bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative analysis of SmartArc‐based dual arc volumetric‐modulated arc radiotherapy (VMAT) versus intensity‐modulated radiotherapy (IMRT) for nasopharyngeal carcinoma
Authors: Lee Tsair‐Fwu , Chao Pei‐Ju , Ting Hui‐Min , Lo Su‐Hua , Wang Yu‐Wen , Tuan Chiu‐Ching , Fang Fu‐Min , Su Te‐Jen
Published: February 2017

The purpose of this study was to evaluate and quantify the planning performance of SmartArc‐based volumetric‐modulated arc radiotherapy (VMAT) versus fixed‐beam intensity‐modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) using a sequential mode treatment plan. The plan quality and performance of dual arc‐VMAT (DA‐VMAT) using the Smart‐Arc system (clinical version 9.0; Philips, Fitchburg, WI, USA) were evaluated and compared with those of seven‐field (7F)‐IMRT in 18 consecutive NPC patients. Analysis parameters included the conformity index (CI) and homogeneity index (HI) for the planning target volume (PTV), maximum and mean dose, normal tissue complication probability (NTCP) for the specified organs at risk (OARs), and comprehensive quality index (CQI) for an overall evaluation in the 11 OARs. Treatment delivery time, monitor units per fraction (MU/fr), and gamma evaluations were also analyzed. DA‐VMAT achieved similar target coverage and slightly better homogeneity than conventional 7F‐IMRT with a similar CI and HI. NTCP values were only significantly lower in the left parotid gland (for xerostomia) for DA‐VMAT plans. The mean value of CQI at indicated a 2% benefit in sparing OARs by DA‐VMAT. The MU/fr used and average delivery times appeared to show improved efficiencies in DA‐VMAT. Each technique demonstrated high accuracy in dose delivery in terms of a high‐quality assurance (QA) passing rate of the criterion. The major difference between DA‐VMAT and 7F‐IMRT using a sequential mode for treating NPC cases appears to be improved efficiency, resulting in a faster delivery time and the use of fewer MU/fr.

PACS number: 87.53.Tf, 87.55.x, 87.55.D, 87.55.dk
Expanding the use of real‐time electromagnetic tracking in radiation oncology
Authors: Shah Amish P. , Kupelian Patrick A. , Willoughby Twyla R. , Meeks Sanford L.
Published: February 2017

In the past 10 years, techniques to improve radiotherapy delivery, such as intensity‐modulated radiation therapy (IMRT), image‐guided radiation therapy (IGRT) for both inter‐ and intrafraction tumor localization, and hypofractionated delivery techniques such as stereotactic body radiation therapy (SBRT), have evolved tremendously. This review article focuses on only one part of that evolution, electromagnetic tracking in radiation therapy. Electromagnetic tracking is still a growing technology in radiation oncology and, as such, the clinical applications are limited, the expense is high, and the reimbursement is insufficient to cover these costs. At the same time, current experience with electromagnetic tracking applied to various clinical tumor sites indicates that the potential benefits of electromagnetic tracking could be significant for patients receiving radiation therapy. Daily use of these tracking systems is minimally invasive and delivers no additional ionizing radiation to the patient, and these systems can provide explicit tumor motion data. Although there are a number of technical and fiscal issues that need to be addressed, electromagnetic tracking systems are expected to play a continued role in improving the precision of radiation delivery.

PACS number: 87.63.‐d
4D CT image acquisition errors in SBRT of liver identified using correlation
Authors: Szegedi Martin , Sarkar Vikren , Rassiah‐Szegedi Prema , Wang Brian , Huang Y.Jessica , Zhao Hui , Salter Bill
Published: February 2017

In the AAPM Report 80,(1) the imaging modality of 4D CT and respiration‐correlated CT was declared a “promising solution for obtaining high‐quality CT data in the presence of respiratory motion”. To gather anatomically correct data over time, the existence of correlation between the internal organ movement and an external surrogate has to be assumed. For the in‐house evaluation of such correlation, we retrospectively analyzed 21 four‐dimensional computer tomography (4D CT) scans of five patients, out of which the artifacts experienced in three patients are shown here. To provide context and a baseline for the analysis of patient motion, a real‐tissue liver phantom was used with a solid water block and liver tissue. The superior–inferior motion of fiducials in phantom and patients was correlated to the recorded anterior–posterior motion of an external surrogate marker on the chest. The use of a solid water block yielded a measurable correlation coefficient of 0.98 or better using a sinusoidal animation pattern. With sinusoidally‐animated liver tissue, the minimum correlation observed was 0.96. Comparing this to retrospective patient data, we found three cases of a change in the correlation coefficient, or simply a low correlation. The source of this low correlation was investigated by careful examination of the breathing traces and the CT‐phase assignments used to reconstruct the datasets. Consequences of nonregular breathing are elaborated on. We demonstrate the impact of wrong phase assignments and missing image information in the 4D CT phase sampling processes. We also show how daily patient‐based correlation analysis can indicate changes in breathing traces, which can be significant enough to decrease, or completely eliminate, previously existing correlation.

PACS numbers: 87.57.‐s, 87.57.Q‐, 87.57.cp, 87.57.N‐, 87.55.Qr
Image quality of an investigational imaging panel for use with the imaging beam line cone‐beam CT
Authors: Beltran Chris
Published: February 2017

The purpose of this study was to measure and compare the contrast‐to‐noise ratio (CNR) as a function of dose for the cone‐beam CT (CBCT) produced by the imaging beam line (IBL) for the standard and an investigational imaging panel. Two Siemens Artiste linear accelerators were modified at our institution such that the MV‐CBCT would operate under an investigational IBL. The imaging panel from one of the machines was replaced with an investigational imaging panel. After the modification, a set of CBCT for a large and small phantom consisting of eight tissue‐equivalent inserts was acquired for the standard imager and for the investigational imager with and without the standard copper plate. Ten dose settings for each phantom using the IBL in combination with the standard and investigational imaging panel were acquired. The CNR for each tissue‐equivalent insert was calculated. Resolution measurements in line pairs per mm (lp/mm) of the CBCT for the various imaging panel setups were made. In addition, CBCT images of two patients that were imaged with each panel configuration were displayed for a group of physicians and therapists who were asked to identify the best and worst CBCT for each patient. This was used as a qualitative judge of practical image quality. The CNR of the muscle insert for the large phantom with 1.5 cGy at isocenter was 1.3 for the standard imager, 1.5 for the investigational imager with the copper plate, and 1.9 without the plate. Under the same conditions, the CNR of the trabecular bone insert was 5.9, 7.3, and 9.7, respectively. For the small phantom with the same dose to isocenter, the CNR for muscle was 1.7, 2.1, and 3.3, respectively. For the trabecular bone, the CNR was 8.1, 9.6, and 12.1 respectively. The resolution for 1 cGy at isocenter was 0.37 lp/mm for the standard imager, 0.32 and 0.33 for the investigational imager with and without the copper plate. The qualitative test ranked the CBCT of the investigational imager without the copper plate to be the best image, and the standard imager to be the worst. The investigational imaging panel improves image quality as compared to the standard imager for IBL CBCTs. A 1 cGy IBL CBCT, no matter which imager is used, is sufficient for bony anatomy localization. The investigational imager without the copper plate was judged clinically to produce the best IBL CBCT.

PACS numbers: 87.57.Q, 87.57.cj
A study of segment weight optimization with the CMS XiO step‐and‐shoot IMRT technique for prostate cancer
Authors: Prabhakar Ramachandran , Cramb Jim , Gehrke Christopher , Anderson Justin , Andrews Judy
Published: February 2017

The aim of this study was to compare IMRT optimization in the CMS XiO radiotherapy treatment planning system, with and without segment weight optimization. Twenty‐one prostate cancer patients were selected for this study. All patients were initially planned with step‐and‐shoot IMRT (S‐IMRT). A new plan was then created for each patient by applying the segment weight optimization tool (SWO‐IMRT). Analysis was performed on the (SWO‐IMRT) and (S‐IMRT) plans by comparing the total number of segments, monitor units, rectal and bladder dose. The study showed a statistically significant reduction in the total number of segments (mean: 25.3%; range: 16.8%–31.1%) with SWO‐IMRT as compared to S‐IMRT . Similarly, a mean reduction of 3.8% (range: 0.4%–7.7%) in the total MU was observed with SWO‐IMRT . The study showed an average rectal dose decrease of 13.7% (range: 7.9%–21.4%) with SWO‐IMRT . We also observed a statistically significant reduction of 26.7% (range: 16.0%–41.4%; p < 0.0001) in the mean dose to the posterior one‐third rectum and an overall reduction in mean bladder dose of 2.2% (range: 0.1%–6.1%) for SWO‐IMRT . This study shows that the segment weight optimization method significantly reduces the total number of segments and the dose to the rectum for IMRT prostate cancer. It also resulted in fewer monitor units for most of the prostate cases observed in this study.

PACS numbers: 85.55.ne; 87.55.de; 87.55.kd
Radiochromic film dosimetry of rectal inhomogeneity and applicator attenuation in high dose rate brachytherapy of uterine cervix
Authors: Uniyal Satish C. , Naithani Umesh C. , Sharma Sunil D. , Srivastava Anoop K.
Published: February 2017

Heterogeneities existing in the patient during treatment are neglected, as the treated subject is considered homogeneous in most of the commercially‐available treatment planning systems (TPSs) used for high dose rate (HDR) brachytherapy. The choice of a suitable dosimeter for experimental dosimetry near the HDR source is crucial, mainly due to existence of steep dose gradients. The present work aimed to assess the effect of rectal air heterogeneity and applicator attenuation in the HDR Ir‐192 brachytherapy treatment of carcinoma uterine cervix by utilizing GAFCHROMIC EBT2 film dosimetry. The dose to rectal walls under the condition of rectal air heterogeneity was measured experimentally using EBT2 film in a rectal phantom, and the measurements were validated by the Monte Carlo (MC) simulations. The applicator attenuation was measured by EBT2 film for a commonly used stainless steel uterine tube in a homogeneous water equivalent phantom. The measured doses were compared with the TPS calculated values. In case of the air cavity, the measured dose at the closest rectal surface was 12.8% less than the TPS calculated value due to lack of back scattering, whereas at the farthest rectal surface, it was higher by 24.5% due to no attenuation. The magnitude of attenuation due to the metal applicator was measured as high as 2% when compared with the TPS calculation. The dose reduction at the nearest rectal surface due to the effect of rectal air has indicated a clinically favorable dose distribution within the rectum, whereas the shielding effect posed by the metallic applicator was found to be less significant. Mutual agreement of the measured doses with the MC calculated dose values confirmed the suitability of EBT2 film for clinical dosimetry in HDR brachytherapy.

