title: Changes of the transverse diameter and volume and dosimetry before the 25th fraction during the course of intensity-modulated radiation therapy (IMRT) for patients with nasopharyngeal carcinoma.
abstract: To quantify changes of the transverse diameter and volume and dosimetry, and to illustrate the inferiority of non-replanning during intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) patients. Fifty-three NPC patients who received IMRT in 33 fractions were enrolled in this prospective trial. Before the 25th fraction, a new simulation computed tomography (CT) scan was acquired for all patients. The dose-volume histograms of the phantom plan were compared with the initial plan. Significant reduction of the transverse diameter of the nasopharyngeal, the neck, and 2 parotid glands volume was observed on second CT compared with the first CT (mean reduction 7.48 ± 4.45 mm, 6.80 ± 15.14 mm, 5.70 ± 6.26 mL, and 5.04 ± 5.85 mL, respectively; p < 0.01). The maximum dose and V-40 of the spinal cord, mean dose, and V30 of the left and right parotid, and V-50 of the brain stem were increased significantly in the phantom plan compared with the initial plan (mean increase 4.75 ± 5.55 Gy, 7.18 ± 10.07%, 4.51 ± 8.55 Gy, 6.59 ± 17.82%, 5.33 ± 8.55 Gy, 11.68 ± 17.11% and 1.48 ± 3.67%, respectively; p < 0.01). On the basis of dose constraint criterion in the RTOG0225 protocol, the dose of the normal critical structures for 52.83% (28/53) of the phantom plans were out of limit compared with 1.89% (1/53) of the initial plans (p < 0.0001). Because of the significant change in anatomy and dose before the 25th fraction during IMRT, replanning should be necessary during IMRT with NPC.
authors.affiliation: Department of Radiation Oncology, Taizhou Hospital, Wenzhou Medical College, Taizhou, Zhejiang, China.
authors.forename: Haihua
authors.initials: H
authors.lastname: Yang
authors.forename: Wei
authors.initials: W
authors.lastname: Hu
authors.forename: Weijun
authors.initials: W
authors.lastname: Ding
authors.forename: Guoping
authors.initials: G
authors.lastname: Shan
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Changhui
authors.initials: C
authors.lastname: Yu
authors.forename: Biyun
authors.initials: B
authors.lastname: Wang
authors.forename: Minghai
authors.initials: M
authors.lastname: Shao
authors.forename: Jianhua
authors.initials: J
authors.lastname: Wang
authors.forename: Weifang
authors.initials: W
authors.lastname: Yang
mesh_terms: D000328:Adult; D000368:Aged; D002277:Carcinoma / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D009305:Nasopharynx / Q000528:radiation effects*; D009333:Neck / Q000528:radiation effects; D009929:Organ Size / Q000528:radiation effects; D010306:Parotid Gland / Q000528:radiation effects; D011446:Prospective Studies; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated