bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐464: A Patient Specific Quality Assurance Study on Absolute Dose Verification Using Ionization Chambers of Different Volumes in RapidArc Treatments
Authors: Syam kumar S.A , Prabakar S , Srinu Aketi , Sriram P , Dhanabalan R , Vivekanandan N
Published: November 2011

Purpose: To evaluate and compare five different ionization chamber ‐ phantom combinations for verification in routine patient specific quality assurance of RapidArc treatments. Methods: Fifteen different RapidArc plans conforming to the clinical standards were selected for the study. Verification plan was subsequently created for each treatment plans with different chamber‐phantom combinations CT scanned. This includes Medtec‐ IMRT phantom with micro ionization chamber (0.007cm3) and pinpoint chamber (0.015cm3), PTW‐Octavius phantom with semiflex chamber (0.125cm3) and 2D array (0.125cm3) and indigenously made Circular wax phantom with 0.6 cm3 chamber. The measured isocentre absolute dose was compared with the TPS planned. Results: Micro ionization chamber shows more deviations when compared to semiflex and 0.6 cm3 with a maximum variation of −4.76%,−1.49% and 2.23% for micro ionization, semiflex and farmer chambers respectively. The positive variations indicate that the chamber with larger volume slightly overestimates. Farmer chamber shows higher deviation when compared to 0.125cm3. In general the deviation was found to be less than 1% with semiflex and farmer chamber. A maximum variation of 2% between the plans was observed for 0.007cm3 ionization chamber, except for few cases. Pinpoint chamber underestimates the calculated isocentre dose by maximum 4%. Conclusions: Absolute dose measurements using semiflex ionization chamber with intermediate volume (0.125cm3) shows good agreement with the TPS calculated among the detectors used in this study. Positioning is very important when using smaller volume chambers as they are more sensitive to geometrical errors within the treatment fields. Also it is suggested to average the dose over the sensitive volume for larger volume chambers. The ionization chamber‐phantom combinations used in this study can be used interchangeably for routine RapidArc patient specific quality assurance with a satisfactory accuracy for clinical practices.
SU‐E‐T‐466: IMRT QA Technique Comparison between Single‐Gantry‐Angle Composite (SGAC) and Patient‐Gantry Angle Using MapCheckTM with Isocentric Mounting Fixture Tool
Authors: Khachonkham S , Changkaew P , Tangboonduangjit P
Published: November 2011

Purpose: This study is to evaluate the difference between two QA IMRT techniques(single‐gantry‐angle composite and patient‐gantry angle) of patient delivery plan. Methods: 7 Head‐and‐Neck(H&N) and 4 Brain IMRT patient plan generated by Varian‐Eclipse treatment planning system are used in this study. Each patient plan was measured using MapCheck diode array(MapCheck2, SunNuclear) with 1527 diode detector. MapCheck array is mounted on the isocentric mounting fixture (IMF) attached to the gantry used for measuring dose. All measurement of two QA IMRT technique with single‐gantry‐angle composite at 0 degree gantry position and patient gantry angle were compared to the TPS dose plane using gamma evaluation. Gamma criteria are set to 3% dose difference and 3 mm distance to agreement(DTA) and 10% threshold criteria for dose comparison. Difference between two QA techniques was evaluated by using the percentage of passing point between measurement and TPS dose plan. Results: The percentage of passing point are different between two QA IMRT technique in the same patient plan. The difference of both relative and absolute pass rate range between 0 to 3% for Head and neck plan and 0– 1.5% for brain plan respectively. Almost all the relative pass rate and absolute pass rate of single‐gantry‐angle composite are higher than patient‐ gantry angle technique in the same plan. The different result of pass rate between two techniques due to the effect of gantry machine and MLC moving in gravity. Other issues might relate to set‐up uncertainty of measurement. The dominant gantry angle dependence is larger in complex H&N IMRT plan with large high dose gradient and smaller in brain IMRT plan. Conclusions: Because of gantry angle dependence, in complex IMRT patient plan should be verified by using patient gantry angle technique in order to achieve the QA result with real situation of patient IMRT treatment.
SU‐E‐T‐651: Radiobiological Effect of Target Volume in SBRT of Lung Tumor: Comparison of Treatment Planning Algorithms Between Pencil Beam Algorithm and Monte Carlo Method
Authors: Liu D , Kumar S , Ajlouni M , Jin J , Glide C , Ryu S , Wen N , Siddiqui M , Li H , Fraser C , Movsas B , Chetty I
Published: November 2011

Purpose: To use equivalent uniform dose (EUD) and tumor control probability (TCP) to retrospectively analyze the radiobiological effect of target volumes in patients with NSCLC planned and treated with Stereotactic Body Radiotherapy (SBRT). Methods: Eighty‐three stage I–II lung cancer patients with 86 lesions treated with SBRT were retrospectively analyzed. For each patient, a Pencil Beam (PB) algorithm‐based treatment plan with a dose regimen of 12 Gy/fraction in 4 fractions was generated. To overcome the known uncertainties of conventional PB algorithm in lung tissue, Monte Carlo (MC) treatment plans were also created in the iPlan (BrainLab) system using the same monitor units derived from the PB‐based plan. Niemierkoˈs EUD and TCP (Poisson model) were computed using different surviving fraction (SF) parameters for each dose calculation algorithm. The radiobiological effects of target volume were analyzed by correlating EUD and TCP with PTV volumes. Results: Mean PTV volume was 39.31 +/− 28.96 cc. The mean PB EUDs were 50.61, 50.60, 50.57 and 50.55 Gy for SF parameter values of 0.36, 0.34, 0.3 and 0.28, compared with MC EUDs 43.97, 43.84, 43.56 and 43.41 Gy. The mean PB TCP values were up to 18% higher than the mean MC TCP. EUDs calculated using both PB and MC were not sensitive to SF parameters, whereas they were for TCP calculation. Overall, MC EUDs were more sensitive to PTV volumes than PB EUDs, measured by Pearson correlation 0.46 vs. 0.07. Larger PTV volume decreased PB TCP values while this was not the case for MC TCP Conclusions: This work demonstrates encouraging evidence that radiobiological effect of target volume and dose calculation algorithm selection is significant in EUD and TCP estimations. Further studies confirming this relationship and relating to treatment outcomes are warranted.

