Treatment Plan Parameters Research Articles

TU-FG-201-03: Automatic Pre-Delivery Verification Using Statistical Analysis of Consistencies in Treatment Plan Parameters by the Treatment Site and Modality

Purpose: A novel computer software system, namely APDV (Automatic Pre-Delivery Verification), has been developed for verifying patient treatment plan parameters right prior to treatment deliveries in order to automatically detect and prevent catastrophic errors. Methods: APDV is designed to continuously monitor new DICOM plan files on the TMS computer at the treatment console. When new plans to be delivered are detected, APDV checks the consistencies of plan parameters and high-level plan statistics using underlying rules and statistical properties based on given treatment site, technique and modality. These rules were quantitatively derived by retrospectively analyzing all the EBRT treatment plans of the past 8 years at authors’ institution. Therapists and physicists will be notified with a warning message displayed on the TMS computer if any critical errors are detected, and check results, confirmation, together with dismissal actions will be saved into database for further review. Results: APDV was implemented as a stand-alone program using C# to ensure required real time performance. Mean values and standard deviations were quantitatively derived for various plan parameters including MLC usage, MU/cGy radio, beam SSD, beam weighting, and the beam gantry angles (only for lateral targets) per treatment site, technique and modality. 2D-based rules of combined MU/cGy ratio and averaged SSD values were also derived using joint probabilities of confidence error ellipses. The statistics of these major treatment plan parameters quantitatively evaluate the consistency of any treatment plans which facilitates automatic APDV checking procedures. Conclusion: APDV could be useful in detecting and preventing catastrophic errors immediately before treatment deliveries. Future plan including automatic patient identify and patient setup checks after patient daily images are acquired by the machine and become available on the TMS computer. This project is supported by the Agency for Healthcare Research and Quality (AHRQ) under award 1R01HS0222888. The senior author received research grants from ViewRay Inc. and Varian Medical System

SU‐F‐T‐242: A Method for Collision Avoidance in External Beam Radiation Therapy

Purpose:We proposed a method for collision avoidance (CA) in external beam radiation therapy (EBRT). The method encompasses the analysis of all positions of the moving components of the beam delivery system such as the treatment table and gantry, including patient specific information obtained from the CT images. This method eliminates the need for time‐consuming dry‐runs prior to the actual treatments.Methods:The QA procedure for EBRT requires that the collision should be checked prior to treatment. We developed a system capable of a rigorous computer simulation of all moving components including positions of the couch and gantry during the delivery, position of the patients, and imaging equipment. By running this treatment simulation it is possible to quantify and graphically represent all positions and corresponding trajectories of all points of the moving parts during the treatment delivery. The development of the workflow for implementation of the CA includes several steps: a) derivation of combined dynamic equation of motion of the EBRT delivery systems, b) developing the simulation model capable of drawing the motion trajectories of the specific points, c) developing the interface between the model and the treatment plan parameters such as couch and gantry parameters for each field.Results:The patient CT images were registered to the treatment couch so the patient dimensions were included into the simulation. The treatment field parameters were structured in the xml‐file which was used as the input into the dynamic equations. The trajectories of the moving components were plotted on the same graph using the dynamic equations. If the trajectories intersect that was the signal that collision exists.Conclusion:This CA method was proved to be effective in the simulation of treatment delivery. The proper implementation of this system can potentially improve the QA program and increase the efficacy in the clinical setup.

MO-FG-CAMPUS-TeP2-03: Multi-Criteria Optimization Using Taguchi Method for SRS of Multiple Lesions by Single Isocenter

