Assessment of developed IMRT and 3D-CRT planning protocols for treating nasopharyngeal cancer patients based on the target and organs at risks common volumes

Background : Various developed intensity modulated radiation therapy (IMRT) and a three dimensional conformal radiation therapy (3D - CRT) protocols were assessed for treating nasopharyngeal cancer (NPC) based on radiobiological parameters. Materials and Methods : Treatment plans were made for 30 NPC patients using 15 developed IMRT and 3D - CRT protocols. The IMRT protocols comprised of three 7 - fields with various collimator (0°, 5°, and 10°) and couch (0°, 4°, 8°, 12°) angles. The 3D - CRT technique included two phases. In the 1st phase a dose of 60 Gy was prescribed to the total PTV, but in the 2nd phase a dose of 10 Gy was prescribed to the PTV - 70. The tumour control probability (TCP), normal tissues complication probability (NTCP), and complication - free tumor control probability (P+) parameters were estimated for assessing the IMRT protocols. Then, the ideal protocol (s) were proposed through comparing the IMRT protocols with each other and 3D - CRT protocol based on TCP, NTCP, and P+ values. Results : The IMRT protocol with 10° collimator and 8° couch angles had the lowest NTCP mean values. Significant differences were observed among the mean NTCP values for the brainstem and parotid glands, and P+ of the developed IMRT and 3D - CRT protocols. However, no significant differences were observed among the mean NTCP values for the spinal cord, optic chiasm and optic nerves among the protocols. Conclusions : The 3D - CRT protocol had a good outcome for the NPC patients having a lower common volume between their total planning target volume and OARs, while the results of the IMRT showed the opposite .