PACS numbers: 87.53.Bn, 87.53.Jw, 87.56.bg, 87.55.Qr
Sensitivity of a helical diode array device to delivery errors in IMRT treatment and establishment of tolerance level for pretreatment QA
Authors: García‐Vicente Feliciano , Fernández Virginia , Bermüdez Rocío , Gómez Alberto , Pérez Leopoldo , Zapatero Almudena , Torres Juan J.
Published: February 2017

The aim of this study is to determine the gantry angle and multileaf collimator (MLC) gap error‐detection threshold of a diode helical array with an inserted microionization chamber in order to use this device for the pretreatment quality assurance (QA) of intensity‐modulated radiation therapy (IMRT) treatments. Implications on the dose‐volume histograms (DVHs) of the patient treatments will also be considered for the establishment of a QA protocol with a reasonable tolerance level. Three dynamic IMRT HN (head and neck) and prostate treatments were studied. Random and systematic variations of gantry angle and systematic errors in MLC gap width of the clinical treatments were analyzed in order to establish the detection sensitivity of the array. The associated clinical significance was studied introducing the same errors in the treatment plan based on the patients' computed tomography (CT) and calculating the corresponding DVHs. The Gamma (3%/3 mm) presented a 4% variation in failure rate for a rotation error of 1° for both types of treatment. Both systematic and random errors in gantry rotation angle have little effect on the patients' DVHs. MLC gap width errors of 1 mm and 2 mm in the prostate treatments imply a mean variation in isocenter‐measured absorbed dose of 2.1% and 4.1%, respectively. In the case of HN, these errors entail a change in measured isocenter dose of 4.7% and 8.6%, respectively. The variation observed in the DVHs of the patients was, basically, a global displacement of the curves proportional to the isocenter dose variation caused by the gap width error. According to the array sensitivity to the analyzed errors and its implication in patient DVHs, a tolerance of 95% point passing rate for the gamma criterion 3%/2 mm and an agreement of 2% in isocenter absolute dose have been established as tolerance criteria for our pretreatment IMRT QA protocol.

PACS number: 87.56.Fc
Skyshine photon doses from 6 and 10 MV medical linear accelerators
Authors: de Paiva Eduardo , da Rosa Luiz A. R.
Published: February 2017

The skyshine radiation phenomenon consists of the scattering of primary photon beams in the atmosphere above the roof of a medical linear accelerator facility, generating an additional dose at ground level in the vicinity of the treatment room. Thus, with respect to radioprotection, this situation plays an important role when the roof is designed with little shielding and there are buildings next to the radiotherapy treatment room. In literature, there are few reported skyshine‐measured doses and these contain poor agreement with empirical calculations. In this work, we carried out measurements of skyshine photon dose rates produced from eight different 6 and 10 MV medical accelerators. Each measurement was performed outside the room facility, with the beam positioned in the upward direction, at a horizontal distance from the target and for a maximum photon field size at the accelerator isocenter. Measured dose‐equivalent rates results were compared with calculations obtained by an empirical expression, and differences between them deviated in one or more order of magnitude.

PACS numbers: 87.53.‐j, 87.53.Bn
Low‐energy broad‐beam photon shielding data for constituents of concrete
Authors: Ogundare Folorunso O. , Ogundele Samuel A. , Akerele Olumide O. , Balogun Fatai A.
Published: February 2017

The ability of concrete to attenuate ionizing radiation intensity is assessed using its linear or mass attenuation coefficient. In this work, the broad‐beam linear and mass attenuation coefficients of different types of soils and cements used for making concrete were measured at different photon energies (60–1333 keV), nearly spanning the diagnostic photon energy range, using a NaI detector. The mass attenuation coefficients of cement decreased from at 60 keV to at 1332.5 keV. For soils, the mass attenuation coefficient of those collected from the beach was the highest, decreasing from at 60 keV to at 1332.5 keV. Land soils had the least value, decreasing from at 60 keV to at 1332.5 keV. Limestone had smaller mass attenuation coefficients than the cement produced using it. The implication of the above is that for making concrete, beach sand should be preferred as the sand component of the concrete. Models of the form and are proposed for fitting the linear attenuation coefficient and mass attenuation coefficient data, respectively.

PACS numbers: 87.55.N‐; 87.50.cm
Impact of the Tiloop Bra mesh in CT images and dose delivery in breast radiotherapy
Authors: Camacho Cristina , Perez‐Calatayud Jose , Lliso Françoise , Carmona Vicente , Tormo Alejandro , Ballester Facundo , Pujades Ma Carmen
Published: February 2017

A new titanized breast mesh, TiLOOP Bra, is currently available for implantation in patients who require radiotherapy. The purpose of this work is to study the dosimetric effect of the presence of a TiLOOP Bra mesh on breast radiation treatment and radiographic imaging. The dosimetric effects have been measured for three X‐ray energies: 1.25 MeV, 6 MV and 18 MV, using radiochromic films placed at three different depths. These depths are representative of mesh location in breast during the radiotherapy treatment and hence, are of interest in this study. In order to assess the disturbance in a radiographic image, different computed tomographic (CT) studies of the mesh have been performed. The absorbed dose differences with and without the mesh are less than 1%. No metallic artifacts have been observed in radiographic images associated with the mesh, nor significant disturbances in Hounsfield Units. The TiLOOP Bra mesh does not disturb the dosimetry of a typical radiotherapy treatment and its influence in the quality of the CT scan required for planning is negligible.

