bluuebunny/crossref_metadata_2025 huggingface dataset:
Migration of implanted markers for image‐guided lung tumor stereotactic ablative radiotherapy
Authors: Hong Julian C. , Eclov Neville C.W. , Yu Yao , Rao Aarti K. , Dieterich Sonja , Le Quynh‐Thu , Diehn Maximilian , Sze Daniel Y. , Loo Billy W. , Kothary Nishita , Maxim Peter G.
Published: February 2017

The purpose of this study was to quantify postimplantation migration of percutaneously implanted cylindrical gold seeds (“seeds”) and platinum endovascular embolization coils (“coils”) for tumor tracking in pulmonary stereotactic ablative radiotherapy (SABR). We retrospectively analyzed the migration of markers in 32 consecutive patients with computed tomography scans postimplantation and at simulation. We implanted 147 markers (59 seeds, 88 coils) in or around 34 pulmonary tumors over 32 procedures, with one lesion implanted twice. Marker coordinates were rigidly aligned by minimizing fiducial registration error (FRE), the root mean square of the differences in marker locations for each tumor between scans. To also evaluate whether single markers were responsible for most migration, we aligned with and without the outlier causing the largest FRE increase per tumor. We applied the resultant transformation to all markers. We evaluated migration of individual markers and FRE of each group. Median scan interval was 8 days. Median individual marker migration was 1.28 mm (interquartile range [IQR] ). Median lesion FRE was 1.56 mm (). Outlier identification yielded 1.03 mm median migration () and 1.97 mm median FRE (). Outliers caused a mean and median shift in the centroid of 1.22 and 0.80 mm (95th percentile 2.52 mm). Seeds and coils had no statistically significant difference. Univariate analysis suggested no correlation of migration with the number of markers, contact with the chest wall, or time elapsed. Marker migration between implantation and simulation is limited and unlikely to cause geometric miss during tracking.

PACS number: 87.57.N‐; 87.57.nm; 87.53.Ly
External respiratory motion analysis and statistics for patients and volunteers
Authors: Quirk Sarah , Becker Nathan , Smith WL
Published: February 2017

We analyzed a large patient and volunteer study of external respiratory motion in order to develop a population database of respiratory information. We analyzed 120 lung, liver, and abdominal patients and 25 volunteers without lung disease to determine the extent of motion using the Varian Real‐Time Position Management system. The volunteer respiratory motion was measured for both abdominal and thoracic placement of the RPM box. Evaluation of a subset of 55 patients demonstrates inter‐ and intrafraction variation over treatment. We also calculated baseline drift and duty cycle for patients and volunteers. The mean peak‐to‐peak amplitude (SD) for the patients was 1.0 (0.5) cm, and for the volunteers it was abdomen 0.8 (0.3) cm and thoracic 0.2 (0.2) cm. The mean period (SD) was 3.6 (1.0) s, 4.2 (1.1) s, and 4.1 (0.8) s, and the mean end exhale position (SD) was 60% (6), 58% (7), and 56% (7) for patient, volunteer abdomen, and volunteer thoracic, respectively. Baseline drift was greater than 0.5 cm for 40% of patients. We found statistically significant differences between the patient and volunteer groups. Peak‐to‐peak amplitude was significantly larger for patients than the volunteer abdominal measurement and the volunteer abdominal measurement is significantly larger than the volunteer thoracic measurement. The patient group also exhibited significantly larger baseline drift than the volunteer group. We also found that peak‐to‐peak amplitude was the most variable parameter for both intra‐ and interfraction motion. This database compilation can be used as a resource for expected motion when using external surrogates in radiotherapy applications.

PACS number: 87.19.Wx, 87.55.Km
Compensation method for respiratory motion in proton treatment planning for mobile liver cancer
Authors: Jeong Hojin , Lee Se Byeong , Yoo Seung Hoon , Lim Young Kyung , Kim Tae Hyun , Park Seyjoon , Chai Gyu Young , Kang Ki Mun , Shin Dongho
Published: February 2017

We evaluated the dosimetric effect of a respiration motion, and sought an effective planning strategy to compensate the motion using four‐dimensional computed tomography (4D CT) dataset of seven selected liver patients. For each patient, we constructed four different proton plans based on: (1) average (AVG) CT, (2) maximum‐intensity projection (MIP) CT, (3) AVG CT with density override of tumor volume (OVR), and (4) AVG CT with field‐specific proton margin which was determined by the range difference between AVG and MIP plans (mAVG). The overall effectiveness of each planning strategy was evaluated by calculating the cumulative dose distribution over an entire breathing cycle. We observed clear differences between AV G and MIP CT‐based plans, with significant underdosages at expiratory and inspiratory phases, respectively. Only the mAVG planning strategy was fully successful as the field‐specific proton margin applied in the planning strategy complemented both the limitations of AVG and MIP CT‐based strategies. These results demonstrated that respiration motion induced significant changes in dose distribution of 3D proton plans for mobile liver cancer and the changes can be effectively compensated by applying field‐specific proton margin to each proton field.

