bluuebunny/crossref_metadata_2025_split huggingface dataset:
Superiority of a soft tissue‐based setup using cone‐beam computed tomography over a bony structure‐based setup in intensity‐modulated radiotherapy for prostate cancer*
Authors: Sato Hiraku , Abe Eisuke , Utsunomiya Satoru , Kaidu Motoki , Yamana Nobuko , Tanaka Kensuke , Ohta Atsushi , Obinata Mika , Liu Junyang , Kawaguchi Gen , Maruyama Katsuya , Ayukawa Fumio , Aoyama Hidefumi 
Published: February 2017

The purpose of this study was to test the superiority of a soft tissue‐based setup using cone‐beam computed tomography (CBCT) to a bony structure‐based setup using the ExacTrac system in intensity‐modulated radiotherapy (IMRT) for prostate cancer. We studied 20 patients with localized prostate cancer who received IMRT between November 2010 and February 2012. After the initial setup, the pelvic bony structure‐based setup and ExacTrac system were applied. After that, CBCT and a soft tissue‐based setup were used. A shift in the isocenter between the ExacTrac‐based and CBCT‐based setup was recorded in the anterior–posterior (AP), superior–inferior (SI), and left–right (LR) axes. The shift was considered an interfractional prostate shift. Post‐treatment CBCT was also taken once a week to measure the intrafractional prostate shift, based on the coordinates of the isocenter between pre‐ and post‐treatment CBCT. The planning target volume (PTV) margins were determined using van Herk's method. We measured the elapsed time required for soft tissue matching and the entire treatment time using CBCT. The of the inter‐ and intrafractional shifts were and in the AP, and in the SI, and and in the LR directions. The PTV margins in the cases of bony structure‐based and soft tissue‐based setups were 7.3 mm and 2.7 mm in the AP, 5.8 mm and 2.3 mm in the SI, and 1.9 mm and 1.2 mm in the LR directions. Even though the median elapsed time using CBCT was expanded in 5.9 min, the PTV margins were significantly reduced. We found the calculated PTV margins in the soft tissue‐based setup using CBCT were small, and this arrangement was superior to the bony structure‐based setup in prostate IMRT.PACS numbers: 87.19.ru, 87.55.T‐
Evaluation of backscatter dose from internal lead shielding in clinical electron beams using EGSnrc Monte Carlo simulations
Authors: de Vries Rowen J. , Marsh Steven 
Published: February 2017

Internal lead shielding is utilized during superficial electron beam treatments of the head and neck, such as lip carcinoma. Methods for predicting backscattered dose include the use of empirical equations or performing physical measurements. The accuracy of these empirical equations required verification for the local electron beams. In this study, a Monte Carlo model of a Siemens Artiste linac was developed for 6, 9, 12, and 15 MeV electron beams using the EGSnrc MC package. The model was verified against physical measurements to an accuracy of better than 2% and 2 mm. Multiple MC simulations of lead interfaces at different depths, corresponding to mean electron energies in the range of 0.2–14 MeV at the interfaces, were performed to calculate electron backscatter values. The simulated electron backscatter was compared with current empirical equations to ascertain their accuracy. The major finding was that the current set of backscatter equations does not accurately predict electron backscatter, particularly in the lower energies region. A new equation was derived which enables estimation of electron backscatter factor at any depth upstream from the interface for the local treatment machines. The derived equation agreed to within 1.5% of the MC simulated electron backscatter at the lead interface and upstream positions. Verification of the equation was performed by comparing to measurements of the electron backscatter factor using Gafchromic EBT2 film. These results show a mean value of to 1σ of the predicted values of electron backscatter. The new empirical equation presented can accurately estimate electron backscatter factor from lead shielding in the range of 0.2 to 14 MeV for the local linacs.PACS numbers: 87.53.Bn, 87.55.K‐, 87.56.bd
Evaluation of detectors for acquisition of pristine depth‐dose curves in pencil beam scanning
Authors: Bäumer Christian , Koska Benjamin , Lambert Jamil , Timmermann Beate , Mertens Thierry , Talla Patrick Takoukam 
Published: February 2017

