Optimization and it's influence on value of doses in HDR and PDR brachytherapy.

The aim of this work is to examine the influence of the dose optimization procedure on the value of radiation doses in organs of risk and to compare value of doses measured in healthy tissues according to chosen different PDR brachytherapy (PDRBT) and HDR brachytherapy (HDRBT) fractionation schedule. Fifty one patients treated with PDRBT were qualified for calculations. This group included patients with head and neck cancer, brain tumor, breast cancer, sarcoma, penile cancer and rectal cancer. The doses were calculated in chosen critical points in surrounded healthy tissues. For all treatment plans the doses were compared with the use of the BED (Biologically Equivalent Dose) formula and PDR along with HDR values were calculated. Differences among total doses in PDRBT and different schemas of HDRBT in critical points before and after dose point and volume optimization, were analyzed. The same dependences were examined also for BEDs. One ascertained that in biologic equivalent (to PDR) HDRBT the increase of fraction dose from 4 Gy to 10 Gy caused the necessity of decrease of total dose in treatment area (p<0,001). The use of HDR instead of PDR essentially lowered physical and biological doses in examined organs of risk. In many examined critical points in organs of risk where biological equivalence dose in the treatment area was the same, one ascertained the decrease of total physical HDR dose according to the growth of the fraction dose. Similar dependences appeared also for biologically equivalent doses. The optimization process in PDRBT improved the dose homogeneity in the treatment area, but simultaneously induced unprofitable (essential statistically) increase of dose in some healthy organs of risk, what makes an increase risk for radiation-induced complications. The use of biologically equivalent HDRBT instead of PDRBT makes for the decrease of physical doses in the treatment area and the decrease of physical and biologically equivalent doses in healthy organs of risk.