Purpose: This study utilizes the Taguchi Method to evaluate the VMAT planning parameters of single isocenter treatment plans for multiple brain metastases. An optimization model based on Taguchi and utility concept is employed to optimize the planning parameters including: arc arrangement, calculation grid size, calculation model, and beam energy on multiple performance characteristics namely conformity index and dose to normal brain. Methods: Treatment plans, each with 4 metastatic brain lesions were planned using single isocenter technique. The collimator angles were optimized to avoid open areas. In this analysis four planning parameters (a–d) were considered: (a)-Arc arrangements: set1: Gantry 181cw179 couch0; gantry179ccw0, couch315; and gantry0ccw181, couch45. set2: set1 plus additional arc: Gantry 0cw179, couch270. (b)-Energy: 6-MV; 6MV-FFF (c)-Calculation grid size: 1mm; 1.5mm (d)-Calculation models: AAA; Acuros Treatment planning was performed in Varian Eclipse (ver.11.0.30). A suitable orthogonal array was selected (L8) to perform the experiments. After conducting the experiments with the combinations of planning parameters the conformity index (CI) and the normal brain dose S/N ratio for each parameter was calculated. Optimum levels for the multiple response optimizations were determined. Results: We determined that the factors most affecting the conformity index are arc arrangement and beam energy. These tests were also used to evaluate dose to normal brain. In these evaluations, the significant parameters were grid size and calculation model. Using the utility concept we determined the combination of each of the four factors tested in this study that most significantly influence quality of the resulting treatment plans: (a)-arc arrangement-set2, (b)-6MV, (c)-calc.grid 1mm, (d)-Acuros algorithm. Overall, the dominant significant influences on plan quality are (a)-arcarrangement, and (b)-beamenergy. Conclusion: Results were analyzed using ANOVA and were found to be within the confidence interval. Further investigation using this methodology. Such parameters might include: virtual OAR and optimization criterion such as normal tissue objective.

A Greedy reassignment algorithm for the PBS minimum monitor unit constraint

Proton pencil beam scanning (PBS) treatment plans are made of numerous unique spots of different weights. These weights are optimized by the treatment planning systems, and sometimes fall below the deliverable threshold set by the treatment delivery system. The purpose of this work is to investigate a Greedy reassignment algorithm to mitigate the effects of these low weight pencil beams. The algorithm is applied during post-processing to the optimized plan to generate deliverable plans for the treatment delivery system. The Greedy reassignment method developed in this work deletes the smallest weight spot in the entire field and reassigns its weight to its nearest neighbor(s) and repeats until all spots are above the minimum monitor unit (MU) constraint. Its performance was evaluated using plans collected from 190 patients (496 fields) treated at our facility. The Greedy reassignment method was compared against two other post-processing methods. The evaluation criteria was the γ-index pass rate that compares the pre-processed and post-processed dose distributions. A planning metric was developed to predict the impact of post-processing on treatment plans for various treatment planning, machine, and dose tolerance parameters. For fields with a pass rate of 90 ± 1% the planning metric has a standard deviation equal to 18% of the centroid value showing that the planning metric and γ-index pass rate are correlated for the Greedy reassignment algorithm. Using a 3rd order polynomial fit to the data, the Greedy reassignment method has 1.8 times better planning metric at 90% pass rate compared to other post-processing methods. As the planning metric and pass rate are correlated, the planning metric could provide an aid for implementing parameters during treatment planning, or even during facility design, in order to yield acceptable pass rates. More facilities are starting to implement PBS and some have spot sizes (one standard deviation) smaller than 5 mm, hence would require small spot spacing. While this is not the only parameter that affects the optimized plan, the perturbation due to the minimum MU constraint increases with decreasing spot spacing. This work could help to design the minimum MU threshold with the goal to keep the γ-index pass rate above an acceptable value.

SU‐F‐T‐416: Dosimetric Comparison of Coplanar and Non‐Coplanar IMRT Plans for Peripheral Lung Lesion

Purpose:The purpose of this study was to compare dosimetric parameters of treatment plans between coplanar and non‐coplanar techniques for treating peripheral lung lesions.Methods:The planning CT scans of 6 patients in supine positions were used in this study. The size of the PTV ranges from 163 c.c. to 782 c.c.. The locations of PTV are mostly at the peripheral of Lung, some spreading to the mediastinum. For each patient, we generated two IMRT plans, one with and the other without non‐coplanar beams. The non‐coplanar beams were carefully selected so that the beams would never exit patient bodies through the contralateral lung. The IMRT plans were generated with Pinnacle 9.8 treatment planning software. The IMRT optimization objectives were kept the same for the corresponding pairs of plans. All plans were normalized such that 95% of PTV receives the prescription dose (full dose).Results:The conformity index (mean±standard deviation of the mean) is 1.49±0.14 and 1.58±0.23 for the coplanar and noncoplanar plans, respectively. The heterogeneity index (mean±standard deviation of the mean) is 7.74 ±2.33 and 6.34±1.40 for the coplanar and non‐coplanar plans, respectively. The maximum heart dose is 60.94±6.22 and 60.42±7.21 Gy, and mean heart dose is 10.22 ±7.57, 9.07 ±6.32 Gy, for the coplanar and non‐coplanar plans, respectively. The ipsilateral lung V20 is 48.0%±2.4% and 47.5%±3.3%, and V5 is 68.2%±10.0% and 69.1%±7.3%, for the coplanar and noncoplanar plans, respectively. Furthermore, with the non‐coplanar beam arrangement, the contralateral lung V20 was reduced from 3.3%±3.7% to 1.3%±0.8%, and the contralateral Lung V5 is reduced significantly from 65.6%±9.3% to 33.5%±20.9% (p value =0.008).Conclusion:The IMRT plans with non‐coplanar beam arrangement could reduce the exit dose to the contralateral lung, and therefore reduce the contralateral lung V5 significantly. This method is especially helpful while the lung lesion doesn't have a symmetric shape.

