bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐452: Identifying Inefficiencies in Radiation Oncology Workflow and Prioritizing Solutions for Process Improvement and Patient Safety
Authors: Bennion N , Driewer J , Jacobs K , Poole M , McMahon R , Wilson K , Denniston K , Zhen W , Yager A , Enke C
Published: June 2015

Purpose:

Successful radiation therapy requires multi‐step processes susceptible to unnecessary delays that can negatively impact clinic workflow, patient satisfaction, and safety. This project applied process improvement tools to assess workflow bottlenecks and identify solutions to barriers for effective implementation.

Methods:

We utilized the DMAIC (define, measure, analyze, improve, control) methodology, limiting our scope to the treatment planning process. From May through December of 2014, times and dates of each step from simulation to treatment were recorded for 507 cases. A value‐stream map created from this dataset directed our selection of outcome measures (Y metrics). Critical goals (X metrics) that would accomplish the Y metrics were identified. Barriers to actions were binned into control‐impact matrices, in order to stratify them into four groups: in/out of control and high/low impact. Solutions to each barrier were then categorized into benefit‐effort matries to identify those of high benefit and low effort.

Results:

For 507 cases, the mean time from simulation to treatment was 235 total hours. The mean process and wait time were 60 and 132 hours, respectively. The Y metric was to increase the ratio of all non‐emergent plans completed the business day prior to treatment from 47% to 75%. Project X metrics included increasing the number of IMRT QAs completed at least 24 hours prior to treatment from 19% to 80% and the number of non‐IMRT plans approved at least 24 hours prior to treatment from 33% to 80%. Intervals from simulation to target contour and from initial plan completion to plan approval were identified as periods that could benefit from intervention. Barriers to actions were binned into control‐impact matrices and solutions by benefit‐effort matrices.

Conclusion:

The DMAIC method can be successfully applied in radiation therapy clinics to identify inefficiencies and prioritize solutions for the highest impact.
SU‐E‐T‐453: Image‐Guided Patient‐Specific Quality Assurance for Multi‐Target Single Isocenter Intracranial VMAT Radiosurgery
Authors: Huang M , Brezovich I , Duan J , Wu X , Shen S , Cardan R. , Fiveash J , Popple R
Published: June 2015

Purpose:

To demonstrate a patient specific, image‐guided quality assurance method that tests both dosimetric and geometric accuracy for single‐isocenter multiple‐target VMAT radiosurgery (SIMT‐VMAT‐SRS)

Method:

We used a new film type, EBT‐XD (optimal range 0.4–40Gy), and an in‐house PMMA phantom having a coronal plane for film and a 0.125 cm3 ionization chamber (IC). The phantom contained fiducial features for kV image guided setup and for accurate film marking. Five patient plans with multiple targets sizes ranging from 3 to 21mm in diameter and prescribed doses from 14 to 18 Gy were selected. Two verification plans were generated for each case with the film plane passing through the center of the largest and smallest targets. For the four largest targets we obtained an IC measurement. For each case, a calibration film was irradiated using a custom designed step pattern. The films were scanned using a flatbed color scanner and converted to dose using the calibration film and the three channel calibration method. Image registration was performed between film and treatment planning system calculations to evaluate the geometric accuracy.

Results:

The mean registration vector had an average magnitude of 0.47 mm (range from 0.13mm to 0.64 mm). For the four largest targets, the mean ratio of the IC and film measurement to expected dose was 0.990 (range 0.968 to 1.009) and 1.032 (1.021 to 1.046), respectively. The fraction of pixels having gamma index < 1 for criteria of 3%/3mm, 3%/2mm, 3%/1mm was 98.8%, 97.5% and 87.2% before geometric registration and 99.1%, 98.3% and 94.8% after registration.

Conclusion:

We have demonstrated an image‐guided QA method can assess both geometric and dosimetric accuracy. The phantom was positioned with sub‐millimeter accuracy. Absolute film dosimetry using EBT‐XD film was sufficiently accurate for assessment of dose to multi‐targets too small for IC measurement in SRS VMAT plans.
SU‐E‐T‐456: Impact of Dose Calculation Algorithms On Biologically Optimized VMAT Plans for Esophageal Cancer
Authors: Thiyagarajan Rajesh , Nambiraj N Arunai , Vikraman S , Karrthick KP , Sigamani Ashokkumar , Subbarao Bargavan , Ramu M , Sambasivaselli R , Senniandavar V , Kataria Tejinder
Published: June 2015

Purpose:

To evaluate the impact of dose calculation algorithm on the dose distribution of biologically optimized Volumatric Modulated Arc Therapy (VMAT) plans for Esophgeal cancer.

Methods:

Eighteen retrospectively treated patients with carcinoma esophagus were studied. VMAT plans were optimized using biological objectives in Monaco (5.0) TPS for 6MV photon beam (Elekta Infinity). These plans were calculated for final dose using Monte Carlo (MC), Collapsed Cone Convolution (CCC) & Pencil Beam Convolution (PBC) algorithms from Monaco and Oncentra Masterplan TPS. A dose grid of 2mm was used for all algorithms and 1% per plan uncertainty maintained for MC calculation. MC based calculations were considered as the reference for CCC & PBC. Dose volume histogram (DVH) indices (D95, D98, D50 etc) of Target (PTV) and critical structures were compared to study the impact of all three algorithms.

