Intensity-modulated Radiation Therapy Quality Assurance Research Articles

Intensity-modulated radiotherapy quality assurance by alanine-EPR and gel dosimetry of a simulated prostate treatment with bilateral metallic prostheses

The presence of metallic prostheses in patients undergoing prostate radiotherapy treatment can lead to scattered doses, compromising treatment reproducibility. This study aims to assess doses in the Planning Target Volume (PTV) and surrounding areas using a water phantom containing pelvic bones and bilateral metallic prostheses. Intensity Modulated Radiotherapy (IMRT) with optimization tools avoiding input dose to the prosthesis was employed. Experimental verification utilized a modified Fricke xylenol orange gel dosimeter (FXO-f) in a 63 mm diameter, 100 mm height cylinder (310 ml volume) for PTV dose checks, and alanine dosimeters for assessing doses in the PTV vicinity and near metallic prostheses. Evaluating doses near prostheses is vital as post-radiotherapy prosthesis loosening has been speculated, possibly linked to overexposure. Gamma evaluation with FXO-f dosimeter yielded approved gamma indices in 97.7% of data points versus TPS, indicating good agreement with linear accelerator-reproduced results. Alanine dosimeter results ranged between (1.0 ± 0.3), (1.2 ± 0.3) Gy, (1.4 ± 0.3) Gy, and (2.0 ± 0.3) Gy, which are comparable to TPS-calculated doses within the dosimeter volume. This result indicates that the heterogeneity correction applied by the Analytical Anisotropic Algorithm used for dose calculation and the avoidance tool employed in the treatment planning could addressed the problem. In summary, this study demonstrates that the treatment technique entering fields towards prostheses, with optimization tools to produce the desirable results.

Error detection using a multi-channel hybrid network with a low-resolution detector in patient-specific quality assurance.

This study aimed to develop a hybrid multi-channel network to detect multileaf collimator (MLC) positional errors using dose difference (DD) maps and gamma maps generated from low-resolution detectors in patient-specific quality assurance (QA) for Intensity Modulated Radiation Therapy (IMRT). A total of 68 plans with 358 beams of IMRT were included in this study. The MLC leaf positions of all control points in the original IMRT plans were modified to simulate four types of errors: shift error, opening error, closing error, and random error. These modified plans were imported into the treatment planning system (TPS) to calculate the predicted dose, while the PTW seven29 phantom was utilized to obtain the measured dose distributions. Based on the measured and predicted dose, DD maps and gamma maps, both with and without errors, were generated, resulting in a dataset with 3222 samples. The network's performance was evaluated using various metrics, including accuracy, sensitivity, specificity, precision, F1-score, ROC curves, and normalized confusion matrix. Besides, other baseline methods, such as single-channel hybrid network, ResNet-18, and Swin-Transformer, were also evaluated as a comparison. The experimental results showed that the multi-channel hybrid network outperformed other methods, demonstrating higher average precision, accuracy, sensitivity, specificity, and F1-scores, with values of 0.87, 0.89, 0.85, 0.97, and 0.85, respectively. The multi-channel hybrid network also achieved higher AUC values in the random errors (0.964) and the error-free (0.946) categories. Although the average accuracy of the multi-channel hybrid network was only marginally better than that of ResNet-18 and Swin Transformer, it significantly outperformed them regarding precision in the error-free category. The proposed multi-channel hybrid network exhibits a high level of accuracy in identifying MLC errors using low-resolution detectors. The method offers an effective and reliable solution for promoting quality and safety of IMRT QA.

Evaluating AAPM-TG-218 recommendations: Gamma index tolerance and action limits in IMRT and VMAT quality assurance using SunCHECK.

