bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐676: Reproducibility and Consistency of Two SunNuclear 3D Scanning Tanks
Authors: Hessler J , DiCostanzo D , Grzetic S , Ayan A , Gupta N , Woollard J
Published: June 2015

Purpose:

To determine if two Sun Nuclear 3D Scanning (SNC 3DS) tanks collect reproducible and consistent data and test the precision of the SNC Dosimetry auto‐setup.

Methods:

Percent depth doses (PDDs) and profiles were collected on two SNC 3DS tanks with a Varian TrueBeam linear accelerator. SNC Dosimetry auto‐setup application was used with CC13 ionization chambers. After auto‐setup, collimator light field was checked manually against the position of the chamber. Comparing measured data for repeated measurements with tank 1 allowed evaluation of SNC‐3DS auto‐setup and tank reproducibility. Comparing measured data between tanks 1 and 2 allowed evaluation of consistency between tanks.

Results:

Preliminary results showed reproducibility of depth of maximum dose (Dmax) of 0.38mm for a 10cmx10cm field and 0.67mm for 30cmx30cm on a single tank. PDD values at 5cm, 10cm, and 20cm depths were reproducible within 0.26%. Consistency of Dmax between tanks was 0.17mm for a 10cmx10cm field and 0.44mm for 30cmx30cm. PDD values at 5cm, 10cm, and 20cmwere consistent within 0.06%. Profiles showed reproducibility in field width within 0.4mm for a 10cmx10cm field and 0.7mm for a 30cmx30cm field. Profiles showed consistency in field width within 0.2mm for 10cmx10cm and 30cmx30cm field sizes. Penumbra width was reproducible and consistent to under 0.5mm except for 30cmx30cm field size at 30cm depth where the reproducibility was 2.2mm and the consistency was 2.6mm.

Conclusion:

In conclusion, the SNC 3DS tank shows good reproducibility in measured data. Since the tank to tank variation in measured data is within the uncertainty of repeated single tank measurements the tanks also perform consistently.
SU‐E‐T‐681: Robust and Monte Carlo‐Based Intensity Modulated Proton Therapy Optimization with GPU Acceleration
Authors: Ma J , Beltran C , Wan Chan Tseung H , Herman M
Published: June 2015

Purpose:

Accuracy of dose calculation models and robustness under various uncertainties are key factors influencing the quality of intensity modulated proton therapy (IMPT) plans. In this work, a robust IMPT optimization based on accurate Monte Carlo (MC) dose calculation is developed.

Methods:

We used an in‐house developed and graphics processing unit (GPU) accelerated MC for dose calculation. For robust optimization, dose volume histograms (DVHs) were computed for each uncertainty scenario at each optimization iteration. A gradient based adaptive method was used to improve the DVHs with adjustable scenario weights. GPUs were employed to accelerate the optimization process. Uncertainties in patient setup and proton range were considered in all cases studied. Additionally, the uncertainty of intra‐fraction relative shift between fields was considered for craniospinal irradiation cases. The adaptive robust optimization method was compared with for clinical cases at several different disease sites.

Results:

Comparing with the traditional optimization target volume (OTV) based method, the adaptive robust optimization spared critical structures better while maintain the target coverage in clinical cases. For example, the right parotid hot spot dose was reduced from 78.5Gy to 74.5Gy as shown in Fig. 1. For craniospinal irradiation, the adaptive method found the robust solution at field junctions without manual feathering of the match lines. Even for relatively large head‐and‐neck cases and craniospinal cases, the whole process of MC dose calculation and robust optimization can be done within 30 minutes on a system of 100 Nvidia GeForce GTX Titan cards.

Conclusion:

A robust IMPT treatment planning system is developed utilizing an adaptive method. The treatment planning optimization is based on MC dose calculation and is accelerated by GPU to be clinically viable.

This work is supported in part by Varian Medical Systems.
SU‐E‐T‐682: Robust Fluence Map Optimization Via Alternating Direction Method of Multipliers with Automatic Parameter Optimization
Authors: Gao H
Published: June 2015

Purpose:

In intensity modulated radiation therapy (IMRT), the beam fluence maps at prescribed angles are often first optimized via fluence map optimization (FMO) under the given dose prescriptions and constraints to conformally deliver the radiation dose to the targets while sparing the organs‐at‐risk (OAR), and then segmented into deliverable MLC apertures via leaf sequencing algorithm. This work is to develop an efficient algorithm for FMO with improved dose conformality.

Methods:

Here we consider FMO with the least‐square cost function and non‐negative fluence constraints, and its solution algorithm is based on alternating direction method of multipliers (ADMM), which is efficient and yet simple‐to‐implement. In particular, the automatic parameter optimization is developed to improve the robustness of the ADMM algorithm so that the optimization parameter tuning is no longer needed in our ADMM algorithm for solving FMO.

Results:

Our ADMM algorithm was compared with the quadratic programming method based on interior‐point method using the MGH public prostate dataset. The comparison results suggested our ADMM algorithm had improved spareness for the OAR and dose conformality. The ADMM testing codes are available at https://sites.google.com/site/robustfmo.

Conclusion:

An efficient and yet simple‐to‐implement ADMM algorithm with no parameter tuning is proposed for solving FMO for IMRT with improved OAR spareness and dose conformality.

Hao Gao was partially supported by the NSFC (#11405105), the 973 Program (#2015CB856000) and the Shanghai Pujiang Talent Program (#14PJ1404500).
SU‐E‐T‐683: Robustness Analysis of Multiple Filed Optimized IMPT Plans for Head & Neck Patients Treated at MD Anderson Cancer Center
Authors: Li Y , Li H , Jingqian W , Zhu X , Li Y , Frank S , Zhang X
Published: June 2015

Purpose:

Our center's clinical outcome data so far indicated that excellent local control for the head and neck patients treated using multiple field optimized (MFO) IMPT technique have been achieved. The purpose is to determine the robustness of those IMPT plans and provide the clinician the knowledge of the degree of the robustness which will not compromise the local control and is safe for the normal tissue.

