Abstract:
In this study effort has been made to assess the variation in rectal surface area, (rectal
volume) from a planning CT scan to a repeat CT scan and also the dynamic interrelationship
between rectal surface area change and anterior posterior (AP) prostate movements were
assessed. This study would be very helpful to have an idea how inter fraction organ motion
affects the planning target volume delineation. About 95 percentage of patients with
localized prostate cancer, who are undergoing radiotherapy as a primary treatment modality
has an average AP prostate motion less than 1cm. One centimeter margin to gross tumour
volume is important to minimize a geographical miss while on radiotherapy. Efforts has
been made to identify 5 percentage of patients, who need repeat CT scanning for replanning
of PTV. According to observations made in this study, it seems to be important to rescan
patients for replanning, those who have a very low initial AP rectal diameter or very large
initial AP rectal diameter. To get a particular rectal diameter to decide, whether to do a
repeat scan or not needs further stidies on this subject. But as a basic guideline, average AP
rectal diameter of 4.43cm +/- 2SD (SD=1.3cm) could be taken to make decision regarding
repeat CT scans for patients with prostate cancer, who are undergoing curative
radiotheraphy.
