Biomedical subjects

D H Pan

Publications and source records attributed to D H Pan.

At least 19 recordsLinked to original sources

PubMed2001

A metastatic pituitary carcinoid tumor successfully treated with gamma knife radiosurgery.

Intracranial metastasis occurs in a certain number of patients with carcinoid tumor. However, carcinoid tumor with metastasis to the pituitary gland is extremely rare. Up to the present, no effective treatment for either a metastatic intracranial carcinoid tumor or a metastatic pituitary lesion of any origin has been documented. We have treated a case of metastatic carcinoid tumor of the pituitary gland with transsphenoidal tumor resection followed by gamma knife radiosurgery. A 59-year-old man presented with headache and left oculomotor palsy. He was treated at the same hospital for bronchial atypical carcinoid tumor one and a half years ago. Magnetic resonance image of the brain showed a pituitary tumor. There were no signs of recurrent or metastatic lesion elsewhere despite thorough investigation. Transsphenoidal approach for removal of tumor was done and the pathology turned out to be a metastatic carcinoid tumor. Subsequent gamma knife radiosurgery was given for residual tumor. The oculomotor palsy improved after radiosurgery. No neurological deficit occurred. Follow-up CT scan of the brain showed complete resolution of the tumor. We concluded that gamma knife radiosurgery could be used to treat a metastatic intracranial carcinoid tumor. It can also be used to treat a metastatic lesion of the pituitary gland without causing neurological deficit.

Carcinoid Tumor↗

PubMed2000

Gamma knife radiosurgery as a primary treatment for prolactinomas.

OBJECT: The purpose of this study was to estimate the efficacy of gamma knife radiosurgery (GKS) in controlling tumor growth and endocrinopathy associated with prolactinomas. METHODS: Between 1993 and 1997, 164 of 469 patients with pituitary adenomas treated by GKS harbored prolactinomas. The dose to the tumor margin ranged from 9 to 35 Gy (mean 31.2 Gy), and the visual pathways were exposed to a dose of less than 10 Gy. The mean tumor diameter was 13.4 mm. The mean follow-up time for 128 cases was 33.2 months (range 6-72 months). Tumor control was observed in all but two patients who underwent surgery 18 and 36 months, respectively, after GKS. Clinical cure was achieved in 67 cases. Clinical improvement was noted with a decrease in the hyperprolactinemia after GKS. Nonetheless, in 31 (29%) of 108 patients who were followed for more than 2 years no improvement in serum prolactin levels was demonstrated, although this could be normalized by bromocriptine administration after treatment. Nine infertile women became pregnant 2 to 13 months after GKS and all gave birth to normal children. There was no visual deterioration related to GKS. Five women experienced premature menopause. In these patients there was subtotal disappearance of the tumor and an empty sella developed. CONCLUSIONS: Gamma knife radiosurgery as a primary treatment for prolactinomas can be safe and effective both for controlling tumor growth and for normalization of prolactin hypersecretion. A higher margin dose (> or = 30 Gy) seemed to be associated with a better clinical outcome. Gamma knife radiosurgery may make prolactinomas more sensitive to the bromocriptine.

Humans↗

PubMed1998

The radiation induced magnetic resonance image intensity change provides a more efficient three-dimensional dose measurement in MRI-Fricke-agarose gel dosimetry.

A detailed methodology has been developed to map the spatial dose distribution in a Fricke-agarose gel based on the radiation induced image intensity change in the gel's magnetic resonance (MR) images. Besides the linear correlation between the change in the gel's spin-lattice relaxation rate and the absorbed dose, it is shown here that the radiation induced image intensity change for T1-weighted spin-echo images with TE << TR correlates exponentially to the absorbed dose. Furthermore, at the lower dose region (< 15 Gy), the correlation is fairly linear and its sensitivity is high. The minimum detectable dose is shown to be equivalent to the one obtained using the conventional R1-based approach. Since only one T1-weighted image is required for the dose evaluation, compared to the R1-based method, the total MR imaging time can be reduced from hours to a few minutes. This extensive time reduction avoids ferric ion diffusion effects and provides a practical way to simply and effectively measure the three-dimensional dose distribution using the Fricke-agarose dosimeter gel.

Gels↗

PubMed1998

The effectiveness and factors related to treatment results of gamma knife radiosurgery for meningiomas.