PACS numbers: 87.55.D; 87.53.Bn; 87.53.Jw; 87.55.dk
A novel daily QA system for proton therapy
Authors: Ding Xiaoning , Zheng Yuanshui , Zeidan Omar , Mascia Anthony , Hsi Wen , Kang Yixiu , Ramirez Eric , Schreuder Niek , Harris Ben
Published: February 2017

We describe the design and use of a daily quality assurance (QA) system for proton therapy. The QA system is designed to check the overall readiness of proton therapy system consistently within certain reference tolerances by a home‐made QA device (the QA device). The QA device is comprised of a commercially available QA device, rf‐Daily QA 3, a home‐made acrylic phantom, a set of acrylic compensators with various thicknesses, and a mechanical indexing jig. The indexing jig indexes the rf‐Daily QA 3, as well as the acrylic phantom, onto the patient treatment couch. Embedded fiducial markers in the acrylic phantom are used to check X‐ray image quality and positioning alignment accuracy of the imaging system. The rf‐Daily QA 3 is used to check proton beam output, range and symmetry with one single beam delivery. We developed in‐house software to calculate beam range and symmetry, based on various ion chambers' readings inside the rf‐Daily QA 3. With a single setup and one beam irradiation, the QA system is employed to check couch movement, laser alignment, image registration, and reference proton beam characteristics. The simplicity and robustness of this QA system allows for a total QA time of less than 20 minutes per room. The system has been in use at three proton therapy centers since June 2009.

PACS numbers: 87.55.Qr, 87.53.Bn
Comprehensive evaluation and clinical implementation of commercially available Monte Carlo dose calculation algorithm
Authors: Zhang Aizhen , Wen Ning , Nurushev Teamour , Burmeister Jay , Chetty Indrin J.
Published: February 2017

A commercial electron Monte Carlo (eMC) dose calculation algorithm has become available in Eclipse treatment planning system. The purpose of this work was to evaluate the eMC algorithm and investigate the clinical implementation of this system. The beam modeling of the eMC algorithm was performed for beam energies of 6, 9, 12, 16, and 20 MeV for a Varian Trilogy and all available applicator sizes in the Eclipse treatment planning system. The accuracy of the eMC algorithm was evaluated in a homogeneous water phantom, solid water phantoms containing lung and bone materials, and an anthropomorphic phantom. In addition, dose calculation accuracy was compared between pencil beam (PB) and eMC algorithms in the same treatment planning system for heterogeneous phantoms. The overall agreement between eMC calculations and measurements was within 3%/2 mm, while the PB algorithm had large errors (up to 25%) in predicting dose distributions in the presence of inhomogeneities such as bone and lung. The clinical implementation of the eMC algorithm was investigated by performing treatment planning for 15 patients with lesions in the head and neck, breast, chest wall, and sternum. The dose distributions were calculated using PB and eMC algorithms with no smoothing and all three levels of 3D Gaussian smoothing for comparison. Based on a routine electron beam therapy prescription method, the number of eMC calculated monitor units (MUs) was found to increase with increased 3D Gaussian smoothing levels. 3D Gaussian smoothing greatly improved the visual usability of dose distributions and produced better target coverage. Differences of calculated MUs and dose distributions between eMC and PB algorithms could be significant when oblique beam incidence, surface irregularities, and heterogeneous tissues were present in the treatment plans. In our patient cases, monitor unit differences of up to 7% were observed between PB and eMC algorithms. Monitor unit calculations were also preformed based on point‐dose prescription. The eMC algorithm calculation was characterized by deeper penetration in the low‐density regions, such as lung and air cavities. As a result, the mean dose in the low‐density regions was underestimated using PB algorithm. The eMC computation time ranged from 5 min to 66 min on a single 2.66 GHz desktop, which is comparable with PB algorithm calculation time for the same resolution level.

PACS number: 87.55.K‐
Local tumor control probability to evaluate an applicator‐guided volumetric‐modulated arc therapy solution as alternative of 3D brachytherapy for the treatment of the vaginal vault in patients affected by gynecological cancer
Authors: Pedicini Piernicola , Strigari Lidia , Caivano Rocchina , Fiorentino Alba , Califano Giorgia , Nappi Antonio , Improta Giuseppina , Storto Giovanni , Cozzolino Mariella , Chiumento Costanza , Fusco Vincenzo , Vavassori Andrea , Benassi Marcello , Orecchia Roberto , Salvatore Marco
Published: February 2017

The purpose of this study was to evaluate the applicator‐guided volumetric‐modulated arc therapy (AGVMAT) solution as an alternative to high‐dose‐rate brachytherapy (HDR‐BRT) treatment of the vaginal vault in patients with gynecological cancer (GC). AGVMAT plans for 51 women were developed. The volumetric scans used for plans were obtained with an implanted CT‐compatible vaginal cylinder which provides spatial registration and immobilization of the gynecologic organs. Dosimetric and radiobiological comparisons for planning target volume (PTV) and organs at risk (OARs) were performed by means of a dose‐volume histogram (DVH), equivalent uniform dose (EUD), and local tumor control probability (LTCP). In addition, the integral dose and the overall delivery time, were evaluated. The HDR‐BRT averages of EUD and minimum LTCP were significantly higher than those of AGVMAT. Doses for the OARs were comparable for the bladder and sigmoid, while, although HDR‐BRT was able to better spare the bowel, AGVMAT provided a significant reduction of , , and () for the rectum. AGVMAT integral doses were higher than HDR‐BRT with low values in both cases. Delivery times were about two or three times higher for HDR‐BRT with respect to the single arc technique (AGVMAT1) and dual arc technique (AGVMAT2), respectively. The applicator‐guided volumetric‐modulated arc therapy seems to have the potential of improving rectum avoidance. However, brachytherapy improves performance in terms of PTV coverage, as demonstrated by a greater EUD and better LTCP curves.

