Intensity-modulated radiotherapy in nasopharyngeal carcinoma: dosimetric advantage over conventional plans and feasibility of dose escalation.
OBJECTIVE
To compare intensity-modulated radiotherapy (IMRT) with two-dimensional RT (2D-RT) and three-dimensional conformal radiotherapy (3D-CRT) treatment plans in different stages of nasopharyngeal carcinoma and to explore the feasibility of dose escalation in locally advanced disease.


METHODS
Three patients with different stages (T1N0M0, T2bN2M0 with retrostyloid extension, and T4N2M0) were selected, and 2D-RT, 3D-CRT, and IMRT treatment plans (66 Gy) were made for each of them and compared with respect to target coverage, normal tissue sparing, and tumor control probability/normal tissue complication probability values. In the Stage T2b and T4 patients, the IMRT 66-Gy plan was combined with a 3D-CRT 14-Gy boost plan using a 3-mm micromultileaf collimator, and the dose-volume histograms of the summed plans were compared with their corresponding 66-Gy 2D-RT plans.


RESULTS
In the dosimetric comparison of 2D-RT, 3D-CRT, and IMRT treatment plans, the T1N0M0 patient had better sparing of the parotid glands and temporomandibular joints with IMRT (dose to 50% parotid volume, 57 Gy, 50 Gy, and 31 Gy, respectively). In the T2bN2M0 patient, the dose to 95% volume of the planning target volume improved from 57.5 Gy in 2D-RT to 64.8 Gy in 3D-CRT and 68 Gy in IMRT. In the T4N2M0 patient, improvement in both target coverage and brainstem/temporal lobe sparing was seen with IMRT planning. In the dose-escalation study for locally advanced disease, IMRT 66 Gy plus 14 Gy 3D-CRT boost achieved an improvement in the therapeutic ratio by delivering a higher dose to the target while keeping the normal organs below the maximal tolerance dose.


CONCLUSIONS
IMRT is useful in treating all stages of nonmetastatic nasopharyngeal carcinoma because of its dosimetric advantages. In early-stage disease, it provides better parotid gland sparing. In locally advanced disease, IMRT offers better tumor coverage and normal organ sparing and allows room for dose escalation.
Kam
Michael K M
MK
Department of Clinical Oncology, Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong SAR, China. kamkm@yahoo.com
Chau
Ricky M C
RM
Suen
Joyce
J
Choi
Peter H K
PH
Teo
Peter M L
PM
D002277:Carcinoma / Q000473:pathology / Q000532:radiotherapy*; D015331:Cohort Studies; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D005240:Feasibility Studies; D006801:Humans; D021621:Imaging, Three-Dimensional; D015182:Lymphatic Irradiation; D009303:Nasopharyngeal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D009367:Neoplasm Staging; D020221:Optic Nerve Injuries / Q000209:etiology / Q000517:prevention & control; D010306:Parotid Gland / Q000293:injuries / Q000528:radiation effects; D011832:Radiation Injuries / Q000517:prevention & control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000009:adverse effects / Q000379:methods*; D013702:Temporal Lobe / Q000293:injuries / Q000528:radiation effects; D016896:Treatment Outcome; D014987:Xerostomia / Q000209:etiology