Dose-guided Radiation Therapy Research Articles

Three-dimensional dose evaluation in breast cancer patients to define decision criteria for adaptive radiotherapy

Background: Dose-guided adaptive radiation therapy (DGART) is the systematic evaluation and adaptation of the dose delivery during treatment for an individual patient. The aim of this study is to define quantitative action levels for DGART by evaluating changes in 3D dose metrics in breast cancer and correlate them with clinical expert evaluation.Material and methods: Twenty-three breast cancer treatment plans were evaluated, that were clinically adapted based on institutional IGRT guidelines. Reasons for adaptation were variation in seroma, hematoma, edema, positioning or problems using voluntary deep inspiration breath hold. Sixteen patients received a uniform dose to the breast (clinical target volume 1; CTV1). Six patients were treated with a simultaneous integrated boost to CTV2. The original plan was copied to the CT during treatment (re-CT) or to the stitched cone-beam CT (CBCT). Clinical expert evaluation of the re-calculated dose distribution and extraction of dose-volume histogram (DVH) parameters were performed. The extreme scenarios were evaluated, assuming all treatment fractions were given to the original planning CT (pCT), re-CT or CBCT. Reported results are mean ± SD.Results: DVH results showed a mean dose (Dmean) difference between pCT and re-CT of -0.4 ± 1.4% (CTV1) and −1.4 ± 2.1% (CTV2). The difference in V95% was −2.6 ± 4.4% (CTV1) and −9.8 ± 8.3% (CTV2). Clinical evaluation and DVH evaluation resulted in a recommended adaptation in 17/23 or 16/23 plans, respectively. Applying thresholds on the DVH parameters: Dmean CTV, V95% CTV, Dmax, mean lung dose, volume exceeding 107% (uniform dose) or 90% (SIB) of the prescribed dose enabled the identification of patients with an assumed clinically relevant dose difference, with a sensitivity of 0.89 and specificity of 1.0. Re-calculation on CBCT imaging identified the same plans for adaptation as re-CT imaging.Conclusions: Clinical expert evaluation can be related to quantitative DVH parameters on re-CT or CBCT imaging to select patients for DGART.

WE-A-BRF-01: Dual-Energy CT Imaging in Diagnostic Imaging and Radiation Therapy

The quantification accuracy of dual-energy imaging is influenced by the fundamentals of x-ray physics, system geometry, data acquisition hardware/protocol, system calibration, and image processing technique. This symposium will provide updates on the following advanced application areas: Mammography. Volumetric breast density techniques based on standard mammograms require estimation of breast thickness, which is difficult to accurately measure. By comparison, calculation of breast density using dual energy mammography does not require measurement of breast thickness. Dual energy mammography has been implemented using both energy integrating flat panel detectors in conjunction with beam energy switching and energy resolved photon counting detectors. These techniques have been optimized using simulation studies and validated using physical phantoms and postmortem breasts. Chemical decomposition was used as the gold standard for volumetric breast density measurement in postmortem breasts. Breast density measurements have also been compared with results from four-category BI-RADS density rankings, standard image thresholding and Fuzzy k-mean clustering techniques. These studies indicate that dual energy mammography can be used to accurately measure volumetric breast density. Cardiovascular CT. The predicative accuracy of risk models for recurrent stroke and cardiac arrest depends heavily on accurate differentiation of thrombus or calcium from iodine in left atrial appendage or coronary arteries. The amount of energy separation is constrained by image noise; therefore, optimal kVp, beam filtration, and balanced flux are essential for the quantification accuracy of iodine and calcium. The basis materials are combined linearly to generate monochromatic energy images, where CT# accuracy and CNR are energy dependent. With optimal monochromatic energy, the mean iodine concentration for the thrombus, circulatory stasis, and control groups are significantly different. Risk classification based on calcium scores shows excellent agreement with classification on the basis of conventional coronary artery calcium scoring. These studies demonstrate dual-energy cardiovascular CT can potentially be a noninvasive and sensitive modality in high risk patients. On-board KV/MV Imaging. To enhance soft tissue contrast and reduce metal artifacts, we have developed a dual-energy CBCT technique and a novel on-board kV/MV imaging technique based on hardware available on modern linear accelerators. We have also evaluated the feasibility of these two techniques in various phantom studies. Optimal techniques (energy, beam filtration, # of overlapping projections, etc) have been investigated with unique calibration procedures, which leads to successful decomposition of imaged material into acrylic-aluminum basis material pair. This enables the synthesis of virtual monochromatic (VM) CBCT images that demonstrate much less beam hardening, significantly reduced metal artifacts, and/or higher soft tissue CNR compared to single-energy CBCT. Adaptive Radiation Therapy. DECT could actually contribute to the area of Dose-Guided Radiation Therapy (or Adaptive Therapy). The application of DECT imaging using 80kV and 140 kV combinations could potentially increase the image quality by reducing the bone or high density material artifacts and also increase the soft tissue contrast by a light contrast agent. The result of this higher contrast / quality images is beneficial for deformable image registration / segmentation algorithm to improve its accuracy hence to make adaptive therapy less time consuming in its recontouring process. The real time re-planning prior to per treatment fraction could become more realistic with this improvement especially in hypofractional SBRT cases. Learning Objectives: 1. Learn recent developments of dual-energy imaging in diagnosis and radiation therapy; 2. Understand the unique clinical problem and required quantification accuracy in each application; 3. Understand the different approaches to optimize dual-energy imaging techniques for different applications.

