| After the electron beam generated by electron accelerator enters the body surface, most of its energy would be absorbed by the superficial region. It is suitable for exterminating superficial tumour cells in the superficial region . As far as breast cancer is concerned, electron beam irradiation can not only kill remaining tumour cell s in tumour region but also prevent recrudesce. However, after long-term clinical application we find that enough dose of irridiation reaching skin and endermic is need when we treat breast cancer patients with electron beam irradiation . Therefore bolus which is a kind of compensative material appendant to precautionary therapy is used when we treat breast cancer chest wall with electron beam irradiation. Appropriate thickness bolus can decrease the irradiation dose of lung former and can also increase the irradiation dose of skin , at the same time the goal that the whole target region will be well treated can be met, therefore bolus can help to increase chest wall local restraining rate and decrease the recrudescent rate, it reduces the occurring of radioactivity pneumonia. Withal. Paraffin, polystyrene and organic glass and other materials have been used as boluses. They can provide the following compensative effects:(1) to compensate the irregular clay silhouette. (2) to regulate the dose distribution of electron beam. (3)to heighten the skin and infra-skin dose. In this experiment we measure and analyze the dose which is generated when different energy electron beam irradiates different thickness bolus. We provide dose experimental data for application of bolus which is produced in the duration of treating the patients after mastectomy with radiotherapy, so it will provide dose foundation to clinical optimization therapy project . In this study standard manikins provided by keyi & company Ltd. was used .To detect the effects of different thickness of bolus , we simulated clinical radiotherapy surrounding, measured and calculated the radiation dose of the manikins skin surface,chest wall and lung surface... In this experiment the instrument of FJ-427A TLD , LiF(Mg,Cu,P)TLD and TLD measure instrument were used. The instrument of wa-li-an 23EX medical electron accelerator is used in this experiment. Field size is 25.0cm×25.0cm.Source-skin Distance (SSD) is 100cm. The extent of the analog coverage field: Upper terminal line: the first rib inferior border lacteal. Lower terminal line: below the level of the opposite breast crease place 2cm. Left: terminal line:midaxillary line. Right:midline. Appending 0.5cm bolus,1.0cm bolus and no-bolus respectively the manikins coverage field was irradiated by 9MeV and 6MeV electron beam, There are three arrays and six times totally. From the dose distribution of the 6MeV electron beam irradiating lung,we may see that the lung was under the electron beam radiation with the same energy (6MeV) the dose is higher without bolus as compared with the treatment of bolus , and the irradiating dose gradient is broader and uneven,; Along with the increase of bolus thickness, the radiating dose ofthe lung reduces. Bolus protected the lung ,so it might reduce the Radiation pneumonitis'occurrence. From the dose distribution of the 9MeV electron beam irradiates lung,we may see when the lung was under the electron beam radiation with the same energy (9MeV), which is no bolus compared to with it , the dose is higher. Along with increasing of bolus thickness, the radiating dose of the lung received reduces. It has protected the lung , so it might reduce the radiation pneumonia's occurrence. The electron beam exists the dose built-up region, 6MeV built-up depth is 1.5cm; 9MeV built-up depth is 2.3cm. With the increase of electron beam energy, the depth of penetration increased and the largest dose depth increased, and high dose field widened. When electron beam energy is identical (6MeV), in the term of appending the bolus with the different thickness, high dose field position of chest wall is different, the highest dose depth moving towards the surface. The center high dose field migrates to the surface after adding bolus. The more bolus thickness increased,the more the dose built-up field moves towards the surface. When 6MeV electron beam was used, the skin surface dose increased and the chest wall irradiated dosage reduced along with the bolus thickness increasing gradually; The average irradiated dose of the lung also reduced with the increasing of bolus thickness. When 9MeV electron beam was used, the skin surface and the chest wall dose increases gradually, the average irradiated dose of the lung also reduces with the increasing of bolus thickness. These experimental data demonstrated fully , that the...
|
PDF Full Text Request