2992 - Can Cone Beam CT Scans Reveal Therapeutic Changes in Prostate Patients?

Purpose/Objective(s):

The advent of cone beam CT (CBCT) scans has provided additional three dimensional imaging information. The goal of this study is to ascertain whether CBCT scans can differentiate radiation dose effects in the prostate gland.

Materials/Methods:

CBCT scans from ten deidentified prostate patients were investigated prior and subsequent to 46Gy of therapeutic radiation. Fiducial gold markers were placed into the prostate to aid in localization. CBCT scans with a 2.0mm slice thickness were taken prior to each patient treatment. Treatment planning CT (TPCT) scans utilized a helical CT scanner with 2.5mm slice thickness and metal artifact reduction (MAR). The prostate was contoured in the TPCT scans by a board-certified physician in advance of treatment. CBCT scans were imported into the treatment planning system (TPS). The gold seeds were contoured in the TPS. CBCT scan slices were matched to TPCT scan slices utilizing patient anatomy. In the CBCT imaging scans, a 2cm diameter circle was placed in the medial prostate for analysis. Imagej was utilized to analyze the CBCT prostate scans. The standard deviation of pixel intensity as well as the pixel intensity inside of the circle were recorded for each image. The ratio was examined as the normalized standard deviation.

Results:

The normalized standard deviation ranged from 0.05 to 0.15 prior to 46Gy of therapeutic radiation to the prostate. After, it ranged from 0.16 to 0.37. Table 1 sumarizes the results. As can be seen in this table, the average normalized standard deviation of pixel intensity after 46Gy of therapeutic radiation increased from 0.09 to 0.22 or approximately 144%.

Conclusion: Subsequent to 46Gy of therapeutic radiation to the prostate, the average normalized standard deviation of pixel intensity increased by about 144%.

Radiation Amount (Gy)	Normalized Standard Deviation Range	Average Standard Deviation
0.0	0.05 - 0.15	0.09
46.0	0.16 - 0.37	0.22