John E. Bayouth

Task Group 142 report: Quality assurance of medical acceleratorsa)

The task group (TG) for quality assurance of medical accelerators was constituted by the American Association of Physicists in Medicines Science Council under the direction of the Radiation Therapy Committee and the Quality Assurance and Outcome Improvement Subcommittee. The task group (TG-142) had two main charges. First to update, as needed, recommendations of Table II of the AAPM TG-40 report on quality assurance and second, to add recommendations for asymmetric jaws, multileaf collimation (MLC), and dynamic/virtual wedges. The TG accomplished the update to TG-40, specifying new test and tolerances, and has added recommendations for not only the new ancillary delivery technologies but also for imaging devices that are part of the linear accelerator. The imaging devices include x-ray imaging, photon portal imaging, and cone-beam CT. The TG report was designed to account for the types of treatments delivered with the particular machine. For example, machines that are used for radiosurgery treatments or intensity-modulated radiotherapy (IMRT) require different tests and/or tolerances. There are specific recommendations for MLC quality assurance for machines performing IMRT. The report also gives recommendations as to action levels for the physicists to implement particular actions, whether they are inspection, scheduled action, or immediate and corrective action. The report is geared to be flexible for the physicist to customize the QA program depending on clinical utility. There are specific tables according to daily, monthly, and annual reviews, along with unique tables for wedge systems, MLC, and imaging checks. The report also gives specific recommendations regarding setup of a QA program by the physicist in regards to building a QA team, establishing procedures, training of personnel, documentation, and end-to-end system checks. The tabulated items of this report have been considerably expanded as compared with the original TG-40 report and the recommended tolerances accommodate differences in the intended use of the machine functionality (non-IMRT, IMRT, and stereotactic delivery).

4DCT-based measurement of changes in pulmonary function following a course of radiation therapy

PURPOSE Radiation therapy (RT) for lung cancer is commonly limited to subtherapeutic doses due to unintended toxicity to normal lung tissue. Reducing the frequency of occurrence and magnitude of normal lung function loss may benefit from treatment plans that incorporate the regional lung and radiation dose information. In this article, the authors propose a method that quantitatively measures the regional changes in lung tissue function following a course of radiation therapy by using 4DCT and image registration techniques. METHODS 4DCT data sets before and after RT from two subjects are used in this study. Nonlinear 3D image registration is applied to register an image acquired near end inspiration to an image acquired near end expiration to estimate the pulmonary function. The Jacobian of the image registration transformation, indicating local lung expansion or contraction, serves as an index of regional pulmonary function. Approximately 120 annotated vascular bifurcation points are used as landmarks to evaluate registration accuracy. The authors compare regional pulmonary function before and after RT to the planned radiation dose at different locations of the lung. RESULTS In all registration pairs, the average landmark distances after registration are on the order of 1 mm. The pulmonary function change as indicated by the Jacobian change ranges from -0.15 to 0.1 in the contralateral lung and -0.22 to 0.23 in the ipsilateral lung for subject A, and ranges from -0.4 to 0.39 in the contralateral lung and -0.25 to 0.5 in the ipsilateral lung for subject B. Both of the subjects show larger range of the increase in the pulmonary function in the ipsilateral lung than the contralateral lung. For lung tissue regions receiving a radiation dose larger than 24 Gy, a decrease in pulmonary function was observed. For regions receiving a radiation dose smaller than 24 Gy, either an increase or a decrease in pulmonary function was observed. The relationship between the pulmonary function change and the radiation dose varies at different locations. CONCLUSIONS With the use of 4DCT and image registration techniques, the pulmonary function prior to and following a course of radiation therapy can be measured. In the preliminary application of this approach for two subjects, changes in pulmonary function were observed with a weak correlation between the dose and pulmonary function change. In certain sections of the lung, detected locally compromised pulmonary function may have resulted from radiation injury.

