bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐489: Radiobiological Evaluation of the Inter‐Fractional Organ Deformations in Cervical Cancer Treatments with HDR Brachytherapy
Authors: Esquivel C , Mavroidis P , Stathakis S , Choi J , Eng T , Papanikolaou N
Published: July 2013

Purpose: The proper combination of the doses by separate brachytherapy fractions affects the estimation of the effectiveness of the treatment since the patient anatomy is not the same between the different brachytherapy fractions. The purpose of this study is to estimate the variation in the effectiveness of the interfractional HDR brachytherapy procedures using dosimetric and radiobiological measures. Methods: The treatment plans of 10 cervical cancer patients (stage III), who were treated with external beam radiotherapy and HDR brachytherapy (using tandem and ovoids), were evaluated. Dose‐volume indices for the cervix and organs‐at‐risk (OARs), along with radiobiological measures, were considered in determining the clinical effectiveness of each fractional dose distribution. The biological effective doses (BED), biologically effective uniform doses (BEUD) and generalized equivalent uniform doses (gEUD) were additionally obtained. Results: For a sample patient, the average physical and BED doses by the external radiotherapy were 46.9 Gy and 45.6 Gy for the target, 35.2 Gy and 30.7 Gy for the rectum, 46.0 Gy and 42.7 Gy for the bladder, respectively. Similarly, for the HDR brachytherapy, the average physical and BED doses were 42.3Gy (SD:1.8) and 65.4Gy (SD:4.6) for the target, 12.8Gy (SD:1.3) and 14.0Gy (SD:2.2) for the rectum, 11.7Gy (SD:1.3) and 12.4Gy (SD:1.8) for the bladder, respectively. The respective gEUD and BEUD values were 36.5Gy (SD:0.5) and 49.2Gy (SD:1.0) for the target, 6.9Gy (SD:1.7) and 35.6Gy (SD:5.8) for the rectum, 7.1Gy (SD:1.2) and 39.9Gy (SD:2.2) for the bladder, respectively. Conclusion: It is shown that the variation in the effectiveness of the different HDR brachytherapy fractions can vary considerably. The calculation of the total dose distribution should be performed by summing up the deformed fractional dose distributions.
SU‐E‐T‐498: Implementation of Clinical Monte Carlo Dose Calculation for CyberKnife On a Web‐Based Treatment Planning System WebTPS
Authors: Zerouali K , Renaud M , DeBlois F , Bouchard H , Carrier J
Published: July 2013

Purpose: The scope of this study is to implement an accurate Cyberknife model on a web‐based tool (WebTPS), which uses the EGSnrc Monte Carlo dose calculation engine. WebTPS will be mostly used as a reference to evaluate clinical treatment plans in highly heterogeneous phantoms. Methods: The WebTPS dose calculation module is linked to the user code DOSxyznrc. WebTPS automatically converts CyberKnife clinical plans to DOSxyznrc input files. Phantoms are created using a tissue segmentation method from HU‐ED calibrated curves and materials are assigned based on CT data and contours performed by radiation oncologists. Parallel computation is run on a high‐performance cluster (Compute Canada) to achieve reasonable simulation time. The CyberKnife model is built on the BEAMnrc system using manufacturer's specifications. Simulated and experimental data are compared to estimate the optimal electron beam parameters. The beam energy estimation is based on percent depth dose (PDD) data comparison, while the spot size is validated using output factor (OF) and off‐axis ratio (OAR) data. An egs_chamber model of a PTW60012 diode is used to simulate OF experimental measurements for different collimator sizes. Results: A preliminary linac model optimization yields a 0.5% agreement between experimental and simulation PDD data; a 0.5% or 1 mm agreement for OAR data and a 2% agreement for OF data. Full treatment plan simulations are achieved with the CyberKnife model using patient heterogeneous phantoms. Uncertainties under 1% are achieved for less than 2 hours of CPU time. Conclusion: This work aims to develop a suitable model for reference plan dose calculation. WebTPS will be used in several clinical and research applications where the CyberKnife embedded ray‐tracing algorithm show significant limitations. Further improvements are yet to be achieved to match experimental data to a level of 1%.
SU‐E‐T‐504: Electron Beam Tuning Methodology for TrueBeam Phase‐Space Library Generation
Authors: Constantin M , Sawkey D , Svatos M
Published: July 2013

Purpose: Field‐independent phase‐space files are an effective means to reduce the time to simulate particle transport through medical linac treatment head components. The purpose of this work is to: (a) introduce the methodology used to newly create the full TrueBeam phase‐space library; (b) generate ∼50GB of data for each of seven photon beams; (c) present the results of the validation against recent gold beam data (GBD) measurements. Methods: An accurate representation of the TrueBeam field‐independent treatment head components was implemented in Geant4 (v.9.4.p02) and deployed on a large cloud‐based cluster with >500 computing cores. The incident electron beam was modeled by assuming Gaussian distributions for the energy spectrum, beam divergence, and spot size. Spot dimensions were fixed by measurements of the electron spots on the same three machines on which GBD was measured. Three remaining electron beam parameters (mean energy, energy spread, beam divergence) were varied one‐by‐one until the slopes of the least‐squares fits to the differences between Monte Carlo and measurement were <1% per fitted region (50 to 300 mm depth for percent depth doses, 0 to ±180 mm off‐axis position for in‐field profiles). Results: Seven photon beams were tuned to within 1% of GBD. The resulting sets of optimal electron beam parameters were used to generate ∼50GB per beam of IAEA‐format phase‐space files on a flat scorer (73.3 cm from isocenter) above the Y‐jaws for the 4MV, 6MV, 6FFF, 8MV, 10MV, 10FFF and 15MV beams, where FFF is the flattening filter free mode. Conclusion: A consistent methodology of electron beam tuning for megavoltage radiotherapy linac simulations allowed generation of a complete library of phase‐space files for TrueBeam freely available to support the majority of modeling needs for TrueBeam worldwide.
SU‐E‐T‐508: Monte Carlo Dosimetric Study of the CSM40 Low Dose Rate Source
Authors: Vijande J , Granero D , Candela‐Juan C , Ballester F , Perez‐Calatayud J
Published: July 2013

