bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interobserver variation in cervical cancer tumor delineation for image‐based radiotherapy planning among and within different specialties
Authors: Wu Dee H. , Mayr Nina A. , Karatas Yasemin , Karatas Rifat , Adli Mustafa , Edwards Susan M. , Wolff James D. , Movahed Allen , Montebello Joseph F. , Yuh William T.C. 
Published: February 2007

Radiation therapy for cervical cancer involves a team of specialists, including diagnostic radiologists (DRs), radiation oncologists (ROs), and medical physicists (MPs), to optimize imaging‐based radiation therapy planning. The purpose of the study was to investigate the interobserver variations in tumor delineation on MR images of cervical cancer within the same and among different specialties. Twenty MRI cervical cancer studies were independently reviewed by two DRs, two ROs, and two MPs. For every study, each specialist contoured the tumor regions of interest (ROIs) on T2‐weighted Turbo Spin Echo sagittal images on all slices containing tumor, and the total tumor volume was computed for statistical analysis. Analysis of variance (ANOVA) was used to compare the differences in tumor volume delineation among the observers. A graph of all tumor‐delineated volumes was generated, and differences between the maximum and minimum volumes over all the readers for each patient dataset were computed. Challenges during the evaluation process for tumor delineation were recorded for each specialist. Interobserver variations of delineated tumor volumes were significant among all observers based on a repeated measures ANOVA, which produced an . The median difference between the maximum delineated volume and minimum delineated volume was 33.5 cm3 (which can be approximated by a sphere of 4.0 cm diameter) across all 20 patients. Challenges noted for tumor delineation included the following: (1) partial voluming by parametrial fat at the periphery of the uterus; (2) extension of the tumor into parametrial space; (3) similar signal intensity of structures proximal to the tumor such as ovaries, muscles, bladder wall, bowel loops, and pubic symphysis; (4) postradiation changes such as heterogeneity and necrosis; (5) susceptibility artifacts from bowels and vaginal tampons; (6) presence of other pathologies such as atypical myoma; (7) factors that affect pelvic anatomy, including the degree of bladder distension, bowel interposition, uterine malposition, retroversion, and descensus. Our limited study indicates significant interobserver variation in tumor delineation. Despite rapid progress in technology, which has improved the resolution and precision of image acquisition and the delivery of radiotherapy to the millimeter level, such “human” variations (at the centimeter level) may overshadow the gain from technical advancement and impact treatment planning. Strategies of standardization and training in tumor delineation need to be developed.PACS number(s):
Technical and dosimetric considerations in IMRT treatment planning for large target volumes
Authors: Malhotra Harish K. , Raina Sanjay , Avadhani Jaiteerth S. , deBoer Steven , Podgorsak Matthew B. 
Published: February 2007

The maximum width of an intensity‐modulated radiotherapy (IMRT) treatment field is usually smaller than the conventional maximum collimator opening because of design limitations inherent in some multileaf collimators (MLCs). To increase the effective field width, IMRT fluences can be split and delivered with multiple carriage positions. However, not all treatment‐planning systems and MLCs support this technique, and if they do, the maximum field width in multiple carriage position delivery is still significantly less than the maximum collimator opening. For target volumes with dimensions exceeding the field size limit for multiple carriage position delivery, such as liver tumors or other malignancies in the abdominal cavity, IMRT treatment can be accomplished with multiple isocenters or with an extended treatment distance. To study dosimetric statistics of large field IMRT planning, an elliptical volume was chosen as a target within a cubic phantom centered at a depth of 7.5 cm. Multiple three‐field plans (one AP and two oblique beams with 160° between them to avoid parallel opposed geometry) with constraints designed to give 100% dose to the elliptical target were developed. Plans were designed with a single anterior field with dual carriage positions, or with the anterior field split into two fields with separate isocenters 8 cm apart with the beams being forcibly matched at the isocenter or with a 1 cm, 2 cm, 3 cm, and 4 cm overlap. The oblique beams were planned with a single carriage position in all cases. All beams had a nominal energy of 6 MV. In the dual isocenter plans, jaws were manually fixed and dose constraints remained unaltered. Dosimetric statistics were studied for plans developed for treatment delivery using both dynamic leaf motion (sliding window) and multiple static segments (step and shoot) with the number of segments varying from 5 to 30. All plans were analyzed based on the dose homogeneity in the isocenter plane, 2 cm anterior and 2 cm posterior to it, along with their corresponding dose‐volume histograms (DVHs). All the dual isocenter plans had slight underdosage anterior to the match point and slight overdosage posterior to it, while the dual carriage plan had a nice blending of the dose distribution without the accompanying hot or cold spots. Based on the dose statistics, it was noted that the dual isocenter plans can be clinically acceptable if they have at least a 3‐cm overlap. In the case of step and shoot IMRT, the number of segments used in a dual carriage plan was found to affect the overall plan dosimetric indices.PACS number: 87.53.Tf
An inhomogeneity correction algorithm for irregular fields of high‐energy photon beams based on Clarkson integration and the 3D beam subtraction method
Authors: Stathakis Sotirios , Kappas Constantin , Theodorou Kiki , Papanikolaou Nikos , Rosenwald Jean‐Claude 
Published: February 2007