Methods:

A fast and approximate dose calculation method is developed to calculate the dose for the IMPT plan under different setup and range uncertainties. The dosimetric index evaluated using this method are compared with those calculated using the dose calculation model in TPS. A worst case scenario robustness analysis method is implemented using the fast dose calculation method. 100 head neck plans treated using MFO IMPT were retrospectively analyzed using implemented robustness analysis method. The lowest dose received by 95% target (D95) and the highest dose received by 5% target (D5) of GTV, CTV1, CTV2, CTV3, mean dose of parotid glands, cochlea and brain and the minimum dose in the most radiated 1 cm3 volume (D1cc) of spinal cord and brain stem were compared between nominal plans and plans in the worst case scenario.

Results:

For GTV, CTV1 CTV2 and CTV3, D95 in worst scenario are lower by 2.08, 4.59, 5.25 and 5.46 Gy than nominal plan, while D5 are higher by 1.14, 0.98, 0.85 and 1.21 Gy. D1cc of brain stem and spinal in worst scenario are higher by 3.37 and 1.95 Gy than nominal plan. The mean dose of parotid glands, cochlea and brain are higher by 3.52, 3.69 and 0.64 Gy respectively.

Conclusion:

The robustness analysis data from the clinically treated patients enables the clinician to gauge the degree of robustness in their clinical practice when adopting MFO IMPT technique for patient treatment.
SU‐E‐T‐687: Scatter Factors Comparison of 6MV FFF and Energy Matched 6MV EqFFF
Authors: Sigamani Ashokkumar , Nambiraj Arunai , Sinha S N , Yadav Girigesh , Rajesh T , Raman Kothanda , Kaviarasu K , Narayanan S , Meerza Kazem
Published: June 2015

Purpose:

To compare the Collimator scatter factor (Sc), Phantom scatter factor (Sp) and Total scatter factors (Sc,p) of 6MV FFF and energy matched 6MV FFF (6MV eqFFF)

Methods:

The flattening filter and primary collimator are the major sources of producing the scattered radiation. In this study, the field sizes from 5 × 5 cm2 to 40 × 40 cm2 compared for 6MV FFF and 6MV eqFFF. We measured Sc,p with CC 13 chamber at the depth of 10 g/cm2 using IBA blue water phantom and Sc measured with CC 13 chamber at the depth of 10 g /cm2 using columnar phantom (TG 74) for 6MV FFF and 6MV eqFFF x‐ray beams from a Siemens — ARTISTE(6MV eqFFF ) and Varian True beam (6MV FFF) linear accelerator. The Sp values derived from the Sc,p and Sc Values.

Results:

All the values of Sc,p, Sc and Sp are normalized to 10 × 10 cm2 field size. The measured values of Sc,p for 6MV FFF and 6MV eqFFF varies from 0.9404 to 1.0760 and 0.9690 to 1.0283 respectively. The Sc values for 6MV FFF and 6MV eqFFF varies from 0.9880 to 1.133 and 0.9882 to 1.0075 respectively. The Sp values for 6MV FFF and 6MV eqFFF varies from 0.9518 to 1.0619 and 0.9806 to 1.0206 respectively. From the measured values, we found that Sc, Sc,p and Sp factors of 6MV FFF less than 10 × 10cm2 field is similar to the 6MV eqFFF. For greater than 10 × 10 cm2 field size Sc, Sc,p and Sp factors higher for 6MV FFF than 6MV eqFFF.

Conclusion:

The energy matched 6MV FFF (6MV eqFFF) photon beam producing lesser Scatter radiation compare to the conventional 6MV FFF photon beams for field size more than 10 × 10 cm2.
SU‐E‐T‐691: Shielding Evaluation of a Treatment Room with An Electronic Brachytherapy System
Authors: Ibanez‐Rosello B , Bautista J , Candela‐Juan C , Villaescusa J , Ballester F , Perez‐Calatayud J
Published: June 2015

Purpose:

Esteya™ (Elekta) is a brachytherapy electronic system used for treating skin cancer lesions. This unit is based on a 69.5 kV X‐ray source and a surface applicator which produces a circular beam of a specific diameter, which varies from 1 to 3 cm. This study aims to establish the radiation protection measures for the system.

Methods:

A characterization of the scattered and leakage radiation of the system was implemented by means of experimental measurements. The scattered radiation measurements were performed with a Berthold LB133 ionization chamber, evaluating the dose rate for different distances from the applicator surface. The patient was simulated through water equivalent solid material of 9 cm thickness. Leakage was evaluated by setting 2 cm thick lead at the output of the radiation beam.From the obtained measurements, the necessary shielding has been estimated following the Report 147 by ICRP, and particularizing those values to a hypothetical installation. The dose received by a person who exceptionally would have to eventually stay inside the room with the patient was also analyzed.

Results:

The scattered dose rate ranges from 17.3 mSv/h at 0.25 m distance to 0.1 mSv/h at 2.5 m. Leakage represents 0.24% of the scattered dose rate. With these measurements and some assumptions on the workload and dimensions of a hypothetical treatment room it was estimated that the overall lead shielding for primary and secondary barriers was well below 1 mm, although it depends on each particular case. The overall absorbed dose to an eventual companion placed 0.5 m away from the patient is below 2 mSv after the complete treatment.

