Calculation of Normal Tissue Complication Probability in Prostate Cancer and Late Side Effects

ABSTRACT

Aim: Calculation of normal tissue complication probability(NTCP) and side-effect evaluation in localized prostate cancer in different plans

Method: NTCP were evaluated in 16 cases with different conformal plans. Target volumes and NTCP values of OAR were calculated with the Lymann-Kutcher-Burman (LKB) model, and comparisons were made in virtual plans with 4-fields and 6 fields for the rectum, bladder and femoral head. The cases were treated with 6-fields; acute-late complicationsfor bladder, rectum and late complications for femoral head were correlated with mean doses, percentage of volume (V%), NTCP values. Paired-t test, Wilcoxon and Spearsman tests were used in the correlation.

Results: The mean organ risk V% values and femoral head NTCP were significant for 4 and 6-fields plans(p=0.008). The relationship between acute genitourinary system complications and NTCP was statistically significant (p=0.019). Significance was observed in the mean bladder dose (p=0.015) and the (V%) that received>50% of thedose in the isocentre (rs=0.5446, p=0.029). For the femoral head, the percentage of volume that received more than 50% dose at the isocenter was found to be significant in favor of 6-fields(paired-t test p=0.0001). Complication probabilities of the femoral head were found to be significantly higher in 4-field plans (p=0.009). There was no statistically significance between late effects and NTCP.

Conclusion: By increasing the number of fields, normal tissues are better protected and tumor control is provided with higher doses. It should be kept in mind that daily area changes and risky organ position changes cannot be calculated with NTCP models.

Key words: Prostate cancer, conformal radiotherapy, NTC