bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐527: Is CTV‐Based Robust Optimized IMPT in Non‐Small‐Cell Lung Cancer Robust Against Respiratory Motion?
Authors: Anetai Y , Takegawa H , Inoue T , Mizuno H , Sumida I , Koizumi M , Ogawa K , van't Veld A , Korevaar E
Published: June 2015

Purpose:

To determine which proton planning technique on average‐CT is more vulnerable to respiratory motion induced density changes and interplay effect among (a) IMPT of CTV‐based minimax robust optimization with 5mm set‐up error considered, (b, c) IMPT/SFUD of 5mm‐expanded PTV optimization.

Methods:

Three planning techniques were optimized in Raystation with a prescription of 60/25 (Gy/fractions) and almost the same OAR constraints/objectives for each of 10 NSCLC patients. 4D dose without/with interplay effect was recalculated on eight 4D‐CT phases and accumulated after deforming the dose of each phase to a reference (exhalation phase). The change of D98% of each CTV caused by density changes and interplay was determined. In addition, evaluation of the DVH information vector (D99%, D98%, D95%, Dave, D50%, D2%, D1%) which compares the whole DVH by η score = (cosine similarity × Pearson correlation coefficient − 0.9) × 1000 quantified the degree of DVH change: score below 100 indicates changed DVH.

Results:

Three 3D plans of each technique satisfied our clinical goals. D98% shift mean±SD (Gy) due to density changes was largest in (c): −0.78±1.1 while (a): −0.11±0.65 and (b): − 0.59±0.93. Also the shift due to interplay effect most was (c): −.54±0.70 whereas (a): −0.25±0.93 and (b): −0.12±0.13. Moreover lowest η score caused by density change was also (c): 69, while (a) and (b) kept around 90. η score also indicated less effect of interplay than density changes. Note that generally the changed DVH were still acceptable clinically. Paired T‐tests showed a significantly smaller density change effect in (a) (p<0.05) than in (b) or (c) and no significant difference in interplay effect.

Conclusion:

CTV‐based robust optimized IMPT was more robust against respiratory motion induced density changes than PTV‐based IMPT and SFUD. The interplay effect was smaller than the effect of density changes and similar among the three techniques.

The JSPS Core‐to‐Core Program (No. 23003), Japan Society for the Promotion of Science Grant‐in‐Aid for Scientific Research (No. 23390300), Grant‐in‐Aid for Young Scientists (B) (No. 21791194) and Grant‐in‐Aid for Cancer Research (H22‐3rd Term Cancer Control‐General‐043)
SU‐E‐T‐530: Knowledge‐Based Treatment Planning and Its Potential Role in the Transition Between Treatment Planning Systems
Authors: Masi K , Archer P , Hamstra D , Matuszak M
Published: June 2015

Purpose:

Commissioning a treatment planning system (TPS) involves many tasks, including making sure users have sufficient training and experience to create quality plans. We investigated the role that knowledge‐based planning (KBP) can play in aiding a clinic's transition to a new TPS.

Methods:

60 clinically treated prostate and prostate bed IMRT plans were exported from an in‐house TPS and used to create a KBP‐model in a newly introduced commercial TPS (Eclipse v13.5, Varian Medical Systems). To determine the benefit that KBP may have in a TPS transition, the model was tested on two groups. Group 1 consisted of the first 10 patients treated in the commercial TPS after the transition from the in‐house TPS, Group 2 consisted of 10 patients planned in the commercial TPS, but without the KBP model, after 8 months of clinical use. The KBP‐generated plan for each patient was compared to the clinically‐used plan in terms of quality and planning efficiency.

Results:

On average, the KBP‐generated plans provided better target coverage for group 1 than the clinical plans,and about equivalent coverage for group 2. The average absolute difference (KBP‐clinical) for D95 for the PTV was 0.48±0.49% and −0.11±0.48% for groups 1 and 2, respectively. For the OARs, the KBP‐generated plans produced lower doses for every normal tissue objective except the maximum dose to 0.1cc of rectum (0.50±0.27Gy and 0.22±0.17Gy for groups 1 and 2, respectively). The time needed for KBP‐generated plans ranged from 6– 15min compared to 30–150 and 15–60min for groups 1 and 2, respectively.

Conclusion:

Knowledge‐based planning is a promising tool to aid in transitions to new TPSs. Our study indicates that high‐quality treatment plans could have been generated in the new TPS more efficiently compared to not using KBP. Even after 8 months of clinical use, KBP still showed a quality and efficiency increase compared to manual planning.

Partially supported by Varian Medical Systems
SU‐E‐T‐531: Large‐‐Scale DVH Quality Study: Correlated Aims Lead Relaxations
Authors: Nohadani O , Roy A , Das I
Published: June 2015

Purpose:

Intensity modulated radiation therapy plans are designed to optimally target a tumor while sparing surrounding tissue. Desired dose distributions are iteratively approached via inverse planning. This leads to tradeoffs between clinical objectives for the planning target volume (PTV), organs at risk, and normal tissues. Dose volume histogram (DVHs) related aims are followed that are either institutional or internationally recommended. We analyze common goals and identify potential reasons that often lead to tradeoffs.

Methods:

524 IMRT plans for various tumor sites were analyzed based on the main institutional DVH goal for PTV (D95) and the recommendations by ICRU‐83 (D2, D50, and D98). Robust statistical tools are developed and applied to ensure that the results are immune to data uncertainties. The probability of violation was measured for each of the DVH goals based on the frequency of not meeting recommended doses. Conditional probabilities for satisfying and/or violating DVH aims were computed to test the hypothesized pair‐wise relations between DVH aims. For example, for plans that satisfied D50, the probability of violating D98 was computed via P(D98 < 95% | 98% ≤ D50 ≤ 102%). The equality constraint D50 = 100% was relaxed to encompass the range [98,102]%.

