الفهرس 
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Abstract
There are more than 200 types of human cancer, each with different causes, symptoms and treatments. In general, cancer is predominantly an environmental disease with 90-95% of cases being attributed to lifestyle factors, and 5-10% due to genetics (Anand P, et al, 2008).
While cancer can affect people of all ages the overall risk of developing cancer generally increases with age, at least up to age 80-85 yrs. Cancer is the major cause of leading deaths in the 21st century in world with 14.1 million cases and 8.2 million deaths occurred in 2012. These rates are rising as more people live to an old age and as lifestyle changes occur in the developing world (Jemal A, et al, 2010).
Prostate cancer is the second most common form of cancer and the fifth leading cause of cancer death among males. The prostate cancer causes death for men over fifty years of age. Most of the deaths from prostate cancer are related to advanced disease that can be prevented with better screening practices. Among the different technologies adopted to cure the prostate cancer; external radiotherapy is recognized as one of the important treatment option (Ferlay J, et al, 2015)
The radiotherapy techniques in the treatment of prostate cancer vary in different institutions, but, in general, the issue of radiation dose delivery to the organs around prostate or to the prostate remains complex (Pollack A, et al, 2002).
The greatest challenge for radiation therapy or any cancer therapy is to attain the highest probability of cure with the least morbidity. The simplest way in theory to increase this therapeutic ratio with radiation is to encompass all cancer cells with sufficient doses of radiation during each fraction, while simultaneously sparing surrounding normal tissues. The ongoing pursuit to achieve an optimal dose distribution has prompted the radiation therapy profession to develop new technique that incorporate advance in technology. In radiation therapy today, modern technique such as the volumetric modulated arc therapy (VMAT) is routinely used in the treatment of cancers (Garibaldi C, et al, 2017).
Accordingly, the current study was conducted aiming to compare between two different radiotherapy techniques: VMAT FF and VMAT FFF in achieving homogenous radiation dose distribution to the tumor while maintaining lower doses to organs at risk in patients with prostate cancer.
This study includes 30 prostate cancer patients divided into two groups. GroupI: included 15 patients treated with VMAT FF. group II:included 15 patients treated with VMATF FF. There two radiotherapy treatment planning techniques were carried out to achieve an optimum plan for specific target and organ at risk. These techniques were designed using VMAT treatment planning system in 10 Megavolt Energy, at El- Hussein Hospital, Cairo, Egypt.
The results of the current study showed that,for the treatment of planning target volume (PTV), the median doses received by PTV of prostate cancer in case of FF plan versus FFF plan.The median doses received by PTV D95% were significantly higher in FFF plan than in FF plan.
In the present study, regarding the volumes % of PTV covered with 95% of the total prescribed dose in VMAT technique,the volume % of PTV covered with 95% was greater in VMAT 10Mev FFF than VMAT 10Mev FF technique.
The better plan should achieve better and homogeneous dose distribution to the PTV. The minimum and maximum acceptable radiation doses to the PTV should be (95% - 107%) which is achieved by VMAT 10Mev FFF. Thus, we can demonstrate that the dose coverage to the PTV was better in VMAT 10Mev FFF plan than VMAT 10Mev FF plan.
For Organs at Risk, with respect to dosimetric parameters for organs at risk, the comparison of VMAT 10Mev FF plan with VMAT 10Mev FFF plan showed that, the median doses delivered to bladder, rectum, the bowel, the head of right femur and the head of left femur irradiated with VMAT 10Mev FF were higher than that for VMAT 10Mev FFF plan. But those doses were still within the dose tolerance of the prostate Cancer Organs at Risk.
The main aim of radiotherapy planning techniques is to achieve a good dose coverage to the treatment target and at the same time spare the organs at risk (which are near or closed to the treatment target) from exposure to radiation doses more than the maximum acceptable values which can be considered acomplex equation. The better technique should achieve that complex equation. Despite of being the OARs received higher doses in VMAT 10Mev FF than in VMAT 10Mev FFF, they were within dose tolerance for every organ and also VMAT 10Mev FFF achieved better dose coverage to the treatment target than VMAT 10Mev FF plan.