bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐681: Patient Dose Distribution Comparison between Monte Carlo Simulation and Treatment Planning System
Authors: Jia Y , Beltran C
Published: November 2011

Purpose: Compare the dose distributions from our Monte Carlo Dose Distribution Verification System (MC‐DDVS) to the Varian Eclipse treatment planning system (TPS) for our pediatric brain‐tumor patients treated with double scattering proton therapy. Method and Materials:Data from 12 pediatric patients, all under 3 years of age, with brain tumors treated with double‐scattering proton therapy were used in this study. Our MC‐DDVS was previously verified for accuracy. Non‐coplanar beam arrangement, patient geometry (including materials and densities), patient‐specific apertures and compensators were modeled in GEANT4 from DICOM data. The dose distribution from MC‐DDVS was scored by cubical mesh, imported to the TPS, and then compared to the TPS dose distribution. The comparisons included field width for each individual field, the distal edge on central axis for each field, and the dose to the CTV for the full plan. Results: Our preliminary results indicate that the distal edge and field width of the MC‐DDVS and TPS matched well, with the largest discrepancy being <3mm. Examining the volumetric data of the full treatment plan for each patient, the mean doses to the CTVs based on the MC‐DDVS were within 1% of the TPS. However, on average the dose to 95% of the CTV in MC‐DDVS was ∼5% lower than the TPS. In general, the CTV dose was lower for the MC‐DDVS near target/bone interface. Conclusion: The preliminary comparison between the MC‐DDVS and the TPS showed reasonable agreement. The main difference appears to be the dose to bone and tissues proximal to bone. This may be due to the fact that the TPS reports dose to water and the MC‐DDVS reports dose to material, further investigation is needed.
SU‐E‐T‐684: Simple Integrated Tissue‐Air Ratio (SITAR)
Authors: Firpo M. A. , Chell E.
Published: November 2011

Purpose: Performing direct depth‐dose measurements on the IRay ophthalmological SRS device (designed to treat wet age‐related macular degeneration), with its narrow (4mm), low energy (100kVp) photon beam is not feasible using currently available equipment. The constant SAD indicates use of Tissue‐Air Ratio (TAR). The imperfect water‐equivalency of available tissue‐equivalent plastics at these energies and the absence of small water‐proof, energy‐independent detectors make it impossible to measure TAR directly. The Simple Integrated Tissue‐Air Ratio (SITAR) is a novel method of determining depth‐dose for this novel device. SITAR is Simple in that it is measured simply using a tissue‐equivalent plastic, and applied simply as if to water. It is Integrated because it integrates all appreciable effects: inverse R‐squared divergence, attenuation in water and in tissue‐equivalent plastic, and scatter. SITAR is used to characterize the depth dose of individual IRay devices. Methods: The attenuation properties of three tissue‐equivalent plastics are compared to those of water by direct measurement. The scatter properties of these plastics are compared to scatter in water using Monte‐Carlo simulation. The most water‐like plastic in attenuation and scatter is selected for use in SITAR. Comparing the properties of plastic to water, determinations are made of the SITAR Correction: values that correct measurements taken through the plastic to measurements in water. The SITAR Correction enables a simple series of measurements through plastic to be corrected to a TAR in water. Results: Plastic Water LR (CIRS, Norfolk, VA) is found to be the most water‐like plastic for the IRay treatment beam. Kerma measurements made through varying thicknesses of Plastic Water LR and converted with the SITAR Correction yield a very good estimate of measurements in water. Conclusions: SITAR allows each IRay device to be characterized for depth dose in water simply by taking measurements through plastic.

Research sponsored by Oraya Therapeutics.

This work is funded by Oraya Therapeutics Inc., Newark, CA
SU‐E‐T‐689: Monte Carlo‐Based Optimization for Lung SBRT Treatment Planning
Authors: Zhong H , Li H , Glide‐Hurst C , Wen N , Siebers J , Nurushev T , Chetty I
Published: November 2011

Purpose: Pencil beam algorithms used for clinical plan optimization have limited accuracy in lung dose calculation. The purpose of this study was to develop a framework for Monte Carlo‐based optimization in IMRT planning of lung tumors treated with SBRT. Methods: The in‐house‐developed planning framework consists of a graphical user interface, EGSnrc‐based dose engine, and an optimization platform. The interface was developed using Qt/C++ in Linux. Modeling of a Varian linear accelerator (21EX, 6MV) was performed using EGSnrc/BEAMnrc. Each particle has its path intersected with a virtual plane partitioned into a 20×20cm grid at 100cm SSD. The intersection index is recorded in the particleˈs LATCH variable. Deposited energy is accumulated based on the particleˈs index using a modified DOSXYZnrc code. 3D doses computed for each beamlet are saved into a binary file in sequential order. Beamlets have dimensions of either 0.5×0.5 or 1×1cm. Structure/organ contours are imported into the planning platform from Pinnacle. Target dose prescription and normal organ constraints are optimized using quadratic objective functions. A gradient‐based method is used for optimization. The dose calculation system was verified against measurements and applied to SBRT lung treatment plans. Results: Depth and profile doses computed in water for square‐shaped beams were, on average within 1%/1mm of measurements. SBRT treatment plans computed using MC for the final dose calculation and PB‐based optimization showed significant underdosage in the minimum PTV doses relative to the plan computed with PB‐based final calculation and optimization. In one example, when MC‐based optimization was employed, the PTV minimum dose coverage was increased from 75.3% to 90.2% relative to the plan with PB‐based optimization and MC‐based final calculation. Conclusions: Initial results suggest that Monte Carlo‐based optimization may help improve plan quality and target dose coverage in planning of small lung tumors.
SU‐E‐T‐693: Surface Dose Reduction from Bone Interface in Superficial X‐Ray Radiation Therapy: A Monte Carlo Study
Authors: Chow J , Owrangi A , Grigorov G
Published: November 2011

