bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐771: Two Dimensional Raman Mapping of Carbon Bonds of Radiochromic Films: An Approach to Micro‐Dosimetry
Authors: Heo T , Ye S
Published: June 2015

Purpose:

To study a feasibility of micro‐dosimetry with high dose‐sensitivity and resolution using two‐dimensional Raman mapping on the basis of carbon bonds concentration of radiochromic films

Methods:

Unlaminated EBT3 films with the purpose of maximal Raman data acquisition were irradiated by 6 MV beam from 5 MU to 1000 MU at the reference condition. Each film was irradiated with shielding material of lead blocking on the half of film as well as the jaw open in half for distinct dose contrast. Raman peaks of 2070 cm‐1, 2095 cm‐1, and 2115 cm‐1 were major subjects to study, which are assumed to be the spectroscopy of carbon triple bonds of monomers, carbon double bonds of polymers, and carbon triple bonds of polymers, respectively. Laser exposure for Raman spectroscopy generated peak's trend due to polymerization by laser output and this trend was utilized to find out basic peaks related to polymerization process. The relative dose contrast in each one film was detected by Raman spectroscopy with the aid of an auto‐scanning stage, comparing the dose contrast between non‐irradiated area and irradiated area. Raman spatial resolution was enhanced up to 20 micrometers, assuming the spatial uniformity of radio¬active rod‐shaped LiPCDA crystals. An optical scanner with 9600 dpi was used to scan the red‐channel intensity to read the dose contrast for 5 MU delivered film.

Results:

The peak intensity for Raman wavenumber of 2070 cm‐1 was used for mapping since it reflected the different peak intensities based on polymerization degree by irradiation. Dose contrast from 1000MU to 5 MU was distinguished by Raman mapping analysis, whereas optical intensity of red‐channel didn't show any difference.

Conclusion:

In consideration of laser effect, the quantitative analysis based on raw data of Raman mapping could provide more statistically reliable dosimetry than point measurements.
SU‐E‐T‐775: Use of Electronic Portal Imaging Device (EPID) for Quality Assurance (QA) of Electron Beams On Varian Truebeam System
Authors: Cai B , Yaddanapudi S , Sun B , Li H , Noel C , Mutic S , Goddu S
Published: June 2015

Purpose:

In a previous study we have demonstrated the feasibility of using EPID to QA electron beam parameters on a single Varian TrueBeam LINAC. This study aims to provide further investigation on (1) reproducibility of using EPID to detect electron beam energy changes on multiple machines and (2) evaluation of appropriate calibration methods to compare results from different EPIDs.

Methods:

Ad‐hoc mode electron beam images were acquired in developer mode with XML code. Electron beam data were collected on a total of six machines from four institutions. A custom‐designed double‐wedge phantom was placed on the EPID detector. Two calibration methods ‐ Pixel Sensitivity Map (PSM) and Large Source‐to‐Imager Distance Flood Field (LSID‐FF) ‐ were used. To test the sensitivity of EPID in detecting energy drifts, Bending Magnet Current (BMC) was detuned to invoke energy changes corresponding to ∼±1.5 mm change in R50% of PDD on two machines from two institutions. Percent depth ionization (PDI) curves were then analyzed and compared with the respective baseline images using LSID‐FF calibration. For reproducibility testing, open field EPID images and images with a standard testing phantom were collected on multiple machines. Images with and without PSM correction for same energies on different machines were overlaid and compared.

Results:

Two pixel shifts were observed in PDI curve when energy changes exceeded the TG142 tolerance. PSM showed the potential to correct the differences in pixel response of different imagers. With PSM correction, the histogram of images differences obtained from different machines showed narrower distributions than those images without PSM correction.

Conclusion:

EPID is sensitive for electron energy changes and the results are reproducible on different machines. When overlaying images from different machines, PSM showed the ability to partially eliminate the intrinsic variation of various imagers.

Research Funding from Varian Medical Systems Inc.Dr. Sasa Mutic receives compensation for providing patient safety training services from Varian Medical Systems, the sponsor of this study.
SU‐E‐T‐782: Using Light Output From Doped Plastic Scintillators to Resolve the Linear Energy Transfer Spectrum of Clinical Electron Beams
Authors: Nusrat H , Pang G , Ahmad S , Keller B , Sarfehnia A
Published: June 2015

Purpose:

This research seeks to develop a portable, clinically‐suitable linear energy transfer (LET) detector. In radiotherapy, absorbed dose is commonly used to measure the amount of delivered radiation, though, it is not a good indicator of actual biological damage. LET is the energy absorbed per unit length by a medium along charged particle's pathway; studies have shown that LET correlates well with relative biological effectiveness (RBE).

Methods:

According to Birks’ law, light output of plastic scintillators is stopping‐power dependent. This dependency can be varied through doping by various high‐Z elements. By measuring light output signals of differently doped plastic scintillators (represented by column vector S, where each row corresponds to different scintillator material), the fluence of charged particles of a given LET (represented by column vector Φ, where each row corresponds to different LET bins) can be unfolded by S=R*Φ where R is system response matrix (each row represents a different scintillator, each column corresponds to different electron LET). Monte Carlo (MC) GEANT4.10.1 was used to evaluate ideal detector response of BC408 scintillating material doped with various concentrations of several high Z dopants. Measurements were performed to validate MC.

Results:

Signal for 1%‐lead doped BC408 and the non‐doped scintillator was measured experimentally by guiding light emitted by the scintillator (via in‐house made taper, fiber system) to a PMT and then an electrometer. Simulations of 1%Pb‐doped scintillator to non‐doped scintillator revealed 9.3% reduction in light output for 6 MeV electrons which compared well (within uncertainty) with measurements showing 10% reduction (6MeV electrons).

