bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and clinical implementation of a TG‐106 compliant linear accelerator data management system and MU calculator
Authors: Adnani Nabil
Published: February 2017

In an attempt to minimize errors and improve patient outcome in radiation therapy, a linear accelerator data management system was developed to provide radiation oncology physicists with a set of computerized tools to manage linear accelerator physics data. The entire program is written in Microsoft Visual Basic and has a user‐friendly, front‐end window with the following features and modules: (1) Generate, edit and approve commissioning and QA reports and other regulatory documents, (2) Configure commissioning tasks, (3) Acquire output factors, (4) Import scanned data, (5) Import PDD, TMRs and OAR tables directly from the scanning software, (6) Query physics data such as TMR, PDDs, OFs, and WFs, (7) Compare physics data to a different machine or a standard, (8) Compare physics data from the same machine (e.g. during annual calibrations), (9) Perform MU calculations on plans exported from the planning system via DICOM RT, (10) Perform TG‐51 calibration, (11) Perform monthly calibration, (12) FTP physics data for purposes of remote peer review and/or inspections.

PACS numbers: 87.53.Dq, 87.55.Qr, 87.56.Fc
Validation of the Eclipse AAA algorithm at extended SSD
Authors: Hussain Amjad , Villarreal‐Barajas Eduardo , Brown Derek , Dunscombe Peter
Published: February 2017

The accuracy of dose calculations at extended SSD is of significant importance in the dosimetric planning of total body irradiation (TBI). In a first step toward the implementation of electronic, multi‐leaf collimator compensation for dose inhomogeneities and surface contour in TBI, we have evaluated the ability of the Eclipse AAA to accurately predict dose distributions in water at extended SSD. For this purpose, we use the Eclipse AAA algorithm, commissioned with machine‐specific beam data for a 6 MV photon beam, at standard SSD (100 cm). The model was then used for dose distribution calculations at extended SSD (179.5 cm). Two sets of measurements were acquired for a 6 MV beam (from a Varian linear accelerator) in a water tank at extended SSD: i) open beam for , , and field sizes (defined at 179.5 cm SSD), and ii) identical field sizes but with a 1.3 cm thick acrylic spoiler placed 10 cm above the water surface. Dose profiles were acquired at 5 cm, 10 cm and 20 cm depths. Dose distributions for the two setups were calculated using the AAA algorithm in Eclipse. Confidence limits for comparisons between measured and calculated absolute depth dose curves and normalized dose profiles were determined as suggested by Venselaar et al. The confidence limits were within 2% and 2 mm for both setups. Extended SSD calculations were also performed using Eclipse AAA, commissioned with Varian Golden beam data at standard SSD. No significant difference between the custom commissioned and Golden Eclipse AAA was observed. In conclusion, Eclipse AAA commissioned at standard SSD can be used to accurately predict dose distributions in water at extended SSD for 6 MV open beams.

PACS numbers: 87.53.Kn, 87.55.D‐, 87.55.de, 87.56.ng
Dwell position inaccuracy in the Varian GammaMed HDR ring applicator
Authors: Stern Robin L. , Liu Tianxiao
Published: February 2017

Varian has issued two Product Notification Letters warning of known inaccuracies in dwell positions for their GammaMed HDR ring applicator. This inaccuracy was measured for two sets of applicators. Autoexposed radiographs were taken of the HDR source at different dwell positions and analyzed per Varian recommendations using tools within the BrachyVision treatment planning program. Comparison between programmed and actual dwell positions showed the actual positions shifted distally by an average of 0.34 cm (0.17 cm–0.59 cm) across all positions in all rings. A correction method was developed and tested. During planning, the tip of the ring was extrapolated distally beyond its actual position in the patient image set and a proximal offset of the same distance was applied to the dwell positions. A global shift of 0.3 mm corrected all but the most proximal actual dwell position to within mm of the planned position.

PACS number: 87.53Jw, 87.56Da
Assessing a set of optimal user interface parameters for intensity‐modulated proton therapy planning
Authors: Hillbrand Martin , Georg Dietmar
Published: February 2017

The purpose was to identify an optimal set of treatment planning parameters and a minimal necessary dose matrix resolution for treatment planning with spot‐scanned protons. Treatment plans based on different combinations of planning parameters and dose grid resolutions (DG) were calculated in a homogeneous geometric phantom for three cubic targets of different size: 8, 64 and . The proton dose was delivered by one single beam. Treatment plans were compared in terms of dose profiles parallel to and perpendicular to the central beam axis, as well as by dose homogeneity and conformity measures. Irrespective of target size, the dose homogeneity and conformity were comparable if the distance between spot layers was in the order of the width of a single Bragg peak, and the lateral distance between spots did not exceed two times the spot sigma. If the distance between spot layers was considerably larger than the width of the Bragg peak, the homogeneity index increased. For the small target, this index escalated from values around 5% to 12% in extreme, and to more than 20% for the two larger targets. Furthermore, the width of the 95% isodose increased. Similar results were found for the variation of the parameter determining the lateral spacing between proton dose spots. The average difference of dose profiles with respect to the profile for a DG of 1 mm was below 3% for all considered settings up to a DG of 6 mm. However, a DG of less than 2–3 mm is required to keep the maximum deviation below this limit. The tests performed in this study are necessary to prevent systematic errors from spot‐scanning proton therapy planning. A separation of dose spots in the dimensions of the Bragg peak in the longitudinal direction and no more than two times the spot sigma in the lateral direction were found to be adequate for IMPT treatment planning in a homogeneous phantom. A DG of 2–3 mm is necessary to accurately resolve the steep dose gradients of proton beams.