Purpose: This study evaluated the dosimetric impact of surface dose reduction due to the loss of backscatter from the bone interface in superficial x‐ray radiation therapy. Monte Carlo simulation was carried out using the EGSnrc code. Methods: An inhomogeneous phantom containing a thin layer of tissue (1,3 and 5 mm) on top of a bone (thickness = 1 cm) was irradiated by a clinical 105 kVp photon beam produced by a Gulmay D3225 kV x‐ray machine. The field size and SSD was equal to 5 cm diameter and 20 cm, respectively. Surface doses for different phantom configurations were calculated using the DOSXYZnrc code. Photon energy spectra at the phantom and bone surface were determined according to phase‐space files at the particle scoring planes. For comparison, all Monte Carlo simulations were repeated in a phantom with the bone replaced by soft tissue. Results: Surface dose reduction was found when a bone was underneath the tissue layer. When the tissue thickness = 1 mm, a surface dose reduction of 3.5% was found. The dose reduction decreased to 2.1% and 1.8% when the tissue thickness increased to 3 and 5 mm, respectively. This shows that the impact of the surface dose uncertainty decreased while the tissue thickness on top of the bone increased. This result was supported by the decrease of intensity in the photon energy spectrum, when the tissue layer was with and over the bone, compared to without the bone. Conclusions: Surface dose reduction of 3.5%–1.8% was found when the tissue layer increased from 1 to 5 mm. This decrease of surface dose results in an overestimation of prescribed dose at the patientˈs surface, and should be a concern when using superficial x‐ray to treat skin tumours in sites such as forehead, chest wall and kneecap.
SU‐E‐T‐699: Evaluation of a Monte Carlo Based TPS for SBRT
Authors: Sethi A , Rusu I , Xu M , Adams J , Dillard J , Nagda S
Published: November 2011

Purpose: Hypo‐fractionated dose regimens used in stereotactic body radiotherapy (SBRT) demand superior dose calculation and delivery accuracy. We evaluate the impact of using Monte Carlo (MC) treatment planning system (TPS) in SBRT of lung patients.Methods: A commercial MC TPS (iPlan 4.1.2, BrainLAB AG, Feldkirchen, Germany) validated in heterogeneous phantom geometry was employed. For lung and bone heterogeneities, iPlan has shown excellent agreement with measurements to within 2–3%/2mm for dose/distance‐to‐agreement. Five lung SBRT patient plans (PTV: 10 – 250 cc, mean = 67.5cc, S.D. = 85.9cc) originally computed with pencil beam (PB) algorithm were retrospectively analyzed using MC. Prescription dose was 50Gy to >99% of PTV in 5 fractions using 10–12 non‐coplanar 6MV beams. For each patient, four delivery modes were considered: 3DCRT, IMRT, dynamic‐conformal arc (DCA), and hybrid‐arc (HA). Monitor units obtained from PB plans were used to recalculate MC dose. All patient plans were compared using PTV and OAR dose indices (Dmin, Dmax, Dmean and D95).Results: MC calculated doses were significantly lower compared to PB plans for PTV surrounded by lung medium. Owing to electron disequilibrium, largest dose discrepancy was seen in superficial (<5mm) regions of target. For a 22mm target (PTV = 38.2cc): PTV Dmean and Dmin were 14.3% and 27.6% lower respectively. Corresponding differences were smaller for ITV (Dmean and Dmin 14% and 7.6% lower respectively) showing better agreement between PB and MC plans. For PTV surrounded by soft‐tissue or adjacent to chest‐wall, MC doses were closer to PB (<5% agreement). Results were relatively insensitive to target size and mode of delivery Conclusions: This study highlights the need for MC based dose calculations in lung SBRT. Closer agreement between PB and MC results for ITV calls for robust and reliable image‐guidance.
SU‐E‐T‐701: Guidance for Early Adoption of Model‐Based Dose Calculation Algorithms in Brachytherapy: Progress Report from AAPM Task Group 186
Authors: Beaulieu L , Tedgren Å Carlsson , Carrier J , Davis S , Mourtada F , Rivard M , Thomson R , Verhaegen F , Wareing T , Williamson J
Published: November 2011

Purpose: The charge of Task Group 186 is to provide guidance to early adopters of model‐based dose calculation algorithms (MBDCA) for brachytherapy dose calculations. Methods: Contrary to external beam radiotherapy (EBRT), the brachytherapy (BT) community has not widely adopted heterogeneity‐correction algorithms. Yet, BT dose calculation accuracy is highly dependent on scatter conditions and photoelectric effect cross‐sections relative to water. In specific situations, differences between the current water‐based BT dose calculation formalism (TG‐43) and MBDCA can lead to differences in dose calculation exceeding a factor of ten. MBDCA raise three major issues that are not addressed by current guidance documents: 1) MBDCA doses are sensitive to specification of dose medium, resulting in energy‐dependent dose differences between computing dose to water in homogeneous water geometry (TG‐43), dose to the local medium in the inhomogeneous geometry, and the intermediate scenario of computing dose to water in the inhomogeneous geometry. 2) MBDCA doses are sensitive to voxel‐by‐voxel interaction probabilities. Neither conventional single‐energy CT nor ICRU/ICRP tissue composition compilations provide useful guidance for the task. 3) Since each patient‐source‐applicator combination is unique, having reference data for each possible combination to benchmark MBDCA is an impractical strategy. Hence, a new commissioning process is required. Results: TG‐186 addresses in detail the above issues through literature review and provides explicit recommendations based on the current state of knowledge. These recommendations include voxel‐by‐voxel tissue/organ material assignments based on modern imaging devices, applicators and shields, transport medium definition, dose scoring medium effects, a proposed commissioning process, possible changes in BT dose prescriptions, and MBDCA limitations. When data are insufficient, interim recommendations are made and potential areas of research are identified. Conclusions: Application of TG‐186 guidance should retain practice uniformity in transitioning from the TG‐43 to the MBDCA approach.
SU‐E‐T‐773: Dosimetric and Geometric Evaluation of a Hybrid Strategy of Online Image Guidance and Offline Adaptive Planning for Prostate Cancer Radiotherapy
Authors: Liu H , Wu Q
Published: November 2011