A retrospective analysis was conducted on 80 patients with intracranial mengiomas treated with Gamma Knife radiosurgery between 1993 and 1996. The purpose was to analyze the efficacy of the treatment and to assess appropriate treatment parameters. The results were assessed by regular MR examinations, and tumor volume was measured at 6-month intervals. Mean follow-up duration was 21 months (range 6-45 months). 63 meningiomas were at the skull base and 17 were distal from the skull base. Tumor volumes <5 ml (n=38), 5-10 ml (n=21), 10-15 ml (n=14), 15-20 ml (n=7). The patients were divided into 3 groups according to the radiation dose. The groups were high-dose (peripheral dose 17-20 Gy, n=19), medium-dose (15-16 Gy, n=33) and low-dose (12-14 Gy, n=28) groups. A statistical method (Generalized Estimation Equation) was applied to compare treatment results in these groups with different doses and tumor volumes. The volume measurement at the latest follow-up showed 74% (59/80) meningiomas decreased in volume, 17% (14/80) had no tumor enlargement and 9% (7/80) had increased in volume. The increased volume was found more frequently in the patients with a short (6-12 months) follow-up period. In this series, the tumors had 32&percnt reduction in average tumor volume at 3 years after radiosurgery. At the range of 12-20 Gy peripheral dose (PD), radiosurgery was effective to reduce tumor volume 0.7% per month (p<0.05). However, higher doses had no significant difference on tumor volume reduction (p>0.05). On the other hand, high-dose (PD>17 Gy) treatment was associated with a higher risk of temporary tumor swelling and the development of adverse radiation effects (AREs). The AREs detected on MR images occurred in (25/80) 31% patients. Only 6/25 AREs were symptomatic and 2 had neurological sequelae. Peripheral doses, tumor volumes and their locations had significant impacts on the ARE (p<0. 05). In conclusion, a peripheral dose of 15-16 Gy may be adequate for meningiomas with small volumes (<5 ml). In larger tumors (>10 ml) a lower PD is preferred (12-14 Gy). To avoid initial tumor swelling and ARE, high-dose irradiation (PD>17 Gy) is not recommended for meningiomas larger than 5 ml.

Adult↗

PubMed1998

Verifying complete obliteration of carotid artery-cavernous sinus fistula: role of color Doppler ultrasonography.

The purpose of this study was to evaluate the role of color Doppler ultrasonography in verifying obliteration of carotid artery-cavernous sinus fistula before and after therapeutic embolization or gamma knife radiosurgery. Before treatment, carotid artery-cavernous sinus fistula showed the following data on color Doppler ultrasonography: (1) increased blood flow in the common carotid artery (220 to 1264 ml/min with mean+/-SD of 728+/-378 ml/min); internal carotid artery (435 to 1097 ml/min with mean+/-SD of 834+/-216 ml/min) in fistulas of the direct type; and external carotid artery (85 to 257 ml/min with mean+/-SD of 170+/-75 ml/min) in fistulas of the indirect type in comparison to the contralateral side; (2) reverse pulsatile flow or spiculated wave form with turbulent flow in the engorged superior ophthalmic vein on the lesion side in all patients. All of the above abnormal hemodynamic changes became normal in six patients immediately after first embolization, in two patients with balloon embolization combined with subsequent direct embolization by direct puncture through the superior orbital fissure or internal carotid artery embolization, and in five patients after gamma knife radiosurgery at 4, 4, 8, 9, and 9 months, respectively. Color Doppler ultrasonography might be a good modality in long-term follow-up of carotid artery-cavernous sinus fistula after gamma knife radiosurgery and embolization.

Adolescent↗

PubMed1996

Whole body radiation exposure with gamma unit radiosurgery.

BACKGROUND: Stereotactic radiosurgery is the use of external radiation in association with a stereotactic device to precisely locate and destroy inaccessible deep-seated lesions within the brain in a single treatment session. Very little attention has been paid to the extracranial sites of radiation exposure measurements. This study evaluates the extracranial absorbed dose due to leakage and scattered radiation of the Gamma Unit used in radiosurgery. METHODS: The absorbed doses were measured with thermoluminescent dosimetry (TLDs). Single and multiple Gamma Unit treatment with the 18mm collimator helmet was given and a Rando tissue equivalent phantom was in place to simulate a patient treatment. TLDs were placed on the phantom to measure the absorbed doses by the organs at risk. Two TLD chips were placed at each of the following organs: eye, thyroid, sternum and gonads. The irradiated TLDs were read with a Vinten TLD system 654D. The TLD factor was determined by irradiating TLDs with a cobalt-60 teletherapy unit of a known dose of radiation. RESULTS: The average maximum target absorbed dose was 30 Gy. The measured absorbed dose in selected organs from Gamma Unit radiosurgery with one or more isocenters was 21-53 cGy for the eye, 4-8 cGy for the thyroid, 3-4 cGy for the sternum and 2-3 cGy for the gonads. The dose to extracranial sites increased with the number of isocenters. The radiation dose to extracranial sites became much more substantial when multiple isocenters were used. CONCLUSIONS: The potential risk of radiation exposure is radiation induced tumors. No cases have been reported in patients treated with Gamma Unit radiosurgery. Given the benefit of Gamma Unit treatment, the clinical significance of these doses is minimal.