Analysis of Interfraction Prostate Motion Using Megavoltage Cone Beam Computed Tomography

PURPOSE Determine the degree of interfraction prostate motion and its components measured by using daily megavoltage (MV) cone beam computed tomography (CBCT) imaging. METHODS AND MATERIALS A total of 984 daily MV CBCT images from 24 patients undergoing definitive intensity-modulated radiotherapy for localized prostate cancer were analyzed retrospectively. Pretreatment couch shifts, based on physician registration of MV CBCT to planning CT data sets, were used as a measure of daily interfraction motion. Off-line bony registration was performed to separate bony misalignment from internal organ motion. Interobserver and intraobserver variation studies were performed on 20 MV CBCT images. RESULTS Mean interfraction prostate motion was 6.7 mm, with the greatest single-axis deviation in the anterior-posterior (AP) direction. The largest positional inaccuracy was accounted for by systematic deviations in bony misalignment, whereas random deviations occurred from bony misalignment and internal prostate motion. In the aggregate, AP motion did not correlate with days elapsed since beginning therapy or on average with rectal size at treatment planning. Interobserver variation was greatest in the AP direction, decreased in experienced observers, and further decreased in intraobserver studies. Mean interfraction motion during the first 6 days of therapy, when used as a subsequent offset, reduced acceptable AP planning target volume margins by 50%. CONCLUSION The MV CBCT is a practical direct method of daily localization that shows significant interfraction motion with respect to conventional three-dimensional conformal and intensity-modulated radiotherapy margins, similar to that measured in other modalities.

IMRT to Escalate the Dose to the Prostate while Treating the Pelvic Nodes

Background and Purpose:To assess and quantify the benefit of introducing intensity–modulated radiotherapy (IMRT) over conventional approaches to cover the pelvic nodes while escalating the dose to the prostate gland.Material and Methods:The pelvic lymphatics were planned to receive 50 Gy at 2 Gy per fraction by four–field box (4FB) technique and standard field blocks drawn on digitally reconstructed radiographs (DRR), 4FB with field blocks according to the position of pelvic nodes as contoured on serial planning CT slices, or IMRT. The lateral fields included three different variations of field blocks to assess the role of various degrees of rectal shielding. The boost consisted in 26 Gy in 13 fractions delivered via six–field three–dimensional conformal radiotherapy (3DCRT) or IMRT. By the combination of a pelvic treatment and boost, several plans were obtained for each patient, all normalized to be isoeffective with regard to prostate–planning target volume (PTV–P) coverage. Plans were compared with respect to dose–volume histogram (DVH) of pelvic nodes/seminal vesicles–PTV (PTV–PN/SV), rectum, bladder and intestinal cavity. Reported are the results obtained in eight patients.Results:Pelvic IMRT with a conformal boost provided superior sparing of both bladder and rectum over any of the 4FB plans with the same boost. For the rectum the advantage was around 10% at V70 and even larger for lower doses. Coverage of the pelvic nodes was adequate with initial IMRT with about 98% of the volume receiving 100% of the prescribed dose. An IMRT boost provided a gain in rectal sparing as compared to a conformal boost. However, the benefit was always greater with pelvic IMRT followed by a conformal boost as compared to 4FB with IMRT boost. Finally, the effect of utilizing an IMRT boost with initial pelvic IMRT was greater for the bladder than for the rectum (at V70, about 9% and 3% for the bladder and rectum, respectively).Conclusion:IMRT to pelvic nodes with a conformal boost allows dose escalation to the prostate while respecting current dose objectives in the majority of patients and it is dosimetrically superior to 4FB. An IMRT boost should be considered for patients who fail to meet bladder dose objectives.Ziel:Evaluation des Vorteils der intensitätsmodulierten Radiotherapie (IMRT) im Vergleich zu konventionellen Methoden, um bei Bestrahlung der Beckenlymphknoten die Prostatadosis zu eskalieren.Material und Methoden:Für die Bestrahlung der Beckenlymphknoten wurde eine Gesamtdosis von 50 Gy, in Fraktionen von 2 Gy, geplant unter Einsatz einer „Vier–Felder–Box“–(4FB–)Technik mit Standard–Blöcken, von 4FB–Technik mit Blöcken entsprechend der in seriellen Planungs–CTs festgestellten Lage der Lymphknoten, oder der IMRT. Die lateralen Felder umfassten drei unterschiedliche Anordnungen der Blöcke, um die Rolle verschiedener Grade der Abschirmung des Rektums zu ermitteln. Der Boost bestand aus 26 Gy in 13 Fraktionen, die mittels dreidimensionaler Sechs–Felder–Radiotherapie oder mittels IMRT verabreicht wurden. Durch Kombination von Beckenbestrahlung und Boost wurden für jeden Patienten mehrere Planungen durchgeführt, die alle isoeffektiv für das Planungszielvolumen der Prostata (PTV–P) waren. Die Planungen wurden hinsichtlich der Dosis–Volumen– Histogramme (DVH) des Planungszielvolumens der Beckenlymphknoten/Bläschendrüsen (PTV–PN/SV), des Rektums, der Blase und des Bauchraumes verglichen. Vorgestellt werden die bei acht Patienten ermittelten Ergebnisse.Ergebnisse:Die IMRT des Beckens mit einem konformalen Boost war hinsichtlich des Schutzes von Blase und Rektum allen 4FBPlanungen mit demselben Boost überlegen. Für das Rektum betrug der Vorteil rund 10% bei V70 und war noch größer bei niedrigerer Strahlungsdosis. Die Bestrahlung der Beckenlymphknoten war bei initialer IMRT voll ausreichend, indem ungefähr 98% des Volumens 100% der vorgesehenen Dosis erhielten. Ein IMRT–Boost bewirkte, verglichen mit dem konformalen Boost, eine wirksamere Abschirmung des Rektums. Der Vorteil war jedoch bei IMRT des Beckens mit konformalem Boost immer größer als bei 4FBReceived: Technik mit IMRT–Boost. Außerdem war der Effekt eines IMRT–Boost mit initialer IMRT des Beckens für die Blase höher als für das Rektum (bei V70 rund 9% und 3% für Blase bzw. Rektum).Schlussfolgerung:IMRT der Beckenlymphknoten mit konformalem Boost erlaubt bei der Mehrzahl der Patienten die Eskalation der Prostatadosis unter Berücksichtigung der Zieldosis und ist dosimetrisch der 4FB–Technik überlegen. Ein IMRT–Boost kommt in Betracht für Patienten, bei denen die Zieldosis der Blase nicht erreicht wird.

