محاسبه درصد دوز عمقي در نقاط مختلف زير يك فيلتر پله اي با استفاده از روش كلاركسون )CLARKSON( در پرتو درماني خارجي با كبالت - 60

Calculation of Percent Depth Doses at Different Points under a Step-Filter using Clarkson Method in External Radiation Therapy with60co

Objectives: Dosimetry of radiotherapy treatment beams is a very important procedure for successlui radiation therapy because it facilitates estimation ofʹ an accurate delivery of radiation dose to ,1 cancerous volume of tissue. It is believed that a decrease of 10%-15% in radiation dose delivery will result in a decrease in the chance of cure by a factor of 2 or 3. While an increase in radiation dose will increase the chance of irreversible damage. "[he aim of this study was an extension of Clarkson method for estimation of percent depth dose (PDD), in order to be able to calculate the PDD under a step-filter as wedge PDI:.) distribution. Methods: The PDDs were calculated with different step-fillers sizes: 8 x 8, 8 x 10, 8 x 12. 8 x 1 ,1, 8 14 and 8* 16 cm^2 in Cobalt-60 fields, the depths of calculations were: 5, l0, 15, 20 cm. The calculated (PDD) results of Ineasurctttents were made by use of 4-5/(PDD)4-45 and(PDD)4-10/(PDD)4-20 relationships find the related values were compared with each other. Dose measurements were carried out at water phantom by Farmer Ionisation Chamber and the related electrometer. Results: The average of the absolute values for 8 * 8 to 8 * 16 cmʹ filters were found to be 0.3861. 0.3347. 0.2381, 02416 and 0.3293 respectively. This value for all fields is equalled to 0.3059. Conclusions: The proposed formula in this study, could be used as a useful guide for measurement PDD and can he time-saving in the treatment planning of patients requiring radiotherapy.