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Comparison of Conventional Radiotherapy Techniques with Different Energies in Treating Prostate Cancer, Employing a Designed Pelvis Phantom

Keywords: Prostate cancer , conventional radiotherapy , dosimetry , linac , TLD

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Abstract:

The aim of this study is to determine and compare the dosimetric consequences of prostate and normal structures (rectum, bladder and right femoral heads) in pelvis region using different conventional radiotherapy techniques 4-field (box), 3-field with one anterior and two oblique 115 and 245 ° fields and anterior-posterior technique) with two different energies of 9 and 18 MV. In this study two high-energy linear accelerators (Neptun 10 and Saturn 20) located in Seyed-Alshohada hospital in Isfahan were used. An anthropomorphic pelvic phantom was designed and fabricated for dosimetry applications based on the pelvic CT images of an adult patient with an average size of prostate cancer patients referring to the medical center. Measurements of the organ doses was performed in phantom using TLD (TLD-100) dosimeters, which was suited at different depth especially in prostate, rectum, bladder and femur head. After drawing the fields on the phantom, the photon beam at a dose of 200 cGy with various levels of photon energy (9 and 18 MV) were used. One way ANOVA test was used to data analysis. The measured percentage depth dose (DD%) in 4-field technique using photon 9 MV to the prostate, rectum, bladder and right femoral heads were 94.8, 85.71, 77.51 and 65.81%, respectively and using 18 MV photon beam they were 95.81, 86.73, 77.5 and 63.45%, respectively. The amount of DD%, in the 3-field technique with 9 MV photon, to the prostate, rectum, bladder and right femoral heads was found to be 91.7, 78.83, 93.4 and 63.25%, respectively and 92.38, 79.05, 93.31 and 62.05% when 18 MV photon beam were used. Using the 9 MV photon beam in AP-PA technique, prostate, rectum, bladder and right femoral heads received 96.23, 96.77, 96.3 and 28.77% of prescribed doses, while with 18 MV photon radiation they were 95.77, 96.91, 95.82 and 26.69%, respectively. Differences among the techniques have been found for all of four considered organs with total prescribed dose of 60 Gy and there was no significant difference among all considered techniques. Technique 3-filed give the best sparing of the rectum; the bladder is better spared with technique box and the best technique for sparing the femoral head is AP-PA. Differences between energies were low and using 18 MV photons give the more satisfied results.

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