Purpose: This study is to compare film and cone‐beam computed tomography (CBCT) based fiducial marker localization results for intensity modulated radiation therapy (IMRT) of prostate cancer patients. Methods: From 2005 to 2011, 290 prostate cancer patients with 3 intra‐prostatic fiducial markers implanted were treated with IMRT boost following 4‐field pelvis radiation. Orthogonal films for 241 patients and CBCT images for 49 patients were taken daily before treatment to localize the prostate glands. The estimated couch shifts were recorded and applied. Total of 4072 fractions were analyzed in this study. Results: The overall standard deviations in the left—right (LR), anterior—posterior (AP), and superior‐ inferior (SI) directions for film and CBCT based localization are 3.90, 4.65, 3.64 mm and 3.94, 4.27, 3.82 mm, respectively. After removing average shifts of each patient, the standard deviations in LR, AP, SI are 3.06, 3.64, 2.63 mm and 3.08, 3.29, 2.48 mm, respectively. The Pearson coefficients of correlation for the frequency distribution of the couch shifts based on films vs. CBCT are 0.99, 0.98, and 0.98 in the LR, AP and SI directions. Conclusions: The CBCT based fiducial marker localization achieves the equivalent accuracy with the orthogonal film based method. The 3–4 mm standard deviations for both film and CBCT groups represent the natural inter‐treatment movements of prostates of this patient population. Any new localization methods should be tested against these standard deviations if the same planned target volume (PTV) margins are used.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging