Biomedical subjects

Hiroya Shiomi

Publications and source records attributed to Hiroya Shiomi.

8 recordsLinked to original sources

PubMed2004

An optimization algorithm of dose distribution using attraction-repulsion model (application to low-dose-rate interstitial brachytherapy).

PURPOSE: To optimize dose distribution for prostate cancer in low-dose-rate interstitial brachytherapy, we have developed a new algorithm named the Attraction-Repulsion Model. The purpose was to find the optimal source configuration. METHODS AND MATERIALS: The Attraction-Repulsion Model is used to optimize the dose distribution by finding the best seed configuration. We arranged grids at intervals of a certain space inside and established target and critical organs as areas of interest. We can make an attribute for grids, and the grids show attraction or repulsion depending on dose delivered from source. Source position is changed by the forces that the grids impose to the sources. A calculation was done repeatedly until the attraction and repulsion forces reached a balance. The optimal configuration was established when the sources reached a stable distribution in time. To evaluate the optimization plan, dose-volume histograms were used. RESULTS: Source configuration can be optimized automatically. The calculation time was approximately 5 min. The V100, V150, V200, and D90 of the target were 95%, 39%, 9%, and 157 Gy, respectively. V150 of the urethra and V80 of the rectum were 2% and 0%, respectively. CONCLUSION: This method can optimize the dose distribution objectively.

Algorithms↗

PubMed2003

Prospective study of HDR (192Ir) versus MDR (137Cs) intracavitary brachytherapy for carcinoma of the uterine cervix.

PURPOSE: The aim of this study was to compare the results of high-dose rate (HDR) and medium-dose rate (MDR) intracavitary brachytherapy for carcinoma of the uterine cervix on the basis of a prospective study and to determine the dose rate conversion factor (DRCF) from low-dose rate (LDR) to MDR via HDR, because a DRCF of 0.54 from LDR to HDR has been widely accepted. MATERIALS AND METHODS: Between August 1991 and July 1999, 104 patients were entered into this trial to compare results between HDR (n=54) and MDR (n=50). Three patients were excluded from this study, leaving 54 HDR patients and 47 MDR patients eligible. Method and dose of external beam radiotherapy were the same for both groups. For HDR intracavitary brachytherapy, point A dose was adjusted to 32 Gy/4 fractions for stages I and II, to 30 Gy/4 fractions for stage III, and to 22.5 Gy/3 fractions for stage IV. The corresponding values for MDR were 35.6 Gy/4 fractions, 34 Gy/4 fractions, and 25.5 Gy/3 fractions. The average dose rate at point A was 30 Gy/hour (9.0-65.2) for HDR and 1.7 Gy/hour (1.3-2.2) for MDR. We assumed a DRCF of 0.9 from MDR to HDR. RESULTS: The 3-year cause-specific survival rates for HDR were 85%, 83%, 75%, and 0% for stages I, II, III, and IV, respectively. The corresponding figures for MDR were 100%, 82%, 58%, and 40%. Six of the HDR patients (11%) and 2 of the MDR patients (4%) developed Kottmeier's grade 2 or 3 late complications. A DRCF of 0.6 from LDR to MDR could be derived from a DRCF of 0.9 from MDR to HDR and one of 0.54 from LDR to HDR. CONCLUSIONS: There were no statistically significant differences in cause-specific survival and incidence of late complications between HDR and MDR. A DRCF of 0.6 from LDR to MDR could be determined. However, because the results of this trial were preliminary, a further study is needed.

Adult↗

PubMed2001

[CyberKnife]

The CyberKnife is an image-guided robotic system designed for stereotactic radiosurgery. This system uses a lightweight, x-band linear accelerator, computer-controlled robotic arm, a pair of orthogonal x-ray imagers (TLS: Target Locating System), and a computer workstation. During the treatment, the TLS determines the location of the lesion and communicates these coordinates to the robot. The robot adjusts the position of the beam to the target. The accuracy of this system is 0.7 mm (median) at Osaka University. The CyberKnife system offers new options for radiosurgery/therapy. Stereotactic fractionated radiotherapy can now be performed with the same accuracy as single-fraction stereotactic radiosurgery. The frameless nature of CyberKnife allows tumors in the chest and abdomen to be treated as well. The real time tracking system option enables one to treat tumors that move with respiration, such as lesions in lung. Tumors in the lower spine, pancreas, and lung have already been treated in the USA. A description of the components, accuracy, and future of the CyberKnife will be presented.

Journal Article↗

PubMedDate not supplied

High dose rate endovascular brachytherapy in aorto-iliac lesion for the prevention of restenosis.

This study examined the applicability of endovascular brachytherapy to larger del arteries such as the abdominal aorta and iliac artery. Endovascular brachytherapy using an Ir-192 HDR source was administered 11 times to nine patients who had undergone percutaneous transluminal angioplasty (PTA) between 1995 and 1999. The follow-up lasted 13 to 55 months after treatment (median, 24 months). Eight of the 11 lesions have been controlled so far. Although one case developed thrombus inside the stent five months later, recanalization was achieved by means of retreatment. One patient who underwent low-dose irradiation (6 Gy) without stent implantation showed restenosis five months after treatment. We used a centering catheter that did not block the blood stream for exact centering of the radiation source in larger vessels such as the abdominal aorta. Although endovascular brachytherapy is a promising and safe procedure, careful follow-up is needed to detect untoward reactions such as thrombosis.