Work supported in part by NIH R01 CA106770
SU‐E‐T‐652: Rectal Equivalent Uniform Dose Analysis on the Prostate IMRT for Interfraction Organ Motion Using the Gaussian Error Function
Authors: Shan W , Chow J , Markel D , Jiang R
Published: November 2011

Purpose: The aim of this study is to verify the calculation of rectal equivalent uniform dose (EUD) using the Gaussian error function (GEF), which can reduce the dose‐volume database to enhance the computing efficiency. Methods: For a group of 20 prostate patients, cumulative dose‐volume histograms (cDVHs) for the rectum, shifted in the anterior—posterior directions based on a 7‐beam IMRT plan, were calculated and modeled using the Pinnacle3 treatment planning system (TPS) and GEF, respectively. The range of rectal shift for each patient was measured by daily electronic portal imaging with fiducial gold markers in the prostate. The shape of cDVH curve was fitted into the GEF model, and then the cDVHs were converted to corresponding differential DVHs to calculate the rectal EUDs in each interfraction organ motion. Results: Rectal EUD was calculated per fraction to determine the equivalent dose at each movement step. Our results showed that rectal EUDs increased as the rectum shifted to anterior direction and decreased in the posterior direction. Moreover, it is found that rectal EUDs have a negative linear relationship with respect to the organ displacement. Based on the results, the patient with the smallest prostate (volume = 40 cc) in the group received the highest rectal EUD when the rectum shifted 8 mm anterior. Percentage difference of rectal EUD using the TPS and GEF has been calculated for each movement. Since the results are less than 0.5%, the GEF model is considered a good potential alternative of the TPS. Conclusions: We concluded that the calculation of rectal EUD using the GEF model was validated with error less than 0.5%.
SU‐E‐T‐653: Dosimetric Evaluation of Prostate Brachytherapy Using Single Isotope and Hybrid Seeds
Authors: Pritz J , Forster K , Saini A , Biagioli M , Zhang G
Published: November 2011

Purpose: Clinically, single isotope, such as I‐125 or Pd‐103, is commonly used in the seeds in brachytherapy for prostate cancer. A mixture of two isotopes in the seeds has been proposed for prostate cancer treatment. This study investigates the differences in biological effective dose (BED) between the treatment plans of such hybrid sources and plans of single isotope. Methods: Five prostate cancer cases previously treated using single isotope seeds were selected for this study. Hybrid seed plans of a 50/50 mixture of I‐125 and Pd‐103 and a single isotope Pd‐103 were generated based on the original I‐125 plans. Number and location of seeds were the same between the plans. A numerical approach was implemented in the BED calculation. Dose and BED homogeneity in PTV, mean BED in organs at risk (OAR) and hot BED to OAR were compared between the plans. Results: To achieve the same BED (110 Gy) to cover 90% of PTV, the corresponding dose is 145, 120 and 136 Gy for I‐125, Pd‐103 and 50/50 hybrid seeds respectively. The hybrid plans demonstrated the most homogeneous dose and BED in PTV. The mean highest BED delivered to a 1.0 cc volume of rectal tissue by the I‐125, Pd‐103, and 50/50 hybrid modality was 49.85±30.24, 93.73±38.33, and 82.52±34.08 Gy respectively, delivered to a 1.0 cc volume of bladder was 41.6±19.5, 66.8±27.9 and 61.6±25.2 Gy respectively, and to other normal tissue was 303.41±63.84, 363.95±197.29, and 319.14±146.72 Gy respectively Conclusions: The prescription dose to cover 90% PTV by a BED of 110 Gy is 145, 120 and 136 Gy for I‐125, Pd‐103 and 50/50 hybrid seeds respectively. Based on the BED data, the best OAR sparing occurs with I‐125 treatment plans, followed by the 50/50 hybrid plans, and finally the Pd‐103 plans.
SU‐E‐T‐654: Calculation of Cumulative Biological Effective Dose Distributions for Multimodality Treatment Regimes
Authors: Schuller B , Kemmis T
Published: November 2011

Purpose: Evidence has recently been reported supporting the role of stereotactic body radiotherapy (SBRT) as a supplemental treatment option in the form of a boost or salvage reirradiation following conventional radiotherapy. It may therefore be desirable to augment the process of physical dose summation in the cumulative plan evaluation process by constructing corresponding biological effective dose (BED) distributions that incorporate the biological effects of the different dose fractionation schemes required for multimodality treatments. To that end, we developed a computational process for calculating cumulative BED distributions for patients receiving conventional radiotherapy followed by SBRT. Methods: We developed a program designed to accept two DICOM dose matrices, as calculated in standard treatment planning systems, and calculate the BED at each matrix element obeying the dose per fraction dependence in the BED formalism. It then calculates the cumulative BED distribution for multimodality treatment regimes by matrix summation and outputs the result in DICOM format. Two clinical head and neck IMRT cases (large field (2.13Gy × 33) and small field (2Gy × 32)) were evaluated as part of a pilot study to demonstrate the overall feasibility of the calculation scheme. Following clinical IMRT planning, each case was planned in a mock SBRT scenario (6Gy × 5) where a smaller planning volume was drawn to simulate a boost or salvage reirradiation. The clinical IMRT and mock SBRT dose matrices were then processed to generate cumulative BED distributions. Results: Our computational process was successful in producing cumulative BED distributions. For the large field IMRT case, the overall BED distribution beyond the initial treated volume was dominated by the initial IMRT course, whereas clear additive increase in the BED distribution beyond the initial treated volume was evident in the small field case. Conclusions: Cumulative BED distributions may reveal useful clinical information during plan evaluation.
SU‐E‐T‐655: GEUD‐Based Optimization for HDR Prostate Brachytherapy: Maximizing Conformal Index
Authors: Giantsoudi D , Baltas D , Karabis A , Mavroidis P , Papanikolaou N
Published: November 2011

