bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Acuros XB algorithm based on RTOG 0813 dosimetric criteria for SBRT lung treatment with RapidArc
Authors: Rana Suresh , Rogers Kevin , Pokharel Shyam , Cheng ChihYao
Published: February 2017

The Radiation Therapy Oncology Group (RTOG) 0813 protocol requires the use of dose calculation algorithms with tissue heterogeneity corrections to compute dose on stereotactic body radiation therapy (SBRT) non‐small cell lung cancer (NSCLC) plans. A new photon dose calculation algorithm called Acuros XB (AXB) has recently been implemented in the Eclipse treatment planning system (TPS). The main purpose of this study was to compare the dosimetric results of AXB with that of anisotropic analytical algorithm (AAA) for RTOG 0813 parameters. Additionally, phantom study was done to evaluate the dose prediction accuracy of AXB and AAA beyond low‐density medium of different thicknesses by comparing the calculated results with the measurements. For the RTOG dosimetric study, 14 clinically approved SBRT NSCLC cases were included. The planning target volume (PTV) ranged from 3.2‐43.0 cc. RapidArc treatment plans were generated in the Eclipse TPS following RTOG 0813 dosimetric criteria, and treatment plans were calculated using AAA with heterogeneity correction (AAA plans). All the AAA plans were then recalculated using AXB with heterogeneity correction (AXB plans) for identical beam parameters and same number of monitor units. The AAA and AXB plans were compared for following RTOG 0813 parameters: ratio of prescription isodose volume to PTV (R100%), ratio of 50% prescription isodose volume to PTV (R50%), maximal dose 2 cm from the PTV in any direction as a percentage of prescription dose , and the percentage of ipsilateral lung receiving dose equal to or larger than 20 Gy . The phantom study showed that the results of AXB had better agreement with the measurements, and the difference ranged from to 2.8%. The AAA results showed larger disagreement with the measurements, with differences from 4.1% to 12.5% for field size and from 1.4% to 6.8% for field size . The results from the RTOG SBRT lung cases showed that, on average, the AXB plans produced lower values for R100%, R50%, and by 4.96%, 1.15%, and 1.60%, respectively, but higher of ipsilateral lung by 1.09% when compared with AAA plans. In the set of AAA plans, minor deviation was seen for R100% (six cases), R50% (nine cases), (four cases), and (one case). Similarly, the AXB plans also showed minor deviation for R100% (one case), R50% (eight cases), (three cases), and (one case). The dosimetric results presented in the current study show that both the AXB and AAA can meet the RTOG 0813 dosimetric criteria.

PACS number: 87.55.D‐, 87.55.dk, 87.55.kd, 87.55.km
A novel approach for superficial intraoperative radiotherapy (IORT) using a 50 kV X‐ray source: a technical and case report
Authors: Schneider Frank , Clausen Sven , Thölking Johannes , Wenz Frederik , Abo‐Madyan Yasser
Published: February 2017

The use of IORT as a treatment modality for patients with close or positive margins has increased over the past decade. For situations where a flat area (up to 6 cm in diameter) has to be treated intraoperatively, new applicators for superficial treatment with a miniature X‐ray source (INTRABEAM system) were developed. Here we report our evaluation of the dosimetric characteristics of these new applicators and their first clinical use. Each of these flat and surface applicators consists of a radiation protective metal tube and a flattening filter, which converts the spherical dose distribution of the X‐ray source into a flat one. The homogeneity of each dose distribution and depth‐dose measurements were evaluated using film dosimetry in a solid water phantom and a soft X‐ray ionization chamber in a water tank. The first patient was treated with 5 Gy delivered in 5 mm using a 4 cm FLAT applicator over 21 minutes. The flat applicators show the maximum homogeneity, with a uniformity ratio of 1.02‐1.08 in certain depths. In 1 mm depth surface applicators show a uniformity ratio of 1.15‐1.28. They also show a higher dose rate and a steeper dose gradient compared to the flat applicators. The results of this investigation demonstrated that the flat and surface applicators have unique dosimetric characteristics that need to be considered during the treatment planning stages. This work also showed that it is possible to perform a superficial localized IORT which provides new application possibilities for use of the INTRABEAM system.

PACS number: 87.55.ne
Measurement and Monte Carlo simulation for energy‐ and intensity‐modulated electron radiotherapy delivered by a computer‐controlled electron multileaf collimator
Authors: Jin Lihui , Eldib Ahmed , Li Jinsheng , Emam Ismail , Fan Jiajin , Wang Lu , Ma C‐M
Published: February 2017