This study aimed to improve the safety and accuracy of radiotherapy by establishing tolerance (TL) and action (AL) limits for the gamma index in patient-specific quality assurance (PSQA) for intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) using SunCHECK software, as per AAPM TG-218 report recommendations. The study included 125 patients divided into six groups by treatment regions (H&N, thoracic and pelvic) and techniques (VMAT, IMRT). SunCHECK was used to calculate the gamma passing rate (%GP) and dose error (%DE) for each patient, for the planning target volume and organs at risk (OARs). The TL and AL were then determined for each group according to TG-218 recommendations. We conducted a comprehensive analysis to compare %DE among different groups and examined the relationship between %GP and %DE. The TL and AL of all groups were more stringent than the common standard as defined by the TG218 report. The TL and AL values of the groups differed significantly, and the values for the thoracic groups were lower for both VMAT and IMRT. The %DE of the parameters D95% , D90% , and Dmean in the planning target volume, and Dmean and Dmax in OARs were significantly different. The dose deviation of VMAT was larger than IMRT, especially in the thoracic group. A %GP and %DE correlation analysis showed a strong correlation for the planning target volume, but a weak correlation for the OARs. Additionally, a significant correlation existed between %GP of SunCHECK and Delta4. The study established TL and AL values tailored to various anatomical regions and treatment techniques at our institution. Establishing PSQA workflows for VMAT and IMRT offers valuable clinical insights and guidance. We also suggest developing a standard combining clinically relevant metrics with %GP to evaluate PSQA results comprehensively.

Comparison of Rapid Arc and Intensity Modulated Radiotherapy in a True Beam Linear Accelerator for 6 MV: Application of AAPM TG‐119 tests in treatment planning and quality assurance

AbstractObjectiveWe developed rapid arc (RA) and intensity‐modulated radiotherapy (IMRT) plans based on the American Association of Physicists in Medicine Task Group‐119 (AAPM TG‐119) proposals and compared the planning and quality assurance results.Materials and MethodsTwo treatment plans were used for each study patient: one using 7–9 IMRT fields and the other using the two full‐arc RA methods. Plan optimization and dose calculations were performed using 6 MV photons and EclipseTM with the anisotropic analytical algorithm (AAA). Task group (TG)‐119 described the planning objectives used to evaluate the treatment plans generated for this study. Point dose, planar fluence measurement, and trajectory log file analysis are used for quality assurance.ResultsThe conformity index (CI) for treatment plans varied between 0.76–0.91 when using IMRT and 0.75–0.93 when using RA. The homogeneity index (HI) was approximately 0.10–0.24 (IMRT) and 0.07–0.23 (RA). The ratio of the total number of monitor units required for IMRT to that required for RA was between 0.87 and 2.14. The treatment log files exhibited higher gamma passing with RA than with IMRT.ConclusionRA plans were more effective than IMRT plans in achieving the test goals. Point dose measurements and electronic portal imaging device (EPID)‐based planar fluence measurements showed statistically insignificant differences between the IMRT and RA plan quality assurance (QA) results. However, the trajectory log file analysis exhibited better gamma‐passing results for RA than for IMRT.

2D IMRT QA passing rate dependency on coronal plane

Intensity modulated radiation therapy (IMRT) delivery involves a complex series of beam angles and multileaf collimator (MLC) arrangements, requiring quality assurance to be performed to validate delivery before treatment. The purpose of this work is to investigate the effect of dose gradient on quality assurance (QA) passing rate. Many (n = 40) IMRT plans were delivered and measured using a 2D planar array of ion chambers; additionally, eleven plans were measured at several coronal planes. For each measurement, dose gradient was assessed using a number of metrics and passing rate assessed at both 3%/3 mm and 3%/2 mm criteria. The passing rates of the various IMRT plans were shown to be generally correlated to gradient, with an average distance correlation of 0.54 ± 0.04 for the lateral dose gradient. The passing rate for an individual plan was shown to vary with coronal slice, though the correlation to dose gradient was not predictable. Even though the passing rate was strongly related to dose gradient for many of the plans, the signs of the correlations were not always negative, as hypothesized. The coronal plane at which QA is performed affects passing rate, though dose gradient may not easily be used to predict slices at which passing rate is higher.