TU‐D‐201‐06: HDR Plan Prechecks Using Eclipse Scripting API

Purpose:Automate brachytherapy treatment plan quality check using Eclipse v13.6 scripting API based on pre‐configured rules to minimize human error and maximize efficiency.Methods:The HDR Precheck system is developed based on a rules‐driven approach using Eclipse scripting API. This system checks for critical plan parameters like channel length, first source position, source step size and channel mapping. The planned treatment time is verified independently based on analytical methods. For interstitial or SAVI APBI treatment plans, a Patterson‐Parker system calculation is performed to verify the planned treatment time. For endobronchial treatments, an analytical formula from TG‐59 is used. Acceptable tolerances were defined based on clinical experiences in our department. The system was designed to show PASS/FAIL status levels. Additional information, if necessary, is indicated appropriately in a separate comments field in the user interface.Results:The HDR Precheck system has been developed and tested to verify the treatment plan parameters that are routinely checked by the clinical physicist. The report also serves as a reminder or checklist for the planner to perform any additional critical checks such as applicator digitization or scenarios where the channel mapping was intentionally changed. It is expected to reduce the current manual plan check time from 15 minutes to <1 minute.Conclusion:Automating brachytherapy plan prechecks significantly reduces treatment plan precheck time and reduces human errors. When fully developed, this system will be able to perform TG‐43 based second check of the treatment planning system's dose calculation using random points in the target and critical structures. A histogram will be generated along with tabulated mean and standard deviation values for each structure. A knowledge database will also be developed for Brachyvision plans which will then be used for knowledge‐based plan quality checks to further reduce treatment planning errors and increase confidence in the planned treatment.

SU-F-T-618: Evaluation of a Mono-Isocentric Treatment Planning Software for Stereotactic Radiosurgery of Multiple Brain Metastases

Purpose: To evaluate planning performance of an automated treatment planning software (BrainLAB; Elements) for stereotactic radiosurgery (SRS) of multiple brain metastases. Methods: Brainlab's Multiple Metastases Elements (MME) uses single isocentric technique to treat up to 10 cranial planning target volumes (PTVs). The planning algorithm of the MME accounts for multiple PTVs overlapping with one another on the beam eyes view (BEV) and automatically selects a subset of all overlapping PTVs on each arc for sparing normal tissues in the brain. The algorithm also optimizes collimator angles, margins between multi-leaf collimators (MLCs) and PTVs, as well as monitor units (MUs) using minimization of conformity index (CI) for all targets. Planning performance was evaluated by comparing the MME-calculated treatment plan parameters with the same parameters calculated with the Volumetric Modulated Arc Therapy (VMAT) optimization on Varian's Eclipse platform. Results: Figures 1 to 3 compare several treatment plan outcomes calculated between the MME and VMAT for 5 clinical multi-targets SRS patient plans. Prescribed target dose was volume-dependent and defined based on the RTOG recommendation. For a total number of 18 PTV's, mean values for the CI, PITV, and GI were comparable between the MME and VMAT within one standard deviation (σ). However, MME-calculated MDPD was larger than the same VMAT-calculated parameter. While both techniques delivered similar maximum point doses to the critical cranial structures and total MU's for the 5 patient plans, the MME required less treatment planning time by an order of magnitude compared to VMAT. Conclusion: The MME and VMAT produce similar plan qualities in terms of MUs, target dose conformation, and OAR dose sparing. While the selective use of PTVs for arc-optimization with the MME reduces significantly the total planning time in comparison to VMAT, the target dose homogeneity was also compromised due to its simplified inverse planning algorithm used.

In-house quality check of external beam plans using 3D treatment planning systems - a DVH comparison.

