bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐54: Benefits of Biological Cost Functions
Authors: Demirag N
Published: July 2014

Purpose:

To verify the benefits of the biological cost functions.

Methods:

TG166 patients were used for the test case scenarios. Patients were planned using Monaco V5.0 (CMS/Elekta, St.Louis, MO) Monaco has 3 biological and 8 physical CFs. In this study the plans were optimized using 3 different scenarios. 1‐ Biological CFs only 2‐Physical CFs only 3‐ Combination of Physical&Biological CFsMonaco has 3 biological CFs. Target EUD used for the targets, derived from the poisson cell kill model, has an α value that controls the cold spots inside the target. α values used in the optimization were 0.5 and 0.8. if cold spots needs to be penalized α value increased. Serial CF: it's called serial to mimic the behaviour of the serial organs, if a high k value like 12 or 14 is used it controls the maximum dose. Serial CF has a k parameter that is used to shape the whole dvh curve. K value ranges between 1–20. k:1 is used to control the mean dose, lower k value controls the mean dose, higher k value controls the higher dose, using 2 serial CFs with different k values controls the whole DVH. Paralel CF controls the percentage of the volume that tolerates higher doses than the reference dose to mimic the behaviour of the paralel organs.

Results:

It was possible to achive clinically accepted plans in all 3 scenarios. The benefit of the biological cost functions were to control the mean dose for target and OAR, to shape the DVH curve using one EUD value and one k value simplifies the optimization process. Using the biological CFs alone, it was hard to control the dose at a point.

Conclusion:

Biological CFs in Monaco doesn' t require the ntcp/tcp values from the labs and useful to shape the whole dvh curve.

I work as an applications support specialist for Elekta and I am a Ph.D. Student in Istanbul University for radiation therapy physics.
SU‐E‐T‐241: Monte Carlo Simulation Study About the Prediction of Proton‐Induced DNA Strand Breakage On the Double Helix Structure
Authors: Shin J , Park S , Jeong J , Jeong C , Lim Y , SHIN D , Incerti S , Lee S
Published: July 2014

Purpose:

In particle therapy and radiobiology, the investigation of mechanisms leading to the death of target cancer cells induced by ionising radiation is an active field of research. Recently, several studies based on Monte Carlo simulation codes have been initiated in order to simulate physical interactions of ionising particles at cellular scale and in DNA. Geant4‐DNA is the one of them; it is an extension of the general purpose Geant4 Monte Carlo simulation toolkit for the simulation of physical interactions at sub‐micrometre scale. In this study, we present Geant4‐DNA Monte Carlo simulations for the prediction of DNA strand breakage using a geometrical modelling of DNA structure.

Methods:

For the simulation of DNA strand breakage, we developed a specific DNA geometrical structure. This structure consists of DNA components, such as the deoxynucleotide pairs, the DNA double helix, the nucleosomes and the chromatin fibre. Each component is made of water because the cross sections models currently available in Geant4‐DNA for protons apply to liquid water only. Also, at the macroscopic‐scale, protons were generated with various energies available for proton therapy at the National Cancer Center, obtained using validated proton beam simulations developed in previous studies. These multi‐scale simulations were combined for the validation of Geant4‐DNA in radiobiology.

Results:

In the double helix structure, the deposited energy in a strand allowed to determine direct DNA damage from physical interaction. In other words, the amount of dose and frequency of damage in microscopic geometries was related to direct radiobiological effect.

Conclusion:

In this report, we calculated the frequency of DNA strand breakage using Geant4‐ DNA physics processes for liquid water. This study is now on‐going in order to develop geometries which use realistic DNA material, instead of liquid water. This will be tested as soon as cross sections for DNA material become available in Geant4‐DNA.
SU‐E‐T‐244: Motion Control Challenges in High Dose Rate Brachytherapy
Authors: Hyvarinen M , Leventouri T , Pella S , Dumitru N
Published: July 2014

Purpose:

High dose rate (HDR) brachytherapy dose distribution is highly localized and has a very sharp fall‐off. Thus the one of the most important part of the treatment is the localization and immobilization of the applicator from the implantation to the setup verification to the treatment delivery. The smallest motions of the patient can induce a small rotation, tilt, or translational movement of the applicator that can convert into miss of a significant part of the tumor or to over irradiating a nearby critical organ. The purpose of this study is to revise most of the HDR types of treatments with their applicators and their localization challenges. Since every millimeter of misplacement counts the study will look into the necessity of increasing the immobilization for several types of applicators.

Methods:

The study took over 136 plans generated by the treatment planning system (TPS) looking into the applicator placement in regard to the organs at risk (OR) and simulated the three possible displacements at the hottest dose point on the critical organ for several accessories to evaluate the variation of the delivered dose at the point due to the displacement.

Results:

Many of the present immobilization devices produced for external radiotherapy can be used to improve the localization of HDR applicators during transportation of the patient and during treatment.

Conclusion:

This study data indicates that an improvement of the immobilization devices for HDR is absolutely necessary. Better applicator fixation devices are required too. Developing new immobilization devices for all the applicators is recommended.
SU‐E‐T‐249: Neutron Model Upgrade for Radiotherapy Patients Monitoring Using a New Online Detector
Authors: Irazola L , Lorenzoli M , Terron J.A. , Bedogni R. , Pola A. , Sanchez Nieto B. , Romero‐Exposito M. , Sanchez Doblado F.
Published: July 2014

Purpose:

The purpose of this work is to improve the existing methodology to estimate neutron equivalent dose in organs during radiotherapy treatments, based on a Static Random Access Memory neutron detector (SRAMnd) [1]. This is possible thanks to the introduction of a new digital detector with improved characteristics, which is able to measure online the neutron fluence rate in the presence of an intense photon background [2]. Its reduced size, allows the direct estimation of doses in specific points inside an anthropomorphic phantom (NORMA) without using passive detectors as TLD or CR‐39. This versatility will allow not only to improve the existing models (generic abdomen and H&N [1]) but to generate more specific ones for any technique.

Methods:

The new Thermal Neutron Rate Detector (TNRD), based on a diode device sensitized to thermal neutrons, have been inserted in 16 points of the phantom. These points are distributed to infer doses to specific organs. Simultaneous measurements of these devices and a reference one, located in front of the gantry, have been performed for the mentioned generic treatments, in order to improve the existing model.

Results:

These new devices have shown more precise since they agree better with Monte Carlo simulations. The comparison of the thermal neutron fluence, measured with TNRD, and the existing models, converted from events to fluence, shows an average improvement of (3.90±3.37) % for H&N and (12.61±9.43) % for abdomen, normalized to the maximum value.

Conclusion:

This work indicates the potential of these new devices for more precise neutron equivalent dose estimation in organs, as a consequence of radiotherapy treatments. The simplicity of the process makes possible to establish more specific models that will provide a better dose estimation. References[1] Phys Med Biol 2012; 57:6167–6191.[2] A new active thermal neutron detector. Radiat. Prot. Dosim. (in press).
SU‐E‐T‐254: Optimization of GATE and PHITS Monte Carlo Code Parameters for Uniform Scanning Proton Beam Based On Simulation with FLUKA General‐Purpose Code
Authors: Kurosu K , Takashina M , Koizumi M , Das I , Moskvin V
Published: July 2014

Purpose:

Monte Carlo codes are becoming important tools for proton beam dosimetry. However, the relationships between the customizing parameters and percentage depth dose (PDD) of GATE and PHITS codes have not been reported which are studied for PDD and proton range compared to the FLUKA code and the experimental data.

Methods:

The beam delivery system of the Indiana University Health Proton Therapy Center was modeled for the uniform scanning beam in FLUKA and transferred identically into GATE and PHITS. This computational model was built from the blue print and validated with the commissioning data. Three parameters evaluated are the maximum step size, cut off energy and physical and transport model. The dependence of the PDDs on the customizing parameters was compared with the published results of previous studies.

Results:

The optimal parameters for the simulation of the whole beam delivery system were defined by referring to the calculation results obtained with each parameter. Although the PDDs from FLUKA and the experimental data show a good agreement, those of GATE and PHITS obtained with our optimal parameters show a minor discrepancy. The measured proton range R90 was 269.37 mm, compared to the calculated range of 269.63 mm, 268.96 mm, and 270.85 mm with FLUKA, GATE and PHITS, respectively.

Conclusion:

We evaluated the dependence of the results for PDDs obtained with GATE and PHITS Monte Carlo generalpurpose codes on the customizing parameters by using the whole computational model of the treatment nozzle. The optimal parameters for the simulation were then defined by referring to the calculation results. The physical model, particle transport mechanics and the different geometrybased descriptions need accurate customization in three simulation codes to agree with experimental data for artifact‐free Monte Carlo simulation.

This study was supported by Grants‐in Aid for Cancer Research (H22‐3rd Term Cancer Control‐General‐043) from the Ministry of Health, Labor and Welfare of Japan, Grants‐in‐Aid for Scientific Research (No. 23791419), and JSPS Core‐to‐Core program (No. 23003). The authors have no conflict of interest.
SU‐E‐T‐257: Output Constancy: Reducing Measurement Variations in a Large Practice Group
Authors: Hedrick K , Fitzgerald T , Miller R
Published: July 2014

Purpose:

To standardize output constancy check procedures in a large medical physics practice group covering multiple sites, in order to identify and reduce small systematic errors caused by differences in equipment and the procedures of multiple physicists.

Methods:

A standardized machine output constancy check for both photons and electrons was instituted within the practice group in 2010. After conducting annual TG‐51 measurements in water and adjusting the linac to deliver 1.00 cGy/MU at Dmax, an acrylic phantom (comparable at all sites) and PTW farmer ion chamber are used to obtain monthly output constancy reference readings. From the collected charge reading, measurements of air pressure and temperature, and chamber Ndw and Pelec, a value we call the Kacrylic factor is determined, relating the chamber reading in acrylic to the dose in water with standard set‐up conditions. This procedure easily allows for multiple equipment combinations to be used at any site. The Kacrylic factors and output results from all sites and machines are logged monthly in a central database and used to monitor trends in calibration and output.

Results:

The practice group consists of 19 sites, currently with 34 Varian and 8 Elekta linacs (24 Varian and 5 Elekta linacs in 2010). Over the past three years, the standard deviation of Kacrylic factors measured on all machines decreased by 20% for photons and high energy electrons as systematic errors were found and reduced. Low energy electrons showed very little change in the distribution of Kacrylic values. Small errors in linac beam data were found by investigating outlier Kacrylic values.