PACS number: 87
Beam modeling and VMAT performance with the Agility 160‐leaf multileaf collimator
Authors: Bedford James L. , Thomas Michael D. R. , Smyth Gregory
Published: February 2017

The Agility multileaf collimator (Elekta AB, Stockholm, Sweden) has 160 leaves of projected width 0.5 cm at the isocenter, with maximum leaf speed . These characteristics promise to facilitate fast and accurate delivery of radiotherapy, particularly volumetric‐modulated arc therapy (VMAT). The aim of this study is therefore to create a beam model for the treatment planning system (Philips Radiation Oncology Systems, Fitchburg, WI), and to use this beam model to explore the performance of the Agility MLC in delivery of VMAT. A 6 MV beam model was created and verified by measuring doses under irregularly shaped fields. VMAT treatment plans for five typical head‐and‐neck patients were created using the beam model and delivered using both binned and continuously variable dose rate (CVDR). Results were compared with those for an MLCi unit without CVDR. The beam model has similar parameters to those of an MLCi model, with interleaf leakage of only 0.2%. The verification of irregular fields shows a mean agreement between measured and planned dose of 1.3% (planned dose higher). The Agility VMAT head‐and‐neck plans show equivalent plan quality and delivery accuracy to those for an MLCi unit, with 95% of verification measurements within 3% and 3 mm of planned dose. Mean delivery time is 133 s with the Agility head and CVDR, 171 s without CVDR, and 282 s with an MLCi unit. has therefore been shown to model the Agility MLC accurately, and to provide accurate VMAT treatment plans which can be delivered significantly faster with Agility than with an MLCi.

PACS number: 87.55kd, 87.55km, 87.56bd, 87.56jk
Evaluation of inhomogeneity correction factors for 6 MV flattening filter‐free beams with brass compensators
Authors: Robinson Joshua , Opp Daniel , Zhang Geoffrey , Feygelman Vladimir
Published: February 2017

The 6 MV flattening filter‐free (FFF) beam has been commissioned for use with compensators at our institution. This novel combination promises advantages in mitigating tumor motion due to the reduced treatment time made possible by the greatly increased dose rate of the FFF beam. Given the different energy spectrum of the FFF beam and the beam hardening effect of the compensator, the accuracy of the treatment planning system (TPS) model in the presence of low‐density heterogeneities cannot be assumed. Therefore, inhomogeneity correction factors (ICF) for an FFF beam attenuated by brass slabs were measured and compared to the TPS calculations in this work. The ICF is the ratio of the point dose in the presence of inhomogeneity to the dose in the same point in a homogeneous medium. The ICFs were measured with an ion chamber at a number of points in a flat water‐equivalent slab phantom containing a 7.5 cm deep heterogeneity (air or wood). Comparisons for the FFF beam were carried out for the field sizes from to with the brass slabs ranging from 0 to 5 cm in thickness. For a low‐density wood heterogeneity in a slab phantom, with the exception of the point 1 cm beyond the proximal buildup interface, the TPS handles the inhomogeneity correction with the brass‐filtered 6 MV FFF beam at the requisite 2% error level. The combinations of field sizes and compensator thicknesses when the error exceeds 2% (2.6% maximum) are not likely to be experienced in clinical practice. In terms of heterogeneity corrections, the beam model is adequate for clinical use.

PACS number: 87.56.ng
Prostate volumetric‐modulated arc therapy: dosimetry and radiobiological model variation between the single‐arc and double‐arc technique
Authors: Chow James C.L. , Jiang Runqing
Published: February 2017

This study investigates the dosimetry and radiobiological model variation when a second photon arc was added to prostate volumetric‐modulated arc therapy (VMAT) using the single‐arc technique. Dosimetry and radiobiological model comparison between the single‐arc and double‐arc prostate VMAT plans were performed on five patients with prostate volumes ranging from . The prescription dose was 78 Gy/39 fractions and the photon beam energy was 6 MV. Dose‐volume histogram, mean and maximum dose of targets (planning and clinical target volume) and normal tissues (rectum, bladder and femoral heads), dose‐volume criteria in the treatment plan ( of PTV; and of rectum and bladder; of femoral heads), and dose profiles along the vertical and horizontal axis crossing the isocenter were determined using the single‐arc and double‐arc VMAT technique. For comparison, the monitor unit based on the RapidArc delivery method, prostate tumor control probability (TCP), and rectal normal tissue complication probability (NTCP) based on the Lyman‐Burman‐Kutcher algorithm were calculated. It was found that though the double‐arc technique required almost double the treatment time than the single‐arc, the double‐arc plan provided a better rectal and bladder dose‐volume criteria by shifting the delivered dose in the patient from the anterior–posterior direction to the lateral. As the femoral head was less radiosensitive than the rectum and bladder, the double‐arc technique resulted in a prostate VMAT plan with better prostate coverage and rectal dose‐volume criteria compared to the single‐arc. The prostate TCP of the double‐arc plan was found slightly increased (0.16%) compared to the single‐arc. Therefore, when the rectal dose‐volume criteria are very difficult to achieve in a single‐arc prostate VMAT plan, it is worthwhile to consider the double‐arc technique.