A hybrid method to improve efficiency of patient specific SRS and SBRT QA using 3D secondary dose verification.

Patient Specific QA (PSQA) by direct phantom measurement for all intensity modulated radiation therapy (IMRT) cases is labor intensive and an inefficient use of the Medical Physicist's time. The purpose of this work was to develop a hybrid quality assurance (QA) technique utilizing 3D dose verification as a screening tool to determine if a measurement is necessary. This study utilized Sun Nuclear DoseCHECK (DC), a 3D secondary verification software, and Fraction 0, a trajectory log IMRT QA software. Twenty-two Lung stereotactic body radiation therapy (SBRT) and thirty single isocentre multi-lesion SRS (MLSRS) plans were retrospectively analysed in DC. Agreement of DC and the TPS dose for selected dosimetric criteria was recorded. Calculated 95% confidence limits (CL) were used to establish action limits. All cases were delivered and measured using the Sun Nuclear stereotactic radiosurgery (SRS) MapCheck. Trajectory logs of the delivery were used to calculate Fraction 0 results for the same criteria calculated by DC. Correlation of DC and Fraction 0 results were calculated. Phantom measured QA was compared to Fraction 0 QA results for the cases which had DC criteria action limits exceeded. Correlation of DC and Fraction 0 results were excellent, demonstrating the same action limits could be used for both and DC can predict Fraction 0 results. Based on the calculated action limits, zero lung SBRT cases and six MLSRS cases were identified as requiring a measurement. All plans that passed the DC screening had a passing measurement based PSQA and agreed with Fraction 0 results. Using 95% CL action limits of dosimetric criteria, a 3D secondary dose verification can be used to determine if a measurement is required for PSQA. This method is efficient for it is part of the normal clinical workflow when verifying any clinical treatment. In addition, it can drastically reduce the number of measurements needed for PSQA.

EVALUATION OF PATIENT-SPECIFIC IMRT QUALITY ASSURANCE AND POINT DOSE MEASUREMENT FOR COMPLEX HEAD AND NECK AND BRAIN CANCER USING GAFCHROMIC EBT3 FILM.

Patient-specific intensity-modulated radiation therapy (IMRT) quality assurance (QA) is essential for complex radiotherapy treatment as it involves complex intensity modulation and high-dose gradient regions. IMRT QA was performed by point dose verification and two-dimensional (2D) dose distribution measurement using gamma method. Calibrated External Beam Therapy 3 (EBT3) film was used for point dose and pre-treatment verification of 10 IMRT plans, five complex Head and Neck (HN) and five brain cases. The gamma passing rate (GPR) was evaluated for 3%/3mm gamma criteria and compared with 2D array. Isocentre dose was measured for all 10 IMRT plans on EBT3 film. Percentage deviation of point dose measurement from TPS calculated was found 0.4% for brain cases and 2.9% for HN cases. The GPR for 3%/3mm criteria was obtained higher than 95% for brain and HN cases. Results suggest that film dosimetry is also a reliable verification system for patient-specific IMRT QA as the 2D array.

An independent Monte Carlo-based IMRT QA tool for a 0.35T MRI-guided linear accelerator.

