bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dosimetric comparison of extended dose range film with ionization measurements in water and lung equivalent heterogeneous media exposed to megavoltage photons
Authors: Charland Paule M. , Chetty Indrin J. , Yokoyama Shigeru , Fraass Benedick A. 
Published: February 2007

In this study, a dosimetric evaluation of the new Kodak extended dose range (EDR) film versus ionization measurements has been conducted in homogeneous solid water and water‐lung equivalent layered heterogeneous phantoms for a relevant range of field sizes (up to a field size of and a depth of 15 cm) for 6 and 15 MV photon beams from a linear accelerator. The optical density of EDR film was found to be linear up to about 350 cGy and over‐responded for larger fields and depths (5% for at depth of 15 cm compared to a , 5 cm depth reference value). Central axis depth dose measurements in solid water with the film in a perpendicular orientation were within 2% of the Wellhöfer IC‐10 measurements for the smaller field sizes. A maximum discrepancy of 8.4% and 3.9% was found for the field at 15 cm depth for 6 and 15 MV photons, respectively (with curve normalization at a depth of 5 cm). Compared to IC‐10 measurements, film measured central axis depth dose inside the lung slab showed a slight over‐response (at most 2%). At a depth of 15 cm in the lung phantom the over‐response was found to be 7.4% and 3.7% for the field for 6 and 15 MV photons, respectively. When results were presented as correction factors, the discrepancy between the IC‐10 and the EDR was greatest for the lowest energy and the largest field size. The effect of the finite size of the ion chamber was most evident at smaller field sizes where profile differences versus film were observed in the penumbral region. These differences were reduced at larger field sizes and in situations where lateral electron transport resulted in a lateral spread of the beam, such as inside lung material. Film profiles across a lung tumor geometry phantom agreed with the IC‐10 chamber within the experimental uncertainties. From this investigation EDR film appears to be a useful medium for relative dosimetry in higher dose ranges in both water and lung equivalent material for moderate field sizes and depths. © 2003 American College of Medical Physics.PACS number(s): 87.53.Dq, 87.66.Cd, 87.66.Jj, 87.66.Xa
Differences in electron beam dosimetry using two commercial ionization chambers and the TG‐21 protocol: Another reason to switch to TG‐51
Authors: Followill David S. , Hanson William F. , Ibbott Geoffrey S. , Eglezopoulos Leon R. , Chui Chen‐Shou 
Published: February 2007

Two of the most popular dosimetry systems used for calibration of megavoltage photon and electron beams in radiation therapy are (i) cylindrical Farmer‐type chambers in liquid water and (ii) Holt Memorial parallel‐plate chambers in clear polystyrene. Since implementation of the AAPM TG‐21 calibration protocol, the Radiological Physics Center (which uses the Farmer in‐water system) has compared machine calibrations on two occasions with those of Memorial Sloan‐Kettering Cancer Center (which uses the Holt in‐polystyrene system). Two years post publication of the TG‐51 protocol, 70% of the clinics monitored by the RPC still use TG‐21. Seventeen photon beams from cobalt‐60 to 18 MV and 31 electron beams from 6 to 20 MeV were compared using the TG‐21 protocol. These data represent the most comprehensive comparison of the two most popular systems in use. Based on the average percent difference, the two systems yielded the same absorbed dose to water at the reference point in phantom to within 1.5% for both modalities. No energy dependence was evident in the results; however, a systematic average percent difference between photons and electrons was seen, with the Farmer in‐water system consistently predicting a dose 1.3% lower for electrons than the Holt in‐polystyrene system. For photons both systems predicted the same dose to within 0.3% on average. When a physicist converts from TG‐21 to TG‐51, these data may be of assistance in explaining unexpected changes in output that are different from previously published values. Implementation of the TG‐51 protocol should eliminate any of the observed differences in electron beam dosimetry between the two dosimetry systems because the Holt system cannot be used with TG‐51.PACS number(s): 87.53.‐j, 87.53.‐j
A fast, independent dose check of HDR plans
Authors: Lachaine Martin E. , Gorman Jason C. , Palisca Madeline G. 
Published: February 2007

