Intensity modulated radiation therapy (IMRT) is a highly accurate technique that is usually implemented in either dynamic or step-and-shoot fashion with many segments each having low monitor units (MUs). The present s...Intensity modulated radiation therapy (IMRT) is a highly accurate technique that is usually implemented in either dynamic or step-and-shoot fashion with many segments each having low monitor units (MUs). The present study evaluated the effects of beam startup characteristics on the dose delivery accuracy for each segment at low MUs for step-and-shoot IMRT with an Elekta Precise accelerator at the highest dose rates. We used a two-dimensional semi-conductor detector for the dose measurements. The field size of each segment was assumed to be 20 ×20 cm2 and each segment was set to deliver 1 - 10 MUs. Our results show a variation in dose delivery accuracy between segments for the same IMRT beam, which can be attributed to the beam startup characteristics. This variability is attributed to the changes in the transient changes in the temperatures of the electron gun filament and the magnetron. That is, the transient increase in the temperature of the filament leads to increasing doses with time and that of the magnetron leads to decreasing doses with time during the first few MUs.展开更多
The inverse planning for a step-and-shoot plan in intensity-modulated radiotherapy (IMRT) is usually a multiple step process. Before being converted into the MLC segments, the optimum intensity profiles of beams, whic...The inverse planning for a step-and-shoot plan in intensity-modulated radiotherapy (IMRT) is usually a multiple step process. Before being converted into the MLC segments, the optimum intensity profiles of beams, which are generated by an optimization algorithm, shall be discretized into a few intensity levels. The discretization process of the optimum intensity profiles can induce deviations in the final dose distribution from the original optimum dose distribution. This paper describes a genetic algorithm for the discretization of given optimum intensity profiles. The algorithm minimizes an objective function written in terms of the intensity levels. Both the dose-based objective function, which is defined by the deviation between the dose distributions before and after the discretization, and the intensity-based objective function, which is defined by the deviation between the optimum intensity profiles and the discretization intensity profiles, have been adopted. To evaluate this algorithm, a series of simulation calculations had been carried out using the present algorithm, the even-spaced discretization and the k-means clustering algorithm respectively. By comparing the resultant discretization-induced deviations (DIDs) in intensity profiles and in dose distributions, we have found that the genetic algorithm induced less DIDs in comparison with that induced in the even-spaced discretization or the k-means clustering algorithm. Additionally, it has been found that the DIDs created in the genetic algorithm correlate with the complexity of the intensity profiles that is measured by the "fluence map complexity".展开更多
Using in vitro leaves of Zizyphus jujuba ‘Kongfusucui’ plantlet as explants,effects of culture method,phytohormone proportion and culture time on induction rate of adventitious shoot from leaves and effects of sucro...Using in vitro leaves of Zizyphus jujuba ‘Kongfusucui’ plantlet as explants,effects of culture method,phytohormone proportion and culture time on induction rate of adventitious shoot from leaves and effects of sucrose concentrations in rooting media on rooting of adventitious shoot were studied.The results show that induction rate of adventitious shoot by two-step culture method(firstly cultured on medium Ⅰ for four weeks then cultured on medium Ⅱ for three weeks) is significantly higher than that by one-step culture method(cultured continuously on medium Ⅰ for seven weeks).Phytohormone proportion in medium Ⅰ has an obviously influence on induction rate of adventitious shoot,which gradually increases with increasing of TDZ concentration in medium Ⅰ.And adding 1.0 mg·L-1 TDZ in medium Ⅰ leads to induction rate with above 80%.With culture time prolonging(cultured for 1,2,3 or 4 weeks on medium Ⅰ,respectively),induction rate increases gradually.Sucrose concentration has a significant effect on rooting of adventitious shoot,sucrose with higher concentration(30 g·L-1) is beneficial to rooting.According to induction rate and growth status of adventitious shoot,it is determined that optimal culture method of adventitious shoot induction from Z.jujuba 'Kongfusucui' leaves is two-step culture method,that is,leaves firstly cultured on WPM medium containing 1.0 mg·L-1 TDZ and 0.5 mg·L-1 IAA for four weeks,and then cultured on WPM medium containing 0.5 mg·L-1 IAA and 1.0 mg·L-1 GA3 till adventitious shoot produced.展开更多
文摘Intensity modulated radiation therapy (IMRT) is a highly accurate technique that is usually implemented in either dynamic or step-and-shoot fashion with many segments each having low monitor units (MUs). The present study evaluated the effects of beam startup characteristics on the dose delivery accuracy for each segment at low MUs for step-and-shoot IMRT with an Elekta Precise accelerator at the highest dose rates. We used a two-dimensional semi-conductor detector for the dose measurements. The field size of each segment was assumed to be 20 ×20 cm2 and each segment was set to deliver 1 - 10 MUs. Our results show a variation in dose delivery accuracy between segments for the same IMRT beam, which can be attributed to the beam startup characteristics. This variability is attributed to the changes in the transient changes in the temperatures of the electron gun filament and the magnetron. That is, the transient increase in the temperature of the filament leads to increasing doses with time and that of the magnetron leads to decreasing doses with time during the first few MUs.