Purpose: There is a LDR 137Cs brachytherapy source, CSM40, developed by Eckert & Ziegler BEBIG. Fundamental dosimetric datasets to be used on treatment planning systems do not exist for this source. This study aims to obtain quality dosimetric data for this source for its use in clinical practice as required by AAPM and ESTRO. Methods: Penelope2008 and GEANT4 Monte Carlo codes were used to characterize this source dosimetry. Water composition and mass density was that recommended by AAPM. Due to the typical energies of the 137 Cs, dose for small distances can be approximated by collisional kerma. Therefore, we have considered collisional kerma for r<20 cm. To provide adequate spatial resolution, cells were 0.05 cm in thickness. Angular sampling was taken every 1°. Additional simulations were performed to obtain SK as recommended by AAPM. Mass‐energy absorption coefficients in water and air were consistently derived and used to calculate collisional kerma. Along‐away tables and TG‐43 formalism parameters and functions were derived, as recommended by HEBD from AAPM‐ESTRO. Results: TG‐43 dosimetry parameters with L = 1.65 cm were obtained. Results performed with both radiation transport codes showed agreement typically within 0.05%. Using Penelope 2008 and GEANT4, an average of α = 0.9265 +/− 0.0005 cGy/(h U) (with k = 1, Type A uncertainties) was obtained. Dose rate constant, radial dose function and anisotropy functions for the CSM40 are compared with published data for other 137 Cs sources. Conclusion: Dosimetric data are provided for the CSM40 source not studied previously in the literature. Using the data provided by this study in the treatment planning systems, it can be used in clinical practice. Partially funded under a research agreement with E&Z BEBIG
SU‐E‐T‐580: Effect of Lung and Target Density On Small Field Dose Coverage
Authors: Higgins P , Dusenbery K
Published: July 2013

Purpose: Dose coverage of small targets in SBRT treatments depends on the density of the target and the surrounding lung. We studied the relationship between field size and dose heterogeneity for different size targets as a function of target and lung density. Methods: A 50 cm3 phantom was created in the Pinnacle (V9.2) planning system. A 23 cm diameter lung ROI was inserted in the phantom. 2 or 3 cm diameter targets were placed in the lung ROI and all centered on a 15 cm deep isocenter. Dose points were set at the lateral edges of each target, normal to the beam direction (i.e., at +/− cm for the 2 cm target and +/−1.5 cm for the 3 cm target). Field size was varied from the diameter of each target up to about 5×5 cm2. 100 cGy was delivered to the isocenter via a single 6 MV field and the ratio of the average dose to the lateral dose points to the isocenter dose was recorded for each combination of lung and target density. Lung densities, relative to water, were 0.25, 0.15, 0.1, 0.05 and 0.0. Target densities were 1.0, 0.9, 0.6, 0.4, 0.3, 0.2 and 0.1. Results: We found that uniformity of dose coverage is mainly influenced by lung density. For a typical average target density of 0.4–0.6 and lung density of 0.25 a 1 cm margin is needed to achieve 90% dose uniformity. If the lung density decreases to 0.1 the margin would have to be increased to 2 cm for the same uniformity. Conclusion: It is possible to create a nomographic‐type relationship between target size and field size as a function of lung and target density which can be used as a planning aid in the selection of adequate margins for SBRT cases, particularly for patients with COPD.
SU‐E‐T‐581: Effect of CT Number to the Dose Calculation in Heterogeneity Correction Algorithm
Authors: Su M
Published: July 2013

Purpose: To study the sensitivity of dose calculation to CT number in Hounsfield units (HU) in three heterogeneity dose correction algorithms. Methods: A set of 24×16×20 cm3 ellipse cylinder phantom was created with smooth HU distribution (HU range [−810, 1000]) in Eclipse treatment planning system. Three heterogeneity dose corrected algorithms, Modified Batho (MB), Batho Power Law (BPL) and Equivalent TAR (eTAR), were applied for dose calculation with 6MV and SAD setup. The dose difference was evaluated by comparing the dose calculated at HU=0 (water) phantom with other HU value phantoms which all had same setup and fixed 100 MU delivered to each one of them for 1) three algorithms, 2) different field size, and 3) different depth. A set of double straight lines, percentage_dose_correction = slope*HU, was calculated based on the least squares error method to best fit the percentage dose correction vs. HU in HU<0 and HU>0 ranges for every algorithm and parameter date set. Results and Conclusion: 1) A straight line fitted very well with every percentage dose correction vs. HU data set (the straight line coefficient of determination: r2>0.995). An over all average slope was −0.021 (standard deviation σ=0.0032) in HU<0 and −0.011 (σ=0.0017) in HU>0 regions. The dose correction showed more sensitive to HU in HU<0 than in HU>0 region. This was caused by the slope difference in HU to electron density conversion curve. 2) As irradiated field size increased, the sensitivity of dose correction to HU decreased in MB. 3) The dose correction sensitivity to HU was proportional to the calculated depth in MB. 4) BPL showed a least dose correction sensitivity to HU comparing with other two algorithms which was nearly 25% lower than MB and eTAB in HU<0 range, and 25% lower than MB and 14% lower than eTAB in HU>0 range.
SU‐E‐T‐582: Modelling of 7MV Unflat Beam of ONCOR in Pinnacle3 Planning System
Authors: Bhangle J , Vatyam S , Randuthaikkal J , Shende R , Sekar D
Published: July 2013