PACS number: 87.55.‐x
Independent evaluation of an in‐house brachytherapy treatment planning system using simulation, measurement and calculation methods
Authors: Shirazi M. A. Mosleh , Faghihi R. , Siavashpour Z. , Nedaie H.A. , Mehdizadeh S. , Sina S.
Published: February 2017

Accuracy of treatment planning systems may significantly influence the efficacy of brachytherapy. The purpose of this work is a detailed, varied and independent evaluation of an in‐house brachytherapy treatment planning software called STPS. Operational accuracy of STPS was investigated. Geometric tests were performed to validate entry and reconstruction of positional information from scanned orthogonal films. MCNP4C Monte Carlo code and TLDs were used for simulation and experimental measurement, respectively. STPS data were also compared with those from a commercial planning system (Nucletron PLATO). Discrepancy values between MCNP and STPS data and also those of PLATO and STPS at Manchester system dose prescription points (AL and AR) of tandem and ovoid configurations were and , respectively. Similar results were achieved for other investigated configurations. Observed discrepancies between MCNP and STPS at the dose prescription point and at 1 cm from the tip of the vaginal applicator were 4.5% and 25.6% respectively, while the discrepancy between the STPS and PLATO data at those points was 2.3%. The software showed submillimeter accuracy in its geometrical reconstructions. In terms of calculation accuracy, similar to PLATO, as attenuation of the sources and applicator body is not considered, dose was overestimated at the tip of the applicator, but based on the available criteria, dose accuracy at most points were acceptable. Our results confirm STPS's geometrical and operational reliability, and show that its dose computation accuracy is comparable to an established commercial TPS using the same algorithm.

PACS number: 87.53.Jw
The effects of motion on the dose distribution of proton radiotherapy for prostate cancer
Authors: Qamhiyeh Sima , Geismar Dirk , Pöttgen Christoph , Stuschke Martin , Farr Jonathan
Published: February 2017

Proton radiotherapy of the prostate basal or whole seminal vesicles using scattering delivery systems is an effective treatment of prostate cancer that has been evaluated in prospective trials. Meanwhile, the use of pencil beam scanning (PBS) can further reduce the dose in the beam entrance channels and reduce the dose to the normal tissues. However, PBS dose distributions can be affected by intra‐ and interfractional motion. In this treatment planning study, the effects of intra‐ and interfractional organ motion on PBS dose distributions are investigated using repeated CT scans at close and distant time intervals. The minimum dose () and the dose to 2% and 98% of the volumes ( and ), as well as EUD in the clinical target volumes (CTV), is used as measure of robustness. In all patients, was larger than 96% and was less than 106% of the prescribed dose. The combined information from , and EUD led to the conclusion that there are no relevant cold spots observed in any of the verification plans. Moreover, it was found that results of single field optimization are more robust than results from multiple field optimizations.

PACS numbers: 87.55.D‐, 87.55.de, 87.53.Bn, 87.55.dk, 87.55.ne
A study of surface dosimetry for breast cancer radiotherapy treatments using Gafchromic EBT2 film
Authors: Nakano Masahiro , Hill Robin F. , Whitaker May , Kim Jung‐Ha , Kuncic Zdenka
Published: February 2017

The present study quantified surface doses on several rectangular phantom setups and on curved surface phantoms for a 6 MV photon field using the Attix parallel‐plate chamber and Gafchromic EBT2 film. For the rectangular phantom setups, the surface doses on a homogenous water equivalent phantom and a water equivalent phantom with 60 mm thick lung equivalent material were measured. The measurement on the homogenous phantom setup showed consistency in surface and near‐surface doses between an open field and enhanced dynamic wedge (EDW) fields, whereas physical wedged fields showed small differences. Surface dose measurements made using the EBT2 film showed good agreement with results of the Attix chamber and results obtained in previous studies which used other dosimeters within the measurement uncertainty of 3.3%. The surface dose measurements on the phantom setup with lung equivalent material showed a small increase without bolus and up to 6.9% increase with bolus simulating the increase of chest wall thickness. Surface doses on the cylindrical CT phantom and customized Perspex chest phantom were measured using the EBT2 film with and without bolus. The results indicate the important role of the presence of bolus if the clinical target volume (CTV) is quite close to the surface. Measurements on the cylindrical phantom suggest that surface doses at the oblique positions of 60° and 90° are mainly caused by the lateral scatter from the material inside the phantom. In the case of a single tangential irradiation onto Perspex chest phantom, the distribution of the surface dose with and without bolus materials showed opposing inclination patterns, whereas the dose distribution for two opposed tangential fields gave symmetric dose distribution. This study also demonstrates the suitability of Gafchromic EBT2 film for surface dose measurements in megavoltage photon beams.

