, I had a technology license agreement with Varian Medical Systems

MO‐D‐BRB‐03: Quality Assurance of SBRT

Increased use of SBRT and hypofractionation in radiation oncology practice has posted a number of challenges to medical physicist, ranging from planning, image‐guided patient setup and on‐treatment monitoring, to quality assurance (QA) and dose delivery. This symposium is designed to provide current knowledge necessary for the safe and efficient implementation of SBRT in various linac platforms, including the emerging digital linacs equipped with high dose rate FFF beams. Issues related to 4D CT, PET and MRI simulations, 3D/4D CBCT guided patient setup, real‐time image guidance during SBRT dose delivery using gated/un‐gated VMAT/IMRT, and technical advancements in QA of SBRT (in particular, strategies dealing with high dose rate FFF beams) will be addressed. The symposium will help the attendees to gain a comprehensive understanding of the SBRT workflow and facilitate their clinical implementation of the state‐of‐art imaging and planning techniques. Learning Objectives: Present background knowledge of SBRT, describe essential requirements for safe implementation of SBRT, and discuss issues specific to SBRT treatment planning and QA. Update on the use of multi‐dimensional and multi‐modality imaging for reliable guidance of SBRT. Discuss treatment planning and QA issues specific to SBRT. Provide a comprehensive overview of emerging digital linacs and summarize the key geometric and dosimetric features of the new generation of linacs for substantially improved SBRT.NIH/NCI; Varian Medical Systems; F. Yin, Duke University has a research agreement with Varian Medical Systems. In addition to research grant, I had a technology license agreement with Varian Medical Systems

MO‐D‐BRB‐00: SBRT Workflow Overview

Increased use of SBRT and hypofractionation in radiation oncology practice has posted a number of challenges to medical physicist, ranging from planning, image‐guided patient setup and on‐treatment monitoring, to quality assurance (QA) and dose delivery. This symposium is designed to provide current knowledge necessary for the safe and efficient implementation of SBRT in various linac platforms, including the emerging digital linacs equipped with high dose rate FFF beams. Issues related to 4D CT, PET and MRI simulations, 3D/4D CBCT guided patient setup, real‐time image guidance during SBRT dose delivery using gated/un‐gated VMAT/IMRT, and technical advancements in QA of SBRT (in particular, strategies dealing with high dose rate FFF beams) will be addressed. The symposium will help the attendees to gain a comprehensive understanding of the SBRT workflow and facilitate their clinical implementation of the state‐of‐art imaging and planning techniques. Learning Objectives: Present background knowledge of SBRT, describe essential requirements for safe implementation of SBRT, and discuss issues specific to SBRT treatment planning and QA. Update on the use of multi‐dimensional and multi‐modality imaging for reliable guidance of SBRT. Discuss treatment planning and QA issues specific to SBRT. Provide a comprehensive overview of emerging digital linacs and summarize the key geometric and dosimetric features of the new generation of linacs for substantially improved SBRT.NIH/NCI; Varian Medical Systems; F. Yin, Duke University has a research agreement with Varian Medical Systems. In addition to research grant, I had a technology license agreement with Varian Medical Systems

TU‐A‐304‐02: Treatment Simulation, Planning and Delivery for SBRT

Increased use of SBRT and hypo fractionation in radiation oncology practice has posted a number of challenges to medical physicist, ranging from planning, image‐guided patient setup and on‐treatment monitoring, to quality assurance (QA) and dose delivery. This symposium is designed to provide updated knowledge necessary for the safe and efficient implementation of SBRT in various linac platforms, including the emerging digital linacs equipped with high dose rate FFF beams. Issues related to 4D CT, PET and MRI simulations, 3D/4D CBCT guided patient setup, real‐time image guidance during SBRT dose delivery using gated/un‐gated VMAT or IMRT, and technical advancements in QA of SBRT (in particular, strategies dealing with high dose rate FFF beams) will be addressed. The symposium will help the attendees to gain a comprehensive understanding of the SBRT workflow and facilitate their clinical implementation of the state‐of‐art imaging and planning techniques.Learning Objectives: Present background knowledge of SBRT, describe essential requirements for safe implementation of SBRT, and discuss issues specific to SBRT treatment planning and QA. Update on the use of multi‐dimensional (3D and 4D) and multi‐modality (CT, beam‐level X‐ray imaging, pre‐ and on‐treatment 3D/4D MRI, PET, robotic ultrasound, etc.) for reliable guidance of SBRT. Provide a comprehensive overview of emerging digital linacs and summarize the key geometric and dosimetric features of the new generation of linacs for substantially improved SBRT. Discuss treatment planning and quality assurance issues specific to SBRT. Research grant from Varian Medical Systems