基金Supported by the National Natural Science Foundation of China (Grant No. 10275045)the Excellent Young Teachers Program of China.
文摘The inverse planning for a step-and-shoot plan in intensity-modulated radiotherapy (IMRT) is usually a multiple step process. Before being converted into the MLC segments, the optimum intensity profiles of beams, which are generated by an optimization algorithm, shall be discretized into a few intensity levels. The discretization process of the optimum intensity profiles can induce deviations in the final dose distribution from the original optimum dose distribution. This paper describes a genetic algorithm for the discretization of given optimum intensity profiles. The algorithm minimizes an objective function written in terms of the intensity levels. Both the dose-based objective function, which is defined by the deviation between the dose distributions before and after the discretization, and the intensity-based objective function, which is defined by the deviation between the optimum intensity profiles and the discretization intensity profiles, have been adopted. To evaluate this algorithm, a series of simulation calculations had been carried out using the present algorithm, the even-spaced discretization and the k-means clustering algorithm respectively. By comparing the resultant discretization-induced deviations (DIDs) in intensity profiles and in dose distributions, we have found that the genetic algorithm induced less DIDs in comparison with that induced in the even-spaced discretization or the k-means clustering algorithm. Additionally, it has been found that the DIDs created in the genetic algorithm correlate with the complexity of the intensity profiles that is measured by the "fluence map complexity".
文摘Using in vitro leaves of Zizyphus jujuba ‘Kongfusucui’ plantlet as explants,effects of culture method,phytohormone proportion and culture time on induction rate of adventitious shoot from leaves and effects of sucrose concentrations in rooting media on rooting of adventitious shoot were studied.The results show that induction rate of adventitious shoot by two-step culture method(firstly cultured on medium Ⅰ for four weeks then cultured on medium Ⅱ for three weeks) is significantly higher than that by one-step culture method(cultured continuously on medium Ⅰ for seven weeks).Phytohormone proportion in medium Ⅰ has an obviously influence on induction rate of adventitious shoot,which gradually increases with increasing of TDZ concentration in medium Ⅰ.And adding 1.0 mg·L-1 TDZ in medium Ⅰ leads to induction rate with above 80%.With culture time prolonging(cultured for 1,2,3 or 4 weeks on medium Ⅰ,respectively),induction rate increases gradually.Sucrose concentration has a significant effect on rooting of adventitious shoot,sucrose with higher concentration(30 g·L-1) is beneficial to rooting.According to induction rate and growth status of adventitious shoot,it is determined that optimal culture method of adventitious shoot induction from Z.jujuba 'Kongfusucui' leaves is two-step culture method,that is,leaves firstly cultured on WPM medium containing 1.0 mg·L-1 TDZ and 0.5 mg·L-1 IAA for four weeks,and then cultured on WPM medium containing 0.5 mg·L-1 IAA and 1.0 mg·L-1 GA3 till adventitious shoot produced.