Purpose: Our previous work suggested the potential of gEUD‐based inverse optimization tool for HDR prostate brachytherapy (Giantsoudi et al AAPM 2010). In this study we attempt to define a default set of parameters for this optimization system that will maximize the conformal index (COIN — Baltas et al 1998) while leading to clinically acceptable dosimetric results. Methods: For given patient geometry, multiple gEUD‐based optimized plans were produced by varying the penalty factors n of the objectives in the range of 0–20 for the prostate‐PTV (target), prostate‐OAR (used as dose constraint structure) and normal tissue (ring surrounding the prostate) structures, for various clinical cases. Calculated COIN values for all the resulting plans were plotted against the penalty factor values. The combination of factors maximizing COIN was then selected and applied in 12 clinical cases. Their dosimetric results were evaluated following the Offenbach clinical protocol. Our methodˈs sensitivity was then examined by varying the n‐parameter values to +/−10% and the gEUD0 values to +/−2% of the default settings. Results: The set of penalty factor values maximizing COIN [n(prostate‐PTV)=18, n(prostate‐OAR)=2, n(NT)=2] led to clinically accepted plans for all 12 clinical cases and is suggested as the default optimization protocol for this method. Introducing deviations to the gEUD0 or n‐parameter values, most of the dosimetric evaluators showed less than 1.6% difference compared to the default optimized solutions. Exception to this rule was the V150 parameter that showed up to 6.08% deviation for 10% change of the n(prostate‐PTV) factor and 6.53% deviation for 2% change of the gEUD0(prostate‐PTV). Conclusions: A default set of penalty factor values is suggested for our gEUD‐based optimization system that leads to maximized COIN and clinically acceptable solutions for a wide range of clinical cases, facilitating HDR prostate brachytherapy inverse optimization. The stability and robustness of our method was also shown.
SU‐E‐T‐658: Calculation of the Prostate Equivalent Uniform Dose for Interfraction Organ Motion Using the Gaussian Error Function Model
Authors: Shan W , Chow J , Markel D , Jiang R
Published: November 2011

Purpose: The Gaussian error function (GEF) model was used to fit into the dose‐volume histograms (DVHs) of prostate IMRT and calculate the prostate equivalent uniform dose (EUD) associated with interfraction organ motion. Methods: Three patients with small (39 cc), medium (60 cc) and large (87 cc) prostate volume were selected from a group of twenty in this study. Cumulative DVHs for the prostate that were shifted in the anterior‐posterior directions based on a 7‐beam IMRT plan were calculated and modeled using the Pinnacle3 treatment planning system (TPS) and GEF. To simulate the interfraction prostate motion, the prostate was shifted 1 cm in the anterior and posterior directions in 2 mm steps, using the dose distribution based on the IMRT plan without actual prostate motion. The prostate cumulative DVHs were converted to corresponding differential DVHs to calculate the prostate EUDs in each interfraction motion using MATLAB. Results: Prostate EUD was computed to per fraction in order to measure the equivalent dose at each movement step. Prostate EUDs were found to decrease as the prostate shifted to both the anterior and posterior directions. The prostate EUD was also expected to have the maximum value at the isocentre, since the target received the best dose coverage when the prostate displacement remains zero. Our result showed that patient with the smallest prostate volume (39 cc) in the group has the smallest prostate EUD, when the prostate was shifted 1 cm anteriorly and posteriorly. Since the percentage difference of the prostate EUD calculated by the TPS and GEF is significantly less than 0.5%, we consider the GEF model a good potential alternative to determine the prostate EUD. Conclusions: We validated our GEF model which can predict the prostate EUD with accuracy less than 0.5% compared to the results from the TPS.
SU‐E‐T‐675: Fast Monte Carlo Simulation for Total Body Irradiation of Co‐60
Authors: Liu X , Rakowski J , Snyder M
Published: November 2011

Purpose: Our institution delivers TBI using a modified Theratron 780 Co‐60 unit. Due to limitations of our treatment planning system in calculating dose at extended SSDs, we have developed an algorithm for fast Monte Carlo simulation of dose to a patient receiving TBI treatment using our setup. The goal is to achieve a high accuracy dose calculation in heterogeneous tissue. Methods: A custom Monte Carlo code was written in C to simulate energy deposition by 1.25 MeV photons over a broad field shape defined by our modified collimator on the Co‐60 unit. A water phantom was constructed to measure dose delivered from the Co‐60 unit using GafChromic film. A two‐piece aluminum insert was fabricated to test the ability of the code to calculate dose near and inside a high density object. Dose measurements were made by placing GafChromic film inside the water phantom at various planes, with and without the aluminum insert, and compared to doses calculated by the Monte Carlo algorithm. Results: Simulations in the water phantom accurately predict the depth of maximum dose in the phantom at 0.5cm. The measured PDD along the central axis of the beam closely matches the PDD generated from the Monte Carlo code, deviating by less than 5% from Dmax to a depth of 20cm. When the aluminum bar is introduced into the simulation, the dose measured at planes inside the aluminum had an average deviation on cross‐profile of 4%. Conclusions: The fast Monte Carlo algorithm is capable of accurately calculating dose in heterogeneous media. Depth‐doses inside high density materials were accurately predicted, and further modification of the algorithm to include density information on a voxel‐by‐voxel basis should allow for the algorithm to provide clinically useful information in planning TBI.
SU‐E‐T‐686: Monte Carlo Study of Material Approximation Introduced Dose Difference in Electron Conformal Therapy Planning
Authors: Zhang R , Zhang G , Harris E , Forster K , Feygelman V
Published: November 2011