PACS number: 87.55.D‐, 87.55.dk, 87.55.K‐, 87.55.Qr
Abdominal and pancreatic motion correlation using 4D CT, 4D transponders, and a gating belt
Authors: Betancourt Ricardo , Zou Wei , Plastaras John P. , Metz James M. , Teo Boon‐Keng , Kassaee Alireza
Published: February 2017

The correlation between the pancreatic and external abdominal motion due to respiration was investigated on two patients. These studies utilized four dimensional computer tomography (4D CT), a four dimensional (4D) electromagnetic transponder system, and a gating belt system. One 4D CT study was performed during simulation to quantify the pancreatic motion using computer tomography images at eight breathing phases. The motion under free breathing and breath‐hold were analyzed for the 4D electromagnetic transponder system and the gating belt system during treatment. A linear curve was fitted for all data sets and correlation factors were evaluated between the 4D electromagnetic transponder system and the gating belt system data. The 4D CT study demonstrated a modest correlation between the external marker and the pancreatic motion with R‐square values larger than 0.8 for the inferior–superior (inf‐sup). Then, the relative pressure from the belt gating system correlated well with the 4D electromagnetic transponder system's motion in the anterior–posterior (ant‐post) and the inf–post directions. These directions have a correlation value of −0.93 and 0.76, while the lateral only had a 0.03 correlation coefficient. Based on our limited study, external surrogates can be used as predictors of the pancreatic motion in the inf–sup and the ant–post directions. Although there is a low correlation on the lateral direction, its motion is significantly shorter. In conclusion, an appropriate treatment delivery can be used for pancreatic cancer when an internal tracking system, such as the 4D electromagnetic transponder system, is unavailable.

PACS number: 87.55.kh
An analytical model to determine interseed attenuation effect in low‐dose‐rate brachytherapy
Authors: Safigholi Habib , Sardari Dariush , Jashni Somaye Karimi , Mahdavi Seied Rabi , Meigooni Ali S.
Published: February 2017

Brachytherapy treatment planning systems (BTPS) are employing the American Association of Physicists in Medicine (AAPM) Task Group 43 (TG‐43)‐recommended dosimetric parameters of sources, which are measured in water. The majority of brachytherapy implant volumes are not homogeneous media. Particularly, an implant with multiple seeds significantly changes homogeneity of the implant volume. Heterogeneities, such as attenuation by adjacent seeds or interseed attenuation (ISA), are neglected to this day in all BTPS. The goal of this project is to determine a novel analytical method to evaluate the impact of the dose perturbations (P‐value) and/or interseed attenuation effect (ISA‐value). This method will be validated for low‐ and high‐energy brachytherapy seeds such as and using Monte Carlo (MC) simulation techniques. In this analytical model, determination of dose perturbation and interseed attenuation in a multisource brachytherapy implant is based on MC‐simulated 3D kernels of P‐values and ISA data for single active and single dummy configurations, arranged at different distances and orientations relative to each other. The accuracy of the final model in multisource implant configurations has been examined by a comparison of the calculated P‐values and ISA‐values with full Monte Carlo water simulations (FMCWS). This model enabled us to determine the total perturbation and ISA values for any multisource implant, and the results are in excellent agreement with the FMCWS data. The advantage of this model to FMCWS for daily clinical application is the speed of the calculations and ease of the implementation. The new perturbation and ISA formulism have shown a better accuracy for than due to Compton scattering and its independence of the atomic number of the chemical composition of the phantom materials. The maximum difference between the ISA model and FMCWS for all cases was less than 5%. This new model can provide inputs for brachytherapy planning software to consider the ISA effect in dose calculations based on TG‐43U1 algorithm. This approach is applicable for energy range of to sources.

PACS number: 87.53.Jw
Effective dose to patients and staff when using a mobile PET/SPECT system
Authors: Studenski Matthew T.
Published: February 2017

The purpose of this study was to determine the number of weekly acquisitions permissible using a mobile PET/SPECT scanner for myocardial perfusion/viability imaging in an intensive care unit (ICU) based on the effective dose to patients and staff. The effective dose to other patients and staff in an ICU was calculated following recommendations from the American Association of Physicists in Medicine Task Group 108 report (AAPM TG‐108). The number of weekly acquisitions using 555 MBq (15 mCi) Tc‐99m for myocardial perfusion or F‐18 for myocardial viability was determined using the regulatory limits described in the Code of Federal Regulations 10 CFR 20. To increase the number of weekly acquisitions allowed, a reduction in administered dose and portable shielding was considered. A single myocardial perfusion image can be acquired with Tc‐99m each week with a dose reduction to 455 MBq (12.3 mCi) without additional shielding. To acquire a myocardial viability image with F‐18, an activity reduction to 220 MBq (5.9 mCi) is required to meet the regulatory effective dose limit without additional shielding. More than one weekly acquisition can be performed if additional shielding or activity reduction is utilized. A method for calculating dose to patients and staff in an ICU has been developed using conservative assumptions and following AAPM TG‐108. This calculation must be repeated for each individual clinic before any acquisition is performed.

PACS number: 87.57.uq
Intensity‐modulated radiotherapy and volumetric‐modulated arc therapy for malignant pleural mesothelioma after extrapleural pleuropneumonectomy
Authors: Krayenbuehl Jerome , Riesterer Oliver , Graydon Shaun , Dimmerling Peter , Kloeck Stephan , Ciernik Ilja F.
Published: February 2017

Radiotherapy reduces the local relapse rate after pleuropneumonectomy of malignant pleural mesothelioma (MPM). The optimal treatment technique with photons remains undefined. Comparative planning for intensity‐modulated radiotherapy (IMRT) and volumetric‐modulated arc therapy (VMAT) was performed. Six MPM patients with significant postoperative intrathoracic air cavities were planned with IMRT and VMAT. A dose comparison for the targets and organ at risks (OAR) was performed. Robustness was assessed in respect to the variation of target dose with change in volume of air cavities. VMAT reduced the dose to the contralateral lung by reducing the volume covered by 13 Gy and 20 Gy by a factor 1.8 and 2.8, in respect to IMRT (). Dose distribution with VMAT was the most stable technique in regard to postsurgical air cavity variation. For IMRT, , and the minimal target dose decreased by 40%, 64%, and 12% compared to 29%, 47%, and 7% with VMAT when air cavity decreased. Two arcs compared to one arc decreased the dose to all the organs at risk (OAR) while leaving PTV dose coverage unchanged. Increasing the number of arcs from two to three did not reduce the dose to the OAR further, but increased the beam‐on time by 50%. Using partial arcs decreased the beam‐on time by 43%. VMAT allows a lower lung dose and is less affected by the air cavity variation than IMRT. The best VMAT plans were obtained with two partial arcs. VMAT seems currently the most suitable technique for the treatment of MPM patients when air cavities are remaining and no adaptive radiotherapy is performed.

PACS number: 87.55.D‐
Self‐expanding stent effects on radiation dosimetry in esophageal cancer
Authors: Francis Samual R. , Anker Christopher J. , Wang Brian , Williams Greg V. , Cox Kristen , Adler Douglas G. , Shrieve Dennis C. , Salter Bill J.
Published: February 2017

It is the purpose of this study to evaluate how self‐expanding stents (SESs) affect esophageal cancer radiation planning target volumes (PTVs) and dose delivered to surrounding organs at risk (OARs). Ten patients were evaluated, for whom a SES was placed before radiation. A computed tomography (CT) scan obtained before stent placement was fused to the post‐stent CT simulation scan. Three methods were used to represent pre‐stent PTVs: 1) image fusion (IF), 2) volume approximation (VA), and 3) diameter approximation (DA). PTVs and OARs were contoured per RTOG 1010 protocol using Eclipse Treatment Planning software. Post‐stent dosimetry for each patient was compared to approximated pre‐stent dosimetry. For each of the three pre‐stent approximations (IF, VA, and DA), the mean lung and liver doses and the estimated percentages of lung volumes receiving 5 Gy, 10 Gy, 20 Gy, and 30 Gy, and heart volumes receiving 40 Gy were significantly lower (p‐values ) than those estimated in the post‐stent treatment plans. The lung V5, lung V10, and heart V40 constraints were achieved more often using our pre‐stent approximations. Esophageal SES placement increases the dose delivered to the lungs, heart, and liver. This may have clinical importance, especially when the dose‐volume constraints are near the recommended thresholds, as was the case for lung V5, lung V10, and heart V40. While stents have established benefits for treating patients with significant dysphagia, physicians considering stent placement and radiation therapy must realize the effects stents can have on the dosimetry.

PACS number: 87.55.dk
Development of a modified head and neck quality assurance phantom for use in stereotactic radiosurgery trials
Authors: Faught Austin M. , Kry Stephen F. , Luo Dershan , Molineu Andrea , Bellezza David , Gerber Russell L. , Davidson Scott E. , Bosch Walter , Drzymala Robert E. , Galvin Jim , Timmerman Robert , Sheehan Jason , Gillin Michael T. , Ibbott Geoffrey S. , Followill David S.
Published: February 2017

An anthropomorphic head phantom, constructed from a water‐equivalent plastic shell with only a spherical target, was modified to include a nonspherical target (pituitary) and an adjacent organ at risk (OAR) (optic chiasm), within 2 mm, simulating the anatomy encountered when treating acromegaly. The target and OAR spatial proximity provided a more realistic treatment planning and dose delivery exercise. A separate dosimetry insert contained two TLD for absolute dosimetry and radiochromic film, in the sagittal and coronal planes, for relative dosimetry. The prescription was 25 Gy to 90% of the GTV, with of the OAR volume receiving for the phantom trial. The modified phantom was used to test the rigor of the treatment planning process and phantom reproducibility using a Gamma Knife, CyberKnife, and linear accelerator (linac)‐based radiosurgery system. Delivery reproducibility was tested by repeating each irradiation three times. TLD results from three irradiations on a CyberKnife and Gamma Knife agreed with the calculated target dose to within ± 4% with a maximum coefficient of variation of . Gamma analysis in the coronal and sagittal film planes showed an average passing rate of 99.4% and 99.5% using criteria, respectively. Results from the linac irradiation were within for TLD with a coefficient of variation of . Distance to agreement was calculated to be 1.2 mm and 1.3 mm along the inferior and superior edges of the target in the sagittal film plane, and 1.2 mm for both superior and inferior edges in the coronal film plane. A modified, anatomically realistic SRS phantom was developed that provided a realistic clinical planning and delivery challenge that can be used to credential institutions wanting to participate in NCI‐funded clinical trials.

PACS number: 87.55 ‐v
Application of failure mode and effects analysis (FMEA) to pretreatment phases in tomotherapy
Authors: Broggi Sara , Cantone Marie Claire , Chiara Anna , Muzio Nadia Di , Longobardi Barbara , Mangili Paola , Veronese Ivan
Published: February 2017

The aim of this paper was the application of the failure mode and effects analysis (FMEA) approach to assess the risks for patients undergoing radiotherapy treatments performed by means of a helical tomotherapy unit. FMEA was applied to the preplanning imaging, volume determination, and treatment planning stages of the tomotherapy process and consisted of three steps: 1) identification of the involved subprocesses; 2) identification and ranking of the potential failure modes, together with their causes and effects, using the risk probability number (RPN) scoring system; and 3) identification of additional safety measures to be proposed for process quality and safety improvement. RPN upper threshold for little concern of risk was set at 125. A total of 74 failure modes were identified: 38 in the stage of preplanning imaging and volume determination, and 36 in the stage of planning. The threshold of 125 for RPN was exceeded in four cases: one case only in the phase of preplanning imaging and volume determination, and three cases in the stage of planning. The most critical failures appeared related to (i) the wrong or missing definition and contouring of the overlapping regions, (ii) the wrong assignment of the overlap priority to each anatomical structure, (iii) the wrong choice of the computed tomography calibration curve for dose calculation, and (iv) the wrong (or not performed) choice of the number of fractions in the planning station. On the basis of these findings, in addition to the safety strategies already adopted in the clinical practice, novel solutions have been proposed for mitigating the risk of these failures and to increase patient safety.

PACS number: 87.55.Qr
Gemstone spectral imaging: determination of CT to ED conversion curves for radiotherapy treatment planning
Authors: Yagi Masashi , Ueguchi Takashi , Koizumi Masahiko , Ogata Toshiyuki , Yamada Sachiko , Takahashi Yutaka , Sumida Iori , Akino Yuichi , Konishi Koji , Isohashi Fumiaki , Tomiyama Noriyuki , Yoshioka Yasuo , Ogawa Kazuhiko
Published: February 2017

The monochromatic images acquired by Gemstone spectral imaging (GSI) mode on the GE CT750 HD theoretically determines the computed tomography (CT) number more accurately than that of conventional scanner. Using the former, the CT number is calculated from (synthesized) monoenergetic X‐ray data. We reasoned that the monochromatic image might be applied to radiotherapy treatment planning (RTP) to calculate dose distribution more accurately. Our goal here was to provide CT to electron density (ED) conversion curves with monochromatic images for RTP. Therefore, we assessed the reproducibility of CT numbers, an important factor on quality assurance, over short and long time periods for different substances at varying energy. CT number difference between measured and theoretical value was investigated. The scanner provided sufficient reproducibility of CT numbers for dose calculation over short and long time periods. The CT numbers of monochromatic images produced by this scanner had reasonable values for dose calculation. The CT to ED conversion curve becomes linear with respect to the relationship between CT numbers and EDs as the energy increases. We conclude that monochromatic imaging from a fast switching system can be applied for the dose calculation, keeping Hounsfield units (HU) stability.

PACS numbers: 87.55.‐x, 87.55.ne, 87.57.N‐, 87.59.bd
Hierarchical enhanced non‐rigid registration for target volume correction and propagation for adaptive external beam radiotherapy of carcinoma of the prostate
Authors: Andronache Adrian , Krayenbuehl Jerome , Szekely Gabor , Ciernik Ilja F.
Published: February 2017

Volumes change during fractionated radiotherapy (RT). We investigate a tool based on the Hierarchical Enhanced Registration Algorithm (HERA) to project a 3D segmentation set of the prostate into the subsequent imaging sets at any time point during RT by using intensity‐based image registration techniques. Sequential CT sets during RT at 15, 30, 45, and 60 Gy of two patients were used. Five expert clinicians outlined the prostate in a blinded fashion, defining intraobserver and interobserver variability on a set of 35 and 25 scans, respectively. The observer variability and positioning for manual correction was compared to both affine and elastic image registration‐based contour propagation. The overall mean error of the registration‐based correction of the planning target volume was comparable to the interobserver variability of manual target volume definition. The correction by affine image fusion was inferior to the results of elastic registration. The maximal deviation for the interobserver segmentation was 15.4 mm, 10.5 mm for the affine and 8.0 mm for the elastic registration. The mean interobserver variability was for the affine, and for the elastic registration. Intensity‐based elastic registration of deformable anatomical structures with HERA is suitable for the assessment of changes of prostate volumes for the purpose of target propagation and adaptive radiotherapy.