To develop an independent log file-based intensity-modulated radiation therapy (IMRT) quality assurance (QA) tool for the 0.35T magnetic resonance-linac (MR-linac) and investigate the ability of various IMRT plan complexity metrics to predict the QA results. Complexity metrics related to tissue heterogeneity were also introduced. The tool for particle simulation (TOPAS) Monte Carlo code was utilized with a previously validated linac head model. A cohort of 29 treatment plans was selected for IMRT QA using the developed QA tool and the vendor-supplied adaptive QA (AQA) tool. For 27 independent patient cases, various IMRT plan complexity metrics were calculated to assess the deliverability of these plans. A correlation between the gamma pass rates (GPRs) from the AQA results and calculated IMRT complexity metrics was determined using the Pearson correlation coefficients. Tissue heterogeneity complexity metrics were calculated based on the gradient of the Hounsfield units. The median and interquartile range for the TOPAS GPRs (3%/3mm criteria) were 97.24% and 3.75%, respectively, and were 99.54% and 0.36% for the AQA tool, respectively. The computational time for TOPAS ranged from 4 to 8h to achieve a statistical uncertainty of <1.5%, whereas the AQA tool had an average calculation time of a few minutes. Of the 23 calculated IMRT plan complexity metrics, the AQA GPRs had correlations with 7 out of 23 of the calculated metrics. Strong correlations (|r|>0.7) were found between the GPRs and the heterogeneity complexity metrics introduced in this work. An independent MC and log file-based IMRT QA tool was successfully developed and can be clinically deployed for offline QA. The complexity metrics will supplement QA reports and provide information regarding plan complexity.

Gamma Index Analysis as a Patient-Specific Quality Assurance Tool for High-Precision Radiotherapy: A Clinical Perspective of Single Institute Experience.

Purpose Patient-specific quality assurance (QA) by gamma (γ) analysis is an important component of high-precision radiotherapy. It is important to standardize institute-specific protocol. In this study, we describe our institutional experience of patient-specific QA for high-precision radiotherapy from a clinical perspective. Methods The planning data of 56 patients treated with intensity-modulated radiotherapy (IMRT)/volumetric modulated arc therapy (VMAT) were included. γ index analysis was done using Octavius 4D IMRT QA phantom(PTW, Freiburg, Germany) using 3 mm/3% criteria. Local, global, and volumetric gammas were calculated and compared. The relationship of γ index in the transverse, coronal, and sagittal direction and anatomical region of treatment was explored. Results Global three-dimensional (3D) γ indices in the coronal, sagittal, and transverse axes were 96.73 ± 2.35, 95.66 ± 3.01, and 93.36 ± 4.87 (p < 0.05). The average local two-dimensional (2D) γ index was 78.23 ± 5.44 and the global γ index was 92.41 ± 2.41 (p < 0.005). The average local 3D γ index was 84.99 ± 4.24 and the global 3D γ index was 95.25 ± 1.72 (p < 0.005, paired t-test). The average local volumetric γ index was 84.29 ± 4.73 and the global volumetric γ index was 95.96 ± 2.08 (p < 0.005). 3D global gamma index was significantly different in different anatomical regions (p < 0.05). Conclusion Our study shows that γ index analysis is a useful parameter for routine clinical IMRT QA. The choice of type of γ index depends on the context of use and degree of stringency in measurement. Average 2D and 3D global γ were different in anatomical regions. The average 3D γ index was significantly different in axes. No difference was observed with techniques of IMRT/VMAT. Localization of failed points in CT anatomy can be advantageous for clinical decision-making.

Design and fabrication of indigenous multi-rotational thorax phantom for patient-specific quality assurance of IMRT and VMAT

Intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) are commonly used treatment modalities in external beam radiotherapy. Precise quality assurance is required for the clinical implementation of IMRT and VMAT to ensure the correct treatment delivery. Square slab phantom is used commonly in developing countries to measure the pre-treatment point dose measurements. The limitation of the slab phantom was that the detector was positioned on the central axis of the beam which caused difficulty in positioning of the chamber at off-axis of the beam and peripheral regions. The new indigenously multi-purpose multi-rotational phantom was fabricated with various chamber provisions in order to address the above challenge. Innovative devices always play a crucial role in radiotherapy to bring significant technological advancement to the field. The quality assurance Multi-Rotational Thorax (MRT) Phantom designing involved slice-wise modelling of an average adult thorax using Poly-methyl methacrylate (PMMA) to perform point dose absolute dosimetry using an ionization chamber and Radio-Photo-Luminescence Glass Dosimeter (RPLGD). The phantom consisted of 35 slices of PMMA material in an axial direction. Each slice had a dimension of 1 cm thickness, 35 cm length and 20 cm height. The phantom had provisions in the target region and multiple provisions in the lungs, heart, surface and spine. The unique manual rotation system was provided on the lungs as well as in the heart. The provisions were capable of holding the detectors such as ionization chambers and RPLGD. The response of the phantom to open the beam in various gantry angles was initially accessed with multiple gantry angles and then pre-treatment verification of IMRT and VMAT plans was also checked. The results showed that the MRT phantom had good capabilities for absolute point dosimetry. In the case of an open beam, multiple gantry angles, the maximum variations for both the detectors were within −1.9% when compared with the TPS dose. The maximum percentage variation on isocentre (T) for IMRT and VMAT between TPS and Semiflex chamber was 1.85%. Similarly, the maximum percentage variation was 1.92% between TPS and RPLGD on isocentre. For Semiflex chamber, maximum percentage variation on peripheral region was 2.68%. Similarly, for RPLGD maximum percentage variation was 2.76%. The overall difference between the measured values for both the detectors were less than 3%. The present dosimetric study concluded that the MRT phantom with a RPLGD and Semiflex chamber was suitable for routine IMRT and VMAT patient-specific QA purposes.

Accelerate treatment planning process using deep learning generated fluence maps for cervical cancer radiation therapy

This study aims to develop a deep learning method that skips the time-consuming inverse optimization process for automatic generation of machine-deliverable intensity-modulated radiation therapy (IMRT) plans. Ninety cervical cancer clinical IMRT plans were collected to train a two-stage convolution neural network, of which 66 plans were assigned for training, 11 for validation, and 13 for test. The neural network took patients' computed tomography (CT) anatomy as the input and predicted the fluence map for each radiation beam. The predicted fluence maps were then imported into a treatment planning system and converted to multileaf collimators motion sequences. The automatic plan was evaluated against its corresponding clinical plan, and its machine deliverability was validated by patient-specific IMRT quality assurance (QA). There were no significant differences in dose parameters between automatic and clinical plans for all 13 test patients, indicating a good prediction of fluence maps and a decent quality of automatic plans. The average dice similarity coefficient of isodose volumes encompassed by 0%-100% isodose lines ranged from 0.94 to 1. In patient-specific IMRT QA, the mean gamma passing rate of automatic plans achieved 99.5% under 3%/3mm criteria, and 97.3% under 2%/2mm criteria, with a low dose threshold of 10%. The proposed deep learning framework can produce machine-deliverable IMRT plans with quality similar to the clinical plans in the test set. It skips the inverse plan optimization process and provides an effective and efficient method to accelerate treatment planning process.

Deep Learning for Patient-Specific Quality Assurance: Predicting Gamma Passing Rates for IMRT Based on Delivery Fluence Informed by log Files.

Objectives: In this study, we propose a deep learning-based approach to predict Intensity-modulated radiation therapy (IMRT) quality assurance (QA) gamma passing rates using delivery fluence informed by log files. Methods: A total of 112 IMRT plans for chest cancers were planned and measured by portal dosimetry equipped on TrueBeam linac. The convolutional neural network (CNN) based learning model was trained using delivery fluence as inputs and gamma passing rates (GPRs) of 4 different criteria (3%/3 mm, 2%/3 mm, 3%/2 mm, and 2%/2 mm) as outputs. Model performance for both validation and test sets was assessed using mean absolute error (MAE), mean squared error (MSE), root MSE (RMSE), Spearman rank correlation coefficients (Sr), and Determination coefficient (R2) between the measured and predicted GPR values. Results: In the test set, the MAE of the prediction model were 0.402, 0.511, 1.724, and 2.530, the MSE were 0.640, 0.986, 6.654, and 9.508, the RMSE were 0.800, 0.993, 2.580, and 3.083, the Sr were 0.643, 0.684, 0.821, and 0.824 (P < .001) and the R2 were 0.4110, 0.4666, 0.6677, and 0.6769 for 3%/3 mm, 3%/2 mm, 2%/3 mm, and 2%/2 mm, respectively. The MAE and RMSE of the prediction model decreased with stricter gamma criteria while the Sr and R2 between measured and predicted GPR values increased. Conclusions: The CNN prediction model based on delivery fluence informed by log files could accurately predict IMRT QA passing rates for different gamma criteria. It could reduce QA workload and improve efficiency in pretreatment QA. Our results suggest that the CNN prediction model based on delivery fluence informed by log files may be a promising tool for the gamma evaluation of IMRT QA.