Purpose: When Monte Carlo (MC) is used in dose calculation with CT data, materials are often assigned based on the local Houndsfield units if the density threshold method is applied. When bolus is used to compensate for body surface irregularities and/or to modulate the therapeutic depth in bolus electron conformal therapy (bolusECT), the bolus material, which is machineable wax, is treated as soft tissue, since the density of bolus overlaps with soft tissue. This study investigates the dose errors introduced by this material misassignment.Methods: BEAMnrc was used to simulate electron beams from a Trilogy accelerator. SPRRZnrc was used to calculate stopping power ratios (SPR) of tissue to wax, SPR(tissue/wax), and tissue to water, SPR(tissue/water), for 12 and 15 MeV electron beams which are the most commonly used energies in bolusECT. DOSXYZnrc was applied in dose distribution calculation in tissue with wax slabs of various thicknesses and a wedge‐bolus on top respectively. The MC dose distributions calculated using different bolus materials were compared.Results: With the same density, the SPR(tissue/wax) for 12 and 15 MeV beams ranges from 0.934 to 0.944, while the SPR(tissue/water) values are between 0.990 and 0.991, indicating higher stopping powers of wax. The 12 MeV beam range is 6.5 cm in wax and 6.7 cm in tissue. For a 12 MeV beam, the dose in tissue immediate under the bolus is overestimated by about 2.5% of maximum dose at 3 cm bolus thickness if wax bolus is treated as tissue. For 15 MeV beams, the error is about 1.4% Conclusions: Due to stopping power differences, dose differences are observed if the bolus material is misassigned in bolusECT dose calculations. Large dose overestimations occur at thick bolus region. However, the error is mostly within clinical tolerance, especially for thin bolus regions.
SU‐E‐T‐695: Dose Calculation of a Breast Cancer Brachytherapy Treatment Using Monte Carlo Simulation
Authors: Graf M , Scanderbeg D , Cerviño L , Yashar C , Jiang S
Published: November 2011

Purpose: To develop a dose calculation package based on Monte Carlo simulation for SAVI breast cancer brachytherapy treatment using patientˈs CT data. Methods: A realistic model of the patient was created using anonymized patient data including images, structures and plans from the treatment planning system. Images were then voxelized and each voxel assigned a density and material value base on its calibrated Hounsfield units. Materials included were fat, muscle, lung, air, bone, and Nitinol. This data was then imported into the penEasy Monte Carlo code. Each source position from the plan was then run individually and the dose was totaled after weighting each source by its dwell time from the original plan. Energies used were those of the VariSource IR‐192. Results: The resulting dose was compared to the dose from the original plan and plotted side by side. Dose differences were considered that occurred outside the air cavity, particularly in the evaluated planning target volume (PTVeval), which is calculated as 1 cm outside the cavity subtracting the cavity itself, the skin and the chest wall. Dose from the Monte simulation looked similar in shape and intensity to the original plan. Conclusions: We have developed a Monte Carlo simulation package to calculate dose distributions for SAVI based breast cancer brachytherapy using patientˈs CT and plan parameters extracted directly from a commercial planning system.
SU‐E‐T‐709: Monte Carlo Evaluation of Superposition‐Algorithm Skin Dose Calculation for Brain Radiotherapy
Authors: Li J , Xiao Y , Yu Y , Shi W
Published: November 2011

Purpose: Skin dose is one of the concerns in brain radiotherapy: over dose will cause patient hair loss. It is important to predict accurate skin dose in treatment planning. Inaccuracy of skin dose calculations using some treatment planning systems has been reported in literatures. Monte Carlo calculation is recognized as the gold standard in radiation dose calculation. The study was aimed to apply Monte Carlo calculation to evaluate the accuracy of skin dose calculation performed with our clinic treatment planning system (CMS XIO), which is based on a superposition algorithm. Methods: A conformal treatment plan for brain tumor treatment was generated in a CMS XIO treatment planning system and the plan was recalculated using a Monte Carlo calculation algorithm for the same linear accelerator with the same beam settings (beam energy, angles, field sizes, and monitor units). The Monte Carlo calculation was performed in a CMS Monaco treatment planning system in the QA mode, with variance of 1%. The treatment plans used 4 photon conformal beams (6 MV). The skin structure was ∼5 mm thick, which represented the thickness of clinic concern. The skin doses calculated using the XIO superposition algorithm were compared against those calculated using the Monte Carlo algorithm. Results: For each individual beam, the differences of the mean skin doses were 0.4%, 0.9%, 1.9%, and –1.4%, respectively, and the differences of the maximum skin doses were –2.6%, –3.1%, 2.9%, and –3.7%, respectively. For the composite beams (4 beams were on), the differences of the mean doses and the maximum doses were 0.6% and –1.4%, respectively. Conclusions: There were no clear trends in the dose differences. The differences in skin dose between the superposition calculation and the Monte Carlo calculation were not significant: < 2% in mean dose and < 4% in maximum dose.
SU‐E‐T‐771: Isodose Line Driven Semi‐Inverse Planning of High Dose Rate Brachytherapy for Cervical Cancer
Authors: Lian J , Cullip T , Zhu J , Jones E , Varia M , Tang X , Potter L , Xu Z , Deschesne K , Chang S
Published: November 2011

