[Presentation of a 3D conformal radiotherapy technique for head-and-neck tumors resulting in substantial protection of the parotid glands].
OBJECTIVE
The aim of this study was to improve the irradiation technique for the treatment of head-and-neck tumors and, in particular, to make use of the advantages found in modern 3D planning to protect the parotid glands.


METHODS
For this investigation the 3D dataset of a standard patient with oropharyngeal carcinoma of UICC stage IVA was used. In the CT scans (slice thickness 5 mm) the planning target volume (PTV), the boost volume and both parotids were delineated. Three different techniques were calculated for two different dose levels (50 Gy for PTV and 64 Gy for boost volume, using single doses of 2 Gy). For technique 1 (T1) a parallel opposed field photon/electron irradiation was designed, for technique 2 (T2) an opposed/arc field irradiation was employed, and for technique 3 (T3) a combination of a static coplanar and arc field irradiation was designed. The sum doses D(min), D(max) and D(mean) for PTV, boost volume, and ipsilateral and contralateral parotid gland were evaluated, and the time needed for calculation of the plans was also determined.


RESULTS
For all techniques used, the calculated doses in the PTV (D(min) 5.6 +/- 0.1 Gy, D(max) 73.7 +/- 0.1 Gy, and D(mean) 57.9 +/- 0.5 Gy) and in the boost volume (D(min) 46.9 +/- 1.5 Gy, D(max) 73.8 +/- 0.12 Gy, and D(mean) 65.8 +/- 0.9 Gy) were equal. Significant differences were found regarding the three different techniques, e.g., for the ipsilateral parotid gland D(min) (T1 = 47.4, T2 = 50.6, and T3 = 38.4 Gy) as well as for the contralateral parotid gland D(min) (T1 = 42.1, T2 = 44.2, and T3 = 17.8 Gy) and D(mean) (T1 = 51.3, T2 = 52.8, and T3 = 32.6 Gy). Regarding the three different techniques, significant differences were found in favor of T3. The determined planning times were as follows: T1 = 90, T2 = 60, and T3 = 90 min.


CONCLUSIONS
The combination of static coplanar and arc field technique (T3) resulted in a substantially better protection as compared to both other techniques. This was especially the case with regard to the contralateral parotid gland, when the dose distributions were calculated equally for PTV and boost volume. In this study, the D(mean) dose of the contralateral parotid gland was lower than the TD(50) of 37 Gy (95% confidence interval 32-43 Gy) previously assumed by the authors. Therefore, it can be concluded that in the present study a more intensive protection of this gland and a reduction in xerostomia were possibly obtained.
Kuhnt
Thomas
T
Universitätsklinik und Poliklinik für Strahlentherapie, Martin-Luther-Universität Halle-Wittenberg, Halle-Wittenberg. thomas.kuhnt@medizin.uni-halle.de
Janich
Martin
M
Götz
Uwe
U
Gerlach
Reinhard
R
Chiricuta
Ion Christian
IC
Hänsgen
Gabriele
G
D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D010305:Parotid Diseases / Q000209:etiology / Q000517:prevention & control*; D011832:Radiation Injuries / Q000209:etiology / Q000517:prevention & control*; D011835:Radiation Protection / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000009:adverse effects* / Q000379:methods*; D016896:Treatment Outcome