Development of Patient-Specific 3D Dose Evaluation Solution for Dose-Guided Adaptive Radiation Therapy

settlement at each fraction of treatment. In this study, the rectum doses associated by kV-CBCT application were investigated during imagining of pelvic region. Materials/Methods: Rando phantom was used. The position of rectum was determined based on CT fusion of a suit patient’s anatomy for Rando phantom. A rectal cavity was created for positioning of dosimeters. For this purpose the three distal slice of Rando phantom replacing with the home-made designed molded paraffin slices, then for each slice the cavity was formed for replacing the intracavitary rectal probe (IRP). IBA, IDF-5 that contained five diodes along 10 cm was used. The diode calibration process was done. LINAC with kV-CBCT unit was used. Our most common imaging protocols of pelvic region “Prostate M10” (M10), “Pelvis M20” (M20), and “Large Pelvis L20” (L20) were included. M10, M20 and L20 mean the field of view (FOV) at isocenter with size of 27 x 26 cm, 41 x 26 cm, and 57 x 26 cm respectively. All protocols contain a 360 rotation scan, 120 kV, 40 ms per frame, with 650 frames per scan. But M10 has 40 mA per frame while others 25 mA. Beside this M20 and L20 protocols were also measured with 40 mA as well. kVp and mAs of Xray tube and response of image receiver were checked and compared to the factory settings. Rectum doses were measured by IRP for each protocol and repeated 10 times. Rectum doses were obtained as an average of 5 measurement points (cranial-caudal direction; r1, r2, r3, r4 and r5). Results: Imaging parameters were compatible with the factory settings (<1%). The rectum average dose for the same imaging parameters in M10, M20 and L20 were 9.15 0.26, 9.45 0.21 and 8.16 0.27 cGy respectively. L20 has the lowest dose for rectum due to window of large FOV is located near to the edge of collimation and the spectrum has less effective high energy photons. As the mA decreased to 25 in M20 and L20 protocols the rectum average dose were reduced to 6.62 0.19 and 5.67 0.22 cGy respectively. Reduction of mA causes approximately 30% lower dose in the rectum. Conclusions: The kV-CBCT imaging technique provides an accurate guidance but on the other hand a high level of dose per fraction to therapeutic radiation doses is given. Treatment planning systems cannot take into account this additional imaging dose. Due to biological dose effects, these imaging doses should be monitored more carefully for critical organs. This study prompts each clinic to establish their protocol for decision making. Author Disclosure: I. Catan: None. N. Tuncel: None. M. Yavuz: None. C. Akbas‚: None. N. Unal: None.

A Tool for the Daily Management of Dose Guided Radiation Therapy for Head and Neck IMRT Patients

A Tool for the Daily Management of Dose Guided Radiation Therapy for Head and Neck IMRT Patients

SU-E-T-204: A Prototype of Dose-Guided Radiation Therapy.

With the advancement in dosimetric devices and the development of dose reconstruction algorithm, the implementation of dose-guided radiation therapy (DGRT) is feasible. In order for DGRT to be performed clinically, a prototype of DGRT was developed in this study. The prototype adopted a strategy for DGRT that adjusted the treatment plan for future fractions to compensate for dosimetric errors from past fractions, which included four main functional modules: management of patient plan information, dose reconstruction, dose evaluation, plan adjustment. we developed our dose reconstruction procedure, including the dosimetric calibration of the portal image acquired using electronic portal image device (EPID) during treatment and three-dimensional (3D) patient dose reconstruction based on Monte Carlo Finite-size pencil beam (MCFSPB) model and Conjugate-gradient (CG) algorithm developed by FDS Team (www.fds.org.cn). The dose evaluation tools including 3D Gamma analysis and dose-volume-histogram (DVH) analysis were also available which were used to compare the reconstruction dose with the planning dose. Finally we re-optimizing the treatment plan according to the information provided by dose evaluation. In order to validate the availability of the workstation prototype, lots of experiments were carried out based on head phantom. The result showed that disagreement between the reconstructed dose and the planning dose (calculated by the Accurate Radiotherapy System (ARTS) developed by FDS Team) was observed by the DGRT prototype when there existed position error for head phantom or the accelerator delivery was not accurate. An effective prototype for DGRT has been developed. With these techniques, the clinical implementation of DGRT is possible in the near future. Supported by the National Natural Science Foundation under grant No.30900386 and the National Science Foundation of Anhui Province (Nos.090413095 and 111040606Q55).