Evaluating the Effects of Dose Rate on Dynamic Intensity-Modulated Radiation Therapy Quality Assurance

Evaluating the Effects of Dose Rate on Dynamic Intensity-Modulated Radiation Therapy Quality Assurance

Survey of IMRT in Japan

This study evaluated the current status, quality assurance (QA) and technique of intensity-modulated radiotherapy (IMRT) in Japan.IMRT is a new technique, introduced in the late 1990s. Since 2000, the number of institutions providing IMRT has increased. Therefore, to recognize the current status of IMRT in Japan, a nation-wide survey was conducted by the Japan 3-Dimensional Conformal External Beam Radiotherapy Group (J-CERG). The questionnaires, which consists of the clinical part and physics part, was sent by mail or e-mail to 835 institutions. By the end of Feb. 2021, 427 institutions and 534 institutions responded to the clinical part and physics part, respectively.In the clinical part, Two-hundreds and ninety-two (68%) institutions indicated that they have used IMRT technique for 44,409 cases out of 177,285 total in a year of 2019. Among these patients, 10,905 (25%) were prostate cancer, 7,772(18%) were head & neck cancer, 2,621 (6%) brain tumor, 2,027 (5%) lung tumor for SBRT, followed by liver tumor for SBRT, GYN cancer, esophageal cancer, breast cancer and GI tumor. The percentage of IMRT in all treatment was 75-100% in 18 institutions (6%), 50-75% in 22 institutions (8%), 20-50% in 144 institutions (49%), 10-20% in 68 institutions (23%), 5-10% in 28 institutions (10%), 5-1% in 11 institutions (4%) and < 1% in 2 institutions (1%). Target and OAR delineation was done by physician in 92% institutions and 69% institutions, respectively. In the physics part, 340 institutions (64%) use IMRT technique, and 80 institutions (24%) have commissioned their treatment planning systems with the beam data provided by the manufacturer. The measurement-based patient specific IMRT QAs are performed by 99% of institutions. The dose distribution measurement on films, 3D arrays, and 2D arrays are 42%, 41%, and 16%, respectively.The updated status of IMRT in 2019 in Japan was surveyed. The number of institutions where IMRT was started continuously increased in number.

Clinical performance of FractionLab in patient-specific quality assurance for intensity-modulated radiotherapy: a retrospective study.

BackgroundThis study was aimed at comparing and analyzing the results of FractionLab (Varian/Mobius Medical System) with those of portal dosimetry that uses an electronic portal imaging device. Portal dosimetry is extensively used for patient-specific quality assurance (QA) in intensity-modulated radiotherapy (IMRT).MethodsThe study includes 29 patients who underwent IMRT on a Novalis-Tx linear accelerator (Varian Medical System and BrainLAB) between June 2019 and March 2021. We analyzed the multileaf collimator DynaLog files generated after portal dosimetry to evaluate the same condition using FractionLab. The results of the recently launched FractionLab at various gamma indices (0.1%/0.1 mm–1%/1 mm) are analyzed and compared with those of portal dosimetry (3%/3 mm).ResultsThe average gamma passing rates of portal dosimetry (3%/3 mm) and FractionLab are 98.1% (95.5%–100%) and 97.5% (92.3%–99.7%) at 0.6%/0.6 mm, respectively. The results of portal dosimetry (3%/3 mm) are statistically comparable with the QA results of FractionLab (0.6%/0.6 mm–0.9%/0.9 mm).ConclusionThis paper presents the clinical performance of FractionLab by the comparison of the QA results of FractionLab using portal dosimetry with various gamma indexes when performing patient-specific QA in IMRT treatment. Further, the appropriate gamma index when performing patient-specific QA with FractionLab is provided.

