Oesophageal Cancer: Conformal Radiotherapy vs. Hybrid-VMAT Technique With Two Different Treatment Planning Systems.

BACKGROUND/AIM: Traditionally, the radiotherapy of oesophageal cancer has been conformal radiotherapy (CRT). We sought to compare dosimetric parameters of conformal radiotherapy (CRT) with those of two treatment planning systems for hybrid-volumetric modulated arc therapy (h-VMAT) for the treatment of oesophageal cancer. PATIENTS AND METHODS: In 11 patients, we compared: i) planning target volume coverage, ii) dose to organs at risk, and iii) the dose rate (DR) of the three techniques. We evaluated two treatment planning systems: i) Eclipse and ii) RayStation. RESULTS: The Conformity Index of the CRT plan was significantly higher for the h-VMAT plans, compared to all other parameters. Normal lung tissue volumes receiving >5, 13, or 20 Gy were lower with the RayStation plan compared to Eclipse. The volume of cardiac tissue receiving >40 Gy was highest with the CRT plan. The minimum DR in VMAT was lowest for the RayStation plan (49.5 MU/min). CONCLUSION: The h-VMAT plan using RayStation is the appropriate choice for reducing lung dose.

Couch modeling optimization for tomotherapy planning and delivery.

We sought to validate new couch modeling optimization for tomotherapy planning and delivery. We constructed simplified virtual structures just above a default setting couch through a planning support system (MIM Maestro, version 8.2, MIM Software Inc, Cleveland, OH, USA). Based on ionization chamber measurements, we performed interactive optimization and determined the most appropriate physical density of these virtual structures in a treatment planning system (TPS). To validate this couch optimization, Gamma analysis and these statistical analyses between a three-dimensional diode array QA system (ArcCHECK, Sun Nuclear, Melbourne, FL, USA) results and calculations from ionization chamber measurements were performed at 3%/2 mm criteria with a threshold of 10% in clinical QA plans. Using a virtual model consisting of a center slab density of 4.2 g/cm3 and both side slabs density of 1.9 g/cm3 , we demonstrated close agreement between measured dose and the TPS calculated dose. Agreement was within 1% for all gantry angles at the isocenter and within 2% in off-axis plans. In validation of the couch modeling in a clinical QA plan, the average gamma passing rate improved approximately 0.6%-5.1%. It was statistically significant (P < 0.05) for all treatment sites. We successfully generated an accurate couch model for a TomoTherapy TPS by interactively optimizing the physical density of the couch using a planning support system. This modeling proved to be an efficient way of correcting the dosimetric effects of the treatment couch in tomotherapy planning and delivery.

A feasibility study of independent verification of dose calculation for Vero4DRT using a Clarkson-based algorithm.

Dose verification for a gimbal-mounted image-guided radiotherapy system, Vero4DRT (Mitsubishi Heavy Industries Ltd., Tokyo, Japan) is usually carried out by pretreatment measurement. Independent verification calculations using Monte Carlo methods for Vero4DRT have been published. As the Clarkson method is faster and easier to use than measurement and Monte Carlo methods, we evaluated the accuracy of an independent calculation verification program and its feasibility as a secondary check for Vero4DRT. Computed tomography (CT)-based dose calculation was performed using a modified Clarkson-based algorithm. In this study, 120 patients' treatment plans were collected in our institute. The treatments were performed using conventional irradiation for lung and prostate, 3-dimensional (3D) conformal stereotactic body radiotherapy (SBRT) for the lung, and intensity-modulated radiation therapy (IMRT) for the prostate. Differences between the treatment planning system (TPS) and the Clarkson-based independent dose verification software were computed, and confidence limits (CLs, mean ± 2 standard deviation %) for Vero4DRT were compared with the CLs for the C-arms linear accelerators in the previous study. The results of the CLs, the conventional irradiation, SBRT, and IMRT showed 2.2 ± 3.5% (CL of the C-arms linear accelerators: 2.4 ± 5.3%), 1.1 ± 1.7% (-0.3 ± 2.0%), 4.8 ± 3.7% (5.4 ± 5.3%), and -0.5 ± 2.5% (-0.1 ± 3.6%) differences, respectively. The dose disagreement between the TPS and CT-based independent dose verification software was less than the 5% action level of American Association of Physicists in Medicine (AAPM) Task Group 114 (TG114). The CLs for the gimbal-mounted Vero4DRT were similar to the deviations for C-arms linear accelerators.

