Intensity-modulated Radiation Therapy Quality Assurance Research Articles

Parallel/Opposed: IMRT QA using treatment log files is superior to conventional measurement-based method.

Parallel/Opposed: IMRT QA using treatment log files is superior to conventional measurement-based method.

Impact of dose rate on accuracy of intensity modulated radiation therapy plan delivery using the pretreatment portal dosimetry quality assurance and setting up the workflow at hospital levels.

The aim of this study was to examine the impact of dose rate on accuracy of intensity modulated radiation therapy (IMRT) plan delivery by comparing the gamma agreement between the calculated and measured portal doses by pretreatment quality assurance (QA) using electronic portal imaging device dosimetry and creating a workflow for the pretreatment IMRT QA at hospital levels. As the improvement in gamma agreement leads to increase in the quality of IMRT treatment delivery, gamma evaluation was carried out for the calculated and the measured portal images for the criteria of 3% dose difference and 3 mm distance-to-agreement (DTA). Three gamma parameters: Maximum gamma, average gamma, and percentage of the field area with a gamma value>1.0 were analyzed. Three gamma index parameters were evaluated for 40 IMRT plans (315 IMRT fields) which were calculated for 400 monitor units (MU)/min dose rate and maximum multileaf collimator (MLC) speed of 2.5 cm/s. Gamma parameters for all 315 fields are within acceptable limits set at our center. Further, to improve the gamma results, we set an action level for this study using the mean and standard deviation (SD) values from the 315 fields studied. Forty out of 315 IMRT fields showed low gamma agreement (gamma parameters>2 SD as per action level of the study). The parameters were recalculated and reanalyzed for the dose rates of 300, 400 and 500 MU/min. Lowering the dose rate helped in getting an enhanced gamma agreement between the calculated and measured portal doses of complicated fields. This may be attributed to the less complex motion of MLC over time and the MU of the field/segment. An IMRT QA work flow was prepared which will help in improving the quality of IMRT delivery.

Validation of fluence-based 3D IMRT dose reconstruction on a heterogeneous anthropomorphic phantom using Monte Carlo simulation.

In this study, we evaluated the performance of a three‐dimensional (3D) dose verification system, COMPASS version 3, which has a dedicated beam models and dose calculation engine. It was possible to reconstruct the 3D dose distributions in patient anatomy based on the measured fluence using the MatriXX 2D array. The COMPASS system was compared with Monte Carlo simulation (MC), glass rod dosimeter (GRD), and 3DVH, using an anthropomorphic phantom for intensity‐modulated radiation therapy (IMRT) dose verification in clinical neck cases. The GRD measurements agreed with the MC within 5% at most measurement points. In addition, most points for COMPASS and 3DVH also agreed with the MC within 5%. The COMPASS system showed better results than 3DVH for dose profiles due to individual adjustments, such as beam modeling for each linac. Regarding the dose‐volume histograms, there were no large differences between MC, analytical anisotropic algorithm (AAA) in Eclipse treatment planning system (TPS), 3DVH, and the COMPASS system. However, AAA underestimated the dose to the clinical target volume and Rt‐Parotid slightly. This is because AAA has some problems with dose calculation accuracy. Our results indicated that the COMPASS system offers highly accurate 3D dose calculation for clinical IMRT quality assurance. Also, the COMPASS system will be useful as a commissioning tool in routine clinical practice for TPS.PACS number: 87.55.Qr, 87.56.Fc, 87.61.Bj

Dosimetric Study on Variations of Gamma Index (GI) in Pre-Treatment Verification Procedure in Intensity Modulated Radiotherapy (IMRT) Plans with Varying Grid Sizes Using 2D Array Detectors

Aim: The main aim of our study was to compare the variation of Gamma Index (GI) in Pre-treatment Verification Procedure in Intensity Modulated Radiotherapy (IMRT) Plans with Varying Grid Sizes Using 2D Array Detectors. Choosing an optimum grid size plays a vital role for planning in radiotherapy cases especially while treating with IMRT. A minimal change of even 1 mm of grid size can result in large variation in treatment planning and is reflected in quality assurance results also. Methods and Material: We compared IMRT plans for a total of 12 patients. Out of these 12 patients 4 were head and neck, 4 were pelvic and 4 were brain patients respectively. For each patient three plans were generated with three different grid sizes. The plan acceptance criteria were 95% of PTV to receive at least 95% of prescribed dose and dose to 1% of PTV not to exceed 107% of prescribed dose. Dose for the organs at risk were respected as per the QUANTEC guidelines. After plan acceptance corresponding Pre-treatment Verification Procedure for IMRT was executed by PTW 729 array detector. The Gamma index (GI) results of each plan were recorded for the three different grid sizes. The passing criteria were kept to be 3% Dose Difference (DD) and 3 mm Distance to Agreement (DTA) for all cases. Results: We estimated the variations in GI quality assurance results for patients undergoing IMRT planning with varying grid sizes of 3 mm, 5 mm and 10 mm respectively. We also evaluated 2% DD and 2 mm DTA, 3% DD, 3 mm DTA and 5% DD, 5 mm DTA criteria for passing result. Stastical analysis: We have calculated the average and standard Deviations (Std. Dev.) for each passing criteria for 2% DD, 2 mm DTA, 3% DD, 3 mm DTA and 5% DD, 5 mm DTA for each IMRT plans with varying grid sizes. Conclusions: Though the present results suggest the gamma criteria of 5% DD and 5 mm DTA as the most suitable criteria for IMRT quality assurance. This gamma criterion of 5% DD and 5 mm DTA favourably exceeds 95% in each case and grid sizes but it is not recommended for strict verification procedure in Intensity Modulated Radiotherapy (IMRT). The criteria of 2% DD and 2 mm DTA, and 3% DD and 3 mm DTA gamma values show below 90% for 5 mm and 10 mm grid sizes but exceeds 95% for the 3 mm grid sizes. Hence 3 mm or less grid sizes should be routinely used in pre-treatment verification procedure IMRT plans using 2D Array Detectors.

Toward optimizing patient-specific IMRT QA techniques in the accurate detection of dosimetrically acceptable and unacceptable patient plans.

The authors investigated the performance of several patient-specific intensity-modulated radiation therapy (IMRT) quality assurance (QA) dosimeters in terms of their ability to correctly identify dosimetrically acceptable and unacceptable IMRT patient plans, as determined by an in-house-designed multiple ion chamber phantom used as the gold standard. A further goal was to examine optimal threshold criteria that were consistent and based on the same criteria among the various dosimeters. The authors used receiver operating characteristic (ROC) curves to determine the sensitivity and specificity of (1) a 2D diode array undergoing anterior irradiation with field-by-field evaluation, (2) a 2D diode array undergoing anterior irradiation with composite evaluation, (3) a 2D diode array using planned irradiation angles with composite evaluation, (4) a helical diode array, (5) radiographic film, and (6) an ion chamber. This was done with a variety of evaluation criteria for a set of 15 dosimetrically unacceptable and 9 acceptable clinical IMRT patient plans, where acceptability was defined on the basis of multiple ion chamber measurements using independent ion chambers and a phantom. The area under the curve (AUC) on the ROC curves was used to compare dosimeter performance across all thresholds. Optimal threshold values were obtained from the ROC curves while incorporating considerations for cost and prevalence of unacceptable plans. Using common clinical acceptance thresholds, most devices performed very poorly in terms of identifying unacceptable plans. Grouping the detector performance based on AUC showed two significantly different groups. The ion chamber, radiographic film, helical diode array, and anterior-delivered composite 2D diode array were in the better-performing group, whereas the anterior-delivered field-by-field and planned gantry angle delivery using the 2D diode array performed less well. Additionally, based on the AUCs, there was no significant difference in the performance of any device between gamma criteria of 2%/2 mm, 3%/3 mm, and 5%/3 mm. Finally, optimal cutoffs (e.g., percent of pixels passing gamma) were determined for each device and while clinical practice commonly uses a threshold of 90% of pixels passing for most cases, these results showed variability in the optimal cutoff among devices. IMRT QA devices have differences in their ability to accurately detect dosimetrically acceptable and unacceptable plans. Field-by-field analysis with a MapCheck device and use of the MapCheck with a MapPhan phantom while delivering at planned rotational gantry angles resulted in a significantly poorer ability to accurately sort acceptable and unacceptable plans compared with the other techniques examined. Patient-specific IMRT QA techniques in general should be thoroughly evaluated for their ability to correctly differentiate acceptable and unacceptable plans. Additionally, optimal agreement thresholds should be identified and used as common clinical thresholds typically worked very poorly to identify unacceptable plans.

The quality assurance of volumetric modulated arc therapy (VMAT) plans for early stage prostate cancer: a technical note.

