Volume and dosimetric analysis of rectum and bladder for prostate carcinoma patients by using kilovoltage cone beam computed tomography (CBCT)

Background: to study and analyze the variations in delivered doses torectum and bladder of carcinoma prostate patients by using kilo voltage (kv)‘cone beam computed tomography’ (cbct) images. materials and methods:2-dimensional kilo voltage (2d kv) imaging and cbct were done for sevenprostate cancer patients. the deviations among their shifts were correlatedand the volumetric changes of the rectum and bladder were analyzed.rectum and bladder contours were redrawn on every boost fractions anddose calculation were performed on cbct images to study the effect on dosevolume histograms. results: a correlation coefficient for set-up variationswas within 0.78 for all directions between cbct soft tissue matching and kvbone match. the mean deviation of bladder and rectum volume over theboost fractions was -12% to +9% (sd 31cc to 70cc) and -10.2% to+12% (sd3.1cc to14.9cc), respectively. bladder mean dose variation was <1.5gy for allthree positions whereas it was <3.65gy for rectum. d1% dose deviation fromreference plan for bladder was 1.1gy (cbct matched position), 1.4gy (kvmatched position), and 1.7gy (no correction), and for rectum, the deviationswere 1.2gy, 2.2gy, 3.6gy, respectively. no significant deviation was foundstatistically significant at the low dose region. conclusion: it is possible toachieve good dose delivery and conformity in target (prostate) with cbctimage guidance rather than kv bone match, but dose contribution to therectum is dependent on the patient’s anatomy, bladder filling, and rectumfilling, pertaining to the day of examination