Effectiveness of Rectal Spacers In Reducing Normal Tissue Complication Probability (NTCP) In Prostate Cancer Radiotherapy
Abstract
Purpose
To evaluate the effectiveness of SpaceOAR in sparing the rectum by calculating the normal tissue complication probability (NTCP) from radiotherapy treatment plans for prostate cancer patients treated with and without a spacer.
Methods
Dose-Volume Histograms (DVHs) of 224 previous prostate cancer treatment plans were anonymized, exported, and analyzed using a Python script to calculate bladder and rectum NTCP values using a linear quadratic model. Three dose fractionation schemes were analyzed: 40 Gy in 5 fractions (SBRT), 70 Gy in 28 fractions (IMRT), and 81 Gy in 45 fractions (IMRT). For each fractionation scheme, NTCPS with and without a spacer were compared using a t-test to assess statistical significance. Additional t-tests were performed between each pair of fractionation schemes to determine whether observed differences were dose-dependent or attributable solely to the presence of a spacer.
Results
SpaceOAR reduced rectal NTCPs across all investigated dose fractionation schemes. Calculated p-values demonstrated a statistically significant difference in rectal NTCP for the 40 Gy, 70 Gy, and 81 Gy plans (Spacer mean=1.83%, 2.10%, 3.37%; No spacer mean= 6.01%, 5.98%, 9.46%; p=0.0031, 0.0005, 0.0015; α=0.05). No statistically significant difference was seen in bladder NTCP values with all averages being ~0% (p=0.523, 0.659, and 0.313). When comparing the values across differing dose levels with a spacer in place, no significant correlation was found (p=0.578 for 40 vs. 70 Gy, p = 0.191 for 40 vs. 81 Gy, and p = 0.280 for 70 vs. 81 Gy).
Conclusion
The collected data suggests implementation of SpaceOAR results in a significant reduction in rectal NTCP. This effect remains consistent across varying dose fractionation schemes analyzed and across a large patient pool (N = 224). These findings indicate that SpaceOAR is a valuable tool for reducing normal tissue complications in the rectum for prostate radiotherapy.