Purpose: Delineation of tumor is indispensible for adequate tumor coverage in inverse planning of cervical cancer brachytherapy. However, target definition is challenging in CT/CBCT planning images. In this project, we developed a tool to convert the isodose lines from traditional source loading, which produces dose distribution with good tumor coverage, to a surrogate treatment volume needed in the optimization. Through this, we integrate the clinical knowledge of conventional loading and advantage of inverse planning to spare organs at risks. Method and Materials: Five cervical cancer patients treated with tandem and ovoids HDR brachytherapy are studied. The clinical plans are point‐based (600cGy to point A) with Fletcher‐type loading pattern. Retrospectively, an inverse plan was made for comparisons. A software tool was developed to convert the isodose curves of the conventional plan to closed anatomic structures. In order to limit the dose of bladder and rectum less than 70% of the prescription dose, their contours were subtracted from the 70% isodose line converted‐volume and this new structure (ISD70‐bladder‐rectum) was placed as the target in Oncentra optimization software (Nucletron). Three dosimetric endpoints, volume coverage of ISD70‐bladder‐rectum and 2cc maximal dose of the bladder and rectum, are used in compassions. Results: The isodose line converted‐ structures are compared with the original dose curves and they are accurate. The inverse planning lowers the dose on the bladder with similar coverage of ISD70‐bladder‐rectum as the conventional plan. The bladder 2cc dose of the inverse plan is 510.4± 92.7 cGy, which is significantly lower than that of conventional plan, 560.3± 93.8 cGy (p=0.05). Conclusion: Isodose surfaces from traditional source loading are good surrogate for 3D treatment volume in HDR inverse planning for cervical cancer. This approach combines the prior clinical experience and strength of inverse planning for better critical structure sparing with the similar tumor coverage.
SU‐E‐T‐782: A Novel Geometric Index to Evaluate Image Guidance Strategies for Prostate Cancer Adaptive Radiotherapy
Authors: Wu Q , Liu H
Published: November 2011

Purpose: Margin has been commonly used to evaluate different image guidance (IG) strategies in prostate cancer radiotherapy. However, it becomes cumbersome when applied to adaptive radiotherapy. In this study, a new index, cumulative index of target volume (CITV), was proposed and compared with other indices. Methods: A hypofractionated protocol was simulated with 28 patients each with at least 16 helical CT scans. Both low‐risk patient (LRP,CTV=prostate) and intermediate‐risk patient (IRP,CTV=prostate+seminal vesicles) were included. The CITV is defined as the quotient of the sum of PTV over the sum of CTV for all treatment fractions. The change of clinical target volume during treatment course is taken into consideration, so is the multiple adaptive planning with different PTVs. For the same target coverage, the smaller value of CITV indicates better strategy. The CITV was calculated and compared for three IG strategies: online IG only protocol, hybrid strategy combining online image guidance and a single offline replanning, and a “rolling average” multiple replanning strategy. In addition, the hybrid and RA strategies were optimized by searching for the optimal number of fractions to determine the patient‐specific plan through the use of CITV. Results: For LRP (IRP), the CITVs are 1.78, 1.62 and 1.59 (2.46, 2.07, 2.00) for online IG only, hybrid and RA strategies, respectively. The optimal number of fraction for the ITV construction is 2 for LRP, and 3 for IRP for both the hybrid and RA strategies. Conclusions: We proposed a new concept based on cumulated target volume for the evaluation of different IG strategies. It is geometric in nature and has advantages over the margins. It is only a function of the underlining patient motion uncertainties. Therefore, it can be generalized and easily adaptable to non‐uniform margins and different clinics where the treatment planning process can be quite different.
SU‐E‐T‐788: DICOM‐Based Electronic Patient Record (ePR) System with Computer‐Aided Evaluation (CAE) of Intensity Modulated Radiation Therapy (IMRT) Plans
Authors: Cheung F , Le A , Law M
Published: November 2011

Purpose: To develop a DICOM‐based electronic patient record system with computer‐aided evaluation (CAE) of intensity modulated radiation therapy (IMRT) plans and to assess the technical aspects of the system and its performance. Methods: The system was developed using the WampServer version 2.0, a package of Apache web server 2.2, PHP 5.2 and MySQL 5.1 to facilitate evaluation of IMRT plans in any Web browser. After tracing the clinical workflow, a set of routines were written to parse key data items from the DICOM‐RT objects. To save planners from tedious manual evaluation, the direct relationships between the DVH curve to the corresponding CT images, RT dose data and ROI contours were visualized. Extraction of both overdose and underdose regions was based on the edge‐based approach. Followed by reconstruction of ROI contours, the grid doses were constructed by multiplying each pixel value stored in the Image pixel module with the Dose Grid Scaling attribute in the RT Dose module. Graphic User Interfaces (GUIs) were created to allow planners to establish customized plan acceptance criteria and query for evaluation results. Thirty IMRT plans were collected for technical verification and performance validation. Results: The CAE system was successfully developed, allowing better appreciation of resultant plans. There was no statistical difference between CAE results and those obtained manually by experienced planners on all datasets. With prompt problem detection feature, the direct relationship between the DVH data to the corresponding inhomogeneity regions on CT slices could be shown within an average of 20 seconds. Conclusions: The CAE system will represent a breakthrough in the routine IMRT planning workflow by eliminating all tedious manual evaluation steps and introducing remote plan evaluation across multiple locations by the local area network and Internet. The concept could also be adopted in the evaluation of plans other than IMRT.
SU‐E‐T‐797: Effects of the Number of Intensity Levels in Step&shoot IMRT for Prostate Treatments
Authors: Garrigo E , Venencia C , Almada M , Descamps C , Pipman Y
Published: November 2011

Purpose: Step&shoot IMRT Treatment planning requires the conversion of an optimized fluence into deliverable sequences of MLC segments. The objective of this paper is to study the effects of varying the intensity levels (ILˈs) number in prostate step&shoot IMRT treatments. Methods: Patient data with prostate cancer and IMRT treatment indication was selected. Treatment planning was done using a 6MV 7‐field arrangement (Primus linac, Optifocus MLC, 10mm leaf‐width) and Konrad v2.2 (Siemens) TPS. The treatment plan includes the simultaneous irradiation of the prostate to 82Gy and the seminal vesicles to 64Gy in 41 fractions. Four plans were generated using 5, 7, 10 and 15 ILˈs and normalized to deliver the same minimum dose to the prostate. Comparisons between plans were done in terms of total segment number, MU, treatment time and DVH for PTVs and OARs (rectum, bladder and femoral heads). Results: The total segment numbers were 44, 60, 84 and 116 from 5 to 15 ILˈs. The MUˈs total numbers decreased with the increase of the ILˈs (527, 522, 518 and 508). Increasing the number of ILˈs was accompanied by the treatment times raise (11%, 23% and 37% in relation to 5 ILˈs, 387seg) and resulted in increases of Prostate PTV dose homogeneity and conformity index (CI). The maximum dose (CI) was 87.7Gy (0.957) and 89.7Gy (0.836) for 15 and 5 IL respectively. No difference in minimum dose and CI was found for the seminal vesicle PTV. All plans showed insignificant OAR DVH differences. Conclusions: The increment in the ILˈs number resulted in an improvement of the Prostate PTV homogeneity and treatment time without any extra sparing to OAR. The benefit of a better uniform dose in the Prostate PTV should be analyzed for each treatment in order to set planning guidelines.
SU‐E‐T‐799: Improvement in Chest Wall Dose with Volumetric Modulated Arc Therapy for the Treatment of SBRT Lung Lesions
Authors: Happersett L , Zhang P , Rimner A , Hunt M , Yorke E , Jackson A , Mageras G , Mechalakos J
Published: November 2011

Purpose: This study evaluates the use of volumetric arc therapy (VMAT) for hypo‐fractionated lung treatments to improve plan conformality and reduce chest wall dose. Methods: Ten patients treated with hypo‐fractionated lung SBRT were retrospectively planned with 270 to 360 degree arc VMAT and results were compared to the 4 – 5 field IMRT plans used for treatment. Prescription doses were 45, 48 or 54Gy in 5, 4 or 3 fractions, respectively. To compare plan quality, various dose‐volume statistics were assessed for the PTV, spinal cord, esophagus, lungs, distal and mainstem bronchi. Conformity index (V(95%Rx)/ V_PTV(95%Rx)) was also evaluated. Monitor units were compared to evaluate plan efficiency. Results: Patient‐averaged PTV D(99%), D(95%), and Dmax were 97.9, 101.2, and 107.8% respectively for VMAT and 98.6, 101.6, and 106.4% respectively for IMRT. Average conformity index was 1.79 for VMAT and 1.96 for IMRT (p<0.01). The most significant normal tissue dose improvement using VMAT was for the chest wall where the average D(30cc) was 24.5 Gy, 19% lower than IMRT (p < 0.01). The average total lung V(20Gy) fell from 5.6% with IMRT to 5% with VMAT but other total lung statistics (V(10Gy), mean dose) were virtually identical. Average contralateral lung mean dose increased with VMAT (1.5 vs 1.1Gy, p<0.01). VMAT and IMRT maximum doses to cord, esophagus, mainstem and distal bronchi did not differ significantly. On average, MU required for VMAT delivery were 32% less than IMRT. Conclusions: PTV coverage and most normal tissue doses were similar for VMAT and IMRT. Conformity index and chest wall D(30cc) improved with VMAT. Although total lung dose was similar for both plans, mean contralateral lung dose on average was higher for VMAT. The VMAT plans showed improved conformality and reduced chest wall D(30cc) at a cost of increased contralateral lung mean dose.

Research agreement with Varian Corporation
SU‐E‐T‐810: Simultaneous Integrated Boost with Forward IMRT for Multiple Brain Metastases: A Planning Study
Authors: Liang X , Ni L , Hu W , Chen W , Ying S , Liu Y , Gong Q
Published: November 2011

Purpose: To evaluate the dose conformity and feasibility of whole brain radiotherapy with a simultaneous integrated boost by forward intensity‐modulated radiation therapy in patients with 1–3 brain metastases. Methods: Forward intensity‐modulated radiation therapy plans were generated for 10 patients with 1–3 brain metastases on Pinnacle 6.2 Treatment Planning System. The prescribed dose was 30Gy to the whole brain (PTVwbrt), 40Gy to individual brain metastases (PTVboost) simultaneously, both doses were given in 10 fractions. The maximum diameters of individual brain metastases ranged from 1.6 to 6 cm, and the summated PTVboost per patient ranged from 1.62 to 69.81 cc . Conformity and feasibility were evaluated and compared with those reported in the literature which had been planned by helical tomotherapy, regarding conformation number (CN) and treatment delivery time. Results: One hundred percent volume of PTVboost received at least 95% of the prescribed dose in all cases. The maximum dose was less than 110% of the prescribed dose to PTVboost . And all of the hot spots were within PTVboost . The volume of PTVwbrt received at least 95% of the prescribed dose ranged from 99.2% to 100%. The mean values of CN were 0.682. The mean treatment delivery time was 2.79 minutes. Ten beams were used on average in these plans. Conclusions: Whole brain radiotherapy with a simultaneous integrated boost by forward IMRT for patients with 1–3 brain metastases is feasible. Dose conformity was comparable to those planned by helical tomotherapy in the literature and treatment delivery time was shorter.
SU‐E‐T‐814: Dosimetric Feasibility of Dose Escalation with Gated IG‐IMRT for Pancreatic Cancer
Authors: Liu Feng , Li X. Allen
Published: November 2011

Purpose: Delivery of curative high dose to the pancreatic tumor is limited by the surrounding radiation sensitive organs at risk (OARs), especially the most dose‐limiting organ duodenum. Image‐guided radiotherapy (IGRT) allows small planning target volume (PTV) margin and intensity‐modulated RT (IMRT) offers sharp dose gradients, permitting dose escalation with minimal OAR damage. We study the dosiemtric feasibility for using IG‐IMRT to escalate dose to pancreatic cancer. Methods: Planning 4D CT datasets for 10 pancreatic cancer patients treated previously were used for evaluation. A PTV margin of 3 mm was added to the clinical target volume (CTV, pancreatic head). This small margin is justified because the patient is to be treated with (1) gating to reduce the intrafractional (respiration) motion below 3 mm, and (2) high quality CT guided repositioning using an in‐room CT (e.g., CTVision, Siemens) to minimize interfractional variations. IMRT plans with prescription doses of 50.4 Gy and 72 Gy in 1.8 Gy fractions were generated using a planning system (Panther, Prowess). Results: A series of dose volume quantities at two prescription doses 50.4 and 72 Gy were compared. For six out of 10 patients, the duodenum volumes irradiated by at least 50.4 Gy (V50.4 Gy) with the prescription dose of 72 Gy are well below 50%, while the doses to other OARs are within the acceptable ranges. for two (seven) out of 10 patients the volumes irradiated by at least the prescription dose of 72 Gy are less than 5 (10) cc. Conclusions: With appropriate selection of patients with pancreatic cancer, the dose escalation to 72 Gy may be feasible by using gated IMRT with daily in‐room CT guidance.
SU‐E‐T‐821: Comparison of Intensity‐Modulated Arc Therapy and Intensity‐Modulated Radiotherapy Plans for Nasopharyngeal Carcinoma Simultaneously Integrated Boost Radiation Therapy
Authors: Liu T , Yin Y , Bai T , Chen J , Lu J , Sun T , Gao M , Ma C
Published: November 2011

Purpose: To compare the dosimetric differences between intensity‐modulated arc therapy (ARC) and intensity‐modulated tadiotherapy (IMRT) plans for nasopharyngeal carcinoma simultaneously integrated boost (SIB) radiation therapy. Methods: 10 nasopharyngeal carcinoma cases treated by SIB radiation therapy were selected. For each case, two treatment plans (ARC and IMRT) were generated using Varian Eclipse ver8.6 treatment planning system. Evaluate the dose parameters of targets, organs at risk (OAR), monitor units and treatment time, using dose‐volume histogram (DVH). Results: There were statistical differences (P<0.05) between CI, but no statistical differences (P>0.05) between HI forPTV, PTV1, PTV2. Mean dose of brain‐stem decreased in ARC plan, while the maximum dose increased. The maximum dose of spinal‐cord in ARC plan were higher than those in IMRT plan, but not statistically significant. There were statistical differences between V15, V20, V25, V30, V35, V40, V45, and V50 of normal tissues. The number of MU resulted to be MU‐IMRT=1308±213, MU‐ARC=606±96. The MU of ARC plan were 702 less on average than IMRT plan. Conclusions: The ARC was equal to IMRT on the target coverage and the dose of OAR, and better on CI. The ARC plan could reduce dose of normal tissues, machine monitor units and treatment time.
SU‐E‐T‐824: Accuracy of Low Doses in Lung for Locoregional Breast Irradiation with TomoTherapy and VMAT
Authors: Ploquin N , Belec J , Caudrelier JM , Clark B G
Published: November 2011

Purpose: To compare low lung doses in treatment plans for left side locoregional breast cancer with TomoTherapy and Volumetric Modulated Arc Therapy (VMAT) where VMAT is planned by Monaco® (Elekta‐CMS) treatment planning system which incorporates a Monte‐Carlo (MC) dose calculation engine. Methods: Four patients previously treated on TomoTherapy were replanned with the VMAT technique for treatment on Elekta Synergy. Plans were optimized and calculated using Pencil Beam (PB) and MC algorithms available in Monaco. As a benchmark, plans were also recomputed using a previously validated and published in‐house Monte Carlo model of TomoTherapy and VMAT. Particular attention was given to the low lung doses (V5Gy and V20Gy), which are considered as important clinical parameters in evaluating the acceptability of this type of treatment plan, but where accuracy is usually lacking with current planning system dose calculation algorithms. Results: Similar dose distribution and time of delivery could be achieved between TomoTherapy plans (V95%=99.1+/− 0.9%). and VMAT plans (V95%=98.5+/−0.6%). The average percentage (+/− 1SD) difference between our in‐house MC model lung doses and Monaco MC lung doses was (2+/−2%) for V5Gy and (4+/−1%) for V20Gy. Slightly larger average percentage differences were observed between our in house MC model for the V5Gy (−11+/−4%) and V20Gy (3+/−1%) for plans calculated using Collapsed Cone Convolution (CCC) algorithm in TomoTherapy. As expected, the largest average percentage differences for V5Gy (−28+/−1%) and V20Gy (−10+/−2%) were found between the in‐house MC model and the PB model in Monaco. Conclusions: We have demonstrated the feasibility of adapting our technique developed on TomoTherapy for treating left sided locoregional breast cancer to VMAT and compared the accuracy of the low isodoses calculated with the Monaco MC algorithm to the TomoTherapy CCC algorithm.
SU‐E‐T‐832: Segmental IMRT Treatment for Mycosis Fungoides of An Extremity
Authors: Cadman P , Mohamed M
Published: November 2011