High dose rate (HDR) brachytherapy often involves optimization routines to calculate the dwell times and positions of a radioactive source along specified applicator paths. These routines optimize the dwells in such a way as to deliver the prescribed dose at one or more points while satisfying various constraints. The importance of independently verifying the doses calculated by the optimization software prior to treatment delivery has been recognized in various works, and is a requirement of various regulatory agencies. Most previous methods are specific to particular treatment configurations, or require a full replanning of the case. In this work we describe an in‐house software which provides an independent verification of dose calculations in less than 3 min, which adds negligible additional waiting time for the patient, regardless of the number of applicators, paths of the applicators, or complexity of the dwell times and positions. In order to verify errors which may occur between the planning and delivery stages, the verification code directly uses the treatment file used to control the HDR afterloader to compute the dose. Since this file references the source positions in the frame of reference of the catheters, an algorithm is described to convert these positions to Cartesian coordinates. We validate the code for various arbitrary cases ranging from a single catheter to complex multicatheter plans, and show results for various clinical plans. The maximum discrepancy observed for these clinical plans is 2%.PACS number(s): 87.53.–j, 87.90.+y
Neutron and capture gamma along the mazes of linear accelerator vaults
Authors: Wu Raymond K. , McGinley Patton H. 
Published: February 2007

Neutron and photon dose equivalents at various points along the mazes of the vaults for two 15 MV linear accelerators were measured. The measurements were made with the machines set at various gantry angles with and without the scattering phantom, and with the collimators set at the maximum and the minimum field sizes. Neutron dose equivalent measurements were made for five other accelerator vaults. Empirical equations were used to fit the dose data at points along the center of the maze, at 1 m above floor level, with the primary radiation beam pointing downward. It is reported here that both the capture gamma and the neutron dose attenuations along the maze are in agreement with the literature. The neutron dose is dependent on the square root of the ratio of the cross‐sectional areas of the inner maze entrance and the maze. The tenth value distance is proportional to the square root of the cross‐sectional area of the maze.PACS number(s): 87.52.Ga
Book Review
Authors: Huda Walter 
Published: February 2007

Applied Imaging Technology. 4th ed. J. C. P. Heggie, N. A. Liddell, and K. P. Maher. St. Vincent's Hospital, Melbourne, Australia, 2001. http://www.life.rmit.edu.au/mrs/kpm/AIT/PACS number(s): 87.57.
Neutron source strength measurements for Varian, Siemens, Elekta, and General Electric linear accelerators
Authors: Followill David S. , Stovall Marilyn S. , Kry Stephen F. , Ibbott Geoffrey S. 
Published: February 2007

The shielding calculations for high energy () linear accelerators must include the photoneutron production within the head of the accelerator. Procedures have been described to calculate the treatment room door shielding based on the neutron source strength (Q value) for a specific accelerator and energy combination. Unfortunately, there is currently little data in the literature stating the neutron source strengths for the most widely used linear accelerators. In this study, the neutron fluence for 36 linear accelerators, including models from Varian, Siemens, Elekta/Philips, and General Electric, was measured using gold‐foil activation. Several of the models and energy combinations had multiple measurements. The neutron fluence measured in the patient plane was independent of the surface area of the room, suggesting that neutron fluence is more dependent on the direct neutron fluence from the head of the accelerator than from room scatter. Neutron source strength, Q, was determined from the measured neutron fluences. As expected, Q increased with increasing photon energy. The Q values ranged from 0.02 for a 10 MV beam to neutrons per photon Gy for a 25 MV beam. The most comprehensive set of neutron source strength values, Q, for the current accelerators in clinical use are presented for use in calculating room shielding.PACS number(s): 87.53.–j, 87.52.–g
Effectiveness of compensating filters in the presence of tissue inhomogeneities
Authors: Sethi A. , Leybovich L. , Dogan N. , Glasgow G. 
Published: February 2007