TU‐A‐304‐00: Imaging, Treatment Planning, and QA for Stereotactic Body Radiation Therapy (SBRT)

Increased use of SBRT and hypo fractionation in radiation oncology practice has posted a number of challenges to medical physicist, ranging from planning, image‐guided patient setup and on‐treatment monitoring, to quality assurance (QA) and dose delivery. This symposium is designed to provide updated knowledge necessary for the safe and efficient implementation of SBRT in various linac platforms, including the emerging digital linacs equipped with high dose rate FFF beams. Issues related to 4D CT, PET and MRI simulations, 3D/4D CBCT guided patient setup, real‐time image guidance during SBRT dose delivery using gated/un‐gated VMAT or IMRT, and technical advancements in QA of SBRT (in particular, strategies dealing with high dose rate FFF beams) will be addressed. The symposium will help the attendees to gain a comprehensive understanding of the SBRT workflow and facilitate their clinical implementation of the state‐of‐art imaging and planning techniques.Learning Objectives: Present background knowledge of SBRT, describe essential requirements for safe implementation of SBRT, and discuss issues specific to SBRT treatment planning and QA. Update on the use of multi‐dimensional (3D and 4D) and multi‐modality (CT, beam‐level X‐ray imaging, pre‐ and on‐treatment 3D/4D MRI, PET, robotic ultrasound, etc.) for reliable guidance of SBRT. Provide a comprehensive overview of emerging digital linacs and summarize the key geometric and dosimetric features of the new generation of linacs for substantially improved SBRT. Discuss treatment planning and quality assurance issues specific to SBRT. Research grant from Varian Medical Systems

TU‐A‐304‐01: Introduction and Workflow of Image‐Guided SBRT

Increased use of SBRT and hypo fractionation in radiation oncology practice has posted a number of challenges to medical physicist, ranging from planning, image‐guided patient setup and on‐treatment monitoring, to quality assurance (QA) and dose delivery. This symposium is designed to provide updated knowledge necessary for the safe and efficient implementation of SBRT in various linac platforms, including the emerging digital linacs equipped with high dose rate FFF beams. Issues related to 4D CT, PET and MRI simulations, 3D/4D CBCT guided patient setup, real‐time image guidance during SBRT dose delivery using gated/un‐gated VMAT or IMRT, and technical advancements in QA of SBRT (in particular, strategies dealing with high dose rate FFF beams) will be addressed. The symposium will help the attendees to gain a comprehensive understanding of the SBRT workflow and facilitate their clinical implementation of the state‐of‐art imaging and planning techniques.Learning Objectives: Present background knowledge of SBRT, describe essential requirements for safe implementation of SBRT, and discuss issues specific to SBRT treatment planning and QA. Update on the use of multi‐dimensional (3D and 4D) and multi‐modality (CT, beam‐level X‐ray imaging, pre‐ and on‐treatment 3D/4D MRI, PET, robotic ultrasound, etc.) for reliable guidance of SBRT. Provide a comprehensive overview of emerging digital linacs and summarize the key geometric and dosimetric features of the new generation of linacs for substantially improved SBRT. Discuss treatment planning and quality assurance issues specific to SBRT. Research grant from Varian Medical Systems