As radiation therapy transitions from intensity modulated radiation therapy (IMRT) to volumetric modulated arc therapy (VMAT) it is important to consider the quality assurance (QA) of VMAT plans in light of what has previously been learned and developed in IMRT QA. This technical note assesses if IMRT based plan QA software, which has reduced the need in IMRT for phantom dose measurements on the linear accelerator, can be incorporated into VMAT QA processes. Twenty prostate cases were retrospectively planned using VMAT with one arc to deliver a prescription of 74 Gy in 37 fractions. A plan QA was performed using both IMSure (version 3.3), a software‐based IMRT QA program, and ArcCHECK (version 6.2.3.5713), a phantom‐based VMAT QA tool. Outcomes assessed included the time needed to perform the QA of both the IMSure and ArcCHECK QA methods, and agreement between planned dose and QA measured dose. On average per case, the ArcCHECK technique needed 31.5 min to perform the VMAT plan QA, while IMSure required 3.5 min to perform the same QA. All 20 cases passed dosimetric QA using ArcCHECK. However, using IMSure, three cases failed dosimetric QA using the departments existing IMRT QA criteria. This research has demonstrated that the IMRT QA software IMSure may be incorporated into the QA of VMAT plans, however the criteria to assess the dosimetry of the VMAT plans may need to be different to that for IMRT cases. The implication of this research for radiation therapists is to be critically aware of the differences between the plan QA requirements and methods for IMRT and those required for VMAT.

Patient-Specific Quality Assurance for the Delivery of 60Co Intensity Modulated Radiation Therapy Subject to a 0.35-T Lateral Magnetic Field

This work describes a patient-specific dosimetry quality assurance (QA) program for intensity modulated radiation therapy (IMRT) using ViewRay, the first commercial magnetic resonance imaging-guided RT device. The program consisted of: (1) a 1-dimensional multipoint ionization chamber measurement using a customized 15-cm(3) cube-shaped phantom; (2) 2-dimensional (2D) radiographic film measurement using a 30- × 30- × 20-cm(3) phantom with multiple inserted ionization chambers; (3) quasi-3D diode array (ArcCHECK) measurement with a centrally inserted ionization chamber; (4) 2D fluence verification using machine delivery log files; and (5) 3D Monte Carlo (MC) dose reconstruction with machine delivery files and phantom CT. Ionization chamber measurements agreed well with treatment planning system (TPS)-computed doses in all phantom geometries where the mean ± SD difference was 0.0% ± 1.3% (n=102; range, -3.0%-2.9%). Film measurements also showed excellent agreement with the TPS-computed 2D dose distributions where the mean passing rate using 3% relative/3 mm gamma criteria was 94.6% ± 3.4% (n=30; range, 87.4%-100%). For ArcCHECK measurements, the mean ± SD passing rate using 3% relative/3 mm gamma criteria was 98.9% ± 1.1% (n=34; range, 95.8%-100%). 2D fluence maps with a resolution of 1 × 1 mm(2) showed 100% passing rates for all plan deliveries (n=34). The MC reconstructed doses to the phantom agreed well with planned 3D doses where the mean passing rate using 3% absolute/3 mm gamma criteria was 99.0% ± 1.0% (n=18; range, 97.0%-100%), demonstrating the feasibility of evaluating the QA results in the patient geometry. We developed a dosimetry program for ViewRay's patient-specific IMRT QA. The methodology will be useful for other ViewRay users. The QA results presented here can assist the RT community to establish appropriate tolerance and action limits for ViewRay's IMRT QA.

Validation of a quick three-dimensional dose verification system for pre-treatment IMRT QA.

In this study, we evaluated the dosimetric performance of the three-dimensional (3D) dose verification system, COMPASS version 3 (IBA Dosimetry, GmbH, Germany). The COMPASS has the function of a dedicated beam modeling and dose calculation. It is able to reconstruct 3D dose distributions on patient CT images, using the incident fluence from a linear accelerator measured with the MatriXX 2D array (IBA Dosimetry). The dose profiles measured with various multi-leaf collimator (MLC) test patterns for the COMPASS were checked by comparison with those of EDR2 (Eastman Kodak, Rochester, NY) films and Monte Carlo (MC) simulations. The COMPASS was also used for dose verification in clinical intensity-modulated radiation therapy (IMRT) plans for head and neck cases. The dose distributions were compared with those measured by 3DVH (Sun Nuclear, Melbourne, FL) and MC. In addition, the quality assurance (QA) times among the COMPASS, 3DVH, and EDR2 were compared. For MLC test patterns, the COMPASS dose profiles agreed within 3% with those of EDR2 films and MC simulations. The physical resolution of the COMPASS detectors was lower than that of film, but the dose resolution for MLC patterns was comparable to that of film. In clinical plans, the dose-volume-histograms were equal for all systems. The average QA times of the COMPASS, 3DVH, and EDR2 film were 40.1, 59.4, and 121.4min, respectively. The COMPASS system provides fast and reliable 3D dose verification for clinical IMRT QA. The COMPASS QA process does not require phantom plans. Therefore, it allows a simple QA workflow.

