Intensity-modulated radiotherapy versus conventional three-dimensional conformal radiotherapy for boost or salvage treatment of nasopharyngeal carcinoma

Purpose: To compare intensity-modulated radiotherapy (IMRT) and conventional three-dimensional conformal radiotherapy (3D-CRT) for the boost treatment of new-onset nasopharyngeal carcinoma (NPC) or the salvage treatment of locally recurrent NPC. Methods and Materials: Between January 14 and February 23, 2000, 5-field 3D-CRT treatment plans were generated for 14 consecutive NPC patients using the ADAC Pinnacle planning system in Chang Gung Memorial Hospital, Kaohsiung, Taiwan. The planning data of these patients were later transferred to Memorial Sloan-Kettering Cancer Center, where new IMRT plans, also using 5–7 radiation fields were created for each patient using an inverse treatment planning system. The IMRT and 3D-CRT plans were compared for all 14 patients. The relationship between the anatomic shapes and locations of targets and the results of different plans were studied. Results: Target doses were more homogeneous in IMRT plans. The average maximal brainstem dose (D 05 , the dose received by 5% of the brainstem volume) decreased from 30.9% of the prescription dose with 3D-CRT to 15.3% and 14.7% with 5- and 7-field IMRT, respectively ( p = 0.004 and 0.003, respectively, compared with 3D-CRT, paired Student's t test). Five anatomic factors were found that predicted greater benefits with IMRT. These factors were ( 1 ) vertical length of target >7 cm, ( 2 ) minimal distance between target and brainstem 3 ) maximal AP overlap of target and brainstem >0.6 cm, ( 4 ) maximal AP overlap of target and spinal cord >1 cm, and ( 5 ) vertical overlap of target and eyes >0 cm. For the 7 patients with at least 1 of these 5 anatomic factors, the benefits achieved by IMRT planning would have been greater than the benefits for the other 7 patients ( p = 0.005, Fisher's exact test). Conclusion: For boost or salvage treatment of NPC, lower normal tissue doses and more homogeneous target doses were achieved with IMRT plans. For NPC patients with at least 1 of the 5 anatomic factors, IMRT is highly recommended.