Conclusion:

Measurements were used to validate MC simulation of light output from doped scintillators. The doping of scintillators is a viable technique to induce LET dependence. Our goal is to use this effect to resolve the LET spectrum of an incident beam.
SU‐E‐T‐785: Using Systems Engineering to Design HDR Skin Treatment Operation for Small Lesions to Enhance Patient Safety
Authors: Saw C , Baikadi M , Peters C , Brereton H
Published: June 2015

Purpose:

Using systems engineering to design HDR skin treatment operation for small lesions using shielded applicators to enhance patient safety.

Methods:

Systems engineering is an interdisciplinary field that offers formal methodologies to study, design, implement, and manage complex engineering systems as a whole over their life‐cycles. The methodologies deal with human work‐processes, coordination of different team, optimization, and risk management. The V‐model of systems engineering emphasize two streams, the specification and the testing streams. The specification stream consists of user requirements, functional requirements, and design specifications while the testing on installation, operational, and performance specifications. In implementing system engineering to this project, the user and functional requirements are (a) HDR unit parameters be downloaded from the treatment planning system, (b) dwell times and positions be generated by treatment planning system, (c) source decay be computer calculated, (d) a double‐check system of treatment parameters to comply with the NRC regulation. These requirements are intended to reduce human intervention to improve patient safety.

Results:

A formal investigation indicated that the user requirements can be satisfied. The treatment operation consists of using the treatment planning system to generate a pseudo plan that is adjusted for different shielded applicators to compute the dwell times. The dwell positions, channel numbers, and the dwell times are verified by the medical physicist and downloaded into the HDR unit. The decayed source strength is transferred to a spreadsheet that computes the dwell times based on the type of applicators and prescribed dose used. Prior to treatment, the source strength, dwell times, dwell positions, and channel numbers are double‐checked by the radiation oncologist. No dosimetric parameters are manually calculated.

Conclusion:

Systems engineering provides methodologies to effectively design the HDR treatment operation that minimize human intervention and improve patient safety.
SU‐E‐T‐786: Utility of Gold Wires to Optimize Intensity Modulation Capacity of a Novel Directional Modulated Brachytherapy Tandem Applicator for Image Guided Cervical Cancer Brachytherapy
Authors: Han D , Safigholi H , Soliman A , Scanderbeg D , Liu Z , Song W
Published: June 2015

Purpose:

To evaluate the impact of using gold wires to differentially fill various channels on plan quality compared with conventional T&R applicator, inside a novel directional modulated brachytherapy (DMBT) tandem applicator for cervical cancer brachytherapy.

Materials and Methods:

The novel DMBT tandem applicator has a 5.4‐mm diameter MR‐compatible tungsten alloy enclosed in a 0.3‐mm thick plastic tubing that wraps around the tandem. To modulate the radiation intensity, 6 symmetric peripheral holes of 1.3‐mm diameter are grooved along the tungsten alloy rod. These grooved holes are differentially filled with gold wires to generate various degrees of directional beams. For example, three different fill patterns of 1) all void, 2) all filled except the hole containing the 192‐Ir source, and 3) two adjacent holes to the 192‐Ir source filled were Monte Carlo simulated. The resulting 3D dose distributions were imported into an in‐house‐coded inverse optimization planning system to generate HDR brachytherapy clinical plans for 19 patient cases. All plans generated were normalized to the same D90 as the clinical plans and D2cc doses of OARs were evaluated. Prescription ranged between 15 and 17.5Gy.

Results:

In general, the plans in case 1) resulted in the highest D2cc doses for the OARs with 11.65±2.30Gy, 7.47±3.05Gy, and 9.84±2.48Gy for bladder, rectum, and sigmoid, respectively, although the differences were small. For the case 2), D2cc doses were 11.61±2.29Gy, 7.41±3.07Gy, and 9.75±2.45Gy, respectively. And, for the case 3), D2cc doses were 11.60±2.28Gy, 7.41±3.05Gy, and 9.74±2.45Gy, respectively. Difference between 1) and 2) cases were small with the average D2cc difference of <0.64%. Difference between 1) and 3) cases were even smaller with the average D2cc difference of <0.1%.

Conclusions:

There is a minimal clinical benefit by differentially filling grooved holes in the novel DMBT tandem applicator for image guided cervical cancer brachytherapy.
SU‐E‐T‐789: Validation of 3DVH Accuracy On Quantifying Delivery Errors Based On Clinical Relevant DVH Metrics
Authors: Ma T , Kumaraswamy L
Published: June 2015

Purpose:

Detection of treatment delivery errors is important in radiation therapy. However, accurate quantification of delivery errors is also of great importance. This study aims to evaluate the 3DVH software's ability to accurately quantify delivery errors.

Methods:

Three VMAT plans (prostate, H&N and brain) were randomly chosen for this study. First, we evaluated whether delivery errors could be detected by gamma evaluation. Conventional per‐beam IMRT QA was performed with the ArcCHECK diode detector for the original plans and for the following modified plans: (1) induced dose difference error up to ±4.0% and (2) control point (CP) deletion (3 to 10 CPs were deleted) (3) gantry angle shift error (3 degree uniformly shift). 2D and 3D gamma evaluation were performed for all plans through SNC Patient and 3DVH, respectively. Subsequently, we investigated the accuracy of 3DVH analysis for all cases. This part evaluated, using the Eclipse TPS plans as standard, whether 3DVH accurately can model the changes in clinically relevant metrics caused by the delivery errors.