Applications of machine and deep learning to patient-specific IMRT/VMAT quality assurance.

In order to deliver accurate and safe treatment to cancer patients in radiation therapy using advanced techniques such as intensity modulated radiation therapy (IMRT) and volumetric‐arc radiation therapy (VMAT), patient specific quality assurance (QA) should be performed before treatment. IMRT/VMAT dose measurements in a phantom using various devices have been clinically adopted as standard method for QA. This approach allows the verification of the accuracy of the dose calculation, data transfer, and the delivery system. However, patient‐specific QA procedures are expensive and require significant time and effort by the physicists. Over the past 5 years, machine learning (ML) and deep learning (DL) algorithms for predictions of IMRT/VMAT QA outcome have been investigated. Various ML and DL models have shown promising prediction accuracy and a high potential as time‐efficient virtual QA tool. In this paper, we review the ML and DL based models that were developed for patient specific IMRT and VMAT QA outcome predictions from algorithmic and clinical applicability perspectives. We focus on comparing the algorithms, the dataset sizes, the input parameters and features, the QA outcome prediction approaches, the validation, the performance, the clinical applicability, and the potential clinical impact. In addition, we discuss the present challenges as well as the future directions in the implementation of these models. To the best of our knowledge, this is the first review on the application of ML and DL based models in IMRT/VMAT QA predictions.

Correlation between the \u03b3 passing rates of IMRT plans and the volumes of air cavities and bony structures in head and neck cancer

BackgroundBoth patient-specific dose recalculation and γ passing rate analysis are important for the quality assurance (QA) of intensity modulated radiotherapy (IMRT) plans. The aim of this study was to analyse the correlation between the γ passing rates and the volumes of air cavities (Vair) and bony structures (Vbone) in target volume of head and neck cancer.MethodsTwenty nasopharyngeal carcinoma and twenty nasal natural killer T-cell lymphoma patients were enrolled in this study. Nine-field sliding window IMRT plans were produced and the dose distributions were calculated by anisotropic analytical algorithm (AAA), Acuros XB algorithm (AXB) and SciMoCa based on the Monte Carlo (MC) technique. The dose distributions and γ passing rates of the targets, organs at risk, air cavities and bony structures were compared among the different algorithms.ResultsThe γ values obtained with AAA and AXB were 95.6 ± 1.9% and 96.2 ± 1.7%, respectively, with 3%/2 mm criteria (p > 0.05). There were significant differences (p < 0.05) in the γ values between AAA and AXB in the air cavities (86.6 ± 9.4% vs. 98.0 ± 1.7%) and bony structures (82.7 ± 13.5% vs. 99.0 ± 1.7%). Using AAA, the γ values were proportional to the natural logarithm of Vair (R2 = 0.674) and inversely proportional to the natural logarithm of Vbone (R2 = 0.816). When the Vair in the targets was smaller than approximately 80 cc or the Vbone in the targets was larger than approximately 6 cc, the γ values of AAA were below 95%. Using AXB, no significant relationship was found between the γ values and Vair or Vbone.ConclusionIn clinical head and neck IMRT QA, greater attention should be paid to the effect of Vair and Vbone in the targets on the γ passing rates when using different dose calculation algorithms.