Conclusion:

While the use of acrylic phantoms introduces an additional source of error through small differences in depth and effective depth, the new standardized procedure eliminates potential sources of error from using many different phantoms and results in more consistent output constancy measurements.
SU‐E‐T‐263: Point Dose Variation Using a Single Ir‐192 HDR Brachytherapy Plan for Two Treatments with a Single Tandem‐Ovoid Insertion for Cervical Cancer
Authors: Liang X , Morrill S , Hardee M , Han E , Penagaricano J , Zhang X , Vaneerat R
Published: July 2014

Purpose:

To evaluate the point dose variations between Ir‐192 HDR treatments on two consecutive days using a single tandem‐ovoid insertion without replanning in cervical cancer patients.

Methods:

This study includes eleven cervical cancer patients undergoing HDR brachytherapy with a prescribed dose of 28 Gy in 4 fractions. Each patient had two tandemovoid insertions one week apart. Each insertion was treated on consecutive days with rescanning and replanning prior to each treatment. To study the effect of no replanning for day 2 treatments, the day 1 plan dwell position and dwell time with decay were applied to the day 2 CT dataset. The point dose variations on the prescription point H (defined according to American Brachytherapy Society), and normal tissue doses at point B, bladder, rectum and vaginal mucosa (based on ICRU Report 38) were obtained.

Results:

Without replanning, the mean point H dose variation was 4.6 ± 10.7% on the left; 2.3 ± 2.9% on the right. The mean B point variation was 3.8 ± 4.9% on the left; 3.6 ± 4.7% on the right. The variation in the left vaginal mucosal point was 12.2 ± 10.7%; 9.5 ± 12.5% on the right; the bladder point 5.5 ± 7.4%; and the rectal point 7.9 ± 9.1%.

Conclusion:

Without replanning, there are variations both in the prescription point and the normal tissue point doses. The latter can vary as much as 10% or more. This is likely due to the steep dose gradient from brachytherapy compounded by shifts in the positions of the applicator in relationship to the patients anatomy. Imaging prior to each treatment and replanning ensure effective and safe brachytherapy are recommended.
SU‐E‐T‐267: Proton Pencil Beam Scanning for Mediastinal Lymphoma: 4‐Dimensional Feasibility Study
Authors: Zeng C , Plastaras J , Tochner Z , Hill‐Kayser C , Hahn S , Both S
Published: July 2014

Purpose:

To assess the feasibility of proton pencil beam scanning (PBS) for the treatment of mediastinal lymphoma.

Methods:

A group of 6 patients were planned using an anterior field with PBS. Spots with ∼5 mm σ were used for all patients, while large spots (∼10 mm σ) were employed for patients with motion perpendicular to the beam (≥5 mm). We considered volumetric repainting such that, in each fraction, the same field would be delivered twice. Four‐dimensional dose was calculated on initial and verification 4‐dimensional computed tomography (4D‐CT) scans (2—3) based on respiratory trace and beam delivery sequence. This was implemented by binning the spots into separate plans on each 4D‐CT phase respectively. Four starting phases were sampled for each painting and 4 energy switching times (0.5 s, 1 s, 3 s, and 5 s) were tested, resulting in 2560 dose distributions for the cohort. Plan robustness was measured for target and critical structures in terms of the percentage difference between delivered dose and planned dose.

Results:

For 5 of the 6 patients, the ITV (internal target volume) D98% was degraded by <3% (standard deviations ∼ 0.1%) when averaged over the whole course (up to 5% per fraction). Deviations of mean lung dose, heart maximum dose, and cord maximum dose were within 5% of prescribed dose. For one patient with motion perpendicular to the beam (up to 5 mm), the degradation of ITV D98% was 9% over the whole course (12% per fraction), which was mitigated to 1% (3% per fraction) by employing large spots and repainting. No significant difference in coverage was observed for different energy switching times.

Conclusion:

This feasibility study demonstrates that, for mediastinal lymphoma, the PBS plan robustness can be maintained during delivery when target motion is measured and volumetric repainting and/or large spots are employed.

This work was supported by Ion Beam Application.
SU‐E‐T‐268: Proton Radiosurgery End‐To‐End Testing Using Lucy 3D QA Phantom
Authors: Choi D , Gordon I , Ghebremedhin A , Wroe A , Schulte R , Bush D , Slater J , Patyal B
Published: July 2014

Purpose:

To check the overall accuracy of proton radiosurgery treatment delivery using ready‐made circular collimator inserts and fixed thickness compensating boluses.

Methods:

Lucy 3D QA phantom (Standard Imaging Inc. WI, USA) inserted with GaFchromicTM film was irradiated with laterally scattered and longitudinally spread‐out 126.8 MeV proton beams. The tests followed every step in the proton radiosurgery treatment delivery process: CT scan (GE Lightspeed VCT), target contouring, treatment planning (Odyssey 5.0, Optivus, CA), portal calibration, target localization using robotic couch with image guidance and dose delivery at planned gantry angles. A 2 cm diameter collimator insert in a 4 cm diameter radiosurgery cone and a 1.2 cm thick compensating flat bolus were used for all beams. Film dosimetry (RIT114 v5.0, Radiological Imaging Technology, CO, USA) was used to evaluate the accuracy of target localization and relative dose distributions compared to those calculated by the treatment planning system.