Results:

2D evaluation seemed to be more sensitive to delivery errors. The average differences between ECLIPSE predicted and 3DVH results for each pair of specific DVH constraints were within 2% for all three types of error‐induced treatment plans, illustrating the fact that 3DVH is fairly accurate in quantifying the delivery errors. Another interesting observation was that even though the gamma pass rates for the error plans are high, the DVHs showed significant differences between original plan and error‐induced plans in both Eclipse and 3DVH analysis.

Conclusion:

The 3DVH software is shown to accurately quantify the error in delivered dose based on clinically relevant DVH metrics, where a conventional gamma based pre‐treatment QA might not necessarily detect.
SU‐E‐T‐793: Validation of COMPASS 3D Dosimetry as Pre Treatment Verification with Commercial TPS Algorithms
Authors: Vikraman S , Manigandan D , Ramu M , Karrthick Kp , Rajesh T , Senniandavar V , Sambasivaselli R , Maragathaveni S , Dhivya N , Muthukumaran M , Tejinder K
Published: June 2015

Purpose:

The purpose of this study was to validate the advent of COMPASS 3D dosimetry as a routine pre treatment verification tool with commercially available CMS Monaco and Oncentra Masterplan planning system.

Methods:

Twenty esophagus patients were selected for this study. All these patients underwent radical VMAT treatment in Elekta Linac and plans were generated in Monaco v5.0 with MonteCarlo(MC) dose calculation algorithm. COMPASS 3D dosimetry comprises an advanced dose calculation algorithm of collapsed cone convolution(CCC). To validate CCC algorithm in COMPASS, The DICOM RT Plans generated using Monaco MC algorithm were transferred to Oncentra Masterplan v4.3 TPS. Only final dose calculations were performed using CCC algorithm with out optimization in Masterplan planning system. It is proven that MC algorithm is an accurate algorithm and obvious that there will be a difference with MC and CCC algorithms. Hence CCC in COMPASS should be validated with other commercially available CCC algorithm. To use the CCC as pretreatment verification tool with reference to MC generated treatment plans, CCC in OMP and CCC in COMPASS were validated using dose volume based indices such as D98, D95 for target volumes and OAR doses.

Results:

The point doses for open beams were observed <1% with reference to Monaco MC algorithms. Comparisons of CCC(OMP) Vs CCC(COMPASS) showed a mean difference of 1.82%±1.12SD and 1.65%±0.67SD for D98 and D95 respectively for Target coverage. Maximum point dose of −2.15%±0.60SD difference was observed in target volume. The mean lung dose of −2.68%±1.67SD was noticed between OMP and COMPASS. The maximum point doses for spinal cord were −1.82%±0.287SD.

Conclusion:

In this study, the accuracy of CCC algorithm in COMPASS 3D dosimetry was validated by compared with CCC algorithm in OMP TPS. Dose calculation in COMPASS is feasible within < 2% in comparison with commercially available TPS algorithms.
SU‐E‐T‐795: Validations of Dose Calculation Accuracy of Acuros BV in High‐Dose‐Rate (HDR) Brachytherapy with a Shielded Cylinder Applicator Using Monte Carlo Simulation
Authors: Li Y , Tian Z , Hrycushko B , Jiang S , Jia X
Published: June 2015

Purpose:

Acuros BV has become available to perform accurate dose calculations in high‐dose‐rate (HDR) brachytherapy with phantom heterogeneity considered by solving the Boltzmann transport equation. In this work, we performed validation studies regarding the dose calculation accuracy of Acuros BV in cases with a shielded cylinder applicator using Monte Carlo (MC) simulations.

Methods:

Fifteen cases were considered in our studies, covering five different diameters of the applicator and three different shielding degrees. For each case, a digital phantom was created in Varian BrachyVision with the cylinder applicator inserted in the middle of a large water phantom. A treatment plan with eight dwell positions was generated for these fifteen cases. Dose calculations were performed with Acuros BV. We then generated a voxelized phantom of the same geometry, and the materials were modeled according to the vendor's specifications. MC dose calculations were then performed using our in‐house developed fast MC dose engine for HDR brachytherapy (gBMC) on a GPU platform, which is able to simulate both photon transport and electron transport in a voxelized geometry. A phase‐space file for the Ir‐192 HDR source was used as a source model for MC simulations.

Results:

Satisfactory agreements between the dose distributions calculated by Acuros BV and those calculated by gBMC were observed in all cases. Quantitatively, we computed point‐wise dose difference within the region that receives a dose higher than 10% of the reference dose, defined to be the dose at 5mm outward away from the applicator surface. The mean dose difference was ∼0.45%–0.51% and the 95‐percentile maximum difference was ∼1.24%–1.47%.

Conclusion:

Acuros BV is able to accurately perform dose calculations in HDR brachytherapy with a shielded cylinder applicator.
SU‐E‐T‐799: Verification of a Simultaneous Treatment of Multiple Brain Metastases Using VMAT Technique by a Composite Alanine‐Gel Dosimeter Phantom
Authors: Pavoni J , Neves W , Silveira M , Ramos P , Haddad C , Filho O Baffa
Published: June 2015

Purpose:

This work presents an end‐to‐end test using a Gel‐Alanine phantom to validate the three‐dimensional (3D) dose distribution (DD) delivered by a single isocenter VMAT technique on the simultaneous treatment of multiple brain metastases.

Methods:

Three cylindrical phantons containing MAGIC‐f gel dosimeter were used to measure the 3D DD of a VMAT treatment, the first two were filled with the gel dosimeter (Gel 1 and 2) and the third one was filled with gel and 12 alanine dosimeters distributed along it (Gel 3). Gels 1 and 3 were irradiated and gel 2 was used to map the magnetic resonance image (MRI) scanner field inomogeneities. A CT scan of gel 3 was used for the VMAT treatment planning and 5 alanine pellets were chosen as lesions, around them a PTV was grown and different dose prescriptions were assigned for each one, varying from 5 to 9Gy. Before treatment, the plan was approved in a QA based on an ionization chamber absolute dose measurement, a radiochromic film planar dose measurement and a portal dosimetry per field verification; and also the phantons positioning were verified by ExacTrac 6D correction and OBI kV Cone Beam CT. The gels were irradiated, the MRIs were acquired 24 hours after irradiation and finally, the alanine dosimeters were analysed in a X‐band Electron Spin Resonance spectrometer.