Results:

Beam models were consistent with measured data. The mean difference observed in reference with MC calculation for D98, D95, D50 & D2 of PTV were 0.37%, −0.21%, 1.51% & 1.18% respectively for CCC and 3.28%, 2.75%, 3.61% & 3.08% for PBC. Heart D25 mean difference was 4.94% & 11.21% for CCC and PBC respectively. Lung Dmean mean difference was 1.5% (CCC) and 4.1% (PBC). Spinal cord D2 mean difference was 2.35% (CCC) and 3.98% (PBC). Similar differences were observed for liver and kidneys. The overall mean difference found for target and critical structures was 0.71±1.52%, 2.71±3.10% for CCC and 3.18±1.55%, 6.61±5.1% for PBC respectively.

Conclusion:

We observed a significant overestimate of dose distribution by CCC and PBC as compared to MC. The dose prediction of CCC is closer (<3%) to MC than that of PBC. This can be attributed to poor performance of CCC and PBC in inhomogeneous regions around esophagus. CCC can be considered as an alternate in the absence of MC algorithm.
SU‐E‐T‐457: Impact of Interfractional Variations On Anterior Vs. Lateral‐Field Proton Therapy of Prostate Cancer
Authors: Moteabbed M , Trofimov A , Sharp G C , Wang Y , Zietman A L , Efstathiou J A , Lu H
Published: June 2015

Purpose:

To investigate the effects of interfractional anatomy and setup variations on plans with anterior‐oblique vs. lateral beams for prostate cancer pencil beam scanning (PBS) and passive scattered (PS) proton therapy.

Methods:

Six patients with low/intermediate risk prostate cancer treated with PS proton therapy at our institution were selected. All patients underwent weekly verification CT scans. Implanted fiducials were used for localization, and endorectal balloons for prostate immobilization. New PBS plans with lateral beams, as well as PBS and PS plans with anterior‐oblique beams (±35 deg) were created. PBS plans used two different spot sizes: ∼10mm (large) and ∼5mm (medium) sigma at 25cm range and optimized as single‐field‐uniform‐dose with ∼8% non‐uniformity. No range uncertainty margins were applied in PBS plans to maximize rectal sparing. Field‐specific apertures were used when planning with large spots to sharpen the penumbrae. The planned dose was recomputed on each weekly CT with fiducials aligned to the simulation CT, scaled and accumulated via deformable image registration.

Results:

The dose volume analysis showed that although difference between planned and accumulated dose remains negligible for plans with conventional lateral beams using both PS and PBS, this is not the case for plans with anterior beams. The target coverage in anterior plans was largely degraded due to the variations in the beam path length and the absence of range margins. The average prostate D95 was reduced by 7.5/15.9% (using PS/PBS) after accumulation for anterior plans, compared with 0/0.4% for lateral plans. The average mean dose in organs‐at‐risk decreased by 1% for lateral and 2% for anterior plans, similarly for PS and PBS. Spot size did not affect the dose changes.

Conclusion:

Prostate plans using anterior beams may undergo clinically relevant interfractional dose degradation. Corrective strategies guided by in‐vivo range measurements should be studied before clinical application of this technique.
SU‐E‐T‐459: Impact of Source Position and Traveling Time On HDR Skin Surface Applicator Dosimetry
Authors: Jeong J , Barker C , Zaider M , Cohen G
Published: June 2015

Purpose:

Observed dosimetric discrepancy between measured and treatment planning system (TPS) predicted values, during applicator commissioning, were traced to source position uncertainty in the applicator. We quantify the dosimetric impact of this geometric uncertainty, and of the source traveling time inside the applicator, and propose corrections for clinical use.

Methods:

We measured the dose profiles from the Varian Leipzig‐style (horizontal) HDR skin applicator, using EBT3 film, photon diode, and optically stimulated luminescence dosimeter (OSLD) and three different GammaMed HDR afterloders. The dose profiles and depth dose of each aperture were measured at several depths (up to about 10 mm, depending on the dosimeter). The measured dose profiles were compared with Acuros calculated profiles in BrachyVision TPS. For the impact of the source position, EBT3 film measurements were performed with applicator, facing‐down and facing‐up orientations. The dose with and without source traveling was measured with diode detector using HDR timer and electrometer timer, respectively.

Results:

Depth doses measured using the three dosimeters were in good agreement, but were consistently higher than the Acuros dose calculations. Measurements with the applicator facing‐up were significantly lower than those in the facing‐down position with maximum difference of about 18% at the surface, due to source sag inside the applicator. Based on the inverse‐square law, the effective source sag was evaluated to be about 0.5 mm from the planned position. The additional dose from the source traveling was about 2.8% for 30 seconds with 10 Ci source, decreasing with increased dwelling time and decreased source activity.

Conclusion:

Due to the short source‐to‐surface distance of the applicator, the small source sag inside the applicator has significant dosimetric impact, which should be considered before the clinical use of the applicator. Investigation of the effect for other applicators that have relatively large source lumen inner diameter may be warranted.

Christopher Barker and Gil'ad Cohen are receiving research support for a study of skin surface brachytherapy from Elekta.
SU‐E‐T‐460: Impact of the LINAC Repetition Rate On a High‐Resolution Liquid Ionization Chamber Array for Patient‐Specific QA
Authors: Wang S , Driewer J , Zheng D , Lei Y , Zhang Q , Zhu X , Li S , Enke C , Xu B , Zhou S
Published: June 2015

Purpose:

The purpose of this study is to investigate the LINAC repetition‐rate (dose‐rate) dependence of OCTAVIUS 1000SRS liquid ionization chamber (LIC) array for patient specific QA of SRT plans delivered with flattening‐filter‐free (FFF) beams.