Results:

A large majority of cases (88%) satisfied the institutional goal for PTV of D95 ≤ 95%. Similar consensus existed for D98. 51% of cases satisfied D2 ≥ 107%. However, only 18% of cases satisfied D50. The conditional probability showed correlations amongst the studied DVH goals. In fact, a negative correlation was revealed between D50 and D95 (and D98), suggesting that these competing goals cannot be satisfied concurrently.

Conclusion:

The majority of plans followed the institutional guidelines. The reason for their deviation from international recommendations seems to be that the latter goals are competing and cannot be satisfied concurrently in clinical practice.
SU‐E‐T‐534: Level of Residual Radioactivity of Activated Parts of a Decommissioned Cyclotron
Authors: Choi HHF , Leung TM , Chiu TL , Yang B , Wu PM , Cheung KY , Yu SK
Published: June 2015

Purpose:

CTI cyclotron RDS‐111 was used at the Hong Kong Sanatorium and Hospital (HKSH) to produce radiopharmaceuticals and radioactive tracers for diagnostic scans between 1999 and 2007. During the operation, some machine components became radioactive by activation. For the safety of staff, decommissioning took place in 2009, two years after the cyclotron had stopped operation. This study investigates the residual radioactivity and radionuclides found in different cyclotron components in 2014 in compliance with the local regulations in Hong Kong for transfer of radioactive waste.

Methods:

A representative sample of each part was counted using a high‐purity germanium detector (manufacturer: ORTECT) for at least four hours. GammaVision, a multichannel analyzer software, was used to identify the radionuclides found in the cyclotron components, as well as the associated activities. A standard library and a Mariscotti peak search algorithm were used to identify the present radionuclides. Only radionuclides with half‐life greater than 180 days were considered.

Results:

Among the components, the Havar target foil has the highest specific activity ((4.6±0.6)×102 Bq/g), with Co‐60 being the most prominent ((3.8±0.5)×102 Bq/g). The total activity of the target foil, however, is still low due to its small mass of 0.04 g. Radioisotopes Mn‐54 (46±6 Bq/g), Na‐22 (6.8±0.8 Bq/g), Co‐57 (7.3±0.9 Bq/g), and Fe‐59 (6.0±0.9 Bq/g) have also been detected in the target foil. The target window holder and the vacuum window register a specific activity of 88.3±0.6 Bq/g and 48.6±0.1 Bq/g, respectively. Other components, such as the collimator, the target tube, the valve body and the beamline, are also found with trace amounts of radionuclides.

Conclusion:

Even seven years after the cyclotron had stopped operation, some components still exhibited residual radioactivity from activation exceeding the IAEA clearance levels. Special consideration for radiological protection may need to be taken in the disposal of the cyclotron parts.
SU‐E‐T‐537: Local Multi‐Criteria Optimization for Clinical Tradeoff Decision Guidance in RT Planning
Authors: Yuan L , Wu Q J , Sheng Y , Liu J , Benitez A , Yin F , Ge Y
Published: June 2015

Purpose:

We present a novel method for generating a local segment of Pareto surface around the best achievable plan predicted by a knowledge model. This local‐MCO will provide an efficient method to enable clinically viable tradeoff decisions in IMRT planning tailored to the patient's specific needs.

Methods:

Multi‐criteria optimization (MCO) methods provide physicians and planners the ability to explore tradeoff options in RT planning. However, generic MCO methods are often time consuming because a global Pareto surface (PS) need to be explored if patient‐specific clinical conditions and planners’ planning experiences are not taken into consideration. We have developed a local‐MCO approach, which incorporates the knowledge model prediction based on the individual patient's features and planning experience into the generation of a local PS around a predicted plan. In the proposed method, the starting points of clinical relevant organ sparing objectives are predicted by the knowledge models, and then a local PS is searched near the model predictions. As an initial assessment, the local PS is compared with the global PS generated for two prostate cancer cases. The mean minimum distance from each plan on the local PS to the global PS and the range of clinical acceptable dosimetric parameters covered by the local and global PS are calculated.

Results:

The local PS agrees well with the global PS. The mean minimum distance between the local and global PS in the PTV‐bladder‐rectum dose objective space are about 3% and 1% of prescription dose for the two plans, respectively. Although the local PS is only a small portion of the global PS, they cover most of the clinically relevant dose range.

Conclusion:

The local MCO results in a smaller but clinically more relevant PS. It is an efficient method to provide physicians with guidance of patient‐specific trade‐off options based on practice experience.

Partially supported by NIH/NCI under grant #R21CA161389 and a master research grant by Varian Medical Systems.
SU‐E‐T‐538: Lung SBRT Dosimetric Comparison of 3D Conformal and RapidArc Planning
Authors: Jiang R , Zhan L , Osei E
Published: June 2015

Purpose:

Dose distributions of RapidArc Plan can be quite different from standard 3D conformal radiation therapy. SBRT plans can be optimized with high conformity or mimic the 3D conformal treatment planning with very high dose in the center of the tumor. This study quantifies the dosimetric differences among 3D conformal plan; flattened beam and FFF beam RapidArc Plans for lung SBRT.

Methods:

Five lung cancer patients treated with 3D non‐coplanar SBRT were randomly selected. All the patients were CT scanned with 4DCT to determine the internal target volume. Abdominal compression was applied to minimize respiratory motion for SBRT patients. The prescription dose was 48 Gy in 4 fractions. The PTV coverage was optimized by two groups of objective function: one with high conformity, another mimicking 3D conformal dose distribution with high dose in the center of PTV. Optimization constraints were set to meet the criteria of the RTOG‐0915 protocol. All VMAT plans were optimized with the RapidArc technique using four full arcs in Eclipse treatment planning system. The RapidArc SBRT plans with flattened 6MV beam and 6MV FFF beam were generated and dosimetric results were compared with the previous treated 3D non‐coplanar plans.

Results:

All the RapidArc plans with flattened beam and FFF beam had similar results for the PTV and OARs. For the high conformity optimization group, The DVH of PTV exhibited a steep dose fall‐off outside the PTV compared to the 3D non‐coplanar plan. However, for the group mimicking the 3D conformal target dose distribution, although the PTV is very similar to the 3D conformal plan, the ITV coverage is better than 3D conformal plan.

Conclusion:

Due to excellent clinical experiences of 3D conformal SBRT treatment, the Rapid Arc optimization mimicking 3D conformal planning may be suggested for clinical use.
SU‐E‐T‐549: Modeling Relative Biological Effectiveness of Protons for Radiation Induced Brain Necrosis
Authors: Mirkovic D , Peeler C , Grosshans D , Titt U , Taleei R , Mohan R
Published: June 2015

Purpose:

To develop a model of the relative biological effectiveness (RBE) of protons as a function of dose and linear energy transfer (LET) for induction of brain necrosis using clinical data.

Methods:

In this study, treatment planning information was exported from a clinical treatment planning system (TPS) and used to construct a detailed Monte Carlo model of the patient and the beam delivery system. The physical proton dose and LET were computed in each voxel of the patient volume using Monte Carlo particle transport. A follow‐up magnetic resonance imaging (MRI) study registered to the treatment planning CT was used to determine the region of the necrosis in the brain volume. Both, the whole brain and the necrosis volumes were segmented from the computed tomography (CT) dataset using the contours drawn by a physician and the corresponding voxels were binned with respect to dose and LET. The brain necrosis probability was computed as a function of dose and LET by dividing the total volume of all necrosis voxels with a given dose and LET with the corresponding total brain volume resulting in a set of NTCP‐like curves (probability as a function of dose parameterized by LET).

Results:

The resulting model shows dependence on both dose and LET indicating the weakness of the constant RBE model for describing the brain toxicity. To the best of our knowledge the constant RBE model is currently used in all clinical applications which may Result in increased rate of brain toxicities in patients treated with protons.

Conclusion:

Further studies are needed to develop more accurate brain toxicity models for patients treated with protons and other heavy ions.
SU‐E‐T‐551: Monitor Unit Optimization in Stereotactic Body Radiation Therapy for Stage I Lung Cancer
Authors: Huang B‐T , Lu J‐Y
Published: June 2015

Purpose:

The study aims to reduce the monitor units (MUs) in the stereotactic body radiation therapy (SBRT) treatment for lung cancer by adjusting the optimizing parameters.

Methods:

Fourteen patients suffered from stage I Non‐Small Cell Lung Cancer (NSCLC) were enrolled. Three groups of parameters were adjusted to investigate their effects on MU numbers and organs at risk (OARs) sparing: (1) the upper objective of planning target volume (UOPTV); (2) strength setting in the MU constraining objective; (3) max MU setting in the MU constraining objective.

Results:

We found that the parameters in the optimizer influenced the MU numbers in a priority, strength and max MU dependent manner. MU numbers showed a decreasing trend with the UOPTV increasing. MU numbers with low, medium and high priority for the UOPTV were 428±54, 312±48 and 258±31 MU/Gy, respectively. High priority for UOPTV also spared the heart, cord and lung while maintaining comparable PTV coverage than the low and medium priority group. It was observed that MU numbers tended to decrease with the strength increasing and max MU setting decreasing. With maximum strength, the MU numbers reached its minimum while maintaining comparable or improved dose to the normal tissues. It was also found that the MU numbers continued to decline at 85% and 75% max MU setting but no longer to decrease at 50% and 25%. Combined with high priority for UOPTV and MU constraining objectives, the MU numbers can be decreased as low as 223±26 MU/Gy.

Conclusion::

The priority of UOPTV, MU constraining objective in the optimizer impact on the MU numbers in SBRT treatment for lung cancer. Giving high priority to the UOPTV, setting the strength to maximum value and the max MU to 50% in the MU objective achieves the lowest MU numbers while maintaining comparable or improved OAR sparing.
SU‐E‐T‐553: Monte Carlo Calculation of Proton Bragg Peak Displacements in the Presence of Al2O3:C Dosimeters
Authors: Young L , Yang F
Published: June 2015

Purpose:

The application of optically stimulated luminescence dosimeters (OSLDs) may be extended to clinical investigations verifying irradiated doses in small animal models. In proton beams, the accurate positioning of the Bragg peak is essential for tumor targeting. The purpose of this study was to estimate the displacement of a pristine Bragg peak when an Al2O3:C nanodot (Landauer, Inc.) is placed on the surface of a water phantom and to evaluate corresponding changes in dose.

Methods:

Clinical proton pencil beam simulations were carried out with using TOPAS, a Monte Carlo platform layered on top of GEANT4. Point‐shaped beams with no energy spread were modeled for energies 100MV, 150MV, 200MV, and 250MV. Dose scoring for 100,000 particle histories was conducted within a water phantom (20cm × 20cm irradiated area, 40cm depth) with its surface placed 214.5cm away from the source. The modeled nanodot had a 4mm radius and 0.2mm thickness.

