Comparison of two different IMRT planning techniques in the treatment of nasopharyngeal carcinoma
Radiotherapy Planning, Computer-Assisted
Nasopharyngeal Neoplasms
Cone-Beam Computed Tomography
Radiation Dosage
Xerostomia
3. Good health
03 medical and health sciences
0302 clinical medicine
Spinal Cord
Lymphatic Metastasis
Humans
Parotid Gland
Computer Simulation
Dose Fractionation, Radiation
Lymph Nodes
Prospective Studies
Radiotherapy, Intensity-Modulated
Radiation Injuries
Brain Stem
DOI:
10.1007/s00066-013-0344-z
Publication Date:
2013-06-07T06:58:44Z
AUTHORS (4)
ABSTRACT
To compare the effect of two different intensity-modulated radiation therapy (IMRT) planning techniques on parotid gland doses in patients with nasopharyngeal carcinoma (NPC).Radiotherapy for 10 NPC patients referred to the University of Istanbul Cerrahpasa Medical School was planned with arc- and static seven-field IMRT. The simultaneous integrated boost (SIB) technique was used to deliver 70 Gy (2.12 Gy per fraction) to the primary tumor and involved nodes; 60 Gy (1.81 Gy per fraction) to the entire nasopharynx and 54 Gy (1.63 Gy per fraction) to elective lymph nodes in 33 fractions. Plans also aimed to keep the mean parotid dose below 26 Gy and limit the maximum doses to the spinal cord and brain stem to 45 and 54 Gy, respectively. Mean parotid gland doses for the two planning techniques were compared using a paired t-test. Target coverage and dose inhomogeneity were evaluated by calculating conformity- (CI) and homogeneity index (HI) values.Target coverage and dose homogeneity were identical and good for both planning techniques: CI = 1.05 ± 0.08 and 1.05 ± 0.08; HI = 1.08 ± 0.02 and 1.07 ± 0.01 for arc- and static field IMRT, respectively. Mean doses to contralateral parotid glands were 25.73 ± 4.27 and 27.73 ± 3.5 Gy(p = 0.008) for arc- and static field IMRT plans, respectively, whereas mean ipsilateral parotid doses were 30.65 ± 6.25 and 32.55 ± 5.93 Gy (non-significant p-value), respectively. Mean monitor units (MU) per fraction for the 10 patients were considerably lower for arc- than for static field treatments-540.5 ± 130.39 versus 1288.4 ± 197.28 (p < 0.001).Normal tissues--particularly the parotid glands--are better spared with the arc technique in patients with NPC. MU and treatment times are considerably reduced in arc IMRT plans.
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