PACS number: 87.53.Bn
Skin dose during radiotherapy: a summary and general estimation technique
Authors: Kry Stephen F. , Smith Susan A. , Weathers Rita , Stovall Marilyn
Published: February 2017

The skin dose associated with radiotherapy may be of interest for clinical evaluation or investigating the risk of late effects. However, skin dose is not intuitive and is difficult to measure. Our objectives were to develop and evaluate a general estimation technique for skin dose based on treatment parameters. The literature on skin dose was supplemented with measurements and Monte Carlo simulations. Using all available data, a general dosimetry system was developed (in the form of a series of equations) to estimate skin dose based on treatment parameters including field size, the presence of a block tray, and obliquity of the treatment field. For out‐of‐field locations, the distance from the field edge was also considered. This dosimetry system was then compared to TLD measurements made on the surface of a phantom. As compared to measurements, the general dosimetry system was able to predict skin dose within, on average, 21% of the local dose (4% of the dose). Skin dose for patients receiving radiotherapy can be estimated with reasonable accuracy using a set of general rules and equations.

PACS numbers: 87.53.‐j, 87.53.Bn, 87.55.ne
Dosimetric properties of a beam quality‐matched 6 MV unflattened photon beam
Authors: Huang Yunfei , Siochi R. Alfredo , Bayouth John E.
Published: February 2017

The purpose of this study was to report the characteristics of an equivalent quality unflattened (eqUF) photon beam in clinical implementation and to provide a generalized method to describe unflattened (UF) photon beam profiles. An unflattened photon beam with a beam quality equivalent to the corresponding flat 6 MV photon beam (WF) was obtained by removing the flattening filter from a Siemens ONCOR Avant‐Garde linear accelerator and adjusting the photon energy. A method independent from the WF beam profile was presented to describe UF beam profiles and other selected beam characteristics were examined. The short‐term beam stability was examined by dynamic beam profiles, recorded every 0.072 s in static and gated delivery, and the long‐term stability was evidenced by the five‐year clinical quality assurance records. The dose rate was raised fivefold using the eqUF beam. The depth of maximum dose () shifted 3 mm deeper, but the percent depth dose beyond was very similar to that of the WF beam. The surface dose and out‐of‐field dose were lower, but the penumbra was slightly wider. The variation in head scatter and phantom scatter with changes in field size was smaller; the variation in the profile shape with change in depth was also smaller. The eqUF beam is stable 0.072 s after the beam is turned on, and the five‐year beam stability was comparable to that of the WF beam. A fivefold dose rate increase was observed in the eqUF beam with similar beam characteristics to other reported UF beam data except for a deeper and a slightly wider penumbra. The initial and long‐term stability of the eqUF beam profile is on parity with the WF beam. The UF beam profile can be described in the generalized method independently without relying on the WF beam profile.

PACS number: 87.55.de
Ion recombination corrections of ionization chambers in flattening filter‐free photon radiation
Authors: Wang Yuenan , Easterling Stephen B. , Ting Joseph Y.
Published: February 2017

The flattening filter free (FFF) X‐rays can provide much higher dose rate at the treatment target compared to the conventional flattened X‐rays. However, the substantial increase of dose rate for FFF beams may affect the ion recombination correction factor, which is required for accurate measurements using ionization chambers in clinical dosimetry. The purpose of this work is to investigate the ion recombination of three types of commonly used ion chambers (Farmer, PinPoint and plane‐parallel) in the FFF photon radiation. Both 6 MV and 10 MV flattened and FFF beams were fully commissioned on a Varian TrueBeam linear accelerator. The ion recombination correction factor, , was determined using the two‐voltage technique for a 0.6 cc Farmer chamber, a 0.015 cc PinPoint chamber, and a 0.02 cc parallel‐plate chamber at different source‐to‐axis distances (SAD) in a solid water phantom or water tank phantom at a depth of 10 cm in a field. Good repeatability of measurements was demonstrated. Less than 1% difference in Pion between the flattened and FFF photons for all three ion chambers was observed. At a SAD of 100 cm and a depth of 10 cm for a field, for the Farmer chamber was 1.004 and 1.008 for the 6 MV flattened and FFF beams, respectively. At the same setup using the Farmer chamber, was 1.002 and 1.015 for the 10 MV flattened and FFF beams, respectively. All results for the Farmer, PinPoint, or parallel plate chamber in the 6 MV and 10 MV flattened and FFF beams were within 2% from the unity (1 ≤ < 1.02). The ratio of the FFF to flattened beams was for both 6 MV and 10 MV photons. The ion recombination effect of the Farmer, PinPoint, and plane‐parallel chamber in the FFF beams is not substantially different from that in the conventional flattened beams.

PACS number: 87.56.bd
Surface dose reduction from bone interface in kilovoltage X‐ray radiation therapy: a Monte Carlo study of photon spectra
Authors: Chow James C. L. , Owrangi Amir M.
Published: February 2017

This study evaluated the dosimetric impact of surface dose reduction due to the loss of backscatter from the bone interface in kilovoltage (kV) X‐ray radiation therapy. Monte Carlo simulation was carried out using the EGSnrc code. An inhomogeneous phantom containing a thin water layer (0.5–5 mm) on top of a bone was irradiated by a clinical 105 kVp photon beam produced by a Gulmay D3225 X‐ray machine. Field sizes of 2, 5, and 10 cm diameter and source‐to‐surface distance of 20 cm were used. Surface doses for different phantom configurations were calculated using the DOSXYZnrc code. Photon energy spectra at the phantom surface and bone were determined according to the phase‐space files at the particle scoring planes which included the multiple crossers. For comparison, all Monte Carlo simulations were repeated in a phantom with the bone replaced by water. Surface dose reduction was found when a bone was underneath the water layer. When the water thickness was equal to 1 mm for the circular field of 5 cm diameter, a surface dose reduction of 6.3% was found. The dose reduction decreased to 4.7% and 3.4% when the water thickness increased to 3 and 5 mm, respectively. This shows that the impact of the surface dose uncertainty decreased while the water thickness over the bone increased. This result was supported by the decrease in relative intensity of the lower energy photons in the energy spectrum when the water layer was with and over the bone, compared to without the bone. We concluded that surface dose reduction of 7.8%–1.1% was found when the water thickness increased from 0.5–5 mm for circular fields with diameters ranging from 2–10 cm. This decrease of surface dose results in an overestimation of prescribed dose at the patient's surface, and might be a concern when using kV photon beam to treat skin tumors in sites such as forehead, chest wall, and kneecap.

