The dosimetric comparison of the radiotherapeutic plans between composite and synchronous planning approaches in sequential IMRT for nasopharyngeal carcinoma

The aim of present study was to compare the dosimetric differences of the radiotherapeutic plans between synchronous and composite planning approaches in sequential intensity-modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC). Twelve patients with NPC treated by sequential IMRT were enrolled. Two planning approaches were used to design sequential IMRT plan. The first was composite planning approach, in which the initial and boost plans were designed and optimized independently. The second was synchronous planning approach, in which the boost IMRT plan was designed on foundation of the initial IMRT plan, and its optimization would be adjusted based on dose distributions of the initial IMRT plan. Dosimetric comparisons in IMRT plans between composite and synchronous planning approaches were analyzed to evaluate (1) dose coverage, conformity, and homogeneity of the planning target volume (PTV), (2) sparing of organs at risk (OARs), and (3) the number of segments and monitor units (MUs). The results showed that both of the summed plans for the entire treatment course were achieved according to the original planning goals, and the dose coverage, conformity and homogeneity for each PTV was similar. With regard to sparing brain stem, spinal cord and parotid glands, there was no significant difference in the summed plans between two planning approaches. However, the boost IMRT plan by composite planning approach tended to have a higher dose coverage (P = 0.000), conformity (P = 0.000), and homogeneity (P = 0.000) than that of the plan by synchronous planning approach. Moreover, the boost plan by composite planning approach reduced the MUs significantly (P = 0.000). The results indicated that the radiotherapeutic plan by composite planning approach provides better dose coverage, conformity and homogeneity for the PTV in the boost plan than that by synchronous planning approach, and reduced MUs in sequential intensity modulated radiotherapy.