Improving intensity-modulated radiation therapy quality assurance by adopting statistical process control

PurposeTo use statistical process control for intensity-modulated radiation therapy (IMRT) quality assurance (QA) and improve tolerance limits and action limits. MethodsAn electronic portal imaging device (EPID) was selected to verify IMRT QA. The I-chart and the exponentially weighted moving averages (EWMA) chart were used to analyze the corresponding results. ResultsTwenty samples were used to enable the sampling requirements for building the control limits to be met. The I-chart showed that isolated data points beyond the control limits were mainly derived from complex plans. The EWMA made predictions of systematic errors earlier than the I-chart. Systematic errors primarily originated from the dose calibration on the EPID, and recalibrating the EPID could eliminate such errors. ConclusionStatistical process control is an effective tool to detect controllable and can be used in IMRT QA. After calibrating the EPID, the tolerance and action limits all improved and satisfied the requirements/recommended values of the AAPM TG-218 report.

Implementation of in-vivo diode dosimetry for intensity modulated radiotherapy as routine patients' quality assurance

The implementation of an in-vivo diode for dose verification of the intensity-modulated radiotherapy (IMRT) during the actual treatment being rare. This work aims to implement in-vivo and in-vitro diode dosimetry for the IMRT technique to verify the accuracy of the dose delivered to the patients undergoing radiation treatment. In total, 279 fields have been investigated for dose verification from 33 cases, including head and neck, prostate, bladder, and breast cancer patients. Additionally, these fields were compared with in-vitro measurements on a perspex phantom. Beforehand, the measurements were tested for an Alderson Rando phantom. In-vivo measurements revealed that 87.1% of the measured doses were within ±5% of the calculated doses. Of the other 12.9%, about 11.1% were more than ±5% and less ±10% and only 1.8% were outside the ±10% of the calculated doses. The corresponding fields for in-vitro measurements show that 96.1% of the measured doses within ±5% and only 3.9% were outside the ±5% of the calculated doses. The results in this study indicated that in-vivo diode dosimetry for IMRT is reliable as a quality assurance (QA) tool in the radiotherapy departments. Moreover, measurements with diodes are a real-time readout during actual treatment compared to the verification tools that have been used for routine IMRT QA. Additionally, the measurements were carried out comfortably and well tolerated by the patients.

Comprehensive Patient-Specific Intensity-Modulated Radiation Therapy Quality Assurance Comparing Mobius3D/FX to Conventional Methods of Evaluation.

PurposeTo determine the appropriateness of implementing Mobius3D/FX (Varian Medical Systems, Inc., Palo Alto, CA, USA) as not only a pretreatment secondary check but as an alternative to measurement-based patient-specific intensity-modulated radiation therapy (IMRT) quality assurance (QA).MethodsMobius3D/FX was commissioned and stock beam models were tweaked so that an independent recalculated 3D dose distribution can be obtained. Then, 50 patient-specific treatment plans for various indications were delivered across a 2D ion chamber array, radiochromic film setup, and electronic portal imager and analyzed with MobiusFX and gamma analysis. The concordance of plans scored as passing between MobiusFX and the conventional methods of QA was determined.ResultsAll analyzed treatment plans passed with a gamma passing rate >90% across all conventional QA methods, most commonly using a 3%/3mm gamma criterion except for film measurements where a 5%/3mm criterion was applied. There was good agreement and concordance between MobiusFX and conventional methods when using a 3%/3mm criteria for MobiusFX, whereas a 2%/2mm criteria appeared too stringent as it failed treatment plans deemed clinically acceptable using conventional methods.ConclusionsUsing a 50-sample subset of clinically delivered treatment plans this non-inferiority-type comparison shows Mobius3D/FX based on log file analysis to be a suitable alternative to conventional QA methods when utilizing the 3%/3mm gamma criterion. Methods based on log file analysis can provide an opportunity for resource sparing, improving the efficiency, and workflow for evaluating IMRT treatment plans.