Results:

The association of the two detectors enabled the 3D dose evaluation by gel and punctually inside target volumes by alanine. In the gamma analyses (3%/3mm) comparing the 5 PTVs’ central images DD with TPS expected DD more than 95% of the points were approved. The alanine absolute dose measurements were in agreement with TPS by less than 5%.

Conclusion:

The gel‐alanine phantom enabled the dosimetric validation of multiple brain metastases treatment using VMAT, being an almost ideal tool for this application.

This work is partially supported by FAPESP.
SU‐E‐T‐802: Verification of Implanted Cardiac Pacemaker Doses in Intensity‐Modulated Radiation Therapy: Dose Prediction Accuracy and Reduction Effect of a Lead Sheet
Authors: Lee J , Chung J
Published: June 2015

Purpose:

To verify delivered doses on the implanted cardiac pacemaker, predicted doses with and without dose reduction method were verified using the MOSFET detectors in terms of beam delivery and dose calculation techniques in intensity‐modulated radiation therapy (IMRT).

Methods:

The pacemaker doses for a patient with a tongue cancer were predicted according to the beam delivery methods [step‐and‐shoot (SS) and sliding window (SW)], intensity levels for dose optimization, and dose calculation algorithms. Dosimetric effects on the pacemaker were calculated three dose engines: pencil‐beam convolution (PBC), analytical anisotropic algorithm (AAA), and Acuros‐XB. A lead shield of 2 mm thickness was designed for minimizing irradiated doses to the pacemaker. Dose variations affected by the heterogeneous material properties of the pacemaker and effectiveness of the lead shield were predicted by the Acuros‐XB. Dose prediction accuracy and the feasibility of the dose reduction strategy were verified based on the measured skin doses right above the pacemaker using mosfet detectors during the radiation treatment.

Results:

The Acuros‐XB showed underestimated skin doses and overestimated doses by the lead‐shield effect, even though the lower dose disagreement was observed. It led to improved dose prediction with higher intensity level of dose optimization in IMRT. The dedicated tertiary lead sheet effectively achieved reduction of pacemaker dose up to 60%.

Conclusion:

The current SS technique could deliver lower scattered doses than recommendation criteria, however, use of the lead sheet contributed to reduce scattered doses.Thin lead plate can be a useful tertiary shielder and it could not acuse malfunction or electrical damage of the implanted pacemaker in IMRT. It is required to estimate more accurate scattered doses of the patient with medical device to design proper dose reduction strategy.
SU‐E‐T‐808: Volumetric Modulated Arc Radiotherapy Vs. Intensity‐Modulated Radiotherapy for Early‐Stage Nasopharyngeal Carcinoma: A Dosimetric Study
Authors: Lu J‐Y , Huang B‐T , Zhang W‐Z
Published: June 2015

Purpose:

To compare volumetric modulated arc radiotherapy (VMAT) technique with fixed‐gantry intensity‐modulated radiotherapy (IMRT) technique for early‐stage nasopharyngeal carcinoma.

Methods:

CT datasets of ten patients with early‐stage nasopharyngeal carcinoma were included. Dual‐arc VMAT and nine‐field IMRT plans were generated for each case, and were then compared in terms of planning‐target‐volume (PTV) coverage, conformity index (CI) and homogeneity index (HI), as well as organ‐at‐risk (OAR) sparing, planning time, monitor units (MUs) and delivery time.

Results:

Compared with the IMRT plans, the VMAT plans provided comparable HI and CI of PTVnx (PTV of primary tumor of nasopharynx), superior CI and inferior HI of PTVnd (PTV of lymph nodes), as well as superior CI and comparable HI of PTV60 (high‐risk PTV). The VMAT plans provided better sparing of the spinal cord, oral cavity and normal tissue, but inferior sparing of the brainstem planning OAR volume (PRV), larynx and parotids, as well as comparable sparing of the spinal cord PRV, brainstem, lenses, optic nerves, optic chiasm. Moreover, the average planning time (181.6 ± 36.0 min) for the VMAT plans was 171% more than that of the IMRT plans (68.1 ± 7.6 min). The MUs of the VMAT plans (609 ± 43) were 70% lower than those of the IMRT plans (2071 ± 262), while the average delivery time (2.2 ± 0.1 min) was 66% less than that of the IMRT plans (6.6 ± 0.4 min).

Conclusion:

Compared with the IMRT technique, the VMAT technique can achieve similar or slightly superior target dose distribution, with no significant advantages on OAR sparing, and it can achieve significant reductions of MUs and delivery time.
SU‐E‐T‐809: Volumetric Modulated Arc Radiotherapy Vs. Intensity‐Modulated Radiotherapy for Locally Advanced Laryngeal Carcinoma: A Dosimetric Study
Authors: Lu J‐Y , Huang B‐T , Zhang W‐Z , Yan L‐J
Published: June 2015

Purpose:

To compare volumetric modulated arc radiotherapy (VMAT) technique with fixed‐gantry intensity‐modulated radiotherapy (IMRT) technique for locally advanced laryngeal carcinoma.

Methods:

CT datasets of eleven patients were included. Dual‐arc VMAT and 7‐field IMRT plans, which were created based on the Eclipse treatment planning system, were compared in terms of dose‐volume parameters, conformity index (CI) and homogeneity index (HI) of planning target volume (PTV), as well as organ‐at‐risk (OAR) sparing, planning time, monitor units (MUs) and delivery time.