Results:

The localization accuracy was estimated by analyzing the GaFchromic films irradiated at gantry 0, 90 and 270 degrees. We observed 0.5 mm shift in lateral direction (patient left), ±0.9 mm shift in AP direction and ±1.0 mm shift in vertical direction (gantry dependent). The isodose overlays showed good agreement (<2mm, 50% isodose lines) between measured and calculated doses.

Conclusion:

Localization accuracy depends on gantry sag, CT resolution and distortion, DRRs from treatment planning computer, localization accuracy of image guidance system, fabrication of ready‐made aperture and cone housing. The total deviation from the isocenter was 1.4 mm. Dose distribution uncertainty comes from distal end error due to bolus and CT density, in addition to localization error. The planned dose distribution was well matched (>90%) to the measured values 2%/2mm criteria. Our test showed the robustness of our proton radiosurgery treatment delivery system using ready‐made collimator inserts and fixed thickness compensating boluses.
SU‐E‐T‐272: Radiation Damage Comparison Between Intensity Modulated Radiotherapy and Field‐In‐Field Technique in Breast Cancer Treatments
Authors: Ai H , Zhang H
Published: July 2014

Purpose:

To compare normal tissue complications between IMRT and FIF treatment in breast cancer.

Methods:

16 patients treated with IMRT plan and 20 patients treated with FIF plan were evaluated in this study. Both kinds of plans were generated using Eclipse treatment planning system by dosimetrist following clinical radiotherapy treatment guidelines. The plans were reviewed and approved by radiation oncologist. The average survival fraction (SF) for three different normal tissue cells of each concerned structure can be calculated from differential dose volume histogram (DVH) using linear quadratic model. The three types of normal tissues include radiosensitive, moderately radiosensitive and radio‐resistant that represents 70%, 50% and 30% survival fractions, respectively, for a 2‐Gy open field. Equivalent uniform doses (EUD) for corresponding normal tissues of each structure were calculated.

Results:

The EUDs of the lungs, heart, healthy breast and spinal cord with both IMRT and FIF treatments were calculated. Considering the average value of all IMRT plans, the lung of treated side absorbed 16.0% of dosage prescribed to the tumor if the radiosensitivity of the lung is similar to the radiosensitive cell line. For moderately radiosensitive and radio‐resistant lung tissue, the average EUDs can be 18.9% and 22.4% of prescription. In contrast, patients treated with FIF plans were delivered 6.0%, 7.5% and 10.3% of prescribed dose for radiosensitive, moderately radiosensitive and radio‐resistant lung tissue, respectively. Comparing heart EUDs between IMRT and FIF plans, average absorbed doses in IMRT treatment were 7.7%, 8.7% and 9.7% of prescription for three types of heart normal tissue cell lines while FIF treatments delivered only 1.3%, 1.5% and 1.6% of prescription dose. For the other organs, the results were similar.

Conclusion:

The results indicated that breast cancer treatment using IMRT technique had more normal tissue damage than FIF treatment. FIF demonstrated more effective normal tissue dose reduction in breast cancer treatment.
SU‐E‐T‐273: Radiation Shielding for a Fixed Horizontal‐Beam Linac in a Shipping Container and a Conventional Treatment Vault
Authors: Hsieh M , Balter P , Beadle B , Chi P , Stingo F , Court L
Published: July 2014

Purpose:

A fixed horizontal‐beam linac, where the patient is treated in a seated position, could lower the overall costs of the treatment unit and room shielding substantially. This design also allows the treatment room and control area to be contained within a reduced space, such as a shipping container. The main application is the introduction of low‐cost, high‐quality radiation therapy to low‐ and middle‐income regions. Here we consider shielding for upright treatments with a fixed‐6MV‐beam linac in a shipping container and a conventional treatment vault.

Methods:

Shielding calculations were done for two treatment room layouts using calculation methods in NCRP Report 151: (1) a shipping container (6m × 2.4m with the remaining space occupied by the console area), and (2) the treatment vault in NCRP 151 (7.8m by 5.4m by 3.4m). The shipping container has a fixed gantry that points in one direction at all times. For the treatment vault, various beam directions were evaluated.

Results:

The shipping container requires a primary barrier of 168cm concrete (4.5 TVL), surrounded by a secondary barrier of 3.6 TVL. The other walls require between 2.8–3.3 TVL. Multiple shielding calculations were done along the side wall. The results show that patient scatter increases in the forward direction and decreases dramatically in the backward direction. Leakage scatter also varies along the wall, depending largely on the distance between the gantry and the wall. For the treatment room, fixed‐beam requires a slightly thicker primary barrier than the conventional linac (0.6 TVL), although this barrier is only needed in the center of one wall. The secondary barrier is different only by 0–0.2 TVL.

Conclusion:

This work shows that (1) the shipping container option is achievable, using indigenous materials for shielding and (2) upright treatments can be performed in a conventional treatment room with minimal additional shielding.

Varian Medical Systems
SU‐E‐T‐276: Radiochromic Film Dosimetry: Solving the Lateral Response Puzzle
Authors: Lewis D , Chan M
Published: July 2014

Purpose:

A known factor affecting the accuracy of radiochromic film dosimetry is the lateral response artifact induced by off‐center placement of film on flatbed scanners. This work reports a practical solution to eliminate such artifacts for IMRT dose QA.