Brain Neoplasms↗

PubMed1995

Early effects of Gamma Knife surgery on malignant and benign intracranial tumors.

To assess the early response of intracranial tumors to Gamma Knife surgery, we performed a prospective investigation of 42 patients treated by Gamma Knife surgery for different types of intracranial tumors. The clinical condition, tumor volume, treatment results and their temporal correlation with the irradiation were analyzed, based on MRI performed on the same MR scanner. Volume reduction in the tumors measured at the latest follow-up ranged from 0.2 to 100%. All except 1 malignant tumor showed decreasing size and improving peritumoral edema 1-7 months after radiosurgery. In 30 benign tumors, 13 showed either a decrease or no change in volume. However, an initial volume increase was observed in 17 tumors, with a maximum at 3-9 months, which subsequently regressed. In 2 meningioma patients, peritumoral edema increased and needed steroid treatment. Sequential PET-FDG imaging of the patients showed decreasing FDG uptake, indicating a decrease tumor in metabolism. The PET findings correlated well with the loss of contrast enhancement on MR images. In conclusion, intracranial tumors respond to Gamma Knife surgery from an early stage. Different tumors have different responses to radiosurgery. It is too early to offer a prognosis of long-term effects based on the limited material. However, sequential clinical, MR and PET follow-ups provide an excellent opportunity to investigate the evolving irradiation effects in vivo.

Brain Neoplasms↗

PubMed1995

Early irradiation effects observed on magnetic resonance imaging and angiography, and positron emission tomography for arteriovenous malformations treated by Gamma Knife radiosurgery.

In 14 patients (7 males and 7 females, age 16-49, mean 29 years), medium-to-large arteriovenous malformations (AVMs; nidus volume 3.5-17.5 cm3, mean 9.4 cm3) were treated by Gamma Knife radiosurgery. Stereotactic MR and conventional angiography were included for targeting to improve targeting accuracy and tissue content in the irradiation volume. Maximum irradiation doses to the nidi were 36-40 Gy (mean 38.9 Gy) and minimum target doses were 18-24 Gy (mean 20 Gy). MR images and MR angiography demonstrated decreasing caliber of feeding vessels and AVM nidus volumes from an early stage, 3 months after radiosurgery, which indicated improvement in cerebral hemodynamics. The improvement correlated well with that observed on PET using [18F]fluorodeoxyglucose (FDG) and with the patients' clinical condition. MR creates an opportunity to monitor treatment effects in a completely noninvasive manner, while conventional angiography remains necessary for verifying complete obliteration of AVMs. More patients and longer follow-ups are needed for clarifying the role of MR techniques in radiosurgery for AVMs.

Adolescent↗

PubMed1991

Percutaneous reposition of dislodged coils in the treatment of a vertebral arteriovenous fistula--with CT follow-up.

We report a case of vertebral arteriovenous fistula in which embolization was complicated by migration of two coils and a partially inflated balloon. In order to relieve compression to the spinal cord, the displaced balloon was punctured percutaneously. For both relieving compression to the spinal cord and obliterating the residual fistula, the dislodged coils in the partially thrombosed epidural venous sinus were removed percutaneously and placed in the fistula, and more coils were implanted in the fistula percutaneously through the needle. CT follow-up half a year later showed complete resolution of compression of the spinal cord and complete recovery from myelopathy was clinically apparent.

Adult↗

PubMed1990

Stereotactic internal irradiation for cystic craniopharyngiomas: a 6-year experience.

Fourteen adults and 4 children with cystic craniopharyngiomas were treated with stereotactic beta-irradiation during a 6-year period. Of these patients, 10 were primary cases, and 8 were recurrences after previous major surgery. Radioactive phosphorus (32P) or yttrium (90Y) in colloidal forms were used as the radiation agents. Cyst volumes (10-130 ml) were assessed intraoperatively by the 99Tc radiodilution method. According to our treatment program, the radiation dose to the cyst wall was 20,000 rad and the total irradiation time 2 weeks. The follow-up period ranged from 1 to 6 years, with an average of 3.8 years. Postoperative shrinkage of the cysts and clinical improvement were observed in most patients. Pertinent clinical data and results of treatment are described.

Adolescent↗

PubMed1987