Results:

A comparative analysis of Monte Carlo depth dose profiles modeled for these proton pencil beams did not demonstrate an energy dependent in the Bragg peak shift. The shifts in Bragg Peak depth for water phantoms modeled with a nanodot on the phantom surface ranged between 2.7 to 3.2 mm. In all cases, the Bragg Peaks were shifted closer to the irradiation source. The peak dose in phantoms with an OSLD remained unchanged with percent dose differences less than 0.55% when compared to phantom doses without the nanodot.

Conclusion:

Monte Carlo calculations show that the presence of OSLD nanodots in proton beam therapy will not change the position of a pristine Bragg Peak by more than 3 mm. Although the 3.0 mm shift will not have a detrimental effect in patients receiving proton therapy, this effect may not be negligible in dose verification measurements for mouse models at lower proton beam energies.
SU‐E‐T‐555: Monte Carlo Evaluation of the Dose Calculation Algorithm of TomoTherapy for Clinical Cases in Dynamic Jaws Mode
Authors: Sterpin E
Published: June 2015

Purpose:

for the TomoTherapy™ system, longitudinal conformation can be improved by selecting a smaller field width but at the expense of longer treatment time. Recently, the TomoEdge™ feature has been released with the possibility to move dynamically the jaws at the edges of the target volume, improving longitudinal penumbra and enabling faster treatments. Such delivery scheme requires additional modeling of treatment delivery. Using a previously validated Monte Carlo model (TomoPen), we evaluated the accuracy of the implementation of TomoEdge in the new dose engine of TomoTherapy for 15 clinical cases.

Methods:

TomoPen is based on PENELOPE. Particle tracking in the treatment head is performed almost instantaneously by 1) reading a particle from a phase‐space file corresponding to the largest field and 2) correcting the weight of the particle depending on the actual jaw and MLC configurations using Monte Carlo pre‐generated data. 15 clinical plans (5 head‐and‐neck, 5 lung and 5 prostate tumors) planned with TomoEdge and with the last release of the treatment planning system (VoLO™) were re‐computed with TomoPen. The resulting dose‐volume histograms were compared.

Results:

Good agreement was achieved overall, with deviations for the target volumes typically within 2% (D95), excepted for small lung tumors (17 cm3), where a maximum deviation of 4.4% was observed for D95. However, such deviations were not observed for quality assurance measurements in homogeneous phantoms and were therefore attributed to dose calculation in patient geometry, not the modeling of TomoEdge. Such deviations for small lung tumors are also consistent with previously reported values for static field widths.

Conclusion:

For the clinical cases considered in the present study, the introduction of TomoEdge did not impact significantly the accuracy of the computed dose distributions.

The author is partially supported by Accuray
SU‐E‐T‐558: Monte Carlo Photon Transport Simulations On GPU with Quadric Geometry
Authors: Chi Y , Tian Z , Jiang S , Jia X
Published: June 2015

Purpose:

Monte Carlo simulation on GPU has experienced rapid advancements over the past a few years and tremendous accelerations have been achieved. Yet existing packages were developed only in voxelized geometry. In some applications, e.g. radioactive seed modeling, simulations in more complicated geometry are needed. This abstract reports our initial efforts towards developing a quadric geometry module aiming at expanding the application scope of GPU‐based MC simulations.

Methods:

We defined the simulation geometry consisting of a number of homogeneous bodies, each specified by its material composition and limiting surfaces characterized by quadric functions. A tree data structure was utilized to define geometric relationship between different bodies. We modified our GPU‐based photon MC transport package to incorporate this geometry. Specifically, geometry parameters were loaded into GPU's shared memory for fast access. Geometry functions were rewritten to enable the identification of the body that contains the current particle location via a fast searching algorithm based on the tree data structure.

Results:

We tested our package in an example problem of HDR‐brachytherapy dose calculation for shielded cylinder. The dose under the quadric geometry and that under the voxelized geometry agreed in 94.2% of total voxels within 20% isodose line based on a statistical t‐test (95% confidence level), where the reference dose was defined to be the one at 0.5cm away from the cylinder surface. It took 243sec to transport 100million source photons under this quadric geometry on an NVidia Titan GPU card. Compared with simulation time of 99.6sec in the voxelized geometry, including quadric geometry reduced efficiency due to the complicated geometry‐related computations.

Conclusion:

Our GPU‐based MC package has been extended to support photon transport simulation in quadric geometry. Satisfactory accuracy was observed with a reduced efficiency. Developments for charged particle transport in this geometry are currently in progress.
SU‐E‐T‐561: Monte Carlo‐Based Organ Dose Reconstruction Using Pre‐Contoured Human Model for Hodgkins Lymphoma Patients Treated by Cobalt‐60 External Beam Therapy
Authors: Jung J , Lee C , Kim J , Pelletier C , Pyakuryal A , Lee C
Published: June 2015

Purpose:

Organ doses for the Hodgkin's lymphoma patients treated with cobalt‐60 radiation were estimated using an anthropomorphic model and Monte Carlo modeling.

Methods:

A cobalt‐60 treatment unit modeled in the BEAMnrc Monte Carlo code was used to produce phase space data. The Monte Carlo simulation was verified with percent depth dose measurement in water at various field sizes. Radiation transport through the lung blocks were modeled by adjusting the weights of phase space data. We imported a precontoured adult female hybrid model and generated a treatment plan. The adjusted phase space data and the human model were imported to the XVMC Monte Carlo code for dose calculation. The organ mean doses were estimated and dose volume histograms were plotted.