Methods:

EBT3 film calibration strips (3.5×32cm2) were exposed at a depth of 5cm on a Varian Trilogy to a 40×40cm2 open field at six doses between 120 and 900cGy using 6MV photons. A sheet of film was similarly exposed with a large IMRT field. Together with a strip of unexposed film from the same lot the films were digitized at different lateral positions on an Epson 10000XL scanner. The calibration strips covered nearly the full width of the scanner window. Calibration and response data were used to generate the IMRT dose map using multi‐channel dosimetry. The scanner response was determined as a function of lateral position of the scanned film. The response at any lateral position L is related to the response at the center, C, of the scanner by Response(C,D) = aL+bL*Response(L,D) where D is dose and the coefficients aL and bL are constant for each lateral location. The coefficients aL and bL were determined by measuring films exposed to different doses at the center of the scanner and various lateral positions.

Results:

Applying this relationship to raw calibration responses, the values at any lateral position can be corrected to an equivalent response as if that film was located centrally. Our study found that calibration curves at the different lateral positions are correlated by a simple two‐point re‐scaling and thereby the correction could be made.

Conclusion:

The work reported elaborates on the process and demonstrates improvements in radiochromic film dosimetry using this simple procedure to eliminate the lateral response artifact. Acknowledgements: Supported in part by a grant from Ashland Inc.

D Lewis is an employee of Ashland Inc., the manufacturer of radiochromic film; M Chan is supported in part by a grant from Ashland Inc.
SU‐E‐T‐279: Realization of Three‐Dimensional Conformal Dose Planning in Prostate Brachytherapy
Authors: Li Z , Jiang S , Yang Z , Bai H , Zhang X
Published: July 2014

Purpose:

Successful clinical treatment in prostate brachytherapy is largely dependent on the effectiveness of pre‐surgery dose planning. Conventional dose planning method could hardly arrive at a satisfy result. In this abstract, a three‐dimensional conformal localized dose planning method is put forward to ensure the accuracy and effectiveness of pre‐implantation dose planning.

Methods:

Using Monte Carlo method, the pre‐calculated 3‐D dose map for single source is obtained. As for multiple seeds dose distribution, the maps are combined linearly to acquire the 3‐D distribution. The 3‐D dose distribution is exhibited in the form of isodose surface together with reconstructed 3‐D organs group real‐timely. Then it is possible to observe the dose exposure to target volume and normal tissues intuitively, thus achieving maximum dose irradiation to treatment target and minimum healthy tissues damage. In addition, the exfoliation display of different isodose surfaces can be realized applying multi‐values contour extraction algorithm based on voxels. The needles could be displayed in the system by tracking the position of the implanted seeds in real time to conduct block research in optimizing insertion trajectory.

Results:

This study extends dose planning from two‐dimensional to three‐dimensional, realizing the three‐dimensional conformal irradiation, which could eliminate the limitations of 2‐D images and two‐dimensional dose planning. A software platform is developed using VC++ and Visualization Toolkit (VTK) to perform dose planning. The 3‐D model reconstruction time is within three seconds (on a Intel Core i5 PC). Block research could be conducted to avoid inaccurate insertion into sensitive organs or internal obstructions. Experiments on eight prostate cancer cases prove that this study could make the dose planning results more reasonable.

Conclusion:

The three‐dimensional conformal dose planning method could improve the rationality of dose planning by safely reducing the large target margin and avoiding dose dead zones for prostate cancer treatment.

1) National Natural Science Foundation of People's Republic of China (No. 51175373); 2) New Century Educational Talents Plan of Chinese Education Ministry (NCET‐10‐0625); 3) Scientific and Technological Major Project, Tianjin (No. 12ZCDZSY10600).
SU‐E‐T‐280: Reconstructed Rectal Wall Dose Map‐Based Verification of Rectal Dose Sparing Effect According to Rectum Definition Methods and Dose Perturbation by Air Cavity in Endo‐Rectal Balloon
Authors: Park J , Park H , Lee J , Kang S , Lee M , Lee B , Suh T
Published: July 2014

Purpose:

Dosimetric effect and discrepancy according to the rectum definition methods and dose perturbation by air cavity in an endo‐rectal balloon (ERB) were verified using rectal‐wall (Rwall) dose maps considering systematic errors in dose optimization and calculation accuracy in intensity‐modulated radiation treatment (IMRT) for prostate cancer patients.

Methods:

When the inflated ERB having average diameter of 4.5 cm and air volume of 100 cc is used for patient, Rwall doses were predicted by pencil‐beam convolution (PBC), anisotropic analytic algorithm (AAA), and AcurosXB (AXB) with material assignment function. The errors of dose optimization and calculation by separating air cavity from the whole rectum (Rwhole) were verified with measured rectal doses. The Rwall doses affected by the dose perturbation of air cavity were evaluated using a featured rectal phantom allowing insert of rolled‐up gafchromic films and glass rod detectors placed along the rectum perimeter. Inner and outer Rwall doses were verified with reconstructed predicted rectal wall dose maps. Dose errors and extent at dose levels were evaluated with estimated rectal toxicity.