This paper presents a new approach towards the quality assurance of external beam plans using in‐house‐developed DICOM import and export software in a clinical setup. The new approach is different from what is currently used in most clinics, viz., only MU and point dose are verified. The DICOM‐RT software generates ASCII files to import/export structure sets, treatment beam data, and dose‐volume histograms (DVH) from one treatment planning system (TPS) to the other. An efficient and reliable 3D planning system, ROPS, was used for verifying the accuracy of treatment plans and treatment plan parameters. With the use of this new approach, treatment plans planned using Varian Eclipse planning system were exported to ROPS planning system. Important treatment and dosimetrical data, such as the beam setup accuracy, target dose coverage, and dose to critical structures, were also quantitatively verified using DVH comparisons. Two external beam plans with diverse photon energies were selected to test the new approach. The satisfactory results show that the new approach is feasible, easy to use, and can be used as an adjunct test for patient treatment quality check.PACS number(s): 87.55.dk, 87.55.D‐, 87.55.Qr

A software tool to automatically assure and report daily treatment deliveries by a cobalt-60 radiation therapy device.

The aims of this study were to develop a method for automatic and immediate verification of treatment delivery after each treatment fraction in order to detect and correct errors, and to develop a comprehensive daily report which includes delivery verification results, daily image‐guided radiation therapy (IGRT) review, and information for weekly physics reviews. After systematically analyzing the requirements for treatment delivery verification and understanding the available information from a commercial MRI‐guided radiotherapy treatment machine, we designed a procedure to use 1) treatment plan files, 2) delivery log files, and 3) beam output information to verify the accuracy and completeness of each daily treatment delivery. The procedure verifies the correctness of delivered treatment plan parameters including beams, beam segments and, for each segment, the beam‐on time and MLC leaf positions. For each beam, composite primary fluence maps are calculated from the MLC leaf positions and segment beam‐on time. Error statistics are calculated on the fluence difference maps between the plan and the delivery. A daily treatment delivery report is designed to include all required information for IGRT and weekly physics reviews including the plan and treatment fraction information, daily beam output information, and the treatment delivery verification results. A computer program was developed to implement the proposed procedure of the automatic delivery verification and daily report generation for an MRI guided radiation therapy system. The program was clinically commissioned. Sensitivity was measured with simulated errors. The final version has been integrated into the commercial version of the treatment delivery system. The method automatically verifies the EBRT treatment deliveries and generates the daily treatment reports. Already in clinical use for over one year, it is useful to facilitate delivery error detection, and to expedite physician daily IGRT review and physicist weekly chart review.PACS number(s): 87.55.km

A graphical user interface (GUI) toolkit for the calculation of three-dimensional (3D) multi-phase biological effective dose (BED) distributions including statistical analyses

A toolkit has been developed for calculating the 3-dimensional biological effective dose (BED) distributions in multi-phase, external beam radiotherapy treatments such as those applied in liver stereotactic body radiation therapy (SBRT) and in multi-prescription treatments. This toolkit also provides a wide range of statistical results related to dose and BED distributions. MATLAB 2010a, version 7.10 was used to create this GUI toolkit. The input data consist of the dose distribution matrices, organ contour coordinates, and treatment planning parameters from the treatment planning system (TPS). The toolkit has the capability of calculating the multi-phase BED distributions using different formulas (denoted as true and approximate). Following the calculations of the BED distributions, the dose and BED distributions can be viewed in different projections (e.g. coronal, sagittal and transverse). The different elements of this toolkit are presented and the important steps for the execution of its calculations are illustrated. The toolkit is applied on brain, head & neck and prostate cancer patients, who received primary and boost phases in order to demonstrate its capability in calculating BED distributions, as well as measuring the inaccuracy and imprecision of the approximate BED distributions. Finally, the clinical situations in which the use of the present toolkit would have a significant clinical impact are indicated.

Treatment Parameters Optimization to Compensate for Interfractional Anatomy Variability and Intrafractional Tumor Motion.