Evaluation of a novel susceptibility weighted imaging MRI sequence for neonate brain scanning

Evaluation of a novel susceptibility weighted imaging MRI sequence for neonate brain scanning

Effects of spatial resolution and noise on gamma analysis for IMRT QA.

We investigated the sensitivity of the gamma index to two factors: the spatial resolution and the noise level in the measured dose distribution. We also examined how the choice of reference distribution and analysis software affect the sensitivity of gamma analysis to these two factors for quality assurance (QA) of intensity‐modulated radiation therapy (IMRT) treatment plans. For ten clinical IMRT plans, the dose delivered to a transverse dose plane was measured with EDR2 radiographic film. To evaluate the effects of spatial resolution, each irradiated film was digitized using three different resolutions (71, 142, and 285 dpi). To evaluate the effects of image noise, 1% and 2% local Gaussian noise was added to the film images. Gamma analysis was performed using 2%/2 mm and 3%/3 mm acceptance criteria and two commercial software packages, OmniPro I'mRT and DoseLab Pro. Dose comparisons were performed with the treatment planning system (TPS)‐calculated dose as the reference, and then repeated with the film as the reference to evaluate how the choice of reference distribution affects the results of dose comparisons. When the TPS‐calculated dose was designated as the reference distribution, the percentage of pixels with passing gamma values increased with both increasing resolution and noise. For 3%/3 mm acceptance criteria, increasing the film image resolution by a factor of two and by a factor of four caused a median increase of 0.9% and 2.6%, respectively, in the percentage of pixels passing. Increasing the noise level in the film image resulted in a median increase in percentage of pixels passing of 5.5% for 1% added local Gaussian noise and 5.8% for 2% added noise. In contrast, when the film was designated as the reference distribution, the percentage of pixels passing decreased with increased film noise, while increased resolution had no significant effect on passing rates. Furthermore, the sensitivity of gamma analysis to noise and resolution differed between OmniPro I'mRT and DoseLab Pro, with DoseLab Pro being less sensitive to the effects of noise and resolution. Noise and high scanning resolution can artificially increase the percentage of pixels with passing gamma values in IMRT QA. Thus, these factors, if not properly taken into account, can potentially affect the results of IMRT QA by causing a plan that should be classified as failing to be falsely classified as passing. In designing IMRT QA protocols, it is important to be aware that gamma analysis is sensitive to these parameters.PACS number: 87.55.Qr, 87.55.km, 87.56.Fc

TU‐C‐17A‐06: Evaluating IMRT Plan Deliverability Via PTV Shape and MLC Motion

Purpose:For step‐and‐shoot intensity‐modulated radiation therapy (IMRT) plans, the dosimetry and deliverability can be affected by the number and shape of the segments used. Thus, plan deliverability is likely related to target volume and shape. We investigated whether the sphericity of target volumes and the previously proposed Modulation Complexity Score (MCS) could be used together to improve the detection of IMRT fields that failed quality assurance (QA).Methods:526 and 353 IMRT fields from 32 prostate and 28 head‐and‐neck (H' N) patients, respectively, were analyzed. MCS was used to quantify the complexity of multi‐leaf collimator shapes and motion patterns for each field. Sphericity was calculated using the surface area and volume of each patient’s planning target volume (PTV). Logistic regression models with MCS‐alone or MCS and sphericity terms were fit to PlanUNC IMRT pass/fail results (5% dose difference, 4mm distance‐to‐agreement criteria) using SAS 9.3 (Cary, NC). Model concordance, discordance and area under the curve (AUC) were used to quantify model accuracy.Results:Mean (±1 standard deviation) MCS for prostate and H' N were 0.58(±0.15) and 0.40 (±0.14), respectively. Mean sphericity scores were 0.75(±0.05) for prostate and 0.63 (±0.12) for H' N. Both metrics were significantly different between treatment locations (p<0.01, Wilcoxon Rank Sum Test) indicating greater complexity in shape and variations for H' N PTVs. For prostate, concordance, discordance and AUC using MCS alone were 80.8%, 18.7% and 0.811. Including sphericity in the model improved these to 81.7%, 17.7% and 0.820. For H' N, the original concordance, discordance and AUC were of 72.9%, 26.9% and 0.729. Including sphericity into the model improved these metrics to 76.5%, 23.2% and 0.729.Conclusion:Sphericity provides a quantitative measure of PTV shape. While improvement in IMRT QA failure detection was modest for both prostate and H' N plans, including sphericity in the model does improve IMRT field failure prediction.