Methods:

1) The repetition‐rate dependence of 1000SRS was measured in a phantom constructed with 5‐cm solid water above and below the array for build‐up and backscatter. A 0.3cc calibrated ion chamber was also placed along the central axis 2.3cm below the center chamber of the array for normalizing LINAC output fluctuation. The signals from the center chamber of the array under different repetition rates in the range of 400–2400 MU/min for 6xFFF and 10xFFF beams on a Varian TrueBeamSTx LINAC, normalized by the independent chamber readings, were analyzed for the array response dependence on repetition rates. 2) Twelve Step‐and‐shoot IMRS QA plans (6xFFF and 10xFFF) were delivered to the array under different repetition rates for analysis and comparison. 3) The absolute doses measured by the center chamber were compared to measurements using an independent ionization chamber with the identical setup, taken as the gold standard. 4) The correction factors based on the actual delivery repetition rate were applied to the measurements, and the results were compared again to the gold standard.

Results:

1) The 1000SRS array exhibited repetition‐rate dependence for FFF beams, up to 5% for 6xFFF and 10% for 10xFFF; 2) The array showed clinically‐acceptable repetition‐rate dependence for regular flattened beams; 3) This repetition‐rate dependence significantly affected the measurement accuracy, thereby affecting IMRS QA results; 4) By applying an empirical repetition‐rate correction, the corrected measurements agreed better with the gold standard ion chamber measurements.

Conclusion:

OCTAVIUS 1000SRS LIC array exhibited considerable repetition‐rate dependence for FFF beams, which will affect the accuracy of the absolute QA measurements, especially for IMRS plans with the step‐and‐shoot technique.
SU‐E‐T‐472: Improvement of IMRT QA Passing Rate by Correcting Angular Dependence of MatriXX
Authors: Chen Q , Watkins W , Kim T , Neal B
Published: June 2015

Purpose:

Multi‐channel planar detector arrays utilized for IMRT‐QA, such as the MatriXX, exhibit an incident‐beam angular dependent response which can Result in false‐positive gamma‐based QA results, especially for helical tomotherapy plans which encompass the full range of beam angles. Although MatriXX can use with gantry angle sensor to provide automatically angular correction, this sensor does not work with tomotherapy. The purpose of the study is to reduce IMRT‐QA false‐positives by correcting for the MatriXX angular dependence.

Methods:

MatriXX angular dependence was characterized by comparing multiple fixed‐angle irradiation measurements with corresponding TPS computed doses. For 81 Tomo‐helical IMRT‐QA measurements, two different correction schemes were tested: (1) A Monte‐Carlo dose engine was used to compute MatriXX signal based on the angular‐response curve. The computed signal was then compared with measurement. (2) Uncorrected computed signal was compared with measurements uniformly scaled to account for the average angular dependence. Three scaling factor (+2%, +2.5%, +3%) were tested.

Results:

The MatriXX response is 8% less than predicted for a PA beam even when the couch is fully accounted for. Without angular correction, only 67% of the cases pass the >90% points γ<1 (3%, 3mm). After full angular correction, 96% of the cases pass the criteria. Of three scaling factors, +2% gave the highest passing rate (89%), which is still less than the full angular correction method. With a stricter γ(2%,3mm) criteria, the full angular correction method was still able to achieve the 90% passing rate while the scaling method only gives 53% passing rate.

Conclusion:

Correction for the MatriXX angular dependence reduced the false‐positives rate of our IMRT‐QA process. It is necessary to correct for the angular dependence to achieve the IMRT passing criteria specified in TG129.
SU‐E‐T‐474: Improvements to Intra‐Oral Shield Design for Electron Beam Treatments: Use of Multi‐Layered Metal Foils
Authors: Butson M
Published: June 2015

Purpose:

Intraoral electron shields used in radiotherapy are designed to minimize radiation exposure to non‐treatment tissue. Sites where shields are used include but are not limited to, the treatment of lips, cheeks and ears whilst shielding the underlying oral cavity, tongue, gingival or temporal region. However their use produces an enhancement in dose on the beam side caused by an increase in electron backscatter radiation. This work designs a new shield incorporating copper, aluminium and wax in a step down filter arrangement to minimise backscatter whilst minimizing overall shield thickness.

Methods:

For electron beams ranging from 6 MeV to 10 MeV, shields of varying designs and thicknesses were assessed to determine the thinnest shield design that could be produced whilst minimising backscattered radiation to a clinically acceptable level. This was performed with conventional lead and wax shields as well as varying quantities of aluminium and copper foils.

Results:

From tested shield designs, a new shield design of 4 mm lead, 0.6 mm copper, 1.0 mm aluminium and 1.5 mm wax (3.1 mm added filtration, 7.1 mm total thickness) provided a clinically acceptable (no greater than 110% dose) backscatter and transmission reduction and matched a standard 4.5 mm lead and 10 mm wax (total thickness 14.5 mm) electron shield. Dose enhancement values of no more than 10 % were measured utilising this shield design with a 50 % reduction in shield thickness.

Conclusion:

The thinner layered shield reduced backscattered radiation dose to less than 10% enhancement for beam energies on 10 MeV and less and will allow easier patient set up. The thinner shields are tolerated better by patients when mucosal reactions occur as they place less physical pressure on these sites during treatment due to their smaller size and thickness.
SU‐E‐T‐475: Improvements to Total Body Irradiation Dosimetry Efficiency with EBT3 Radiochromic Film and a Template System
Authors: Butson M , Pope D , Whitaker M
Published: June 2015

Purpose:

Total Body Irradiation (TBI) treatments are mainly used in a preparative regimen for haematopoietic stem cell (or bone marrow) transplantation. Our standard regimen is a 12 Gy / 6 fraction bi‐daily technique. To evaluate the delivered dose homogeneity to the patient, EBT3 Gafchromic film is positioned at the head, neck, chest, pelvis and groin for all fractions. A system has been developed to simply and accurately prepare and readout the films for patient dose assessment.

Methods:

A process involving easy preparation and analysis has been produced to minimise the time requirements for TBI dosimetry. One sheet of EBT3 film is used to prepare treatment dosimeters for all fractions, including calibration films, and an automated dose analysis system for easy evaluation and calculation of estimated in‐vivo doses was developed. A desktop scanner is used with a dedicated TBI film template to accurately position the films for Image J analysis and extraction. Dental wax bolus and zip‐lock bag holders are used to hold the EBT3 film in place during irradiation.

Results:

To adequately provide dosimetry information for a 6 fraction, TBI patient, only one sheet of Gafchromic EBT3 film is required. The dosimeters are cut, using a template, into 19 mm squares which are then placed between two 30 mm × 30 mm × 4.5 mm wax blocks for bolus. All packages are prepared before the first treatment fraction. The scanning and analysis process can be completed in less than 10 minutes after a 240 min development period. Results have shown that a high level of accuracy and reproducibility can be achieved using the template system provided.

Conclusion:

Gafchromic EBT3 film provides an adequate in‐vivo dosimetry measure for TBI patients. Using a template based system on a dedicated desktop scanner, in‐vivo results can be ascertained quickly and accurately.
SU‐E‐T‐480: IMRT/VMAT QA Employing a High Resolution Measurement Array: Initial Experience and Limitations
Authors: Gainey M , Saum R , Rothe T , Knobe S , Luebke J , Kuechler S , Wiehle R , Kollefrath M , Bruggmoser G
Published: June 2015

Purpose:

Patient specific QA for IMRT/VMAT is time‐consuming. A high resolution ionization chamber array was employed which rotates synchronously with the gantry. Commissioning, initial experience and limitations of this measurement technique will be discussed.

Methods:

A high resolution ionization chamber array, Octavius1500 (PTW‐Freiburg, Germany), was employed with the Octavius4D rotating cylindrical phantom. Measured plans are reconstructed into a 3D dose distribution using measured depth dose curves (Verisoft 6.0 PTW‐Freiburg). Plans of varying complexity were selected from our patient collective treated at a TrueBeam 1.5 linac (Varian Medical Systems) with HD120 MLC (VMS). Cross‐calibration was performed using a thimble chamber (30016, PTW‐Freiburg) placed within the cylindrical phantom (SSD 840mm, SCD 1000mm). All dose distributions were recalculated using a 1.5mm dose grid (Eclipse, AAA10.0.28/Acuros10.0.28, VMS) using a virtual homogeneous cylindrical phantom provided by the array manufacturer (density 1.016 gcm‐3). All analyses were performed using Verisoft and compared to routine QA analysis (Octavius729 with octagonal phantom) results.

Results:

Depth dose curves from 1cm × 1cm to 26cm × 26cm were measured for 3D dose calculation commissioning in Verisoft 6.0. Excellent agreement was observed between TPS PDD and PDD derived from the Octavius1500 array measurement. For highly modulated plans the overall 3D gamma (2.0mm, 3.0%) ranged between 91.3% to 96.9%. The Octavius729 (2D) array results ranged from 97.9 to 100.0% for PTVs.

Conclusion:

The Octavius1500 and 4D cylindrical phantom provides an integrated QA solution. Complex VMAT plans, comprising multiple PTVs, can be verified with a single (rotating) measurement of all arcs. Hitherto two measurements (horizontal and vertical) had to be performed per PTV. Overall the results are good. However, some refinement may need to be made to the reconstruction. Further work needs to be done to determine appropriate action levels for routine analysis.
SU‐E‐T‐481: In Vivo and Post Mortem Animal Irradiation: Measured Vs. Calculated Doses
Authors: Heintz P , Heintz B , Sandoval D , Weber W , Melo D , Guilmette R
Published: June 2015

Purpose:

Computerized radiation therapy treatment planning is performed on almost all patients today. However it is seldom used for laboratory irradiations. The first objective is to assess whether modern radiation therapy treatment planning (RTP) systems accurately predict the subject dose by comparing in vivo and decedent dose measurements to calculated doses. The other objective is determine the importance of using a RTP system for laboratory irradiations.

Methods:

5 MOSFET radiation dosimeters were placed enterically in each subject (2 sedated Rhesus Macaques) to measure the absorbed dose at 5 levels (carina, lung, heart, liver and rectum) during whole body irradiation. The subjects were treated with large opposed lateral fields and extended distances to cover the entire subject using a Varian 600C linac. CT simulation was performed ante‐mortem (AM) and post‐mortem (PM). To compare AM and PM doses, calculation points were placed at the location of each dosimeter in the treatment plan. The measured results were compared to the results using Varian Eclipse and Prowess Panther RTP systems.

Results:

The Varian and Prowess treatment planning system agreed to within in +1.5% for both subjects. However there were significant differences between the measured and calculated doses. For both animals the calculated central axis dose was higher than prescribed by 3–5%. This was caused in part by inaccurate measurement of animal thickness at the time of irradiation. For one subject the doses ranged from 4% to 7% high and the other subject the doses ranged 7% to 14% high when compared to the RTP doses.

Conclusions:

Our results suggest that using proper CT RTP system can more accurately deliver the prescribed dose to laboratory subjects. It also shows that there is significant dose variation in such subjects when inhomogeneities are not considered in the planning process.
SU‐E‐T‐482: In Vivo Dosimetry of An Anthropomorphic Phantom by Using the RADPOS System for Proton Beam Therapy
Authors: Kohno R , Yamaguchi H , Motegi K , Hotta K , Nishioka S , Dohmae T , Akimoto T
Published: June 2015

Purpose:

Delivered doses in an anthropomorphic phantom were evaluated by using the RADPOS system for proton beam therapy.

Methods:

The RADPOS in vivo dosimetry system combines an electromagnetic positioning sensor with MOSFET dosimetry, allowing simultaneous online measurements of dose and spatial position. Through the RADPOS system, dose evaluation points can be determined. In vivo proton dosimetry was evaluated by using the RADPOS system and anthropomorphic head and neck phantom. MOSFET doses measured at 3D positions obtained with the RADPOS were compared to the treatment plan values that were calculated by a simplified Monte Carlo (SMC) method. Although the MOSFET response depends strongly on the linear energy transfer (LET) of proton beam, the MOSFET responses to proton beams were corrected with the SMC. Here, the SMC calculated only dose deposition determined by the experimental depth–dose distribution and lateral displacement of protons due to both multiple scattering effect in materials and incident angle. As a Result, the SMC could quickly calculate accurate doses in even heterogeneities.

Results:

In vivo dosimetry by using the RADPOS, as well as the MOSFET doses agreed in comparison with calculations by the SMC in the range of −3.0% to 8.3%. Most measurement errors occurred because of the uncertainties of dose calculations due to the position error of 1 mm.

Conclusion:

We evaluated the delivered doses in the anthropomorphic phantom by using the RADPOS system for proton beam therapy. The MOSFET doses agreed in comparison with calculations by the SMC within the measurement error. Therefore, we could successfully control the uncertainties of the measurement positions by using the RADPOS system within 1 mm in in vivo proton dosimetry. We aim for the clinical application of in vivo proton dosimetry with this RADPOS system.
SU‐E‐T‐485: In Vivo Dosimetry with EBT3 Radiochromic Films for TBI Treatments
Authors: Lozares S , Gracia M , Olasolo J , Gallardo N , Fuentemilla N , Pellejero S , Miquelez S , Maneru F , Martin M , Bragado L , Rubio A
Published: June 2015

Purpose:

Total body irradiation (TBI) is a technique that requires special equipment to control “in vivo” the dose to the patient because it is a complex technique performed in extraordinary conditions. There are several devices to perform this task (diodes, TLDs, ionization chambers, MOSFET). In this paper we study the possibility of performing these measurements with radiochromic films EBT3 properly calibrated. This method has been compared to the PTW diodes system for TBI.

Methods:

Once made the TC to the patients, we measured different thicknesses of the relevant areas of the body (head, neck, chest with or without arms, umbilicus area, knees and ankles); for each of these thicknesses we measured dose rate (cGy / UM) in RW3 phantom, in TBI conditions, with ionization chamber in the center; in turn, the input diode and the output of each configuration is placed to assign dose to each set of diodes. Movie calibration is performed according to manufacturer's recommendations but TBI conditions. The dose at the center of each thickness compared to a linear interpolation of the dose at the entrance and exit, resulting in an adequate approximation. Finally in each session for each patient put a piece of film (2×2 cm2) at the entrance and another at the exit in each area, obtaining these readings and interpolating the estimated center dose, as with the diodes.

Results:

These results show a greater homogeneity in the distribution for use with film and validate the use of the same for this task and, if necessary, to avoid purchasing diode group if they have not.

Conclusion:

By using radiochromic films for this technique gives us a proper calculation of the dose received by the patient in the absence of other methods, or gives us a second additional track that already used normally.
SU‐E‐T‐493: Influence of Filtered and Flatting Filter Free Photon Beam of 10 Megavolts Energy On Rapid Arc Radiotherapy Planning for Cervix Carcinoma
Authors: Girigesh Y , Kumar L , Raman K , Mishra M
Published: June 2015

Purpose:

Aim of this study is to determine the dosimetric influence of Filtered and Flatting Filter Free Photon Beam of 10 MV energy on RA planning for Ca. Cervix.

Methods:

CT data sets of eleven patients reported with carcinoma cervix were used for RA planning for 10MV _FFB and 10MV_FFFB. RA plans were generated using two full arcs.All RA plans were generated to deliver a dose of 50.4Gy in 28 fractions for PTV and ALARA for OAR's. All plans were analysed for PTV Coverage, conformity Index, homogeneity index, dose to OAR's, integral dose to normal tissue and total monitor units were studied.

Results:

DVH was used to evaluate RA plans for both 10MV_FFB and 10MV_FFFB photon beam. Planning results show a comparable PTV coverage for both energies. Results shows volume of PTV receiving prescription dose were 95.10+ 0.09% and 95.09 +0.11%, and volume of PTV receiving a dose of 107% is 0.45+0.96% and 5.25+8.9%, homogeneity index (HI) were 1.051+0.007 and 1.066+0.008, Conformity Index(CI) were 1.003+0.019 and 1.012+0.013, Mean Integral dose were 2.65+0.34 and 2.60+0.33(*10−5Gy.cm3) for 10MV_FFB and 10MV_FFFB respectively. 10MV_FB shows statistically significant (p<0.05) improvement in mean doses to bladder, rectum, bowel and mean total number of MU's and also shows remarkable decrease in mean total no. of MU's by 43.7% in comparison to 10MV_FFFB. There is statistically significant (p<0.05) difference found in CI and HI for 10MV_FB in comparison to 10MV _FFF beam. 10MV_FFFB shows statistically significant (p<0.05) for mean NTID and delivers 1.65 % less NTID in comparison to 10 MV_ FB.

Conclusion:

10MV_FB is superior to 10MV_FFFB for rapid arc planning in case of Cervix carcinomas, it offers better target coverage and OAR's sparing, comparable mean Integral dose to normal tissues and 10 MV_ FB also produced highly conformal and homogeneous dose distribution in comparison to 10MV_FFFB.
SU‐E‐T‐499: Initial Developments of An OpenCL‐Based Cross‐Platform Monte Carlo Dose Engine for Carbon Ion Therapy
Authors: Qin N , Pinto M , Tian Z , Dedes G , Pompos A , Jiang S , Parodi K , Jia X
Published: June 2015

Purpose

Dose calculation is of critical importance for carbon ion therapy. Monte Carlo (MC) simulation is considered to be the most accurate method for calculation of absorbed dose and of all the more fundamental physical quantities related to biological effects. The long computation time, however, limits its routine clinical applications. We have recently started developing a fast MC package, gCMC for carbon therapy on a parallel processing platform, e.g. GPU, aiming at achieving sufficient efficiency to enable MC in clinically important tasks. This abstract reports our progress.

Methods

gCMC was developed in OpenCL environment. Our initial developments focused on water material. gCMC supported carbon ion transport in the energy range of 1–450 MeV/u. A Class II condensed history algorithm was implemented for charged particle transport simulations with stopping power computed via Bethe‐Bloch equation. Energy straggling and multiple scattering were modeled. Total cross section of nuclear interaction was extracted from Geant4. At present, nuclear interaction events were sampled but transports of secondary particles were not included.

Results

We tested cases with a homogeneous water phantom and a pencil carbon ion beam with energy of 200–400 MeV/u. When only electro‐magnetic channel was included, dose/fluence difference between gCMC and Geant4 results averaged within 10% isodose line was <0.5% of the maximum dose/fluence. After enabling nuclear interactions without transporting secondary particles, dose and fluence agreed with the corresponding results computed by Geant4 with <1% difference. Due to the support for multiple platforms of OpenCL, gCMC was executable on NVidia and AMD GPUs, and Intel CPUs. It took ∼50 sec to transport 107 200MeV/u source carbon ions on an NVidia Titan GPU card.

Conclusion

Preliminary studies have demonstrated the accuracy and efficiency of gCMC. With further developments in near future, gCMC will potentially achieve clinically acceptable fast and accurate MC simulations for carbon ion therapy.
SU‐E‐T‐509: Inter‐Observer and Inter‐Modality Contouring Analysis for Organs at Risk for HDR Gynecological Brachytherapy
Authors: Sadeghi P , Banerjee R , Alghamdi M , Phan T , Taggar A , Smith W
Published: June 2015

Purpose

This study quantifies errors associated with MR‐guided High Dose Rate (HDR) gynecological brachytherapy. Uncertainties in this treatment results from contouring, organ motion between imaging and treatment delivery, dose calculation, and dose delivery. We focus on interobserver and inter‐modality variability in contouring and the motion of organs at risk (OARs) in the time span between the MR and CT scans (∼1 hour). We report the change in organ volume and position of center of mass (CM) between the two imaging modalities.

Methods

A total of 8 patients treated with MR‐guided HDR brachytherapy were included in this study. Two observers contoured the bladder and rectum on both MR and CT scans. The change in OAR volume and CM position between the MR and CT imaging sessions on both image sets were calculated.

Results

The absolute mean bladder volume change between the two imaging modalities is 67.1cc. The absolute mean inter‐observer difference in bladder volume is much lower at 15.5cc (MR) and 11.0cc (CT). This higher inter‐modality volume difference suggests a real change in the bladder filling between the two imaging sessions. Change in Rectum volume inter‐observer standard error of means (SEM) is 3.18cc (MR) and 3.09cc (CT), while the inter‐modality SEM is 3.65cc (observer 1), and 2.75cc (observer 2). The SEM for rectum CM position in the superior‐inferior direction was approximately three times higher than in other directions for both the inter—observer (0.77 cm, 0.92 cm for observers 1 and 2, respectively) and inter‐modality (0.91 cm, 0.95 cm for MR and CT, respectively) variability.