Results:

Compared with the IMRT plans, the VMAT plans provided lower D2% and better CI/HI for the high‐risk PTV (PTV1), and provided better CI and comparable HI for the low‐risk PTV (PTV2). Concerning the OAR sparing, the VMAT plans demonstrated significantly lower Dmax of the spinal cord (planning OAR volume, PRV) and brainstem (PRV), as well as lower Dmean and V30Gy of the right parotid. No significant differences were observed between the two plans concerning the doses delivered to the thyroid, carotid, oral cavity and left parotid. Moreover, the VMAT planning (147 ± 18 min) consumed 213% more time than the IMRT planning (48 ± 10 min). The MUs of the VMAT plans (556 ± 52) were 64% less than those of the IMRT plans (1684 ± 409), and the average delivery time (2.1 ± 0.1 min) was 66% less than that of the IMRT plans (6.3 ± 0.7 min).

Conclusion:

Compared with the IMRT technique, the VMAT technique can achieve superior target dose distribution and better sparing of the spinal cord, brainstem and right parotid, with less MUs and less delivery time. It is recommended for the radiotherapy of locally advanced laryngeal carcinoma.
SU‐E‐T‐811: Volumetric Modulated Arc Therapy Vs. C‐IMRT for the Treatment of Upper Thoracic Esophageal Cancer
Authors: Zhang W , Wu L , Lu J , Chen C
Published: June 2015

Purpose:

To compare plans using volumetric‐modulated arc therapy (VMAT) with conventional sliding window intensity‐modulated radiation therapy (c‐IMRT) to treat upper thoracic esophageal cancer (EC).

Methods:

CT datasets of 11 patients with upper thoracic EC were identified. Four plans were generated for each patient: c‐IMRT with 5 fields (5F) and VMAT with a single arc (1A), two arcs (2A), or three arcs (3A). The prescribed doses were 64 Gy/32 F for the primary tumor (planning target volume 64, PTV64). The dose‐volume histogram data, the number of monitoring units (MUs) and the treatment time (TT) for the different plans were compared.

Results:

All of the plans generated similar dose distributions for PTVs and organs at risk (OARs), except that the 2A‐ and 3A‐VMAT plans yielded a significantly higher conformity index (CI) than the c‐IMRT plan. The CI of the PTV64 was improved by increasing the number of arcs in the VMAT plans. The maximum spinal cord dose and the planning risk volume of the spinal cord dose for the two techniques were similar. The 2A‐ and 3A‐VMAT plans yielded lower mean lung doses and heart V50 than the c‐IMRT. The V20 and V30 for the lungs in all of the VMAT plans were lower than those in the c‐IMRT plan, at the expense of increasing V5, V10 and V13. The VMAT plan resulted in significant reductions in MUs and TT.

Conclusion:

The 2A‐VMAT plan appeared to spare the lungs from moderate‐dose irradiation most effectively of all plans, at the expense of increasing the low‐dose irradiation volume, and also significantly reduced the number of required MUs and the TT. The CI of the PTVs and the OARs was improved by increasing the arc‐number from 1 to 2. however, no significant improvement was observed using the 3A‐VMAT, except for an increase in the TT.

This work was sponsored by Shantou University Medical College Clinical Research Enhancement Initiative(NO.201424)
SU‐E‐T‐813: What Is the “real” Field‐Size in Photon Dosimetry?
Authors: Gainey M , Kollefrath M , Saum R , Bruggmoser G
Published: June 2015

Purpose:

The definition of field sizes in photon dosimetry and the measurement of profiles are non‐trivial. Current definitions are nominal, geometric, dosimetric (actual) or equivalent field size. In reality most detectors are not water equivalent since they contain air or high density materials. These materials can blur profiles, particularly in small fields. If necessary, detector and field size‐specific volume dependent effects need to be considered.

Methods:

A TrueBeam‐linac (Varian Medical Systems) was used. All measurements were performed within a water phantom (MP3, PTW‐Freiburg), with filter (WFF) and without filter (FFF), using ionization chambers, shielded and unshielded diodes and diamond detectors. The position of the jaws was verified according to our QA‐system. Field size profiles were taken at a defined depth (SSD =90 cm, SCD=100 cm). The penumbra of the profiles measured with the various detectors was compared to determine the dosimetric field size. For the evaluation of the field sizes the inclination points were also calculated.

Results:

The field size, both for the WFF and the FFF‐mode, coincided within 1 mm of the nominal field size. Due to the fact that the jaws were adjusted properly, the dosimetric field size coincides with the geometric field size. Exceptions are very small fields, where the dosimetric field size, defined by the inclination points, becomes broader than the geometric field size.

Conclusion:

Profiles, particularly of small fields, have to be measured very carefully using a suitable detector. For this purpose, a detector with a negligible volume correction factor should be used. The dosimetric field size can be found by evaluating the inclination points for both WFF and FFF beams. For dosimetric purposes it is necessary to find the dosimetric size. Alternatively, if the measurements are basic data for a TPS, both, the geometric and the dosimetric sizes should be recorded.
SU‐E‐T‐814: Whole Breast Irradiation with Two Different Intensity Modulation Radiotherapy Techniques
Authors: Sun T , Yin Y , Lin X , Zhang G
Published: June 2015

Purpose:

Breast cancer now mainly received forward intensity modulation radiotherapy (f‐IMRT) and inverse IMRT (i‐IMRT). The purpose of this study was to observe the differences of two treatment methods.