CT based 3D treatment planning systems (3DTPS) can be used to design compensating filters that, in addition to missing tissue compensation, can account for tissue inhomogeneities. The use of computer‐driven systems provides a practical, convenient, and accurate method of fabricating compensating filters. In this work, we have evaluated a commercially available PAR Scientific DIGIMILL milling machine linked with FOCUS 3DTPS. Compensating filters were fabricated using refined gypsum material with no additives. Thus, filters were of manageable dimensions and were not sensitive to common machining errors. Compensating filters were evaluated using a homogeneous step phantom and step phantoms containing various internal inhomogeneities (air, cork, and bone). The accuracy of two planning algorithms used to design filters was experimentally evaluated. The superposition algorithm was found to produce better agreement with measurements than the Clarkson algorithm. Phantom measurements have demonstrated that compensating filters were able to produce a uniform dose distribution along the compensation plane in the presence of tissue inhomogeneity. However, the dose variation was greatly amplified in planes located beyond the inhomogeneity when a single compensated beam was used. The use of parallel‐opposed compensated beams eliminated this problem. Both lateral and depth‐dose uniformity was achieved throughout the target volume.PACS number(s): 87.53.–j, 87.66.–a
A spreadsheet solution for off‐axis, noncentral enhanced dynamic wedge factors
Authors: Wichman B. D. 
Published: February 2007

Enhanced dynamic wedges can be very useful in increasing radiation therapy treatment efficiency. A drawback to their use is finding a factor analogous to a conventional wedge factor to calculate the dose to a point in a dynamically wedged field. A formalism has previously been published [J. Gibbons, Med. Phys. 25, 1411–1418 (1998)] to determine this factor at the central point of a dynamically wedged field. This paper expands the use of the previous formalism to show efficacy at any point under a dynamically wedged field, provided the point is not in a penumbra region. Results of measurements taken with four clinically relevant field sizes, both symmetric and asymmetric, are given. These results show acceptable correlation between the original formalism and its expanded use to noncentral points.PACS number(s): 87.53.–j, 87.66.–a
Comparison of dose calculated by an intensity modulated radiotherapy treatment planning system and an independent monitor unit verification program
Authors: Haslam J. J. , Bonta D. V. , Lujan A. E. , Rash C. , Jackson W. , Roeske J. C. 
Published: February 2007

A comparison of isocenter dose calculated by a commercial intensity modulated radiation therapy treatment planning system and independent monitor unit verification calculation (MUVC) software was made. The percent disparity between the treatment plan and MUVC doses were calculated for 507 treatments (head and neck, prostate, abdomen, female pelvis, rectum and anus, and miscellaneous) from 303 patients. The MUVC calculated dose was, on average, 1.4% higher than the treatment planning dose, with a 1.2% standard deviation. The distribution of the disparities appeared to be Gaussian in shape with some variation by treatment site. Based on our analysis, disparities outside the range of about the mean value should be checked and resolved prior to treatment delivery.PACS number(s): 87.53.–j, 87.66.–a
Shielding evaluation for IMRT implementation in an existing accelerator vault
Authors: Price R. A. , Chibani O. , Ma C.‐M. 
Published: February 2007

A formalism is developed for evaluating the shielding in an existing vault to be used for IMRT. Existing exposure rate measurements are utilized as well as a newly developed effective modulation scaling factor. Examples are given for vaults housing 6, 10 and 18 MV linear accelerators. The use of an 18 MV Siemens linear accelerator is evaluated for IMRT delivery with respect to neutron production and the effects on individual patients. A modified modulation scaling factor is developed and the risk of the incurrence of fatal secondary malignancies is estimated. The difference in neutron production between 18 MV Varian and Siemens accelerators is estimated using Monte Carlo results. The neutron production from the Siemens accelerator is found to be approximately 4 times less than that of the Varian accelerator resulting in a risk of fatal secondary malignancy occurrence of approximately 1.6% when using the SMLC delivery technique and our measured modulation scaling factors. This compares with a previously published value of 1.6% for routine 3D CRT delivery on the Varian accelerator.PACS number(s): 87.52.Ga, 87.52.Px, 87.53.Qc, 87.53.Wz
Automatic detection of small lung nodules on CT utilizing a local density maximum algorithm
Authors: Zhao Binsheng , Gamsu Gordon , Ginsberg Michelle S. , Jiang Li , Schwartz Lawrence H. 
Published: February 2007