Acquisition of quasi‐monoenergetic ("pristine") depth‐dose curves is an essential task in the frame of commissioning and quality assurance of a proton therapy treatment head. For pencil beam scanning delivery modes this is often accomplished by measuring the integral ionization in a plane perpendicular to the axis of an unscanned beam. We focus on the evaluation of three integral detectors: two of them are plane‐parallel ionization chambers with an effective radius of 4.1 cm and 6.0 cm, respectively, mounted in a scanning water phantom. The third integral detector is a 6.0 cm radius multilayer ionization chamber. The experimental results are compared with the corresponding measurements under broad field conditions, which are performed with a small radius plane‐parallel chamber and a small radius multilayer ionization chamber. We study how a measured depth‐dose curve of a pristine proton field depends on the detection device, by evaluating the shape of the depth‐dose curve, the relative charge collection efficiency, and intercomparing measured ranges. Our results show that increasing the radius of an integral chamber from 4.1 cm to 6.0 cm increases the collection efficiency by 0%–3.5% depending on beam energy and depth. Ranges can be determined by the large electrode multilayer ionization chamber with a typical uncertainty of 0.4 mm on a routine basis. The large electrode multilayer ionization chamber exhibits a small distortion in the Bragg Peak region. This prohibits its use for acquisition of base data, but is tolerable for quality assurance. The good range accuracy and the peak distortion are characteristics of the multilayer ionization chamber design, as shown by the direct comparison with the small electrode counterpart.PACS number: 87.55.Qr
Determination of optimal PTV margin for patients receiving CBCT‐guided prostate IMRT: comparative analysis based on CBCT dose calculation with four different margins
Authors: Gill Sukhdeep K. , Reddy Krishna , Campbell Nina , Chen Changhu , Pearson David 
Published: February 2017

Variations in daily setup and rectum/bladder filling lead to uncertainties in the delivery of prostate IMRT. The purpose of this study is to determine the optimal PTV margin for CBCT‐guided prostate IMRT based on daily CBCT dose calculations using four different margins. Five patients diagnosed with low‐risk prostate cancer were treated with prostate IMRT to 70 Gy in 28 fractions using daily CBCT for image guidance. The prostate CTV and OARs were contoured on all CBCTs. IMRT plans were created using 1 mm, 3 mm, 5 mm, and 7 mm CTV to PTV expansions. For each delivered fraction, dose calculations were generated utilizing the pretreatment CBCT translational shifts performed and dosimetric analysis was performed. One hundred and forty total treatment fractions (CBCT sessions) were evaluated. The planned prostate CTV V100% was 100% for all PTV margins. Based on CBCT analysis, the actual cumulative CTVs V100% were , and for 1, 3, 5, and 7 mm uniform PTV margins, respectively. Delivered rectum and bladder doses were different as compared to expected planned doses, with the magnitude of differences increasing with PTV margin. Daily setup variation during prostate IMRT yields differences in the actual vs. expected doses received by the prostate CTV, rectum, and bladder. The magnitude of these differences is significantly affected by the PTV margin utilized. It was found that when daily CBCT was used for soft‐tissue alignment of the prostate, a 3 mm PTV margin allowed for CTV to be covered for 99% of cases.PACS numbers: 87.55.dk‐, 87.57.Q‐
Comparison of VMAT‐SABR treatment plans with flattening filter (FF) and flattening filter‐free (FFF) beam for localized prostate cancer
Authors: Chung Jin‐Beom , Kim Jae‐Sung , Eom Keun‐Yong , Kim In‐Ah , Kang Sang‐Won , Lee Jeong‐Woo , Kim Jin‐Young , Suh Tae‐Suk 
Published: February 2017

The purpose of this study is to investigate the feasibility of using a flattening filter‐free (FFF) beam with an endorectal balloon for stereotactic ablative body radiotherapy (SABR) of clinically localized prostate cancer. We assessed plans of SABR with volumetric‐modulated arc therapy (VMAT) that used a flattening filter (FF) beam and an FFF beam and compared the verification results of dosimetric quality assurance for all pretreatment plans. A total of 20 patients with prostate cancer were enrolled in the study. SABR plans using VMAT with two full arcs were optimized in the Eclipse treatment planning system. All plans prescribed 42.7 Gy in 7 fractions of 6.1 Gy each. Four SABR plans were computed for each patient: two with FF beams and two with FFF beams of 6 and 10 MV. For all plans, the cumulative dose‐volume histograms (DVHs) for the target volumes and organs at risk (OARs) were recorded and compared. Pretreatment quality assurance (QA) was performed using the I'mRT MatriXX system and radiochromic EBT3 film to verify treatment delivery, and gamma analysis was used to quantify the agreement between calculations and measurements. In addition, total monitor units (MUs) and delivery time were investigated as technical parameters of delivery. All four plans achieved adequate dose conformity to the target volumes and had comparable dosimetric data. The DVHs of all four plans for each patient were very similar. All plans were highly conformal with and , and the doses were homogeneous (HI = 0.08–0.15). Sparing for the bladder and rectum was slightly better with the 10 MV FF and FFF plans than with the 6 MV FF and FFF plans, but the difference was negligible. However, there was no significant difference in sparing for the other OARs. The mean agreement with the criterion was higher than 97% for verifying all plans. For the criterion, the corresponding agreement values were more than 90%, which showed that the plans were acceptable. The mean MUs and delivery time used were and min for 6 MV FF, and min for 6 MV FFF, and min for 10 MV FF, and and min for 10 MV FFF, respectively. In the current study, the dose distributions of the prostate SABR plans using 6 and 10 MV FFF beams were similar to those using 6 and 10 MV FF beams. However, this study confirmed that SABR treatment using an FFF beam had an advantage with respect to delivery time. In addition, all pretreatment plans were verified as acceptable and their results were comparable. Therefore, the results of this study suggest that the use of an FFF beam for prostate SABR is a feasible and efficient technique, if carefully applied.PACS numbers: 87.55.D, 87.55.dk
Alignment of multiradiation isocenters for megavoltage photon beam
Authors: Zhang Yin , Ding Kai , Cowan Garth , Tryggestad Erik , Armour Elwood , Wang Ken Kang‐Hsin 
Published: February 2017

The accurate measurement of the linear accelerator (linac) radiation isocenter is critical, especially for stereotactic treatment. Traditional quality assurance (QA) procedure focuses on the measurement of single radiation isocenter, usually of 6 megavoltage (MV) photon beams. Single radiation isocenter is also commonly assumed in treatment planning systems (TPS). Due to different flattening filters and bending magnet and steering parameters, the radiation isocenter of one energy mode can deviate from another if no special effort was devoted. We present the first experience of the multiradiation isocenters alignment on an Elekta linac, as well as its corresponding QA procedure and clinical impact. An 8 mm ball‐bearing (BB) phantom was placed at the 6 MV radiation isocenter using an Elekta isocenter search algorithm, based on portal images. The 3D radiation isocenter shifts of other photon energy modes relative to the 6 MV were determined. Beam profile scanning for different field sizes was used as an independent method to determine the 2D multiradiation isocenters alignment. To quantify the impact of radiation isocenter offset on targeting accuracy, the 10 MV radiation isocenter was manually offset from that for 6 MV by adjusting the bending magnet current. Because our table isocenter was mechanically aligned to the 6 MV radiation isocenter, the deviation of the table isocentric rotation from the "shifted" 10 MV radiation isocenter after bending magnet adjustment was assessed. Winston‐Lutz test was also performed to confirm the overall radiation isocenter positioning accuracy for all photon energies. The portal image method showed the radiation isocenter of the 10 MV flattening filter‐free mode deviated from others before beam parameter adjustment. After the adjustment, the deviation was greatly improved from 0.96 to 0.35 mm relative to the 6 MV radiation isocenter. The same finding was confirmed by the profile‐scanning method. The maximum deviation of the table isocentric rotation from the 10 MV radiation isocenter was observed to linearly increase with the offset between 6 and 10 MV radiation isocenter; 1 mm radiation isocenter offset can translate to almost 2 mm maximum deviation of the table isocentric rotation from the 10 MV radiation isocenter. The alignment of the multiradiation isocenters is particularly important for high‐precision radiotherapy. Our study provides the medical physics community with a quantitative measure of the multiradiation isocenters alignment. A routine QA method should be considered, to examine the radiation isocenters alignment during the linac acceptance.PACS number: 87.55.Qr, 87.56.bd, 87.56.Fc
A method to improve dose gradient for robotic radiosurgery
Authors: Li Tianfang , Ozhasoglu Cihat , Burton Steven , Flickinger John , Heron Dwight E. , Huq M. Saiful 
Published: February 2017

