[Postoperative external radiotherapy of differentiated thyroid carcinoma: when is radioiodine therapy alone inadequate? The dosimetric considerations with a Monte Carlo simulation].
Indication for postoperative external radiation of differentiated thyroid cancer has remained an issue of controversial discussion and is generally restricted to those cases where local tumor control by I-131 therapy alone seems doubtful. This may be the case when lymph node metastases are present or occult micrometastasis are suspected, as the beta(-)-radiation caused by the incorporated I-131 may be deposited partly outside the tumor. This problem of dose distribution is analysed in a simulation model by Monte Carlo techniques where tumors are tissue equivalent spheres of various size (r = 20 microns to 2 cm). Homogeneous I-131 distribution in the whole tumor volume (a) is analysed as well as peripheral deposition confined to the tumour surface (b). In tumors of r = 0.5 mm or less, the percentage of the total dose deposited inside the tumor rapidly decreases, r = 20 microns: 4.1% (a) and 0.9% (b), respectively. Furthermore, extensive dose inhomogeneities appear in tumors of similar sizes. As in local lymph node metastases tumoricidal radiation doses are not necessarily achievable by I-131 therapy alone, postoperative external radiation should be taken into account in the above mentioned clinical situations.
Sautter-Bihl
M L
ML
Klinik für Strahlentherapie und Nuklearmedizin, Städtisches Klinikum Karlsruhe.
Herbold
G
G
Heinze
H G
HG
Bihl
H
H
D003131:Combined Modality Therapy; D003198:Computer Simulation; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008207:Lymphatic Metastasis; D008954:Models, Biological; D009010:Monte Carlo Method; D011182:Postoperative Care; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D013964:Thyroid Neoplasms / Q000532:radiotherapy*
D007457:Iodine Radioisotopes
Postoperative externe Radiotherapie des differenzierten Schilddrüsenkarzinoms: wann ist eine alleinige Radiojodtherapie unzureichend? Dosimetrische Uberlegungen anhand einer Monte-Carlo-Simulation.