A treatment planning analysis of inverse-planned and forward-planned intensity-modulated radiation therapy in nasopharyngeal carcinoma.
OBJECTIVE
To compare dose-volume histograms of target volumes and organs at risk in 57 patients with nasopharyngeal carcinoma (NPC) with inverse- (IP) or forward-planned (FP) intensity-modulated radiation treatment (IMRT).


METHODS
The DVHs of 57 patients with NPC with IMRT with or without chemotherapy were reviewed. Thirty-one patients underwent IP IMRT, and 26 patients underwent FP IMRT. Treatment goals were to prescribe a minimum dose of 66-70 Gy for gross tumor volume and 59.4 Gy for planning target volume to greater than 95% of the volume. Multiple selected end points were used to compare dose-volume histograms of the targets, including minimum, mean, and maximum doses; percentage of target volume receiving less than 90% (1-V90%), less than 95% (1-V95%), and greater than 105% (1-V105%). Dose-volume histograms of organs at risk were evaluated with characteristic end points.


RESULTS
Both planning methods provided excellent target coverage with no statistically significant differences found, although a trend was suggested in favor of improved target coverage with IP IMRT in patients with T3/T4 NPC (p = 0.10). Overall, IP IMRT statistically decreased the dose to the parotid gland, temporomandibular joint, brain stem, and spinal cord overall, whereas IP led to a dose decrease to the middle/inner ear in only the T1/T2 subgroup.


CONCLUSIONS
Use of IP and FP IMRT can lead to good target coverage while maintaining critical structures within tolerance. The IP IMRT selectively spared these critical organs to a greater degree and should be considered the standard of treatment in patients with NPC, particularly those with T3/T4. The FP IMRT is an effective second option in centers with limited IP IMRT capacity. As a modification of conformal techniques, the human/departmental resources to incorporate FP-IMRT should be nominal.
Department of Radiation Oncology, Toronto-Sunnybrook Regional Cancer Centre, University of Toronto, Toronto, Ontario, Canada. ian.poon@sunnybrook.ca
Ian
I
Poon
Ping
P
Xia
Vivien
V
Weinberg
Khalil
K
Sultanem
Clayton
C
Akazawa
Pamela
P
Akazawa
Lynn
L
Verhey
Jeanne Marie
JM
Quivey
Nancy
N
Lee
D000704:Analysis of Variance; D001933:Brain Stem; D002277:Carcinoma / Q000473:pathology / Q000532:radiotherapy; D007758:Ear, Inner; D004432:Ear, Middle; D006801:Humans; D015182:Lymphatic Irradiation; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D009367:Neoplasm Staging; D009900:Optic Nerve; D010306:Parotid Gland; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013116:Spinal Cord; D013704:Temporomandibular Joint; D047368:Tumor Burden