For targets with substantial volume, collimators of relatively large size are usually selected to minimize the treatment time in robotic radiosurgery. Their large penumbrae may adversely affect the dose gradient around the target. In this study, we implement and evaluate an inner‐shell planning method to increase the dose gradient and reduce dose to normal tissues. Ten patients previously treated with CyberKnife M6 system were randomly selected with the only criterion being that PTV be larger than . A new plan was generated for each patient in which the PTV was split into two regions: a 5 mm inner shell and a core, and a 7.5 mm Iris collimator was exclusively applied to the shell, with other appropriate collimators applied to the core depending on its size. The optimization objective, functions, and constraints were the same as in the corresponding clinical plan. The results were analyzed for V12 Gy, V9 Gy, V5 Gy, and gradient index (GI). Volume reduction was found for the inner‐shell method at all studied dose levels as compared to the clinical plans. The absolute dose‐volume reduction ranged from to with a mean of for 12 Gy, from to with a mean of for 9 Gy, and from to with a mean of for 5 Gy, respectively. The GI reduction ranged from 3.2% to 23.6%, with a mean of 12.6%. Paired t‐test for GI has a p‐value of 0.0014. The range for treatment time increase is from ‐3 min to 20 min, with a mean of 7.0 min. We conclude that irradiating the PTV periphery exclusively with the 7.5 mm Iris collimator, rather than applying mixed collimators to the whole PTV, can substantially improve the dose gradient, while maintaining good coverage, conformity, and reasonable treatment time.PACS number: 87.55.de
Clinical implementation of photon beam flatness measurements to verify beam quality
Authors: Goodall Simon , Harding Nicholas , Simpson Jake , Alexander Louise , Morgan Steve 
Published: February 2017

This work describes the replacement of Tissue Phantom Ratio (TPR) measurements with beam profile flatness measurements to determine photon beam quality during routine quality assurance (QA) measurements. To achieve this, a relationship was derived between the existing energy metric and beam flatness, to provide baseline values and clinically relevant tolerances. The beam quality was varied around two nominal beam energy values for four matched Elekta linear accelerators (linacs) by varying the bending magnet currents and reoptimizing the beam. For each adjusted beam quality the was measured using an ionization chamber and Solid Water phantom. Two metrics of beam flatness were evaluated using two identical commercial ionization chamber arrays. A linear relationship was found between and both metrics of flatness, for both nominal energies and on all linacs. Baseline diagonal flatness () values were measured to be 103.0% (ranging from 102.5% to 103.8%) for 6 MV and 102.7% (ranging from 102.6% to 102.8%) for 10 MV across all four linacs. Clinically acceptable tolerances of for 6 MV, and for 10 MV, were derived to equate to the current clinical tolerance of . Small variations in the baseline diagonal flatness values were observed between ionization chamber arrays; however, the rate of change of with diagonal flatness was found to remain within experimental uncertainty. Measurements of beam flatness were shown to display an increased sensitivity to variations in the beam quality when compared to TPR measurements. This effect is amplified for higher nominal energy photons. The derivation of clinical baselines and associated tolerances has allowed this method to be incorporated into routine QA, streamlining the process whilst also increasing versatility. In addition, the effect of beam adjustment can be observed in real time, allowing increased practicality during corrective and preventive maintenance interventions.PACS number: 87.56.Fc
Comparison of volumetric‐modulated arc therapy and dynamic conformal arc treatment planning for cranial stereotactic radiosurgery
Authors: Molinier Jessica , Kerr Christine , Simeon Sebastien , Ailleres Norbert , Charissoux Marie , Azria David , Fenoglietto Pascal 
Published: February 2017

