Biomedical subjects

Seung S Hahn

Publications and source records attributed to Seung S Hahn.

7 recordsLinked to original sources

PubMed2005

Gamma knife surgery for trigeminal neuralgia: improved initial response with two isocenters and increasing dose.

OBJECT: The authors sought to evaluate the initial response of trigeminal neuralgia (TN) to gamma knife surgery (GKS) based on the number of shots delivered and radiation dose. METHODS: Between September 1998 and September 2003, some 63 patients with TN refractory to medical or surgical management underwent GKS at Upstate Medical University. Ten patients had multiple sclerosis and 25 patients had undergone prior invasive treatment. Gamma knife surgery was delivered to the trigeminal nerve root entry zone in one shot in 27 patients or two shots in 36 patients. The radiation dose was escalated to less than or equal to 80 Gy in 20 patients, 85 Gy in 21 patients, and greater than or equal to 90 Gy in 22 patients. Pain before and after GKS was assessed using the Barrow Neurological Institute Pain Scale and the improvement score was analyzed as a function of dose grouping and number of shots. Sixty patients were available for evaluation, with an initial overall and complete response rate of 90% and 27%, respectively. There was a greater improvement score for patients who were treated with two shots compared with one shot, mean 2.83 compared with 1.72 (p < 0.001). There was an increased improvement in score at each dose escalation level: less than or equal to 80 Gy (p = 0.017), 85 Gy (p < 0.001), and greater than or equal to 90 Gy (p < 0.001). Linear regression analysis also indicated that there was a greater response with an increased dose (p = 0.021). Patients treated with two shots were more likely to receive a higher dose (p < 0.001). There were no severe complications. Five patients developed mild facial numbness. CONCLUSIONS: Gamma knife surgery is an effective therapy for TN. Initial response rates appear to correlate with the number of shots and dose.

Adult↗

PubMed2004

A dwell position verification method for high dose rate brachytherapy.

Misplacement of dwell positions is a potential source of misadministration in high dose rate brachytherapy. In this work we present a dwell position verification method using fluoroscopic images. A mobile C-arm fluoroscopic machine is used to take a snapshot of the treatment machine's check cable as it reaches the most distal dwell position. This fluoroscopic image is displayed side-by-side with a treatment planning image on a dual monitor relay station at the HDR treatment console. Any discrepancy between the check cable's position on the verification image and the intended dwell position on the planning image can be identified immediately, thus avoiding the possibility of treating the wrong target volume.

Brachytherapy↗

PubMed2003

The linear-quadratic model and fractionated stereotactic radiotherapy.

PURPOSE: To determine the dose per fraction that could be used when gamma knife or linear accelerator-based stereotactic treatments are delivered in 2 or more fractions. METHODS AND MATERIALS: The linear-quadratic (LQ) model was used to calculate the dose per fraction for a multiple-fraction regimen which is biologically equivalent to a given single-fraction treatment. The results are summarized in lookup tables. RESULTS AND CONCLUSION: The tables can be used by practicing clinicians as a guide in planning fractionated treatment. For the large doses used in typical stereotactic treatments and for small fraction numbers, the model is not very sensitive to the value of the alpha/beta ratio in the LQ model. A simple rule of thumb is found that for two-fraction and three-fraction treatments the dose per fraction is roughly two-thirds and one-half of the single-fraction treatment dose, respectively.

Linear Models↗

PubMed2003

On the use of C-arm fluoroscopy for treatment planning in high dose rate brachytherapy.

Treatment planning for brachytherapy requires the acquisition of geometrical information of the implant applicator and the patient anatomy. This is typically done using a simulator or a computed tomography scanner. In this study, we present a different method by which orthogonal images from a C-arm fluoroscopic machine is used for high dose rate brachytherapy treatment planning. A typical C-arm is not isocentric, and it does not have the mechanical accuracy of a simulator. One solution is to place a reconstruction box with fiducial markers around the patient. However, with the limited clearance of the C-arm this method is very cumbersome to use, and is not suitable for all patients and implant sites. A different approach is adopted in our study. First, the C-arm movements are limited to three directions only between the two orthogonal images: the C-orbital rotation, the vertical column, and the horizontal arm directions. The amounts of the two linear movements and the geometric parameters of the C-arm orbit are used to calculate the location of the crossing point of the two beams and thus the magnification factors of the two images. Second, the fluoroscopic images from the C-arm workstation are transferred in DICOM format to the planning computer through a local area network. Distortions in the fluoroscopic images, with its major component the "pincushion" effect, are numerically removed using a software program developed in house, which employs a seven-parameter polynomial filter. The overall reconstruction accuracy using this method is found to be 2 mm. This filmless process reduces the overall time needed for treatment planning, and greatly improves the workflow for high dose rate brachytherapy procedures. Since its commissioning nearly three years ago, this system has been used extensively at our institution for endobronchial, intracavitary, and interstitial brachytherapy planning with satisfactory results.