PACS number: 87.55.K‐; 87.55.ne; 87.57.uq
Errors introduced by dose scaling for relative dosimetry
Authors: Watanabe Yoichi , Hayashi Naoki
Published: February 2017

Some dosimeters require a relationship between detector signal and delivered dose. The relationship (characteristic curve or calibration equation) usually depends on the environment under which the dosimeters are manufactured or stored. To compensate for the difference in radiation response among different batches of dosimeters, the measured dose can be scaled by normalizing the measured dose to a specific dose. Such a procedure, often called “relative dosimetry”, allows us to skip the time‐consuming production of a calibration curve for each irradiation. In this study, the magnitudes of errors due to the dose scaling procedure were evaluated by using the characteristic curves of BANG3 polymer gel dosimeter, radiographic EDR2 films, and GAFCHROMIC EBT2 films. Several sets of calibration data were obtained for each type of dosimeters, and a calibration equation of one set of data was used to estimate doses of the other dosimeters from different batches. The scaled doses were then compared with expected doses, which were obtained by using the true calibration equation specific to each batch. In general, the magnitude of errors increased with increasing deviation of the dose scaling factor from unity. Also, the errors strongly depended on the difference in the shape of the true and reference calibration curves. For example, for the BANG3 polymer gel, of which the characteristic curve can be approximated with a linear equation, the error for a batch requiring a dose scaling factor of 0.87 was larger than the errors for other batches requiring smaller magnitudes of dose scaling, or scaling factors of 0.93 or 1.02. The characteristic curves of EDR2 and EBT2 films required nonlinear equations. With those dosimeters, errors larger than 5% were commonly observed in the dose ranges of below 50% and above 150% of the normalization dose. In conclusion, the dose scaling for relative dosimetry introduces large errors in the measured doses when a large dose scaling is applied, and this procedure should be applied with special care.

PACS numbers: 87.56.Da, 06.20.Dk, 06.20.fb
Implementation and evaluation of an end‐to‐end IGRT test
Authors: Kry Stephen F. , Jones Jimmy , Childress Nathan L.
Published: February 2017

The goal of this work was to develop and evaluate an end‐to‐end test for determining and verifying image‐guided radiation therapy setup accuracy relative to the radiation isocenter. This was done by placing a cube phantom with a central tungsten sphere directly on the treatment table and offset from isocenter either by 5.0 mm in the longitudinal, lateral, and vertical dimensions or by a random amount. A high‐resolution cone‐beam CT image was acquired and aligned with the tungsten sphere in the reference CT image. The table was shifted per this alignment, and megavoltage anterior–posterior and lateral images were acquired with the electronic portal imaging device. Agreement between the radiation isocenter (based on the MV field) and the center of the sphere (i.e., the alignment point based on kV imaging) was determined for each image via Winston‐Lutz analysis. This procedure was repeated 10 times to determine short‐term reproducibility, and then repeated daily for 51 days in a clinical setting. The short‐term reproducibility test yielded a mean 3D vector displacement of between the imaging‐based isocenter and the radiation isocenter, with a maximum displacement of 1.1 mm. The clinical reproducibility test yielded a mean displacement of with a maximum of 2.0 mm when the cube was offset by 5.0 mm, and a mean displacement of with a maximum of 1.8 mm when the cube was offset by a random amount. These differences were observed in all directions and were independent of the magnitude of the couch shift. This test was quick and easy to implement clinically and highlighted setup inaccuracies in an image‐guided radiation therapy environment.

PACS numbers: 87.55.km; 87.55.Qr; 87.56.Fc
Monte Carlo modeling of a Novalis TX Varian 6 MV with HD‐120 multileaf collimator
Authors: Vazquez‐Quino Luis Alberto , Massingill Brian , Shi Chengyu , Gutierrez Alonso , Esquivel Carlos , Eng Tony , Papanikolaou Nikos , Stathakis Sotirios
Published: February 2017

A Monte Carlo model of the Novalis Tx linear accelerator equipped with high‐definition multileaf collimator (HD‐120 HD‐MLC) was commissioned using ionization chamber measurements in water. All measurements in water were performed using a liquid filled ionization chamber. Film measurements were made using EDR2 film in solid water. Open rectangular fields defined by the jaws or the HD‐MLC were used for comparison against measurements. Furthermore, inter‐ and intraleaf leakage calculated by the Monte Carlo model was compared against film measurements. The statistical uncertainty of the Monte Carlo calculations was less than 1% for all simulations. Results for all regular field sizes show an excellent agreement with commissioning data (percent depth‐dose curves and profiles), well within 1% of difference in the relative dose and 1 mm distance to agreement. The computed leakage through HD‐MLCs shows good agreement with film measurements. The Monte Carlo model developed in this study accurately represents the new Novalis Tx Varian linac with HD‐MLC and can be used for reliable patient dose calculations.