Purpose: Beam modelling of 7MV unflat beam of Siemens ONCOR linear accelerator using Pinnacle3 planning system. Methods: Siemens ONCOR Impression plus linear accelerator equipped with 6MV (300MU/min, with FF) has recently approved beam of 7MV UF (2000MU/min, without FF). Beam quality index has been measured over last two years and has been consistent, varying within 1.0%. The output calibration was done with 0.65cc chamber following TRS398 protocol. KQ value was interpolated for the new beam. Output factors were measured at 10cm depth with 0.65cc chamber for field sizes above 5×5cm; and with 0.13cc chamber for smaller fields. The depth dose curves and beam profiles at different depths for various field sizes were collected using 0.13cc chamber in Blue phantom RFA (IBA dosimetry). The collected beam data (ASCII format) was imported into the Pinnacle3 V9.2 (Philips) treatment planning system. Results: Beam modelling was done in Pinnacle3 system. Measured beam data was compared against the available beam spectra of comparative beam energy. E_Tune All InSections sequence from the auto modelling option gave us a best fit for the measured data. Beam profiles were modelled as arbitrary beam profile. Few parameters obtained after completion of 7MV UF beam modelling were compared against 6MV flat beam data that was already modelled before. Beam spectrum for 7UF beam differs from 6MV spectrum. Maximum number of relative photons per energy is reached at 2MeV and 1.5MeV for 7UF and 6MV respectively. This slight increase in energy is also shown in beam quality index which is 0.681 for 7UF and 0.672 for 6MV. There is reduction in spectral off axis softening factor to 1.6878 (7UF) from 13.9628 (6MV) Conclusion: The modelled beam profiles at dmax were compared with the measured ones for three different field sizes and found be within 1% variation. This confirms the correctness of the modelling.
SU‐E‐T‐583: Optimizing Dosimetric Indices for HDR Brachytherapy Using CVaR
Authors: Holm Å , Larsson T , Tedgren Å Carlsson
Published: July 2013

Purpose: To develop a new model for automated optimization of HDR brachytherapy (BT) dose distributions that operates on the dose volume indices used in plan evaluation. The model can be solved to optimality, with constraints that are easy to interpret and modify for the clinical user. Recent research has shown that the optimization model hitherto used corresponds only weakly to such dosimetric indices. Alternative models that include such dosimetric indices have been presented; however, the explicit inclusion of dosimetric indices yields intractable models. Methods: An approach for optimizing HDR BT dose distributions is presented where dosimetric indices are taken into account through surrogates based on the conditional value‐at‐risk concept (CVaR). This yields a linear optimization model that is easy to solve, and has the additional advantage that the constraints are easy to interpret and modify to obtain satisfactory dose distributions. Results: Experimental comparisons have shown that our proposed model corresponds well with constraining dosimetric indices. All modifications of the parameters in our model yield the expected Result. Both our approach and those presented earlier for optimization of dosimetric indices include an approximation, earlier models solve the models approximately, and we use a model based on an approximation. This gives us better control of the optimization. The dose distributions generated by the proposed optimization model are comparable to those generated by the standard model with respect to dosimetric indices. Conclusion: Our new model is a viable surrogate to optimizing BT dosimetric indices that quickly and easily yield high‐quality dose distributions. New optimization models that are capable of optimizing dosimetric indices will become of increasing importance in new applications involving more degrees of freedom than conventional HDR 192Ir BT such as electronic BT.
SU‐E‐T‐584: Evaluation of Collapsed Cone Dose Calculation Algorithm for HDR Brachytherapy Using Monte Carlo
Authors: Volken W , Terribilini D , Fix MK , Loessl K , van Veelen B , Manser P
Published: July 2013

Purpose: In clinical routine, dose calculation for HDR brachytherapy plans is usually based on the AAPM‐TG43 formalism. Because the patient's anatomy is not taken into account, the resulting dose calculation may be inaccurate. Monte Carlo (MC) methods are able to calculate dose distributions accurately, but due to long computation times they are mainly used for benchmarking purposes. In this work, a test version of the collapsed cone (CC) algorithm from Nucletron was evaluated using MC. Methods: The Nucletron brachytherapy source micro Selectron‐HDR v2 has been implemented in the MC environment. CC and MC calculated dose distributions for a single source placed in a water phantom are validated against published AAPM‐TG43 data. Furthermore, dose distributions for clinical breast cancer patient treatment plans are calculated with CC and MC. Primary and scatter dose components are separated and compared individually. Results: The local differences between the MC calculated dose distributions in the water phantom and the AAPM‐TG43 data are less than 1%, while the differences between MC and CC for distances > 2 cm from the source are up to 2% of the reference dose (dose at 1 cm from the source in its equatorial plane). These differences are assigned to the first and residual scatter dose components. For the clinical breast cancer patients, CC underestimates the MC dose up to 2% in the high‐dose region (> 100% of the prescribed dose). This deviation is correlated with the scan‐length of the patient CT data set. If the CT data set extends the PTV by an appropriate amount, the underestimation falls below 1%. Conclusion: The CC algorithm is an accurate dose calculation algorithm and improves the dose calculation accuracy in brachytherapy compared to AAPM‐TG43 based algorithms. This work was supported by Nucletron. This work was supported by Nucletron.
SU‐E‐T‐585: Inverse Optimization Using Smoothness Control for Rotating Shield Brachytherapy
Authors: Liu Y , Flynn R , Kim Y , Wu X
Published: July 2013