Scanned ion beam therapy of lung tumors is severely limited in its clinical applicability by intrafractional organ motion, interference effects between beam and tumor motion (interplay), as well as interfractional anatomic changes. To compensate for dose deterioration caused by intrafractional motion, motion mitigation techniques, such as gating, have been developed. However, optimization of the treatment parameters is needed to further improve target dose coverage and normal tissue sparing. The aim of this study was to determine treatment-planning parameters that permit to recover good target coverage for each fraction of lung tumor treatments. For 9 lung tumor patients from MD Anderson Cancer Center (Houston, Texas), a total of 70 weekly time-resolved computed tomography (4DCT) datasets, which depict the evolution of the patient anatomy over the several fractions of the treatment, were available. Using the GSI in-house treatment planning system TRiP4D, 4D simulations were performed on each weekly 4DCT for each patient using gating and optimization of a single treatment plan based on a planning CT acquired prior to treatment. The impact on target dose coverage (V 95%,CTV) of variations in focus size and length of the gating window, as well as different additional margins and the number of fields was analyzed. It appeared that interfractional variability could potentially have a larger impact on V 95%,CTV than intrafractional motion. However, among the investigated parameters, the use of a large beam spot size, a short gating window, additional margins, and multiple fields permitted to obtain an average V 95%,CTV of 96.5%. In the presented study, it was shown that optimized treatment parameters have an important impact on target dose coverage in the treatment of moving tumors. Indeed, intrafractional motion occurring during the treatment of lung tumors and interfractional variability were best mitigated using a large focus, a short gating window, additional margins, and three fields.

Submental-Cervical Angle: Perceived Attractiveness and Threshold Values of Desire for Surgery

The submental-cervical angle may alter as a result of mandibular orthognathic surgery and/or the ageing process and is therefore an important facial aesthetic parameter for comparative diagnosis and treatment planning. The purpose of this study was to undertake a quantitative evaluation of the influence of the submental-cervical angle on perceived attractiveness and threshold values of desire for surgery. The submental-cervical angle of an idealized profile silhouette image was altered incrementally between 90° and 130°. The images were rated on a seven-point Likert scale by pre-treatment orthognathic patients (n=75), laypeople (n=75), and clinicians (n=35). A submental-cervical angle of 90°-105° was deemed acceptable. Angles up to 120° were deemed slightly unattractive by the lay and clinician groups, but very unattractive by the patient group. By 125°-130° all groups perceived the angle as very unattractive. The threshold value of desire for surgery was 110° for patients, 115° for lay people and 125° for clinicians. Patients appear to be more critical than lay and clinician groups. These ranges of normal variability of the submental-cervical angle and threshold values of desire for surgery, in terms of observer acceptance, should be considered by clinicians in planning mandibular orthognathic surgery and aesthetic surgical procedures of the submental-cervical region.

Lhermitte's Sign following VMAT-Based Head and Neck Radiation-Insights into Mechanism.

Purpose/ObjectivesWe observed a number of patients who developed Lhermitte’s sign (LS) following radiation to the head and neck (H/N), since instituting volumetric modulated arc therapy (VMAT). We aimed to investigate the incidence of LS following VMAT-based RT without chemotherapy, and determine the dosimetric parameters that predict its development. We explored whether the role of inhomogeneous dose distribution across the spinal cord, causing a “bath-and-shower” effect, explains this finding.Methods and MaterialsFrom 1/20/2010–12/9/2013, we identified 33 consecutive patients receiving adjuvant RT using VMAT to the H/N without chemotherapy at our institution. Patients’ treatment plans were analyzed for dosimetric parameters, including dose gradients along the anterior, posterior, right, and left quadrants at each cervical spine level. Institutional Review Board approval was obtained.Results5 out of 33 (15.2%) patients developed LS in our patient group, all of whom had RT to the ipsilateral neck only. LS patients had a steeper dose gradient between left and right quadrants across all cervical spine levels (repeated-measures ANOVA, p = 0.030). Within the unilateral treatment group, LS patients received a higher mean dose across all seven cervical spinal levels (repeated-measures ANOVA, p = 0.046). Dose gradients in the anterior-posterior direction and mean doses to the cord were not significant between LS and non-LS patients.ConclusionsDose gradients along the axial plane of the spinal cord may contribute to LS development; however, a threshold dose within the high dose region of the cord may still be required. This is the first clinical study to suggest that inhomogeneous dose distributions in the cord may be relevant in humans. Further investigation is warranted to determine treatment-planning parameters associated with development of LS.

Monte Carlo Dosimetry of the 60Co BEBIG High Dose Rate for Brachytherapy.

