RESUMEN
Radiation treatment planning systems (RTPS) are evolving on a rapid and continual basis. After the evaluation of several commercial systems, we have developed a list of features we consider desirable in a product. The goal in the compilation of these criteria was a comprehensive worksheet which categorized the characteristics of RTPS into hardware (computer and peripheral devices), 2-D planning tools, 3-D planning tools, irregular field planning tools, and brachytherapy planning. With these distinctions, one can evaluate a system conforming to the specific planning needs, e.g., conformal therapy, dynamic therapy capabilities, or optimized remote afterloading brachytherapy, of a department. The rationales of the special requirements are provided for justification.
Asunto(s)
Planificación de la Radioterapia Asistida por Computador , Braquiterapia , Recolección de Datos , Estudios de Evaluación como Asunto , Humanos , Procesamiento de Imagen Asistido por Computador , Dosificación Radioterapéutica , Radioterapia de Alta Energía , Tomografía Computarizada por Rayos XRESUMEN
PURPOSE: Radiotherapy plans based on physical dose distributions do not necessarily entirely reflect the biological effects under various fractionation schemes. Over the past decade, the linear-quadratic (LQ) model has emerged as a convenient tool to quantify biological effects for radiotherapy. In this work, we set out to construct a mechanism to display biologically oriented dose distribution based on the LQ model. METHODS AND MATERIALS: A computer program that converts a physical dose distribution calculated by a commercially available treatment planning system to a biologically effective dose (BED) distribution has been developed and verified against theoretical calculations. This software accepts a user's input of biological parameters for each structure of interest (linear and quadratic dose-response and repopulation kinetic parameters), as well as treatment scheme factors (number of fractions, fractional dose, and treatment time). It then presents a two-dimensional BED display in conjunction with anatomical structures. Furthermore, to facilitate clinicians' intuitive comparison with conventional fractionation regimen, a conversion of BED to normalized isoeffective dose (NID) is also allowed. RESULTS: Two sample cases serve to illustrate the application of our tool in clinical practice. (a) For an orthogonal wedged pair of x-ray beams treating a maxillary sinus tumor, the biological effect at the ipsilateral mandible can be quantified, thus illustrates the so-called "double-trouble" effects very well. (b) For a typical four-field, evenly weighted prostate treatment using 10 MV x-rays, physical dosimetry predicts a comparable dose at the femoral necks between an alternate two-fields/day and four-fields/day setups. However, our BED display reveals an approximate 21% higher BED for the two-fields/day scheme. This excessive dose to the femoral necks can be eliminated if the treatment is delivered with a 3:2 (anterio-posterior/posterio-anterior (AP/PA): bilaterally opposed (BLO)) dose weighting. With Co-60 beams, the increase of BED with alternate two-fields/day, 1:1 setup was even more pronounced (26%). CONCLUSION: We have demonstrated the feasibility of constructing a biologically oriented dose distribution for clinical practice of radiotherapy. The discordance between physical dose distributions and the biological counterparts based on the given treatment schemes was quantified. The computerized display of BED at nonprescription points greatly enhanced the versatility of this tool. Although the routine use of this implementation in clinical radiotherapy should be cautiously done, depending largely on the accuracy of the published biological parameters, it may, nevertheless, help the clinicians derive an optimal treatment plan with a particular fractionation scheme or use it as a quantitative tool for outcome analysis in clinical research.
Asunto(s)
Modelos Lineales , Radiobiología , Dosificación Radioterapéutica , Efectividad Biológica Relativa , Estudios de Factibilidad , Humanos , Masculino , Seno Maxilar , Neoplasias de los Senos Paranasales/radioterapia , Neoplasias de la Próstata/radioterapiaRESUMEN
Some of the women undergoing radiation therapy may be pregnant and the scatter radiation to the fetus and gonads is a matter of great concern. Quantitative measurement of the scatter dose in polystyrene solid phantoms with a Farmer type chamber and effects of shielding blocks under the collimators were studied. The scatter dose outside of the primary beam was found to be decreasing exponentially with increasing distance from the radiation beam edge. When the distance increased from 10 cm to 60 cm, the scatter dose drops from 1-2% to 0.15% for the Co-60 beam and from 1-2% to 0.02% for the 10 MV X-rays. The collimation system was a major source of scatter radiation because the scatter dose could be substantially reduced by placing shielding blocks under the collimators and the scatter dosed varied with field sizes. The lead apron used in diagnostic radiographic procedures reduced the scatter dose by 5-6% only. The scatter dose distribution in the body outside of the radiation field was also analyzed.
Asunto(s)
Feto/efectos de los fármacos , Genitales Femeninos/efectos de la radiación , Dosis de Radiación , Femenino , Humanos , Embarazo , Dispersión de RadiaciónRESUMEN
In the past our laboratory has reported a method of measuring trabecular bone mineral density (TBMD) in the calcaneus in vivo by using the coherent-to-Compton scattering ratio. In the present work the distribution of TBMD in the calcaneus has been studied, and the reproducibility of this technique in vivo has been determined. It is found that although the TBMD may vary within the calcaneus, a region exists over which the variation in density is not large. This region coincides with the midportion of the heel and is the site chosen for the measurement of TBMD by the coherent-to-Compton scattering ratio technique. The reproducibility of this technique in vivo has been determined to be 3.4%.