Results:

While AXB showed insignificant difference of target dose coverage, Rwall doses underestimated by up to 20% in dose optimization for the Rwhole than Rwall at all dose range except for the maximum dose. As dose optimization for Rwall was applied, the Rwall doses presented dose error less than 3% between dose calculation algorithm except for overestimation of maximum rectal dose up to 5% in PBC. Dose optimization for Rwhole caused dose difference of Rwall especially at intermediate doses.

Conclusion:

Dose optimization for Rwall could be suggested for more accurate prediction of rectal wall dose prediction and dose perturbation effect by air cavity in IMRT for prostate cancer.

This research was supported by the Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (MSIP) (Grant No. 200900420)
SU‐E‐T‐281: Reduction of Treatment Times in CyberKnife Prostate SBRT Using a Water Filled Rectal Balloon
Authors: Desai P , Caroprese B , McKellar H
Published: July 2014

Purpose:

To illustrate 25% reduction in CyberKnife prostate SBRT treatment times using a water filled rectal balloon.

Methods:

We perform prostate SBRT using a 3800cGy in 4 fraction regimen prescribed between 51% 59% iso‐dose lines to 95% of PTV using a CyberKnife System. The resultant heterogeneous dosimetry is analogous to HDR dosimetry. Our patients are treated in a feet first supine position to decrease treatment couch sag and also to position the prostate anatomy closer to the robot. CT imaging is performed with a Radiadyne Immobiloc rectal balloon filled with 45‐50cc water placed firmly inside the patient's rectum. A treatment plan is developed from this CT study using Multiplan. The patient is treated every other day for 4 days using the rectal balloon for each fraction. Gold fiducials previously implanted inside the prostate are used for tracking by the CyberKnife system.

Results:

Critical structures comprise the usual GU anatomy of bladder, rectum, urethra, femoral‐heads along with emphasis on doses to anterior rectal wall and rectal mucosa. The water filled rectal balloon localizes the rectum, which enables the physician to accurately contour both anterior rectal wall, and rectal mucosa. The balloon also has a gas release valve enabling better patient comfort. Rectum localization enables the CyberKnife system to make fewer corrections resulting in fewer treatment interruptions and time lost to re‐adjustment for rectal motion, bowel filling and gas creation. Effective treatment times are reduced by 25% to approximately 45 minutes. Adoption of the balloon has required minimal change to our planning strategy and plan evaluation process.

Conclusion:

Patient follow‐up comparisons show no difference in effectiveness of treatment with and without balloons We conclude that rectal balloons enhance patient comfort and decrease effective treatment times.
SU‐E‐T‐283: Research of the Irradiation Damage to the Skin Cell by the Contaminative Electron in External Radiotherapy
Authors: Xiong Z , Lin H , Jing J , Cai J , Dai Y
Published: July 2014

Purpose:

To investigate the micro‐damage mechanism of the contaminative electron to the skin cell in external radiotherapy, the cell damage yield was simulated.

Methods:

The physical interaction and the energy deposited events of contaminative electrons in the cell DNA were modeled based on Geant4‐DNA low energy physical model. The densitybased cluster mining algorithm was used to analyze the micro‐damage yield and obtain its detailed compositive information. By taking the irradiation sensitive parameter and the clinical feature dose threshold of the skin cell into consideration, the damage features of the low energy contaminative electron to the skin cell were studied. The DSB and SSB yield and ratio, the cluster size and the root mean square radius, the cell SF and the lethal coefficient ε of the complex cDSB were researched.

Results:

For some very low energy electrons such as 20keV and 100keV, the cluster size can be more than 5 SSBs. The irradiation protection will be more crucial for the later response and the high α tissue. The lethal coefficient ε of the complex cDSB will increase with the incident electron number and the accumulative dose increasing for the dose square term in LQ model. However, the ε increment will increase 3%∼15% when the incident electron increases up to 100000.

Conclusion:

The simulation of the direct physical damage of the cell can be adjusted by a probability parameter to offset the simulation of the indirect biochemical damage. Thus the micro‐damage mechanism of the contaminative electron to the skin cell can be detected at a certain extent by Monte Carlo physical simulation. This damage model of the low energy electron to DNA and these simulated results could be used to evaluate the damage effect of the low energy contaminative electron to the skin cells in the external radiotherapy.

Strategic Priority Research Program of the Chinese Academy of Sciences (XDA03040000), Fundamental Research Funds for the Central Universities (2012HGXJ0057,2013HGXJ0193), Seed Foundation of Hefei University of Technology (2012HGZY0007) and Hefei University of Technology undergraduate innovative experiment project(2012CXCY431)
SU‐E‐T‐288: Root Cause Analysis for a Wrong Isocenter Error
Authors: Cao N , Sponseller P , Yang F , Kim E , Ford E
Published: July 2014

Purpose:

This study is to explore root cause analysis (RCA) in the context of a departmental incident reporting system through a case report of a wrong isocenter. RCA of this incident provides a means to undercover and address underlying causal factors to prevent such an event in the future.

Methods:

The wrong isocenter error was detected on port films, making it a near‐miss, but the potential impact was severe. Following the modified London Protocol for RCA, we interviewed all the staff involved, including the simulation and treatment therapists, the dosimetrist, the physicist and the physician. A timeline of events leading up to the incident and its discovery was created. We then generated a list of care delivery problems and associated contributing factors. Finally, solutions were identified to address the contributing factors and prevent future recurrences of such an incident.