IntroductionThe use of high-dose-rate brachytherapy is currently a widespread practice worldwide. The most common isotope source is 192Ir, but 60Co is also becoming available for HDR. One of main advantages of 60Co compared to 192Ir is the economic and practical benefit because of its longer half-live, which is 5.27 years. Recently, Eckert & Ziegler BEBIG, Germany, introduced a new afterloading brachytherapy machine (MultiSource®); it has the option to use either the 60Co or 192Ir HDR source. The source for the Monte Carlo calculations is the new 60Co source (model Co0.A86), which is referred to as the new BEBIG 60Co HDR source and is a modified version of the 60Co source (model GK60M21), which is also from BEBIG.Objective and MethodsThe purpose of this work is to obtain the dosimetry parameters in accordance with the AAPM TG-43U1 formalism with Monte Carlo calculations regarding the BEBIG 60Co high-dose-rate brachytherapy to investigate the required treatment-planning parameters. The geometric design and material details of the source was provided by the manufacturer and was used to define the Monte Carlo geometry. To validate the source geometry, a few dosimetry parameters had to be calculated according to the AAPM TG-43U1 formalism. The dosimetry studies included the calculation of the air kerma strength S k, collision kerma in water along the transverse axis with an unbounded phantom, dose rate constant and radial dose function. The Monte Carlo code system that was used was EGSnrc with a new cavity code, which is a part of EGS++ that allows calculating the radial dose function around the source. The spectrum to simulate 60Co was composed of two photon energies, 1.17 and 1.33 MeV. Only the gamma part of the spectrum was used; the contribution of the electrons to the dose is negligible because of the full absorption by the stainless-steel wall around the metallic 60Co. The XCOM photon cross-section library was used in subsequent simulations, and the photoelectric effect, pair production, Rayleigh scattering and bound Compton scattering were included in the simulation. Variance reduction techniques were used to speed up the calculation and to considerably reduce the computer time. The cut-off energy was 10 keV for electrons and photons. To obtain the dose rate distributions of the source in an unbounded liquid water phantom, the source was immersed at the center of a cube phantom of 100 cm3. The liquid water density was 0.998 g/cm3, and photon histories of up to 1010 were used to obtain the results with a standard deviation of less than 0.5% (k = 1). The obtained dose rate constant for the BEBIG 60Co source was 1.108±0.001 cGyh-1U-1, which is consistent with the values in the literature. The radial dose functions were compared with the values of the consensus data set in the literature, and they are consistent with the published data for this energy range.

Prognostic factors associated with pain palliation after spine stereotactic body radiation therapy.

OBJECT The number of patients with spinal tumors is rapidly increasing; spinal metastases develop in more than 30% of cancer patients during the course of their illness. Such lesions can significantly decrease quality of life, often necessitating treatment. Stereotactic radiosurgery has effectively achieved local control and symptomatic relief for these patients. The authors determined prognostic factors that predicted pain palliation and report overall institutional outcomes after spine stereotactic body radiation therapy (SBRT). METHODS Records of patients who had undergone treatment with SBRT for either primary spinal tumors or spinal metastases from June 2008 through June 2013 were retrospectively reviewed. Data were collected at the initial visit just before treatment and at 1-, 3-, 6-, and 12-month follow-up visits. Collected clinical data included Karnofsky Performance Scale scores, pain status, presence of neurological deficits, and prior radiation exposure at the level of interest. Radiation treatment plan parameters (dose, fractionation, and target coverage) were recorded. To determine the initial extent of epidural spinal cord compression (ESCC), the authors retrospectively reviewed MR images, assessed spinal instability according to the Bilsky scale, and evaluated lesion progression after treatment. RESULTS The study included 99 patients (mean age 60.4 years). The median survival time was 9.1 months (95% CI 6.9-17.2 months). Significant decreases in the proportion of patients reporting pain were observed at 3 months (p < 0.0001), 6 months (p = 0.0002), and 12 months (p = 0.0019) after treatment. Significant decreases in the number of patients reporting pain were also observed at the last follow-up visit (p = 0.00020) (median follow-up time 6.1 months, range 1.0-56.6 months). Univariate analyses revealed that significant predictors of persistent pain after intervention were initial ESCC grade, stratified by a Bilsky grade of 1c (p = 0.0058); initial American Spinal Injury Association grade of D (p = 0.011); initial Karnofsky Performance Scale score, stratified by a score of 80 (p = 0.002); the presence of multiple treated lesions (p = 0.044); and prior radiation at the site of interest (p < 0.0001). However, when multivariate analyses were performed on all variables with p values less than 0.05, the only predictor of pain at last follow-up visit was a prior history of radiation at the site of interest (p = 0.0038), although initial ESCC grade trended toward significance (p = 0.073). Using pain outcomes at 3 months, at this follow-up time point, pain could be predicted by receipt of radiation above a threshold biologically effective dose of 66.7 Gy. CONCLUSIONS Pain palliation occurs as early as 3 months after treatment; significant differences in pain reporting are also observed at 6 and 12 months. Pain palliation is limited for patients with spinal tumors with epidural extension that deforms the cord and for patients who have previously received radiation to the same site. Further investigation into the optimal dose and fractionation schedule are needed, but improved outcomes were observed in patients who received radiation at a biologically effective dose (with an a/b of 3.0) of 66.7 Gy or higher.