Purpose: To present an optimization method for Rotating‐Shield Brachytherapy (RSBT) treatment plans that produces smoothly‐varying dwell time distributions, enabling the efficient delivery of smooth dose distributions. Methods: For each of 5 cervical cancer cases, a beamlet set with fine azimuthal emission angle (11.25 degree) were generated by TG‐43 dose calculation model. These beamlets are called baseline beamlets. Delivery plans that use baseline beamlets are called baseline plans. To optimize a baseline plan, a dose optimizer was used to assign dwell times to each beamlet with two objectives balanced: (i) the total dif‐ference between the delivered dose and the prescribed dose of the surface voxels is minimized; and (ii) the total variation (TV) of the dwell times is minimized. The optimization was done by solving a quadratic programming (QP) problem. For comparison, a simulated annealing based inverse optimization was performed and the computational time was limited by 5 minutes per case. The impact of the smoothness was investigated by performing dual rotating‐shield brachytherapy (D‐RSBT) planning with the baseline plans. Results: The total variation of the dwell times from the QP‐generated plans decreased by a factor ranging from 5 to 93 relative to the SA‐generated plans. The delivery efficiency curves were improved given delivery time budget limited below ∼20 min/fx. With the delivery time specified at 15 min/fx, the high‐risk clinical target volume D90 from D‐RSBT was improved by 15% on average compared to SA method, ranging from −20% to 30%. Conclusions: Improving the smoothness of baseline plans potentially improves the delivery quality of RSBT as the dose distribution quality of a smoothed baseline plan is easier to maintain with limited delivery time than an unsmoothed one. Minimizing the total variation in the optimization process increases the smoothness of D‐RSBT dose distributions relative to techniques that neglect dwell time smoothness.
SU‐E‐T‐586: Brachytherapy Application with in Situ Dose‐Painting Administered Via Gold‐Nanoparticle Eluters (BANDAGE) for Prostate Cancer (PCa)
Authors: Sinha N , Sajo E , Korideck H , Makrigiorgos G , Ngwa W
Published: July 2013

Purpose: A potential new therapeutic strategy to help prevent prostate cancer (PCa) recurrence involves loading routinely used brachytherapy spacers with non‐toxic/biocompatible radiosensitizing gold nanoparticles (GNPs), which can be sustainably released in situ for radiation boosting of high‐risk tumor subvolume. In this study, we investigated the intra‐tumor biodistribution and corresponding dose enhancement (DEF) over time for the released GNPs, as a function of nanoparticle size. Methods: An experimentally determined diffusion coefficient (D) for 10 nm nanoparticles in mouse PCa tumor model from previous studies was employed to estimate D for other sizes using the Stoke‐Einstein equation. The error function diffusion model in the experimental study was applied to generate the intratumor concentration profile for released GNPs from the spacer over time. The corresponding DEF profiles were then determined based on previously published results of DEF versus concentration when GNPs are employed during Pd‐103 and I‐125 brachytherapy. Results: As expected, the generated profiles showed greater DEF over time for smaller GNPs sizes at sample distances from the spacer. For example, for a centrally located spacer, clinically significant DEF (> 20%) could be achieved near the tumor periphery (for average PCa tumor size of about 2 cm diameter) after 14, and 65 days, respectively for GNPs sizes 2 nm, and 10 nm, when treating with I‐125. Meanwhile for Pd‐103, clinically significant DEF could be achieved at the same position after 13, and 57 days, respectively, for 2 nm and 10 nm nanoparticles. Conclusion: Our preliminary results verify that intra‐tumor dose enhancement or sub‐volume boosting profiles can be customized by varying the sizes of nanoparticle released or eluted from nanoparticle‐loaded brachytherapy spacers. These results provide a useful reference for further studies towards development of Brachytherapy Application with in situ Dose‐painting Administered via Gold‐nanoparticle Eluters (BANDAGE) for prostate cancer.
SU‐E‐T‐588: A Novel IMRT Plan Optimization Algorithm for Physician‐Driven Plan Tuning
Authors: Zarepisheh M , Li N , Cervino L , Moore K , Jia X , Jiang S
Published: July 2013

Purpose: To greatly speed up the time‐consuming treatment planning procedure by developing a new optimization algorithm allowing the physicians to interactively fine‐tune the DVHs and iso‐dose lines of an IMRT plan. Methods: The conventional treatment planning procedure is a time‐consuming and resource‐demanding task that may need multiple iterations between the dosimetrists and clinicians after an initial plan is developed. We develop a new optimization algorithm to speed up this procedure by allowing the physician to interactively fine‐tune the DVH and iso‐dose lines on top of the initially optimized plan. After the physician modifies the DVH and iso‐dose lines of the current plan towards a more desired one through an interactive graphical interface, the algorithm will adjust the voxel‐dependent optimization parameters to guide the plan towards the modified one. To ease the fine‐tuning procedure, the algorithm enables the physician to lock some DVH curves as well as to change the priorities of the organs. The algorithm explores a large Pareto surface by adjusting voxel‐dependent parameters to find out a plan that is the closest to the physicians desired plan. Results: The algorithm was tested using a series of clinically realistic patient data and found to have desirable performance. It can adjust the voxel‐dependent parameters and guide a plan towards the physician‐driven fine‐tuned plan. This algorithm has been implemented on GPU for high efficiency, and the updating procedure is near real time. Conclusion: The conventional treatment planning procedure can be significantly improved in terms of efficiency and physician satisfactory by utilizing the new GPU‐based algorithm allowing the physician to interactively fine‐tune the plan in near real time.
SU‐E‐T‐589: A Robust 4D Treatment Planning Approach for Lung Radiotherapy
Authors: Pokhrel C , Heath E
Published: July 2013