A number of treatment‐planning systems still use conventional correction methods for body inhomogeneities. Most of these methods (power law method, tissue—air ratio (TAR), etc.) consider only on‐axis points, rectangular fields, and inhomogeneous slabs covering the whole irradiating field. A new method is proposed that overcomes the above limitations. The new method uses the principle of the Clarkson method on sector integration to take into account the position and lateral extent of the inhomogeneity with respect to the point of calculation, as well as the shape of the irradiating field. The field is divided into angular sectors, and each sector is then treated separately for the presence of inhomogeneities using a conventional correction method. Applying this method, we can predict the correction factors for Co‐60 and 6‐MV photon beams for irregular fields that include inhomogeneities of lower or higher densities relative to water. Validation of the predicted corrections factors was made against Monte Carlo calculations for the same geometries. The agreement between the predicted correction factors and the Monte Carlo calculations was within 1.5%. In addition, the new method was able to predict the behavior of the correction factor when the point of calculation was approaching or moving away from the interface between two materials.PACS number(s): 87.53.Bn, 87.53.Wz
Commissioning and quality assurance of a commercial stereotactic treatment‐planning system for extracranial IMRT
Authors: Wang Lu , Li Jinsheng , Paskalev Kamen , Hoban Peter , Luo Wei , Chen Lili , McNeeley Shawn , Price Robert , Ma Charlie 
Published: February 2007

A 3D treatment‐planning system (TPS) for stereotactic intensity‐modulated radiotherapy (IMRT) using a micro‐multileaf collimator has been made available by Radionics. In this work, we report our comprehensive quality assurance (QA) procedure for commissioning this TPS. First, the accuracy of stereotaxy established with a body frame was checked to ensure accurate determination of a target position within the planning system. Second, the CT‐to‐electron density conversion curve used in the TPS was fitted to our site‐specific measurement data to ensure the accuracy of dose calculation and measurement verification in a QA phantom. Using the QA phantom, the radiological path lengths were verified against known geometrical depths to ensure the accuracy of the ray‐tracing algorithm. We also checked inter‐ and intraleaf leakage/transmission for adequate jaw settings. Measurements for dose verification were performed in various head/neck and prostate IMRT treatment plans using the patient‐specific optimized fluence maps. Both ion chamber and film were used for point dose and isodose distribution verifications. To ensure that adjacent organs at risk receive dose within the expectation, we used the Monte Carlo method to calculate dose distributions and dose‐volume histograms (DVHs) for these organs at risk. The dosimetric accuracy satisfied the published acceptability criteria. The Monte Carlo calculations confirmed the measured dose distributions for target volumes. For organs located on the beam boundary or outside the beam, some differences in the DVHs were noticed. However, the plans calculated by both methods met our clinical criteria. We conclude that the accuracy of the XKnife™ RT2 treatment‐planning system is adequate for the clinical implementation of stereotactic IMRT.PACS numbers: 87.53.Xd, 87.53.Ly, 87.53.Wz
Experimental verification of the application of lateral buildup ratio on the 4‐MeV electron beam
Authors: Chow James C.L. , Newman Scott 
Published: February 2007