SU-E-T-504: Incident Fluence Reconstruction Based on Monte Carlo Finite-Size Pencil Beam Model for Dose Guided Radiation Therapy.

In dose guided radiation therapy, incident fluence is one of the important parameters for both influence verification and dose reconstruction. The objective of this investigation was to develop a method to obtain the incident fluence for dose reconstruction in dose guided radiation therapy (DGRT). An incident fluence reconstruction model based on Monte Carlo Finite-size pencil beam (MCFSPB) model and "Matthew Effect" Conjugate-gradient (CG) algorithm was developed, where the MCFSPB model was developed by FDS Team (www.fds.org.cn) and the "Matthew Effect" was proposed to advance the accuracy of CG lgorithm. Then, by measuring dose with amorphous silicon flat panel (a-Si flat panel), the incident fluence was unfolded. An artifical head phantom was used to test sample. By using the incident fluence to dose calculation with MCFSPB, the 2D and 3D dose was also reconstructed and compared with the measurement dose and the planing dose respectively. The Passing Rate of Dose Difference (PRDD) in 3% was used to learn the accuracy. Two representative cases (6MV and 10MV) with both five beams were used for beam-by-beam verification, and the corresponding incident fluence was obtained. By comparing the measurement dose with the calculation dose on measurement plane, the results showed that the PRDD (3%) in field was 100%. And by comparing 3D plannning dose with 3D reconstructed dose, the results indicated that the PRDD (3%) in field was 95%∼98%. The incident fluence reconstruction model based on MCFSPB model and "Matthew Effect" Conjugate-gradient algorithm was developed. The tested results indicated its accuracy. This study is expected to be applied to 3D dose reconstruction and 3D dosimetric verification in DGRT. Supported by the National Natural Science Foundation under grant No.30900386 and the National Science Foundation of Anhui Province (Nos.090413095 and 111040606Q55).

Dosimetric uncertainties related to the elasticity of bladder and rectal walls: Adenocarcinoma of the prostate

Purpose Radiotherapy is an important treatment for prostate cancer. During treatment sessions, bladder and rectal repletion is difficult to quantify and cannot be measured with a single and initial CT scan acquisition. Some methods, such as image-guided radiation therapy and dose-guided radiation therapy, aim to compensate this missing information through periodic CT acquisitions. The aim is to adapt patient's position, beam configuration or prescribed dose for a dosimetric compliance. Methods We evaluated organ motion (and repletion) for 54 patients after having computed the original ballistic on a new CT scan acquisition. A new delineation was done on the prostate, bladder and rectum to determine the new displacements and define organ doses mistakes (equivalent uniform dose, average dose and dose–volume histograms). Results The new CT acquisitions confirmed that bladder and rectal volumes were not constant during sessions. Some cases showed that previously validated treatment plan became unsuitable. A proposed solution is to correct dosimetries when bladder volume modifications are significant. The result is an improvement for the stability of bladder doses, D50 error is reduced by 25.3%, mean dose error by 5.1% and equivalent uniform dose error by 2.6%. For the rectum this method decreases errors by only 1%. This process can reduce the risk of mismatch between the initial scan and following treatment sessions. Conclusion For the proposed method, the cone-beam CT is necessary to properly position the isocenter and to quantify bladder and rectal volume variation and deposited doses. The dosimetries are performed in the event that bladder (or rectum) volume modification limits are exceeded. To identify these limits, we have calculated that a tolerance of 10% for the equivalent uniform dose (compared to the initial value of the first dosimetry), this represents 11% of obsolete dosimetries for the bladder, and 4% for the rectum.

Dose Recalculation and the Dose-Guided Radiation Therapy (DGRT) Process Using Megavoltage Cone-Beam CT

At the University of California San Francisco, daily or weekly three-dimensional images of patients in treatment position are acquired for image-guided radiation therapy. These images can be used for calculating the actual dose delivered to the patient during treatment. In this article, we present the process of performing dose recalculation on megavoltage cone-beam computed tomography images and discuss possible strategies for dose-guided radiation therapy (DGRT). A dedicated workstation has been developed to incorporate the necessary elements of DGRT. Patient image correction (cupping, missing data artifacts), calibration, completion, recontouring, and dose recalculation are all implemented in the workstation. Tools for dose comparison are also included. Examples of image correction and dose analysis using 6 head-and-neck and 2 prostate patient datasets are presented to show possible tracking of interfraction dosimetric endpoint variation over the course of treatment. Analysis of the head-and-neck datasets shows that interfraction treatment doses vary compared with the planning dose for the organs at risk, with the mean parotid dose and spinal cord D(1) increasing by as much as 52% and 10%, respectively. Variation of the coverage to the target volumes was small, with an average D(5) dose difference of 1%. The prostate patient datasets revealed accurate dose coverage to the targeted prostate and varying interfraction dose distributions to the organs at risk. An effective workflow for the clinical implementation of DGRT has been established. With these techniques in place, future clinical developments in adaptive radiation therapy through daily or weekly dosimetric measurements of treatment day images are possible.