MLC quality assurance techniques for IMRT applications

Intensity modulated radiotherapy (IMRT) requires extensive knowledge of multileaf collimator (MLC) leaf positioning accuracy, precision, and long-term reproducibility. We have developed a technique to efficiently measure the absolute position of each MLC leaf, over the range of leaf positions utilized in IMRT, based on dosimetric information. A single radiographic film was exposed to 6 MV x-rays for twelve exposures: one open field with a radio-opaque marker tray present, and eleven fields (1 x 28 cm strips via 1 cm gaps between opposed leaf pairs) separated by 2 cm center to center. The process was repeated while varying direction of leaf travel; each film was digitized using a commercial film dosimetry system. The digital images were manipulated to remove translation and rotation of the film data with respect to the collimator coordinate system by extraction of radiation dose profiles perpendicular to the MLC leaf motion and measuring the center of the x-ray leakage between leaves. Radiation dose profiles in the direction of leaf motion were acquired through the center of each leaf pair (leaves 2-28), which provided leaf position information every 2 cm with 0.2 mm precision. Nine separate leaf reproducibility studies over a 90 day period which evaluated 600 measurement points on each film show 0.3 mm precision for 95% confidence, while hysteresis studies show 0.5 mm precision. Absolute leaf position error measurements demonstrated a radial dependence, with a maximum of 1.5 mm at 16.4 cm from central axis, due to rotational error at calibration. Recalibration of the MLC leaves based utilizing this tool yields absolute leaf position measurements where 91.5% of all leaves/positions were within 0.5 mm, with a mean error of 0.1 mm and a maximum error less than 1.0 mm.