PACS number: 87.55.D‐; 7.55.de
Characterization of Nyquist ghost in EPI‐fMRI acquisition sequences implemented on two clinical 1.5 T MR scanner systems: effect of readout bandwidth and echo spacing
Authors: Giannelli Marco , Diciotti Stefano , Tessa Carlo , Mascalchi Mario
Published: February 2017

In EPI‐fMRI acquisitions, various readout bandwidth (BW) values are used as a function of gradients' characteristics of the MR scanner system. Echo spacing (ES) is another fundamental parameter of EPI‐fMRI sequences, but the employed ES value is not usually reported in fMRI studies. Nyquist ghost is a typical EPI artifact that can degrade the overall quality of fMRI time series. In this work, the authors assessed the basic effect of BW and ES for two clinical 1.5 T MR scanner systems (scanner‐A, scanner‐B) on Nyquist ghost of gradient‐echo EPI‐fMRI sequences. BW range was: scanner‐A, 1953‐3906 Hz/pixel; scanner‐B, 1220‐2894 Hz/pixel. ES range was: scanner‐A, scanner‐B: 0.75‐1.33 ms. The ghost‐to‐signal ratio of time series acquisition and drift of ghost‐to‐signal ratio were measured in a water phantom. For both scanner‐A (93% of variation) and scanner‐B (102% of variation) the mean significantly increased with increasing BW. values of scanner‐A did not significantly depended on ES. On the other hand, values of scanner‐B significantly varied with ES, showing a downward trend (81% of variation) with increasing ES. In addition, a spike point at indicating a potential resonant effect was revealed. For both scanners, no significant effect of ES on was revealed. values of scanner‐B did not significantly vary with BW, whereas values of scanner‐A significantly depended on BW showing an upward trend from negative to positive values with increasing BW. and can significantly vary with BW and ES, and the specific pattern of variation may depend on gradients performances, EPI sequence calibrations and functional design of radiofrequency coil. Thus, each MR scanner system should be separately characterized. In general, the employment of low BW values seems to reduce the intensity and temporal variation of Nyquist ghost in EPI‐fMRI time series. On the other hand, the use of minimum ES value might not be entirely advantageous when the MR scanner is characterized by gradients with low performances and suboptimal EPI sequence calibration.

PACS numbers: 87.61.‐c, 87.61.Qr, 87.61.Hk
Commissioning and quality assurance for a respiratory training system based on audiovisual biofeedback
Authors: Cui Guoqiang , Gopalan Siddharth , Yamamoto Tokihiro , Berger Jonathan , Maxim Peter G. , Keall Paul J.
Published: February 2017

A respiratory training system based on audiovisual biofeedback has been implemented at our institution. It is intended to improve patients' respiratory regularity during four‐dimensional (4D) computed tomography (CT) image acquisition. The purpose is to help eliminate the artifacts in 4D‐CT images caused by irregular breathing, as well as improve delivery efficiency during treatment, where respiratory irregularity is a concern. This article describes the commissioning and quality assurance (QA) procedures developed for this peripheral respiratory training system, the Stanford Respiratory Training (START) system. Using the Varian real‐time position management system for the respiratory signal input, the START software was commissioned and able to acquire sample respiratory traces, create a patient‐specific guiding waveform, and generate audiovisual signals for improving respiratory regularity. Routine QA tests that include hardware maintenance, visual guiding‐waveform creation, auditory sounds synchronization, and feedback assessment, have been developed for the START system. The QA procedures developed here for the START system could be easily adapted to other respiratory training systems based on audiovisual biofeedback.

PACS number: 87.56.Fc
Breast in vivo dosimetry by EPID
Authors: Fidanzio Andrea , Greco Francesca , Mameli Alessandra , Azario Luigi , Balducci Mario , Gambacorta Maria Antonietta , Frascino Vincenzo , Cilla Savino , Sabatino Domenico , Piermattei Angelo
Published: February 2017

An electronic portal imaging device (EPID) is an effective detector for in vivo transit dosimetry. In fact, it supplies two‐dimensional information, does not require special efforts to be used during patient treatment, and can supply data in real time. In the present paper, a new procedure has been proposed to improve the EPID in vivo dosimetry accuracy by taking into account the patient setup variations. The procedure was applied to the breast tangential irradiation for the reconstruction of the dose at the breast midpoint, . In particular, the patient setup variations were accounted for by comparing EPID images versus digitally reconstructed radiographies. In this manner, EPID transit signals were obtained corresponding to the geometrical projections of the breast midpoint on the EPID for each therapy session. At the end, the ratios R between and the doses computed by the treatment planning system (TPS) at breast midpoints, , were determined for 800 therapy sessions of 20 patients. Taking into account the method uncertainty, tolerance levels equal to have been determined for the ratio R.

