Determination of the effects 3D Margins around the treatment volume in radiotherapy planning

In radiotherapy treatment there are many potential error sources, which can increase the uncertainty in the dose delivery to a patient to unacceptable values.Potential error sources can be divided into four categories (1,2) ; (1) errors in the data transfer from treatment planning system (TPS) to treatment equipment, (2) errors in the functioning of the treatment equipment, (3) errors that that may arise from organ motion and (4) inaccuracies during the treatment planning process.Various solutions can be chosen to detect and correct some of these four errors categories, but few solutions can be utilized to detect errors in all four categories.Several margin 'recipes' are described to calculate the CTV-PTV margin (5,6) .Once the target volume is accurately delineated, treatment fields can be defined and the distribution of the delivered dose can be calculated, optimized with utmost minimization of doses to surrounding healthy tissues.Management of organ motion has become most difficult challenges in radiation oncology.Anatomic models that describe geometric changes in organs over time offer a unique opportunity to tackle various issues related to dose planning , monitoring and to radiation delivery.To account for temporal and spatial anatomic changes during radiation treatment, real means to specify organ and/or tumor motion are required .This work aims to evaluate the safety margins for all planning tumor volume inside the radiation beam taking into consideration the possible movements of organs adjacent to the tumor location, e.g rectum and the urinary bladder.Results: Mean 3D displacement was 7.3 mm (SD, 4.4 mm) and 7.6 mm (SD, 4.2 mm) for laser and port film, respectively.Simulated setup with the EPID mean displacement of 3.2 mm (SD, 1.2 mm).Distance analysis resulted in mean distances of 5.1 mm (SD, 4.9 mm), 4.3 mm (SD, 5.6 mm), and 1.6 mm (SD, 2.4 mm) for laser, port film, and EPID , respectively.Bladder and Rectum motion at isocenter were less than 5 mm, with a mean of 4.5 mm (SD, 1.1 mm).In comparison with different studies were done the average margins about 12 mm in agreement with current study.Conclusions: Prostate displacement due effect of bladder and rectum varied within 5 mm to 12 mm , the variation of displacement in average 5 mm.