Purpose: 4D treatment planning optimizes the cumulative dose delivered over the whole respiratory cycle to generate a plan that compensates for a patients individual respiratory motion. However, changes in the time spent in the each respiratory state may render a 4D plan invalid. We introduced and evaluate two robust treatment planning approaches to compensate for respiratory motion. Methods: A 4D optimization method was developed which optimizes the phase‐weighted dose distribution. Two robust 4D treatment planning approaches were tested: (1) planning on the average motion pdf (AVE_PDF); and (2) combining 4D plans designed on the “worst case” pdfs (WC_PDF). The sensitivity of nominal and robust 4D treatment plans to respiratory motion variations was tested for two scenarios where respiratory phase weights were modified to model changes in amplitude as well as the relative proportion of the respiratory cycle spent inhaling vs. exhaling. Results: The DVHs of robust plans show less sensitivity to variation in breathing pattern. Compared to the nominal 4D plan, robust plans improve the V95 by 2 to 6 Gy and CTV min dose by 1 to 5 Gy. Conclusion: Robust 4D plan can be designed either using average pdf approach or worst case pdf approach. We find that nominal 4D plans are very sensitive to the variation in respiration pattern while robust 4D plans are less sensitive under the similar changes. As compared to static 4D plan, healthy tissue sparing is also better in robust plan. This research is supported by the Natural Sciences and Engineering Research Council of Canada (NSERC).
SU‐E‐T‐590: Automate IMRT Planning in Pinnacle: A Study in Head‐And‐Neck Cancer
Authors: Kusters M , Bzdusek K , Kumar P , van Kollenburg P , Kunze‐Busch M , Kaanders H
Published: July 2013

Purpose: We investigated whether the auto‐planning prototype included in a research version of Pinnacle 9.700 (Philips Healthcare) is able to create treatment plans with consistent quality, independent of the experience of the planner using a single template. Methods: The auto‐planning module requires the user to define a template with prioritized optimization goals for PTV‐coverage and dose constraints for organ at risks (OARs). Prioritized optimization goals are used by the auto‐planning engine to formulate optimization objectives. Multiple optimization loops iteratively reformulate and adjust the optimization objectives to meet the goals and further lower dose to OAR with minimal compromise to the target coverage. Dose conformality and uniformity to the target(s) are also controlled automatically. The quality of ten oropharynx IMRT auto‐planned plans was evaluated by calculating the target coverage (V95) and conformity index (CI) of the PTVs (prescribed dose to PTV> was 50.3 Gy and 68 Gy to PTV<), the maximum dose to the cord, and mean dose to parotids and oral cavity. Efficiency was evaluated by measuring the total planning time. Results: All auto‐planned plans fulfilled the clinical dose criteria for OARs and PTV coverage. The average V95 and CI to PTV> were 99.1% +/−1.6% and 0.8 +/−0.1, respectively and to PTV< 96.2% +/−1.5% and 0.6 +−0.1, respectively. The average maximum dose to the cord was 44.9 +/−2.0 Gy, average mean dose to the parotids was 28.4 +/−4.5 Gy and 33.7 +/−7.0 Gy to the oral cavity. Total planning time could be reduced from about 4 hours to less than 30 minutes. Conclusion: The auto‐planning module generates plans with consistent quality and reduces total planning time significantly. The tool is designed to automatically perform many of the manual operations in the current IMRT process, any further optimization for an individual patient has to be done outside auto‐plan.
SU‐E‐T‐591: Geometry‐Based Non‐Coplanar Beam Selection for Intensity Modulated Robotic Radiotherapy
Authors: Wang B , Wang J , Li J , Fan J , Kang J , Ma C
Published: July 2013

Purpose: The MLC‐based CyberKnife system has been shown promising in treatment‐time reduction and plan‐quality improvement, comparing with the cone‐based models. The improved treatment efficiency can be attributed to the enhanced coverage of larger lesions and the capability of realizing high‐quality plans with less beams due to improved target conformity. The purpose of this study is to develop an efficient non‐coplanar beam selection program for CyberKnife‐based IMRT. Methods: The candidate beam‐set consists of 94 non‐coplanar beams, each defined by a vector connecting a CyberKnife node and a target point. The MLC leaves are configured to approximate a circle, whose radius R at 80cm SSD can be chosen such that the beam cross‐sections fully covers the PTV. We aim to choose an adequate number of beams that will cover as much body surface area as possible, considering the facts that to deliver a certain dose to the PTV, the larger the total covered surface area is, the lower the surface dose will be and that the more the beams are, the longer the treatment time will be. A beam‐selection program was developed based on the constraint on the body surface overlap. To evaluate its effectiveness, several IMRT plans with the selected beams for different treatment sites were generated using the Varian Eclipse treatment‐planning‐system. Results: Our program efficiently selected much less number of beams without compromising the desired surface coverage. For example, a set of 17 beams were selected for a pancreas case, covering 92.5% of the surface area covered by the 94 beams for R=5cm with 20% maximal overlap. The IMRT plans with the selected beams show superior quality with dramatically improved critical structure sparing, comparing with the clinically approved IMRT plans. Conclusion: One can efficiently select effective sets of non‐coplanar beams with our program, which allow the generation of high‐quality plans for MLC‐based robotic radiotherapy.
SU‐E‐T‐593: Comparison of Three IMRT Adaptive Methods: The Case of Prostate Cancer
Authors: Cantin A , Octave N , Goudreault J , Foster W , Lachance B , Beaulieu L , Archambault L , Gingras L
Published: July 2013