Aged↗

PubMedDate not supplied

CyberKnife stereotactic irradiation for metastatic brain tumors.

BACKGROUND: The CyberKnife provides a new technique for performing frameless stereotactic irradiation. So far, few reports have been published on clinical outcomes obtained with the CyberKnife. This report summarizes our clinical experience with CyberKnife irradiation for metastatic brain tumors. MATERIALS AND METHODS: Seventy-seven lesions (48 patients) were evaluated and analyzed, and 66 lesions in 41 patients were treated with stereotactic radiosurgery (SRS). The prescribed dose was 9 to 30 Gy. RESULTS: Freedom from progression of the tumors was more likely with a prescribed dose of at least 24 Gy than with one of less than 20 Gy (p=0.0244; log-rank test). The CR (complete response) rate was significantly higher when D99 was at least 24 Gy (p=0.0045). There were no severe side effects. CONCLUSION: Stereotactic irradiation with the CyberKnife for metastatic brain tumors is effective and safe. D99 should be at least 24 Gy for CyberKnife SRS treatment.

Brain Neoplasms↗

PubMedDate not supplied

Monte Carlo calculation of depth doses for small field of CyberKnife.

PURPOSE: A Monte Carlo (MC) model of CyberKnife was developed as a quality assurance tool. The percentage depth dose (%dd) was verified by using this model. MATERIALS AND METHODS: An MC model was developed with Electron Gamma Shower version 4 (EGS4) in two steps: (1) a model of the CyberKnife treatment head and (2) a model of the collimator and phantom. The bremsstrahlung spectrum was calculated using the first model, and this spectrum was then used to calculate %dds with the second model. The calculated %dds for a large field (60 mm diameter) and three small fields (30, 15, and 5 mm diameter) were compared with those measured with a diamond detector. RESULTS AND DISCUSSION: The MC-calculated and measured %dd-curves for the 60 mm diameter field were in excellent agreement (<1.85%), thus confirming the validity of the model. Discrepancies between the calculated and measured %dd-curves increased with decreasing field size, with considerable discrepancy (11.62%) for the 5 mm diameter field due to lateral electron disequilibrium. Accurate dose can be determined with MC even in small fields. CONCLUSION: The MC technique can provide reliable standard data for accurate dose delivery with high-technology radiotherapies using small beams.

Humans↗

PubMedDate not supplied

Treatment results of radiotherapy with or without surgery for posterior pharyngeal wall cancer of oropharynx and hypopharynx: prognostic value of tumor extension.

PURPOSE: We have been treating posterior pharyngeal wall cancer of the oropharynx and hypopharynx with external radiotherapy according to our policy reported in the 1970s. MATERIALS AND METHODS: Between 1968 and 1995, 51 patients were treated. Treatment policy was decided on the basis of the treatment response after 40 Gy of radiotherapy. Thirty-six good responders were treated with radical radiotherapy, eight poor responders received radical surgery, and the other seven patients could not receive radical treatment because of tumor or patient factors. RESULTS: The 5-year local control and cause-specific survival rates were 56% and 48% for all 51 patients. The 5-year local control rate was 52% for radical radiotherapy. Tumors limited to the posterior wall showed better treatment results (76% for both local control and cause-specific survival) than tumors involving the postcricoid area (0% and 10%). CONCLUSION: Radiotherapy for carefully selected patients dependent on response after 40 Gy of radiotherapy is a useful policy. Tumor extension is an important prognostic factor.

Adult↗

PubMedDate not supplied

Quantitative evaluation of changes in irradiated lung fields after stereotactic irradiation by the Polygon Method.

PURPOSE: To evaluate areas of change in lung after thoracic stereotactic irradiation (STI). MATERIALS AND METHODS: We developed a method of evaluation named the Polygon Method, to measure the irradiated lung fields of 12 lung tumors treated by STI. Before treatment, each targeted field was divided into several circular zones of 2 cm in width centered at the tumor on high resolution computed tomography, and the areas of each zone before and after treatment were compared. RESULTS: Six months after treatment, the areas of the zone within 2 cm from the tumor decreased, and the mean ratio of areas after and before STI was 0.849 (range, 0.515 to 1.052, p=0.0254). By contrast, the areas of zones located at 4 to 6, 6 to 8, 8 to 10, and more than 10 cm from the tumor tended to increase, with mean ratios of 1.059, 1.058, 1.089 (p=0.0374), and 1.084, respectively. CONCLUSION: After thoracic STI, volume loss in the lung is limited to the field in close proximity to the tumor, while compensatory expansion of the lung occurs in fields distant from the tumor.

Adenocarcinoma↗