Conclusion:

Esteya shielding requirements are minimal, which facilitate its integration into conventional rooms. Furthermore, the presence of a companion during treatment is possible if absolutely necessary, recommending the use of a leaded apron and thyroid shielding.
SU‐E‐T‐699: Simulation of Bone Tissue Interface to Study Perturbation Effect in Gamma Knife Radiosurgery
Authors: Natanasabapathi Gopishankar , Vivekanandhan S , Kale SS , Rath GK , Bisht Raj Kishor , Sharma BS
Published: June 2015

Purpose:

To study perturbing effect of bone tissue interface in Gamma Knife dose distribution.

Methods:

PAGAT polymer gel was manufactured in‐house and poured into two PET cylinders for 3D measurement. Small vials were used for calibration.For 2D measurement EBT2 film was placed in mid portion of third gel filled PET cylinder. A bone material (+1400HU) of length 7cm and width 1.3cm was placed in the path of radiation beam at a distance of 4.5cm from measurement region to investigate its influence on dose distribution. For treatment planning each gel cylinder was fixed in Leksell frame and imaged in X‐Ray CT with scanning parameters: Tube Voltage — 120kVp, Tube Current — 130mAs, Slice Thickness — 1mm. Acquired images were transferred to Leksell Gamma Plan TPS (LGP Version 10.1). A treatment plan consisting of single 16mm collimator with coordinates x=100, y=100, z=100 was generated using convolution algorithm based planning (CABP). Each cylinder was positioned in treatment table and exposed to time calculated by the TPS. Irradiated gel was imaged with MRI (GE Medical Systems) to extract dose information from R2 maps and to determine subtle influence of bone material in the radiation path. Scanning parameter used: TE — 13.6ms, TR — 5000ms, slice thickness — 1.2mm, no of echoes — 8, FOV — 256×256mm2. Similarly exposed EBT2 film was scanned with EPSON scanner (Expression 10000XL) to measure dose.

Results:

3D and 2D measurement showed altered dose distribution in profile measurement, isodose overlay and dose volume histogram (DVH) comparison. For a gamma pass criteria of 1%/1mm voxel pass rate was around 76%.

Conclusion:

Presence of bone material in the radiation path perturbed the dose distribution unnoticeable in TPS calculation. Any HU value above +1024 is truncated by CABP hence need to incorporate higher HU values for accurate dose calculation in Gamma Knife TPS.

The scientific resources used in this work were from the completed project N‐964 provided by AERB, Mumbai.
SU‐E‐T‐700: Single Isocenter Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiotherapy (IMRT) for Intact Left Breast Cancer Patients with Internal Mammary (IM) and Supraclavicular (S/C) Nodes ‐ a Treatment Planning Study
Authors: Lee G , Algan O , Keeling V , Higby C , Ahmad S , Hossain S
Published: June 2015

Purpose:

To investigate treatment plan quality and feasibility of VMAT for treatment delivery of intact left breast cancer patients with involved internal mammary (IM) and supraclavicular (S/C) nodes.

Methods:

Ten patients were selected for this retrospective study. All PTVs (Intact left breast, IM & S/C nodes) were contoured by a single radiation oncologist. Four 200° partial arcs with 2cm overlapping jaws (two clockwise and two counterclockwise; gantry angle 300°–140°) and ten fixed‐field equally spaced coplanar modulated fields were used to optimize single isocenter VMAT (RapidArc) and IMRT treatment plans, respectively, using Eclipse TPS. Prescribed dose to PTV was 46Gy in 23 fractions with prescription dose covering 95% of the PTV.

Results:

Four of the 10 patients had PTV > 1200cc. The mean PTV volume was 1200.17±571.51cc (findings are reported as mean ± 1 SD). All plans were judged clinically acceptable while satisfying dose‐volume constraints, with VMAT showing significantly better conformity than IMRT. The mean Paddick conformity index (PCI) was 0.88±0.03 for VMAT vs. 0.82±0.06 for IMRT plans (p=0.001). However, maximum doses were within ±1.0% of 111% of the prescription dose for both plans. The heart mean dose was 5.00±0.99Gy for VMAT vs. 7.09±1.70Gy for IMRT (p<0.001), heart volume receiving >30Gy was 0.18±0.29% for VMAT vs. 0.68±1.24% for IMRT (p=0.19), and V5Gy and V7Gy were 31.67±11.56% and 14.93±7.41% for VMAT vs. 67.15±17.66% and 36.55±16.59% for IMRT plans, respectively (p<0.001). The mean total lung dose was 8.95±0.52Gy vs. 8.48±0.81Gy (p=0.06) and V20Gy was 10.65±2.00% vs. 8.12±1.37% (p=0.055) for VMAT and IMRT plans, respectively. The right breast mean dose was 2.83±0.46Gy for VMAT vs. 4.06±0.61Gy for IMRT plans (p<0.001).

Conclusion:

VMAT plans achieved intended dose coverage to the intact left breast, IM & S/C nodes at ≥ 95% with significantly lower dose to critical structures, especially, to heart and contralateral breast compared to IMRT plans.
SU‐E‐T‐707: Soft‐Tissue / Bone Interface Backscatter Prediction by Two Commercial Electron Treatment Planning Algorithms
Authors: Catt B , Yudelev M
Published: June 2015

Purpose:

In this work, we investigate the accuracy of two commercial Monte Carlo algorithms used for electron treatment planning in their prediction of dose enhancement near a soft‐tissue / bone interface. The calculated doses at the interface of a heterogeneous phantom are compared with results obtained from measurements, simulations with EGSnrc, and calculations using an empirical formula.