Results:

The percent depth dose agreement between measurement and calculation in water phantom was within 2% for all field sizes. The mean organ doses of heart, left breast, right breast, and spleen for the selected case were 44.3, 24.1, 14.6 and 3.4 Gy, respectively with the midline prescription dose of 40.0 Gy.

Conclusion:

Organ doses were estimated for the patient group whose threedimensional images are not available. This development may open the door to more accurate dose reconstruction and estimates of uncertainties in secondary cancer risk for Hodgkin's lymphoma patients.

This work was partially supported by the intramural research program of the National Institutes of Health, National Cancer Institute, Division of Cancer Epidemiology and Genetics.
SU‐E‐T‐562: Motion Tracking Optimization for Conformal Arc Radiotherapy Plans: A QUASAR Phantom Based Study
Authors: Xu Z , Wang I , Yao R , Podgorsak M
Published: June 2015

Purpose:

This study is to use plan parameters optimization (Dose rate, collimator angle, couch angle, initial starting phase) to improve the performance of conformal arc radiotherapy plans with motion tracking by increasing the plan performance score (PPS).

Methods:

Two types of 3D conformal arc plans were created based on QUASAR respiratory motion phantom with spherical and cylindrical targets. Sinusoidal model was applied to the MLC leaves to generate motion tracking plans. A MATLAB program was developed to calculate PPS of each plan (ranges from 0–1) and optimize plan parameters. We first selected the dose rate for motion tracking plans and then used simulated annealing algorithm to search for the combination of the other parameters that resulted in the plan of the maximal PPS. The optimized motion tracking plan was delivered by Varian Truebeam Linac. In‐room cameras and stopwatch were used for starting phase selection and synchronization between phantom motion and plan delivery. Gaf‐EBT2 dosimetry films were used to measure the dose delivered to the target in QUASAR phantom. Dose profiles and Truebeam trajectory log files were used for plan delivery performance evaluation.

Results:

For spherical target, the maximal PPS (PPSsph) of the optimized plan was 0.79: (Dose rate: 500MU/min, Collimator: 90°, Couch: +10°, starting phase: 0.83π). For cylindrical target, the maximal PPScyl was 0.75 (Dose rate: 300MU/min, Collimator: 87°, starting phase: 0.97π) with couch at 0°. Differences of dose profiles between motion tracking plans (with the maximal and the minimal PPS) and 3D conformal plans were as follows: PPSsph=0.79: %ΔFWHM: 8.9%, %Dmax: 3.1%; PPSsph=0.52: %ΔFWHM: 10.4%, %Dmax: 6.1%. PPScyl=0.75: %ΔFWHM: 4.7%, %Dmax: 3.6%; PPScyl=0.42: %ΔFWHM: 12.5%, %Dmax: 9.6%.

Conclusion:

By achieving high plan performance score through parameters optimization, we can improve target dose conformity of motion tracking plan by decreasing total MLC leaf travel distance and leaf speed.
SU‐E‐T‐564: Multi‐Helix Rotating Shield Brachytherapy for Cervical Cancer
Authors: Dadkhah H , Flynn R , Wu X , Kim Y
Published: June 2015

Purpose:

To present a novel and practical brachytherapy technique, called multi‐helix rotating shield brachytherapy (H‐RSBT), for the precise positioning of a partial shield in a curved applicator. H‐RSBT enables RSBT delivery using only translational motion of the radiation source/shield combination. H‐RSBT overcomes the challenges associated with previously proposed RSBT approaches based on a serial (S‐RSBT) step‐and‐shoot delivery technique, which required independent translational and rotational motion.

Methods:

A Fletcher‐type applicator, compatible with the combination of a Xoft Axxent™ electronic brachytherapy source and a 0.5 mm thick tungsten shield, is proposed. The wall of the applicator contains six evenly‐spaced helical keyways that rigidly define the emission direction of the shield as a function of depth. The shield contains three protruding keys and is attached to the source such that it rotates freely. S‐RSBT and H‐RSBT treatment plans with 180° and 45° azimuthal emission angles were generated for five cervical cancer patients representative of a wide range of high‐risk clinical target volume (HR‐CTV) shapes and applicator positions. The number of beamlets used in the treatment planning process was nearly constant for S‐RSBT and H‐RSBT by using dwell positions separated by 5 and 1.7 mm, respectively, and emission directions separated by 22.5° and 60°, respectively. For all the treatment plans the EQD2 of the HR‐CTV was escalated until the EQD2cc tolerance of either the bladder, rectum, or sigmoid colon was reached.

Results:

Treatment times for H‐RSBT tended to be shorter than for S‐RSBT, with changes of −38.47% to 1.12% with an average of −8.34%. The HR‐CTV D90 changed by −8.81% to 2.08% with an average of −2.46%.

Conclusion:

H‐RSBT is a mechanically feasible technique in the curved applicators needed for cervical cancer brachytherapy. S‐RSBT and H‐RSBT dose distributions were clinically equivalent for all patients considered, with the H‐RSBT deliveries tending to be faster.

Ryan Flynn has ownership interest in pxAlpha, LLC, which is a startup company developing a rotating shield brachytherapy system.
SU‐E‐T‐569: Neutron Shielding Calculation Using Analytical and Multi‐Monte Carlo Method for Proton Therapy Facility
Authors: Cho S , Shin E H , Kim J , Ahn S H , Chung K , Kim D‐H , Han Y , Choi D H
Published: June 2015

Purpose:

To evaluate the shielding wall design to protect patients, staff and member of the general public for secondary neutron using a simply analytic solution, multi‐Monte Carlo code MCNPX, ANISN and FLUKA.