The dosimetric advantage of modulated electron radiotherapy (MERT) has been explored by many investigators and is considered to be an advanced radiation therapy technique in the utilization of electrons. A computer‐controlled electron multileaf collimator (MLC) prototype, newly designed to be added onto a Varian linac to deliver MERT, was investigated both experimentally and by Monte Carlo simulations. Four different electron energies, 6, 9, 12, and 15 MeV, were employed for this investigation. To ensure that this device was capable of delivering the electron beams properly, measurements were performed to examine the electron MLC (eMLC) leaf leakage and to determine the appropriate jaw positioning for an eMLC‐shaped field in order to eliminate a secondary radiation peak that could otherwise appear outside of an intended radiation field in the case of inappropriate jaw positioning due to insufficient radiation blockage from the jaws. Phase space data were obtained by Monte Carlo (MC) simulation and recorded at the plane just above the jaws for each of the energies (6, 9, 12, and 15 MeV). As an input source, phase space data were used in MC dose calculations for various sizes of the eMLC shaped field (, , and ) with respect to a water phantom at source‐to‐surface distance , while the jaws, eMLC leaves, and some accessories associated with the eMLC assembly as well were modeled as modifiers in the calculations. The calculated results were then compared with measurements from a water scanning system. The results showed that jaw settings with 5 mm margins beyond the field shaped by the eMLC were appropriate to eliminate the secondary radiation peak while not widening the beam penumbra; the eMLC leaf leakage measurements ranged from 0.3% to 1.8% for different energies based on in‐phantom measurements, which should be quite acceptable for MERT. Comparisons between MC dose calculations and measurements showed agreement within based on percentage depth doses (PDDs) and off‐axis dose profiles for a range of field sizes for each of the electron energies. Our current work has demonstrated that the eMLC and other relevant components in the linac were correctly modeled and simulated via our in‐house MC codes, and the eMLC is capable of accurately delivering electron beams for various eMLC‐shaped field sizes with appropriate jaw settings. In the next stage, patient‐specific verification with a full MERT plan should be performed.

PACS number: 87.55.ne
AAPM Medical Physics Practice Guideline 2.a: Commissioning and quality assurance of X‐ray‐based image‐guided radiotherapy systems
Authors: Fontenot Jonas D. , Alkhatib Hassaan , Garrett Jeffrey A. , Jensen Andrew R , McCullough Steven P. , Olch Arthur J. , Parker Brent C. , Yang Ching‐Chong Jack , Fairobent Lynne A.
Published: February 2017

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8,000 members and is the principal organization of medical physicists in the United States.

The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner.

Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized.
Quality assurance measurements for high‐dose‐rate brachytherapy without film
Authors: Jursinic Paul A.
Published: February 2017

The purpose of this study was to develop new and modified tools that allow HDR brachytherapy quality assurance tests to be carried out efficiently without film, video cameras, stopwatches, and mechanical rulers; and to devise methods that use these new tools for daily and quarterly check procedures, which are efficient and provide increased accuracy compared to previous methods. The HDR brachytherapy system tested was the GammaMedplus iX, Ir‐192 HDR. Various catheters and treatment applicators designed for this system were tested. To measure the absolute position of the source, a simple tool was built that uses a Plexiglas frame, a template for applicator positioning, and a diode for radiation detection. For daily reproducibility and source strength tests, modifications were made of a Model 70008, HDR brachytherapy Ir‐192 quality assurance tool, which is used with the HDR‐1000‐Plus well‐type reentrant chamber. Measurement procedures and analysis protocols were developed that use the Microsoft Excel spreadsheet program. Independent determination of source positions was made with a computer video camera and radiochromic film. Using the new tool, for a straight catheter the measured source position is found to be within of the mechanically set distance, for a ring applicator , for a tandem , and for an ovoid . Using the modified insert, daily dwell position can be determined with an accuracy of 0.3 mm and timer accuracy can be determined with an accuracy of 0.3% over a 20 s time frame. The time needed to carry out quarterly tests is estimated to be reduced by two‐to four‐fold compared to previous methods. New and modified equipment and procedures have been developed for measuring HDR brachytherapy dwell position and dwell times efficiently with high accuracy. The equipment described in this work can be built and modifications can be made in most clinics. Location of dwell position can be determined in straight catheters and ring and ovoid applicators. Timer linearity and accuracy can be determined. Source strength can be confirmed. Measurement efficiency is improved compared to previous methods that used film, video cameras, mechanical rulers, and stopwatches.

PACS number: 87.56.Fc
Local reference dose evaluation in conventional radiography examinations in Iran
Authors: Shandiz M. Shirin , Toossi M.T. Bahreyni , Farsi S. , Yaghobi K.
Published: February 2017

The goal of this study was to establish local diagnostic reference levels (LDRLs) for conventional radiography examinations in Sistan‐Baluchestan province of Iran, using dose area product (DAP) measurements followed by a comparison with international dose levels. DAP factor evaluation was carried out at eight radiography rooms in six public and one private health‐care centers. The study employed DAP, exposure, and demographic data (weight, age, height) for 1069 patients who presented for one of the 11 routine radiography examinations: chest (AP, PA, LAT), abdomen (AP), lumbar spine (AP, LAT), pelvis (AP), skull (AP/PA, LAT), and cervical spine (AP, LAT). The data were analyzed statistically and the minimum, median, mean, maximum, and third quartile DAP values were calculated. It was observed that LDRLs for chest PA (0.26 Gy.cm2) and chest LAT (0.66 Gy.cm2) projections were up to 136% and 113% higher, respectively, than their corresponding NRPB 2005 values. Other radiographic procedures had lower recommended reference doses compared with recently recommended national reference doses published in recent NRPB reports and other studies. Wide variations in DAP values and exposure parameters were observed for similar radiographic procedures between patients in different rooms and for different patients in the same room. These and other observations, such as poor radiographic techniques, high rate of radiographic reject/repeat, and lack of modern X‐ray machines and equipment, show that the need to carry out quality assurance programs is critical in Iran.