The lateral buildup ratio (LBR) used to estimate the depth dose distribution of electron beams for an irregular cutout field was obtained for a 4‐MeV energy beam from a Varian 21 EX linear accelerator. The depth‐dose curves for a group of circular cutout fields starting from a 2‐cm diameter were measured. Electron diodes were used in a large water tank to measure the LBR values for 6, 9, 12, and 16 MeV electron beam energies and a applicator. The results agreed with the published data. When the same equipment, setup, and technique were used to determine the LBR values for the 4‐MeV energy beam, the values were only reasonable, being within the clinical treatment range (i.e., LBR ) for the smallest applicator. The calculated LBR values were clinically unacceptable for the circular cutout fields with a diameter larger than 2 cm with the applicator. The difficulty in the LBR measurement may be due to the significant contribution of scattered electrons from the beam defining system. This study also focused on how well the sigma values for the 4‐MeV beam can predict depth‐dose curves for other field sizes and whether the values are applicator‐dependent.PACS numbers: 87.53.Fs; 87.53.Hv; 87.66.Jj
Dosimetric characteristics of a new linear accelerator under gated operation
Authors: Kriminski Sergey , Li Alex N. , Solberg Timothy D. 
Published: February 2007

Respiratory gated radiotherapy may allow reduction of the treatment margins, thus sparing healthy tissue and/or allowing dose escalation to the tumor. However, current commissioning and quality assurance of linear accelerators do not include evaluation of gated delivery. The purpose of this study is to test gated photon delivery of a Siemens ONCOR Avant‐Garde linear accelerator. Dosimetric characteristics for gated and nongated delivery of 6‐MV and 15‐MV photons were compared for the range of doses, dose rates, and for several gating regimes. Dose profiles were also compared using Kodak EDR2 and X‐Omat V films for 6‐MV and 15‐MV photons for several dose rates and gating regimes. Results showed that deviation is less than or equal to 0.6% for all dose levels evaluated with the exception of the lowest dose delivered at 25 MU at an unrealistically high gating frequency of 0.5 Hz. At 400 MU, dose profile deviations along the central axes in in‐plane and cross‐plane directions within 80% of the field size are below 0.7%. No unequivocally detectable dose profile deviation was observed for 50 MU. Based on the comparison with widely accepted standards for conventional delivery, our results indicate that this LINAC is well suited for gated delivery of nondynamic fields.PACS numbers: 87.56‐By, 87.66‐Cd, 87.66‐Jj
Total body irradiation with a reconditioned cobalt teletherapy unit
Authors: Evans Michael D.C. , Larouche Renée‐Xavière , Olivares Marina , Léger Pierre , Larkin Joe , Freeman Carolyn R. , Podgorsak Ervin B. 
Published: February 2007

While the current trend in radiotherapy is to replace cobalt teletherapy units with more versatile and technologically advanced linear accelerators, there remain some useful applications for older cobalt units. The expansion of our radiotherapy department involved the decommissioning of an isocentric cobalt teletherapy unit and the replacement of a column‐mounted 4‐MV LINAC that has been used for total body irradiation (TBI). To continue offering TBI treatments, we converted the decommissioned cobalt unit into a dedicated fixed‐field total body irradiator and installed it in an existing medium‐energy LINAC bunker. This article describes the logistical and dosimetric aspects of bringing a reconditioned cobalt teletherapy unit into clinical service as a total body irradiator.PACS numbers: 87.53.Dq, 87.53.Mr
A graphical user interface for an electron monitor unit calculator using a sector‐integration algorithm and exponential curve‐fitting method
Authors: Chow James C.L. , Grigorov Grigor N. , MacGregor Christopher 
Published: February 2007