Methods:

Phantoms were constructed and modeled in Eclipse 10.0 (Varian) and Monaco 5.0 (Elekta) treatment planning systems. Slabs of bone equivalent material (CIRS Inc.) were inserted into a stack of solid water and situated at 2.9 cm depth, equivalent to dmax for a 12 MeV electron beam. This setup was chosen as an exaggeration of any clinically relevant inconsistencies which may be seen near interfaces. Plans were run on these phantoms and doses at the interface were compared with results obtained using a similar phantom within EGSnrc. The measurements were performed in a 12 MeV electron beam, using a parallel plate ion chamber.

Results:

General agreement was observed between calculated and measured dose distributions along the beam's central axis in the regions away from the heterogeneity; however, Varian's eMC algorithm could not properly account for backscatter from higher density materials, instead predicting a decrease in dose just before the interface. This leads to an underestimation of dose by up to 9% at the interface, when compared with ion chamber measurements. Elekta's VMC++ algorithm was able to more accurately account for the presence of the backscatter material, demonstrating an agreement within 1.7% of ion chamber measurements at the interface.

Conclusions:

Although Monte Carlo algorithms are widely regarded as the gold standard for accuracy, care must still be taken when using implementations which have been optimized for calculation efficiency, especially within regions lacking electronic equilibrium such as those found near interfaces with bone.
SU‐E‐T‐708: Spatial Accuracy of Small‐Target SRS Using Conebeam CT Guidance and Static Arcs with MLC‐Defined Fields
Authors: Brezovich I , Popple R , Duan J , Wu X , Shen S , Huang M , Cardan R
Published: June 2015

Purpose:

To measure the spatial accuracy of dose delivery under conebeam CT guidance to small targets using static arcs with MLC‐defined fields.

Methods:

A plastic (PMMA) phantom simulating a small brain lesion was constructed. The lesion was a cylindrical air cavity having 3 mm length and 3.175 mm diameter. Gafchromic EBT 2 film passing through the cavity was pin pricked at the exact geometric cavity center. Following CT simulation treatment plans involving static arcs with MLC‐defined fields were designed, similar to radiotherapy with circular tertiary cones. 5×2 mm fields were generated by opening two centrally located leaf pairs of a high‐definition MLC to 2.0 mm. The target was irradiated with 6 MV photons on a STx linac under conebeam CT image guidance to 600 cGy at isocenter. Films from coronal and sagittal planes were scanned and evaluated using the ImageJ software. The distance between the centroid of the 50% isodose line and the center of the pin prick was the measure of geographic accuracy.

Results:

Single arcs resulted in ellipsoidal 50% isodose surfaces having diameters of 5.0 mm along the gantry axis and 7.7 mm in the cross‐sectional directions. 4‐arc delivery at couch angles of 0, 45, 90 and 315 degrees produced 50% isodose surfaces having diameters of 5.6, 5.7 and 7.5 mm diameters along the lateral, longitudinal and anterior‐posterior directions, respectively. In any of the experiments, the largest distance by which the centroid of the 50% isodose line missed the center of the target was 0.36 mm or less.

Conclusion:

MLC‐defined static arcs delivered under conebeam CT guidance provide precise irradiation of small targets. The method is very efficient since no special attachments or modifications of the accelerator are required. Since MLC leaves are stationary throughout the treatment, patient‐specific QA involving phantoms should not be required.
SU‐E‐T‐713: Study On Application of Beam Angle Optimization for Multiple Intracranial Metastases
Authors: Lin X , Sun T , Yin Y
Published: June 2015

Purpose:

To study the dosimetric impact of different angle fields IMRT and the feasibility of beam angle optimization (BAO) for multiple intracranial metastases.

Methods:

11 patients with multiple intracranial metastases were included in this analysis. In Varian Eclipse TPS two treatment techniques were designed for each patient: the 7 equal spaced fields and 7 fields by beam angle optimization IMRT. Two plans were designed for each patient with the same dose‐volume constraints and prescription dose. All plans were normalized to the mean dose to PTV. The dose distribution in the target, the dose to the organs at risk and normal brain tissues and total MU in two techniques were compared to explore the dosimetric differences.

Results:

For the target dose, conformity and homogeneity in PTV, no statistically differences were observed in the two plans. Compared to 7 equal spaced fields IMRT plans, IMRT plans with BAO reduced the maximum dose to left and right lens by an average of 45%, 37%, the mean dose to left and right eyes were reduced by an average of 42.6%,44.5% .The maximum dose of the right optic nerve and the mean dose of normal brain tissue were reduced by an average of 23%,3% respectively. The above data were statistically significant. IMRT plans with BAO reduced the maximum dose of the brainstem and the optic chiasm, the number of MU, but the Result were not statistically significant (p> 0.05).

Conclusion:

Compared to 7 equal spaced fields IMRT plans, IMRT plans with BAO showed the similar target dose and reduced the dose of the organs at risk. For multiple intracranial metastases, IMRT plans with BAO were feasible and beneficial.
SU‐E‐T‐716: Suitability Study of a Unique 3D Dosimeter for Commissioning Radiation Treatment Machines
Authors: Roed Y , Tailor R , Pinsky L , Ibbott G
Published: June 2015

Purpose:

To determine the suitability of a methacrylic acid‐based MAGAT gel dosimeter to serve as a 3D commissioning tool

Methods:

Different sized MAGAT gel dosimeters were fabricated in‐house to perform dose response, depth dose and dose rate measurements using an orthovoltage treatment unit. Dose response data were obtained by irradiating dosimeters to six dose levels at three different effective beam energies. Depth dose measurements were taken using one dose at one energy. Dose rate dependence was measured by varying only distances for the gel irradiations while dose level and energy remained unchanged. A Bruker Biospecs 4.7T MRI scanner was used to acquire spin‐spin relaxation rates on axial slices at different depths throughout each dosimeter 24h after irradiation.

