96 Background: The few recent studies showed that regional lymph node metastases of prostate cancer (PCa) could be successfully treated. It means that role of pelvic nodes (PN) irradiation could increase in next period. A problem is rectal and bladder toxicities of this treatment. Intensity modulated dynamic irradiation techniques (DT) may potentially help to reduce treatment related side effects. The aim of study is to compare three different radiotherapy techniques: conformal (CRT), static field intensity modulated (SF IMRT) and rapid arc (RA) for elective pelvic lymph nodes irradiation. Methods: We analyzed CRT, IMRT and RA plans of irradiation PN for ten patients. PTVs included PN iliac, iliac external upper then acetabulum, iliac internal and obturatory. Prescribed doses were 44 Gy/22 fractions. We compared the doses delivered to PTV rectum and bladder using dose volume histograms. The U Mann-Whitney, W Shapiro-Wilk and ANOVA rang Kruskal-Wallis tests were used for statistical analysis. Results: The median PTV doses were not statistically different in analyzed plans. The minimum doses for PTV were significantly lower in IMRT and RA plans but the differences were not clinically significant. Maximum doses were significantly higher for CRT plans. The doses calculated for rectum and bladder were statistically significantly lower for dynamic techniques in whole range of volumes and doses. SF IMRT is the most efficient technique in reducing the dose to bladder. The doses observed in half of the rectum and bladder volumes bladder were also statistically significant different (p=0.002 for rectum and 0.001 for bladder). The median doses for rectum were 43.6 Gy for CRT plans, 33.5 Gy for IMRT and 37.9 Gy for RA, median doses calculated for bladder were 44 Gy for CRT, 35.6 Gy for IMRT and 39.6 Gy for RA. Conclusions: CRT does not allow to reduce the dose to organs at risk. Both DT reduce the doses to bladder and rectum while maintaining the high homogenous dose to PTV. SF IMRT is more efficient in reducing the dose to bladder than RA. SF IMRT technique seems to be better than Rapid Arc for PN irradiation. It is probably because the nodal PTVs are large and their structures are complicated. No significant financial relationships to disclose.
Comparison of dose volume histograms for supine and prone position in patients irradiated for prostate cancer—A preliminary study