Purpose: Mycosis fungoides is a rare, but potentially lethal cutaneous T‐cell lymphoma that is traditionally treated with Total Skin Electron Irradiation, TSEI. We investigated the novel use of segmental IMRT for treatment of a patient with mycosis fungoides of the foot and report on dosimetric accuracy and clinical outcome. Methods: Pinnacle V9.0 was used to create a 9‐field segmental IMRT plan delivered using 6 MV photons on our Clinac 21EX with 120 leaf Millenium MLC. The target volume included the clinically assessed disease from the skin surface to a depth of 1 cm. The prescription dose was 30 Gy in 15 fractions. Planning objectives were chosen to create a uniform dose to the PTV while limiting dose to the underlying normal tissue as much as possible. The addition of a planning region of interest that extended 1 cm beyond the skin surface allowed the MLC leaves to open to create “skin flash”. A cylindrical dosimetry phantom was planned in the same manner to determine the accuracy of Pinnacle dose calculations. Gafchromic film placed in the axial plane of the phantom and subsequently analyzed in terms of absolute dose. Results: 92% of all film measurement points in the axial plane passed the gamma analysis criteria of 3% dose difference and 3 mm DTA. Measured doses near the surface (1 mm) were typically 85% of the prescription dose. Four months after completion of treatment the lesions in the foot had regressed completely and the patient was also able to walk unencumbered. Conclusions: Our results confirm that Pinnacle dose calculations are reasonable accurate for this type of IMRT delivery and that skin doses are within clinical range. Segtmental IMRT may be an excellent choice for treating extremities with mycosis fungoides when sparing of underlying tissues is a major concern.
SU‐E‐T‐839: Treatment Planning Comparison Between IMRT and Protons Involving Patch Fields
Authors: Ly A , Nookala P , Watt D , Patyal B
Published: November 2011

Purpose: To compare treatment plans on select complex cases using IMRT and protons involving patch‐field technique Methods: IMRT is used to treat tumors adjacent to critical structures. This is achieved by a dose optimizing algorithm that creates field segments using MLC and modulating the photon fluence to treat different parts of the tumor and conformally avoiding nearby critical structures. Proton beams offer an alternate way to treat such tumors and avoid critical structures. Properties of proton beams important to treatment planning are the ease with which a proton beam can be stopped at the desired depth in a medium as well as its sharp distal dose fall off near the end of the range. In a patch‐field proton beam arrangement a shoot through beam is used to treat majority of the tumor and a patching beam treats remaining tumor near the critical structures. The patching beam stops distally on the lateral edge of the shoot through beam. The weighting and the distal overlap between the shoot‐through and the patching beams are optimized to conformally cover the entire tumor. Here we are comparing treatment plans for different tumor sites using IMRT and proton beams involving patch‐field arrangements. Results: The isodose distributions and dose volume histograms (DVH) were compared between the two treatment modalities. Both IMRT and proton plans do a good job of conformally irradiating the tumor. But overall, proton plans do a better job of sparing the critical structures. One clear advantage of proton beams is the avoidance of low dose to normal tissues surrounding the tumor leading to a lower integral dose Conclusions: Complex tumors surrounding critical structures can be treated effectively with IMRT or proton beams. But protons are more effective in sparing critical structures and they give lower dose to normal tissues than IMRT.
SU‐E‐T‐852: Determining Objective Function Weights in Prostate IMRT Using Inverse Optimization
Authors: Chan T C Y , Lee T , Craig T , Sharpe M B
Published: November 2011

Purpose: To quantify organ‐specific objective function weights in a multi‐objective optimization formulation of prostate IMRT treatments; to demonstrate that optimized weights can be used to generate clinical plans with fewer objective functions more efficiently than current practice. Methods: Starting with a simple prostate IMRT inverse planning formulation involving four weighted OAR objectives, we developed an inverse optimization model (IOM) to determine optimal weights for each objective. The objectives were: penalize bladder and rectum voxels with dose above 50 Gy, and minimize maximum dose to the left and right femoral heads. Tumor objectives were modeled as hard constraints. A historical, clinical prostate treatment plan was input to the IOM, and optimized objective function weights were output. The clinical plan was generated in Pinnacle using 15 objective functions. The IOM was formulated as a linear optimization problem and solved using the CPLEX optimization solver. Using the optimized weights and the original inverse planning formulation, a new treatment plan was generated and then compared to the clinical plan. Results: The optimized weight on the rectum objective was almost exactly three times the bladder objective weight. The weights for the femoral heads were negligible. A new treatment plan generated using the optimized weights and four objectives was nearly identical to the clinical plan. All required clinical dosimetric criteria were satisfied by the new plan. Conclusions: A treatment planning formulation with optimized objective function weights can generate plans that are nearly identical to clinical plans that were generated using many more objective functions. With optimized weights and fewer objectives, it may be possible to significantly reduce the need for parameter tuning and trial‐and‐error approaches in treatment planning. While parameter tuning may be unavoidable, inverse optimization can be used to significant reduce the size of the parameter space that needs to be searched.