Dose reduction in cone-beam CT scanning for intracranial stent deployment before coil embolization of intracranial wide-neck aneurysms.

PURPOSE: Flat panel detector (FD)-equipped angiography machines are increasingly used for neuro-angiographic imaging. During intracranial stent-assisted coil embolization procedures, it is very important to clearly and quickly visualize stent shape after deployment in the vessel. It is necessary to quickly visualize stents by cone-beam computed tomography (CBCT). The aim of this study was to compare CBCTs at 10 and 20 s, and to confirm that this method is useful for neuro-endovascular treatment procedures. MATERIALS AND METHODS: We treated 30 patients with wide-necked intracranial aneurysms with a flexible, self-expanding neurovascular stent and subsequent aneurysm embolization with platinum micro-coils. We performed the CBCT after stent deployment. We compared the 10 s and 20 s CBCTs, using the full width one-half maximum (FWHM) visualization. RESULTS: Accurate stent placement with subsequent coil occlusion of the aneurysms was feasible in all patients. Stent struts were clearly visualized on both 10 s and 20 s CBCTs. Importantly, 10 s CBCT can reduce the radiation dose by about 42%, compared with 20 s CBCT. Performing 10 s CBCT with a 14% dilution of the contrast medium may significantly improve image acquisition during stent-assisted coil embolization. CONCLUSIONS: Reduced-dose, 10 s CBCT can visualize stents in clinical cases, while significantly reducing radiation exposure.

Detectability of a lung nodule displayed on a liquid-crystal display monitor with different maximum luminance settings.

Our purpose in this study was to examine the detectability of a lung nodule at different maximum luminance settings of a liquid-crystal display (LCD) monitor by utilizing receiver operating characteristic (ROC) analysis. The LCD monitor used in this study was calibrated to the grayscale standard display function with different maximum luminance settings (670, 450, and 170 cd/m(2)). The average area under the ROC curve (AUC) and the standard deviation for all observers at 670, 450, and 170 cd/m(2) were 0.837 +/- 0.076, 0.832 +/- 0.051, and 0.830 +/- 0.078, respectively. There was no statistically significant difference in AUC as a function of the maximum luminance setting of the LCD monitor. Considering the results, setting the maximum luminance of an LCD monitor at a higher level may not provide a significant advantage in the detectability of a lung nodule.

[Application of the grayscale standard display function to general purpose liquid-crystal display monitors for clinical use].

Interpretations of medical images have been shifting to soft-copy readings with liquid-crystal display (LCD) monitors. The display function of the medical-grade LCD monitor for soft-copy readings is recommended to calibrate the grayscale standard display function (GSDF) in accordance with the guidelines of Japan and other countries. In this study, the luminance and display function of five models of eight general purpose LCD monitors were measured to gain an understanding of their characteristics. Moreover, the display function (gamma 2.2 or gamma 1.8) of general purpose LCD monitors was converted to GSDF through the use of a look-up table, and the detectability of a simulated lung nodule in the chest x-ray image was examined. As a result, the maximum luminance, contrast ratio, and luminance uniformity of general purpose LCD monitors, except for one model of two LCD monitors, met the management grade 1 standard in the guideline JESRA X-0093-2005. In addition, the detectability of simulated lung nodule in the mediastinal space was obviously improved by converting the display function of a general purpose LCD monitor into GSDF.