TH‐EF‐BRD‐08: A Retrospective Statistical Analysis of Consistencies in Treatment Plan Parameters by the Treatment Site and Modality

Purpose:Simple rules and common senses based on prior knowledge could be powerful tools for medical physicists to identify and prevent severe errors in radiation therapy (RT) treatment plans. However, rules, e.g. the acceptable MU/cGy ratio for different treatment sites, are not yet available quantitatively and therefore cannot be utilized effectively. In this study, we have retrospectively analyzed all the EBRT treatment plans of the past 8 years at authors’ institution. The goal is to better understand the most common treatment plan data statistics, involving MU/cGy ratio, numbers of beams and segments, and ranges of gantry angles for lateral targets, in order to quantitatively define the common sense‐based rules that could be used to guide manual or automatic physics checks.Methods:15844 previous treatment plans were obtained from Mosaiq. Plan data were extensively processed including 1) reducing data size, 2) removing empty and unapproved site and fields, 3) deriving common site names from names of prescriptions and beams that were spelled and misspelled extremely diversely, and 4) removing the plans not covered by this study, e.g. HDR plans. Processed data was then statistically analyzed using multivariate regression algorithms to quantitatively investigate the relationships between the input parameters, i.e. treatment site, technique, modality, and laterality, and the output parameters, i.e. MU/cGy radio, the total number of treatment beams and segments, and the beam gantry angles (only for lateral targets).Results:Mean values and standard deviations of the output parameters were calculated and tabulated per treatment site, technique and modality. Beam gantry angle range and mean gantry angle were analyzed per site for plans treating lateral targets.Conclusion:The results of this study, as the statistics of the major treatment plan parameters, could be useful to quantitatively evaluate the consistency of new treatment plans in either manual or automatic plan checking procedures.

SU‐E‐J‐199: A Software Tool for Quality Assurance of Online Replanning with MR‐Linac

Purpose:To develop a quality assurance software tool, ArtQA, capable of automatically checking radiation treatment plan parameters, verifying plan data transfer from treatment planning system (TPS) to record and verify (R&amp;V) system, performing a secondary MU calculation considering the effect of magnetic field from MR‐Linac, and verifying the delivery and plan consistency, for online replanning.Methods:ArtQA was developed by creating interfaces to TPS (e.g., Monaco, Elekta), R&amp;V system (Mosaiq, Elekta), and secondary MU calculation system. The tool obtains plan parameters from the TPS via direct file reading, and retrieves plan data both transferred from TPS and recorded during the actual delivery in the R&amp;V system database via open database connectivity and structured query language. By comparing beam/plan datasets in different systems, ArtQA detects and outputs discrepancies between TPS, R&amp;V system and secondary MU calculation system, and delivery. To consider the effect of 1.5T transverse magnetic field from MR‐Linac in the secondary MU calculation, a method based on modified Clarkson integration algorithm was developed and tested for a series of clinical situations.Results:ArtQA is capable of automatically checking plan integrity and logic consistency, detecting plan data transfer errors, performing secondary MU calculations with or without a transverse magnetic field, and verifying treatment delivery. The tool is efficient and effective for pre‐ and post‐treatment QA checks of all available treatment parameters that may be impractical with the commonly‐used visual inspection.Conclusion:The software tool ArtQA can be used for quick and automatic pre‐ and post‐treatment QA check, eliminating human error associated with visual inspection. While this tool is developed for online replanning to be used on MR‐Linac, where the QA needs to be performed rapidly as the patient is lying on the table waiting for the treatment, ArtQA can be used as a general QA tool in radiation oncology practice.This work is partially supported by Elekta Inc.

