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 degrees, 5 degrees, and 10 degrees) and couch (0 degrees, 4 degrees, 8 degrees, 12 degrees) 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 degrees collimator and 8 degrees 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.

Automated summary

This study evaluated the effectiveness of various IMRT and 3D-CRT protocols for the treatment of nasopharyngeal cancer. The results showed that the IMRT protocol with a collimator angle of 10 degrees and a couch angle of 8 degrees had the lowest normal tissue complication probability, while the 3D-CRT protocol performed better in patients with a lower common volume between the total planning target volume and organs at risk.