[Lessons from incidents and accidents in radiotherapy].
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Humans↗
Biomedical subjects
Yoshiharu Watanabe
Publications and source records attributed to Yoshiharu Watanabe.
Three-dimensional conformal setup (3D-CSU) of patients using the coordinate system provided by three internal fiducial markers and two orthogonal diagnostic X-ray systems in the treatment room.
PURPOSE: To test the accuracy of a system for correcting for the rotational error of the clinical target volume (CTV) without having to reposition the patient using three fiducial markers and two orthogonal fluoroscopic images. We call this system "three-dimensional conformal setup" (3D-CSU). METHODS AND MATERIALS: Three 2.0-mm gold markers are inserted into or adjacent to the CTV. On the treatment couch, the actual positions of the three markers are calculated based on two orthogonal fluoroscopies crossing at the isocenter of the linear accelerator. Discrepancy of the actual coordinates of gravity center of three markers from its planned coordinates is calculated. Translational setup error is corrected by adjustment of the treatment couch. The rotation angles (alpha, beta, gamma) of the coordinates of the actual CTV relative to the planned CTV are calculated around the lateral (x), craniocaudal (y), and anteroposterior (z) axes of the planned CTV. The angles of the gantry head, collimator, and treatment couch of the linear accelerator are adjusted according to the rotation of the actual coordinates of the tumor in relation to the planned coordinates. We have measured the accuracy of 3D-CSU using a static cubic phantom. RESULTS: The gravity center of the phantom was corrected within 0.9 +/- 0.3 mm (mean +/- SD), 0.4 +/- 0.2 mm, and 0.6 +/- 0.2 mm for the rotation of the phantom from 0-30 degrees around the x, y, and z axes, respectively, every 5 degrees. Dose distribution was shown to be consistent with the planned dose distribution every 10 degrees of the rotation from 0-30 degrees. The mean rotational error after 3D-CSU was -0.4 +/- 0.4 (mean +/- SD), -0.2 +/- 0.4, and 0.0 +/- 0.5 degrees around the x, y, and z axis, respectively, for the rotation from 0-90 degrees. CONCLUSIONS: Phantom studies showed that 3D-CSU is useful for performing rotational correction of the target volume without correcting the position of the patient on the treatment couch. The 3D-CSU will be clinically useful for tumors in structures such as paraspinal diseases and prostate cancers not subject to large internal organ motion.
Humans↗
Feasibility of synchronization of real-time tumor-tracking radiotherapy and intensity-modulated radiotherapy from viewpoint of excessive dose from fluoroscopy.
PURPOSE: Synchronization of the techniques in real-time tumor-tracking radiotherapy (RTRT) and intensity-modulated RT (IMRT) is expected to be useful for the treatment of tumors in motion. Our goal was to estimate the feasibility of the synchronization from the viewpoint of excessive dose resulting from the use of fluoroscopy. METHODS AND MATERIALS: Using an ionization chamber for diagnostic X-rays, we measured the air kerma rate, surface dose with backscatter, and dose distribution in depth in a solid phantom from a fluoroscopic RTRT system. A nominal 50-120 kilovoltage peak (kVp) of X-ray energy and a nominal 1-4 ms of pulse width were used in the measurements. RESULTS: The mean +/- SD air kerma rate from one fluoroscope was 238.8 +/- 0.54 mGy/h for a nominal pulse width of 2.0 ms and nominal 100 kVp of X-ray energy at the isocenter of the linear accelerator. The air kerma rate increased steeply with the increase in the X-ray beam energy. The surface dose was 28-980 mGy/h. The absorbed dose at a 5.0-cm depth in the phantom was 37-58% of the peak dose. The estimated skin surface dose from one fluoroscope in RTRT was 29-1182 mGy/h and was strongly dependent on the kilovoltage peak and pulse width of the fluoroscope and slightly dependent on the distance between the skin and isocenter. CONCLUSION: The skin surface dose and absorbed depth dose resulting from fluoroscopy during RTRT can be significant if RTRT is synchronized with IMRT using a multileaf collimator. Precise estimation of the absorbed dose from fluoroscopy during RT and approaches to reduce the amount of exposure are mandatory.
Calibration↗
[Accuracy of absorbed dose calculation and measurement of scatter factors with different depth of mini-phantoms using a pinpoint ionization chamber].
The output factor of high-energy X-ray machines varies with collimation. According to Khan's theory, collimator and phantom scatter factors contribute to total scatter factor. For precise X-ray irradiation, the two factors need to be taken into consideration. To obtain proper factors, we made two original polystyrene cylindrical mini-phantoms. These phantoms are both 4 cm in diameter and have a pinpoint ion chamber placed at a depth of 5 cm and 10 cm, respectively. Using a 6 MV X-ray machine, collimator scatter factors were calculated for various field arrangements (i.e., field sizes ranging from 4 cm x 4 cm to 40 cm x 40 cm at isocenter). To determine if calculated values were appropriate, we measured point doses of 20 X-ray irradiation patterns using a Farmer-type ion chamber with a water equivalent phantom at depths of 5 cm and 10 cm, respectively. Two hundred MUs were irradiated to the above-mentioned depths for each field. Based on the measured doses, variations were obtained for four calculation methods. Accounting for 1) secondary collimator (jaw) setting, 2) blocked field (multi-leaf collimator) setting, 3) Khan's theory using a 5 cm mini-phantom, and 4) Khan's theory using a 10 cm mini-phantom. Dose variations in each method of calculation were as follows: 1) +0.3 to +10.2% (mean, +2.0 to +3.2%) , 2) -2.3 to 0.0% (mean, -0.8 to -0.6%), 3) 0.0 to +1.5% (mean, +0.1 to +0.3%), 4) 0.0 to +1.4% (mean, -0.1 to +0.1%).
Phantoms, Imaging↗
[Dosimetry in radiotherapy].
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Electronic Data Processing↗
[Changes in postural control mechanism after a long-time tilt].
In order to investigate the time-dependent dynamics of otolith organ-spinomotor function, we analyzed postural control biomechanically, in eight healthy adult volunteers, using a dynamic posturography (EquiTest System), before and after a four-hours lateral head and body tilt (90 degrees). After the tilt, a half of the subjects exhibited some changes. Their equilibrium scores decreased; i.e., the dependence on their vestibular inputs decreased, but in contrast, those on the visual and the somatosensory inputs increased. These changes were diminished by repeating the tests along the time course. The present findings confirmed [correction of comfirmed] the importance of vestibular gravity information for the maintenance of delicate postural stability.
Adult↗
[Gated Radiotherapy]
Recent external radiotherapy requires precise localization of the target because advance in diagnostic imaging has made it possible to visualize a tiny tumor which would be curable with focused high dose irradiation. However, tumors in respiratory and bowel organs have been difficult to be given the high dose because of 1 to 3 cm movement during delivery of irradiation. Respiratory-gating techniques have been used with medical linear accelerators and particle therapy machines. Real-time tumor-tracking radiotherapy has been realized using fluoroscopic x-rays, internal gold-markers, and pattern recognition technology. Advantage and disadvantage of each gating technique have been realized. Active breath control method would be a cost-effective way of precise treatment without gating. More work is required to find the relationship between abdominal wall and internal movement of the tumor in many respiratory-gating radiotherapy and between the internal markers and target volume in real-time tracking radiotherapy.
Journal Article↗