The improvement of in vivo dosimetry results obtained (taking into account patient misalignment) has been pointed out comparing the R values obtained with and without considering patient setup variations. In particular, when patient misalignments were taken into account, the R values were within for 93% of the checks; when patient setup variations were not taken into account, the R values were within in 72% of the checks. This last result points out that the transit dosimetry method overestimates the dose discrepancies if patient setup variations are not taken into account for dose reconstruction. In this case, larger tolerance levels have to be adopted as a trade‐off between workload and ability to detect errors, with the drawback being that some errors (such as the ones in TPS implementation or in beam calibration) cannot be detected, limiting the in vivo dosimetry efficacy.

The paper also reports preliminary results about the possibility of reconstructing a dose profile perpendicular to the beam central axis reaching from the apex to the lung and passing through the middle point of the breast by an algorithm, similar to the one used for dose reconstruction at breast midpoint. In particular, the results have shown an accuracy within for the dose profile reconstructed in the breast (excluding the interface regions) and an underestimation of the lung dose.

PACS numbers: 87.55.Qr, 87.55.km, 87.53.Bn
Providing solid angle formalism for skyshine calculations
Authors: Gossman Michael S. , Pahikkala A. Jussi , Rising Mary B. , McGinley Patton H.
Published: February 2017

We detail, derive and correct the technical use of the solid angle variable identified in formal guidance that relates skyshine calculations to dose‐equivalent rate. We further recommend it for use with all National Council on Radiation Protection and Measurements (NCRP), Institute of Physics and Engineering in Medicine (IPEM) and similar reports documented. In general, for beams of identical width which have different resulting areas, within maximum deviation the analytical pyramidal solution is 1.27 times greater than a misapplied analytical conical solution through all field sizes up to . Therefore, we recommend determining the exact results with the analytical pyramidal solution for square beams and the analytical conical solution for circular beams.

PACS number(s): 87.52.‐g, 87.52.Df, 87.52.Tr, 87.53.‐j, 87.53.Bn, 87.53.Dq, 87.66.‐a, 89., 89.60.+x
Comparison of tumor and normal tissue dose for accelerated partial breast irradiation using an electronic brachytherapy eBx source and an Iridium‐192 source
Authors: Ahmad Salahuddin , Johnson Daniel , Hiatt Jessica R. , Still D. Timothy , Furhang Eli E. , Marsden David , Kearly Frank , Bernard Damian A. , Holt Randall W.
Published: February 2017

The objective of this study has been to compare treatment plans for patients treated with electronic brachytherapy (eBx) using the Axxent System as adjuvant therapy for early stage breast cancer with treatment plans prepared from the same CT image sets using an Ir‐192 source. Patients were implanted with an appropriately sized Axxent balloon applicator based on tumor cavity size and shape. A CT image of the implanted balloon was utilized for developing both eBx and Ir‐192 brachytherapy treatment plans. The prescription dose was 3.4 Gy per fraction for 10 fractions to be delivered to 1 cm beyond the balloon surface. Iridium plans were provided by the sites on 35 of the 44 patients enrolled in the study. The planning target volume coverage was very similar when comparing sources for each patient as well as between patients. There were no statistical differences in mean %V100. The percent of the planning target volume in the high dose region was increased with eBx as compared with Iridium . The mean maximum calculated skin and rib doses did not vary greatly between eBx and Iridium. By contrast, the doses to the ipsilateral lung and the heart were significantly lower with eBx as compared with Iridium . The total nominal dwell times required for treatment can be predicted by using a combination of the balloon fill volume and planned treatment volume (PTV). This dosimetric comparison of eBx and Iridium sources demonstrates that both forms of balloon‐based brachytherapy provide comparable dose to the planning target volume. Electronic brachytherapy is significantly associated with increased dose at the surface of the balloon and decreased dose outside the PTV, resulting in significantly increased tissue sparing in the heart and ipsilateral lung.

PACS numbers: 87,53.Jw, 87.55.dk, 87.55.D‐,87.56 b‐,87.56.bg
Use of reduced dose rate when treating moving tumors using dynamic IMRT
Authors: Court Laurence , Wagar Matthew , Bogdanov Madeleine , Ionascu Dan , Schofield Deborah , Allan Aaron , Berbeco Ross , Lingos Tania
Published: February 2017

The purpose was to evaluate the effect of dose rate on discrepancies between expected and delivered dose caused by the interplay effect. Fifteen separate dynamic IMRT plans and five hybrid IMRT plans were created for five patients (three IMRT plans and one hybrid IMRT plan per patient). The impact of motion on the delivered dose was evaluated experimentally for each treatment field for different dose rates (200 and ), and for a range of target amplitudes and periods. The maximum dose discrepancy for dynamic IMRT fields was 18.5% and 10.3% for dose rates of 400 and , respectively. The maximum dose discrepancy was larger than this for hybrid plans, but the results were similar when weighted by the contribution of the IMRT fields. The percentage of fields for which 98% of the target never experienced a 5% or 10% dose discrepancy increased when the dose rate was reduced from to . For amplitudes up to 2 cm, reducing the dose rate to is effective in keeping daily dose discrepancies for each field within 10%.

