Analysis of influence factors of cone beam CT calibration in prostate cancer

Abstract

Objective To deeply explore influence of three objective factors-rectal muscle tension, intra-abdominal pressure and bone in pelvic on cone beam CT calibration data of prostate cancer before radiotherapy and obtain the main factors affecting prostate target movement, so as to provide reference for optimizing radiotherapy plan design and improving image guidance accuracy. Methods Ten eligible patients with prostate cancer were screened according to the inclusion-exclusion criteria for test and scanned twice a week before random treatment by using cone beam CT to obtain prostate target calibration data. After the scanning, the influence of rectal muscle tension was quantified by using shear wave elastography, the influence of intra-abdominal pressure was indirectly quantified by air bag pressure gauge which measured the intra-bladder pressure, and the influence of bone in pelvic was quantified by using root mean square. The relationships between the three factors and cone beam CT calibration data were analyzed by using regression analysis. Results The cone beam CT calibration result was 0.513 mm±0.072 mm, 1.369 mm±0.162 mm, 1.335 mm±0.271 mm on left-right, anterior-posterior and superior-inferior direction respectively for all the patients. Young’s modulus value was 8.965 kpa±1.391 kpa, 10.211 kpa±1.544 kpa, 3.926 kpa±0.693 kpa on three directions respectively, intra-abdominal pressure (without direction) was 4.844 mmhg±1.347 mmhg (1mmhg = 133.3 Pa) and root mean square was 0.020 mm±0.011 mm, 0.069 mm±0.049 mm, 0.062 mm±0.029 mm on three directions respectively. Rectal muscle tension (R = 0.895) and intra-abdominal pressure (R = 0.523) on anterior-posterior direction were statistically correlated with the cone beam CT calibration data, and intra-abdominal pressure (R = 0.717) on superior-inferior direction was statistically correlated. Conclusions Rectal muscle tension on anterior-posterior direction and intra-abdominal pressure on superior-inferior direction were the main factors that caused prostate cancer target movement. The results were of great significance to optimize radiotherapy plan design and improve image guidance accuracy and provided methodological guidance for future target displacement reduction.