Results:

The dose response curves exhibited a separation when compared for the measured energies. MAGAT depth dose data, normalized to ion chamber data at 2 cm depth, showed an increasing divergence with increasing depth. The dose rate decreased when distances were increased and demonstrated a significant dose rate dependence of the measurements. Consequently, dose rate corrections were applied to all measurements, thus, aligning the dose response curves for all three energies and reducing the divergence between MAGAT and ion chamber depth dose data.

Conclusion:

The MAGAT dosimeter was intended to serve as a 3D commissioning tool for testing radiation treatment plans of small fields with steep dose gradients and complex treatment volumes. A suitable detector for commissioning needs to be dependent on dose but independent of dose rate. This study, however, showed a dose rate dependence of up to 30% eliminating the current composition of MAGAT as a suitable dosimeter. Further investigations of chemical compositions need to be performed.
SU‐E‐T‐724: Testing the Limitations of a Photon Dose Algorithm in Commissioning
Authors: Xue J , Choi M , Park J , LaCouture T , Ibbott G
Published: June 2015

Purpose:

This work is to test the limitations of a photon dose algorithm during the commissioning of a treatment planning system.

Methods:

Commissioning tests for a model‐based dose calculation algorithm typically involve the verification of PDD, output and dose profiles, but often those tests are performed at one SSD, one depth and one nominal gantry position. Those tests are useful to validate the modeling of radiation beams, but they may not be sufficient to detect the limitations of an algorithm. Additional tests were performed at several SSDs, various depths, oblique gantry angles and off‐axis conditions to demonstrate the accuracy and limitations of the dose calculation algorithm. Dose profiles were measured by in‐water scanning with a three‐dimensional scanning system and calculated in the TPS using a virtual water phantom.

Results:

Dose profiles from both the measurement and the calculation were plotted for comparison. Also plotted were the difference in absolute dose between the measurement and the calculation. For the off‐axis MLC field tests, larger discrepancies were observed at the open portion and the far edge of the field, which became greater with short SSD and deep depth. In addition, the shape of the profile appeared different for the open portion of the field. For the oblique MLC field tests, the largest difference was seen around the high‐dose shoulder of the profile. Differences in some point doses were observed to be greater than 10% of the maximum field dose.

Conclusion:

We have learned the limitations of the superposition dose algorithm in the XiO planning system through some specific tests, which are related to the parallel kernel approximation and the simplified energy spectra employed by the algorithm to calculate field‐size dependent fluence.
SU‐E‐T‐736: The Impact of Beam Angle Optimization of Intensity‐Modulated Radiotherapy for Postoperative Radiotherapy of Cervical Cancer
Authors: Sun T , Yin Y , Lin X , Liu T , Zhang G
Published: June 2015

Purpose:

To evaluate the dosimetric characteristics of intensity‐modulated radiotherapy (IMRT) treatment plan with beam angle optimization.

Methods:

Ten post‐operation patients with cervical cancer were included in this analysis. Two IMRT plans using seven beams were designed in each patient. A standard coplanar equi‐space beam angles were used in the first plan (plan 1), whereas the selection of beam angle was optimized by beam angle optimization algorithm in Varian Eclipse treatment planning system for the same number of beams in the second plan (plan 2). Two plans were designed for each patient with the same dose‐volume constraints and prescription dose. All plans were normalized to the mean dose to PTV. The dose distribution in the target, the dose to the organs at risk and total MU were compared.

Results:

For conformity and homogeneity in PTV, no statistically differences were observed in the two plans. For the mean dose in bladder, plan 2 were significantly lower than plan 1(p<0.05). No statistically significant differences were observed between two plans for the mean doses in rectum, left and right femur heads. Compared with plan1, the average monitor units reduced 16% in plan 2.

Conclusion:

The IMRT plan based on beam angle optimization for cervical cancer could reduce the dose delivered to bladder and also reduce MU. Therefore there were some dosimetric advantages in the IMRT plan with beam angle optimization for cervical cancer.
SU‐E‐T‐738: The Limit of Detectability and Resolution of a Cylindrical Diode Array Phantom for VMAT and SRS Quality Assurance
Authors: Gray T , Pearson D
Published: June 2015

Purpose:

To determine the limit of detectability and resolution of a cylindrical QA phantom for quality assurance of VMAT and SRS procedures in small field sizes.

Methods:

Eight different square field sizes were delivered onto a cylindrical QA phantom with 1386 diodes at gantry angles of 0, 90, 180 and 270 degrees, using a 6 MV beam at a maximum dose rate of 600 MU/min on a dedicated stereotactic linear accelerator with 2.5mm and 5mm leaves. After verifying pass rates of normal square field sizes, errors were introduced into the quality‐assurance analysis, including an expansion of the field size by 1 mm for all jaws on all sides, an expansion of the field size by 1 mm on one side of the X and Y jaws,MLC errors, and a table shift by 1 mm vertically and longitudinally at 270 and 90 degrees and a table shift of 1mm laterally and longitudinally for angles of 0 and 180 degrees. Treatment planning system calculated dose distributions for measured square field size dose data was imported into the QA phantom software and compared against a treatment planning system calculated 3D dose distribution. Percent pass rates were computed using gamma analysis with 2mm/2% analysis criteria with a background threshold value of 30%.

Results:

QA software comparison between measured fields and treatment planning system calculations indicate that the passing rate of square fields decreases significantly when errors are induced in the quality assurance analysis. Adding two opposing MLC leaves on opposing sides of each square field in the treatment planning system produced a 31.2% average difference from normally measured square field sizes compared between the treatment planning system and what was measured by the QA software.

Conclusion:

This work indicates the potential for detecting errors in VMAT quality assurance in small field sizes using a cylindrical QA phantom.
SU‐E‐T‐739: The Logistic Regression and Cox Regression Model for Predicting Local Recurrence, Distant Metastases, and Overall Survival of Rectal Cancer Patients
Authors: Zhou Z , Zhang Z , Hu W , Zhong H , Wang J
Published: June 2015

Purpose:

The purpose was to develop predicting models for the local recurrence, distant metastases, and overall survival for rectal cancer patients treated with chemoradiotherapy. These models were based on different statistical methods for indicating various relationships between clinical features and follow‐up results, which may provide support on decision‐making in treatment.

Methods:

Models were developed based on logistic regression and cox proportional hazards model using patient data (N=277) from Fudan University Shanghai Cancer Center. The patient data set was randomly split into two proportions as the training and validation datasets. The clinical features used as variables include sex, age, tumor location, RT dose, adjuvant chemotherapy, surgery procedure, clinical tumor stage, and pTNM stage. The Bootstrapping was used for constructing confidence intervals; and the model performance was evaluated by the concordance index (c‐index).

Results:

The logistic regression model is easy to use because the conditional independence assumption is unnecessary. The Cox regression model can dispose data with time factors so follow‐up over a certain time period can be predicted. For the logistic regression model, the c‐index for validation are 0.73 (LR), 0.77 (DM), and 0.76(OS), while numerical values for the cox regression model are 0.72 (LR), 0.77 (DM), and 0.70(OS). Both models show the probability to predict follow‐up events based on c‐index. Clinical tumor stage and pathologic stage are crucial features for both models (p<0.05).

Conclusion:

The Logistic Regression and Cox Regression Model can be used for Predicting Local Recurrence, Distant Metastases, and Overall Survival of Rectal Cancer Patients. The performance of models can be further improved with additional parameters provided from different facilities.
SU‐E‐T‐744: The Study of Total Marrow Irradiation Based On Rotational Intensity‐Modulated Techniques
Authors: Xu S , Xie C , Qu B , Yu W , Xu W , Ge R , Cong X
Published: June 2015

Purpose:

This study is to compare the dosimetric characteristics and efficiency of RapidArc and Tomotherapy in total marrow irradiation (TMI) for hematologic malignancies in order to get the reference data for the choice of clinical application.

Methods:

Eight patient plans were retrospectively designed and analyzed for RapidArc and Tomotherapy. Total bone morrow was contoured as clinical target volume excluding the cubitus and hand part, then plus a 3.0mm margin as planning target volume. The prescription was 12Gy in 10 fractions. ArcCHECK system was used for dose verification, and the safety and accuracy of clinical delivery would be evaluated.

Results:

It showed that the two techniques could well achieve the target coverage. The conformity indexes of RapidArc and Tomotherapy were 0.54±0.05 vs 0.52±0.07 (p=0.45), but Tomotherapy plans have a visible advantage over RapidArc plans in the dose uniformity of target. The homogeneity indexes were 0.19±0.02 vs 0.13±0.02 (p=0.00). Tomotherapy plans showed better in sparing of the critical organs apart from the whole brain, oral, parotid gland, the small intestine, rectum, and the maximum dose of lens of Tomotherapy plans was reduced by 41% comparing to RapidArc plans. The MUs and treatment delivery time of RapidArc and Tomotherapy were 2608MU/560s vs 12842MU/891s. The γ‐analysis passing rates for head‐neck, chest‐abdomen, pelvic were 98.9±1.9%, 98.4±1.8%, 97.4±2.1% for RapidArc and 94.3±1.5%, 96.5±1.2%, 94.1±1.9% for Tomotherapy plans.

Conclusion:

The two methods using RapidArc and Tomotherapy could achieve the acceptable dose of TMI, and the delivery efficiency of RapidArc was better than Tomotherapy. Two kinds of techniques are promising and can solve the clinic implementation of TMI.

This work was supported in part by the grant from Chinese Natural Science Foundation (Grant No. 11105225).
SU‐E‐T‐752: Three‐Dimensional Carcinogenic Maps Induced by Photons and Protons
Authors: Manem V , Paganetti H
Published: June 2015

Purpose:

Evaluate the excess relative risk (ERR) induced by photons and protons in each voxel of the lung, and display it as a three‐dimensional map, known as the ERRM (i.e. excess relative risk map) along with the dose distribution map. In addition, we also study the effect of variations in the linear energy transfer (LET) distribution on ERRM for a given proton plan.

Methods:

The excess relative risk due to radiation is estimated using the initiation‐inactivation‐proliferation formalism. This framework accounts for three biological phenomenon: mutation induction, cell kill and proliferation. Cell kill and mutation induction are taken as a function of LET using experimental data. LET distributions are calculated using a Monte Carlo algorithm. ERR is then estimated for each voxel in the organ, and displayed as a three dimensional carcinogenic map.

Results:

The differences in the ERR's between photons and protons is seen from the three‐dimensional ERR map. In addition, we also varied the LET of a proton plan and observed the differences in the corresponding ERR maps demonstrating variations in the ERR maps depend on features of a proton plan. Additionally, our results suggest that any two proton plans that have the same integral dose does not necessarily imply identical ERR maps, and these changes are due to the variations in the LET distribution map.

Conclusion:

Clinically, it is important to have a three dimensional display of biological end points. This study is an effort to introduce 3D ERR maps into the treatment planning workflow for certain sites such as pediatric head and neck tumors.
SU‐E‐T‐753: Three‐Dimensional Dose Distributions of Incident Proton Particle in the Polymer Gel Dosimeter and the Radiochromic Gel Dosimeter: A Simulation Study with MCNP Code
Authors: Park M , Kim G , Ji Y , Kim K , Park S , Jung H
Published: June 2015

Purpose:

The purpose of this study is to estimate the three‐dimensional dose distributions in the polymer and the radiochromic gel dosimeter, and to identify the detectability of both gel dosimeters by comparing with the water phantom in case of irradiating the proton particles.

Methods:

The normoxic polymer gel and the LCV micelle radiochromic gel were used in this study. The densities of polymer and the radiochromic gel dosimeter were 1.024 and 1.005 g/cm3, respectively. The dose distributions of protons in the polymer and radiochromic gel were simulated using Monte Carlo radiation transport code (MCNPX, Los Alamos National Laboratory). The shape of phantom irradiated by proton particles was a hexahedron with the dimension of 12.4 × 12.4 × 15.0 cm3. The energies of proton beam were 50, 80, and 140 MeV energies were directed to top of the surface of phantom. The cross‐sectional view of proton dose distribution in both gel dosimeters was estimated with the water phantom and evaluated by the gamma evaluation method. In addition, the absorbed dose(Gy) was also calculated for evaluating the proton detectability.

Results:

The evaluation results show that dose distributions in both gel dosimeters at intermediated section and Bragg‐peak region are similar with that of the water phantom. At entrance section, however, inconsistencies of dose distribution are represented, compared with water. The relative absorbed doses in radiochromic and polymer gel dosimeter were represented to be 0.47 % and 2.26 % difference, respectively. These results show that the radiochromic gel dosimeter was better matched than the water phantom in the absorbed dose evaluation.

Conclusion:

The polymer and the radiochromic gel dosimeter show similar characteristics in dose distributions for the proton beams at intermediate section and Bragg‐peak region. Moreover the calculated absorbed dose in both gel dosimeters represents similar tendency by comparing with that in water phantom.
SU‐E‐T‐760: Tolerance Design for Site‐Specific Range in Proton Patient QA Process Using the Six Sigma Model
Authors: Lah J , Shin D , Kim G
Published: June 2015

Purpose:

To show how tolerance design and tolerancing approaches can be used to predict and improve the site‐specific range in patient QA process in implementing the Six Sigma.

Methods:

In this study, patient QA plans were selected according to 6 site‐treatment groups: head &neck (94 cases), spine (76 cases), lung (89 cases), liver (53 cases), pancreas (55 cases), and prostate (121 cases), treated between 2007 and 2013. We evaluated a model of the Six Sigma that determines allowable deviations in design parameters and process variables in patient‐specific QA, where possible, tolerance may be loosened, then customized if it necessary to meet the functional requirements. A Six Sigma problem‐solving methodology is known as DMAIC phases, which are used stand for: Define a problem or improvement opportunity, Measure process performance, Analyze the process to determine the root causes of poor performance, Improve the process by fixing root causes, Control the improved process to hold the gains.

Results:

The process capability for patient‐specific range QA is 0.65 with only ±1 mm of tolerance criteria. Our results suggested the tolerance level of ±2–3 mm for prostate and liver cases and ±5 mm for lung cases. We found that customized tolerance between calculated and measured range reduce that patient QA plan failure and almost all sites had failure rates less than 1%. The average QA time also improved from 2 hr to less than 1 hr for all including planning and converting process, depth‐dose measurement and evaluation.

Conclusion:

The objective of tolerance design is to achieve optimization beyond that obtained through QA process improvement and statistical analysis function detailing to implement a Six Sigma capable design.
SU‐E‐T‐765: Treatment Planning Comparison of SFUD Proton and 4Ï€ Radiotherapy for Prostate Cases
Authors: Tran A , Zhang J , Woods K , Yu V , Nguyen D , Sheng K
Published: June 2015

Purpose:

Single‐Field Uniform Dose (SFUD) proton scanning beams and non‐coplanar 4π intensity‐modulated radiation therapy (IMRT) represent the most advanced treatment methods based on heavy ion and X‐rays, respectively. Here we compare their performance for prostate treatment.

Methods:

Five prostate patients were planned using 4π radiotherapy and SFUD to an initial dose of 54Gy to a planning target volume (PTV) that encompassed the prostate and seminal vesicles, then a boost prescription dose of 25.2Gy to the prostate for a total dose of 79.2 Gy. 4π plans were created by inversely selecting and optimizing 30 beams from 1162 candidate non‐coplanar beams using a greedy column generation algorithm. The SFUD plans utilized two coplanar, parallel‐opposing lateral scanning beams. The SFUD plan PTV was modified to account for range uncertainties while keeping an evaluation PTV identical to that of the X‐ray plans for comparison. PTV doses, bladder and rectum dose volumes (V40, V45, V60, V70, V75.6, and V80), R50, and PTV homogeneity index (D95/D5) were evaluated.

Results:

Compared to SFUD, 4π resulted in 6.8% lower high dose spillage as indicated by R50. Bladder and rectum mean doses were 38.3% and 28.2% lower for SFUD, respectively. However, bladder and rectum volumes receiving >70Gy were 13.1% and 12% greater using proton SFUD. Due to the parallel‐opposing beam arrangement, SFUD resulted in greater femoral head (87.8%) and penile bulb doses (43.7%). 4π PTV doses were slightly more homogeneous (HI 0.99 vs. 0.98) than the SFUD dose.

Conclusion:

Proton is physically advantageous to reduce the irradiated normal volume and mean doses to the rectum and bladder but it is also limited in the beam orientations and entrance dose, which resulted in greater doses to the femoral heads and penile bulb, and larger volumes of rectum and bladder exposed to high dose due to the required robust PTV definition.