PACS number: 87.55Qr
Correlation functions for Elekta aSi EPIDs used as transit dosimeter for open fields
Authors: Cilla Savino , Fidanzio Andrea , Greco Francesca , Sabatino Domenico , Russo Aniello , Gargiulo Laura , Azario Luigi , Piermattei Angelo
Published: February 2017

In‐vivo dosimetry techniques are currently being applied only by a few Centers because they require time‐consuming implementation measurements, and workload for detector positioning and data analysis. The transit in‐vivo dosimetry performed by the electronic portal imaging device (EPID) avoids the problem of solid‐state detector positioning on the patient. Moreover, the dosimetric characterization of the recent Elekta aSi EPIDs in terms of signal stability and linearity make these detectors useful for the transit in‐vivo dosimetry with 6, 10 and 15 MV photon beams. However, the implementation of the EPID transit dosimetry requires several measurements. Recently, the present authors have developed an in‐vivo dosimetry method for 3D CRT based on correlation functions defined by the ratios between the transit signal, , by the EPID and the phantom midplane dose, , at the source to axis distance (SAD) as a function of the phantom thickness, w, and the square field dimensions, L. When the phantom midplane was positioned at distance, d, from the SAD, the ratios were used to take into account the variation of the scattered photon contributions on the EPID as a function of d and L.

The aim of this paper is the implementation of a procedure that uses generalized correlation functions obtained by nine Elekta Precise linac beams. The procedure can be used by other Elekta Precise linacs equipped with the same aSi EPIDs, assuming the stabilities of the beam output factors and the EPID signals. The procedure here reported avoids measurements in solid water equivalent phantoms needed to implement the in‐vivo dosimetry method in the radiotherapy department. A tolerance level ranging between and (depending on the type of tumor) was estimated for the comparison between the reconstructed isocenter dose, , and the computed dose, , by the treatment planning system (TPS).

PACS number: 87.55.Qr; 87.56.Fc
Evaluation and commissioning of a surface based system for respiratory sensing in 4D CT
Authors: Spadea Maria Francesca , Baroni Guido , Gierga David P. , Turcotte Julie C. , Chen George T.Y. , Sharp Gregory C.
Published: February 2017

The purpose of this study is to assess the temporal and reconstruction accuracy of a surface imaging system, the GateCT under ideal conditions, and compare the device with a commonly used respiratory surrogate: the Varian RPM. A clinical CT scanner, run in cine mode, was used with two optical devices, GateCT and RPM, to detect respiratory motion. A radiation detector, GM‐10, triggers the X‐ray on/off to GateCT system, while the RPM is directly synchronized with the CT scanner through an electronic connection. Two phantoms were imaged: the first phantom translated on a rigid plate along the anterior–posterior (AP) direction, and was used to assess the temporal synchronization of each optical system with the CT scanner. The second phantom, consisting of five spheres translating 3 cm peak‐to‐peak in the superior–inferior direction, was used to assess the quality of rebinned images created by GateCT and RPM. Calibration assessment showed a nearly perfect synchronization with the scanner for both the RPM and GateCT systems, thus demonstrating the good performance of the radiation detector. Results for the volume rebinning test showed discrepancies in volumes for the 3D reconstruction (compared to ground truth) of up to 36% for GateCT and up to 40% for RPM. No statistical difference was proven between the two systems in volume sorting. Errors are mainly due to phase detection inaccuracies and to the large motion of the phantom. This feasibility study assessed the consistency of two optical systems in synchronizing the respiratory signal with the image acquisition. A new patient protocol based on both RPM and GateCT will be soon started.

PACS number: 87
Image‐guided bolus electron conformal therapy – a case study
Authors: Zeidan Omar A. , Chauhan Bhavin D. , Estabrook William W. , Willoughby Twyla R. , Manon Rafael R. , Meeks Sanford L.
Published: February 2017

We report on our initial experience with daily image guidance for the treatment of a patient with a basal cell carcinoma of the nasal dorsum using bolus electron conformal therapy. We describe our approach to daily alignment using treatment machine‐integrated megavoltage (MV) planar imaging in conjunction with cone beam CT (CBCT) volumetric imaging to ensure the best possible setup reproducibility. Based on MV imaging, beam aperture misalignment with the intended treatment region was as large as 0.5 cm in the coronal plane. Four of the five fractions analyzed show induced shifts when compared to digitally reconstructed radiographs (DRR), in the range of . Daily inspection of CBCT images show that the bolus device can have significant tilt in any given direction by as much as 13° with respect to beam axis. In addition, we show that CBCT images reveal air gaps between bolus and skin that vary from day to day, and can potentially degrade surface dose coverage. Retrospective dose calculation on CBCT image sets shows that when daily shifts based on MV imaging are not corrected, geometrical miss of the planning target volume (PTV) can cause an underdosing as large as 14% based on DVH analysis of the dose to the 90% of the PTV volume.

PACS number: 87.55.kh
Dosimetry of oblique tangential photon beams calculated by superposition/convolution algorithms: a Monte Carlo evaluation
Authors: Chow James C. L. , Jiang Runqing , Leung Michael K. K.
Published: February 2017