Conclusion

Bladder contours display good consistency between different observers on both CT and MR images. For rectum contouring the highest inconsistency stems from the observers’ choice of the superior‐inferior borders. A complete analysis of a larger patient cohort will enable us to separate the true organ motion from the inter‐observer variability.
SU‐E‐T‐520: Investigation of the Impact of Respiratory Motion On Spine SAbR Dose Distributions
Authors: Foster R , Ding C , Jiang S
Published: June 2015

Purpose

Spine SRS/SAbR treatment plans typically require very steep dose gradients to meet spinal cord constraints and it is crucial that the dose distribution be accurate. However, these plans are typically calculated on helical free‐breathing CT scans, which often contain motion artifacts. While the spine itself doesn't exhibit very much intra‐fraction motion, tissues around the spine, particularly the liver, do move with respiration. We investigated the dosimetric effect of liver motion on dose distributions calculated on helical free‐breathing CT scans for spine SAbR delivered to the T and L spine.

Methods

We took 5 spine SAbR plans and used density overrides to simulate an average reconstruction CT image set, which would more closely represent the patient anatomy during treatment. The value used for the density override was 0.66 g/cc. All patients were planned using our standard beam arrangement, which consists of 13 coplanar step and shoot IMRT beams. The original plan was recalculated with the same MU on the “average” scan and target coverage and spinal cord dose were compared to the original plan.

Results

The average changes in minimum PTV dose, PTV coverage, max cord dose and volume of cord receiving 10 Gy were 0.6%, 0.8%, 0.3% and 4.4% (0.012 cc), respectively.

Conclusion

SAbR spine plans are surprisingly robust relative to surrounding organ motion due to respiration. Motion artifacts in helical planning CT scans do not cause clinically significant differences when these plans are re‐calculated on pseudo‐average CT reconstructions. This is likely due to the beam arrangement used because only three beams pass through the liver and only one beam passes completely through the density override. The effect of the respiratory motion on VMAT plans for spine SAbR is being evaluated.
SU‐E‐T‐521: Investigation of the Uncertainties Involved in Secondary Neutron/gamma Production in Geant4/MCNP6 Monte Carlo Codes for Proton Therapy Application
Authors: Mirzakhanian L , Giusti V , Enger S
Published: June 2015

Purpose:

A major concern in proton therapy is the production of secondary neutrons causing secondary cancers, especially in young adults and children. Most utilized Monte Carlo codes in proton therapy are Geant4 and MCNP. However, the default versions of Geant4 and MCNP6 do not have suitable cross sections or physical models to properly handle secondary particle production in proton energy ranges used for therapy. In this study, default versions of Geant4 and MCNP6 were modified to better handle production of secondaries by adding the TENDL‐2012 cross‐section library.

Methods:

In‐water proton depth‐dose was measured at the “The Svedberg Laboratory” in Uppsala (Sweden). The proton beam was mono‐energetic with mean energy of 178.25±0.2 MeV. The measurement set‐up was simulated by Geant4 version 10.00 (default and modified version) and MCNP6. Proton depth‐dose, primary and secondary particle fluence and neutron equivalent dose were calculated. In case of Geant4, the secondary particle fluence was filtered by all the physics processes to identify the main process responsible for the difference between the default and modified version.

Results:

The proton depth‐dose curves and primary proton fluence show a good agreement between both Geant4 versions and MCNP6. With respect to the modified version, default Geant4 underestimates the production of secondary neutrons while overestimates that of gammas. The “ProtonInElastic” process was identified as the main responsible process for the difference between the two versions. MCNP6 shows higher neutron production and lower gamma production than both Geant4 versions.

Conclusion:

Despite the good agreement on the proton depth dose curve and primary proton fluence, there is a significant discrepancy on secondary neutron production between MCNP6 and both versions of Geant4. Further studies are thus in order to find the possible cause of this discrepancy or more accurate cross‐sections/models to handle the nuclear interactions of protons with energy ranges used for therapy.

NSERC‐CRSNG’ CREATE Medical Physics Research Training Network compute calcul CANADA; McGill University health center research institute the fast foundation; LM acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering; Research Council Grant number 432290
SU‐E‐T‐533: LET Dependence Correction of Radiochromic Films for Application in Low Energy Proton Irradiation
Authors: Reinhardt S , Wuerl M , Greubel C , Wilkens J , Hillbrand M , Mairani A , Assmann W , Parodi K
Published: June 2015

Purpose:

Many cell irradiation experiments with low‐energy laser‐driven ions rely on radiochromic films (RCF), because of their dose‐rate independent response and superior spatial resolution. RCF dosimetry in low‐energy ion beams requires a correction of the LET dependent film response. The relative efficiency (RE), the ratio of photon to proton dose that yields the same film darkening, is a measure for the film's LET dependence. A direct way of RE determination is RCF irradiation with low‐energy mono‐energetic protons and hence, well‐defined LET. However, RE is usually determined using high energy proton depth dose measurements where RE corrections require knowledge of the average LET in each depth, which can be either track (tLET) or dose (dLET) averaged. The appropriate LET concept has to be applied to allow a proper film response correction.

Methods:

Radiochromic EBT2 and EBT3 films were irradiated in clinical photon and proton beams. For each depth of the 200 MeV proton depth dose curve, tLET and dLET were calculated by special user routines from the Monte Carlo code FLUKA. Additional irradiations with mono‐energetic low energy protons (4–20 MeV) serve as reference for the RE determination.

Results:

The difference of dLET and tLET increases with depth, with the dLET being almost twice as large as the tLET for the maximum depth. The comparison with mono‐energetic measurements shows a good agreement of the RE for the dLET concept, while a considerably steeper drop in RE is observed when applying the tLET.

Conclusion:

RCF can be used as reference dosimeter for biomedical experiments with low‐energy proton beams if appropriate LET corrections are applied. When using depth dose measurements from clinical proton accelerators for these corrections, the concept of dLET has to be applied.