TU‐A‐304‐03: Quality Assurance, Safety, and Other Practical Aspects of SBRT

Increased use of SBRT and hypo fractionation in radiation oncology practice has posted a number of challenges to medical physicist, ranging from planning, image‐guided patient setup and on‐treatment monitoring, to quality assurance (QA) and dose delivery. This symposium is designed to provide updated knowledge necessary for the safe and efficient implementation of SBRT in various linac platforms, including the emerging digital linacs equipped with high dose rate FFF beams. Issues related to 4D CT, PET and MRI simulations, 3D/4D CBCT guided patient setup, real‐time image guidance during SBRT dose delivery using gated/un‐gated VMAT or IMRT, and technical advancements in QA of SBRT (in particular, strategies dealing with high dose rate FFF beams) will be addressed. The symposium will help the attendees to gain a comprehensive understanding of the SBRT workflow and facilitate their clinical implementation of the state‐of‐art imaging and planning techniques.Learning Objectives: Present background knowledge of SBRT, describe essential requirements for safe implementation of SBRT, and discuss issues specific to SBRT treatment planning and QA. Update on the use of multi‐dimensional (3D and 4D) and multi‐modality (CT, beam‐level X‐ray imaging, pre‐ and on‐treatment 3D/4D MRI, PET, robotic ultrasound, etc.) for reliable guidance of SBRT. Provide a comprehensive overview of emerging digital linacs and summarize the key geometric and dosimetric features of the new generation of linacs for substantially improved SBRT. Discuss treatment planning and quality assurance issues specific to SBRT. Research grant from Varian Medical Systems

SU-E-J-223: A Method to Remove the Streaking Artifacts Caused by Calypso Couch Table Add-On in the MV Portal Images

Purpose: Calypso EM tracking is widely used to setup the prostate patient and to track prostate motion while daily MV portal images are used as the secondary method to verify patient setup. The severe streaking artifacts, caused by the Calypso couch table add-on, make the MV portal images almost impossible to review. The purpose of this work is to develop a novel method to reduce the streaking artifacts so that the portal images are usable to verify patient setup. Methods: We analyzed the corrupted portal images and identified that most streaking artifacts are stable horizontally but has more dramatic change vertically. Based on signal processing theory, we developed an artifact reduction algorithm 1) to filter out the low frequency signal along the horizontal direction using a ideal low-pass filter in the Fourier domain, and 2) to smooth the intensity variation in the vertical direction and to reduce the remaining high frequency noises by using 2D Gaussian low-pass filter with a small window size. Results: We have successfully applied the proposed algorithm on the corrupted MV portal images in both PA and lateral directions from multiple Calypso prostate patients. The results show that the algorithm is very effective to reduce the artifacts introduced by the Calypso couch table add-on. Patient anatomical structures are much more clearly after processing to support reviews of patient setup. Conclusion: In this work an effective method is proposed to reduce artifacts caused by the Calypso table in MV portal images while preserving the key components of original image. The method could assist the verification of Calypso guided patient setup using portal images.

SU‐E‐I‐72: First Experimental Study of On‐Board CBCT Imaging Using 2.5MV Beam On a Radiotherapy Linac

Purpose:Varian TrueBeam version 2.0 comes with a new inline 2.5MV beam modality for image guided patient setup. In this work we develop an iterative volumetric image reconstruction technique specific to the beam and investigate the possibility of obtaining metal artifact free CBCT images using the new imaging modality.Methods:An iterative reconstruction algorithm with a sparse representation constraint based on dictionary learning is developed, in which both sparse projection and low dose rate (10 MU/min) are considered. Two CBCT experiments were conducted using the newly available 2.5MV beam on a Varian TrueBeam linac. First, a Rando anthropomorphic head phantom with and without a copper bar inserted in the center was scanned using both 2.5MV and kV (100kVp) beams. In a second experiment, an MRI phantom with many coils was scanned using 2.5MV, 6MV, and kV (100kVp) beams. Imaging dose and the resultant image quality is studied.Results:Qualitative assessment suggests that there were no visually detectable metal artifacts in MV CBCT images, compared with significant metal artifacts in kV CBCT images, especially in the MRI phantom. For a region near the metal object in the head phantom, the 2.5MV CBCT gave a more accurate quantification of the electron density compared with kV CBCT, with a ∼50% reduction in mean HU error. As expected, the contrast between bone and soft‐tissue in 2.5MV CBCT decreased compared with kV CBCT.Conclusion:On‐board CBCT imaging with the new 2.5MV beam can effectively reduce metal artifacts, although with a reduced softtissue contrast. Combination of kV and MV scanning may lead to metal artifact free CBCT images with uncompromised soft‐tissue contrast.