SU‐E‐T‐422: Correlation Between 2D Passing Rates and 3D Dose Differences for Pretreatment VMAT QA

Purpose:Volumetric modulated arc therapy (VMAT) quality assurance (QA) is typically using QA methods and action levels taken from fixedbeam intensity‐modulated radiotherapy (IMRT) QA methods. However, recent studies demonstrated that there is no correlation between the percent gamma passing rate (%GP) and the magnitude of dose discrepancy between the planned dose and the actual delivered dose for IMRT. The purpose of this study is to investigate whether %GP is correlated with clinical dosimetric difference for VMAT.Methods:Twenty nasopharyngeal cancer (NPC) patients treated with dual‐arc simultaneous integrated boost VMAT and 20 esophageal cancer patients treated with one‐arc VMAT were enrolled in this study. Pretreatment VMAT QA was performed by a 3D diode array ArcCheck. Acceptance criteria of 2%/2mm, 3%/3mm, and 4%/4mm were applied for 2D %GP. Dose values below 10% of the per‐measured normalization maximum dose were ignored.Mean DVH values obtained from 3DVH software and TPS were calculated and percentage dose differences were calculated. Statistical correlation between %GP and percent dose difference was studied by using Pearson correlation.Results:The %GP for criteria 2%/2mm, 3%/3mm, and 4%/4mm were 82.33±4.45, 93.47±2.31, 97.13±2.41, respectively. Dose differences calculated from 3DVH and TPS for beam isocenter, mean dose of PTV, maximum dose of PTV, D2 of PTV and D98 of PTV were ‐1.04±3.24, ‐0.74±1.71, 2.92±3.62, 0.89±3.29, ‐1.46±1.97, respectively. No correction were found between %GP and dose differences.Conclusion:There are weak correlations between the 2D %GP and dose differences calculated from 3DVH. The %GP acceptance criteria of 3%/3mm usually applied for pretreatment QA of IMRT and VMAT is not indicating strong clinical correlation with 3D dose difference. 3D dose reconstructions on patient anatomy may be necessary for physicist to predict the accuracy of delivered dose for VMAT QA.

Reproducibility in patient-specific IMRT QA.

The purpose of this study was to determine the reproducibility of patient‐specific, intensity‐modulated radiation therapy (IMRT) quality assurance (QA) results in a clinical setting. Six clinical patient plans were delivered to a variety of devices and analyses, including 1) radiographic film; 2) ion chamber; 3) 2D diode array delivered and analyzed in three different configurations (AP delivery with field‐by‐field analysis, AP delivery with composite analysis, and planned gantry angle delivery); 4) helical diode array; and 5) in‐house‐designed multiple ion chamber phantom. The six clinical plans were selected from a range of treatment sites and were of various levels of complexity. Of note, three of the plans had failed at least preliminary evaluation with our in‐house IMRT QA; the other three plans had passed QA. These plans were delivered three times sequentially without changing the setup, and then delivered two more times after breaking down and rebuilding the setup between each. This allowed for an investigation of reproducibility (in terms of dose, dose difference or percent of pixels passing gamma) of both the delivery and the physical setup. This study showed that the variability introduced from the setup was generally higher than the variability from redelivering the plan. Radiographic film showed the poorest reproducibility of the dosimeters investigated. In conclusion, the various IMRT QA systems demonstrated varying abilities to reproduce QA results consistently. All dosimetric devices demonstrated a reproducibility (coefficient of variation) of less than 4% in their QA results for all plans, with an average reproducibility of less than 2%. This work provides some quantification for the variability that may be seen for IMRT QA dosimeters.PACS numbers: 87.55.Qr, 87.56.Fc

Japanese structure survey of high-precision radiotherapy in 2012 based on institutional questionnaire about the patterns of care.

