Purpose To investigate the influence of treatment plan data and image guidance (IG) on positioning uncertainty during prostate cancer (PCa) radiotherapy (RT). Methods Body mass index (BMI), planning target volume (PTV), bladder volume (BV), and rectal cross section area (RCS) were collected for 267 consecutive PCa patients undergoing daily IGRT. Radiographic isocenter corrections to intra-prostatic fiducials for 12,490 treatment fractions were used to derive random (RE) and systematic (SE) inter-fraction uncertainties for the cardinal axes. These data were used to simulate RE and SE for weekly IG and Action Level (AL)-IG treatment protocols. Results SE and RE were 2-5 and 3-4 mm in the cardinal axes, respectively, during simulation of no IG. Without IG, positive correlations (p < 0.01) were noted for (1) anterior-posterior RE vs. RCS and BV and (2) cranio-caudal RE vs. RCS, BV and BMI. The RE increase was 3 mm for the highest quartile of RCS, BV and BMI. Daily IGRT eliminated this relationship. 3D IG corrections of 1 cm or more occured in 27% of treatment fractions and in 97% of patients. Conclusion PCa patients with elevated pre-treatment BV, RCS and BMI have increased inter-fractionation positioning uncertainty and appear the primary candidates for daily IGRT.
- Image guided radiotherapy
- Interfraction motion
- Prostate cancer
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging