Evaluation of robustness in hybrid intensity-modulated radiation therapy plans generated by commercial software for automated breast planning.

This study aimed to evaluate the robustness against geometric uncertainties in the hybrid intensity-modulated radiation therapy (IMRT) plans generated by commercially available software for automated breast planning (ABP). The ABP plans were compared with commonly used forward-planned field-in-field (FIF) technique plans. The planning computed tomography datasets of 20 patients who received left-sided breast-conserving surgery were used for both the ABP and FIF plans. Geometric uncertainties were simulated by shifting beam isocenters by 2, 3, 5, and 10 mm in the six directions: anterior/posterior, left/right, and superior/inferior. A total of 500 plans (20 patients and 25 scenarios, including the original plan) were created for each of the ABP and FIF plans. The homogeneity index of the target volume in the ABP plans was significantly better (p < 0.001) than the value in the FIF plans in the scenarios of shifting beam isocenters by 2, 3, and 5 mm. Mean heart dose and percentage volume of lungs receiving a dose more than 20 Gy were clinically acceptable in all scenarios. The hybrid IMRT plans generated by commercially available ABP software provided better robustness against geometric uncertainties than forward-planned FIF plans.

Evaluation of prediction and classification performances in different machine learning models for patient-specific quality assurance of head-and-neck VMAT plans.

PURPOSE: The purpose of this study is to evaluate the prediction and classification performances of the gamma passing rate (GPR) for different machine learning models and to select the best model for achieving machine learning-based patient-specific quality assurance (PSQA). METHODS: The measurement verification of 356 head-and-neck volumetric modulated arc therapy plans was performed using a diode array phantom (Delta4 Phantom), and GPR values at 2%/2 mm with global normalization and 3%/2 mm with local normalization were calculated. Machine learning models, including ridge regression (RIDGE), random forest (RF), support vector regression (SVR), and stacked generalization (STACKING), were used to predict the GPR. Each machine learning model was trained using 260 plans, and the prediction accuracy was evaluated using the remaining 96 plans. The prediction error between the measured and predicted GPR was evaluated. For the classification evaluation, the lower control limit for the measured GPR and lower control limit for predicted GPR (LCLp ) was defined to identify whether the GPR values represent a "pass" or a "fail." LCLp values with 99% and 99.9% confidence levels were calculated as the upper prediction limits for the GPR estimated from the linear regression between the measured and predicted GPR. RESULTS: There was an overestimation trend of the low measured GPR. The maximum prediction errors for RIDGE, RF, SVR, and STACKING were 3.2%, 2.9%, 2.3%, and 2.2% at the global 2%/2 mm and 6.3%, 6.6%, 6.1%, and 5.5% at the local 3%/2 mm, respectively. In the global 2%/2 mm, the sensitivity was 100% for all the machine learning models except RIDGE when using 99% LCLp . The specificity was 76.1% for RIDGE, RF, and SVR and 66.3% for STACKING; however, the specificity decreased dramatically when 99.9% LCLp was used. In the local 3%/2 mm, however, only STACKING showed 100% sensitivity when using 99% LCLp . The decrease in the specificity using 99.9% LCLp was smaller than that in the global 2%/2 mm, and the specificity for RIDGE, RF, SVR, and STACKING was 61.3%, 61.3%, 72.0%, and 66.8%, respectively. CONCLUSIONS: STACKING had better prediction accuracy for low GPR values than other machine learning models. Applying LCLp to a regression model enabled the consistent evaluation of quantitative and qualitative GPR predictions. Adjusting the confidence level of the LCLp helped improve the balance between the sensitivity and specificity. We suggest that STACKING can assist the safe and efficient operation of PSQA.

Algorithm for an automatic treatment planning system using a single-arc VMAT for prostate cancer.