Purpose: In fractionated radiotherapy of prostate cancer, both online and offline image‐guided strategies have been used to manage uncertainties such as setup errors and organ motions. In general, online image guidance is more effective than offline image guidance and is currently widely implemented. The purpose of this study is to evaluate the dosimetric and geometric benefit of a hybrid strategy of online image guidance and offline adaptive replanning in terms of margin reduction. Methods: A hypofractionated treatment protocol was simulated with 28 patients each having at least 16 helical CT scans. Both low‐risk patient (LRP, CTV=prostate) and intermediate‐risk patient (IRP, CTV=prostate+seminal vesicles) were studied. The hybrid strategy consists of online image guidance and offline adaptive planning. The online positioning correction was simulated by the shift of CTV center‐of‐mass (COM). Two registration methods were performed for IRP: COM shift of entire CTV (Type A) and prostate only (Type B). In offline adaptive planning, the internal target volume was constructed from the CTVs in the first five fractions. Both 3D‐CRT and IMRT were investigated. The dosimetry was evaluated for CTV, bladder and rectum. Results: Compared with online image guidance only, the hybrid strategy improves the target dose coverage significantly for both 3D‐CRT and IMRT at small margin. As margin increase, the magnitude of improvement decreases. Type A registration is better than Type B registration for IRP. The dosimtric margin benefit depended on the criteria and varied from 0 to 1.3 mm. Doses to rectum and bladder were significantly lower in IMRT than in 3D‐CRT, also lower in hybrid than online image guidance. Conclusions: The hybrid strategy can effectively account for the residual and patient‐specific interfractional organ deformation. It can further reduce the margins safely from the online image guidance alone. However, the dosimetric margin is smaller than its geometric counterpart.
SU‐E‐T‐775: Toward Web‐Based Real‐Time VMAT and IMRT Inverse Planning Using Cloud Computing
Authors: Na Y , Suh T , Xing L
Published: November 2011

Purpose: To provide an efficient cloud computing infrastructure for VMAT and IMRT inverse planning. Methods: Amazon Elastic Compute Cloud (EC2) with a master node (17.1 GB memory, 2 virtual cores, 420 GB instance storage, 64‐bit platform) is used as the backbone of cloud computing for VMAT and IMRT dose optimization. The master node is scalable on an “on‐demand” basis. It can lunch more workers if the CPU usage exceeds the upper limit for given time (e.g., over 90% usage for 2 minutes), or terminate the workers if there are finished tasks. A quadratic objective function with volumetric constraints is expressed as a function of the aperture shapes and weights of the incident beams. A Monte Carlo simulation is employed to generate accurate dose kernel by parallel tasks. The number of parallel tasks is approximately the same as or less than the total number of beamlets in iterative simulation for all beams. The cloud optimization is implemented for a Varian TrueBeam STX linac beams with and without flattening filters available. The filed output from EC2 is sent down to the Simple Storage Service (S3). Three clinical cases have been studied for the purpose of evaluating the performance of the new planning platform. Results: A cloud computing environment leads to speedups of 150–300 times for the cases considered in this study. The speedup scales approximately linearly with the number of nodes used for computing. The resultant plans from the cloud computing are found almost identical to that obtained using a desktop PC, indicating the reliability of the cloud computing platform. Conclusions: A cloud computing infrastructure has been established for VMAT and IMRT inverse planning with different beam characteristics. The cloud computing environment substantially improves the speed of inverse planning and makes future on‐treatment adaptive replanning possible.

This work was supported by grants from the National Research Foundation of Korea (NRFK) of the Korea Government (MEST) (Grant No. K20901000001‐09E0100‐ 00110)
SU‐E‐T‐784: Automated VMAT Treatment Planning for Stage III Lung Cancer: How Does It Compare with IMRT?
Authors: Quan E , Chang J , Liao Z , Xia T , Liu H , Li X , Balter P , Zhang X
Published: November 2011

Purpose: To develop a version of an automated inverse planning system (mdaccAutoPlan) for VMAT based on the previous developed system for IMRT in order to improve the efficiency and quality of VMAT treatment planning, and to discover the plan quality of VMAT in comparison to IMRT for stage III lung cancer. Methods: Two groups of patients with stage III lung cancer were randomly selected in this study. For each patient, three plans were studied — two IMRT plans respectively designed by an experienced dosimetrist from our institution and by mdaccAutoPlan, and a VMAT plan generated by mdaccAutoPlan. For group I, the dosimetrists have spent their best effort in designing the IMRT plans in order to compete with mdaccAutoPlan; however, in group II, the dosimetrists were not in competition and has spent their regular effort. Dosimetric measurements were performed to evaluate the plan quality of the three types of plans. An experienced radiation oncologist blind‐reviewed the three plans of each patient and ranked them based on their plan quality. Results: For both groups, the VMAT plans resulted in comparable plan quality to the IMRT plans generated by the mdaccAutoPlan system. Compared to the IMRT plans generated by dosimetrists — for group I, the VMAT plans show similar overall quality and better PTV conformality, esophagus sparing and complication‐free tumor control probability (p+); for group II, the VMAT plans show superior plan quality in terms of PTV conformality, lung, heart, and esophagus sparing, and p+. On average, the VMAT plans received better ranking from the oncologist than the IMRT plans. Conclusions: Combining with our in‐house mdaccAutoPlan system, VMAT is capable of generating high quality treatment plans for stage III lung cancer. VMAT plans result in superior/similar quality to the IMRT plans that were designed from mdaccAutoPlan or from a dosimetristˈs best effort.
SU‐E‐T‐786: Fully Integrated Computerized Beam Angle Optimization for Coplanar and Non‐Coplanar IMRT Treatments of Head and Neck‐Cancer Patients and Implications for VMAT
Authors: Dirkx M , Voet P , Breedveld S , Heijmen B
Published: November 2011