PACS numbers: 87.53.Bn, 87.59.B
Patient radiation exposure during general fluoroscopy examinations
Authors: Wambani Jeska S. , Korir Geoffrey K. , Tries Mark A. , Korir Ian K. , Sakwa Jedidah M.
Published: February 2017

The purpose of this study was to assess the level of patient radiation dose received in general fluoroscopy examinations, compare the findings with the international diagnostic reference levels (IDRLs), and establish the initial institutional (local) LDRLs. A comprehensive survey was conducted for general fluoroscopy examinations using the medical records of a Radiology Department of a leading regional hospital over a period close to one year. The cumulative reference point air kerma , kerma area product (KAP) and fluoroscopy time (FT) were recorded for six hundred and fifty (30% pediatric and 70% adult) patients undergoing routine fluoroscopy examinations using X‐ray equipment with built‐in integrated dose measuring system. Results which were obtained for adult general fluoroscopy indicated that 83% and 33% were below the IDRLs for KAP and fluoroscopy time, respectively. In children, 60% were found to be below the only available KAP diagnostic reference levels. Local diagnostic reference levels (LDRLs) have been proposed with respect to the missing DRLs for the Ka r, KAP, and fluoroscopy time. The majority of the examinations in the study were performed with longer fluoroscopy time, patient dose values per examination type were found to be broad and the mean values above the international diagnostic reference levels. This calls for proper and improved training and radiation protection skills for the responsible personnel, especially the equipment operators.

PACS numbers: 87.53.Bn, 87.59.C‐, 87.59.cf, 87.53.Bn, 87.50.‐a, 87.53.‐j
Patient safety considerations concerning the scheduling of emergency‐off system tests
Authors: Brezovich Ivan A. , Popple Richard A.
Published: February 2017

Emergency‐off systems (EOS) are essential to the safe operation of medical accelerators and other high‐risk equipment. To assure reliable functioning, some states require weekly tests; others permit monthly, tri‐monthly or even six‐monthly tests, while some do not specify test intervals. We investigate the relative safety of the various test schedules by computing the fraction of time during which a nonfunctional state of the EOS may remain undetected. Special attention is given to the effect of flexibility (i.e., to regulations that specify the number of tests that have to be done in any given time interval, but allow a range within the interval during which a test can be done). Compared to strict test intervals, a schedule that provides flexibility increases risk only marginally. Performing tests on any arbitrary day of the week when weekly tests are required increases the time span during which a nonfunctionality goes undetected by only 17%, compared to an exact one‐week schedule. The same ratio applies for monthly tests. For a three‐month schedule, the relative risk increases by only 2% if tests are done on an arbitrarily chosen day during each due‐month, compared to tests done on an exact three‐month schedule. The most irregular time intervals possible in a three‐calendar month schedule increase the relative risk by 11%. For the six‐month and the 12‐month schedule the ratio of risks is even smaller. The relative risk is virtually independent of the mean time between failures of the EOS, but the absolute risk decreases in proportion the mean time between failures. Adherence to strict, resource‐intensive test intervals provides little extra safety compared to flexible intervals that require the same number of tests per year. Regulations should be changed to provide the practicality offered by flexible test schedules. Any additional increase in patient safety could be achieved by strict regulations concerning reliability of emergency‐stop (e‐stop) systems.

PACS numbers: 87.55.N‐, 87.55.Qr, 87.56.bd
Effect of skull contours on dose calculations in Gamma Knife Perfexion stereotactic radiosurgery
Authors: Nakazawa Hisato , Komori Masataka , Mori Yoshimasa , Hagiwara Masahiro , Shibamoto Yuta , Tsugawa Takahiko , Hashizume Chisa , Kobayashi Tatsuya
Published: February 2017

In treatment planning of Leksell Gamma Knife (LGK) radiosurgery, the skull geometry defined by generally dedicated scalar measurement has a crucial effect on dose calculation. The LGK Perfexion (PFX) unit is equipped with a cone‐shaped collimator divided into eight sectors, and its configuration is entirely different from previous model C. Beam delivery on the PFX is made by a combination of eight sectors, but it is also mechanically available from one sector with the remaining seven blocked. Hence the treatment time using one sector is more likely to be affected by discrepancies in the skull shape than that of all sectors. In addition, the latest version (Ver. 10.1.1) of the treatment planning system Leksell GammaPlan (LGP) includes a new function to directly generate head surface contouring from computed tomography (CT) images in conjunction with the Leksell skull frame. This paper evaluates change of treatment time induced by different skull models. A simple simulation using a uniform skull radius of 80 mm and anthropomorphic phantom was implemented in LGP to find the trend between dose and skull measuring error. To evaluate the clinical effect, we performed an interobserver comparison of ruler measurement for 41 patients, and compared instrumental and CT‐based contours for 23 patients. In the phantom simulation, treatment time errors were less than 2% when the difference was within 3 mm. In the clinical cases, the variability of treatment time induced by the differences in interobserver measurements was less than 0. 91%, on average. Additionally the difference between measured and CT‐based contours was good, with a difference of (mean ±1 standard deviation) on average and a maximum of 3.4%. Although the skull model created from CT images reduced the dosimetric uncertainty caused by different measurers, these results showed that even manual skull measurement could reproduce the skull shape close to that of a patient's head within an acceptable range.