Optimization process in treatment planning for intensity-modulated radiation therapy varies with the treatment planner. Therefore, a large variation in the quality of dose distribution is usually observed. To reduce variation, an automatic optimizing toolkit was developed for the Monaco treatment planning system (Elekta AB, Stockholm, Sweden) for prostate cancer using volumetric-modulated arc therapy (VMAT). This toolkit was able to create plans automatically. However, most plans needed two arcs per treatment to ensure the dose coverage for targets. For prostate cancer, providing a plan with a single arc was advisable in clinical practice because intrafraction motion management must be considered to irradiate accurately. The purpose of this work was to develop an automatic treatment planning system with a single arc per treatment for prostate cancer using VMAT. We designed the new algorithm for the automatic treatment planning system to use one arc per treatment for prostate cancer in Monaco. We constructed the system in two main steps: (1) Determine suitable cost function parameters for each case before optimization, and (2) repeat the calculation and optimization until the conditions for dose indices are fulfilled. To evaluate clinical suitability, the plan quality between manual planning and the automatic planning system was compared. Our system created the plans automatically in all patients within a few iterations. Statistical differences between the plans were not observed for the target and organ at risk. It created the plans with no human input other than the initial template setting and system initiation. This system offers improved efficiency in running the treatment planning system and human resources while ensuring high-quality outputs.

VMAT Planning With Xe-CT Functional Images Enables Radiotherapy Planning With Consideration of Lung Function.

Background/Aim: The most severe adverse event of radiotherapy in lung cancer is radiation pneumonitis (RP). Some indices commonly used to prevent RP are evaluated based on the anatomical lung volume. The irradiation dose may be more accurately assessed by using functional lung volume. We evaluated the usefulness of computed tomography (CT) incorporating functional ventilation images acquired by the inhalation of xenon (Xe) gas (Xe-CT functional images). Patients and Methods: Two plans were created for twelve patients: volumetric modulated arc therapy (VMAT) planning using conventional chest CT images (anatomical plans) and VMAT planning using Xe-CT functional images (functional plans), and the dosimetric parameters were compared. Results: Compared to the anatomical plans, the functional plans had significantly reduced V 20Gy in the high-functional lungs (p=0.005), but significant differences were not seen in the moderate-functional and low-functional lungs. Conclusion: The incorporation of Xe-CT functional images into VMAT plans enables radiotherapy planning with consideration of lung function.

Evaluation of geometrical uncertainties on localized prostate radiotherapy of patients with bilateral metallic hip prostheses using 3D-CRT, IMRT and VMAT: A planning study.

OBJECTIVE: Since most radiation treatment plans are based on computed tomography (CT) images, which makes it difficult to define the targeted tumor volume located near a metal implant, this study aims to evaluate and compare three treatment plans in order to optimally reduce geometrical uncertainty in external radiation treatment of localized prostate cancer. METHODS: Experimental subjects were three prostate patients with bilateral hip prosthesis who had undergone radical radiotherapy. The treatment plans were five-field three-dimensional conformal radiation therapy (3D-CRT), fixed 5-field intensity-modulated radiation therapy (IMRT) using similar gantry angles, and single-arc volumetric modulated arc therapy (VMAT). The monitor units (MUs), dose volume histograms (DVHs), the dose indices of planning target volume (PTV), clinical target volume (CTV) and rectum were compared among the three techniques. The geometrical uncertainties were evaluated by shifting the iso-center (2- 10 mm in the anterior, posterior, left, right, superior, and inferior directions). The CTV and rectum dose indexes with and without the iso-center shifts were compared in each plan. RESULTS: The Conformity Index of PTV were 1.35 in 3D-CRT, 1.12 in IMRT, and 1.04 in VMAT, respectively. The rectum doses in 3D-CRT are also higher than those in IMRT and VMAT. The iso-center shift little affected the CTV dose when smaller than the margin size. The rectum dose increased especially after a posterior shift. Additionally, this dose increase was larger in the VMAT plan than in the 3D- CRT plan. However, the VMAT achieved a superior rectum DVH to that of 3D- CRT, and this effect clearly exceeded the rectum-dose increase elicited by the iso-center shift. CONCLUSION: For radiotherapy treatment of localized prostate cancer in patients with hip prosthesis, the dose distribution was better in the VMAT and Metal Artifact Reduction (MAR)-CT image methods than the conventional methods. Because the anatomical structure of the male pelvic region is relatively constant among individuals, we consider that VMAT is a valid treatment plan despite analyzing just three cases.

[Feasibility Study for the Development of an Application for Simulated Virtual Reality Radiation Therapy Experiences Using Android and iOS Devices].

Using virtual reality (VR) technology such as head-mounted displays, users can be immersed in a virtual world and perceive it as reality. In radiation therapy departments, pretreatment patients and students rarely observe treatment rooms and treatment devices, making it difficult to understand the overall flow of radiation therapy. In this study, to facilitate the understanding and teaching of radiation therapy, we suggest the implementation of VR technology and develop software compatible with VR to enable a pertinent comprehension of radiation therapy. With versatility and accessibility in mind, the software is developed as an application for Android and iOS devices.Omnidirectional movies in treatment rooms were acquired from both the patient view and a third-person view using an omnidirectional camera. The Android/iOS devices used were AQUOS R (SHARP), iPhone 7 Plus (Apple), and iPad air (Apple). The software was developed using Unity 2018.4.7f (Unity Technologies). The main components of the software were as follows: (i) a home window featuring a user interface with which people can access arbitrarily rooms by tapping on floor maps or a list of treatment rooms, (ii) a snapshot mode providing 2D images of a treatment room as a slide show, and (iii) a movie mode displaying omnidirectional movies from the patient view or a third-person view. The virtual radiation therapy experience was executed by attaching the Android/iOS devices to 3D VR goggles (SAMONIC).The main components of the application operated in good conjunction on the Android/iOS devices, and live viewing in the virtual world ran smoothly with the VR technology. However, there were resolution limitations due to the specs of the camera and the devices. It will therefore be necessary to adjust the resolution and the frame rate according to the performance of the relevant devices. The application is instructive for both patients and students because the virtual radiation therapy experience is immersive when using the VR technology. In addition, the developed software can transfer data in a single package and has the ability to substitute images and omnidirectional movies with those appropriate for diagnostic radiology and nuclear medicine departments. Therefore, the developed application is highly versatile.

Evaluation of a new commercial automated planning software for tangential breast intensity-modulated radiation therapy.

Automated treatment planning may decrease the effort required in planning and promote increased routine clinical use of intensity-modulated radiation therapy (IMRT) for many breast cancer patients. The aim of this study was to evaluate a new commercial automated planning software for tangential breast IMRT by comparing it with clinical plans from whole-breast irradiation. We prospectively enrolled 150 patients with Stage 0-1 breast cancer who underwent breast-conserving surgery at our institution between September 2016 and August 2017. Total doses of 42.56 Gy in 16 fractions (n = 98) or 50 Gy in 25 fractions (n = 44) were used. All treatment plans were retrospectively re-planned using the automated breast planning (ABP) software. All automated plans generated clinically deliverable beam parameters with no patient body collision and no contralateral breast pass through. The mean homogeneity index of the automatically generated clinical target volume, percentage volume of lungs receiving dose more than 20 Gy, mean heart dose, and dose to the highest irradiated 2-cc volumes of the irradiated volume were 0.077 ± 0.019, 4.2% ± 1.2%, 142 ± 69 cGy, and 105.8% ± 1.7% (prescribed dose: 100%), respectively. The mean planning time was 4.8 ± 1.4 min. The ABP software demonstrated high clinical acceptability and treatment planning cost efficiency for tangential breast IMRT. The ABP software may be useful for delivering high-quality treatment to a majority of patients with early-stage breast cancer.

Commissioning of the Mobius3D independent dose verification system for TomoTherapy.

