Evaluation of various common prostate IMRT techniques based on estimated tumor control and normal tissue complication probabilities in correlation with patients anatomical parameters derived from the CT scans

Background: The relationship between the prostate IMRT techniques and patients anatomical parameters has been rarely investigated.

Objective: to evaluate various prostate IMRT techniques based on tumor control and normal tissue complication probability (TCP and NTCP) values and also the correlation of such techniques with patients anatomical parameters. Methods: Four IMRT techniques (9, 7 and 5 fields and also automatic) were planned on the CT scans of 63 prostate cancer patients. The sum of distances between the organs at risk (OARs) and target tissue and also their average joint volumes were measured and assumed as anatomical parameters. Selected dosimetric and radiobiological parameters (TCP and NTCP) values were compared among various techniques and the correlation with the above anatomical parameters were assessed using Pearsons’ correlation.

Results: High correlations were found between the dosimetric/radiobiological parameters of OARs with the joint volumes and with the distances between the OARs and target tissue in all the techniques. The TCP and complication free tumor control probability (P₊) values were decreased with increasing the joint volume and decreasing the distances between the OARs and target tissue (as poly-nominal functions). The NTCP values were increased with increasing the joint volumes and decreasing the distances (3-degree poly-nominal functions). For the low percent joint volumes (<20%) and high distances (>7 cm), The TCP, NTCP and P₊ showed no statistical differences between various techniques (P-value>0.07). However, 9 and 7 fields techniques indicated better radiobiological results (P-value<0.05) in almost other ranges (>20% joint volumes and <7 cm distances).

Conclusion: Based on our results, it would be possible to compare radiobiological effects of various common IMRT techniques and choose the best one regarding to patients anatomical parameters derived from the CT scans.