Purpose: Independant movements of prostate and pelvic lymph nodes during IMRT can limit margin reduction and affect the protection of organs‐at‐risk (OAR). In this study we perform an analysis of three adaptive treatments that combine information from both bony and gold marker registrations. The efficiency of those treatments against interfraction prostate movements was evaluated. Methods: A retrospective study was conducted on four prostate cancer patients with 5 to 10 daily CBCTs. Clinical target volumes (CTVs) consisting of pelvic lymph nodes, prostate and seminal vesicles (SV) and OAR were delineated on each CBCT and on the initial CT. Three adaptive methods were analyzed. Two methods relied on a double patient positioning at each fraction. For these, nodal CTVs prescription was delivered on bony registration. Gold markers match was then used either to: (1) complete the dose delivered to prostate and SV (Complement); (2) give almost the entire prescription to prostate and SV with slow gradient between targets to compensate for motions (Controlled Gradient). The third method (COR) used a pool of pre‐calculated plans from anterior fractions where the plan with the prostate center of mass closest to the daily anatomy was chosen. Adaptive techniques were compared to the standard non‐corrected CT plan. Results: With adaptive techniques, prostate and SV V(100%) is improved by 4% compared to non‐corrective method. This improvement does not Result in dose increase to OAR. EUD to bladder is reduced with an average reduction of 15% for COR. Conclusion: Because of their increase in CTV coverage and OAR sparing, COR and Complement methods may be good candidates for simple and effective adaptive treatment strategies for prostate cancer. Further improvements may be obtained by tuning CTV margins. A cumulative dose to simulate a complete treatment will show real effects and allow better comparison between each method. Ministere de la Sante et des Services Sociaux
SU‐E‐T‐595: A Study of Sequential and Simultaneously Integrated Boost IMRT Methods in Head and Neck Cancer
Authors: Jang S , Pyakuryal A , Cahlon O , Greenberg A , Tsai H , Lee S , Sio T , Hanley J
Published: July 2013

Purpose: The purpose of this study was to obtain the characteristics of the sequential (SqB) and simultaneous integrated boost (SIB) IMRT methods in head and neck cancer using HART (Histogram Analysis in Radiation Therapy) program. Methods: Ten SqB and seventeen SIB IMRT cases were studied retrospectively. A cumulative mean dose of 71.3 Gy was prescribed sequentially, and a mean dose of 66.2 Gy for SIB method. Homogeneity (HI), radiation conformality indices (RCI) and quality factor (QF) were calculated from dose‐volume histograms (DVHs). In order to estimate the radiobiological outcomes of NTCP, DVH statistics for the critical and hot spots were utilized with Poisson statistics and JT Lyman models in HART. Results: HI, RCI, and QF were 1.11±0.02, 0.97±0.01, 1.00±0.02 in SIB method; and 1.10±0.01, 0.98±0.01, and 0.93±0.03 in SqB method, respectively. Critical spots for parotids, larynx, and esophagus were 0.75±0.03, 0.06±0.02, and 0.34±0.02 in SqB method, and 0.29±0.07, <0.01, and 0.22±0.06 in SIB method, respectively. Hot spots for parotids, larynx, and esophagus were 0.34±0.03, 0.54±0.02, and <0.01, respectively in SqB method whereas 0.10±0.05, <0.01, and 0.05±0.03 in SIB method, respectively. NTCP estimates for parotids, larynx, and esophagus were 0.45±0.14, 0.03±0.01, and 0.17±0.09 in SqB method, and 0.09±0.04, <0.01, and 0.18±0.04 in SIB method, respectively. Conclusion: For both boost methods mean HIs were comparable while mean RCI was better with SqB than SIB method. QF was significantly better in SIB than in SqB. Critical spots and hot spots were reduced in SIB method. Both SqB and SIB methods yielded similar NTCP for larynx and esophagus. Although better parotid sparing with SIB method than SqB was observed; due to the differences in tumors, stages and doses more patient data and detailed analyses should be followed for comparison. The radiobiological outcome‐related analysis using DVHs can be utilized to evaluate different treatment planning techniques.
SU‐E‐T‐596: A Comprehensive Comparison of Plan Quality: Non‐Coplanar IMRT Vs. RapidArc and Conventional IMRT
Authors: Wang J , Wang B , Wang R , Fan J , Lin M , Li J , Ma C
Published: July 2013

Purpose: Careful selection of beam number and orientation is of critical importance for external beam treatment planning. The utilization of well‐chosen non‐coplanar beams could allow the generation of high‐quality plans. This study is to evaluate the quality of the IMRT plans generated with the non‐coplanar (NCP) beams selected with our in‐house program by comparing it with coplanar (CP) IMRT and RapidArc (ARC) plans for prostate and pancreatic cancer treatments. Methods: Ten patients with prostate and pancreas cancer treated previously were selected for this study. A set of 13 non‐coplanar beams was selected with our in‐house program based on the CT data of one patient and was used to generate NCP plans for the ten cases. For each case we also generated an eight‐beam CP and a double‐arc ARC plan. All plans were generated with the Varian Eclipse TPS. For individual cases, the same dose‐volume constraints and weightings were used for all three plans. Results: All plans provided conformal and complete converge of the PTV and led to clinically acceptable doses to the organs‐at‐risk. The NCP plans show the best quality in terms of PTV Dmean, Dmax and HI, while the ARC plans are best in terms of PTV Dmin and CI. For the prostate cases, the NCP plans show the best V40 and V60 for rectum and bladder, and best D2% for the right‐femoral head, while the ARC plans show the best left‐femoral head D2%. For the pancreas cases, the NCP plans show the best sparing of the left‐and right‐kidney as well as the spinal cord. However, the NCP plans lead to slightly worse Dmean and D1/3 to the liver than the CP plans. Conclusion: We have shown that the non‐coplanar beams selected with our program allow the generation of high‐quality IMRT plans, by comparing them with the conventional IMRT and RapidArc plans.
SU‐E‐T‐598: Variability of Computer‐Generated Organ at Risk Contours as Part of An Automated Deformable Registration Workflow for Prostate Cancer
Authors: Gardner S , Zaorsky N , Yamoah K , Cui Y , Xiao Y , Den R , Studenski M
Published: July 2013