Re-irradiation of spinal column metastases by IMRT: impact of setup errors on the dose distribution

BackgroundThis study investigates the impact of an automated image guided patient setup correction on the dose distribution for ten patients with in-field IMRT re-irradiation of vertebral metastases.Methods10 patients with spinal column metastases who had previously been treated with 3D-conformal radiotherapy (3D-CRT) were simulated to have an in-field recurrence. IMRT plans were generated for treatment of the vertebrae sparing the spinal cord. The dose distributions were compared for a patient setup based on skin marks only and a Cone Beam CT (CBCT) based setup with translational and rotational couch corrections using an automatic robotic image guided couch top (Elekta - HexaPOD™ IGuide® - system). The biological equivalent dose (BED) was calculated to evaluate and rank the effects of the automatic setup correction for the dose distribution of CTV and spinal cord.ResultsThe mean absolute value (± standard deviation) over all patients and fractions of the translational error is 6.1 mm (±4 mm) and 2.7° (±1.1 mm) for the rotational error. The dose coverage of the 95% isodose for the CTV is considerable decreased for the uncorrected table setup. This is associated with an increasing of the spinal cord dose above the tolerance dose.ConclusionsAn automatic image guided table correction ensures the delivery of accurate dose distribution and reduces the risk of radiation induced myelopathy.

SU-E-J-210: Lung Tumor Target Volume Contours on EPID Cine Mode Images.

While real time imaging of treatment through an electronic portal imaging device (EPID) is a powerful tool to monitor treatment, limited field of view and lower contrast from an MV beam can make assessment difficult for physicians. This work will develops a method to register and project contour outlines for the internal target volume (ITV) and planning target volume (PTV) of lung tumor cases onto cine mode EPID images to help physicians in interpretation during treatment. A sequence of EPID images, acquired during treatment, was registered to treatment planning computed tomography (CT) by machine geometry and patient setup with cone-beam computed tomography (CBCT). The planning CT was converted from Hounsfield scale to electron density by calibration curves of our CT simulator and digitally reconstructed radiographs (DRRs) were produced to match the EPID geometry, pixel for pixel. ITV and PTV structures as defined on the planning CT were then projected onto the DRRs. The DRRs were registered to the EPID images using cross correlation of a single template defined within the treatment aperture of each image. Once registered, the contours from the DRR were transferred to the EPID. We were able to successfully register MV DRRs to EPID images and display the projected target volumes. Without introduced motion, geometric registration and CBCT guided patient setup up were sufficient to register the contours within a single pixel, as normalized cross correlations produced no additional shift. We expect the DRR/EPID registration to be an important step when looking at cases with substantial tumor movement. The visualization of target volumes provides a tool for physicians to interpret EPID images and assess treatment, especially in cases with tumor movement. The methods developed will serve as the basis for a clinical tool providing real time contours.

TU‐A‐BRB‐08: A Technique to Determine the Gantry Laser and the Proton Pencil Beam Coincidence Using Computer Radiography Detector for Routine Quality Checks

Purpose: A computed radiography (CR) detector with photostimulable phosphors can detect both direct and indirect ionization radiation, and is even sensitive to photons in the visible range. The purpose of this work is to develop and validate a technique using CR to check both proton radiation versus localization laser coincidence and spot positioning accuracy for magnetically scanned proton pencil beam spots (PPBS). Methods: CR plate is removed from its cassette and set up perpendicular to the incident beam and exposed to an array of PPBS irradiated at predefined coordinates. Upon exposure of the particle radiation, the CR detector is then exposed to the gantry's laser systems. The plate is then put through a digital scanner which then reads the photo stimulated luminescence and converts the signal into a digital image pixel map. MATLAB®‐based analysis software and ImageJ® image processing tools were used to compute the dose gradient from the laser bleaching of the proton exposure of the detector and for quantification of the results of this QA check procedure. The technique further allows quantitative determination of both spot positions, and the relationship between X ray system used for image guided patient setup and the PPBS delivery. Results: Both the coincidence between laser representing the gantry isocenter and center of PPBS along the central axis and spot positions can be checked within 1mm accuracy with the CR detector. Conclusions: We have demonstrated that our technique allows determining the coincidence between the laser and radiation beam. The technique described here is found to be suitable for periodic QA checks of relative positions of the spot center relative to the gantry isocenter and beam central axis. Improvements of this technique by considering the effect of detector's quantum yield and modulation transfer function on the data remain subject of further study.