Although there are many works on evaluating dose calculations of the anisotropic analytical algorithm (AAA) using various homogeneous and heterogeneous phantoms, related work concerning dosimetry due to tangential photon beam is lacking. In this study, dosimetry predicted by the AAA and collapsed cone convolution (CCC) algorithm was evaluated using the tangential photon beam and phantom geometry. The photon beams of 6 and 15 MV with field sizes of(or),and, produced by a Varian 21 EX linear accelerator, were used to test performances of the AAA and CCC using Monte Carlo (MC) simulation (EGSnrc‐based code) as a benchmark. Horizontal dose profiles at different depths, phantom skin profiles (i.e., vertical dose profiles at a distance of 2 mm from the phantom lateral surface), gamma dose distributions, and dose‐volume histograms (DVHs) of skin slab were determined. For dose profiles at different depths, the CCC agreed better with doses in the air‐phantom region, while both the AAA and CCC agreed well with doses in the penumbra region, when compared to the MC. Gamma evaluations between the AAA/CCC and MC showed that deviations of 2D dose distribution occurred in both beam edges in the phantom and air‐phantom interface. Moreover, the gamma dose deviation is less significant in the air‐phantom interface than the penumbra. DVHs of skin slab showed that both the AAA and CCC underestimated the width of the dose drop‐off region for both the 6 and 15MV photon beams. When the gantry angle was 0°, it was found that both the AAA and CCC overestimated doses in the phantom skin profiles compared to the MC, with various photon beam energies and field sizes. The mean dose differences with doses normalized to the prescription point for the AAA and CCC were respectively:andfor afield, 6 MV;andfor afield, 6 MV;andfor a, 15 MV;andfor a, 15 MV. However, underestimations of doses in the phantom skin profile were found with small fields ofandfor the 6 and 15 MV photon beams, respectively, when the gantry was turned 5° anticlockwise. As surface dose with tangential photon beam geometry is important in some radiation treatment sites such as breast, chest wall and sarcoma, it is found that neither of the treatment planning system algorithms can predict the dose well at depths shallower than 2 mm. The dosimetry data and beam and phantom geometry in this study provide a better knowledge of a dose calculation algorithm in tangential‐like irradiation.

PACS numbers: 87.55.‐x, 87.53.Bn, 87.55.K‐, 87.55.kh, 87.56.jf
Book Review
Authors: McLemore Luke
Published: February 2017

The Checklist Manifesto: How to Get Things Right by Atul Gawande, M.D. Metropolitan Books, Henry Hold and Company, LLC, 2009, ISBN 978‐0‐8050‐9174‐8
An analysis of the regulatory program of quality audits in radiotherapy in Brazil from 1995 to 2007
Authors: de Paiva Eduardo , Rosa Luiz A. R. da , Brito Ricardo R. A. , de Sá Lidia V. , Dovales Ana C. M. , Batista Delano V. S. , Giannoni Ricardo A. , Velasco Alexandre F.
Published: February 2017

The Brazilian Institute of Radiation Protection and Dosimetry (IRD/CNEN) carried out quality assurance regulatory audits in Brazilian radiotherapy facilities from 1995 to 2007. In this work, the set of data collected from 195 radiotherapy facilities that use high‐energy photon beams are analyzed. They include results from audits in linear electron accelerators and/or Co‐60 units. The inspectors of IRD/CNEN performed the dosimetry of high‐energy radiotherapy photon beams according to the IAEA dosimetry protocols TRS 277 and TRS 398, and the values of measurements were compared to stated values. Other aspects of radiological protection were checked during on‐site audits such as calibration certification of clinical dosimeters and portable monitors, existence and use of check source, use of barometer and thermometer, individual dose registry and training of staff. It was verified that no check source was available in 38% of the visited facilities; the training of personnel was not adequate in 9% of the facilities and the registry of accumulated individual doses was not being done in 6% of the facilities. Measurements of absorbed dose have indicated deviations in the range for 67.6% of the cobalt‐60 units and 79.6% of medical linear accelerators; 18.5% of Co‐60 irradiators and 9.6% of linear accelerators presented deviations in the range . Finally, 13.9% of Co‐60 facilities and 10.8% of linear accelerator facilities presented dosimetry deviations above 5%. The effort in dosimetric quality control performed by IRD/CNEN audits has yielded positive changes that make radiation treatment facilities more reliable.

PACS number: 87.55.Qr
Applications of IMAT in cervical esophageal cancer radiotherapy: a comparison with fixed‐field IMRT in dosimetry and implementation
Authors: Yin Yong , Chen Jinhu , Xing Ligang , Dong Xiaoling , Liu Tonghai , Lu Jie , Yu Jinming
Published: February 2017

This study aimed to compare fixed‐field, intensity‐modulated radiotherapy (f‐IMRT) with intensity‐modulated arc therapy (IMAT) treatment plans in dosimetry and practical application for cervical esophageal carcinoma. For ten cervical esophageal carcinoma cases, f‐IMRT plan (seven fixed‐fields) and two IMAT plans, namely RA (coplanar 360° arcs) and RAx (coplanar 360° arcs without sectors from 80° to 110°, and 250° to 280°), were generated. DVHs were adopted for the statistics of above parameters, as well as conformal index (CI), homogeneity index (HI), dose‐volumetric parameters of normal tissues, total accelerator output MUs and total treatment time. There were differences between RAx and f‐IMRT, as well as RA in PTV parameters such as HI, and , but not in CI. RAx reduced lung from ( in f‐IMRT and ( in RA to ( in RAx . However, lung and MLD increased in RAx. There was no difference in the mean heart dose in three plans. Total MU was reduced from in f‐IMRT to in RA and in RAx . Compared with f‐IMRT, IMAT reduced low dose volumes of lung and total MU on the basis of meeting clinical requirements.