Methods:

10 patients after left breast‐conserving surgery were selected to receive radiotherapy. For each patient, two treatment plans (f‐IMRT and i‐IMRT) were designed. For f‐IMRT plans, two tangent beams were designed to the target, and in each tangent orientation two or three segment beams were designed to reduced high dose region in the target and the dose of lung received. For i‐IMRT plans, two tangent beams were designed to the target and the treatment planning system optimize the dose according to the optimization parameters. For each plan 50Gy was prescribed.

Results:

In f‐IMRT and i‐IMRT plans, the average target conformal index (CI) were (0.67±0.06) and (0.66±0.06), (P>0.05); average homogeneity index (HI) were (28.2±6.0)% and (26.1±6.8)%, (P>0.05); volume of left lung received 20Gy (V20) were (18.7±3.3)% and (17.0±2.8)%, (P<0.05), V30 were (15.5±3.0)% and (14.0±2.6)%, (P<0.05); V30 of heart were (4.1±3.1)% and (3.5±2.5)%, (P>0.05); Monitor Unit (MU) were (262±5)MU and (308±14)MU.

Conclusion:

Compared with i‐IMRT plan, for breast cancer, the differences of CI and HI were not significant. Because of fewer MU, f‐IMRT plan could reduce the machine abrasion and treatment time, but dose of normal tissue received were higher significantly than i‐IMRT plan.
SU‐F‐BRD‐01: A Novel 4D Robust Optimization Mitigates Interplay Effect in Intensity‐Modulated Proton Therapy for Lung Cancer
Authors: Liu W , Schild S , Chang J , Liao Z , Wen Z , Shen J , Stoker J , Wong W , Sahoo N , Herman M , Mohan R , Bues M
Published: June 2015

Purpose:

To compare the impact of interplay effect on 3D and 4D robustly optimized intensity‐modulated proton therapy (IMPT) plans to treat lung cancer.

Methods:

Two IMPT plans were created for 11 non‐small‐cell‐lung‐cancer cases with 6–14 mm spots. 3D robust optimization generated plans on average CTs with the internal gross tumor volume density overridden to deliver 66 CGyE in 33 fractions to the internal target volume (ITV). 4D robust optimization generated plans on 4D CTs with the delivery of prescribed dose to the clinical target volume (CTV). In 4D optimization, the CTV of individual 4D CT phases received non‐uniform doses to achieve a uniform cumulative dose. Dose evaluation software was developed to model time‐dependent spot delivery to incorporate interplay effect with randomized starting phases of each field per fraction. Patient anatomy voxels were mapped from phase to phase via deformable image registration to score doses. Indices from dose‐volume histograms were used to compare target coverage, dose homogeneity, and normal‐tissue sparing. DVH indices were compared using Wilcoxon test.

Results:

Given the presence of interplay effect, 4D robust optimization produced IMPT plans with better target coverage and homogeneity, but slightly worse normal tissue sparing compared to 3D robust optimization (unit: Gy) [D95% ITV: 63.5 vs 62.0 (p=0.014), D5% ‐ D95% ITV: 6.2 vs 7.3 (p=0.37), D1% spinal cord: 29.0 vs 29.5 (p=0.52), Dmean total lung: 14.8 vs 14.5 (p=0.12), D33% esophagus: 33.6 vs 33.1 (p=0.28)]. The improvement of target coverage (D95%,4D – D95%,3D) was related to the ratio RMA3/(TVx10−4), with RMA and TV being respiratory motion amplitude (RMA) and tumor volume (TV), respectively. Peak benefit was observed at ratios between 2 and 10. This corresponds to 125 – 625 cm3 TV with 0.5‐cm RMA.

Conclusion:

4D optimization produced more interplay‐effect‐resistant plans compared to 3D optimization. It is most effective when respiratory motion is modest compared to TV.

NIH/NCI K25CA168984; Eagles Cancer Research Career Development; The Lawrence W. and Marilyn W. Matteson Fund for Cancer Research; Mayo ASU Seed Grant; The Kemper Marley Foundation
SU‐F‐BRD‐02: Incorporating Uncertainty Analysis in Plan Comparison of VMAT, Double Scattering Proton Plan and IMPT for Lung Irradiation
Authors: Cheng C , Wessels B , Mansur D , Machtay M
Published: June 2015

Purpose:

We investigate the effect of residual setup and motion errors in lung irradiation for VMAT, double scattering (DS) proton beams and spot scanning (IMPT) in a case study.

Methods:

The CT image and contour sets of a lung patient treated with 6 MV VMAT is re‐planned with DS as well as IMPT subject to the same constraints; V20(lung), V10(lung) and V5(lung)< 15%, 20% and 25% respectively, V20(heart)<25% and V100%(PTV)≥95%. In addition, uncertainty analysis in the form of isocenter shifts (±1–3mm) was incorporated in the DVH calculations to assess the plan robustness.

Results:

Only the IMPT plan satisfies all the specified constraints. The 3D‐conformal DS proton plan is able to achieve better sparing of the lung and heart dose compared to VMAT. For the lung, V20, V10 and V5 are 13%, 19% and 25% respectively for IMPT, 18%, 23% and 30% respectively for DS, and 20%, 30% and 42% respectively for VMAT. For heart: 0.6% for IMPT, 2.4% for DS and 30% for VMAT. When incorporating isocenter shifts in DVH calculations, the maximum changes in V20, V10 and V5 for lung are 14%, 21% and 28% respectively for IMPT. The corresponding max changes are19%, 24% and 32% respectively for DS, and 22%, 32% and 44% respectively for VMAT. The largest change occurs in the PTV coverage. For IMPT, V100%(PTV) varies between 88–96%, while V100%(PTV) for VMAT suffers a larger change compared to DS (Δ=5.5% vs 3.3%).

