Background: Different radiotherapy techniques were developed to deliver optimal dose to prostate cancer while sparing nearby organs at risk (OARs).
Aim: To compare different dosimetric methods used to evaluate sparing of OARs and to select radiotherapy plan which provides the most OARs sparing during prostate cancer treatment.
Methods: We used computed tomography data sets of 10 patients. For each data set, six plans were calculated; two RapidArc, two intensity-modulated radiation therapy (IMRT), and two 3-dimensional conformal radiotherapy (3DCRT) plans. Isodose distribution and dose volume histograms (DVHs) were used for plan analysis and evaluation. The dose to OAR was compared by calculating the DVH for each OAR in different plans. The dose (D) delivered to certain percentage (n) of an organ (Dn) was then determined. In addition, the Critical Organ Scoring Index (COSI) and the modified COSI (mCOSI) were calculated.
Results: 3DCRT with 5 fields produced the lowest rectal dose, RapidArc with bladder avoidance sector (RapidArc-Bladder) produced the lowest bladder dose and IMRT with 9 beams produced the lowest dose to the femoral heads. The COSI and MCOSI values of the two IMRT plans were significantly lower than those of 3DCRT and RapidArc (<0.0001). The calculation of mCOSI produced similar results to that obtained with COSI (<0.0001).
Conclusion: The results of this study showed that COSI and MCOSI are better dosimetric methods in selecting the plan with more sparing of OARs than Dn. Meanwhile among advanced radiotherapy techniques, RapidArc and 3DCRT are more sparing of OARs than IMRT.