PACS number: 87.53.Ly
Dosimetric advantages of O‐ring design radiotherapy system for skull‐base tumors
Authors: Ogura Kengo , Mizowaki Takashi , Ishida Yuichi , Hiraoka Masahiro
Published: February 2017

The purpose of this study was to investigate whether a new O‐ring design radiotherapy delivery system has advantages in radiotherapy planning for skull‐base tumors. Twenty‐five patients with skull‐base tumors were included in this study. Two plans were made using conventional (Plan A) or new (Plan B) techniques. Plan A consisted of four dynamic conformal arcs (DCAs): two were horizontal, and the other two were from cranial directions. Plan B was created by converting horizontal arcs to those from caudal directions making use of the O‐ring design radiotherapy system. The micromultileaf collimators were fitted to cover at least 99% of the planning target volume with prescribed doses, 90% of the dose at the isocenter. The two plans were compared in terms of target homogeneity, conformity, and irradiated volume of normal tissues, using a two‐sided paired t‐test. For evaluation regarding target coverage, the homogeneity indices defined by the International Commission on Radiation Units and Measurements 83 were (mean ± standard deviation) and , the conformity indices defined by the Radiation Therapy Oncology Group were and , and the Paddick's conformity indices were and , in Plans A and B, respectively. For evaluation of irradiated normal tissue, the Paddick's gradient indices were and in Plans A and B, respectively. All of these differences were statistically significant (p‐values ). The mean doses of optic nerves, eyes, brainstem, and hippocampi were also significantly lower in Plan B. The DCA technique from caudal directions using the new O‐ring design radiotherapy system can improve target homogeneity and conformity compared with conventional DCA techniques, and can also decrease the volume of surrounding normal tissues that receives moderate doses.

PACS numbers: 87.55.‐x, 87.55.D‐, 87.55.dk
Assessment of potential jaw‐tracking advantage using control point sequences of VMAT planning
Authors: Kim Jung‐in , Park Jong Min , Park So‐Yeon , Choi Chang Heon , Wu Hong‐Gyun , Ye Sung‐Joon
Published: February 2017

This study aims to evaluate the potential jaw‐tracking advantage using control point sequences of volume volumetric‐modulated arc therapy (VMAT) planning. VMAT plans for patients with prostate and head and neck (H&N) cancers were converted into new static arc (SA) plans. The SA plan consisted of a series of static fields at each control point of the VMAT plan. All other machine parameters of the SA plan were perfectly identical to those of the original VMAT plan. The jaw‐tracking static arc (JTSA) plans were generated with fields that closed the jaws of each SA field into the multileaf collimators (MLCs) aperture. The dosimetric advantages of JTSA over SA were evaluated in terms of a dose‐volume histogram (DVH) of organ at risk (OAR) after renormalizing both plans to make the same target coverage. Both plans were delivered to the MatriXX‐based COMPASS system for 3D volume dose verification. The average jaw size reduction of the JTSA along the X direction was for prostate patients and for H&N patients. For prostate patients, the organs far from the target showed larger sparing (3.7%—8.1% on aver‐age) in JTSA than the organs adjacent to the target (1.1%—1.5%). For the H&N plans, the mean dose reductions for all organs ranged from 4.3% to 11.9%. The dose reductions were more significant in the dose regions of , and than the dose regions of , and for all patients. Likewise, the deliverability and reproducibility of jaw‐tracking plan were validated. The measured dosimetric advantage of JTSA over SA coincided with the calculated one above.

PACS numbers: 87.55.D‐, 87.55.ne
Commissioning and verification of the collapsed cone convolution superposition algorithm for SBRT delivery using flattening filter‐free beams
Authors: Foster Ryan D. , Speiser Michael P. , Solberg Timothy D.
Published: February 2017

Linacs equipped with flattening filter‐free (FFF) megavoltage photon beams are now commercially available. However, the commissioning of FFF beams poses challenges that are not shared with traditional flattened megavoltage X‐ray beams. The planning system must model a beam that is peaked in the center and has an energy spectrum that is softer than the flattened beam. Removing the flattening filter also increases the maximum possible dose rates from 600 MU/min up to 2400 MU/min in some cases; this increase in dose rate affects the recombination correction factor, , used during absolute dose calibration with ionization chambers. We present the first‐reported experience of commissioning, verification, and clinical use of the collapsed cone convolution superposition (CCCS) dose calculation algorithm for commercially available flattening filter‐free beams. Our commissioning data are compared to previously reported measurements and Monte Carlo studies of FFF beams. Commissioning was verified by making point‐dose measurement of test plans, irradiating the RPC lung phantom, and performing patient‐specific QA. The average point‐dose difference between calculations and measurements of all test plans and all patient specific QA measurements is 0.80%, and the RPC phantom absolute dose differences for the two thermoluminescent dosimeters (TLDs) in the phantom planning target volume (PTV) were 1% and 2%, respectively. One hundred percent (100%) of points in the RPC phantom films passed the RPC gamma criteria of 5% and 5 mm. Our results show that the CCCS algorithm can accurately model FFF beams and calculate SBRT dose distributions using those beams.