Results:

Though not obvious at the outset of this RCA, the main care delivery problem turned out to be a misidentification of the ball‐bearing (BB) location on the treatment planning CT. A metal wire used to mark a drain site was identified as an isocenter mark rather than the BB on the AP surface as intended. Contributing factors include: 1)no policy implemented regarding the location of BBs and metal wire; 2) wires with similar diameter and feature as BBs in CT images; 3)lack of communication when confusion and uncertainties exist. A solution was chosen to help visualize the drain site. When drain site needs to be marked, a marker different from the regular wire will be used (e.g. plastic washer).

Conclusion:

Through RCA of an incorrect isocenter placement case, we identified the causal factors and also proposed solutions. RCA is a crucial tool for incident learning. This case study serves as valuable guidance for this particular problem and for RCA more generally.
SU‐E‐T‐290: Secondary Dose Monitoring Using Scintillating Fibers in Proton Therapy of Prostate Cancer: A Geant4 Monte Carlo Simulation
Authors: Tesfamicael B , Gueye P , Lyons D , Avery S , Mahesh M
Published: July 2014

Purpose:

To monitor the secondary dose distribution originating from a water phantom during proton therapy of prostate cancer using scintillating fibers.

Methods:

The Geant4 Monte Carlo toolkit version 9.6.p02 was used to simulate prostate cancer proton therapy based treatments. Two cases were studied. In the first case, 8 × 8 = 64 equally spaced fibers inside three 4 × 4 × 2.54 cmm3 DuPont™ Delrin blocks were used to monitor the emission of secondary particles in the transverse (left and right) and distal regions relative to the beam direction. In the second case, a scintillating block with a thickness of 2.54 cm and equal vertical and longitudinal dimensions as the water phantom was used. Geometrical cuts were used to extract the energy deposited in each fiber and the scintillating block.

Results:

The transverse dose distributions from secondary particles in both cases agree within <5% and with a very good symmetry. The energy deposited not only gradually increases as one moves from the peripheral row fibers towards the center of the block (aligned with the center of the prostate) but also decreases as one goes from the frontal to distal region of the block. The ratio of the doses from the prostate to the ones in the middle two rows of fibers showed a linear relationship with a slope (−3.55±2.26) × 10−5 MeV per treatment Gy. The distal detectors recorded a very small energy deposited due to water attenuation.

Conclusion:

With a good calibration and the ability to define a good correlation between the dose to the external fibers and the prostate, such fibers can be used for real time dose verification to the target.
SU‐E‐T‐292: Sensitivity of Fractionated Lung IMPT Treatments to Setup Uncertainties and Motion Effects
Authors: Dowdell S , Grassberger C , Paganetti H
Published: July 2014

Purpose:

Evaluate the sensitivity of intensity‐modulated proton therapy (IMPT) lung treatments to systematic and random setup uncertainties combined with motion effects.

Methods:

Treatment plans with single‐field homogeneity restricted to ±20% (IMPT‐20%) were compared to plans with no restriction (IMPT‐full). 4D Monte Carlo simulations were performed for 10 lung patients using the patient CT geometry with either ±5mm systematic or random setup uncertainties applied over a 35 × 2.5Gy(RBE) fractionated treatment course. Intra‐fraction, inter‐field and inter‐fraction motions were investigated. 50 fractionated treatments with systematic or random setup uncertainties applied to each fraction were generated for both IMPT delivery methods and three energy‐dependent spot sizes (big spots – BS σ=18‐9mm, intermediate spots – IS σ=11‐5mm, small spots – SS σ=4‐2mm). These results were compared to a Monte Carlo recalculation of the original treatment plan, with results presented as the difference in EUD (ΔEUD), V95 (ΔV95) and target homogeneity (ΔD1–D99) between the 4D simulations and the Monte Carlo calculation on the planning CT.

Results:

The standard deviations in the ΔEUD were 1.95±0.47(BS), 1.85±0.66(IS) and 1.31±0.35(SS) times higher in IMPT‐full compared to IMPT‐20% when ±5mm systematic setup uncertainties were applied. The ΔV95 variations were also 1.53±0.26(BS), 1.60±0.50(IS) and 1.38±0.38(SS) times higher for IMPT‐full. For random setup uncertainties, the standard deviations of the ΔEUD from 50 simulated fractionated treatments were 1.94±0.90(BS), 2.13±1.08(IS) and 1.45±0.57(SS) times higher in IMPTfull compared to IMPT‐20%. For all spot sizes considered, the ΔD1‐D99 coincided within the uncertainty limits for the two IMPT delivery methods, with the mean value always higher for IMPT‐full. Statistical analysis showed significant differences between the IMPT‐full and IMPT‐20% dose distributions for the majority of scenarios studied.

Conclusion:

Lung IMPT‐full treatments are more sensitive to both systematic and random setup uncertainties compared to IMPT‐20%.