The purpose of this study was to clarify operational situations, treatment planning and processes, quality assurance and quality control with relevance to stereotactic radiotherapy, intensity-modulated radiotherapy and image-guided radiotherapy in Japan. We adopted 109 items as the quality indicators of high-precision radiotherapy to prepare a questionnaire. In April 2012, we started to publicly open the questionnaire on the website, requesting every institution with radiotherapy machines for response. The response ratio was 62.1% (490 out of 789 institutions responded). Two or more radiotherapy technologists per linear accelerator managed linear accelerator operation in ∼90% of the responded institutions while medical physicists/radiotherapy quality managers were engaged in the operation in only 64.9% of the institutions. Radiotherapy certified nurses also worked in only 18.4% of the institutions. The ratios of the institutions equipped for stereotactic radiotherapy of lung tumor, intensity-modulated radiotherapy and image-guided radiotherapy were 43.3, 32.6 and 46.8%, respectively. In intensity-modulated radiotherapy planning, radiation oncologists were usually responsible for delineation while medical physicists/radiotherapy quality managers or radiotherapy technologists set up beam in 33.3% of the institutions. The median time required for quality assurance of intensity-modulated radiotherapy at any site of brain, head and neck and prostate was 4 h. Intensity-modulated radiotherapy quality assurance activity had to be started after clinical hours in >60% of the institutions. This study clarified one major issue in the current high-precision radiotherapy in Japan. A manpower shortage should be corrected for high-precision radiotherapy, especially in the area relevant to quality assurance/quality control.

Using a Novel Dose QA Tool to Quantify the Impact of Systematic Errors Otherwise Undetected by Conventional QA Methods: Clinical Head and Neck Case Studies

Recent studies have demonstrated that per-beam planar intensity-modulated radiation therapy (IMRT) quality assurance (QA) passing rates may not predict clinically relevant patient dose errors. This work is to evaluate the effect of dose variations introduced in dynamic multi-leaf collimator (DMLC) modeling and delivery processes on clinically relevant metrics for IMRT. Ten head and neck (HN) IMRT plans were randomly selected for this study. The conventional per-beam IMRT QA was performed for each plan by 2 different methods: (1) with gantry angle of 0 (gantry pointing downward) for all IMRT fields and (2) with gantry at specific angles as designed in the IMRT plan. For each patient, a batch analysis was done for each scenario and then imported to the 3DVH (Sun Nuclear Corp.) for processing. A "corrected DVH" was generated and compared to the DVH from the treatment plan. Their differences represented errors introduced from the combination of the treatment planning system (TPS) dose calculation algorithm and beam-delivery. The dose metrics from the two scenarios were compared with the corresponding calculated doses, and then their differences were analyzed. Although all per-beam planar IMRT QA had high Gamma passing rates 99.3 ± 1.3% (92.3-100%) for "2%/3 mm" criteria, there were significant errors in some of the calculated clinical dose metrics. Such as, for all the plans studied, there were as much as 3.2%, 5.7%, 5.6%, 2.3%, 4.1%, and 23.8% errors found in max cord dose, max brainstem dose, mean parotid dose, larynx dose, oral cavity dose, and PTV(D95) dose, respectively. The differences in errors for clinical metrics obtained between the two scenarios (zero gantry angle vs. true gantry angles) can also be significant: max cord dose (2.9% vs. 0.2%), max brainstem dose (3.8% vs. 0.4%), mean parotid dose (2.3% vs. 4.5%), mean larynx dose (3.9% vs. 2.0%), mean oral cavity dose (1.6% vs. 3.9%), and PTV(D95) dose (-0.4% vs. -2.6%). However, in the two scenarios, a strong and clear correlation between the dose differences for each of the organ structures was observed. This study confirms that conventional IMRT QA performance metrics are not predictive of dose errors in PTV and organs-at-risk. The clinically-relevant-dose QA has allowed us to predict the patient dose-volume relationships.