Conclusion:

While only IMPT satisfies the stringent dose‐volume constraints for the lung irradiation, it is not as robust as the 3D conformal DS plan. DS also has better sparing in lung and heart compared to VMAT and similar PTV coverage. By including isocenter shifts in dose‐volume calculations in treatment planning of lung, DS appears to be more robust than VMAT.
SU‐F‐BRD‐03: Evaluation of Head‐Neck IMPT Plans Quality Using a Knowledge Based Model
Authors: Jingqian W , Yuan L , Li Y , Li H , Frank S , Wu Q , Zhang X
Published: June 2015

Purpose:

To develop and evaluate a model that predicts the dose volume histogram (DVH) of head and neck IMPT plans based on knowledge of prior plans.

Methods:

Total of forty Head‐Neck cancer patients underwent IMPT were used in the study. Using thirty patient CT, contours, IMPT treatment plans and calculated dose as input, significant factors that predicts the dose volume histogram (DVH) for organs at risks (OARs) including right/left parotid, oral cavity, esophagus, brain stem, larynx, and spinal cord were identified using principle component analysis (PCA) method. The model was then evaluated by comparing model predicted DVH for with planned DVH for ten additional IMPT plans.

Results:

Combined distance‐to‐target Histogram (DTH) Principal Components (PCs) were found to be the most important in the first principal component of parotids, oral cavity, and esophagus. The quality of the model prediction is correlated to the knowledge or quantities of the plans that model learned. For patients with tumor and OARs geometry deviates from the training data set, the predicted DVH may be inferior to the actual treatment plans. For patients with tumor and OARs geometry similar to the training data set, the model was able to predict the performance of the actual treatment plan.

Conclusion:

The quality of DVH prediction knowledge base model was investigated using head‐neck plans. The results indicated that the performance of the model is dependent on the quality and quantity of the training data set. The prediction model may provide real time evaluations for plan optimization in complex patient geometries such as head and neck cancer with multiple dose levels.

Supported by Research agreement with Varian Medical Systems.
SU‐F‐BRD‐04: Robustness Analysis of Proton Breast Treatments Using An Alpha‐Stable Distribution Parameterization
Authors: Van den Heuvel F , Hackett S , Fiorini F , Taylor C , Darby S , Vallis K
Published: June 2015

Purpose:

Currently, planning systems allow robustness calculations to be performed, but a generalized assessment methodology is not yet available. We introduce and evaluate a methodology to quantify the robustness of a plan on an individual patient basis.

Methods:

We introduce the notion of characterizing a treatment instance (i.e. one single fraction delivery) by describing the dose distribution within an organ as an alpha‐stable distribution. The parameters of the distribution (shape(α), scale(γ), position(δ), and symmetry(β)), will vary continuously (in a mathematical sense) as the distributions change with the different positions. The rate of change of the parameters provides a measure of the robustness of the treatment. The methodology is tested in a planning study of 25 patients with known residual errors at each fraction. Each patient was planned using Eclipse with an IBA‐proton beam model. The residual error space for every patient was sampled 30 times, yielding 31 treatment plans for each patient and dose distributions in 5 organs. The parameters’ change rate as a function of Euclidean distance from the original plan was analyzed.

Results:

More than 1,000 dose distributions were analyzed. For 4 of the 25 patients the change in scale rate (γ) was considerably higher than the lowest change rate, indicating a lack of robustness. The sign of the shape change rate (α) also seemed indicative but the experiment lacked the power to prove significance.

Conclusion:

There are indications that this robustness measure is a valuable tool to allow a more patient individualized approach to the determination of margins. In a further study we will also evaluate this robustness measure using photon treatments, and evaluate the impact of using breath hold techniques, and the a Monte Carlo based dose deposition calculation. A principle component analysis is also planned.
SU‐F‐BRD‐10: Improving Plan Delivery Efficiency of Intensity Modulated Proton Plans with Prioritized Optimization
Authors: Müller BS , Wilkens JJ
Published: June 2015

Purpose:

To integrate treatment delivery time into plan optimization in spot scanning intensity modulated proton therapy. Utilizing a dedicated research treatment planning system we present an optimization approach to explore the trade‐off between the correlated parameters treatment time and plan quality on an astrocytoma patient case.

Methods:

The planning system is based on prioritized optimization, a stepwise approach of implementing clinical goals. After each optimization step, dosimetric achievements are turned into hard constraints to maintain the achieved plan quality. Prior achievements can be violated by a so‐called slip‐factor which allows to study possible trade‐offs of conflicting goals. Plan quality is obtained in the first two steps, while the third step optimizes delivery efficiency by working on the spot weight distribution via four alternative

Methods:

elimination of low weighted spots (1), elimination of spots hardly contributing to PTV dose, followed by reoptimization of the resulting smaller optimization problem (2), reduction of spot weights variance within each energy layer (3), and reduction of the overall spot weight sum (4). Treatment times were calculated assuming either constant or variable beam current depending on the lowest spot weight.

Results:

Delivery efficiency can be improved remarkably without influencing the plan quality. Absolute time savings depend on the utilized method and facility properties. By varying slip‐factor and spot reduction limits, a border of worsening quality is detectable for all methods.Deleting low weighted spots by 10% results in a noticeable decrease in minimum target dose. Further reduction results in more heterogeneous dose distributions and insufficient coverage. Option 2 showed constant plan quality for spot reductions of more than 10%.

Conclusion:

Including treatment time optimization as a final step into prioritized optimization allows for more efficient treatment plans by redistributing the spot patterns without compromising plan quality, which has to remain the main intent of radiotherapy treatment.