This work was supported by the NIH R01 CA111590.
SU‐E‐T‐293: Simplifying Assumption for Determining Sc and Sp
Authors: King R , Cheung A , Anderson R , Thompson G , Fletcher M
Published: July 2014

Purpose:

Scp(mlc,jaw) is a two‐dimensional function of collimator field size and effective field size. Conventionally, Scp(mlc,jaw) is treated as separable into components Sc(jaw) and Sp(mlc). Scp(mlc=jaw) is measured in phantom and Sc(jaw) is measured in air with Sp=Scp/Sc. Ideally, Sc and Sp would be able to predict measured values of Scp(mlc,jaw) for all combinations of mlc and jaw. However, ideal Sc and Sp functions do not exist and a measured two‐dimensional Scp dataset cannot be decomposed into a unique pair of one‐dimensional functions.If the output functions Sc(jaw) and Sp(mlc) were equal to each other and thus each equal to Scp(mlc=jaw)^0.5, this condition would lead to a simpler measurement process by eliminating the need for in‐air measurements. Without the distorting effect of the buildup‐cap, small‐field measurement would be limited only by the dimensions of the detector and would thus be improved by this simplification of the output functions. The goal of the present study is to evaluate an assumption that Sc=Sp.

Methods:

For a 6 MV x‐ray beam, Sc and Sp were determined both by the conventional method and as Scp(mlc=jaw)^0.5. Square field benchmark values of Scp(mlc,jaw) were then measured across the range from 2×2 to 29×29. Both Sc and Sp functions were then evaluated as to their ability to predict these measurements.

Results:

Both methods produced qualitatively similar results with <4% error for all cases and >3% error in 1 case. The conventional method produced 2 cases with >2% error, while the squareroot method produced only 1 such case.

Conclusion:

Though it would need to be validated for any specific beam to which it might be applied, under the conditions studied, the simplifying assumption that Sc = Sp is justified.
SU‐E‐T‐294: Simulations to Investigate the Feasibility of ‘dry’ Optical‐CT Imaging for 3D Dosimetry
Authors: Chisholm K , Rankine L , Oldham M
Published: July 2014

Purpose:

To perform simulations investigating the feasibility of “dry” optical‐CT, and determine optimal design and scanning parameters for a novel dry tank telecentric optical‐CT 3D dosimetry system. Such a system would have important advantages in terms of practical convenience and reduced cost.

Methods:

A Matlab based ray‐tracing simulation platform, ScanSim, was used to model a telecentric system with a polyurethane dry tank, cylindrical dosimeter, and surrounding fluid. This program's capabilities were expanded for the geometry and physics of dry scanning. To categorize the effects of refractive index (RI) mismatches, simulations were run for several dosimeter (RI = 1.5−1.48) and fluid (RI = 1.55−1.33) combinations. Additional simulations examined the effect of increasing gap size (1–5mm) between the dosimeter and tank wall, and of changing the telecentric lens tolerance (0.5°−5°). The evaluation metric is the usable radius; the distance from the dosimeter center where the measured and true doses differ by less than 2%.

Results:

As the tank/dosimeter RI mismatch increases from 0–0.02, the usable radius decreases from 97.6% to 50.2%. The fluid RI for matching is lower than either the tank or dosimeter RI. Changing gap sizes has drastic effects on the usable radius, requiring more closely matched fluid at large gap sizes. Increasing the telecentric tolerance through a range from 0.5°–5.0° improved the usable radius for every combination of media.

Conclusion:

Dry optical‐CT with telecentric lenses is feasible when the dosimeter and tank RIs are closely matched (<0.01 difference), or when data in the periphery is not required. The ScanSim tool proved very useful in situations when the tank and dosimeter have slight differences in RI by enabling estimation of the optimal choice of RI of the small amount of fluid still required. Some spoiling of the telecentric beam and increasing the tolerance helps recover the usable radius.
SU‐E‐T‐296: Single Field Per Day Vs. Multiple Fields Per Day and the Impact On BED in Proton Therapy Treatment
Authors: Grantham K , Wooten H , Zhao T , Klein E
Published: July 2014

Purpose:

A common practice, in proton therapy, is to deliver a rotating subset of fields from the treatment plan for the daily fractions. This study compares the impact this practice has on the biological effective dose (BED) versus delivering all planned fields daily.

Methods:

For two scenarios (a phantom with a geometry approximating the anatomy of a prostate treatment with opposing lateral beams, and a clinical 3‐field brain treatment), treatment plans were produced in Eclipse (Varian) to simulate delivery of one, two, and three fields per fraction. The RT‐Dose file, structure set, and α/β ratios were processed using in‐house MATLAB code to return a new RT‐Dose file containing the BED (including a proton RBE of 1.1) which was imported back into Eclipse for analysis.

Results:

For targets and regions of field overlap in the treatment plan, BED is not affected by delivery regimen. In the phantom, BED in the femoral heads showed increased by 20% when a single field was used rather than two fields. In the brain treatment, the minimum BED to the left optic nerve and the pituitary gland increased by 13% and 10% respectively, for a one‐field regime compared to three‐fields per fraction. Comparing the two‐field and threefield regimes, the optic nerve BED was not significantly affected and the minimum pituitary BED was 4% higher for two fields per day.

Conclusion:

Hypo‐fractionation effects, in regions of non‐overlap of fields, significantly increase the BED to the involved tissues by as much as 20%. Care should be taken to avoid inadvertently sacrificing plan effectiveness in the interest of reduced treatment time.