PACS number: 87.55.kh
Clinical evaluation of an anatomy‐based patient specific quality assurance system
Authors: Hauri Pascal , Verlaan Sarah , Graydon Shaun , Ahnen Linda , Klöck Stephan , Lang Stephanie
Published: February 2017

The Delta4DVH Anatomy 3D quality assurance (QA) system (ScandiDos), which converts the measured detector dose into the dose distribution in the patient geometry was evaluated. It allows a direct comparison of the calculated 3D dose with the measured back‐projected dose. In total, 16 static and 16 volumetric‐modulated arc therapy (VMAT) fields were planned using four different energies. Isocenter dose was measured with a pinpoint chamber in homogeneous phantoms to investigate the dose prediction by the Delta4DVH Anatomy algorithm for static fields. Dose distributions of VMAT fields were measured using GAFCHROMIC film. Gravitational gantry errors up to 10° were introduced into all VMAT plans to study the potential of detecting errors. Additionally, 20 clinical treatment plans were verified. For static fields, the Delta4DVH Anatomy predicted the isocenter dose accurately, with a deviation to the measured phantom dose of . For VMAT fields the predicted Delta4DVH Anatomy dose in the isocenter plane corresponded to the measured dose in the phantom, with an average gamma agreement index (GAI) of . The Delta4DVH Anatomy detected the induced systematic gantry error of 10° with a relative GAI change of . The conventional Delta4PT QA system detected a GAI change of . The conventional Delta4PT GAI was for the clinical treatment plans. The mean body and PTV‐GAI for the Delta4DVH Anatomy were and ; however, this dropped to and for passing criteria of . The anatomy‐based patient specific quality assurance system predicts the dose distribution correctly for a homogeneous case. The limiting factor for the error detection is the large variability in the error‐free plans. The dose calculation algorithm is inferior to that used in the TPS (Eclipse).

PACS numbers: 87.56.Fc, 87.56.‐v
Performance of dose calculation algorithms from three generations in lung SBRT: comparison with full Monte Carlo‐based dose distributions
Authors: Ojala Jarkko J. , Kapanen Mika K. , Hyödynmaa Simo J. , Wigren Tuija K. , Pitkänen Maunu A.
Published: February 2017

The accuracy of dose calculation is a key challenge in stereotactic body radiotherapy (SBRT) of the lung. We have benchmarked three photon beam dose calculation algorithms — pencil beam convolution (PBC), anisotropic analytical algorithm (AAA), and Acuros XB (AXB) — implemented in a commercial treatment planning system (TPS), Varian Eclipse. Dose distributions from full Monte Carlo (MC) simulations were regarded as a reference. In the first stage, for four patients with central lung tumors, treatment plans using 3D conformal radiotherapy (CRT) technique applying 6 MV photon beams were made using the AXB algorithm, with planning criteria according to the Nordic SBRT study group. The plans were recalculated (with same number of monitor units (MUs) and identical field settings) using BEAMnrc and DOSXYZnrc MC codes. The MC‐calculated dose distributions were compared to corresponding AXB‐calculated dose distributions to assess the accuracy of the AXB algorithm, to which then other TPS algorithms were compared. In the second stage, treatment plans were made for ten patients with 3D CRT technique using both the PBC algorithm and the AAA. The plans were recalculated (with same number of MUs and identical field settings) with the AXB algorithm, then compared to original plans. Throughout the study, the comparisons were made as a function of the size of the planning target volume (PTV), using various dose‐volume histogram (DVH) and other parameters to quantitatively assess the plan quality. In the first stage also, 3D gamma analyses with threshold criteria and were applied. The AXB‐calculated dose distributions showed relatively high level of agreement in the light of 3D gamma analysis and DVH comparison against the full MC simulation, especially with large PTVs, but, with smaller PTVs, larger discrepancies were found. Gamma agreement index (GAI) values between 95.5% and 99.6% for all the plans with the threshold criteria were achieved, but threshold criteria showed larger discrepancies. The TPS algorithm comparison results showed large dose discrepancies in the PTV mean dose , nearly 60%, for the PBC algorithm, and differences of nearly 20% for the AAA, occurring also in the small PTV size range. This work suggests the application of independent plan verification, when the AAA or the AXB algorithm are utilized in lung SBRT having PTVs smaller than 20‐25 cc. The calculated data from this study can be used in converting the SBRT protocols based on type ‘a’ and/or type ‘b’ algorithms for the most recent generation type ‘c’ algorithms, such as the AXB algorithm.

PACS numbers: 87.55.‐x, 87.55.D‐, 87.55.K‐, 87.55.kd, 87.55.Qr
Efficacy evaluation of retrospectively applying the Varian normal breathing predictive filter for volume definition and artifact reduction in 4D CT lung patients
Authors: Malone Ciaran , Rock Luke , Skourou Christina
Published: February 2017

Phase‐based sorting of four‐dimensional computed tomography (4D CT) datasets is prone to image artifacts due to patient's breathing irregularities that occur during the image acquisition. The purpose of this study is to investigate the effect of the Varian normal breathing predictive filter (NBPF) as a retrospective phase‐sorting parameter in 4D CT. Ten 4D CT lung cancer datasets were obtained. The volumes of all tumors present, as well as the total lung volume, were calculated on the maximum intensity projection (MIP) images as well as each individual phase image. The NBPF was varied retrospectively within the available range, and changes in volume and image quality were recorded. The patients' breathing trace was analysed and the magnitude and location of any breathing irregularities were correlated to the behavior of the NBPF. The NBPF was found to have a considerable effect on the quality of the images in MIP and single‐phase datasets. When used appropriately, the NBPF is shown to have the ability to account for and correct image artifacts. However, when turned off (0%) or set above a critical level (approximately 40%), it resulted in erroneous volume reconstructions with variations in tumor volume up to 26.6%. Those phases associated with peak inspiration were found to be more susceptible to changes in the NBPF. The NBPF settings selected prior to exporting the breathing trace for patients evaluated using 4D CT directly affect the accuracy of the targeting and volume estimation of lung tumors. Recommendations are made to address potential errors in patient anatomy introduced by breathing irregularities, specifically deep breath or cough irregularities, by implementing the proper settings and use of this tool.