SU-FF-J-50: Dose-Guided Radiation Therapy Strategies with Megavoltage Cone-Beam CT

Dose Guided Radiation Therapy (DGRT) is an extension of adaptive radiation therapy where dosimetric considerations constitute the basis of treatment modification and validation. The objective of this work is to elaborate two DGRT scenarios, treatment-time and progressive, and gather all the required functionalities within the same workstation to use it in a clinical environment. The proposed DGRT strategies use a density-calibrated Megavoltage Cone-Beam CT (MVCBCT) image acquired at treatment time, the reference dose plan imported from the planning system and an independent dose calculation engine. A DGRT workstation was created to compare the initial plan with the dose distribution of the day. The beam arrangement is copied to the pre-registered MVCBCT and dose distribution is calculated. Side by side comparison, dose difference maps and DVH differences are used to assess the clinical situation. Phantom experiments and patient data were used to test the DGRT scenarios. A Pinnacle dose calculation was performed to validate the local dose calculation engine. The DGRT workstation integrates the following steps; image registration, correction and conversion of MVCBCT images into density, dose re-calculation, dose comparison with the reference plan and a data extraction module for statistical analysis. Dose re-calculation on MVCBCT images is performed with a precision better than 3%, enabling the progressive DGRT scenario. When performed on a patient treated for a base of tongue tumor with IMRT, the DGRT scenario showed a mean dose increase from 26 to 42 Gy in the left parotid. DGRT brings together the knowledge of 3D imaging and the 3D dose distribution to assess the clinical situation. By making dose re-calculation fast and accurate, the DGRT workstation allows dosimetric studies on a large scale. Results from on-going clinical studies will determine how frequently significant dose differences occur and lead to site-specific adaptation strategies. Research sponsored by Siemens OCS.

Proton therapy is the best radiation treatment modality for prostate cancer

Proton therapy is the best radiation treatment modality for prostate cancer

Dose-guided radiation therapy with megavoltage cone-beam CT

Recent advances in fractionated external beam radiation therapy have increased our ability to deliver radiation doses that conform more tightly to the tumour volume. The steeper dose gradients delivered in these treatments make it increasingly important to set precisely the positions of the patient and the internal organs. For this reason, considerable research now focuses on methods using three-dimensional images of the patient on the treatment table to adapt either the patient position or the treatment plan, to account for variable organ locations. In this article, we briefly review the different adaptive methods being explored and discuss a proposed dose-guided radiation therapy strategy that adapts the treatment for future fractions to compensate for dosimetric errors from past fractions. The main component of this strategy is a procedure to reconstruct the dose delivered to the patient based on treatment-time portal images and pre-treatment megavoltage cone-beam computed tomography (MV CBCT) images of the patient. We describe the work to date performed to develop our dose reconstruction procedure, including the implementation of a MV CBCT system for clinical use, experiments performed to calibrate MV CBCT for electron density and to use the calibrated MV CBCT for dose calculations, and the dosimetric calibration of the portal imager. We also present an example of a reconstructed patient dose using a preliminary reconstruction program and discuss the technical challenges that remain to full implementation of dose reconstruction and dose-guided therapy.

TU-D-ValB-01: Mega-Voltage Cone-Beam Computerized Tomography

Mega‐Voltage Cone‐Beam Computed Tomography (MVCBCT) systems have been in clinical use at UCSF since February 2005. This lecture will provide a general description of the MVCBCT system, image acquisition,reconstruction and registration. The practical clinical applications as well as the guidance strategies will be presented through a number case studies including the following anatomical sites; head&neck, lung, spine, prostate and pelvic sites. Educational Objectives 1. Understand the basics concepts of MV Cone‐Beam CTimaging. 2. Understand the range of clinical applications made possible by MVCBCT in the following categories: a. Patient and organ positioning b. Monitoring of anatomical changes and tumordose response c. Tomosythesis d. Dosimetric impact e. Dose planning in presence of CT non‐compatible objects f. Brachytherapy g. Dose‐guided radiation therapy (DGRT). This work was supported by Siemens Oncology Care Systems.

Low-dose megavoltage cone-beam CT for dose-guided radiation therapy

Low-dose megavoltage cone-beam CT for dose-guided radiation therapy