Purpose: To quantify whether salivary gland sparing in head and neck‐cancer treatments may be improved if planning is based on integrated computerized optimization of beam directions and intensity profiles. We also assessed the impact of optimized non‐zero couch angles in VMAT. Methods: We used iCycle, an algorithm developed in‐house for integrated, multi‐criteria beam angle optimization (Breedveld, PMB 2009). For 20 head and neck‐cancer patients five plans with maximum salivary gland sparing were generated: a 7‐ and 9‐beam equi‐angular coplanar plan, a 9‐beam coplanar plan with optimized beam angles, a 9‐beam non‐coplanar plan with optimized gantry and couch angles, and a 9‐beam coplanar plan with one optimized couch angle. Using one wish‐list with hard constraints and prioritized objectives all plans were generated fully automatically. To quantify differences in plan quality, we derived NTCP values for the salivary glands. VMAT plans were generated using the optimized couch angle derived by iCycle. Results: The non‐coplanar plans showed the best salivary gland sparing. Relative to these plans the NTCP values for the glands were up to 20% higher for the 7‐beam plans. Nine equi‐angular beams performed better than seven beams. Application of computer‐optimized beam angles further improved sparing of the salivary glands, often resulting in substantially lower NTCP values than for IMRT plans with manually selected beam angles. For 18 of the 20 patients, coplanar plans with one optimized couch angle, requiring less treatment delivery time, were similar to fully non‐coplanar plans. Relative to VMAT plans without couch rotation, application of the optimized couch angle improved the NTCP for the glands by up to 4%. Conclusions: Integrated computerized optimization of beam profiles and angles for IMRT treatment of head and neck‐cancer patients can substantially improve sparing of salivary glands. By optimizing the couch angle, VMAT plans can generally be improved as well.
SU‐E‐T‐787: Noncoplanar Intensity‐Modulated Radiation Therapy for Young Female Patients with Mediastinal Lymphoma
Authors: Chen X , Jin D , Dai J
Published: November 2011

Purpose: To propose a new technique, noncoplanar intensity‐modulated radiation therapy (Nonco_IMRT), for young female patients with mediastinal lymphoma, and to evaluate its dosimetric features. Methods: We used to adopt a coplanar IMRT technique (Co_IMRT) to treat patients with mediastinal lymphoma. Typically it has 7 equal‐spaced beams starting from gantry angle of 206°. Large volume of lungs were irradiated, and also bilitaral breasts if the patient were female. Recently, we switched to apply Nonco_IMRT technique which use 2 noncoplanr beams in sagital plane (couch angle 90°, collimator angle 90°,gantry angle 330° and 30°) replace the 2 beams of Co_IMRT that irradiate breasts and lungs directly. Nonco_IMRT was compared against Co_IMRT through a planning comparison study of 15 young female patients. PTV coverage and OAR dose parameters were analyzed. Results: For all patients, the PTV coverage, heart V30 and spinal cord dose were approximately equal between two techniques (P>0.05). But the mean dose and low dose region of bilateral breasts and lungs significantly decreased in noncoplanar IMRT (P<0.05). The reduction of the breast V2.5 and lung V5 was 33.1% and 9.28%, respectively. Conclusions: Compared to conventional Co_IMRT, Nonco_IMRT significantly reduces dose to breasts and lungs, and consequently reduces the possibility of breast second cancer and pulmonary toxity. Besides young female patients,Nonco_IMRT can benefit other mediastinal lymphoma patients as well.
SU‐E‐T‐789: A Study on the Sensitivity of VMAT and IMRT Prostate Plans Considering Uncertainties in Treatment Delivery and Patient Positioning
Authors: Arumugam S , Xing A , Holloway L , Goozee G
Published: November 2011

Purpose: During the course of radiotherapy random uncertainties in patient positioning and the fluctuation of machine parameters are inevitable. In this study we compared the impact of these errors on the quality of delivered Volumetric Modulated Arc Therapy and Intensity Modulated Radiation Therapy prostate plans. Methods: VMAT and IMRT plans were generated for two representative contour sets in Pinnacle. The uncertainty in patient setup and machine parameters during delivery was simulated by introducing random errors in isocenter position, MLC leaf positions and gantry angles for each fraction of the treatment. Random error ranges of ±3mm, ±1mm and ±1deg were used for isocenter position, MLC leaf positions and gantry angles respectively. The simulated plans were recalculated in Pinnacle and the impact of random errors on the plan quality was studied by comparing the Dose Volume Histogram of target volumes and OARs for both VMAT and IMRT plans. Results: The introduction of random errors resulted in dose smearing of both VMAT and IMRT plans. Less than 1% difference in the dose to the CTV was seen between the planning and error simulated plans for both VMAT and IMRT. However the difference in dose between the planned and error simulated plans for the PTV was greater for VMAT compared with IMRT. TheV95 of PTV was reduced by less than 1% for IMRT, whereas a difference of up to 2% was observed in VMAT. A variation of less than 1% in EUD for both the rectum and bladder was observed between the planned and error plans for both VMAT and IMRT. Conclusions: VMAT plans are relatively more sensitive to random errors in treatment delivery and patient positioning compared to IMRT plans when considering dose to the PTV, however only small variations are seen in both the CTV and OARs for both VMAT and IMRT plans.
SU‐E‐T‐798: Phantom and Clinical Study of Whole‐Abdominal Radiation Therapy on a TrueBeam Linac: A Comparison Between Traditional Treatment and Volumetric Intensity—modulated Arc Therapy
Authors: Yuen P , Vaidya K , Sharma R
Published: November 2011

Purpose: To assess the dosimetric characteristics of volumetric intensity‐modulated arc therapy (Rapid Arc) versus traditional anterior‐posterior beam arrangement with kidney blocks, and to demonstrate the feasibility of whole‐abdominal rapid arc being used in a routine clinical setting.Methods: A rapid arc plan was optimized (with 3 isocenters and 6 arcs) and a traditional AP/PA plan was generated with posterior kidney blocks for a patient prescribing 30 Gy to the whole abdomen. Both plans were copied onto a Rando phantom and optically stimulated luminescent detectors (OSLs) were placed on the phantom to measure the dose delivered by a Varian TrueBeam linac. OSLs were also placed on the patient and the measurements were evaluated. Pre‐treatment quality assurance was evaluated utilizing the Octavius QA device and analyzed using the criteria of 3%/3mm threshold for the gamma index.Results: Mean dose to PTV with rapid arc was 28.3Gy and with AP/PA was 28.5Gy. Target homogeneity was improved for the rapid arc plan. For organs at risk, the dose to the bone marrow was V90% = 18.4% in the rapid arc plan and V90% = 95.13% in the AP/PA plan. Mean doses to the kidneys were comparable in both plans. The OSL results were within 3% for the phantom study and within 6% for the patient measurements. Pre‐treatment QA passed with gamma index in the range of 93.9%–99.4% for all the arcs Conclusions: Rapid arc is a feasible alternative to the traditional therapy. Rapid arc for whole abdominal irradiation in patients offers better homogeneity with the same level of kidney sparing while providing more sparing of organs at risk, such as the bone marrow.
SU‐E‐T‐800: Evaluation of Left‐Sided Breast Cancer Treatment Using Rotational and Fixed‐Gantry Radiotherapy
Authors: Qi S , Hu A , Newman F , Liu A , Kavanagh B , Rabinovitch R
Published: November 2011

Purpose: To compare treatment planning for left‐sided breast cancer using the full spectrum of external beam delivery platforms: 3‐dimensional conformal radiotherapy (3DCRT), TomoDirect (TD), fixed‐beam intensity‐modulated radiotherapy (IMRT), and rotational therapy including both volumetric modulated arc therapy (VMAT) and Tomotherapy helical (TH). Methods: Ten left‐sided breast cancer patients with and without positive lymph nodes treated with 3DCRT or fixed‐gantry IMRT to the entire breast were re‐planned with rotational Monaco VMAT, TH and TD. The dosimetric metrics, such as PTV coverage, organ‐at‐risk sparing, DVHs, minimum/maximum/mean doses are evaluated. The VMAT plans were delivered using an Elekta Synergy beam modulator accelerator, the treatment delivery parameters such as the total MUs and delivery time from different techniques are compared. Results: For plans providing comparable PTV coverage, the VMAT plans (HI=1.13) were generally more inhomogeneous than the TH (HI=1.08) and TD (HI=1.04) plans, while TD is less conformal. For the cases with regional node involvement, averaged across the patient, the heart mean doses were 9.2 and 8.8Gy in the VMAT and TH plans, compared to 11.9 and 11.8 Gy for the 3DCRT and TD plans; the mean contra‐lateral lung doses were 4.4 and 3.2Gy for the VMAT and TH, 3.8 and 1.3Gy for the 3DCRT and TD plans. VMAT plans require shorter delivery time compared to TH. On average, the total MUs for VMAT plans are approximately 11.6% of those TH plans Conclusions: Rotational VMAT and TH offer certain dosimetric advantages over the conventional breast treatment requiring regional nodal coverage at the cost of slightly higher doses to contra‐lateral lung and/or breast. In comparison to TH, VMAT offers more efficiently dose delivery to achieve comparable dosimetric plans. For early stage breast cancer patients requiring no nodal coverage, 3DCRT and TD are potentially more beneficial in terms of heart, contra‐lateral lung/breast sparing.
SU‐E‐T‐802: Dosimetric Examination and Verification of Megavoltage Computed Tomography (MVCT) Based IMRT Treatment Planning with Helical TomoTherapy
Authors: Chao M , Huang J , Chen X , Yan Y , Xie Y , Boyd K , Moros E
Published: November 2011

Purpose: Intensity modulated radiation therapy (IMRT) planning using pre‐treatment megavoltage computed tomography (MVCT) provides a viable solution to adaptive radiotherapy. A strategy was developed to assess the impact of MVCT image quality on treatment plans using Helical TomoTherapy. Methods: The Octavius phantom (PTW) was scanned with a Philips CT‐scanner and the Helical TomoTherapy unit for kilovoltage CT (kVCT) and MVCT, respectively. MVCT images were acquired with three modes (slice thickness): coarse (6‐mm), normal (4‐mm) and fine (2‐mm). Contours from existing head‐and‐neck plans were transferred from the Pinnacle treatment planning system to phantom images and IMRT plans were generated using the TomoTherapy planning station. Comparison between the kVCT‐based plan (benchmark plan) and MVCT‐based plans were conducted to evaluate dosimetric variations. Dose volume histograms (DVH) were examined for plan quality. Plans using MVCTs acquired with three modes were also evaluated for dosimetric differences. Additional plan evaluations were performed with retrospective dose reconstruction based on the delivered leaf sequences. Results: Isodose distributions of four plans are comparable despite the intrinsic difference between MVCT and kVCT images. No significant variations on the target coverage were found from DVHs. However, plan using coarse MVCT images gave largest dose deviations (> 50%) for critical structures from that of benchmark plan while the best agreement was observed between fine MVCT and kVCT. Plan parameters were found to be consistent among four plans. Comparisons between planning doses and reconstructed treatment doses revealed high fidelity delivery. Conclusions: IMRT planning using MVCTs proved to be equivalent with that using standard kVCT when fine imaging mode was selected. Target coverage on MVCT plans is comparable to that on the standard kVCT plan. MVCT thicknesses were shown to have impact on plan quality. Caution is needed when performing treatment planning with MVCTs.
SU‐E‐T‐804: Total Scalp Irradiation Using Volumetric Modulated Arc Therapy and Comparison with IMRT and Conventional Photon/Electron Field Combination
Authors: Wang C , Wang H , Tung S , Chung H , Wong P , Martel M
Published: November 2011