PACS numbers: 87.55.D, 87.55.dk, 87.55.ne
Influence of reconstruction settings on the performance of adaptive thresholding algorithms for FDG‐PET image segmentation in radiotherapy planning
Authors: Matheoud Roberta , Monica Patrizia Della , Loi Gianfranco , Vigna Luca , Krengli Marco , Inglese Eugenio , Brambilla Marco
Published: February 2017

The purpose of this study was to analyze the behavior of a contouring algorithm for PET images based on adaptive thresholding depending on lesions size and target‐to‐background (TB) ratio under different conditions of image reconstruction parameters. Based on this analysis, the image reconstruction scheme able to maximize the goodness of fit of the thresholding algorithm has been selected. A phantom study employing spherical targets was designed to determine slice‐specific threshold (TS) levels which produce accurate cross‐sectional areas. A wide range of TB ratio was investigated. Multiple regression methods were used to fit the data and to construct algorithms depending both on target cross‐sectional area and TB ratio, using various reconstruction schemes employing a wide range of iteration number and amount of postfiltering Gaussian smoothing. Analysis of covariance was used to test the influence of iteration number and smoothing on threshold determination.

The degree of convergence of ordered‐subset expectation maximization (OSEM) algorithms does not influence TS determination. Among these approaches, the OSEM at two iterations and eight subsets with a 6–8 mm post‐reconstruction Gaussian three‐dimensional filter provided the best fit with a coefficient of determination for cross‐sectional areas 2 and for cross‐sectional areas 2. The amount of post‐reconstruction smoothing has been directly incorporated in the adaptive thresholding algorithms. The feasibility of the method was tested in two patients with lymph node FDG accumulation and in five patients using the bladder to mimic an anatomical structure of large size and uniform uptake, with satisfactory results.

Slice‐specific adaptive thresholding algorithms look promising as a reproducible method for delineating PET target volumes with good accuracy.

PACS numbers: 87.57.nm, 87.55.D‐, 87.57.uk
Commissioning compensator‐based IMRT on the Pinnacle treatment planning system
Authors: Opp Daniel , Forster Kenneth , Feygelman Vladimir
Published: February 2017

We present a systematic approach to commissioning of the compensator‐based IMRT in Pinnacle treatment planning system for commercially manufactured brass compensators. Some model parameters for the beams modulated by the variable‐thickness compensators can only be associated with a single compensator thickness. To intelligently choose that thickness for beam modeling, we empirically determined the most probable filter thickness occurring within the modulated portion of the compensators typically used in clinics. We demonstrated that a set of relative output factors measured with the brass slab of most probable thickness (2 cm) differs from the traditionally used open field set, and leads to improved agreement between measurements and calculations, particularly for the larger field sizes. By iteratively adjusting the modifier scatter factor and filter density, the calculated effective attenuation of the flat filters was brought to within 2% of the ion chamber measurement for the clinically‐relevant range of filter thicknesses, depths and filed sizes. Beam hardening representation in Pinnacle provides for adequate depth dose modeling beyond the depth of about 5 cm. Disagreement at shallower depth for the large field sizes is likely due to the algorithm's inability to account for the low‐energy scattered photons generated in the filter. The average ion chamber point dose error at isocenter for ten clinical compensator‐based IMRT plans was under 1%. A biplanar 3D diode dosimeter was calibrated and validated for use with the compensators. The average gamma analysis (3%/3 mm) passing rate for ten IMRT plans was . The device is particularly attractive because it easily generates dose comparisons at both the fraction and beam levels. Overlaying dose profiles for individual beams would easily uncover any errors in compensator orientation.

PACS number: 87.55Qr
Clinical usefulness of a newly developed body surface navigation and monitoring system in radiotherapy
Authors: Takagi Hitoshi , Obata Yasunori , Kobayashi Hidetoshi , Takenaka Kazuyuki , Hirose Yasujirou , Goto Hajime , Hattori Tomohiko
Published: February 2017

In radiotherapy, setup precision has great influence on the therapeutic effect. In addition, body movements during the irradiation and physical alternations during the treatment period might cause deviation from the planned irradiation dosage distribution. Both of these factors could undesirably influence the dose absorbed by the target. In order to solve these problems, we developed the “body surface navigation and monitoring system” (hereafter referred to as “Navi‐system”). The purpose of this study is to review the precision of the Navi‐system as well as its usefulness in clinical radiotherapy. The Navi‐system consists of a LED projector, a CCD camera, and a personal computer (PC). The LED projector projects 19 stripes on the patient's body and the CCD camera captures these stripes. The processed image of these stripes in color can be displayed on the PC monitor along with the patient's body surface image, and the digitalized results can be also displayed on the same monitor. The Navi‐system calculates the height of the body contour and the transverse height centroid for the 19 levels and compares them with the reference data to display the results on the monitor on a real‐time basis. These results are always replaced with new data after they are used for display; so, if the results need to be recorded, such recording commands should be given to the computer. 1) Evaluating the accuracy of the body surface height measurement: from the relationship between actual height changes and calculated height changes with torso surface by the Navi‐system, for the height changes from 0.0 mm to , the changes show the underestimation of 1.0–1.5 mm and for to , the underestimation of 1.5–3.0 mm. 2) Evaluating the accuracy of the transverse height centroid measurement: displacement of the inclined flat panel to the right by 5.0 mm, 10.0 mm, 15.0 mm and 20.0 mm showed the transverse height centroid calculated by the Navi‐system for line/pair line/pair, line/pair and line/pair, respectively. Also, displacement of the inclined flat panel to the left by 5.0 mm, 10.0 mm, 15.0 mm and 20.0 mm showed the transverse height centroid calculated by the Navi‐system for line/pair line/pair, line/pair and line/pair, respectively. 3) Clinical usefulness of the Navi‐system: on using the Navi‐system, the frequency of radiotherapy replanning increased from 5.2% to 21.8%, especially in pelvic or abdominal irradiation. We developed a new navigation system for the purpose of compensating for the weakness of MVCT, CBCT and other systems, as well as for having a screening function. This Navi‐system can monitor the patient continuously and measure change in height of the patient's body surface from the basic plane, in real time. It can also show the results both qualitatively and quantitatively on the PC monitor.