PACS number: 87.57.nj
Migration from full‐head mask to “open‐face” mask for immobilization of patients with head and neck cancer
Authors: Li Guang , Lovelock D. Michael , Mechalakos James , Rao Shyam , Della‐Biancia Cesar , Amols Howard , Lee Nancy
Published: February 2017

To provide an alternative device for immobilization of the head while easing claustrophobia and improving comfort, an “open‐face” thermoplastic mask was evaluated using video‐based optical surface imaging (OSI) and kilovoltage (kV) X‐ray radiography. A three‐point thermoplastic head mask with a precut opening and reinforced strips was developed. After molding, it provided sufficient visible facial area as the region of interest for OSI. Using real‐time OSI, the head motion of ten volunteers in the new mask was evaluated during mask locking and 15 minutes lying on the treatment couch. Using a nose mark with reference to room lasers, forced head movement in open‐face and full‐head masks (with a nose hole) was compared. Five patients with claustrophobia were immobilized with open‐face masks, set up using OSI and kV, and treated in 121 fractions, in which 61 fractions were monitored during treatment using real‐time OSI. With the open‐face mask, head motion was found to be and in volunteers during the experiment, and and in patients during treatment. These agree with patient motion calculated from pre‐/post‐treatment OSI and kV data using different anatomical landmarks. In volunteers, the head shift induced by mask‐locking was and , and the range of forced movements in the open‐face and full‐head masks were found to be similar. Most (80%) of the volunteers preferred the open‐face mask to the full‐head mask, while claustrophobic patients could only tolerate the open‐face mask. The open‐face mask is characterized for its immobilization capability and can immobilize patients sufficiently during radiotherapy. It provides a clinical solution to the immobilization of patients with head and neck (HN) cancer undergoing radiotherapy, and is particularly beneficial for claustrophobic patients. This new open‐face mask is readily adopted in radiotherapy clinic as a superior alternative to the standard full‐head mask.

PACS numbers: 87.19.xj, 87.63.L‐, 87.59.‐e, 87.55.tg, 87.55.‐x
Evaluation of two synchronized external surrogates for 4D CT sorting
Authors: Glide‐Hurst Carri K. , Smith Megan Schwenker , Ajlouni Munther , Chetty Indrin J.
Published: February 2017

The purpose of this study was to quantify the performance and agreement between two different external surrogate acquisition systems: Varian's Real‐Time Position Management (RPM) and Philips Medical Systems' pneumatic bellows, in the context of waveform and 4D CT image analysis. Eight patient displacement curves derived from RPM data were inputted into a motion platform with varying amplitudes (0.5 to 3 cm) and patterns. Simultaneous 4D CT acquisition, with synchronized X‐ray on detection, was performed with the bellows and RPM block placed on the platform. Bellows data were used for online retrospective phase‐based sorting, while RPM data were used for off‐line reconstruction of raw 4D CT data. RPM and bellows breathing curves were resampled, normalized, and analyzed to determine associations between different external surrogates, relative amplitude differences, and system latency. Maximum intensity projection (MIP) images were generated, phantom targets were delineated, and volume differences, overlap index, and Dice similarity coefficient differences were evaluated. A prospective patient study of ten patients was performed and waveforms were evaluated for latency (i.e., absolute time differences) and overall agreement. 4D CT sorting quality and subtraction images were assessed. Near perfect associations between the RPM and bellows‐acquired breathing traces were found . Target volumes were for RPM and bellows targets, respectively, which was not significantly different . Negligible centroid variations were observed between bellows and RPM‐contoured MIP targets ( in superior‐inferior direction). The maximum volume difference was observed for an RPM target 2.5 cc (1%) less than bellows, yielding the largest difference in centroid displacement (0.9 mm). Strong correlations in bellows and RPM waveforms were observed for all patients . Latency between external surrogates was for phantom and patient data. Negligible differences were observed between MIP, end‐exhale, and end‐inhale phase images for all cases, with delineated RPM and bellows lung volumes demonstrating a mean difference of . Dice similarity coefficients and overlap indices were near unity for phantom target volumes and patient lung volumes. Slight differences were observed in waveform and latency analysis between Philips bellows and Varian's RPM, although these did not translate to differences in image quality or impact delineations. Therefore, the two systems were found to be equivalent external surrogates in the context of 4D CT for treatment planning purposes.