The authors report grants from German Research Foundation (DFG) during the conduct of the study.
SU‐F‐BRD‐15: Quality Correction Factors in Scanned Or Broad Proton Therapy Beams Are Indistinguishable
Authors: Sorriaux J , Testa M , Paganetti H , Bertrand D , de Xivry J Orban , Lee J , Palmans H , Vynckier S , Sterpin E
Published: June 2015

Purpose:

The IAEA TRS‐398 code of practice details the reference conditions for reference dosimetry of proton beams using ionization chambers and the required beam quality correction factors (kQ). Pencil beam scanning (PBS) requires multiple spots to reproduce the reference conditions. The objective is to demonstrate, using Monte Carlo (MC) calculations, that kQ factors for broad beams can be used for scanned beams under the same reference conditions with no significant additional uncertainty. We consider hereafter the general Alfonso formalism (Alfonso et al, 2008) for non‐standard beam.

Methods:

To approach the reference conditions and the associated dose distributions, PBS must combine many pencil beams with range modulation and shaping techniques different than those used in passive systems (broad beams). This might lead to a different energy spectrum at the measurement point. In order to evaluate the impact of these differences on kQ factors, ion chamber responses are computed with MC (Geant4 9.6) in a dedicated scanned pencil beam (Q_pcsr) producing a 10×10cm2 composite field with a flat dose distribution from 10 to 16 cm depth. Ion chamber responses are also computed by MC in a broad beam with quality Q_ds (double scattering). The dose distribution of Q _pcsr matches the dose distribution of Q_ds. k_(Q_pcsr,Q_ds) is computed for a 2×2×0.2cm3 idealized air cavity and a realistic plane‐parallel ion chamber (IC).

Results:

Under reference conditions, quality correction factors for a scanned composite field versus a broad beam are the same for air cavity dose response, k_(Q_pcsr,Q_ds) =1.001±0.001 and for a Roos IC, k_(Q_pcsr,Q_ds) =0.999±0.005.

Conclusion:

Quality correction factors for ion chamber response in scanned and broad proton therapy beams are identical under reference conditions within the calculation uncertainties. The results indicate that quality correction factors published in IAEA TRS‐398 can be used for scanned beams in the SOBP of a high‐energy proton beam.

Jefferson Sorriaux is financed by the Walloon Region under the convention 1217662. Jefferson Sorriaux is sponsored by a public‐private partnership IBA ‐ Walloon Region
SU‐F‐BRB‐04: Comparison of Coplanar VMAT, Non‐Coplanar VMAT, and 4π Treatment Plans
Authors: Woods K , Nguyen D , Tran A , Yu V , Cao M , Sheng K
Published: June 2015

Purpose:

The 4π non‐coplanar radiotherapy delivery technique has demonstrated significantly better normal tissue sparing and dose conformality than the clinically used volumetric modulated arc therapy (VMAT). It is unclear whether this is a fundamental limitation of VMAT delivery or the coplanar nature of its typical clinical plans. The non‐coplanar basis of 4π is incorporated into VMAT treatment planning to compare its effect on plan quality.

Methods:

Clinical stereotactic body radiation therapy plans for 9 liver patients treated with 30–60 Gy using coplanar VMAT (cVMAT) were re‐planned using non‐coplanar VMAT (nVMAT) with 3 arcs and 4 π with 20 intensity‐modulated non‐coplanar fields. All plans were optimized to deliver 100% of the prescribed dose to 95% of the planning target volume (PTV), and nVMAT and 4π plans were tailored to match the maximum and mean PTV dose from the clinical plan. The conformality index (CI), 50% dose spillage volume (R50), normal liver volume receiving >15 Gy (VL>15), and doses to organs at risk (OARs) were compared for all three treatment plans.

Results:

Compared to cVMAT, the nVMAT and 4π plans reduced VL>15 by an average of 30.6 cm3 and 96.3 cm3, respectively. The average CI was also reduced from 1.22 (cVMAT) to 1.17 (nVMAT) and 1.14 (4π), indicating higher conformality in the same order. Similarly, R50 was reduced from 3.87 (cVMAT) to 3.58 (nVMAT) and 2.74 (4π). With the exception of the mean right kidney dose, which increased by an average of only 0.6 Gy for nVMAT, the dose differences to OARs were not statistically significant between the two VMAT plans. 4π plans either significantly decreased or maintained OAR doses.

Conclusion:

While the manual selection of intuitive non‐coplanar arcs does show some improvement over coplanar VMAT, the automated beam selection for 4π still results in superior plan quality.

This project is supported in part by Varian Medical Systems and NIH R43 CA183390.
SU‐F‐BRB‐05: Collision Avoidance Mapping Using Consumer 3D Camera
Authors: Cardan R , Popple R
Published: June 2015

Purpose:

To develop a fast and economical method of scanning a patient's full body contour for use in collision avoidance mapping without the use of ionizing radiation.

Methods:

Two consumer level 3D cameras used in electronic gaming were placed in a CT simulator room to scan a phantom patient set up in a high collision probability position. A registration pattern and computer vision algorithms were used to transform the scan into the appropriate coordinate systems. The cameras were then used to scan the surface of a gantry in the treatment vault. Each scan was converted into a polygon mesh for collision testing in a general purpose polygon interference algorithm. All clinically relevant transforms were applied to the gantry and patient support to create a map of all possible collisions. The map was then tested for accuracy by physically testing the collisions with the phantom in the vault.

Results:

The scanning fidelity of both the gantry and patient was sufficient to produce a collision prediction accuracy of 97.1% with 64620 geometry states tested in 11.5 s. The total scanning time including computation, transformation, and generation was 22.3 seconds.

Conclusion:

Our results demonstrate an economical system to generate collision avoidance maps. Future work includes testing the speed of the framework in real‐time collision avoidance scenarios.

Research partially supported by a grant from Varian Medical Systems