Artifacts↗

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

Radiotherapy for moderate-to-severe Graves' ophthalmopathy: improved outcomes with early treatment.

PURPOSE: The purpose of this review is to quantify the response to radiotherapy delivered early in the active inflammatory phase of moderate-to-severe Graves' ophthalmopathy. MATERIALS AND METHODS: A retrospective review of radiotherapy delivered early in the active phase of Graves' ophthalmopathy was performed. All 47 cases had moderate-to-severe ophthalmopathy, and 30 cases had optic neuropathy. Variables examined included exophthalmos, color vision, and resistance to retropulsion. Statistical analyses comparing these variables at presentation and at 3 and 6 months after radiotherapy were performed. Subset analyses comparing responses of patients with symptoms lasting longer or less than 6 months were also performed. RESULTS: At 6 months after radiotherapy, there was improvement in exophthalmos in 74.5% of cases and improvement in retropulsion in 83.0%, and all cases of previous color deficiency improved. The mean improvement in exophthalmos was 1.38 mm, color vision was two plates, and retropulsion was 1 grade. On subset analyses, there was a trend toward greater improvement in patients treated earlier in the course of their symptoms. CONCLUSIONS: Radiotherapy may play an important role in the treatment of Graves' ophthalmopathy, especially for patients with optic neuropathy. Early intervention (symptoms < 6 months) with radiotherapy may be the optimal timing for this treatment.

Analysis of Variance↗

PubMedDate not supplied

Radiotherapy for the clinically negative neck in supraglottic laryngeal cancer.

PURPOSE: The supraglottic larynx has rich lymphatic drainage, resulting in a high incidence of occult cervical metastases, and the optimal treatment of the clinically uninvolved neck in supraglottic laryngeal cancer remains controversial. Selected retrospective series report a greater than 20% regional failure after treatment by radiotherapy alone, and some investigators recommend routine prophylactic neck dissection. We report on our series of patients who received radiotherapy as sole treatment to the clinically negative neck, either to the bilateral neck for N0 disease or to the contralateral neck for ipsilateral lymphatic involvement. PATIENTS AND METHODS: Between 1971 and 1998, 150 patients with supraglottic laryngeal cancer received radiotherapy alone to the clinically negative neck. Fifty-two patients had ipsilateral lymph node metastases (N1 = 16, N2a = 12, N2b = 20, N3 = 4), and 98 patients had no clinical nodal involvement. The primary site (T1/T2 = 74, T3/T4 = 76) was treated with radiotherapy (N = 91) or laryngectomy plus radiotherapy (N = 59). Neck dissection was performed on the involved neck in 36/52 node-positive patients for either multiple involved nodes (N = 20) or size > 3 cm (N = 16). Radiotherapy was delivered in standard fractionation and field arrangement. The median dose to the clinically negative neck was 5000 cGy (range: 4860-6000 cGy). RESULTS: With a median follow-up of 48 months, the clinically negative neck was the first site of failure in 3.3% of patients. The contralateral neck remained disease free in all patients. Five failures occurred in the N0 neck, and the median time to recurrence was 12 months (range: 5-30 months). Salvage therapy was neck dissection for the N0 neck failures. The 5-year locoregional control, disease-specific survival, and overall survival were 69%, 74%, and 61%, respectively. DISCUSSION: Our data support the use of radiotherapy as a prophylactic treatment for the clinically negative neck. Tumor control in the clinically uninvolved cervical lymphatics is comparable to that in surgical series, suggesting that routine neck dissection may not be necessary. Prospective trials are necessary to further define the role of radiotherapy in this patient population.

Adult↗