Methods:

An analytical and multi‐Monte Carlo method were calculated for proton facility (Sumitomo Heavy Industry Ltd.) at Samsung Medical Center in Korea. The NCRP‐144 analytical evaluation methods, which produced conservative estimates on the dose equivalent values for the shielding, were used for analytical evaluations. Then, the radiation transport was simulated with the multi‐Monte Carlo code. The neutron dose at evaluation point is got by the value using the production of the simulation value and the neutron dose coefficient introduced in ICRP‐74.

Results:

The evaluation points of accelerator control room and control room entrance are mainly influenced by the point of the proton beam loss. So the neutron dose equivalent of accelerator control room for evaluation point is 0.651, 1.530, 0.912, 0.943 mSv/yr and the entrance of cyclotron room is 0.465, 0.790, 0.522, 0.453 mSv/yr with calculation by the method of NCRP‐144 formalism, ANISN, FLUKA and MCNP, respectively. The most of Result of MCNPX and FLUKA using the complicated geometry showed smaller values than Result of ANISN.

Conclusion:

The neutron shielding for a proton therapy facility has been evaluated by the analytic model and multi‐Monte Carlo methods. We confirmed that the setting of shielding was located in well accessible area to people when the proton facility is operated.
SU‐E‐T‐575: Novel Quality Assurance Procedure for the Small Animal Radiation Research Platform Using Commercial OSLDs
Authors: Keller J , Lockamy V , Glenn S , Harrison A
Published: June 2015

Purpose:

To support radiobiological research with the Xstrahl small animal radiation research platform (SARRP) by developing a simple and effective method using commercially available optically stimulated luminescent dosimeters (OSLDs) that ensures dose output consistency.

Methods:

The SARRP output is calibrated according to the vendor standards and TG‐61 protocol utilizing an ADCL calibrated ion chamber and electrometer at 2 cm depth of solid water. A cross calibration is performed by replacing the ion chamber with five OSLDs at the 2 cm depth. The OSLDs are irradiated to 500 cGy with 220 keV at 13 mA (78s delivery time) with a copper filter for an uncollimated 17×17 cm2 aperture. Instead of the absolute dose, the total amount of raw counts are collected from the OSLD reader and used for analysis. This constancy procedure was performed two more times over the course of three weeks with two OLSDs for validity.

Results:

The average reading for all OSLDs is 494939 with a 1‐sigma standard deviation of the 5.8%. With an acceptable dose output range of ±10%, the OSLD readings have a counts range of [445445, 544433].

Conclusion:

This method of using nanoDot™ OSLDs to perform output constancy checks for the SARRP ensures the output of the device is within 10% from the time of calibration and is convenient as well as time efficient. Because this, the frequency of output checks can be increased, which can improve the output stability for research with this device. The output trend of the SARRP will continue to be monitored in the future to establish a timeline for constancy checks and recalibration.
SU‐E‐T‐580: On the Significance of Model Based Dosimetry for Breast and Head and Neck 192Ir HDR Brachytherapy
Authors: Peppa V , Pappas E , Pantelis E , Major T , Polgar C , Papagiannis P
Published: June 2015

Purpose:

To assess the dosimetric and radiobiological differences between TG43‐based and model‐based dosimetry in the treatment planning of 192Ir HDR brachytherapy for breast and head and neck cancer.

Methods:

Two cohorts of 57 Accelerated Partial Breast Irradiation (APBI) and 22 head and neck (H&N) patients with oral cavity carcinoma were studied. Dosimetry for the treatment plans was performed using the TG43 algorithm of the Oncentra Brachy v4.4 treatment planning system (TPS). Corresponding Monte Carlo (MC) simulations were performed using MCNP6 with input files automatically prepared by the BrachyGuide software tool from DICOM RT plan data. TG43 and MC data were compared in terms of % dose differences, Dose Volume Histograms (DVHs) and related indices of clinical interest for the Planning Target Volume (PTV) and the Organs‐At‐Risk (OARs). A radiobiological analysis was also performed using the Equivalent Uniform Dose (EUD), mean survival fraction (S) and Tumor Control Probability (TCP) for the PTV, and the Normal Tissue Control Probability (N TCP) and the generalized EUD (gEUD) for the OARs. Significance testing of the observed differences performed using the Wilcoxon paired sample test.

Results:

Differences between TG43 and MC DVH indices, associated with the increased corresponding local % dose differences observed, were statistically significant. This is mainly attributed to their consistency however, since TG43 agrees closely with MC for the majority of DVH and radiobiological parameters in both patient cohorts. Differences varied considerably among patients only for the ipsilateral lung and ribs in the APBI cohort, with a strong correlation to target location.

Conclusion:

While the consistency and magnitude of differences in the majority of clinically relevant DVH indices imply that no change is needed in the treatment planning practice, individualized dosimetry improves accuracy and addresses instances of inter‐patient variability observed.

Research co‐financed by the ESF and Greek funds through the Operational Program Education and Lifelong Learning Investing in Knowledge Society of the NSRF. Research Funding Program Aristeia. Nucletron, an Elekta company (Veenendaal, The Netherlands) is gratefully acknowledged for providing Oncentra Brachy v4.4 for research purposes.
SU‐E‐T‐582: On‐Line Dosimetric Verification of Respiratory Gated Volumetric Modulated Arc Therapy Using the Electronic Portal Imaging Device
Authors: Schaly B , Xhaferllari I , Gaede S
Published: June 2015

Purpose:

To investigate the clinical utility of on‐line verification of respiratory gated VMAT dosimetry during treatment.

