To investigate the feasibility and benefits of target re-delineation and dose prescription for adaptive replanned radiotherapy in nasopharyngeal carcinoma (NPC) patients who underwent intensity-modulated radiotherapy (IMRT).
Fifty-four consecutive NPC patients who underwent IMRT were enrolled in this study. The replanning CT (CT-II) for each patient was generated at the 22nd fraction of the IMRT. In Plan-I, GTVnx-I was defined as all detected gross disease. The high-risk clinical target volume (CTV1-I), as subclinical disease consisting of a 1-cm margin surrounding the GTVnx-I. The low-risk clinical target volume (CTV2), as a 0.5- to 1.0-cm margin surrounding the CTV1-I. In Plan-II, the GTVnx-II, as all detected gross disease detected after 22 fractions. CTV1-II maintained the extent of the originally irradiated CTV1-I, including the area in which the tumor disappeared/dissolved after 22 fractions. The CTV2 was not delineated. The doses prescribed were as follows: Plan-I: PGTVnx/rpn/nd 53-54 Gy/25 F; PCTV1/nd 47.5-48 Gy/25 F; PCTV2 45 Gy/25 F; and Plan-II: PGTVnx/rpn/nd: 15-15.5 Gy/7 F; PCTV1/nd 13.5 Gy/7 F. The parameters were compared. Clinical outcomes and toxicities were evaluated.
The median reductions in the GTVnx, GTVnd-R, bilateral parotids and bilateral submandibular glands were 25.07%, 38.17%, 23.43% (left), 21.12% (right), 23.37% (left) and 23.00% (right) (P < 0.05), respectively; bilateral RPLN and GTVnd-L exhibited median reductions of 22.50% (left), 25.00% (right), and 32.80% (P > 0.05), respectively. The average V95% of PGTVnx reached nearly 100% in the two plans. Plan-II significantly reduced the Dmean% in the optic chiasma, thyroid gland, hypopharynx, spinal cord, brain stem, pituitary, oropharynx and oral cavity compared with Plan-A (P < 0.05). Recurrence did not occur in the regression area, and the acute reactions were mild. The 3-year OS/LRFFS/DMFS rates were 93.3%/90.5%/91.4%, respectively.
Adaptive replanned IMRT in NPC provided a new perspective for target re-delineation and dose prescription. The results of this study showed significant dosimetric and clinical benefits without recurrence and reducing survival.
Clinical trial identification
Legal entity responsible for the study
Sun Yat-sen University Cancer Center.
Has not received any funding.
The author has declared no conflicts of interest.