PACS number: 87.10.Rt
Comparing post‐operative human breast specimen radiograph and MRI in lesion margin and volume assessment
Authors: Abe Hiroyuki , Shimauchi Akiko , Fan Xiaobing , River Jonathan N. , Sattar Husain , Mueller Jeffrey , Karczmar Gregory S. , Newstead Gillian M.
Published: February 2017

The purpose of this research is to evaluate the potential for identifying malignant breast lesions and their margins on large specimen MRI, in comparison to specimen radiography and clinical dynamic contrast enhanced MRI (DCE‐MRI). Breast specimens were imaged with an MR scanner immediately after surgery, with an IRB‐approved protocol and with the patients' informed consent. Specimen sizes were at least 5 cm in diameter and approximately 1 to 4 cm thick. Coronal and axial gradient echo MR images without fat suppression were acquired over the whole specimens using a 9.4T animal scanner. Findings on specimen MRI were compared with findings on specimen radiograph, and their volumes were compared with measurements obtained from clinical DCE‐MRI. The results showed that invasive ductal carcinoma (IDC) lesions were easily identified using MRI and the margins were clearly distinguishable from nearby tissue. However, ductal carcinoma in situ (DCIS) lesions were not clearly discernible and were diffused with poorly defined margins on MRI. Calcifications associated with DCIS were visualized in all specimens on specimen radiograph. There is a strong correlation between the maximum diameter of lesions as measured by radiograph and MRI (), as well as the maximum diameter measured by pathology and radiograph/MRI (). The volumes of IDC measured on specimen MRI were slightly smaller than those measured on DCE‐MRI. Imaging of excised human breast lumpectomy specimens with high magnetic field MRI provides promising results for improvements in lesion identification and margin localization for IDC. However, there are technical challenges in visualization of DCIS lesions. Improvements in specimen imaging are important, as they will provide additional information to standard radiographic analysis.

PACS numbers: 87.61.Tg; 87.59.B
Evaluation of mechanical accuracy for couch‐based tracking system (CBTS)
Authors: Lee Suk , Chang Kyung‐Hwan , Shim Jand Bo , Cao Yuanjie , Lee Chang Ki , Cho Sam Ju , Yang Dae Sik , Park Young Je , Yoon Won Seob , Kim Chul Yong
Published: February 2017

This study evaluated the mechanical accuracy of an in‐house–developed couch‐based tracking system (CBTS) according to respiration data. The overall delay time of the CBTS was calculated, and the accuracy, reproducibility, and loading effect of the CBTS were evaluated according to the sinusoidal waveform and various respiratory motion data of real patients with and without a volunteer weighing 75 kg. The root mean square (rms) error of the accuracy, the reproducibility, and the sagging measurements were calculated for the three axes (X, Y, and Z directions) of the CBTS. The overall delay time of the CBTS was 0.251 sec. The accuracy and reproducibility in the Z direction in real patient data were poor, as indicated by high rms errors. The results of the loading effect were within 1.0 mm in all directions. This novel CBTS has the potential for clinical application for tumor tracking in radiation therapy.

PACS number: 87.55.ne
MAGAT gel and EBT2 film‐based dosimetry for evaluating source plugging‐based treatment plan in Gamma Knife stereotactic radiosurgery
Authors: Gopishankar N. , Vivekanandhan S. , Kale S.S. , Rath G.K. , Senthilkumaran S. , Thulkar S. , Subramani V. , Laviraj M.A. , Bisht R.K. , Mahapatra A.K.
Published: February 2017

This work illustrates a procedure to assess the overall accuracy associated with Gamma Knife treatment planning using plugging. The main role of source plugging or blocking is to create dose falloff in the junction between a target and a critical structure. We report the use of MAGAT gel dosimeter for verification of an experimental treatment plan based on plugging. The polymer gel contained in a head‐sized glass container simulated all major aspects of the treatment process of Gamma Knife radiosurgery. The 3D dose distribution recorded in the gel dosimeter was read using a 1.5T MRI scanner. Scanning protocol was: CPMG pulse sequence with 8 equidistant echoes, , echo , pixel mm x 0.5 mm, and slice thickness of 2 mm. Using a calibration relationship between absorbed dose and spin‐spin relaxation rate (R2), we converted R2 images to dose images. Volumetric dose comparison between treatment planning system (TPS) and gel measurement was accomplished using an in‐house MATLAB‐based program. The isodose overlay of the measured and computed dose distribution on axial planes was in close agreement. Gamma index analysis of 3D data showed more than 94% voxel pass rate for different tolerance criteria of , and . Film dosimetry with GAFCHROMIC EBT 2 film was also performed to compare the results with the calculated TPS dose. Gamma index analysis of film measurement for the same tolerance criteria used for gel measurement evaluation showed more than 95% voxel pass rate. Verification of gamma plan calculated dose on account of shield is not part of acceptance testing of Leksell Gamma Knife (LGK). Through this study we accomplished a volumetric comparison of dose distributions measured with a polymer gel dosimeter and Leksell GammaPlan (LGP) calculations for plans using plugging. We propose gel dosimeter as a quality assurance (QA) tool for verification of plug‐based planning.

PACS number: 87.53.Ly, 87.55.‐x, 87.56.N‐
Measurements of the dose delivered during CT exams using AAPM Task Group Report No. 111
Authors: Descamps C. , Gonzalez M. , Garrigo E. , Germanier A. , Venencia D.
Published: February 2017

The computed tomography dose index (CTDI) measured with a 10 cm long pencil ionization chamber placed in a 14 cm long PMMA phantom is typically used to evaluate the doses delivered during CT procedure. For the new generation of CT scanners, the efficiency of this methodology is low because it excludes the contribution of radiation scattered beyond the 100 mm range of integration along z. The AAPM TG111 Report proposes a new measurement modality using a small volume ionization chamber positioned in a phantom long enough to establish dose equilibrium at the location of the chamber. In this work, the AAPM report was implemented. The minimum scanning length needed to obtain cumulative dose equilibrium was evaluated. The equilibrium dose was determined and compared to CTDI values informed by the CT scanner, and the dose values were confirmed with TLD measurements. The difference between doses measured with TLD and with the ionization chamber (IC) was below 1% and the repeatability of the measurements' setup was 0.4%. The measurements showed that the scanning lengths needed to reach the cumulated dose equilibrium were 450 mm and 380 mm for the central and peripheral axes, respectively, which justifies the phantom length. For the studied clinical protocols, the doses measured were about 30% higher than those informed by the CT scanner. For the new generation of CT systems with wider longitudinal detector size or cone‐beam technology, the current CTDI measurements may no longer be adequate, and the informed CTDI tends to undervalue the dose delivered. It is therefore important to evaluate CT radiation doses following the AAPM TG111 methodology.

PACS number: 87.57.qp, 87.53.Bn
Impact of proton beam availability on patient treatment schedule in radiation oncology
Authors: Miller Eric D. , Derenchuk Vladimir , Das Indra J. , Johnstone Peter A. S.
Published: February 2017

Proton beam therapy offers unique physical properties with potential for reduced toxicity and better patient care. There is an increased interest in radiation oncology centers to acquire proton therapy capabilities. The operation of a proton treatment center is quite different than a photon‐based clinic because of the more complex technology involved, as well as the single proton beam source serving multiple treatment rooms with no backup source available. There is limited published data which investigates metrics that can be used to determine the performance of a proton facility. The purpose of this study is to evaluate performance metrics of Indiana University Cyclotron Operations (IUCO), including availability, mean time between failures, and mean time to repair, and to determine how changes in these metrics impact patient treatments. We utilized a computerized maintenance management system to log all downtime occurrences and servicing operations for the facility. These data were then used to calculate the availability as well as the mean time between failures and mean time to repair. Impact on patient treatments was determined by analyzing delayed and missed treatments, which were recorded in an electronic medical record and database maintained by the therapists. The availability of the IUCO proton beam has been increasing since beginning of operation in 2003 and averaged 96.9% for 2009 through 2011. The mean time between failures and mean time to repair were also determined and correlated with improvements in the maintenance and operating procedures of the facility, as well as environmental factors. It was found that events less than 15 minutes in duration have minimal impact on treatment delays, while events lasting longer than one hour may result in missed treatments. The availability of the proton beam was more closely correlated with delayed than with missed treatments, demonstrating the utility and limitations of the availability metric. In conclusion, we suggest that the availability metric and other performance parameters, such as the mean time between failures and the mean time to repair, should be used in combination with downtime impact on patient treatments in order to adequately evaluate the operational success of a proton therapy facility.

PACS number: 87.55.‐x
Accuracy and sensitivity of four‐dimensional dose calculation to systematic motion variability in stereotatic body radiotherapy (SBRT) for lung cancer
Authors: Chan Mark K.H. , Kwong Dora L.W. , Ng Sherry C.Y. , Tong Anthony S.M. , Tam Eric K.W.
Published: February 2017

The dynamic movement of radiation beam in real‐time tumor tracking may cause overdosing to critical organs surrounding the target. The primary objective of this study was to verify the accuracy of the 4D planning module incorporated in CyberKnife treatment planning system. The secondary objective was to evaluate the error that may occur in the case of a systematic change of motion pattern. Measurements were made using a rigid thorax phantom. Target motion was simulated with two waveforms (sin and ) of different amplitude and frequency. Inversely optimized dose distributions were calculated in the CyberKnife treatment planning system using the 4D Monte Carlo dose calculation algorithm. Each plan was delivered to the phantom assuming (1) reproducible target motion, and (2) systematic change of target motion pattern. The accuracy of 4D dose calculation algorithm was assessed using GAFCHROMIC EBT2 films based on γ criteria. Treatment plans were considered acceptable if the percentage of pixels passing the γ criteria was greater than 90%. The mean percentages of pixels passing were 95% for the target and 91% for the static off‐target structure, respectively, with reproducible target motion. When systematic changes of the motion pattern were introduced during treatment delivery, the mean percentages of pixels passing decreased significantly in the off‐target films (48%; ), but did not change significantly in the target films (92%; ) compared to results of reproducible target motion. These results suggest that the accuracy of 4D dose calculation, particularly in off‐target stationary structure, is strongly tied to the reproducibility of target motion and that the solutions of 4D planning do not reflect the clinical nature of nonreproducible target motion generally.

PACS numbers: 87.53.Ly, 87.55.km