PACS number:87.52.‐g
Role of adaptive radiation therapy for pediatric patients with diffuse pontine glioma
Authors: Beltran Chris , Sharma Saumya , Merchant Thomas E.
Published: February 2017

We investigate the role of adaptive radiation therapy in pediatric patients with diffuse pontine glioma and the impact of steroid‐related weight gain on treatment parameters utilizing cone‐beam CT. Fifteen patients with diffuse pontine glioma were treated with three‐dimensional conformal radiation therapy and enrolled on a daily localization protocol. The median age was 6 years (range: 2–13 years). Patient charts were examined to obtain the prescribed daily dose of dexamethasone and weight. The original treatment plan was recalculated based on the data obtained from the daily cone‐beam CT. The changes in target and critical structure doses were calculated using gEUD. Correlations between prescribed dexamethasone, weight gain, source‐to‐skin distance (SSD) changes and dosimetric changes were investigated. Eleven of the 15 patients gained weight during radiation therapy, with an average gain of 2.2 kg (8.0%). The mean gEUD decreased was 0.57 Gy (range: 0.24–1.4 Gy) for the PTV, and the mean gEUD increase for critical structures was 1.14%. No strong correlations between prescribed dexamethasone doses, weight gain and dosimetric changes were found. Change in SSD vs. dose to PTV was correlated . Weight gain and changes to the external surface are apparent in these patients; however, the dosimetric changes to the target and critical structures were small and in most cases did not warrant an adaptive plan. The potential exists for a decrease in target dose in these patients; therefore, they should be monitored to assess for replanning when necessary.

PACS number: 87.53Jw
Fast volumetric registration method for tumor follow‐up in pulmonary CT exams
Authors: Silva José Silvestre , Cancela João , Teixeira Luísa
Published: February 2017

An oncological patient may go through several tomographic acquisitions during a period of time, needing an appropriate registration. We propose an automatic volumetric intrapatient registration method for tumor follow‐up in pulmonary CT exams. The performance of our method is evaluated and compared with other registration methods based on optimization techniques. We also compared the metrics behavior to inspect which metric is more sensitive to changes due to the presence of lung tumors.

PACS numbers: 87.57.nj; 87.57.Q‐; 87.57.N‐
Feasibility of using respiratory correlated mega voltage cone beam computed tomography to measure tumor motion
Authors: Chen Mingqing , Siochi R. Alfredo
Published: February 2017

The purpose of this study was to test the feasibility of using respiratory correlated mega voltage cone‐beam computed tomography (MVCBCT), taken during patient localization, to quantify the size and motion of lung tumors. An imaging phantom was constructed of a basswood frame embedded with six different‐sized spherical pieces of paraffin wax. The Quasar respiratory motion phantom was programmed to move the imaging phantom using typical respiratory motion. The moving imaging phantom was scanned using various MVCBCT imaging parameters, including two beam line types, two protocols with different ranges of rotation and different imaging doses. A static phantom was also imaged as a control. For all the 3D volumetric images, the contours of the six spherical inserts were measured manually. Compared with the nominal sphere diameter, the average relative error in the size of the respiratory correlated MVCBCT spheres ranged from 5.3% to 12.6% for the four largest spheres, ranging in size from 3.6 cc to 29 cc. Larger errors were recorded for the two smallest inserts. The average relative error in motion was 5.1% smaller than the programmed amplitude of 3.0 cm. We are able to conclude that it is feasible to use respiratory correlated MVCBCT to quantify tumor motion for lung cancer patients.

PACS numbers: 87.19.Wx, 87.57.Q
Pectoral muscle identification in mammograms
Authors: Camilus K. Santle , Govindan V. K. , Sathidevi P.S.
Published: February 2017

In most of the approaches of computer‐aided detection of breast cancer, one of the preprocessing steps applied to the mammogram is the removal/suppression of pectoral muscle, as its presence within the mammogram may adversely affect the outcome of cancer detection processes. Through this study, we propose an efficient automatic method using the watershed transformation for identifying the pectoral muscle in mediolateral oblique view mammograms. The watershed transformation of the mammogram shows interesting properties that include the appearance of a unique watershed line corresponding to the pectoral muscle edge. In addition to this, it is observed that the pectoral muscle region is oversegmented due to the existence of several catchment basins within the pectoral muscle. Hence, a suitable merging algorithm is proposed to combine the appropriate catchment basins to obtain the correct pectoral muscle region. A total of 84 mammograms from the mammographic image analysis database were used to validate this approach. The mean false positive and mean false negative rates, obtained by comparing the results of the proposed approach with manually‐identified (ground truth) pectoral muscle boundaries, respectively, were 0.85% and 4.88%. A comparison of the results of the proposed method with related state‐of‐the‐art methods shows that the performance of the proposed approach is better than the existing methods in terms of the mean false negative rate. Using Hausdorff distance metric, the comparison of the results of the proposed method with ground truth shows low Hausdorff distances, the mean and standard deviation being .