Purpose: To compare the contouring variability of organs at risk (OAR) on planning CT (PCT), first day cone‐beam computed tomography (CBCT1), and computer‐generated contours on subsequent fractions (CBCTf) through the use of a deformable registration workflow, as could be used for an adaptive radiotherapy planning scheme for prostate cancer. Methods: Eleven observers (6 physician‐residents, 5 physicists; all with extensive experience with prostate anatomy, treatment planning) contoured the bladder, rectum, and patient skin, using Elekta Focal on PCT (GE HiLite) and CBCT (Elekta XVI). These contours were compared to consensus contours generated with STAPLE method (CERR) which combined the contours of two recognized physician experts. This was done for the PCT and CBCT1. The CBCT1 contours were transformed via deformable registration workflow (MIM software) to 10 subsequent fractions (CBCTf) creating 333 computer‐generated OAR contours in total. The computer‐generated contours were compared to manually segmented reference contours, which were reviewed with the leading physicist and physician of the study. Dice coefficient was used to quantify variability. Statistical analysis utilized two‐sided t‐test; p‐values<0.05 significant. Results: The average Dice coefficient among all users for the bladder: PCT‐91.3%, CBCT1‐89.4%, CBCTf‐87.4% (average Dice coefficient over 10 fractions of computer‐generated contours). Rectum: PCT‐83.3%, CBCT1‐76.2%, CBCTf‐72.9%. Patient skin: PCT‐99.6%, CBCT1‐99.5%, CBCTf‐97.7%. The Dice coefficient difference between PCT and CBCT1 was statistically significant for bladder and rectum (p‐values 0.045 and 0.0013, respectively). CBCTf contours exhibited comparable variability to CBCT1 contour (average Dice coefficient difference 2–4%). Conclusion: The largest variability in computer‐generated contours occurred at superior‐inferior borders of rectum and patient skin. Our results show computer‐generated contours using deformable registration do not contribute significant additional variability to OAR contours. Further investigation which includes dosimetric impact of contouring variability of OAR is needed to assess the viability of computer‐generated contours for adaptive planning.
SU‐E‐T‐602: Dynamic Electron Arc Radiotherapy (DEAR): A Planning Study
Authors: Rodrigues A , Yin F , Wu Q
Published: July 2013

Purpose: Electron beam therapy is under‐utilized in radiation treatment of cancer and has remained practically unchanged for decades. We propose a new technique, Dynamic Electron Arc Radiotherapy (DEAR) with synchronized couch motion. In DEAR, gantry rotation, dose rate, and intensities are modulated to create desirable dose distributions free of hot and/or cold spots, with high homogeneity, and narrow penumbra. This study demonstrates the potential of DEAR in improving dose distributions. Methods: Dose distributions for single‐field and two‐field were compared to DEAR with equal and optimized beam weights on a 32 cm diameter cylindrical phantom. Plans were designed to irradiate equivalent field size on the phantom surface, with the target dimension extending from 315° –45° in radial angle and target depth at 1 cm (6 MeV) or 2 cm (9 MeV). Penumbra (20–80%), dose homogeneity, and dose area histogram (DAH) were evaluated at target depths. Plans were calculated with the eMC algorithm in Eclipse v10. Results: In‐plane (longitudinal direction) penumbra was comparable across all plans as expected. Cross‐plane (along curved surface) penumbra was 5.0, 1.5, and 2.0 cm (6 MeV) and 5.6, 1.7, and 2.1 (9 MeV), for single‐field, two‐field, and DEAR, respectively. While the two‐field penumbra was better, it exhibited a hot spot 60% higher than the target mean at the beam junction covering approximately 20% of the target. DEAR plans displayed homogenous dose distributions with variations of less than ±1.5%. DAH of the single‐field failed to achieve optimal coverage, while the two‐field displayed a high‐dose tail (>100%). 90% of the target receives at least 95% (two‐field) and 88% (DEAR) of the target dose. Conclusion: Preliminary findings show that DEAR can produce homogenous dose distributions over large and curved targets without hot and/or cold spots while maintaining narrow penumbra. Future work includes planning for various target shapes and desired dose distributions.
SU‐E‐T‐606: Forward Planned Fluence‐Painted Reduced Fields with Tangential Parent Beams for Total Breast Irradiation
Authors: Hawkins M , Wentworth S , Sintay B , Wiant D
Published: July 2013