Does microwave interstitial hyperthermia prior to high-dose-rate brachytherapy change prostate volume or therapy plan parameters?

Purpose: In this prospective preliminary study we evaluated changes of prostate volume and changes of brachytherapy treatment plan parameters due to interstitial hyperthermia (IHT) applied prior to high-dose-rate brachytherapy (HDRBT), compared to our standard HDRBT procedure. Material and methods: In a group of 60 consecutive patients with prostate adenocarcinoma, 30 were treated with HDRBT alone and 30 with IHT preceding HDRBT. Prior to catheter implantation, a ‘virtual’ treatment plan (VP) was complied, a ‘live’ plan (LP) was prepared before patient irradiation, and a ‘post’ plan (PP) was drawn up after completing the irradiation procedure. In each plan, based on transrectal ultrasound images, the contours of the prostate, urethra, and rectum were delineated and the respective volumes and dose–volume histogram parameters were evaluated. These parameters, established for the LP, were then compared with those of the PP. Results: Changes in prostate volume and in parameters of the treatment plans were observed, but differences between the two patient groups were not statistically significant. For all 60 patients treated, the average prostate volume in the VP was 32 cm3, in the LP 41 cm3, and the PP 43 cm3. Average values of relative changes in the therapy planning parameters between LP and PP were for the prostate D90 −5.7%, V100 −5.6%, V200 −13.2%, for the urethra D0, 1 cm3 −1.6%, and for rectum D2 cm3 0%. Conclusion: Hyperthermia prior to HDRBT does not significantly change the volume of the prostate and there is no need to perform the new treatment plan after the hyperthermia session.

Comparing Proton Beam to Intensity Modulated Radiation Therapy Planning in Esophageal Cancer

Abstract Purpose: To compare passive-scatter proton beam therapy (PBT) versus intensity-modulated radiation therapy (IMRT) for reducing heart/lung dose in esophageal cancer, and to identify anatomy and treatment planning parameters that can lead to suboptimal proton plans. Patients and Methods: Passive-scatter PBT versus IMRT mean doses and coverage to the lung/heart were evaluated for 55 patients with esophageal cancer from 2007 to 2010. Geometric relationships between the tumor (distance from planning target volume to carina, and percentage of uninvolved heart) and doses to the lung/heart, respectively, were used to predict expected doses to these normal tissues. Cross-comparisons of heart versus lung dose and proton versus photon mean lung/heart dose were used to identify suboptimal proton dosimetry. Results: Dose–volumetric analysis showed that, for the lung and heart, although protons resulted in smaller volumes receiving lower doses (5–30 Gy), photons achieved smaller volumes receiving higher doses ...

Patient performance–based plan parameter optimization for prostate cancer in tomotherapy

The purpose of this study is to evaluate the influence of treatment-planning parameters on the quality of treatment plans in tomotherapy and to find the optimized planning parameter combinations when treating patients with prostate cancer under different performances. A total of 3 patients with prostate cancer with Eastern Cooperative Oncology Group (ECOG) performance status of 2 or 3 were included in this study. For each patient, 27 treatment plans were created using a combination of planning parameters (field width of 1, 2.5, and 5cm; pitch of 0.172, 0.287, and 0.43; and modulation factor of 1.8, 3, and 3.5). Then, plans were analyzed using several dosimetrical indices: the prescription isodose to target volume (PITV) ratio, homogeneity index (HI), conformity index (CI), target coverage index (TCI), modified dose HI (MHI), conformity number (CN), and quality factor (QF). Furthermore, dose-volume histogram of critical structures and critical organ scoring index (COSI) were used to analyze organs at risk (OAR) sparing. Interestingly, treatment plans with a field width of 1cm showed more favorable results than others in the planning target volume (PTV) and OAR indices. However, the treatment time of the 1-cm field width was 3 times longer than that of plans with a field width of 5cm. There was no substantial decrease in treatment time when the pitch was increased from 0.172 to 0.43, but the PTV indices were slightly compromised. As expected, field width had the most significant influence on all of the indices including PTV, OAR, and treatment time. For the patients with good performance who can tolerate a longer treatment time, we suggest a field width of 1cm, pitch of 0.172, and modulation factor of 1.8; for the patients with poor performance status, field width of 5cm, pitch of 0.287, and a modulation factor of 3.5 should be considered.