Optimal threshold of a control parameter for tomotherapy respiratory tracking: A phantom study.

BACKGROUND: Radixact Synchrony® , a real-time motion tracking and compensating modality, is used for helical tomotherapy. Control parameters are used for the accurate application of irradiation. Radixact Synchrony® uses the potential difference, which is an index of the accuracy of the prediction model of target motion and is represented by a statistical prediction of the 3D distance error. Although there are several reports on Radixact Synchrony® , few have reported the appropriate settings of the potential difference threshold. PURPOSE: This study aims to determine the optimal threshold of the potential difference of Radixact Synchrony® during respiratory tumor-motion-tracking irradiation. METHODS: The relationship among the dosimetric accuracy, motion tracking accuracy, and control parameter was evaluated using a moving platform, a phantom with a basic respiratory model (the fourth power of a sinusoidal wave), and several irregular respiratory model waveforms. The dosimetric accuracy was evaluated by gamma analysis (3%, 1 mm, 10% dose threshold). The tracking accuracy was measured by the distance error of the difference between the tracked and driven positions of the phantom. The largest potential difference for 95% of treatment time was evaluated, and its correlation with the gamma-pass ratio and distance error was investigated. The optimal threshold of the potential difference was determined by receiver operating characteristic (ROC) analysis. RESULTS: A linear correlation was identified between the potential difference and the gamma-pass ratio (R = -0.704). A linear correlation was also identified between the potential difference and distance error (R = 0.827). However, as the potential difference increased, it tended to underestimate the distance error. The ROC analysis revealed that the appropriate cutoff value of the potential difference was 3.05 mm. CONCLUSION: The irradiation accuracy with motion tracking by Radixact Synchrony® could be predicted from the potential difference, and the threshold of the potential difference should be set to ∼3 mm.

[Usefulness of an Ultrasound System with Automatic Bladder Urine Volume Measurement Using Artificial Intelligence Technology in Radiotherapy].

PURPOSE: We aimed to investigate the usefulness of iViz air ver.4 Convex (FUJIFILM, Tokyo) as a tool to determine the bladder capacity before prostate radiotherapy by comparing it with the existing BladderScan BVI 6100 (Verathon Inc., Bothell, Washington). METHODS: We investigated the usefulness of iViz air as a tool to determine the bladder capacity before prostate radiotherapy by comparing it with the current BladderScan. RESULTS: The absolute value of each error rate was approximately 30.9%±27.2% and 26.4%±18.9% for the BladderScan and iViz air, respectively, with no significant differences between the instruments (p=0.16). Evaluated by urine volume, the mean error rates for bladder volumes >50 ml were 26.9%±19.0% and 26.1%±18.5% for the Bladder Scan and iViz air, respectively, with no significant differences (p=0.56). However, the BladderScan and iViz air had significantly higher error rates of 89.5%±52.5% and 31.5%±25.1%, respectively, if the bladder volume was <50 ml (p=0.005). CONCLUSION: The iViz air has limited measurement error to confirm images, especially in limited volumes, suggesting that it is a useful bladder capacity measurement device in performing prostate radiotherapy.

A first report of tumour-tracking radiotherapy with helical tomotherapy for lung and liver tumours: A double case report.

There are only a limited number of previous reports on clinical cases using tumour tracking with tomotherapy. Therefore, we present two cases of patients treated with tumour tracking with tomotherapy. First, a 74-year-old man with an inoperable lung cancer type T1bN0M0 underwent stereotactic body radiotherapy at a total dose of 48 Gy in four fractions. Second, a 68-year-old man with hepatocellular carcinoma with a portal venous tumour thrombosis and history of liver stereotactic body radiotherapy with fiducial marker implantation received radiotherapy at a total dose of 48 Gy in 20 fractions. The results of patient-specific quality assurance and tracking radiotherapy were sufficient to irradiate tumours. Tumour tracking with tomotherapy successfully delivered radiation in a total of 24 treatment fractions in both patients. Tumour tracking with tomotherapy is feasible in lung and liver cancer treatment. This study's findings suggest the clinical use of tumour tracking with tomotherapy.

Characteristics of a bolus created using thermoplastic sheets for postmastectomy radiation therapy.

This study applied a "shell bolus," an immobilizing thermoplastic shell locally thickened with extra layers over the radiation target, during postmastectomy radiation therapy (PMRT). We performed ion chamber and film measurements for a solid water phantom for thermoplastic sheets and a gel bolus for dosimetric characterization using a 6-MV X-ray flattening-filter-free (FFF) beam. The air gaps between the body surface for the gel and shell bolus were measured using computed tomography (CT) images in patients who underwent PMRT. This included seven and 13 patients treated with the gel and shell boluses, respectively. A comparison of the dose differences between a 10-mm gel bolus and a 9.6-mm-thick thermoplastic sheet at the surface and 5 cm below the surface showed a 4.2% higher surface dose and 0.5% lower dose at 5-cm depth for the thermoplastic sheet compared to those for the gel bolus. The mean (p = 0.029) and maximum (p < 0.001) air gaps of the shell bolus were significantly thinner than those of the gel bolus. Thus, the shell bolus provided a close fit and robust bolus effect. In addition, the shell bolus reduced respiratory motion and eliminated the need for skin marking. Therefore, this system can be effectively used as a bolus for PMRT.

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.