Purpose: Whole breast radiotherapy is routinely planned with tangential fields and forward planned reduced fields. We compare this technique to a novel method of tangential fields and forward planned sliding window IMRT reduced fields. Planning time and dose homogeneity were compared.Methods and Materials: We reviewed the dosimetry for 10 patients planned in Eclipse 10 (Varian Medical Systems, Palo Alto, CA) and in XiO (Elekta AB, Stockholm, Sweden). Plans were initially created in XiO using 6MV tangents. Reduced fields were iteratively created with higher energy (10/18MV) and weighted appropriately until a clinically acceptable plan was reached. One field per tangent was usually required (although more were allowed if necessary). In our novel technique, initial beams were recreated in Eclipse and weighted to produce a symmetric plan. One higher energy (10/15MV) reduced field from each side was created, and weighted 10% of the total dose. An electronic compensator was created (using a penetration depth of 50%) for each reduced field. Their fluences were manually edited to reduce hotspots to produce a clinically acceptable plan. For dosimetric comparison, the maximum point dose and the volumes of tissue receiving 108%, 105%, and 100% of prescription were compared. A homogeneity estimation was made by comparing ratios of tissue volumes receiving 105%/100%. Finally, planning time for each method was recorded. Results: The planning time for each technique was similar. Dose homogeneity and global maximum point dose were uniformly improved with the fluence painted technique. Maximum dose was reduced on average by 1.93% using the flunece painted method. The volumes receiving 105% and 108% of the prescribed dose were reduced by an average of 82.1 cc and 6.2 cc, respectively, for the fluence painted method. Conclusion: Our technique shows improvements to dosimetric measures that may Result in better outcomes including less toxicity for our breast patients.
SU‐E‐T‐608: Feasibility Study of Stereotactic Radiosurgery Using a Non‐Commercial VMAT Treatment Planning System with a Non‐Coplanar Delivery Technique
Authors: Song Y , Mueller B , Obcemea C , Burman C , Mychalczak B
Published: July 2013

Purpose: Conventional beamlet‐based SRS procedures have several fundamental deficiencies. To address these issues, we recently conducted a study to explore the feasibility of implementing SRS using our newly‐developed VMAT treatment planning system. Our goal was to investigate the possibility of replacing IMRT with VMAT using a non‐coplanar delivery technique for intracranial SRS. Methods: A commercial SRS head phantom was CT‐scanned. The hypothetical PTV and OARs were delineated on the CT scan. Other optimization‐related dose tuning structures were also delineated. The VMAT plan was optimized with one coplanar full arc and two non‐coplanar partial arcs. Our VMAT adopts an aperture‐based technique to optimize both MLC apertures and MU weights simultaneously. The MLC interdigitation modulation was employed to increase the MLC relative speed and the dose gradient. For the comparison purpose, the conventional IMRT plan with 7 beams was also computed with the same optimization constraints. Results: VMAT‐SRS plan exhibits superior target conformity compared to the IMRT plan. The conformity index PITV, defined as the volume covered by the prescription isodose surface (PI) divided by the planning target volume (TV): PITV = PI/TV, were 0.9713 and 0.9416, respectively. VMAT plan was also found to present a huge advantage over IMRT plan in delivery efficiency. The Monitor Units (MU) for the VMAT and IMRT plans were 2706 and 4296, respectively, for a prescription dose of 1800 cGy/fraction. The MU‐to‐cGy coefficient was 1.537 for the VMAT plan and 2.388 for the IMRT plan. The VMAT plan demonstrated superiority in sparing the OARs. The dose to the brainstem was reduced by 31.63% and the dose to the scalp was reduced by 19.79. Conclusion: Non‐coplanar VMAT should replace the conventional IMRT to become the treatment of the choice for intracranial SRS procedures.
SU‐E‐T‐609: Treatment Planning Evaluation of Various Modalities for the Tretment of Skin Cancer On Foot
Authors: Park J , Kim K , Kim J , Choi C , Ye S
Published: July 2013

Purpose: To investigate the characteristics of various treatment modalities for skin cancer on foot. Methods: Right foot was immersed in water reservoir and CT image was taken. Total 6 targets were virtually generated at the skin of foot. Targets are contoured at heel pad (PTV1), inner ankle (PTV2), inner arch (PTV3), dorsal surface (PTV4), inner big toe mound (PTV5) and outer little toe mound (PTV6). Four types of treatment plans using tangential‐photon‐beams (TPB), electron‐beams (EB), high‐dose‐rate (HDR) brachytherapy technique with Freiburg flap applicator and volumetric‐modulated arc therapy (VMAT) technique were generated for each 6 target (single‐target plans) and the summed target of every 6 target (multi‐target plans). TrueBeam STx™ and Microselectron™ were used for external beam and brachytherapy planning, respectively. Plan normalization was performed to cover 95% of target volume by 95% of prescribed dose. Conformity indices (CI) and homogeneity indices (HI) and the mean doses to the foot except targets were investigated. Results: The averaged CI of single‐target plans using TPB, EB, HDR and VMAT was 1.97, 2.39, 1.6 and 0.8, respectively. The averaged HI of single‐target plans using aforementioned 4 techniques was 1.05, 1.1, 1.52 and 1.04, respectively. For the multi‐target, CI was 3.99, 2.39, 1.6 and 0.8. The HI was 1.1, 1.36, 1.43 and 1.04. The averaged mean dose to the foot except target was 2.48 Gy, 2.66 Gy, 3.57Gy and 2.91 Gy for the single‐target while it was 21.3 Gy, 14.6 Gy, 14.2 Gy and 13.1 Gy for the multi‐target. Conclusion: The VMAT technique showed better target conformity and homogeneity not only at the single‐target plan but also at the multi‐target plan than the other techniques to treat skin cancer on foot. In case of single‐target treatment, the mean dose to normal tissue was lowest when using tangential‐photon‐beams while VMAT was best for multi‐target treatment.