Residual setup errors and dose variations with less-than-daily image guided patient setup in external beam radiotherapy for esophageal cancer

Background and purposeTo evaluate residual patient setup errors and daily dose variations of different less-than-daily image guidance (IG) strategies in the delivery of external beam radiotherapy for esophageal cancer. Material and methodsDaily image-guided setup data for 25 consecutive esophageal cancer patients treated with helical tomotherapy were evaluated. Seven less-than-daily IG strategies with different imaging frequencies were simulated. For each IG strategy, the daily residual setup errors were calculated. Using TomoTherapy Planned Adaptive software, daily dose variations to the clinical target volume, heart, and lungs were evaluated in five representative patients. ResultsWith 0% (60%) IG frequency, the margins required for adequate coverage of the clinical target volume were 13mm (10mm), 14mm (11mm), and 5mm (5mm) in the left–right, superior–inferior, and anterior–posterior directions, respectively. Even with 60% IG frequency, 10% of the fractions had more than 10% decrease in the dose level covering 95% of the target, and 14% and 13% of the fractions had more than 10% increase in total lung volume receiving at least 0.8Gy per fraction, and heart volume receiving at least 1.2Gy per fraction, respectively. ConclusionSubstantial residual setup errors would occur for treatment fractions without IG even if the most frequent less-than-daily IG strategy was to be used, which could lead to significant daily dose variations for the target volume and adjacent normal tissues. Daily image guidance is recommended throughout the course of treatment in conformal radiotherapy for esophageal cancer.

Impact of Daily Image Guided Patient Setup on Bone Marrow Sparing in Cervical Cancer Patients Undergoing IMRT

Impact of Daily Image Guided Patient Setup on Bone Marrow Sparing in Cervical Cancer Patients Undergoing IMRT

TH-D-351-07: Evaluation of Automatic Volume Match Function for Kilovoltage Cone-Beam CT (CBCT) Guided Patient Setup

Purpose: To evaluate the automatic volume match function provided by a commercial Cone‐beam CT(CBCT) guided patient setup system. Method and Materials:CBCTimages from 10 patients treated with stereotactic body radiotherapy for primary livercancers in the stereotactic frame were acquired by On‐board Imager (OBI, Varian Medical System) following initial treatment setup. Manual volume registration of CBCT to the planning CT was performed by physicians to adjust patient positioning. Retrospective automatic volume match was also performed for each dataset and compared to the manual registration. To further assess the automatic volume match, simulation of patient rotational offsets was generated. Automatic volume matching of the simulated data was used to investigate potential setup errors due to patient roll. Results: A total of 27 CBCT datasets were acquired and analyzed. The average differences between manual and automatic match are 2.4±1.7mm, 3.2±2.6mm and 1.8±1.6mm in the right‐left, superior‐inferior and anterior‐posterior directions, respectively. The simulation study demonstrated a significant limitation of the automatic 4 degrees of freedom (4DOF) correction mode with regard to the patient's rotational offset. This occurs because the 6 degrees of freedom (6DOF) registration algorithm is always internally applied, even in 4DOF shift calculation mode, although the two dimensions of pitch/roll offsets are not displayed. Our simulation revealed that this can cause patient setup error which becomes significant as the distance between the patient rotation axis and the treatment isocenter increases. Conclusion: Caution needs to be taken when using automatic volume match function for CBCT‐guided patient setup since the conventional treatment couch is only capable of translational and limited rotational shifts. Using the full degrees of freedom automatic volume match without caution can lead to significant error in patient treatment.

Ultrasound image guided patient setup for prostate cancer conformal radiotherapy

The radiotherapy planning procedure is achieved using images obtained from computed tomography (CT) or magnetic resonance imaging (MR). These images are realised before the treatment which is performed in several sessions over several weeks. At the beginning of each session, the patient has to be positioned on the treatment couch under the linear accelerator in the same position as during MR or CT imaging and planning, and the organs are assumed to be in the same place. Currently, the methods used for this repositioning are based on the external anatomy of the patient and assume that the internal structures do not move. In this study, we present a new approach, suited to clinical practice, for the automatic repositioning of patients in prostate cancer radiotherapy. It is based on localization by ultrasound images and optical stereolocalization and on a matching with images regenerated in the planning volume. The method exploits a statistical model of the prostate to automatically extract its contours. The first tests in conditions of a radiotherapy session show that the method is able to obtain a patient setup with an accuracy of about 1.4 mm.