Purpose: Irradiation of total scalp with conventional photon/electron fields has been challenging. The unique target shape adds complexity to the beam setup and poses difficulties in achieving a homogeneous plan. Patient setup can be cumbersome and time consuming. IMRT provides excellent dose distributions and simplifies the process of field boundary matching; however beam delivery time is still long due to large number of fields. VMAT has the capability to deliver a homogeneous dose with reduced set‐up and treatment time. VMAT will be compared to other techniques in this work.Methods: Seven patients have been planned for total scalp irradiation using conventional photon/electron planning, IMRT, and SmartArc VMAT. After optimized plans have been achieved using Pinnacle3 planning system, dosimetric comparisons were made between different methods on each patient. Results: Compared with conventional therapy, both IMRT and VMAT yield more homogeneous plan on all the patients. V100% target coverage can easily increase to 98% or higher from approximately 75%. Maximum dose reduces to less than 108% of prescribed dose from 150%. The conventional method performs better in protecting critical organs. However, brain volume at D50%, maximum and mean doses to the cord and brainstem can all be reduced by more than 50% compared to IMRT and VMAT. As a comparison between VMAT and IMRT, in all the cases, IMRT plans are slightly more uniform, while VMAT generally demonstrates better critical organ protection. Different dose levels can be easily achieved without boost using IMRT or VMAT. An added bonus of VMAT is shortened beam delivery time, which is 2.5 minutes at maximum with double arc. Conclusions: VMAT offers a viable alternative to conventional techniques in treatment of the total scalp. Advantages are improved dose distributions to the target volumes compared to conventional, and shorter treatment times compared to IMRT.
SU‐E‐T‐805: A GPU‐Based Re‐Planning System for Online Adaptive Radiotherapy
Authors: Gautier Q , Gu X , Men C , Jia X , Uribe‐Sanchez A , Choi D , Majumdar A , Jiang S
Published: November 2011

Purpose: To develop a re‐planning platform based on Graphics Processing Unit (GPU). Methods: Our project is based on the Qt framework to build a multi‐platforms GUI and allowing the user to have a control on every step of the process. The GUI is designed to be extended each time a feature is needed. Into this GUI, we have integrated several different modules for each part of the workflow. We have modules for DICOM file handling, image pre‐processing, including structure identification from the contours, automatic rigid registration, CT to Cone Beam CT structure propagation and manual structure alignment. We also have modules for deformable image registration based on the demons algorithm, dose calculation and plan re‐optimization. Most of the modules have been implemented on a GPU to allow high efficiency treatment re‐planning. Also each module comes with a visualization tool to always have control of the entire procedure. Results: We have developed a Qt‐based GUI for online ART. GPU modules for image pre‐processing, deformable registration, dose calculation and plan optimization have been integrated within this GUI. Conclusions: We transformed stand‐alone efficient processing tools into a user‐friendly platform, that can be used by clinicians, in order to have a fast treatment re‐planning, and an overview of the results for plan inspection and approval.
SU‐E‐T‐811: A Comparative Study of Replanning at the Midcourse and the Latter Course during Intensity‐Modulated Radiotherapy for Patients with Nasopharyngeal Carcinoma
Authors: Yang H , Wang W , Yu C , Shan G , Hu W
Published: November 2011

Purpose: The aim of replanning at the midcourse and the latter course was to illustrate the superior timing of replanning during intensity‐modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) patients. Methods: Twenty‐three NPC patients received IMRT in 33 fractions were enrolled. Each patient with two repeated CT scans before the 16 fraction and before the 25 fraction, respectively. The anatomic changes were determined in the three CT scans. The differences of the dose distribution were compared in inital plan vs. phantom plan 1 and replanning 1vs. phantom plan 2. Results: The mean decrements of the transverse diameter of nasopharyngeal level (d1) and the transverse diameter of the neck level (d2) were 4.66mm, 2.63mm and 7.94mm, 5.78mm before the 16th and 25th fraction. The target volume reduced mainly in the first half. The mean decrements of volume GTVnx and GTVnd were 12.20cc, 8.91cc and 18.25cc, 13.71cc before the 16th and 25th fraction. While the volume of the parotid glands reduced mainly in the second half. The mean decrements of the left and right parotid glands volume were 1.40cc, 1.98cc and 6.31cc, 6.08cc before the 16th and 25th fraction. But the dose changes of bilateral parotids were more prominent in the first half than in the second half. There was a statistically significant increase in the mean dose and V30 to the bilateral parotid only in the first half (P < 0.05). Based on dose constraint criterion in the RTOG0225 protocol, the dose of the normal critical structures for 39.13% (9/23) were out of limit comparing to in the first half than 17.39(4/23) in the second half. Conclusions: Replanning at the midcourse may reach more benefits both in the coverage of the targets and sparing of normal structures for NPC patients.

This study was supported by Zhejiang Provincial Medical and Health science Foundation of China (2008B198).
SU‐E‐T‐815: Deformable Registration and Cumulative Dose Records as Applied to Patients with Cervical Carcinoma
Authors: Hooker C , Scanderbeg D , Yashar C , Cerviño L
Published: November 2011

Purpose: Use daily patient imaging to calculate cumulative dose to target and organs at risk during the course of radiation treatment for cervical cancer patients and compare with the planned dose.Methods: Daily cone beam CT (CBCT) scans were taken for 10 patients during their cervical cancer radiation therapy treatment course. Dose from the treatment plan was calculated on each of the CBCTs. Deformable registration was performed on each of the daily CBCTs in order to map the patientˈs daily anatomy and dose onto the planning CT (reference). The cumulative dose was then calculated and the Dose Volume Histogram (DVH) of the cumulative dose was compared to the DVH of the original planned dose. Results: The DVH for the calculated cumulative dose deviated from the DVH of the actual dose due to changes in the patientsˈ daily anatomy. The planning target volume (PTV) showed similar coverage; however, the dose received by the organs at risk (OARs) differed from the original plan. Conclusions: Since patient anatomy varies on a daily basis, daily imaging combined with deformable registration and cumulative dose calculations yields an accurate dose to target and organs at risk. This dose information can then be used by the clinician to guide additional radiation therapy to boost target dose and spare OARs.

This work was supported by Varian Medical Systems, Inc.
SU‐E‐T‐822: Dosimetric Comparison of Intensity Modulated Radiotherapy Modes for Breast Cancer after Radical Mastectomy: Forward IMRT vs. IMRT
Authors: Zhang G , Sun T , Yin Y
Published: November 2011

Purpose: To evaluate the dose distribution of target volume and normal tissues in forward intensity modulated radiotherapy (f‐IMRT) and inverse intensity modulated radiotherapy (IMRT) plans for breast cancer after radical mastectomy. Methods: Ten patients with breast cancer who received radical mastectomy were enrolled in this study. On each patientˈs CT images the supraclavicular, chest wall and internal mammary areas were delineated. F‐IMRT and IMRT plans were performed for each patient. The prescription dose was 50 Gy in 25 fractions. F‐IMRT plans for the supraclavicular and the chest wall area using 6 MV X‐ray irradiation; internal mammary area with 9‐12 MeV electron irradiation, according to the three regions of dose adjust the doses of cold and hot fit. The supraclavicular, chest wall and internal mammary area were considered as a whole target in the IMRT plans, using 6 MV X‐ray. The dose‐volume parameters of target volume and normal tissues, CI and HI of f‐IMRT and IMRT plans were analyzed, using paired t‐test. Results: The target volume coverage of f‐IMRT plans were similar to that of the IMRT plans (93% and 94.5%). The mean CI and mean HI were 0.67±0.02/1.18±0.02 in f‐IMRT and 0.75±0.03/1.14±0.01 in IMRT (P<0.05). The differences of V10, V20, V25, V30 and Dmean of ipsilateral lung were not statistically significant. However, the V15 of ipsilateral lung in IMRT was 4.5% less than that in f‐IMRT, which was statistically significant (P<0.05). There was no significant difference in Dmean and V30 of heart, Dmean of contralateral lung and contralateral breast between two modes. Conclusions: Compared with f‐IMRT, IMRT plans resulted in better conformal dose distribution and homogeneity, with comparable target volume coverage and sparing of lung, heart and contralateral breast.
SU‐E‐T‐828: Dosimetric Comparison of IMRT Prostate Treatment Using Step&shoot (MLC and MMLC), Dynamic MLC and Tomotherapy
Authors: Venencia C , Delgado J , Caballero C , Zunino S , Pipman Y
Published: November 2011

Purpose: To perform an inter‐comparison of TPS results for different IMRT delivery systems. Methods: Patient data with prostate cancer was selected. Same geometries and energy were employed for fixed gantry angle plans. Treatment includes simultaneous irradiation, prostate to 82Gy and seminal vesicles to 64Gy (41 fractions). Plans were normalized to achieve 82Gy minimum dose to prostate. Plan 1 : step&shoot with 1cm leaf‐width (MLC‐Optifocus), TPS Konrad v2.2 (Siemens). Plan 2: same plan 1 but with TPS iPlan v4.1 (BrainLAB). Plan 3: step&shoot with 0.25cm leaf‐width (mMLC‐Moduleaf, Siemens), TPS iPlan v4.1. Plan 4: dynamic with 0.5cm leaf‐width (MLC‐Millenium), TPS Eclipse v8.1 (Varian). Plan 5: Tomotherapy TPS v3.1.4.7. Longitudinal field size 2.5cm, pitch 0.277 and modulation factor 1.783, leaf width 6.25mm Results: Total numbers of MU were 508, 488, 570, 577 and 3219 for Plan 1 to 5. D98% (V82Gy) for PTV prostate were 81.6Gy (95.7%), 80.7Gy (94.9%), 81.8Gy (97.4%), 80.1Gy (84.6%) and 79.9Gy (82.6%) for Plan 1 to 5. V64Gy for PTV seminal vesicle were 98.2%, 99.9%, 100%, 92.1% and 97.8% for Plan 1 to 5. Rectum EUD (V40Gy) were 65.1Gy (56.6%), 62.7Gy (53.1%), 61.9Gy (44.3%), 63.3Gy (55.7%) and 61.9Gy (39%) for Plan 1 to 5. Rectum wall EUD was 66.4Gy, 65.2Gy, 64.8Gy, 64.9Gy and 65.2Gy for Plan 1 to 5. Bladder EUD (V65Gy) were 47.9Gy (27.4%), 47.4Gy (24.8%), 46.6Gy (24.6%), 46.2Gy (24.4%) and 45.8Gy (20.1%) for Plan 1 to 5. Femoral head D10% were 31.8Gy, 34.5Gy, 33.9Gy, 39.3Gy and 26.1Gy for Plan 1 to 5. Conclusions: MUs are lower with step&shoot MLC. MicroMLC produces slightly better conformation of PTVs. Better sparing of rectum and bladder with mMLC and Tomotherapy. For rectum wall EUD shows that mMLC produce the better results. Better sparing of femoral head is obtained with Tomotherapy. All techniques give the OARˈs similar EUD (+/−2Gy), except for femoral heads.
SU‐E‐T‐840: The Clinical Application of Filed‐In‐Arc Technique
Authors: Chang C , Hwang J , Chuang K
Published: November 2011