PACS numbers: 87.57.Q‐, 87.57.C‐, 87.57.N‐, 87.57.nf, 87.55.D‐.
Dose modification factor analysis of multilumen balloon brachytherapy applicator with Monte Carlo simulation
Authors: Pearson David , Williams Eric A.
Published: February 2017

The Contura brachytherapy applicator is a silicone balloon with five lumens in which a high‐dose‐rate brachytherapy source can traverse. Multilumen applicators, like the Contura, are used in accelerated partial breast irradiation (APBI) brachytherapy in instances where asymmetric dose distributions are desired; for example, when the applicator surface‐to‐skin thickness is small (< 7 mm). In these instances, the air outside the patient and the lung act as a poor scattering medium, scattering less dose back into the breast and affecting the dose distribution. The recent report by Task Group 186 of the American Association of Physicists in Medicine (AAPM) has outlined the importance of moving towards brachytherapy dose calculations using heterogeneity corrections. However, at this time, many commercial treatment planning systems do not correct for tissue heterogeneity, which can result in inaccuracies in the planned dose distribution. To quantify the deviation in the skin dose we utilize the dose modification factor (DMF), defined as the ratio of the dose rate at 1 cm beyond the applicator surface with homogenous medium, to the dose rate at 1 cm with heterogeneous medium. This investigation models the Contura applicator with the Monte Carlo N‐Particle code version 5, and determines a DMF through simulation. Taking all geometrical considerations into account, an accurate model of the Contura balloon applicator was created in MCNP and used to run simulations. The dose modification factor was found to be only slightly dependent on whether the dose distribution was symmetric or asymmetric. These results indicate that the dose delivered to part of the PTV may be lower than the planned dose by up to 12%, and that these brachytherapy plans should be viewed with caution. In addition to studying the effects of backscatter, an evaluation was made regarding the capabilities of the Contura device to shape an asymmetric dose distribution. We compared these results to a previous study of a MammoSite ML and a SAVI device and found that the dose shaping capabilities of the Contura were quite similar to that of the MammoSite ML, but markedly inferior to the SAVI.

PACS number: 87.53.Jw
Dosimetric impact of gold markers implanted closely to lung tumors: a Monte Carlo simulation
Authors: Shiinoki Takehiro , Sawada Akira , Ishihara Yoshitomo , Miyabe Yuki , Matsuo Yukinori , Mizowaki Takashi , Kokubo Masaki , Hiraoka Masahiro
Published: February 2017

We are developing an innovative dynamic tumor tracking irradiation technique using gold markers implanted around a tumor as a surrogate signal, a real‐time marker detection system, and a gimbaled X‐ray head in the Vero4DRT. The gold markers implanted in a normal organ will produce uncertainty in the dose calculation during treatment planning because the photon mass attenuation coefficient of a gold marker is much larger than that of normal tissue. The purpose of this study was to simulate the dose variation near the gold markers in a lung irradiated by a photon beam using the Monte Carlo method. First, the single‐beam and the opposing‐beam geometries were simulated using both water and lung phantoms. Subsequently, the relative dose profiles were calculated using a stereotactic body radiotherapy (SBRT) treatment plan for a lung cancer patient having gold markers along the anteriorposterior (AP) and right‐left (RL) directions. For the single beam, the dose at the gold marker‐phantom interface laterally along the perpendicular to the beam axis increased by a factor of 1.35 in the water phantom and 1.58 in the lung phantom, respectively. Furthermore, the entrance dose at the interface along the beam axis increased by a factor of 1.63 in the water phantom and 1.91 in the lung phantom, while the exit dose increased by a factor of 1.00 in the water phantom and 1.12 in the lung phantom, respectively. On the other hand, both dose escalations and dose de‐escalations were canceled by each beam for opposing portal beams with the same beam weight. For SBRT patient data, the dose at the gold marker edge located in the tumor increased by a factor of 1.30 in both AP and RL directions. In clinical cases, dose escalations were observed at the small area where the distance between a gold marker and the lung tumor was ≤ 5 mm, and it would be clinically negligible in multibeam treatments, although further investigation may be required.

PACS number: 87.10.Rt
Dosimetric benefits of IMRT and VMAT in the treatment of middle thoracic esophageal cancer: is the conformal radiotherapy still an alternative option?
Authors: Wu Zhiqin , Xie Congying , Hu Meilong , Han Ce , Yi Jinling , Zhou Yongqiang , Yan Huawei , Jin Xiance
Published: February 2017