Image guided radiation therapy (IGRT) technologies for radiation therapy localization and delivery.

Image Guided Radiation Therapy (IGRT) Technologies for Radiation Therapy Localization and Delivery Jennifer De Los Santos, MD,* Richard Popple, PhD,* Nzhde Agazaryan, PhD,y John E. Bayouth, PhD,z Jean-Pierre Bissonnette, PhD,x Mary Kara Bucci, MD,k Sonja Dieterich, PhD,{ Lei Dong, PhD, Kenneth M. Forster, PhD,** Daniel Indelicato, MD,yy Katja Langen, PhD,zz Joerg Lehmann, PhD,{ Nina Mayr, MD,xx Ishmael Parsai, PhD,{{ William Salter, PhD, Michael Tomblyn, MD, MS,*** William T.C. Yuh, MD, MSEE,kk and Indrin J. Chetty, PhDyyy *Department of Radiation Oncology, University of Alabama at Birmingham, Birmingham, Alabama; yDepartment of Radiation Oncology, University of California Los Angeles, Los Angeles, California; zDepartment of Radiation Oncology, University of Iowa, Iowa City, Iowa; xDepartment of Radiation Physics, Princess Margaret Hospital, Toronto, Ontario, Canada; kAnchorage Radiation Therapy Center, Anchorage, Alaska; {Department of Radiation Oncology, University of California Davis, Sacramento, California; Scripps Proton Therapy Center, San Diego, California; **Department of Radiation Oncology, University of South Alabama, Mobile, Alabama; yyDepartment of Radiation Oncology, University of Florida Proton Therapy Institute, Jacksonville, Florida; zzDepartment of Radiation Oncology, MD Anderson Cancer Center Orlando, Orlando, Florida; Departments of xxRadiation Oncology and kkRadiology, Ohio State University, Columbus, Ohio; {{Department of Radiation Oncology, University of Toledo College of Medicine, Toledo, Ohio; Department of Radiation Oncology, Huntsman Cancer Hospital, Salt Lake City, Utah; ***Department of Radiation Oncology, Moffitt Cancer Center, Tampa, Florida; and yyyDepartment of Radiation Oncology, Henry Ford Hospital and Health Centers, Detroit, Michigan

Optimal Co-Segmentation of Tumor in PET-CT Images With Context Information

Positron emission tomography (PET)-computed tomography (CT) images have been widely used in clinical practice for radiotherapy treatment planning of the radiotherapy. Many existing segmentation approaches only work for a single imaging modality, which suffer from the low spatial resolution in PET or low contrast in CT. In this work, we propose a novel method for the co-segmentation of the tumor in both PET and CT images, which makes use of advantages from each modality: the functionality information from PET and the anatomical structure information from CT. The approach formulates the segmentation problem as a minimization problem of a Markov random field model, which encodes the information from both modalities. The optimization is solved using a graph-cut based method. Two sub-graphs are constructed for the segmentation of the PET and the CT images, respectively. To achieve consistent results in two modalities, an adaptive context cost is enforced by adding context arcs between the two sub-graphs. An optimal solution can be obtained by solving a single maximum flow problem, which leads to simultaneous segmentation of the tumor volumes in both modalities. The proposed algorithm was validated in robust delineation of lung tumors on 23 PET-CT datasets and two head-and-neck cancer subjects. Both qualitative and quantitative results show significant improvement compared to the graph cut methods solely using PET or CT.

Globally optimal tumor segmentation in PET-CT images: a graph-based co-segmentation method

Tumor segmentation in PET and CT images is notoriously challenging due to the low spatial resolution in PET and low contrast in CT images. In this paper, we have proposed a general framework to use both PET and CT images simultaneously for tumor segmentation. Our method utilizes the strength of each imaging modality: the superior contrast of PET and the superior spatial resolution of CT. We formulate this problem as a Markov Random Field (MRF) based segmentation of the image pair with a regularized term that penalizes the segmentation difference between PET and CT. Our method simulates the clinical practice of delineating tumor simultaneously using both PET and CT, and is able to concurrently segment tumor from both modalities, achieving globally optimal solutions in low-order polynomial time by a single maximum flow computation. The method was evaluated on clinically relevant tumor segmentation problems. The results showed that our method can effectively make use of both PET and CT image information, yielding segmentation accuracy of 0.85 in Dice similarity coefficient and the average median hausdorff distance (HD) of 6.4 mm, which is 10% (resp., 16%) improvement compared to the graph cuts method solely using the PET (resp., CT) images.

