Evaluation of treatment planning results using helical tomotherapy, vmat and three-dimensional conformal radiotherapy techniques in pediatric craniospinal irradiation depending on physical and biological parameters

Radiotherapy plays an important role in the treatment of medulloblastomas, the most common childhood cancer. With modern radiotherapy techniques, the main purpose of radiotherapy treatment today is to keep the morbidity and mortality rates at the lowest level while providing long-term disease control. For this reason, the late morbidity and the possibility of secondary cancer caused by radiation should be taken into account when determining the indications related to radiotherapy, and the highest level of care should be taken in the selection and application of the ideal treatment plan. In this study, in the comparison of craniospinal radiotherapy plans using tomotherapy, volumetric arc therapy (VMAT) and three-dimensional conformal radiotherapy (3D-CRT) planning techniques, it was aimed to draw attention to the evaluation of the treatment plan based on biological parameters in order to evaluate the secondary cancer risks and side effects apart from the conventional physical evaluations. For this study, tomotherapy, VMAT and 3D-CRT plans were prepared based on computed tomography images of 10 pediatric patients who were diagnosed with medulloblastoma and received radiotherapy. Standard risk medulloblastoma treatment doses were used as the treatment dose. When comparing treatment plans, the dosimetric parameter results of PTV, critical organ doses, homogeneity index (HI), conformity index (CI) criteria were cosidered. Normal tissue complication probability (NTCP) was calculated for the estimation of long-term complication probabilities from biological parameters. When the planning results based on physical parameters were examined, it was seen that Tomotherapy plans were superior in dosimetric results. Tomotherapy plans in HI results and VMAT plans in CI results were found to be closer to the expected criteria. It was observed that there are advantages and disadvantages among planning techniques in the protection of critical organs. In the NTCP results, it was concluded that with modern radiotherapy techniques, especially the thyroid, lenses, heart and cochlea were better protected, and accordingly, the possibility of complications was lower. In this thesis, it was seen that the treatment techniques had advantages and disadvantages compared to each other in the comparisons based on physical and biological parameters. As a result, long-term cardiac problems can be prevented by reducing the heart mean doses with modern radiotherapy techniques in pediatric patients with craniospinal irradiation who are expected to survive for a long time, and the possibility of complications related to the occurrence of secondary thyroid cancers, hypothyroidism and hyperthyroidism can be prevented by lowering the thyroid dose. In the case of high survival rates and long life expectancy, the selection of effective treatment modalities with less side effects in the treatment of childhood cancers, medulloblastoma is very important. Keywords: Medulloblastoma, Craniospinal radiotherapy, Tomotherapy, VMAT, 3D-CRT, Plan evaluation