Razi Journal of Medical Sciences

Background and Aim: Increased mortality rate�due to prostate cancer shows the growth of this disease.Prostate cancer is the second most widespread malignancy after lung cancer in men.It is important to use new methods in the radiation therapy of prostate cancer that are associated with lower exposure of the normal tissues. Nowadays, in most of the radiotherapy centers in our country, the Co-60 Unit with 2-dimensional treatment planning system is used for radiotherapy of prostate cancer. Therefore, it is essential to evaluate and verify the absorbed dose in the�critical organs such as bladder and rectum to prevent the side effects.In this study, the absorbed dose by these organs was measured in the process of radiotherapy of prostate cancer.

Materials and Methods: In this experimental study the received dose by rectum and bladder, in the 2-dimensional treatment planning for radiotherapy of prostate cancer, was measured on tissue-equivalent and anthropomorphic phantom using Thermoluminescent dosimeters (TLD-100). The results were compared with the calculated values in the treatment planning software by t-test statistical method. One-sample Kolmogorov-Smirnov was also used for data analysis. SPSS V.15 was used for data evluation.

Results: The measured values of the absorbed dose by bladder and rectum were 236.8±14.9 cGy and 257.3±17.5 cGy, respectively. Results showed the measured absorbed doses in the phantom were significantly higher than estimated values (bladder: 162.4±2.2 cGy and rectum: 158.9±2.4 cGy)than from the treatment planning software (p <0.05).

Conclusion: As the results show, the absorbed doses of bladder and rectum are higher than the calculated values by the software. In practice in the 2D treatment planning, one slice of CT-scan image is used for drawing.Meanwhile the tissue inhomogeneties in the body are 3-dimensional therefore the calculated volume of the target and organs at risk will be unprecise. This will lead to uncertainty in the calculation of the absorbed dose. In addition the effect of scattering due to tissue inhomogenities is added to this uncertainty.Thus, when using the�2D treatment planning, it is recommended to remember that the absorbed doses of bladder and rectum are significantly higher than those calculated on software.