The aim was to analyze arc therapy techniques according to the number and position of the brain lesions reported by comparing dynamic noncoplanar conformal arcs (DCA), two coplanar full arcs () with volumetric‐modulated arc therapy (VMAT), multiple noncoplanar partial arcs with VMAT (), and two full arcs with VMAT and 10° table rotation (). Patients with a single lesion (n = 10), multiple lesions (n = 10) or a single lesion close to organs at risk (n = 5) and previously treated with DCA were selected. For each patient, the DCA treatment was replanned with all VMAT techniques. All DCA plans were compared with VMAT plans and evaluated in regard to the different quality indices and dosimetric parameters. For single lesion, homogeneity index (HI) better results were found for the technique () compared with DCA procedure (). Concerning conformity index (CI), the technique gave higher and better values () compared with those obtained with the DCA technique (). DCA improved healthy brain protection ( vs. for ) and reduced monitor unit numbers ( MU vs. for ), even if global room occupation was higher. For multiple lesions, VMAT techniques provided better HI (0.16) than DCA (). The CI was improved with ( for vs. for DCA). The healthy brain was better protected with DCA (). Regarding the MU numbers: . For a single lesion close to OAR, achieved high degrees of homogeneity ( vs. for DCA) and conformity ( vs. for DCA) while sparing organs at risk ( vs. for DCA, and vs. for DCA). On the other hand, MU numbers were lower with DCA ( MU vs. MU for ) even if overall time was inferior with . For a single lesion, DCA provide better plan considering low doses to healthy brain even if quality indexes are better for the others techniques. For multiple lesions, seems to be the best compromise, due to the ability to deliver a good conformity and homogeneity plan while sparing healthy brain tissue. For a single lesion close to organs at risk, is the most appropriate technique.PACS numbers: 87.55. dk, 87.56.bd
Radiation intensity () and visibility of anatomical structures in head CT examinations
Authors: Tipnis Sameer , Thampy Rajesh , Rumboldt Zoran , Spampinato Maria , Matheus Gisele , Huda Walter 
Published: February 2017

The purpose of this study was to quantify how changing the amount of radiation used to perform routine head CT examinations () affects visibility of key anatomical structures. Eight routine noncontrast head CT exams were selected from six CT scanners, each of which had a different setting (60 to 75 mGy). All exams were normal and two slices were selected for evaluation, one at the level of basal ganglia and the other at the fourth ventricle. Three experienced neuroradiologists evaluated the visibility of selected structures, including the putamen, caudate nucleus, thalamus, internal capsule, grey/white differentiation, and brainstem. Images were scored on a five‐point scoring scheme (1, unacceptable, 3, satisfactory, and 5, excellent). Reader scores, averaged over the cases obtained from each scanner, were plotted as a function of the corresponding . Average scores for the fourth ventricle were and for the basal ganglia were . No image received a score of 1. Two readers showed no clear trend of an increasing score with increasing . One reader showed a slight trend of increasing score with increasing , but the increase in score from a 25% increase in was a fraction of the standard deviation associated average scores. Collectively, results indicated that there were no clear improvements in visualizing neuroanatomy when increased from 60 to 75 mGy in routine head CT examinations. Our study showed no apparent benefit of using more than 60 mGy when performing routine noncontrast head CT examinations.PACS number(s): 87.57.C‐
Size‐based protocol optimization using automatic tube current modulation and automatic kV selection in computed tomography
Authors: MacDougall Robert D. , Kleinman Patricia L. , Callahan Michael J. 
Published: February 2017

Size‐based diagnostic reference ranges (DRRs) for contrast‐enhanced pediatric abdominal computed tomography (CT) have been published in order to establish practical upper and lower limits of CTDI, DLP, and SSDE. Based on these DRRs, guidelines for establishing size‐based SSDE target levels from the SSDE of a standard adult by applying a linear correction factor have been published and provide a great reference for dose optimization initiatives. The necessary step of designing manufacturer‐specific CT protocols to achieve established SSDE targets is the responsibility of the Qualified Medical Physicist. The task is straightforward if fixed‐mA protocols are used, however, more difficult when automatic exposure control (AEC) and automatic kV selection are considered. In such cases, the physicist must deduce the operation of AEC algorithms from technical documentation or through testing, using a wide range of phantom sizes. Our study presents the results of such testing using anthropomorphic phantoms ranging in size from the newborn to the obese adult. The effect of each user‐controlled parameter was modeled for a single‐manufacturer AEC algorithm (Siemens CARE Dose4D) and automatic kV selection algorithm (Siemens CARE kV). Based on the results presented in this study, a process for designing mA‐modulated, pediatric abdominal CT protocols that achieve user‐defined SSDE and kV targets is described.PACS numbers: 87.57.Q‐, 87.57.qp, 87.53.Bn