Patient Specific Pre-Treatment QA Verification Using an EPID Approach

A software program [MU-EPID], has been developed to perform patient specific pre-treatment quality assurance (QA) verification for intensity modulated radiation therapy (IMRT) using fluence maps measured with an electronic portal imaging device (EPID). The software converts the EPID acquired images of each IMRT beam, to fluence maps that are equivalent to those calculated by the treatment planning system (TPS). The software has the capability to process Varian, Elekta and Siemens EPID DICOM images. In the present investigation, several IMRT plans for different treatment sites were used to validate the software using the Varian a-Si 1000 EPID with the Pinnacle TPS. A total of 20 IMRT plans of different treatment sites were analyzed. Isodose distributions, dose profiles, dose volume histograms (DVH's) and gamma analysis comparisons were performed to evaluate the accuracy of our method. A gamma index analysis of the isocenter coronal plane was done for each plan and showed an average of 97.44% of gamma passing rate using a 3% and 3 mm gamma criterion. Isodose, DVH and dose profile comparisons were conducted between the original calculated plan and the measured reconstructed plan from the EPID images processed through the MU-EPID software. The results suggest that MU-EPID can be used clinically for patient specific IMRT QA, providing a comprehensive 3D dosimetric evaluation through DVH comparison as well as an option for a 2D gamma analysis.

Establishing a process of irradiating small animal brain using a CyberKnife and a microCT scanner

Establish and validate a process of accurately irradiating small animals using the CyberKnife G4 System (version 8.5) with treatment plans designed to irradiate a hemisphere of a mouse brain based on microCT scanner images. These experiments consisted of four parts: (1) building a mouse phantom for intensity modulated radiotherapy (IMRT) quality assurance (QA), (2) proving usability of a microCT for treatment planning, (3) fabricating a small animal positioning system for use with the CyberKnife's image guided radiotherapy (IGRT) system, and (4)in vivo verification of targeting accuracy. A set of solid water mouse phantoms was designed and fabricated, with radiochromic films (RCF) positioned in selected planes to measure delivered doses. After down-sampling for treatment planning compatibility, a CT image set of a phantom was imported into the CyberKnife treatment planning system--MultiPlan (ver. 3.5.2). A 0.5 cm diameter sphere was contoured within the phantom to represent a hemispherical section of a mouse brain. A nude mouse was scanned in an alpha cradle using a microCT scanner (cone-beam, 157 × 149 pixels slices, 0.2 mm longitudinal slice thickness). Based on the results of our positional accuracy study, a planning treatment volume (PTV) was created. A stereotactic body mold of the mouse was "printed" using a 3D printer laying UV curable acrylic plastic. Printer instructions were based on exported contours of the mouse's skin. Positional reproducibility in the mold was checked by measuring ten CT scans. To verify accurate dose delivery in vivo, six mice were irradiated in the mold with a 4 mm target contour and a 2 mm PTV margin to 3 Gy and sacrificed within 20 min to avoid DNA repair. The brain was sliced and stained for analysis. For the IMRT QA using a set of phantoms, the planned dose (6 Gy to the calculation point) was compared to the delivered dose measured via film and analyzed using Gamma analysis (3% and 3 mm). A passing rate of 99% was measured in areas of above 40% of the prescription dose. The final inverse treatment plan was comprised of 43 beams ranging from 5 to 12.5 mm in diameter (2.5 mm size increments are available up to 15 mm in diameter collimation). Using the Xsight Spine Tracking module, the CyberKnife system could not reliably identify and track the tiny mouse spine; however, the CyberKnife system could identify and track the fiducial markers on the 3D mold.In vivo positional accuracy analysis using the 3D mold generated a mean error of 1.41 mm ± 0.73 mm when fiducial markers were used for position tracking. Analysis of the dissected brain confirmed the ability to target the correct brain volume. With the use of a stereotactic body mold with fiducial markers, microCT imaging, and resolution down-sampling, the CyberKnife system can successfully perform small-animal radiotherapy studies.

