Comparing two radiotherapy techniques of whole central nervous system tumors, considering tumor and critical organs' dose provided by treatment planning system and direct measurement

Aims: In central nervous system (CNS) tumors, surgery combined with radiotherapy may cure many tumors. The basic technique in conventional radiotherapy is craniospinal radiotherapy; in this technique, spinal cord can be treated with electron or photon beams. This study was aimed to compare two radiotherapy techniques in craniospinal radiotherapy, (a) treatment of spine with a single photon beam and (b) with a combination of photon and electron beams. Materials and Methods: The two techniques were planned. In the first technique, both brain and spine were irradiated with 6 MV photon beams. In the second technique, brain was irradiated with 6 MV photon and spine with 18 MeV electron beams. To compensate the dose deficiency in lumbar area, an anterior field of 15 MV photon beam was also applied in the second technique. The dose to target volume and organ at risks (OARs) were measured by thermoluminescent dosimeter and compared with the corresponding values calculated by Isogray treatment planning system. Results: OARs including heart, mandible, thyroid, and lungs received lower dose from technique 2 compared with technique 1; kidneys were exceptions which received higher dose in the technique 2. Conclusions: The dose to thyroid, mandible, heart, and lungs were lower in technique 2, while kidneys received higher dose in technique 2. This was caused by using the anterior 15 MV photon beam. Based on these results, for children, instead of photon beam for treatment of spinal cord, it is wiser to use electron beam.