In radiation therapy, a secondary independent dose verification is an important component of a quality control system. Mobius3D calculates three-dimensional (3D) patient dose using reference beam data and a collapsed cone convolution algorithm and analyzes dose-volume histogram automatically. There are currently no published data on commissioning and determining tolerance levels of Mobius3D for TomoTherapy. To verify the calculation accuracy and adjust the parameters of this system, we compared the measured dose using an ion chamber and film in a phantom with the dose calculated using Mobius3D for nine helical intensity-modulated radiation therapy plans, each with three nominal field widths. We also compared 126 treatment plans used in our institution to treat prostate, head-and-neck, and esophagus tumors based on dose calculations by treatment planning system for given dose indices and 3D gamma passing rates with those produced by Mobius3D. On the basis of these results, we showed that the action and tolerance levels at the average dose for the planning target volume (PTV) at each treatment site are at µ ± 2σ and µ ± 3σ, respectively. After adjusting parameters, the dose difference ratio on average was -0.2 ± 0.6% using ion chamber and gamma passing rate with the criteria of 3% and 3 mm on average was 98.8 ± 1.4% using film. We also established action and tolerance levels for the PTV at the prostate, head-and-neck, esophagus, and for the organ at risk at all treatment sites. Mobius3D calculations thus provide an accurate secondary dose verification system that can be commissioned easily and immediately after installation. Before clinical use, the Mobius3D system needs to be commissioned using the treatment plans for patients treated in each institution to determine the calculational accuracy and establish tolerances for each treatment site and dose index.

Retrospective analysis of multi-institutional, patient-specific treatment planning results of high-dose-rate intracavitary brachytherapy for gynecological cancer using V100.

The objective of this study was to clarify the usefuleness of the K parameters of the independent verification method using V100% (the volume of water receiving 100% of the prescription dose) for institutions implementing the high-dose-rate (HDR) intracavitary brachytherapy for gynecological cancer. The data of 249 plans of 11 institutions in Japan were used, and the constant K value obtained by a parameter fit for single-192Ir, two-192Ir, and three-192Ir systems was calculated. The predicted total dwell time calculated using the constant K value was defined as Tpr, and the total dwell time calculated using a radiation treatment planning system was defined as TRTP. The ratio of Tpr and TRTP for each plan was calculated. The constant K values (95% CI) obtained for each system outlined above were 1233 (1227-1240), 1205 (1199-1211), and 1171 (1167-1175), respectively. Regarding the Tpr/TRTP, the entire data were within 0.9-1.1. For accurate verification, it was clarified that constant K values should be calculated for each system. The Nuclear Regulatory Commission considers a difference of 20% between the prescribed total dose and the administered total dose as a reportable medical event. There is a need for a quick method to verify the accuracy with a minimum of 10% threshold of a plan. The constant K values in this study were obtained from multiple institutions, and the variation in the values among these institutions was small. The data obtained by this study may be used as a parameter of this verification method employed by numerous institutions, particularly those who have recently initiated HDR brachytherapy. In addition, for institutions already using this method, this data might be useful for the validation of the parameters which were used in such institutions.

Simple index for validity of the evaluation point for dosimetric verification results of intensity-modulated radiation therapy using a Farmer-type ionization chamber.

PURPOSE: Based on a retrospective analysis, this study aims to develop a simple index for validity of the evaluation point for the dosimetric verification of intensity-modulated radiation therapy (IMRT). METHODS: The results for the dosimetric verifications of a total of 69 IMRT plans were analyzed in this study. A Farmer-type ion chamber was used as a dose detector, and a solid water-equivalent phantom was used. Index values were obtained by dividing the difference between the maximum and minimum dosages by the mean dosage of the 69 plans, and the values were classified into five groups with index value <4, 4-8, 8-12, 12-16, and >16. A t-test was used to assess the statistical significance of the mean differences of the absolute values of the relative errors among these groups. RESULTS: We found that there was no significant difference between the groups with index value <4 and 4-8 (p = 0.152); however, there were significant differences between the other groups (p < 0.01). In addition, when the index values were smaller than 8, the pass ratio of 3% tolerance was 96.2% and the pass ratio of 5% tolerance was 99.9%. We observed that the smaller the index value, the smaller the uncertainty of the dose measurement. CONCLUSIONS: The results obtained in this study may prove to be useful for accurate dosimetric verifications of IMRTs when ion chambers are used.

Determination of the appropriate physical density of internal metallic ports in temporary tissue expanders for the treatment planning of post-mastectomy radiation therapy.