The purpose of this study is to investigate the dosimetric differences among conformal radiotherapy (CRT), intensity‐modulated radiotherapy (IMRT), and volumetric‐modulated radiotherapy (VMAT) in the treatment of middle thoracic esophageal cancer, and determine the most appropriate treatment modality. IMRT and one‐arc VMAT plans were generated for eight middle thoracic esophageal cancer patients treated previous with CRT. The planning target volume (PTV) coverage and protections on organs at risk of three planning schemes were compared. All plans have sufficient PTV coverage and no significant differences were observed, except for the conformity and homogeneity. The lung V5, V10, and V13 in CRT were 47.9% ± 6.1%, 36.5% ± 4.6%, and 33.2% ± 4.2%, respectively, which were greatly increased to 78.2% ± 13.7% (p < 0.01), 80.8% ± 14.9% (p < 0.01), 48.4% ± 8.2% (p = 0.05) in IMRT and 58.6% ± 10.5% (p = 0.03), 67.7% ± 14.0% (p < 0.01), and 53.0% ± 10.1% (p < 0.01) in VMAT, respectively. The lung V20 (p = 0.03) in VMAT and the V30 (p = 0.04) in IMRT were lower than those in CRT. Both IMRT and VMAT achieved a better protection on heart. However, the volumes of the healthy tissue outside of PTV irradiated by a low dose were higher for IMRT and VMAT. IMRT and VMAT also had a higher MU, optimization time, and delivery time compared to CRT. In conclusion, all CRT, IMRT, and VMAT plans are able to meet the prescription and there is no clear distinction on PTV coverage. IMRT and VMAT can only decrease the volume of lung and heart receiving a high dose, but at a cost of delivering low dose to more volume of lung and normal tissues. CRT is still a feasible option for middle thoracic esophageal cancer radiotherapy, especially for the cost‐effective consideration.

PACS numbers: 87.53.Kn, 87.55.x 87.55.D 87.55.dk
Monte Carlo modeling of HD120 multileaf collimator on Varian TrueBeam linear accelerator for verification of 6X and 6X FFF VMAT SABR treatment plans
Authors: Bergman Alanah M. , Gete Ermias , Duzenli Cheryl , Teke Tony
Published: February 2017

A Monte Carlo (MC) validation of the vendor‐supplied Varian TrueBeam 6 MV flattened (6X) phase‐space file and the first implementation of the Siebers‐Keall MC MLC model as applied to the HD120 MLC (for 6X flat and 6X flattening filterfree (6X FFF) beams) are described. The MC model is validated in the context of VMAT patient‐specific quality assurance. The Monte Carlo commissioning process involves: 1) validating the calculated open‐field percentage depth doses (PDDs), profiles, and output factors (OF), 2) adapting the Siebers‐Keall MLC model to match the new HD120‐MLC geometry and material composition, 3) determining the absolute dose conversion factor for the MC calculation, and 4) validating this entire linac/MLC in the context of dose calculation verification for clinical VMAT plans. MC PDDs for the 6X beams agree with the measured data to within 2.0% for field sizes ranging from 2 × 2 to 40 × 40 cm2. Measured and MC profiles show agreement in the 50% field width and the 80%‐20% penumbra region to within 1.3 mm for all square field sizes. MC OFs for the 2 to 40 cm2 square fields agree with measurement to within 1.6%. Verification of VMAT SABR lung, liver, and vertebra plans demonstrate that measured and MC ion chamber doses agree within 0.6% for the 6X beam and within 2.0% for the 6X FFF beam. A 3D gamma factor analysis demonstrates that for the 6X beam, > 99% of voxels meet the pass criteria (3%/3 mm). For the 6X FFF beam, > 94% of voxels meet this criteria. The TrueBeam accelerator delivering 6X and 6X FFF beams with the HD120 MLC can be modeled in Monte Carlo to provide an independent 3D dose calculation for clinical VMAT plans. This quality assurance tool has been used clinically to verify over 140 6X and 16 6X FFF TrueBeam treatment plans.

PACS number: 87.55.K‐
A Monte Carlo evaluation of beam characteristics for total body irradiation at extended treatment distances
Authors: Chakarova Roumiana , Krantz Marcus
Published: February 2017

The aim is to study beam characteristics at large distances when focusing on the electron component. In particular, to investigate the utility of spoilers with various thicknesses as an electron source, as well as the effect of different spoiler‐to‐surface distances (STSD) on the beam characteristics and, consequently, on the dose in the superficial region. A MC model of a 15 MV Varian accelerator, validated earlier by experimental data at isocenter and extended distances used in large‐field total body irradiation, is applied to evaluate beam characteristics at distances larger than 400 cm. Calculations are carried out using BEAMnrc/DOSXYZnrc code packages and phase space data are analyzed by the beam data processor BEAMdp. The electron component of the beam is analyzed at isocenter and extended distances, with and without spoilers as beam modifiers, assuming vacuum or air surrounding the accelerator head. Spoiler thickness of 1.6 cm is found to be optimal compared to thicknesses of 0.8 cm and 2.4 cm. The STSD variations should be taken into account when treating patients, in particular when the treatment protocols are based on a fixed distance to the patient central sagittal plane, and also, in order to maintain high dose in the superficial region.