Acknowledgement:

This work was funded by the DFG Cluster of Excellence ‘Munich‐Centre for Advanced Photonics’ (MAP).

This work was funded by the DFG Cluster of Excellence Munich‐Centre for Advanced Photonics (MAP).
SU‐E‐T‐539: Maximum Energy of Helium and Carbon Ions Clinically Needed for Spine, Lung, Prostate and Pancreas Cancer
Authors: Pompos A , Choy H , Jia X , Jiang S , Timmerman R
Published: June 2015

Purpose:

Maximum available kinetic energy of accelerated heavy ions is a critical parameter to consider during the establishment of a heavy ion therapy center. It dictates the maximum range in tissue and determines the size and cost of ion gantry. We have started planning our heavy ion therapy center and we report on the needed ion range.

Methods:

We analyzed 50 of random SBRT‐spine, SBRT‐ lung, prostate and pancreatic cancer patients from our photon clinic. In the isocentric axial CT cut we recorded the maximum water equivalent depth (WED4Field) of PTV's most distal edge in four cardinal directions and also in a beam direction that required the largest penetration, WEDGantry. These depths were then used to calculate the percentage of our patients we would be able to treat as a function of available maximum carbon and helium beam energy. Based on the Anterior‐Posterior WED for lung patients and the maximum available ion energy we estimated the largest possible non‐coplanar beam entry angle φ (deviation from vertical) in the isocentric vertical sagittal plane.

Results:

We found that if 430MeV/u C‐12, equivalently 220MeV/u He‐4, beams are available, more than 96% (98%) of all patients can be treated without any gantry restrictions (in cardinals angles only) respectively. If the energy is reduced to 400MeV/u C‐12, equivalently 205MeV/u He‐4, the above fractions reduce to 80% (87%) for prostate and 88% (97%) for other sites. This 7% energy decrease translates to almost 5% gantry size and cost decrease for both ions. These energy limits in combination with the WED in the AP direction for lung patients resulted in average non‐coplanar angles of φ430MeV/u = 68°±8° and φ400MeV/u = 65°±10° if nozzle clearance permits them.

Conclusion:

We found that the two worldwide most common maximum carbon beam energies will treat above 80% of all our patients.
SU‐E‐T‐543: Measurement of Neutron Activation From Different High Energy Varian Linear Accelerators
Authors: Thatcher T , Meigooni A Soleimani , Madsen S , Sudowe R
Published: June 2015

Purpose:

Linear accelerators producing photons above 10 MeV may induce photonuclear reactions in high Z components of the accelerator. These liberated neutrons can then activate the structural components of the accelerator and other materials in the beam path through neutron capture reactions. The induced activity within the accelerator may contribute to additional dose to both patients and personnel. This project seeks to determine the total activity and activity per activated isotope following irradiation in different Varian accelerators at energies above 10 MeV.

Methods:

A Varian 21IX accelerator was used to irradiate a 30 cm × 30 cm × 20 cm solid water phantom with 15 MV x‐rays. The phantom was placed at an SSD of 100 cm and at the center of a 20 cm × 20 cm field. Activation induced gamma spectra were acquired over a 5 minute interval after 1 and 15 minutes from completion of the irradiation. All measurements were made using a CANBERRA Falcon 5000 Portable HPGe detector. The majority of measurements were made in scattering geometry with the detector situated at 90° to the incident beam, 30 cm from the side of the phantom and approximately 10 cm from the top. A 5 minute background count was acquired and automatically subtracted from all subsequent measurements. Photon spectra were acquired for both open and MLC fields.

Results:

Based on spectral signatures, nuclides have been identified and their activities calculated for both open and MLC fields. Preliminary analyses suggest that activities from the activation products in the microcurie range.

Conclusion:

Activation isotopes have been identified and their relative activities determined. These activities are only gross estimates since efficiencies have not been determined for this source‐detector geometry. Current efforts are focused on accurate determination of detector efficiencies using Monte Carlo calculations.
SU‐E‐T‐544: Microscopic Dose Enhancement of Gold Nanoparticles in Water for Proton Therapy: A Simulation Study
Authors: Newpower M , Ahmad S , Chen Y
Published: June 2015

Purpose:

To quantify the microscopic dose and linear energy transfer (LET) enhancement of gold nanoparticles (GNPs) in water for proton therapy.

Methods:

The GEANT4 toolkit (version 10) with low energy electromagnetic classes was used to create a series of simulations where three radii (r=5, 20, 100 nm) of gold nanoparticles (GNPs) were irradiated with 5 × 106 80 MeV protons. A cubic detector (10 × 10 × 10 um, divided in 25 × 25 × 25 voxels) were placed in a water phantom where the GNP rests in the center. The size of incident proton beam was set to be same as the GNPs and perpendicularly aiming to the target. Dose deposited to each voxel were recorded to calculate the overall deposited dose and the dose‐averaged LET. The emitted secondary electron spectra were also collected in a spherical customized scorer (radius = 150 nm).

Results:

The average dose from a single GNP in a cubic water phantom was increased by 0.12 %, 1.12% and 2.3% and the mean dose‐averaged LET was increased by 5.87% and 27.67% and 0.31% for GNP radius of 5 nm, 20 nm and 100 nm, respectively.

Conclusion:

The dose enhancement effect from the presence of a single GNP was qualified in a water phantom. A significant increase in the mean dose‐averaged LET was found for 20 nm GNP.