Craniospinal radiotherapy faces technical challenges which are due to the sensitivity of the location in which the gross tumor is, and to organs at risk around planning target volume. Using modern treatment planning systems causes a reduction in the complexities of the treatment techniques. The most effective method to assess the dosimetric accuracy and the validity of the software used for treatment planning is to investigate the radiotherapy and treatment planning by means of a

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... Rando phantom which was used here for treatment planning and practical dosimetry for craniospinal radiotherapy. Studying the absorbed dose by the organs at risk was the secondary objective discussed in this paper. Materials and Methods: Treatment planning in craniospinal radiotherapy was done using CorePlan 3D treatment planning software. Radiotherapy was administered on a anthropomorphic Rando phantom and practical dosimetry was done using GR-200 TLDs. Varian Clinac 2100C/D was used for radiotherapy. Results: The absorbed dose by regions of interest was separately calculated for treatment planning and radiotherapy. Except the conjunction areas of the cranial and spinal radiation fields, the difference among the results was not more than 5%. Full comparison of the results for each part has been presented. Conclusion: The comparison the results of practical dosimetry and treatment planning software supports the validity of CorePlan treatment planning system. Also analysis of the absorbed dose through organs at risk showed that the absorbed dose by organs at risk have an acceptable value with respect to tolerance dose of these organs. The only unacceptable result was related to thyroid. Iran. J. Radiat. Res., 2011; 9(3): 151­158