PACS numbers: 87.57.Q‐, 07.07.Df
A new approach for the pixel map sensitivity (PMS) evaluation of an electronic portal imaging device (EPID)
Authors: Boriano Alberto , Lucio Francesco , Calamia Elisa , Russi Elvio , Marchetto Flavio
Published: February 2017

When using an electronic portal imaging device (EPID) for dosimetric verifications, the calibration of the sensitive area is of paramount importance. Two calibration methods are generally adopted: one, empirical, based on an external reference dosimeter or on multiple narrow beam irradiations, and one based on the EPID response simulation. In this paper we present an alternative approach based on an intercalibration procedure, independent from external dosimeters and from simulations, and is quick and easy to perform. Each element of a detector matrix is characterized by a different gain; the aim of the calibration procedure is to relate the gain of each element to a reference one. The method that we used to compute the relative gains is based on recursive acquisitions with the EPID placed in different positions, assuming a constant fluence of the beam for subsequent deliveries. By applying an established procedure and analysis algorithm, the EPID calibration was repeated in several working conditions. Data show that both the photons energy and the presence of a medium between the source and the detector affect the calibration coefficients less than 1%. The calibration coefficients were then applied to the acquired images, comparing the EPID dose images with films. Measurements were performed with open field, placing the film at the level of the EPID. The standard deviation of the distribution of the point‐to‐point difference is 0.6%. An approach of this type for the EPID calibration has many advantages with respect to the standard methods — it does not need an external dosimeter, it is not related to the irradiation techniques, and it is easy to implement in the clinical practice. Moreover, it can be applied in case of transit or nontransit dosimetry, solving the problem of the EPID calibration independently from the dose reconstruction method.

PACS number: 87.56.‐v
A critical evaluation of the PTW 2D‐ARRAY seven29 and OCTAVIUS II phantom for IMRT and VMAT verification
Authors: Hussein Mohammad , Adams Elizabeth J. , Jordan Thomas J. , Clark Catharine H. , Nisbet Andrew
Published: February 2017

Quality assurance (QA) for intensity‐ and volumetric‐modulated radiotherapy (IMRT and VMAT) has evolved substantially. In recent years, various commercial 2D and 3D ionization chamber or diode detector arrays have become available, allowing for absolute verification with near real time results, allowing for streamlined QA. However, detector arrays are limited by their resolution, giving rise to concerns about their sensitivity to errors. Understanding the limitations of these devices is therefore critical. In this study, the sensitivity and resolution of the PTW 2D‐ARRAY seven29 and OCTAVIUS II phantom combination was comprehensively characterized for use in dynamic sliding window IMRT and RapidArc verification. Measurement comparisons were made between single acquisition and a multiple merged acquisition techniques to improve the effective resolution of the 2D‐ARRAY, as well as comparisons against GAFCHROMIC EBT2 film and electronic portal imaging dosimetry (EPID). The sensitivity and resolution of the 2D‐ARRAY was tested using two gantry angle 0° modulated test fields. Deliberate multileaf collimator (MLC) errors of 1, 2, and 5 mm and collimator rotation errors were inserted into IMRT and RapidArc plans for pelvis and head & neck sites, to test sensitivity to errors. The radiobiological impact of these errors was assessed to determine the gamma index passing criteria to be used with the 2D‐ARRAY to detect clinically relevant errors. For gamma index distributions, it was found that the 2D‐ARRAY in single acquisition mode was comparable to multiple acquisition modes, as well as film and EPID. It was found that the commonly used gamma index criteria of 3% dose difference or 3 mm distance to agreement may potentially mask clinically relevant errors. Gamma index criteria of 3%/2 mm with a passing threshold of 98%, or 2%/2 mm with a passing threshold of 95%, were found to be more sensitive. We suggest that the gamma index passing thresholds may be used for guidance, but also should be combined with a visual inspection of the gamma index distribution and calculation of the dose difference to assess whether there may be a clinical impact in failed regions.

PACS numbers: 87.55.Qr, 87.56.Fc
Assessment of tumor motion reproducibility with audio‐visual coaching through successive 4D CT sessions
Authors: Goossens Samuel , Senny Frédéric , Lee John Aldo , Janssens Guillaume , Geets Xavier
Published: February 2017

This study aimed to compare combined audio‐visual coaching with audio coaching alone and assess their respective impact on the reproducibility of external breathing motion and, one step further, on the internal lung tumor motion itself, through successive sessions. Thirteen patients with NSCLC were enrolled in this study. The tumor motion was assessed by three to four successive 4D CT sessions, while the breathing signal was measured from magnetic sensors positioned on the epigastric region. For all sessions, the breathing was regularized with either audio coaching alone (AC, ) or combined with a real‐time visual feedback (A/VC, ) when tolerated by the patients. Peak‐to‐peak amplitude, period and signal shape of both breathing and tumor motions were first measured. Then, the correlation between the respiratory signal and internal tumor motion over time was evaluated, as well as the residual tumor motion for a gated strategy. Although breathing and tumor motions were comparable between AC and AV/C groups, A/VC approach achieved better reproducibility through sessions than AC alone (mean tumor motion of vs. , and mean breathing motion of vs. , respectively). High internal/external correlation reproducibility was achieved in the superior‐inferior tumor motion direction for all patients. For the anterior‐posterior tumor motion direction, better correlation reproducibility has been observed when visual feedback has been used. For a displacement‐based gating approach, A/VC might also be recommended, since it led to smaller residual tumor motion within clinically relevant duty cycles. This study suggests that combining real‐time visual feedback with audio coaching might improve the reproducibility of key characteristics of the breathing pattern, and might thus be considered in the implementation of lung tumor radiotherapy.

PACS number: 87