Some patients undergoing breast reconstruction require post-mastectomy radiation therapy, but the metallic ports used in temporary tissue expanders attenuate the X-rays. In this study, we evaluated by the film method, the attenuation of 4 MV and 6 MV X-rays after passing through a metallic port, with the aim of identifying a useful method for determining the appropriate density to use in the radiation treatment planning system (RTPS), taking into account the distance between the metallic port and the targets. Radiochromic film was used to measure depth doses after the X-rays passed through the metallic port. The physical density allotted to the metal port portion was varied on the RTPS within the range 1-16 g/cm3, and the physical density values were calculated that best reproduced the depth-dose distribution extrapolated from the film method. When the metallic port was orientated perpendicularly, the attenuation of the X-rays peaked at ~7% at both 4 MV and 6 MV. In the parallel orientation, the X-rays were attenuated by up to ~40% at 4 MV and by up to ~30% at 6 MV. We estimated the optimum physical density to be 9.8 g/cm3, which yielded the best fit with the actual measurements. We demonstrated the most likely range for the target depth from the CT images of actual patients and, within this range, we identified the optimum physical density at which the measured and calculated values were most consistent with each other.

Correction of stopping power and LET quenching for radiophotoluminescent glass dosimetry in a therapeutic proton beam.

To measure the absorbed dose to water D w in proton beams using a radiophotoluminescent glass dosimeter (RGD), a method with the correction for the change of the mass stopping power ratio (SPR) and the linear energy transfer (LET) dependence of radiophotoluminescent efficiency [Formula: see text] is proposed. The calibration coefficient in terms of D w for RGDs (GD-302M, Asahi Techno Glass) was obtained using a 60Co γ-ray. The SPR of water to the RGD was calculated by Monte Carlo simulation, and [Formula: see text] was investigated experimentally using a 70 MeV proton beam. For clinical usage, the residual range R res was used as a quality index to determine the correction factor for the beam quality [Formula: see text] and the LET quenching effect of the RGD [Formula: see text]. The proposed method was evaluated by measuring D w at different depths in a 200 MeV proton beam. For both non-modulated and modulated proton beams, [Formula: see text] decreases rapidly where R res is less than 4 cm. The difference in [Formula: see text] between a non-modulated and a modulated proton beam is less than 0.5% for the R res range from 0 cm to 22 cm. [Formula: see text] decreases rapidly at a LET range from 1 to 2 keV µm-1. In the evaluation experiments, D w using RGDs, [Formula: see text] showed good agreement with that obtained using an ionization chamber and the relative difference was within 3% where R res was larger than 1 cm. The uncertainty budget for [Formula: see text] in a proton beam was estimated to investigate the potential of RGD postal dosimetry in proton therapy. These results demonstrate the feasibility of RGD dosimetry in a therapeutic proton beam and the general versatility of the proposed method. In conclusion, the proposed methodology for RGDs in proton dosimetry is applicable where R res > 1 cm and the RGD is feasible as a postal audit dosimeter for proton therapy.

Contrast enhancement for portal images by combination of subtraction and reprojection processes for Compton scattering.

For patient setup of the IGRT technique, various imaging systems are currently available. MV portal imaging is performed in identical geometry with the treatment beam so that the portal image provides accurate geometric information. However, MV imaging suffers from poor image contrast due to larger Compton scatter photons. In this work, an original image processing algorithm is proposed to improve and enhance the image contrast without increasing the imaging dose. Scatter estimation was performed in detail by MC simulation based on patient CT data. In the image processing, scatter photons were eliminated and then they were reprojected as primary photons on the assumption that Compton interaction did not take place. To improve the processing efficiency, the dose spread function within the EPID was investigated and implemented on the developed code. Portal images with and without the proposed image processing were evaluated by the image contrast profile. By the subtraction process, the image contrast was improved but the EPID signal was weakened because 15.2% of the signal was eliminated due to the contribution of scatter photons. Hence, these scatter photons were reprojected in the reprojection process. As a result, the tumor, bronchi, mediastinal space and ribs were observed more clearly than in the original image. It was clarified that image processing with the dose spread functions provides stronger contrast enhancement while maintaining a sufficient signal-to-noise ratio. This work shows the feasibility of improving and enhancing the contrast of portal images.