Pre-Treatment Dose Verification of Imrt Using Gafchromic Ebt3 Film and 2DArray

Purpose: The present work deals with pre-treatment dosimetric verification of 10 prostate intensity-modulated radiotherapy (IMRT) plans obtained by Gafchromic EBT3 film and 2D-Array seven29 to establish quality control protocol for the delivery of prostate IMRT in our clinic. Methods: 10 prostate patients were irradiated according to IMRT techniques with 6 MV photon beams produced by a Varian DHX linear accelerator. Dose plans were computed using Eclipse 8.9 (version8.9, Varian, Palo Alto, CA, United States) treatment planning system (TPS). Pre-treatment dosimetric verification was carried out on field-perfield and total IMRT plan basis measuring 2D dose distributions in RW3 solid water phantom (PTW-Freiburg, Germany). For 10 patient plans, the dose distribution was re-calculated with the phantom CT scan and delivered to the phantom with the original and 0 degrees gantry, collimator and table angles. Thus IMRT quality control (QC) plans were generated. Dose distribution measurements were measured with Gafchromic EBT3 film and 2D-Array seven29 (PTW-Freiburg, Germany) two dimensional ionization chamber system. Verification measurements of total IMRT plans and each individual beams were compared with expected dose maps, and differences were evaluated by Verisoft program (PTW-Freiburg, Germany). To provide comparisons of multidimensional dose distributions, dose comparison tools such as gamma dose distribution, distance- to- agreement (DTA) and dose difference (DD) have been developed. The gamma dose distribution tool was used in our study. Three different gamma criteria of dose difference (DD) and distance to agreement (DTA) (3%/3 mm, 4%/4 mm and 5%/5 mm DD / DTA) are selected. These criteria are evaluated while suppressing the dose of 5% from dose distribution. Criterion validity accepted as section with gamma value less than or equal to 1 (γ ≤ 1) to be 90%. Results: In the comparison of dose distributions obtained from TPS and the results of PTW 2D-Array seven29 and Gafchromic EBT3 film dosimetry systems, it was showed that the compatibility of both methods were above 90% with respect to 3% DD and 3mm DTA criteria. PTW 2D-Array seven29 results compared to the results of the film was closer to the TPS data and this difference was statistically meaningful (p 0.05). Conclusions: The measurements performed with PTW 2D-Array seven29 were closer to the TPS data than film measurements and it takes less time during clinical use, so it could be preferred for routine use. The present results suggest the gamma criteria of 3%/3 mm as the most suitable criteria for prostate IMRT quality assurance.

Collaborating with Ontario cancer centers to ensure coordinated access to safe, evidence-based, high-quality IMRT treatment.

187 Background: In 2007, CCO identified variability in access to Intensity Modulated Radiation Therapy (IMRT) across the province. To ensure access to this technology, a three-year IMRT implementation Project was started in 2008, focusing on the development of: disease site guidelines and targets, cost-effectiveness analyses, a provincial quality assurance program, disease and discipline specific communities of practice and knowledge-sharing platforms. Methods: Needs assessments were conducted to identify educational and training needs in all disciplines. Systematic reviews were undertaken to establish disease site specific IMRT indications, set targets and conduct cost effective analyses. Educational courses and hands on expert-based coaching, were made available and a provincial IMRT quality assurance program was established. Results: The needs assessments identified a strong interest in educational and coaching opportunities. IMRT indication guidelines were developed for 10 disease sites and utilization targets were set for 6 disease sites. Results from two cost effectiveness analyses confirmed IMRT as a standard of care over 3D Conformal Radiation Therapy. 11 cancer centres received IMRT expert-based coaching, which included hands on-training, site visits, and educational support. Knowledge sharing and educational opportunities were provided to over 949 radiation therapists, oncologists and physicists. 13 cancer centres participated in external IMRT quality assurance testing for head and neck and prostate cancer. IMRT utilization has increased without affecting wait times or patient safety with no increase in incidents during this time period. All six disease sites have me their targets for 2012/13. Conclusions: IMRT knowledge and expertise across the province has grown along with a dramatic increase in the percentage of patients being treated for curative intent receiving IMRT. This jurisdictional implementation project was successful in making this treatment available to all Ontarians who would benefit. The lessons learned from this experience may be useful in the future rollout of other new technologies in Ontario and in other health care settings.

Clinical validation of an in-house EPID dosimetry system for IMRT QA at the Prince of Wales Hospital

In this study a simple method using standard flood-field corrected Electronic Portal Imaging Device (EPID) images for routine Intensity Modulated Radiation Therapy (IMRT) Quality Assurance (QA) was investigated. The EPID QA system was designed and tested on a Siemens Oncor Impression linear accelerator with an OptiVue 1000ST EPID panel (Siemens Medical Solutions USA, Inc, USA) and an Elekta Axesse linear accelerator with an iViewGT EPID (Elekta AB, Sweden) for 6 and 10 MV IMRT fields with Step-and-Shoot and dynamic-MLC delivery. Two different planning systems were used for patient IMRT field generation for comparison with the measured EPID fluences. All measured IMRT plans had >95% agreement to the planning fluences (using 3 cGy / 3 mm Gamma Criteria) and were comparable to the pass-rates calculated using a 2-D diode array dosimeter.