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J Seco

Publications and source records attributed to J Seco.

4 recordsLinked to original sources
PubMed2002

An optimization algorithm that incorporates IMRT delivery constraints.

An intensity-modulated beam optimization algorithm is presented which incorporates the delivery constraints into the optimization cycle. The optimization algorithm is based on the quasi-Newton method of iteratively solving minimization problems. The developed algorithm iteratively corrects the incident, pencil-beam-like, fluence to incorporate the delivery constraints. In the present study, the goal of the optimization algorithm is to achieve the best deliverable radiotherapy plan, subject to the constraints of the delivery technique described by a leaf-sequencing algorithm being applied concurrently. In general, if they are applied after, rather than during, the optimization cycle, the delivery constraints associated with the IMRT technique can produce local variations up to 6% in the 'optimized' dose (i.e., distribution without applied constraints) and reduce the degree of conformity, of the dose, to the PTV region. The optimization method has been applied to three IMRT delivery techniques: dynamic multileaf (DMLC), multiple-static-field (MSF) and slice-by-slice tomotherapy (NOMOS MIMiC). The beam profiles were generated for a prostate tumour with organs at risk being the rectum, bladder and femoral heads. The optimization method described was shown to generate optimum and deliverable IMRT plans for these three delivery techniques. In the case of the DMLC and MSF the optimization converged within 3-5 iterations to a mean PTV dose of 69.60 +/- 1.34 Gy and 69.71 +/- 1.34 Gy, respectively, while for NOMOS MIMiC approximately 10 iterations were needed to obtain 69.68 +/- 1.55 Gy. In addition to this, the IMRT optimization also yielded optimum fluence profiles when clustering was performed concurrently with the leaf-sequencer. An optimum between 8 and 15 clusters of equal fluence 'intensity' was shown to establish the best compromise between the number of fluence levels and the PTV dose coverage.

Algorithms↗
PubMed2002

The type, amount, frequency and timing of dietary supplement use by elite players in the First Spanish Basketball League.

The aims of this study were to determine the type, frequency and amount of dietary supplement consumption among a group of professional basketball players. The type, amount and specific timing of supplement use were recorded by 55 professional basketball players from seven different teams of the First Spanish Basketball League. Most participants (58%) consumed dietary supplements. Multivitamins and vitamins were the most frequently used supplements among the athletes (50.9%), followed by sport drinks (21.8%), miscellaneous supplements (21.8%), amino acids (14.5%), proteins (12.7%) and carbohydrates (12.7%). The average daily dietary supplement was one capsule of multivitamins, one capsule of antioxidant vitamins, 0.2-1.0 g vitamin C, 10.3 g protein, 1.9 g amino acids, 16.2 g carbohydrates and 377 ml of a commercial sport drink. Although the proportion of participants who consumed dietary supplements before, during and immediately after exercise was 25.4%, 16.3% and 7.3% respectively, only a few consumed a potentially ergogenic supplement at these times. It would appear unlikely that the type or amount of dietary supplements consumed had a beneficial effect on the physical performance of these professional basketball players, with the possible exception of antioxidant vitamins and the commercial sport drinks.

Adult↗
PubMed2001

Analysis of the effects of the delivery technique on an IMRT plan: comparison for multiple static field, dynamic and NOMOS MIMiC collimation.

The process of delivering an IMRT treatment may involve various beam-modifying techniques such as multileaf collimators (MLCs), the NOMOS MIMiC, blocks, wedges, etc. In the case of the MLC, the spatial/temporal variation of the position of the leaves and diaphragms in the beam allows the delivery of modulated beam profiles either by the multiple-static-field (MSF) method or by the dynamic multileaf collimator (DMLC) method. The constraints associated with the IMRT delivery technique are usually neglected in the process of obtaining the 'optimal' inverse treatment plan. Consequently, dose optimization may be significantly reduced when the 'optimal' beam profiles are converted to leaf/diaphragm positions via a leaf-sequencing interpreter. The paper presented here assesses the effects on the optimum treatment plan of the following leaf-sequencing algorithms: MSF, DMLC and NOMOS MIMiC. The results obtained suggest that the delivery of an 'optimum' plan produces an overdosage of the PTV region due to various factors such as leaf/diaphragm transmission effects, head-scatter and phantom-scatter contributions. The overdosage observed for a cohort of ten patients was 2.5, 3.7 and 5.7%, respectively, for the DMLC, MSF and NOMOS MIMiC, after normalizing the delivered fluence to account for IMRT effects (using the method of Convery et al (Convery D J, Cogrove V P and Webb S 2000 Proc. 13th Int. Conf. on Computers in Radiotherapy (Heidelberg, 2000)) such as to obtain 70 Gy at the isocentre. The IMRT techniques DMLC, MIMiC and MSF were compared for the organs at risk: rectum, bladder, and left and right femoral heads.

Algorithms↗