Increasingly, computed tomography (CT) offers higher resolution and faster acquisition times. This has resulted in the opportunity to detect small lung nodules, which may represent lung cancers at earlier and potentially more curable stages. However, in the current clinical practice, hundreds of such thin‐sectional CT images are generated for each patient and are evaluated by a radiologist in the traditional sense of looking at each image in the axial mode. This results in the potential to miss small nodules and thus potentially miss a cancer. In this paper, we present a computerized method for automated identification of small lung nodules on multislice CT (MSCT) images. The method consists of three steps: (i) separation of the lungs from the other anatomic structures, (ii) detection of nodule candidates in the extracted lungs, and (iii) reduction of false‐positives among the detected nodule candidates. A three‐dimensional lung mask can be extracted by analyzing density histogram of volumetric chest images followed by a morphological operation. Higher density structures including nodules scattered throughout the lungs can be identified by using a local density maximum algorithm. Information about nodules such as size and compact shape are then incorporated into the algorithm to reduce the detected nodule candidates which are not likely to be nodules. The method was applied to the detection of computer simulated small lung nodules (2 to 7 mm in diameter) and achieved a sensitivity of 84.2% with, on average, five false‐positive results per scan. The preliminary results demonstrate the potential of this technique for assisting the detection of small nodules from chest MSCT images.PACS number(s): 87.57.–s, 87.90.+y
Use of intensity modulation for missing tissue compensation of pediatric spinal fields
Authors: Phillips M. H. , Cho P. S. , Parsai H. , Douglas J. G. 
Published: February 2007

Irradiation of the cranio‐spinal axis is often one of the treatment modalities of certain childhood cancers, e.g., medulloblastoma. In order to achieve a uniform dose to the spinal cord, missing tissue compensators are required. In the past, our practice was to fabricate compensators out of strips of lead. We report on the use of intensity modulated fields to achieve the desired compensation. Seven cases of pediatric cancer whose treatment involved irradiation of the cranio‐spinal axis had compensators designed using a beam intensity modulation method rather than making mechanical compensators. The compensators only adjusted for missing tissue along the spinal axis. Comparisons between calculated and measured doses were made at depth in phantoms and on the surface of the patient. The intensity modulated fields were delivered using a step‐and‐shoot delivery on an Elekta SL20 accelerator equipped with multileaf collimator. The intensity‐modulated compensators provided more flexibility in design than the physical compensator method. Finer intensity steps were achievable, more accurate dose distributions were able to be calculated, and adjustments during treatment, e.g., junction changes, were more easily implemented. Convolution/superposition dose calculations were within of measurements. Intensity modulated fields are a practical and more efficient method of delivering uniform doses to the spine in pediatric cancer treatments. They provide many advantages over mechanical compensators with regard to time and flexibility.PACS number(s): 87.53.–j, 87.90.+y
Reference photon dosimetry data: A preliminary study of in‐air off‐axis factor, percentage depth dose, and output factor of the Siemens Primus linear accelerator
Authors: Cho S. H. , Ibbott G. S. 
Published: February 2007

The dosimetric characteristics for modern computer‐controlled linear accelerators with the same make, model, and nominal energy are known to be very similar, as long as the machines are unaltered from the manufacturer's original specifications. In this preliminary study, a quantitative investigation of the similarity in the basic photon dosimetry data from the Siemens Primus linear accelerators at eight different institutions is reported. The output factor, percentage depth dose (PDD), and in‐air off‐axis factor (OAF) for the 6 and 18 MV photon beams measured or verified by the Radiological Physics Center (RPC) were analyzed. The RPC‐measured output factors varied by less than about 2% for each field size. The difference between the maximum and minimum RPC‐verified PDD values at each depth was less than about 3%. The difference between the maximum and minimum RPC‐measured in‐air OAF was no more than 4% at all off‐axis distances considered in this study. These results strongly suggest that it is feasible to establish a reference photon dosimetry data set for each make, model, and nominal energy, universally applicable to those machines unaltered from the manufacturers' original specifications, within a clinically acceptable tolerance (e.g., ).PACS number(s): 87.53.–j, 87.66.–a
Utilizing an electronic portal imaging device to monitor light and radiation field congruence
Authors: Prisciandaro J. I. , Herman M. G. , Kruse J. J. 
Published: February 2007

