Dosimetric Comparisons between 2D and 3D Plans for Prostate Cancer

This study, to compare between 2-dimensional and 3-dmensional techniques for external-beam radiation treatment for prostate cancer was conducted at the National Cancer Institute, Cairo University, EGYPT. Method: Dose homogeneity within the target volume and doses to critical organs, OAR were evaluated. CT scans of 30 patients with localized prostate cancer (T2N0M0) were acquired and transferred to the treatment planning systems (TPS). The target volume and uninvolved structures were contoured on axial CT slices throughout the volume of interest. A comparison of the two treatment techniques was performed using isodose distributions, and dose-volume histograms.  Results and discussion: Using multiple 3D field conformal technique, did not result in major difference in target coverage as compared to the conformal 2D techniques. For the planning target volume, the average (V95%, V107%) in 2D technique 90.6%, 5.7% while, for 3D technique 94.9%, 3.8 respectively. However, a better distribution of dose received by the organs at risk is achieved using 3D as compared to that of 2D technique, with considerable sparing of bladder, rectum and head of both femora, which received unnecessary radiation doses using 2D techniques. The discrepancy is very noticeable in the: rectum, where the average (V70, V75 and D95) in 2D technique was found to be 35.5%, 32.2%, 34% while for 3D 8.4%, 0.2%, 12% respectively; and the bladder where the average (V40, V65) in 2D technique was found to be 80.8%, 74.9% while for 3D it was 20.4%, 17% respectively. Conclusions: 3D planning only for prostate cancer treatment provides better target coverage and reduces the dose to the organs at risk and is thus more appropriate for prostate cancer therapy.