Evaluation of Artifacts and Distortions of Titanium Applicators on 3.0-Tesla MRI: Feasibility of Titanium Applicators in MRI-Guided Brachytherapy for Gynecological Cancer

PURPOSE The aim of this study was to characterize the levels of artifacts and distortions of titanium applicators on 3.0-Tesla magnetic resonance imaging (MRI). METHODS AND MATERIALS Fletcher-Suit-Delclos-style tandem and ovoids (T&O) and tandem and ring applicator (T&R) were examined. The quality assurance (QA) phantoms for each applicator were designed and filled with copper sulphate solution (1.5 g/l). The artifacts were quantified with the registration of corresponding computed tomography (CT) images. A favorable MR sequence was searched in terms of artifacts. Using the sequence, the artifacts were determined. The geometric distortions induced by the applicators were quantified through each registration of CT and MRI without applicators. The artifacts of T&O were also evaluated on in vivo MRI datasets of 5 patients. RESULTS T1-weighted MRI with 1-mm slice thickness was found as a favorable MR sequence. Applying the sequence, the artifacts at the tandem tip of T&O and T&R were determined as 1.5 ± 0.5 mm in a superior direction in phantom studies. In the ovoids of T&O, we found artifacts less than 1.5 ± 0.5 mm. The artifacts of a T&O tandem in vivo were found as less than 2.6 ± 1.3 mm on T1-weighted MRI, whereas less than 6.9 ± 3.4 mm on T2-weighted MRI. No more than 1.2 ± 0.6 mm (3.0 ± 1.5 mm) of distortions, due to a titanium applicator, were measured on T1-weighted MRI (T2-). CONCLUSION In 3.0-Tesla MRI, we found the artifact widths at the tip of tandem were less than 1.5 ± 0.5 mm for both T&O and T&R when using T1-weighted MRI in phantom studies. However, exclusive 3.0-Tesla MRI-guided brachytherapy planning with a titanium applicator should be cautiously implemented.

Changing failure patterns in oropharyngeal squamous cell carcinoma treated with intensity modulated radiotherapy and implications for future research.

Objective:Review the University of Iowa experience with intensity modulated radiation treatment (IMRT) in oropharyngeal squamous cell carcinoma. Methods:From January 2000 to July 2004, 66 patients with oropharyngeal cancer were treated with IMRT, 62 with definitive IMRT and 4 postoperative IMRT. Three target volumes (CTV1, CTV2, and CTV3) were defined. The prescribed doses to CTV1, CTV2, and CTV3 were 70 to 74 Gy, 60 Gy, and 54 Gy, respectively, for definitive IMRT, and 60 to 66 Gy, 60 Gy, and 54 Gy, respectively, for postoperative IMRT. Results:Median follow-up was 27.3 months and all living patients had a follow-up of at least 11.5 months. The 3-year estimate of locoregional progression free survival was 98.8%. However, there is a high incidence of distant metastasis with a 3-year estimate of distant metastasis-free survival of 80.4%. In addition, there is a high incidence of second primary tumor. The 3-year overall survival and 3-year disease-free survival were 78.1% and 64.4%, respectively. Treatment was well tolerated with 1 death resulting from treatment toxicity. Conclusions:IMRT offers an excellent locoregional control for oropharyngeal cancer patients. Failure patterns have changed with an increased portion of patients who failed distantly, either with metastasis or second primary tumor. Therefore, survival for these patients is still poor. Future research should focus on identifying patients at high risk of distant diseases and developing effective systemic treatment and prevention for distant diseases.