Intensity-modulated radiation therapy dose verification using fluence and portal imaging device

Patient-specific quality assurance for intensity-modulated radiation therapy (IMRT) dose verification is essential. The aim of this study is to provide a new method based on the relative error distribution by comparing the fluence map from the treatment planning system (TPS) and the incident fluence deconvolved from the electronic portal imaging device (EPID) images. This method is validated for 10 head and neck IMRT cases. The fluence map of each beam was exported from the TPS and EPID images of the treatment beams were acquired. Measured EPID images were deconvolved to the incident fluence with proper corrections. The relative error distribution between the TPS fluence map and the incident fluence from the EPID was created. This was also created for a 2D diode array detector. The absolute point dose was measured with an ionization chamber, and the dose distribution was measured by a radiochromic film. In three cases, MLC leaf positions were intentionally changed to create the dose error as much as 5% against the planned dose and our fluence-based method was tested using gamma index. Absolute errors between the predicted dose of 2D diode detector and of our method and measure­ments were 1.26% ± 0.65% and 0.78% ± 0.81% respectively. The gamma passing rate (3% global / 3 mm) of the TPS was higher than that of the 2D diode detector (p< 0.02), and lower than that of the EPID (p < 0.04). The gamma passing rate (2% global / 2 mm) of the TPS was higher than that of the 2D diode detector, while the gamma passing rate of the TPS was lower than that of EPID (p < 0.02). For three modified plans, the predicted dose errors against the measured dose were 1.10%, 2.14%, and -0.87%. The predicted dose distributions from the EPID were well matched to the measurements. Our fluence-based method provides very accurate dosimetry for IMRT patients. The method is simple and can be adapted to any clinic for complex cases

Measurement of the Top Pair Production Cross Section in the Dilepton Decay Channel in ppbar Collisions at sqrt s = 1.96 TeV

Submitted to Phys. Rev. DA measurement of the \ttbar production cross section in \ppbar collisions at $\sqrt{{\rm s}}$ = 1.96 TeV using events with two leptons, missing transverse energy, and jets is reported. The data were collected with the CDF II Detector. The result in a data sample corresponding to an integrated luminosity 2.8 fb$^{-1}$ is: \sigma_{\ttbar} = 6.27 $\pm$ 0.73(stat) $\pm$ 0.63(syst) $\pm$ 0.39(lum) pb. for an assumed top mass of 175 GeV/$c^{2}$.A measurement of the tt̅ production cross section in pp̅ collisions at √s=1.96  TeV using events with two leptons, missing transverse energy, and jets is reported. The data were collected with the CDF II detector. The result in a data sample corresponding to an integrated luminosity 2.8  fb-1 is σtt̅ =6.27±0.73(stat)±0.63(syst)±0.39(lum)  pb. for an assumed top mass of 175  GeV/c2.Peer reviewe

The effect of beam shape on physical parameters of head and neck simultaneous-integrated boost intensity-modulated radiation therapy

AimTo evaluate the influence of the beam shape created by X-rays with “flat beams” and without “flattening-filter-free [FFF] beams” a flattening filter, and the isocenter locations for FFF beams on the treatment of a large irradiated volume for tumours.BackgroundThe increase of dose rate and the decrease of out-of-field dose can be expected for FFF beams and lead to effective and safety radiotherapy. On the other hand, the bell-shaped dose profile is thought to be a factor of negating these advantages.Materials and methodsTreatment plans for 15 patients with head and neck cancer were created using XiO (Elekta, Stockholm AB, Sweden) in fixed-gantry step-and-shoot delivery under the same dose constraints. Seven fields of FFF beams with 7 MV and flat beams with 6 MV were used with the technique of intensity-modulated radiation therapy (IMRT). We compared the dose homogeneity and conformity of targets and dose constraints for organs as the plan quality and evaluated physical parameters: monitor unit (MU) values, number of segments and their locations from the isocenter in beam's-eye-view.ResultsNo significant differences were found in the plan quality. The isocenter locations do not affect the physical parameters for FFF beams. It has been confirmed that the number of segments and MU values were 40% higher with FFF beams than with flat beams (p

A new plan quality objective function for determining optimal collimator combinations in prostate cancer treatment with stereotactic body radiation therapy using CyberKnife.

Stereotactic body radiation therapy with CyberKnife for prostate cancer has long treatment times compared with conventional radiotherapy. This arises the need for designing treatment plans with short execution times. We propose an objective function for plan quality evaluation, which was used to determine an optimal combination between small and large collimators based on short treatment times and clinically acceptable dose distributions. Data from 11 prostate cancer patients were used. For each patient, 20 plans were created based on all combinations between one small (⌀ 10-25 mm) and one large (⌀ 35-60 mm) Iris collimator size. The objective function was assigned to each combination as a penalty, such that plans with low penalties were considered superior. This function considered the achievement of dosimetric planning goals, tumor control probability, normal tissue complication probability, relative seriality parameter, and treatment time. Two methods were used to determine the optimal combination. First, we constructed heat maps representing the mean penalty values and standard deviations of the plans created for each collimator combination. The combination giving a plan with the smallest mean penalty and standard deviation was considered optimal. Second, we created two groups of superior plans: group A plans were selected by histogram analysis and group B plans were selected by choosing the plan with the lowest penalty from each patient. In both groups, the most used small and large collimators were assumed to represent the optimal combination. The optimal combinations obtained from the heat maps included the 25 mm as a small collimator, giving small/large collimator sizes of 25/35, 25/40, 25/50, and 25/60 mm. The superior-group analysis indicated that 25/50 mm was the optimal combination. The optimal Iris combination for prostate cancer treatment using CyberKnife was determined to be a collimator size between 25 mm (small) and 50 mm (large)

Comparison of gamma index based on dosimetric error and clinically relevant dose–volume index based on three-dimensional dose prediction in breast intensity-modulated radiation therapy

Abstract Background Measurement-guided dose reconstruction has lately attracted significant attention because it can predict the delivered patient dose distribution. Although the treatment planning system (TPS) uses sophisticated algorithm to calculate the dose distribution, the calculation accuracy depends on the particular TPS used. This study aimed to investigate the relationship between the gamma passing rate (GPR) and the clinically relevant dose–volume index based on the predicted 3D patient dose distribution derived from two TPSs (XiO, RayStation). Methods Twenty-one breast intensity-modulated radiation therapy plans were inversely optimized using XiO. With the same plans, both TPSs calculated the planned dose distribution. We conducted per-beam measurements on the coronal plane using a 2D array detector and analyzed the difference in 2D GPRs between the measured and planned doses by commercial software. Using in-house software, we calculated the predicted 3D patient dose distribution and derived the predicted 3D GPR, the predicted per-organ 3D GPR, and the predicted clinically relevant dose–volume indices [dose–volume histogram metrics and the value of the tumor-control probability/normal tissue complication probability of the planning target volume and organs at risk]. The results derived from XiO were compared with those from RayStation. Results While the mean 2D GPRs derived from both TPSs were 98.1% (XiO) and 100% (RayStation), the mean predicted 3D GPRs of ipsilateral lung (73.3% [XiO] and 85.9% [RayStation]; p < 0.001) had no correlation with 2D GPRs under the 3% global/3 mm criterion. Besides, this significant difference in terms of referenced TPS between XiO and RayStation could be explained by the fact that the error of predicted V5Gy of ipsilateral lung derived from XiO (29.6%) was significantly larger than that derived from RayStation (− 0.2%; p < 0.001). Conclusions GPR is useful as a patient quality assurance to detect dosimetric errors; however, it does not necessarily contain detailed information on errors. Using the predicted clinically relevant dose–volume indices, the clinical interpretation of dosimetric errors can be obtained. We conclude that a clinically relevant dose–volume index based on the predicted 3D patient dose distribution could add to the clinical and biological considerations in the GPR, if we can guarantee the dose calculation accuracy of referenced TPS

Impact of different Ir-192 source models on dose calculations in high-dose-rate brachytherapy

In high-dose-rate brachytherapy, the geometry of the radioactive source is sometimes updated. Some institutions use a different source model for the dose calculation in treatment planning and treatment. The effects of this discrepancy were examined for four types of treatment plans, and ten patients were selected for each treatment plan. The impact of different source models depended on the types of treatment plan, patients, and dose index. To reduce the uncertainty and improve the reliability of the data, it would be better to use more robust metrics (D90 and D2cc) for treatment planning evaluation in facilities with this problem. Keywords: High-dose-rate brachytherapy, Source model, Dose calculatio

Preventing Complications from High-Dose Rate Brachytherapy when Treating Mobile Tongue Cancer via the Application of a Modular Lead-Lined Spacer

<div><p>Purpose</p><p>To point out the advantages and drawbacks of high-dose rate brachytherapy in the treatment of mobile tongue cancer and indicate the clinical importance of modular lead-lined spacers when applying this technique to patients.</p><p>Methods</p><p>First, all basic steps to construct the modular spacer are shown. Second, we simulate and evaluate the dose rate reduction for a wide range of spacer configurations.</p><p>Results</p><p>With increasing distance to the source absorbed doses dropped considerably. Significantly more shielding was obtained when lead was added to the spacer and this effect was most pronounced on shorter (i.e. more clinically relevant) distances to the source.</p><p>Conclusions</p><p>The modular spacer represents an important addition to the planning and treatment stages of mobile tongue cancer using HDR-ISBT.</p></div