Purpose: To present Field‐in‐Arc technique and demonstrate clinical application from treatment planning dosimetric analysis. Methods: Two group patients consist of four hepatoma and four lung cases. The average volume of Lung is 104.88 cm3 and hepatoma is 73.98 cm3. All cases include field‐in‐arc、IMRT and RapidArc three different technique treatment plannings. The Filed‐in‐Arc technique composed of one partial conformal arc and several static fileds. The static field has effect of weighting enhancement and dose compensation. Results: Monitor unit average ratio of Field‐in‐Arc over IMRT and its over RapidArc shows 0.4445 and 0.8414. Average conform index of hepatoma group shows 1.47 for Field‐in‐Arc 2289; 1.24 for IMRT and 1.04 for RapidArc. The average of gradient measurement from 1.71 to 1.88 shows on significant different. Average conform index of lung group shows 0.99 to 1.13 and average of gradient measurement from 1.92 to 2.09. But V20 of Right lung the dose ratio shows Field‐in‐Arc technique higher than other two techniques approximate 1.3 times. Forward method to create simple intensity during arc rotation which is has similar PTV coverage dosimetric result as IMRT and RapidArc but less intensity change to result in poor sparing of organ at risk. Conclusions: This work indicates the potential of Field‐in‐Arc technique in clinical. The inverse method and better OAR sparing will develop in the future.
SU‐E‐T‐848: Dose Mass — Based IMRT Inverse Planning for Radiotherapy of Thoracic Cancer
Authors: Chen X , Chao M , Penagaricano J , Yan Y , Corry P , Ratanatharathorn V , Moros E
Published: November 2011

Purpose: The heterogeneity of lung tissue compromises the therapeutic quality of conventional dose‐volume based intensity modulated radiation therapy (IMRT) treatment planning, particularly when the lung volume varies with patientˈs respiration. An innovative inverse planning strategy was developed based on the concept of dose mass constraint as a more physical descriptor of dose delivered to lung. Methods: To better represent the actual lung cells being damaged by ionizing radiation, lung mass rather than lung volume was introduced in the inverse planning process. The conversion from volume of each voxel to mass was achieved with its local density, which was obtained from the computed tomography (CT or Hounsfield) number as a function of density relationship that is used by the treatment planning system. The dose mass constraints for targets and critical structures were integrated into the optimization cost function. For instance, a mass constraint would limit the dose to 20% of the lung mass to 20 Gy or less(coined as M20). The dose‐mass based inverse planning was applied on six thoracic cancer patients. To assess the dosimetric impact, comparisons were made between the dose mass histograms (DMH) and the dose volume histograms (DVH) and resulting dose distributions. Results: While the same planning target volume was covered, dose to lung from the DMH based plans were about 2% lower than DVH based plans. Lower doses could have important implications in terms of therapeutic effects. Conclusions: Dose mass‐based IMRT inverse planning framework was successfully implemented to take into account tissue density variations during plan optimization. Preliminary results suggest that gains in terms of lower dose to healthy lung are possible.
SU‐E‐T‐854: Key Anatomical Factors Influencing OAR Dose‐Volume Distribution in Prostate IMRT Plans
Authors: Yuan L , Ge Y , Li T , Zhu X , Yin F , Wu Q
Published: November 2011

Purpose: To identify the key factors of patient anatomy that influence the optimal dose volume histograms (DVHs) for the organs‐at‐risk (OARs) and to explore the tradeoffs between different OAR sparing goals. Methods: 88 prostate IMRT plans were studied retrospectively. The PTV‐OAR (bladder and rectum) geometry was described by the distance‐to‐target histogram (DTH) with a variable distance model to reflect the co‐planar beam configuration. Principal Component (PC) analysis was applied to DVH and DTH distributions in the patient pool to extract their salient features. The PCs were interpreted in terms of the patient anatomy and dose‐volume distribution metrics. The correlation coefficients between the PCs and these metrics were calculated. Finally, a stepwise multiple regression method was used to quantify the influence of these key anatomy parameters on the quality of corresponding DVHs. Results: The first PCs of DTH and DVH characterize the means of the histograms; the second PCs characterize the gradients of the histograms within a range. The most significant factor contributing to the first PC score (PC1) of DVH is the PC1 of DTH. It represents the correlation between the mean distance and the mean dose. The DVH PC2 is correlated with the DTH PC2, indicating the influence of DTH gradient on the gradient of DVH. Another significant factor affecting DVH PC2 is the fraction of OAR volume outside treatment fields with co‐planar beam setting. These factors combined account for significant majority of the cross patient DVH variation in the OARs: with the determination coefficients R, 2=0.88 and R, 2=0.85 for PC1 and PC2 of bladder, respectively, and R, 2=0.68 and R, 2=0.69 for PC1 and PC2 of rectum, respectively. Conclusions: Key factors representing the influence of patientˈs anatomy on the corresponding DVHs are extracted and quantified. This knowledge can be used to predict patient specific DVHs in IMRT planning.

Duke Univesity has a master research agreement with VARIAN Systems, Inc..