Biomedical subjects

J Palta

Publications and source records attributed to J Palta.

4 recordsLinked to original sources

PubMed1994

Systematic analysis of errors in target localization and treatment delivery in stereotactic radiosurgery (SRS).

PURPOSE: To systematically analyze the spatial uncertainties associated with each step of the stereotactic radiosurgery (SRS) procedure and the overall spatial accuracy in the treatment delivery. METHODS AND MATERIALS: A special test device has been designed and fabricated to permit accurate simulation, localization and treatment portal verification of a SRS target. This device with simulated targets dispersed in 3-D space can be rigidly attached to the BRW CT or angio frame for localization, to the BRW phantom base for target coordinate determination, and to the floor stand for portal verification. The setup allows evaluation of the accuracy of each procedure separately as well as the overall accuracy in the delivery of SRS treatment. RESULTS: Biplanar film localizations reveal a systematic error in the phantom base pointer of the order of 0.1 mm that is applied as a correction to the measured target coordinates. Targets localized by planar film angiography had a mean positional error of 0.38 +/- 0.1 mm compared to 1.0 +/- 0.7 mm for digital angiographic localization. The positional accuracy associated with CT localization was superior when a 2 mm vs. 4 mm slice thickness was used (0.9 +/- 0.3 mm vs. 1.6 +/- 0.5 mm error). Cumulative mean errors, including inaccuracies associated with treatment setup, were 1.0 +/- 0.4 mm for radiographic localization, 1.2 +/- 0.5 mm for CT with a 512 x 512 matrix and 2 mm slice thickness, and 2.0 +/- 0.6 mm for CT at a 4 mm slice thickness (256 x 256 matrix). Larger errors would be expected in the clinical setting. CONCLUSION: Spatial errors in stereotactic radiosurgery are best estimated using a systematic approach to isolate independent contributing factors. The accuracy in target localization determines the overall accuracy of SRS procedure, provided the mechanical accuracy of the treatment apparatus is assured. Biplanar treatment portal verification with a fiducial localization frame is an accurate method of verifying the target coordinates before delivering treatment.

Humans↗

PubMed1994

Current radiosurgery practice: results of an ASTRO survey. Task Force on Stereotactic Radiosurgery, American Society for Therapeutic Radiology and Oncology.

PURPOSE: Although there is increasing interest in radiosurgery, little quantitative data regarding current patterns of radiosurgery practice are available. We developed a radiosurgery questionnaire to obtain information on radiosurgery practice. METHODS AND MATERIALS: We distributed the questionnaire to the entire membership of the American Society of Therapeutic Radiology and Oncology in early 1993. Responses were obtained from 74 facilities that practice radiosurgery, corresponding to over 6000 treatments carried out since 1983 by 135 radiation oncologists and 130 physicists. RESULTS: Most respondents were found to work within a multidisciplinary team, consisting of the following specialists (average hours devoted per patient on day of treatment in parentheses): radiation oncologist (3.8), neurosurgeon (3.2), physicist (6.1), radiologist (0.7), nurse (2.7), other (3.0). On average, neurosurgeons and nurses who perform Gamma Knife radiosurgery devote significantly more time-per-patient on the day of treatment than their peers who perform linac radiosurgery. On average, less experienced radiation oncologists and physicists (< or = 24 months experience, or < or = 50 patients treated) devote significantly more time-per-patient on the day of treatment than their more experienced peers. Although there are many more linac radiosurgery facilities than Gamma Knife facilities, on average the number of patients treated per month per facility is significantly larger at the latter. On average, follow-up responsibilities are nearly equally shared by radiation oncologists and neurosurgeons, except at Gamma Knife facilities, where neurosurgeons assume a larger percentage of follow-up responsibility. The percentages of patients treated at linac facilities for metastases or primary CNS malignancy are larger than the corresponding percentages at Gamma Knife facilities; the opposite is true for arteriovenous malformation, acoustic neuroma, and meningioma. CONCLUSION: Current radiosurgery practice usually involves a team approach, with participation of specialists from radiation oncology, neurosurgery, physics, radiology, and nursing. The average number of M.D. and Ph.D. hours required per treatment on the day of radiosurgery is high.

Canada↗

PubMed1992

Vertex field verification in the treatment of central nervous system neoplasms.

Increasing sophistication of computerized brain tumor treatment plans has enabled clinicians to devise increasingly complex field combinations to spare as much normal brain tissue as possible. These treatment plans often call for the use of a vertex field. This report describes a simple, useful technique for the verification of the vertex (or any non-coplanar) field on the treatment machine--a procedure that is impossible with conventional port film techniques.

Brain Neoplasms↗

PubMedDate not supplied

Optimization of parameters for fitting linear accelerator photon beams using a modified CBEAM model.

Measured beam profiles and central-axis depth-dose data for 6- and 25-MV photon beams are used to generate a dose matrix which represents the full beam. A corresponding dose matrix is also calculated using the modified CBEAM model. The calculational model uses the usual set of three parameters to define the intensity at beam edges and the parameter that accounts for collimator transmission. An additional set of three parameters is used for the primary profile factor, expressed as a function of distance from the central axis. An optimization program has been adapted to automatically adjust these parameters to minimize the chi 2 between the measured and calculated data. The average values of the parameters for small (6 X 6 cm2), medium (10 X 10 cm2), and large (20 X 20 cm2) field sizes are found to represent the beam adequately for all field sizes. The calculated and the measured doses at any point agree to within 2% for any field size in the range 4 X 4 to 40 X 40 cm2.

Humans↗