Biomedical subjects

Masao Tago

Publications and source records attributed to Masao Tago.

5 recordsLinked to original sources

PubMed2003

Dynamic conical conformal radiotherapy using a C-arm-mounted accelerator: dose distribution and clinical application.

PURPOSE: The aim of this study was to solve anisotropy in the dose distributions from rotational conformal radiotherapy (RCRT) by using a C-arm-mounted accelerator. MATERIALS AND METHODS: The linac head was designed to move along the C-arm with a maximum angle of 60 degrees (from a vertical position toward the gantry). Simultaneous rotation of the gantry creates a dynamic conical irradiation technique. Dynamic conical conformal radiation therapy (Dyconic CRT) was developed by combining the technique with continuous motion of a multileaf collimator. Dose distributions were measured in phantoms using film densitometry and compared with conventional RCRT. Dose distributions in actual radiation therapy patients are also presented. RESULTS: Dyconic CRT enabled the precise delivery of noncoplanar beams without rotating the table. The measurements showed that three-dimensionally isotropic dose falloff was achieved with Dyconic CRT. Dose inhomogeneity in the sagittal direction with Dyconic CRT was compensated for by use of wedge filters. CONCLUSIONS: The drawbacks of the dose distributions produced by RCRT were overcome with the use of Dyconic CRT.

Dose-Response Relationship, Radiation↗

PubMed2002

Retrospective analysis of a 10-year experience of stereotactic radio surgery for arteriovenous malformations in children and adolescents.

OBJECT: To obtain information essential to the decision to perform radiosurgery for arteriovenous malformations (AVMs) in children and adolescents, the authors retrospectively analyzed their experience with gamma knife surgery for AVMs in 100 patients ranging in age from 4 to 19 years. METHODS: Follow-up periods ranged from 6 to 124 months (median 71 months), and the actuarial obliteration rates demonstrated by angiography were 84.1, 89.4, and 94.7% at 3, 4, and 5 years, respectively. Factors associated with better obliteration rates in univariate analysis included the following: a patient age of 12 years or younger; a mean nidus diameter of 2 cm or less; a nidus volume of 3.8 cm3 or less; a maximum diameter of the nidus less than 3 cm; and a Spetzler-Martin grade of III or less. Radiation-induced neuropathy was seen in four patients, and the risk factors were considered to be a nidus in the brainstem and a maximum radiation dose greater than 40 Gy. Hemorrhage developed during the latency interval in four patients, and one patient with a cerebellar AVM died of the hemorrhage. The annual bleeding rate was 1.5%. Feeding arteries located in the posterior cranial fossa and an AVM nidus located in the cerebellum were significantly associated with the risk of hemorrhage. After angiographically verified obliteration of the nidus, 51 patients continued to be observed from 1 to 110 months (median 67 months); hemorrhage developed in one patient 38 months after nidus obliteration. CONCLUSIONS: Radiosurgery is an acceptable treatment for small AVMs in children and adolescents in whom a higher obliteration rate can be achieved with lower risks of interval hemorrhage compared with the reported results in the general population. Careful follow-up observation seems to be required, however, even after angiographically verified obliteration.

Adolescent↗

PubMed2002

Radiosurgery for residual or recurrent nonfunctioning pituitary adenoma.

OBJECT: Nonfunctioning pituitary adenomas comprise approximately 30% of all pituitary tumors. The purpose of this retrospective study is to evaluate the efficacy and role of gamma knife radiosurgery (GKS) in the management of residual or recurrent nonfunctioning pituitary adenomas. METHODS: A review was conducted of the data obtained in 42 patients who underwent adjuvant GKS at the University of Pittsburgh between 1987 and 2001. Prior treatments included transsphenoidal resection, craniotomy and resection, or conventional radiotherapy. Endocrinological, ophthalmological, and radiological responses were evaluated. The duration of follow-up review varied from 6 to 102 months (mean 31.2 months). Fifteen patients were observed for more than 40 months. The mean radiation dose to the tumor margin was 16 Gy. Conformal radiosurgery planning was used to restrict the dose to the optic nerve and chiasm. Tumor control after GKS was achieved in 100% of patients with microadenomas and 97% of patients with macroadenomas. Gamma knife radiosurgery was equally effective in controlling adenomas with cavernous sinus invasion and suprasellar extension. No patient developed a new endocrinological deficiency following GKS. One patient's tumor enlarged with an associated decline in visual function. Another patient experienced a deterioration of visual fields despite a decrease in tumor size. CONCLUSIONS: Gamma knife radiosurgery can achieve tumor control in virtually all residual or recurrent nonfunctioning pituitary adenomas. Dose sparing facilitates tumor management even when the adenoma is close to the optic apparatus or invades the cavernous sinus.

Adenoma↗

PubMedDate not supplied

Two-dimensional magnetic resonance digital subtraction angiography using array spatial sensitivity encoding techniques in the assessment of intracranial hemodynamics.

OBJECTIVE: Array spatial sensitivity encoding techniques (ASSET) were employed to improve the temporal resolution of two-dimensional (2D) thick-slice contrast-enhanced magnetic resonance digital subtraction angiography (MRDSA). METHODS: 2D MRDSA using ASSET was performed in 28 patients via fast spoiled gradient-echo sequence (TR/TE 5.4/1.5 ms; FA 60; FOV 24x24 cm; matrix size 256x256; slicethickness 50-70 mm), followed by a bolus injection of gadolinium chelate and subsequent saline flush, for 40 seconds on a sagittal plane. Images were evaluated for visualization of normal intracranial vessels and brain lesions utilizing a three-point scale; additionally, in 10 of the 28 patients, results were compared with those of conventional 2D MRDSA. RESULTS: 2D MRDSA using ASSET, which improved temporal resolution from 1.45 to 0.77 seconds, displayed image quality comparable to that of conventional 2D MRDSA. Moreover, this technique afforded superior detectability with respect to early venous filling in patients with arteriovenous malformations (AVMs). CONCLUSION: ASSET improves the temporal resolution of 2D MRDSA without compromising spatial resolution.

Brain Neoplasms↗

PubMedDate not supplied

Intercomparison of dose distribution between gamma knife and C-arm-mounted linac.

Although the Gamma Knife is widely used as a standard tool of radiosurgery for intracranial diseases, recent innovations in medical accelerators have actualized equivalent dose distribution. Most commonly, multiple non-coplanar arc beams through a combination of gantry and couch rotations are used in linac-based radiosurgery, but beam entry geometry is different from that with the Gamma Knife. We have developed a C-arm-mounted medical accelerator and realized conical beam entry without couch rotation. A combination of several conical rotation beams with different C-arm angles comprises multi-orbit dynamic conical radiation therapy (MODCRT) and resembles radiation beam entry with the Gamma Knife. Intercomparison of dose distributions and dose-volume histograms for the same brain tumor demonstrated that MODCRT delivers a similar dose fall-off pattern to that obtained with the Gamma Knife, though the low-dose spread patterns differ.

Brain Neoplasms↗