A method to investigate light and radiation field congruence utilizing a commercially available amorphous silicon electronic portal imaging device (EPID) was developed. This method employed an EPID, the associated EPI software, and a diamond‐shaped template. The template was constructed from a block tray in which Sn/Pb wires, 1 mm in diameter, were embedded into a diamond shaped groove milled into the tray. The collimator jaws of the linac were aligned such that the light field fell directly on the corners of the diamond. A radiation detection algorithm within the EPI software determined the extent of the radiation field. The light and radiation field congruence was evaluated by comparing the vertexes of the diamond reference structure to the detected radiation field. In addition, the digital jaw settings were recorded and later compared to the light field detected on the films and EPIs. Three linear accelerators were tracked for a period ranging from 2–8 months. Light radiation field congruence tests with films and EPIs were comparable, yielding a difference of less than 0.6 mm, well within the allowed 2‐mm tolerance. A disparity was observed in the magnitude of the detected light field. The X and Y dimensions of the light field measured with film differed by less than or equal to 1.4 mm from the digital collimator settings, whereas the values extracted from the EPIs differed by up to 2.5 mm. Based on these findings, EPIs were found to be a quick and reliable alternative to film for qualitative and relative analyses.PACS number(s): 87.53.Xd, 87.56.Fc, 87.53.Oq, 87.52.–g, 87.53.–j
Reduction of downtime and improvement of the utility of a conventional radiotherapy simulator
Authors: Sawchuk S. P. , Knibutat K. , Moriarity L. 
Published: February 2007

The modifications made to a radiotherapy simulator that improve its functionality and minimize its downtime are described. Functionality was enhanced with some simple effective improvements. Decreasing the frequency and time spent on repairs reduced downtime. These “in‐house” improvements were made to a Varian Ximatron simulator at the Tom Baker Cancer Center. Now there is easier access to the field light and optical distance indicator (ODI). Projections of the field light and ODI are much brighter and ODI adjustment is more reproducible. A crosshair was etched onto the clear x‐ray exit window to optically overlap with the crosshair of the reticule. Now, the time required to replace a field light is up to seven times faster and the time to realign a reticule is reduced to the order of three times faster. Only one quality control (QC) check is required after these adjustments. Removal of excess heat within the gantry head has eliminated two major problems: (A) the metal rod supporting the mirror assembly for the field light no longer expands and contracts causing a misalignment of the field light projection, and (B) the damage to the bearing in the cooling fan assembly has been eliminated. The simulator is now more functional and these improvements have reduced downtime significantly, making repairs and adjustments much more convenient and efficient.PACS number(s): 87.53.Vb, 87.53.Xd
Dose calculation accuracy of lung planning with a commercial IMRT treatment planning system
Authors: McDermott Patrick N. , He Tongming , DeYoung A. 
Published: February 2007

The dose calculation accuracy of a commercial pencil beam IMRT planning system is evaluated by comparison with Monte Carlo calculations and measurements in an anthropomorphic phantom. The target volume is in the right lung and mediastinum and thus significant tissue inhomogeneities are present. The Monte Carlo code is an adaptation of the msnp code and the measurements were made with TLD and film. Both the Monte Carlo code and the measurements show very good agreement with the treatment planning system except in regions where the dose is high and the electron density is low. In these regions the commercial system shows doses up to 10% higher than Monte Carlo and film. The average calculated dose for the CTV is 5% higher with the commercial system as compared to Monte Carlo.PACS number(s): 87.53.‐j, 87.66.‐a