Methods:

Portal dose images were acquired during treatment in integrated mode on a Varian TrueBeam (v. 1.6) linear accelerator for gated lung and liver patients that used flattening filtered beams. The source to imager distance (SID) was set to 160 cm to ensure imager clearance in case the isocenter was off midline. Note that acquisition of integrated images resulted in no extra dose to the patient. Fraction 1 was taken as baseline and all portal dose images were compared to that of the baseline, where the gamma comparison and dose difference were used to measure day‐to‐day exit dose variation. All images were analyzed in the Portal Dosimetry module of Aria (v. 10). The portal imager on the TrueBeam was calibrated by following the instructions for dosimetry calibration in service mode, where we define 1 calibrated unit (CU) equal to 1 Gy for 10×10 cm field size at 100 cm SID. This reference condition was measured frequently to verify imager calibration.

Results:

The gamma value (3%, 3 mm, 5% threshold) ranged between 92% and 100% for the lung and liver cases studied. The exit dose can vary by as much as 10% of the maximum dose for an individual fraction. The integrated images combined with the information given by the corresponding on‐line soft tissue matched cone‐beam computed tomography (CBCT) images were useful in explaining dose variation. For gated lung treatment, dose variation was mainly due to the diaphragm position. For gated liver treatment, the dose variation was due to both diaphragm position and weight loss.

Conclusion:

Integrated images can be useful in verifying dose delivery consistency during respiratory gated VMAT, although the CBCT information is needed to explain dose differences due to anatomical changes.
SU‐E‐T‐585: Optically‐Stimulated Luminescent Dosimeters for Monitoring Pacemaker Dose in Radiation Therapy
Authors: Apicello L , Riegel A , Jamshidi A
Published: June 2015

Purpose:

A sufficient amount of ionizing radiation can cause failure to components of pacemakers. Studies have shown that permanent damage can occur after a dose of 10 Gy and minor damage to functionality occurs at doses as low as 2 Gy. Optically stimulated thermoluminescent dosimeters (OSLDs) can be used as in vivo dosimeters to predict dose to be deposited throughout the treatment. The purpose of this work is to determine the effectiveness of using OSLDs for in vivo dosimetry of pacemaker dose.

Methods:

As part of a clinical in vivo dosimetry experience, OSLDs were placed at the site of the pacemaker by the therapist for one fraction of the radiation treatment. OSLD measurements were extrapolated to the total dose to be received by the pacemaker during treatment. A total of 79 measurements were collected from November 2011 to December 2013 on six linacs. Sixty‐six (66) patients treated in various anatomical sites had the dose of their pacemakers monitored.

Results:

Of the 79 measurements recorded, 76 measurements (96 %) were below 2 Gy. The mean and standard deviation were 50.12 ± 76.41 cGy. Of the 3 measurements that exceeded 2 Gy, 2 measurements matched the dose predicted in the treatment plan and 1 was repeated after an unexpectedly high Result. The repeated measurement yielded a total dose less than 2 Gy.

Conclusion:

This analysis suggests OSLDs may be used for in vivo monitoring of pacemaker dose. Further research should be performed to assess the effect of increased backscatter from the pacemaker device.
SU‐E‐T‐586: Optimal Determination of Tolerance Level for Radiation Dose Delivery Verification in An in Vivo Dosimetry System
Authors: Chen Y , Souri S , Gill G , Rea A , Kuruvilla A , Riegel A , Cao Y , Jamshidi A
Published: June 2015

Purpose:

To statistically determine the optimal tolerance level in the verification of delivery dose compared to the planned dose in an in vivo dosimetry system in radiotherapy.

Methods:

The LANDAUER MicroSTARii dosimetry system with screened nanoDots (optically stimulated luminescence dosimeters) was used for in vivo dose measurements. Ideally, the measured dose should match with the planned dose and falls within a normal distribution. Any deviation from the normal distribution may be redeemed as a mismatch, therefore a potential sign of the dose misadministration. Randomly mis‐positioned nanoDots can yield a continuum background distribution. A percentage difference of the measured dose to its corresponding planned dose (ΔD) can be used to analyze combined data sets for different patients. A model of a Gaussian plus a flat function was used to fit the ΔD distribution.

Results:

Total 434 nanoDot measurements for breast cancer patients were collected across a period of three months. The fit yields a Gaussian mean of 2.9% and a standard deviation (SD) of 5.3%. The observed shift of the mean from zero is attributed to the machine output bias and calibration of the dosimetry system. A pass interval of −2SD to +2SD was applied and a mismatch background was estimated to be 4.8%. With such a tolerance level, one can expect that 99.99% of patients should pass the verification and at most 0.011% might have a potential dose misadministration that may not be detected after 3 times of repeated measurements. After implementation, a number of new start breast cancer patients were monitored and the measured pass rate is consistent with the model prediction.

Conclusion:

It is feasible to implement an optimal tolerance level in order to maintain a low limit of potential dose misadministration while still to keep a relatively high pass rate in radiotherapy delivery verification.
SU‐E‐T‐588: Optimization of Imaging Following 223Ra Administration in Targeted Alpha‐Emitting Radionuclide Therapy of Bone Metastases
Authors: Benabdallah N , Bernardini M , Desbree A , de Labriolle‐Vaylet C , Franck D
Published: June 2015

Purpose:

With a growing demand of alpha‐emitting radiopharmaceuticals, especially Xofigo (223RaCl2) which is used in the treatment of metastatic bone disease, the optimization of dosimetry becomes necessary. Indeed, in Europe, as stated on the council directive 2013/59/euratom, exposures of target volumes for radiotherapeutic purposes shall be individually planned taking into account that doses to non‐target volumes and tissues shall be as low as reasonably achievable. To that aim, the possibility of imaging 223Ra was first investigated.

