Photon and carbon ion irradiation of a rat prostate carcinoma: does a higher fraction number increase the metastatic rate?
In a recent published study, we investigated the response of an experimental prostate carcinoma (R3327-AT1) after irradiation with 1, 2 or 6 fractions of carbon ions or photons, respectively. The original intention of this study was to measure the dose-dependent local control probability as well as the related relative biological effectiveness of carbon ions. However, we now report an increased metastatic rate when the number of fractions was increased from 2 to 6. In a total of 246 animals, the actuarial metastatic rates for 1, 2 and 6 fractions were 5.1 ± 3.5%, 5.7 ± 4.0% and 15.3 ± 7.1% for photons and 9.8 ± 7.5%, 4.0 ± 3.9% and 20.3 ± 6.5% for carbon ions, respectively. The increase was significant only for carbon ions (6 vs. 2 fractions,P = 0.03). Although the original experiment was not designed to investigate metastatic rates, this observation may be of general interest to researchers studying radiation-modulated metastatic activity.
a  Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany;
Christian P
CP
Karger
Michael
M
Scholz
Peter E
PE
Huber
Jürgen
J
Debus
Peter
P
Peschke
D000818:Animals; D002277:Carcinoma / Q000473:pathology / Q000532:radiotherapy*; D063193:Heavy Ion Radiotherapy / Q000009:adverse effects*; D006801:Humans; D008297:Male; D009362:Neoplasm Metastasis; D009374:Neoplasms, Experimental / Q000473:pathology / Q000532:radiotherapy*; D017785:Photons; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D051381:Rats