PACS numbers: 87.57.R, 87.57.nm, 87.59.ej, 87.85.Ng, 87.85.Pq
Feasibility of using two‐dimensional array dosimeter for in vivo dose reconstruction via transit dosimetry
Authors: Chung Heeteak , Li Jonathan , Samant Sanjiv
Published: February 2017

Two‐dimensional array dosimeters are commonly used to perform pretreatment quality assurance procedures, which makes them highly desirable for measuring transit fluences for in vivo dose reconstruction. The purpose of this study was to determine if an in vivo dose reconstruction via transit dosimetry using a 2D array dosimeter was possible. To test the accuracy of measuring transit dose distribution using a 2D array dosimeter, we evaluated it against the measurements made using ionization chamber and radiochromic film (RCF) profiles for various air gap distances (distance from the exit side of the solid water slabs to the detector distance; 0 cm, 30 cm, 40 cm, 50 cm, and 60 cm) and solid water slab thicknesses (10 cm and 20 cm). The backprojection dose reconstruction algorithm was described and evaluated. The agreement between the ionization chamber and RCF profiles for the transit dose distribution measurements ranged from ‐ (average 1.79%). Using the backprojection dose reconstruction algorithm, we found that, of the six conformal fields, four had a 100% gamma index passing rate (3%/3 mm gamma index criteria), and two had gamma index passing rates of 99.4% and 99.6%. Of the five IMRT fields, three had a 100% gamma index passing rate, and two had gamma index passing rates of 99.6% and 98.8%. It was found that a 2D array dosimeter could be used for backprojection dose reconstruction for in vivo dosimetry.

PACS number: 87.55.N‐
Collision indicator charts for gantry‐couch position combinations for Varian linacs
Authors: Becker Stewart J.
Published: February 2017

The use of non‐coplanar radiation fields can potentially lead to collisions between the gantry and the couch or patient. The collisions are often not realized until the plan is finished and the fields are checked on the machine, or even later when the patient is already on the table. This paper presents an easy method of gauging if a collision is likely between the gantry and couch or patient during treatment planning. The method involves creating a chart of allowable gantry and couch combinations. The charts contain curves on a polar graph of the gantry and couch angle “plane”. The curves display the limits of collisions for each gantry and couch combination for vertical couch positions 10, 15 and 20 cm below isocenter and for couch lateral positions of , covering the majority of couch positions encountered in patient treatments. All combinations in the region within the curves (containing the origin) are valid, while all combinations outside the curves will result in a collision. The data for the charts are collected from measurements of the gantry angle that just clears each couch angle. The patient presence was modeled by placing a stereotactic body frame on the top of the couch. Separate charts were created for couch angles between 0° and 90° and between 360° and 270° over all gantry angles. The graphs are easy to create, implement, and use in the clinic and help reduce the time, complications, and uncertainties of planning with non‐coplanar fields.

PACS numbers: 87.55.‐x; 87.56.‐v
3D heterogeneous dose distributions for total body irradiation patients
Authors: Lavallée Marie‐Claude , Aubin Sylviane , Larochelle Marie , Vallières Isabelle , Beaulieu Luc
Published: February 2017

One major objective of total body irradiation (TBI) treatments is to deliver a uniform dose in the entire body of the patient. Looking at 3D dose distributions for constant speed (CstSpeed) and variable speed (VarSpeed) translating couch TBI treatments, dose uniformity and the effect of body heterogeneities were evaluated. This study was based on retrospective dose calculations of 10 patients treated with a translating couch TBI technique. Dose distributions for CstSpeed and VarSpeed TBI treatments have been computed with Pinnacle3 treatment planning system in homogeneous (Homo) and heterogeneous (Hetero) dose calculation modes. A specific beam model was implemented in Pinnacle3 to allow an accurate dose calculation adapted for TBI special aspects. Better dose coverages were obtained with Homo/VarSpeed treatments compared to Homo/CstSpeed cases including smaller overdosage areas. Large differences between CstSpeed and VarSpeed dose calculations were observed in the brain, spleen, arms, legs, and lateral parts of the abdomen (differences between V100% mean values up to 57.5%). Results also showed that dose distributions for patients treated with CstSpeed TBI greatly depend on the patient morphology, especially for pediatric and overweight cases. Looking at heterogeneous dose calculations, underdosages (2%–5%) were found in high‐density regions (e.g., bones), while overdosages (5%–15%) were found in low‐density regions (e.g., lungs). Overall, Homo/CstSpeed and Hetero/VarSpeed dose distributions showed more hot spots than Homo/VarSpeed and were greatly dependent on patient anatomy. CstSpeed TBI treatments allow a simple optimization process but lead to less dose uniformity due to the patient anatomy. VarSpeed TBI treatments require more complex dose optimization, but lead to a better dose uniformity independent of the patient morphology. Finally, this study showed that heterogeneities should be considered in dose calculations in order to obtain a better optimization and, therefore, to improve dose uniformity.

PACS number: 87.55.D