Methods:

The experiments were conducted at the Hopital Europeen Georges Pompidou with an Infinia Hawkeye 4 gamma camera, equipped with a medium‐energy collimator. Imaging parameters, such as sensibility, spatial resolution and energy spectrum, were determined using several physical phantoms with a source of 6 MBq of 223Ra. Bone metastases were modeled with a NEMA Body Phantom to investigate image degradation based on the concentration of 223Ra.

Results:

The acquired energy spectrum allowed to visualize several photon peaks: at 85, 154 and 270 keV. Camera sensitivity measured from the phantom study was 102.3 cps/MBq for the 85 keV ± 20 %, 89.9 cps/MBq for the 154 ± 20 % window and 65.4 cps/MBq for the 270 ± 10 % window. The spatial resolution (full‐width at half‐maximum) was respectively 1.7, 1.9 and 1.8 cm for the three energy windows. SPECT/CT images of NEMA Body Phantom without and with attenuation have permitted to determine the best reconstruction parameters.

Conclusion:

This study has demonstrated that it is possible to obtain clinically relevant information from images of 223Ra. All these results will be valuable to analyze biodistribution imaging of the radiopharmaceutical in the patient body and go further in the reconstruction of patient images in order to personalize the dosimetry.
SU‐E‐T‐590: Optimizing Magnetic Field Strengths with Matlab for An Ion‐Optic System in Particle Therapy Consisting of Two Quadrupole Magnets for Subsequent Simulations with the Monte‐Carlo Code FLUKA
Authors: Baumann K , Weber U , Simeonov Y , Zink K
Published: June 2015

Purpose:

Aim of this study was to optimize the magnetic field strengths of two quadrupole magnets in a particle therapy facility in order to obtain a beam quality suitable for spot beam scanning.

Methods:

The particle transport through an ion‐optic system of a particle therapy facility consisting of the beam tube, two quadrupole magnets and a beam monitor system was calculated with the help of Matlab by using matrices that solve the equation of motion of a charged particle in a magnetic field and field‐free region, respectively. The magnetic field strengths were optimized in order to obtain a circular and thin beam spot at the iso‐center of the therapy facility. These optimized field strengths were subsequently transferred to the Monte‐Carlo code FLUKA and the transport of 80 MeV/u C12‐ions through this ion‐optic system was calculated by using a user‐routine to implement magnetic fields. The fluence along the beam‐axis and at the iso‐center was evaluated.

Results:

The magnetic field strengths could be optimized by using Matlab and transferred to the Monte‐Carlo code FLUKA. The implementation via a user‐routine was successful. Analyzing the fluence‐pattern along the beam‐axis the characteristic focusing and de‐focusing effects of the quadrupole magnets could be reproduced. Furthermore the beam spot at the iso‐center was circular and significantly thinner compared to an unfocused beam.

Conclusion:

In this study a Matlab tool was developed to optimize magnetic field strengths for an ion‐optic system consisting of two quadrupole magnets as part of a particle therapy facility. These magnetic field strengths could subsequently be transferred to and implemented in the Monte‐Carlo code FLUKA to simulate the particle transport through this optimized ion‐optic system.
SU‐E‐T‐592: OSL Response of Al2O3:C Detectors Exposed to Therapeutic Proton Beams
Authors: Granville DA , Flint DB , Sawakuchi GO
Published: June 2015

Purpose:

To characterize the response of Al2O3:C optically stimulated luminescence (OSL) detectors (OSLDs) exposed to therapeutic proton beams of differing beam quality.

Methods:

We prepared Al2O3:C OSLDs from the same material as commercially available nanoDot dosimeters (Landauer, Inc). We irradiated the OSLDs in modulated proton beams of varying quality, as defined by the residual range. An absorbed dose to water of 0.2 Gy was delivered to all OSLDs with the residual range values varying from 0.5 to 23.5 cm (average LET in water from ∼0.5 to 2.5 keV/µm). To investigate the beam quality dependence of different emission bands within the OSL spectrum, we performed OSLD readouts using both continuous‐wave stimulation (CW‐OSL) and pulsed stimulation (P‐OSL) with two sets of optical filters (Hoya U‐340 and Kopp 5113). For all readout modes, the relative absorbed dose sensitivity (Srel) for each beam quality was calculated using OSLDs irradiated in a 6 MV photon beam as a reference.

Results:

We found that the relative absorbed dose sensitivity was highly dependent on both readout mode and integration time of the OSL signal. For CW‐OSL signals containing only the blue emission band, Srel was between 0.85 and 0.94 for 1 s readouts and between 0.82 and 0.93 for 10 s readouts. Similarly, for P‐OSL readouts containing only the blue emission band Srel ranged from 0.86 to 0.91, and 0.82 to 0.93 for 1 s and 10 s readouts, respectively. For OSLD signals containing only the UV emission band, Srel ranged from 1.00 to 1.46, and 0.97 to 1.30 for P‐OSL readouts of 1 s and 10 s, respectively.

Conclusion:

For measurements of absorbed dose using Al2O3:C OSLDs in therapeutic proton beams, dependence on beam quality was smallest for readout protocols that selected the blue emission band with small integration times.

DA Granville received financial support from the Natural Sciences and Engineering Research Council of Canada