A new electron monitor unit (MU) calculator program called “eMUc” was developed to provide a convenient electron MU calculation platform for the physics and radiotherapy staff in electron radiotherapy. The program was written using the Microsoft Visual Basic.net framework and has a user‐friendly front‐end window with the following features: (1) Apart from using the well‐known polynomial curve‐fitting method for the interpolation and extrapolation of relative output factors (ROFs), an exponential curve‐fitting method was used to obtain better results. (2) A new algorithm was used to acquire the radius in each angular segment in the irregular electron field during the sector integration. (3) A comprehensive graphical user interface running on the Microsoft Windows operating system was used. (4) Importing irregular electron cutout field images to the calculator program was simplified by using only a commercial optical scanner. (5) Interlocks were provided when the input patient treatment parameters could not be handled by the calculator database accurately. (6) A patient treatment record could be printed out as an electronic file or hard copy and transferred to the patient database. The data acquisition mainly required ROF measurements using various circular cutouts for all the available electron energies and applicators for our Varian 21 EX linear accelerator. To verify and implement the calculator, the measured results using our specific designed irregular and clinical cutouts were compared to those predicted by the calculator. Both agreed well with an error of .PACS number(s): 87.53.Fs; 87.53.Hv; 87.66.‐a
Fractionated stereotactic radiotherapy for pediatric patients with retinoblastoma
Authors: Higgins Patrick D. , Gerbi Bruce J. , Macedon Mark , Dusenbery Kathryn E. 
Published: February 2007

In this report, we discuss the application of a modified Gill‐Thomas‐Cosman (GTC) relocatable head frame to enable fractionated stereotactic radiotherapy (SRT) of infants under anesthesia. This system has been used to treat two infants, ages 12 and 18 months, for bilateral retinoblastoma on a Varian 6/100 linear accelerator. The GTC head frame was used to reproducibly position and treat the orbits of these children to between 2520 cGy and 3960 cGy in 180‐cGy fractions. A standard head and neck tray, with accompanying thermoplastic mask, was adapted to mount to the head frame to enable these treatments. We found the maximum average deviation in the repeat fixations, as compared with the initial fitting data, to be . The overall average difference and standard deviation in measurement was for the first case and for the second case, with a combined average of overall from a total of 381 point measurements. The stereotactic treatment plan (Radionics®) incorporated a single isocenter for each orbit and 3 or 4 arcs per isocenter. An intercomparison has been made between this technique and a standard lateral field technique, designed using the stereotactic radiosurgery (SRS) planning system. Dose‐volume histograms and corresponding normal tissue complication probabilities (NTCP) based on pediatric bone growth inhibition have been calculated for each method for the orbital bone areas. We found that the NTCP is reduced from 95% or more in the standard treatment method to 16% or less with SRT. Use of the modified head frame provides excellent setup reproducibility, facilitates access to patients for anesthesia, and reduces the chances of a poor cosmetic result in these growing children.PACS number: 87.53.Ly
Verifying monitor unit calculations for tangential breast fields
Authors: Kay Ian , Dunscombe Peter 
Published: February 2007

An essential component of quality assurance in radiation therapy is verifying the accuracy of monitor unit calculations. Differences between sophisticated algorithms using 2.5D or 3D calculations and simpler monitor unit check algorithms or hand calculations assuming a flat water phantom must be expected. For many anatomical sites, such differences are small and of little or no consequence in the context of expected clinical impact. However, for tangential breast fields the discrepancies are considerably larger than those that would generally be considered acceptable. A simple model to reconcile the differences between sophisticated and simple algorithms is presented, based on replacing the breast contour with a triangular or elliptical contour and using this to estimate an equivalent rectangular prism providing equivalent scatter to the prescription point. The elliptical approximation reconciles the observed differences in calculated monitor units. The analysis we present can assist the treatment planning physicist in selecting a method and tolerance window for verifying monitor unit calculations for tangential breast fields.PACS: 87.53.Kn, 87.53.Tf, 87.53.Xd
Extracranial doses in stereotactic and conventional radiotherapy for pituitary adenomas
Authors: Ram Thomas Samuel , Ravindran Paul B. , Viswanathan Faith R. , Viswanathan Perungulam Narayan , Pavamani Simon P. 
Published: February 2007

The purpose of this study is to determine the extracranial dose in patients treated for pituitary adenoma with conventional and stereotactic radiotherapy (SRT). Twelve patients receiving treatment with radiation for pituitary adenoma were selected. Six patients underwent SRT, and six patients underwent conventional radiotherapy. Extracranial doses were measured with pre‐irradiation annealed lithium fluoride thermoluminscent dosimetry (TLD) chips. The chips were wrapped and placed on the patients’ skin, over each eyelid, the thyroid, chest, and scrotum for males and over the suprapubic region for females. Postradiation annealing was done, and the TLDs were read in a TLD reader system. The results were analyzed using the Wilcoxon matched‐pairs signed rank test by SPSS, version 6.01. The doses to the thyroid, center, and gonads were significantly higher (, , and , respectively) in patients receiving SRT than in conventional radiotherapy portals (, , and ). But the average doses to the right eye () and to the left eye () in the stereotactic group were less when compared with the patients treated with conventional radiotherapy, who received and , respectively. In conclusion, SRT is definitely superior to conventional radiotherapy as far as dose to the surrounding normal structures is concerned. The higher extracranial doses in SRT seem to be within the acceptable range; however, the clinical significance of this is still unclear and needs longer followup.PACS number: 87.53.Ly
PTV margin for dose‐escalated radiation therapy of prostate cancer with daily online realignment using internal fiducial markers: Monte Carlo approach and dose population histogram (DPH) analysis
Authors: Zhang Miao , Moiseenko Vitali , Liu Mitchell 
Published: February 2007

Using internal fiducial markers and electronic portal imaging (EPI) to realign patients has been shown to significantly reduce positioning uncertainties in prostate radiation treatment. This creates the possibility of decreasing the planning target volume (PTV) margin added on the clinical target volume (CTV), which in turn may allow for dose escalation. We compared the outcome of two plans: 70 Gy/35 fx, 10‐mm PTV margin without patient realignment (Reference Plan) and 78 Gy/39 fx, 5‐mm PTV margin with patient realignment (Escalated Plan). Four‐field‐oblique (gantry angles 35°, 90°, 270°, 325°) beam arrangement was used. Monte Carlo code was used to simulate the daily organ motion. Dose to each organ was calculated. Tumor control probability (TCP) and the effective dose to critical organs were calculated using the biologically normalized dose‐volume histograms. By comparing the biological factors, we found that the prescription dose can be escalated to 78 Gy/39 fx with a 5‐mm PTV margin when using internal fiducial markers and EPI. Based on the available dose‐response data for intermediate risk prostate patients, this will result in a 20% increase of local control and significantly reduced rectal complications provided that less serial dose‐volume behavior of rectum is proven.PACS number: 87.50.‐a
Applicator volume elimination methods and their influence on DVH analysis of HDR prostate implants
Authors: Vivekanandan Nagarajan , Kunjithapatham Bhuvana , Kanakavelu Nithya , Irde Balakrishnan Shankarrao , Vaidyanathan Lakshmanan Alathurmadam 
Published: February 2007

In CT anatomy‐based inverse treatment planning of interstitial high‐dose rate (HDR) brachytherapy planning, the planning target volume (PTV) delineated by the radiation oncologist includes the applicator volume. The applicator volume can be eliminated with the help of two methods: one based on Boolean operations and the other using the erasing option of the application software. Both methods are compared, and the results are discussed. Elimination of the applicator volume results in the proper estimation of the PTV and the exclusion of the clinically insignificant hot volume from the PTV in the dose‐volume histogram (DVH) analysis. Five cases of prostate cancer are considered for analysis. The PTV, applicator volume, maximum, mean, modal, and minimum dose, and the percentage volume of the PTV structure receiving the percent dose for both cases, that is, with and without applicator volume, are tabulated and analyzed. The elimination of the applicator volume results in the proper volume estimation of the PTV structure and leads to better DVH analysis of interstitial HDR prostate implants. The procedure would have little relevance in routine planning but improves dose reporting. It is too early to conclude its clinical significance or insignificance.PACS numbers: 57.53.Jw, 87.53.Tf