PACS numbers: 87.55.D‐, 87.55.de, 87.55.K‐
Applying the technique of volume‐modulated arc radiotherapy to upper esophageal carcinoma
Authors: Ma Pan , Wang Xiaozhen , Xu Yingjie , Dai Jianrong , Wang Luhua
Published: February 2017

This study aims to evaluate the possibility of using the technique of volume‐modulated arc therapy (VMAT) to combine the advantages of simplified intensity ‐ modulated radiation therapy (sIMRT) with that of regular intensity‐modulated radiation therapy (IMRT) in upper esophageal cancer. Ten patients with upper esophageal carcinoma were randomly chosen in this retrospective study. sIMRT, IMRT, and VMAT plans were generated to deliver 60 Gy in 30 fractions to the planning target volume (PTV). For each patient, with the same clinical requirements (target dose prescription, and dose/dose‐volume constraints to organs at risk (OARs)), three plans were designed for sIMRT (five equispaced coplanar beams), IMRT (seven equispaced coplanar beams), and VMAT (two complete arcs). Comparisons were performed for dosimetric parameters of PTV and of OARs (lungs, spinal cord PRV, heart and normal tissue (NT)). All the plans were delivered to a phantom to evaluate the treatment time. The Wilcoxon matched‐pairs, signed‐rank test was used for intragroup comparison. For all patients, compared to sIMRT plans, VMAT plans statistically provide: a) significant improvement in HI and CI for PTV; b) significant decrease in delivery time, lung V20, MLD, heart V30 and spinal cord PRV D1cc; c) significant increase in NT V5; and d) no significant reduction in lung V5, V10, and heart MD. For all patients, compared to IMRT plans, VMAT plans statistically provide: a) significant improvement in CI for PTV; b) significant decrease in delivery time, lung V20, MLD, NT and spinal cord PRV D1cc; c) significant increase in NT V5; and d) no significant reduction in HI for PTV, lung V5, V10, heart V30 and heart MD. For patients with upper esophageal carcinoma, using VMAT significantly reduces the delivery time and the dose to the lungs compared with IMRT, and consequently saves as much treatment time as sIMRT. Considering those significant advantages, compared to sIMRT and IMRT, VMAT is the first choice of radiotherapy techniques for upper esophageal carcinoma.

PACS number: 87.55. D‐
Evaluation of six TPS algorithms in computing entrance and exit doses
Authors: Tan Yun I. , Metwaly Mohamed , Glegg Martin , Baggarley Shaun P. , Elliott Alex
Published: February 2017

Entrance and exit doses are commonly measured in in vivo dosimetry for comparison with expected values, usually generated by the treatment planning system (TPS), to verify accuracy of treatment delivery. This report aims to evaluate the accuracy of six TPS algorithms in computing entrance and exit doses for a 6 MV beam. The algorithms tested were: pencil beam convolution (Eclipse PBC), analytical anisotropic algorithm (Eclipse AAA), AcurosXB (Eclipse AXB), FFT convolution (XiO Convolution), multigrid superposition (XiO Superposition), and Monte Carlo photon (Monaco MC). Measurements with ionization chamber (IC) and diode detector in water phantoms were used as a reference. Comparisons were done in terms of central axis point dose, 1D relative profiles, and 2D absolute gamma analysis. Entrance doses computed by all TPS algorithms agreed to within 2% of the measured values. Exit doses computed by XiO Convolution, XiO Superposition, Eclipse AXB, and Monaco MC agreed with the IC measured doses to within 2%‐3%. Meanwhile, Eclipse PBC and Eclipse AAA computed exit doses were higher than the IC measured doses by up to 5.3% and 4.8%, respectively. Both algorithms assume that full backscatter exists even at the exit level, leading to an overestimation of exit doses. Despite good agreements at the central axis for Eclipse AXB and Monaco MC, 1D relative comparisons showed profiles mismatched at depths beyond 11.5 cm. Overall, the 2D absolute gamma (3%/3 mm) pass rates were better for Monaco MC, while Eclipse AXB failed mostly at the outer 20% of the field area. The findings of this study serve as a useful baseline for the implementation of entrance and exit in vivo dosimetry in clinical departments utilizing any of these six common TPS algorithms for reference comparison.

PACS numbers: 87.55.‐x, 87.55.D‐, 87.55.N‐, 87.53.Bn
Implementation of an improved dose‐per‐MU model for double‐scattered proton beams to address interbeamline modulation width variability
Authors: Lin Liyong , Shen JiaJien , Ainsley Christopher G. , Solberg Timothy D. , McDonough James E.
Published: February 2017

Because treatment planning systems (TPSs) generally do not provide monitor units (MUs) for double‐scattered proton plans, models to predict MUs as a function of the range and the nominal modulation width requested of the beam delivery system, such as the one developed by the MGH group, have been proposed. For a given nominal modulation width, however, the measured modulation width depends on the accuracy of the vendor's calibration process and may differ from this nominal value, and also from one beamline to the next. Although such a difference can be replicated in our TPS, the output dependence on range and modulation width for each beam option or suboption has to be modeled separately for each beamline in order to achieve maximal 3% inaccuracy. As a consequence, the MGH output model may not be directly transferable. This work, therefore, serves to extend the model to more general clinic situations. In this paper, a parameterized linear‐quadratic transformation is introduced to convert the nominal modulation width to the measured modulation width for each beam option or suboption on a per‐beamline basis. Fit parameters are derived for each beamline from measurements of 60 reference beams spanning the minimum and maximum ranges, and modulation widths from 2 cm to full range per option or suboption. Using the modeled modulation width, we extract the MGH parameters for the output dependence on range and modulation width. Our method has been tested with 1784 patient‐specific fields delivered across three different beamlines at our facility. For these fields, all measured outputs fall within 3%, and 64.4% fall within 1%, of our model. Using a parameterized linear‐quadratic modulation width, MU calculation models can be established on a per‐beamline basis for each double scattering beam option or suboption.

PACS number: 87.53.Qc