This project is supported by Varian Medical Systems.
SU‐E‐T‐766: Treatment Planning Comparison Study On Two Different Multileaf Collimators Delivered with Volumetric Modulated Arc Therapy
Authors: Zhang R , Xiaomei F , Bai W , Zhang X , Gao Y
Published: June 2015

Purpose:

To compare and evaluate the performance of two different multileaf collimators(MLCi2 and Agility) delivery with volumetric modulated arc therapy techniques.

Methods:

Treatment plans were graded four (Low, Moderate, Moderate‐High and High complexity) accorrding to the complexity. This includes 1 Low complexity(brain metastasis), 2 Moderate complexity(Lung and Liver), 1 Moderate‐High complexity(prostate) and 1 High complexity ( head and neck) cases. Total dose of 60 Gy was given for all the plans. All cases were desigined two VMAT plans, one with MLCi2(group A) and the other with Agility(group B). All plans were done on Elekta VMAT with Monaco treatment planning system. All plans were generated with 6 MV X‐rays for both Plan A and Plan B. Plans were evaluated based on the ability to meet the dose volume histogram, radiation conformity index, estimated radiation delivery time, dose homogeneity index(HI) and monitor units(MU) needed to deliver the prescribed dose.

Results:

Plans of group B achieved the best HI (HI = 1.05 Vs. 1.06) at the Low complexity cases while plans of group A were slightly better at the high complexity cases (HI = 1.12 Vs. 1.14). Faster VMAT plan delivery with Agility than with MLCi2 as plan complexity increased (Low complexity:52s Vs.52s, Moderate complexity:58s Vs. 55s, Moderate‐High complexity: 171s Vs.152s, High complexity : 326s Vs. 202s ), especially for the most complex paradigms delivered time can be decresed 38%. No Significant changes were observed between the group B and group A plans in terms of the healthy tissue mean dose and MU. Both plans respected the planning objective for all organs at risk.

Conclusion:

The study concludes that VMAT plans with the novel Agility MLC can significant decrease the delivering time at the high complexity cases, while a slight compromise in the dose homogeneity index should be noted.

This work was supported by The Medical Science Foundation of The health department of Hebei Province (No. 20130253)
SU‐E‐T‐769: T‐Test Based Prior Error Estimate and Stopping Criterion for Monte Carlo Dose Calculation in Proton Therapy
Authors: Hong X , Gao H , Schuemann J , Paganetti H
Published: June 2015

Purpose:

The Monte Carlo (MC) method is a gold standard for dose calculation in radiotherapy. However, it is not a priori clear how many particles need to be simulated to achieve a given dose accuracy. Prior error estimate and stopping criterion are not well established for MC. This work aims to fill this gap.

Methods:

Due to the statistical nature of MC, our approach is based on one‐sample t‐test. We design the prior error estimate method based on the t‐test, and then use this t‐test based error estimate for developing a simulation stopping criterion. The three major components are as follows.First, the source particles are randomized in energy, space and angle, so that the dose deposition from a particle to the voxel is independent and identically distributed (i.i.d.).Second, a sample under consideration in the t‐test is the mean value of dose deposition to the voxel by sufficiently large number of source particles. Then according to central limit theorem, the sample as the mean value of i.i.d. variables is normally distributed with the expectation equal to the true deposited dose.Third, the t‐test is performed with the null hypothesis that the difference between sample expectation (the same as true deposited dose) and on‐the‐fly calculated mean sample dose from MC is larger than a given error threshold, in addition to which users have the freedom to specify confidence probability and region of interest in the t‐test based stopping criterion.

Results:

The method is validated for proton dose calculation. The difference between the MC Result based on the t‐test prior error estimate and the statistical Result by repeating numerous MC simulations is within 1%.

Conclusion:

The t‐test based prior error estimate and stopping criterion are developed for MC and validated for proton dose calculation.

Xiang Hong and Hao Gao were partially supported by the NSFC (#11405105), the 973 Program (#2015CB856000) and the Shanghai Pujiang Talent Program (#14PJ1404500).
SU‐E‐T‐770: Tumor Control in Ion Beam Radiotherapy with Different Ions in Presence of Hypoxia
Authors: Attili A , Torriani F , Russo G , Dalmasso F , Giordanengo S , Ourhaleb F , Battistoni G , Kraan A , Cirio R
Published: June 2015

Purpose:

The reduced concentration of oxygen in cells (hypoxia) results in a lower cell death rate after irradiation that can lead to treatment failure. The effect can be expressed by the oxygen enhancement ratio (OER). So far, only few attempts to include OER in treatment planning for ion beam therapy were made, which are based on the dose averaged LET estimates and do not distinguish among ion species and fractionation schemes. To overcome these limitations, we implemented a new OER model and used it to estimate tumor control in clinical cases.

Methods:

The model, based on the microdosimetric kinetic model, was benchmarked with in‐vitro data from different ions irradiation. It was included in the simulation of treatments of a set of clinical cases (glioblastoma) using p, Li, He, C and O ion beams. Tumor Control Probability (TCP) was estimated as a function of oxygen partial pressure, dose per fraction and primary ion type.

Results:

The modelized OER was found to be strongly dependent on both LET and ion type, and showed a decreasing OER for increasing dose per fraction with a slope that depends on the LET and ion type, in good agreement with the experimental data. In the clinical cases studied, an increase in TCP by increasing ion charge and dose per fraction (more than 30% variation from p to O for moderate hypoxia) was found. Higher OER decrease rates as function of dose per fraction were found for lighter ions (up to 20% varying from 2 to 8 Gy(RBE)).

Conclusions:

A novel modeling of the OER that explicitly includes the dependence on ion type and dose per fraction was implemented. The model was exploited to evaluate the impact of hypoxia in ion beam radiotherapy, facilitating the identification of the treatment condition optimality, including fractionation scheme and ion type.