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 (RapidArcBladder) 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.

Background:The reduction in tumor volume during the treatment of locally advanced non-small cell lung cancer (NSCLC) with chemoradiotherapy allows the application of adaptive radiotherapy strategy. Adaptive planning has the potential for improving radiotherapy planning indices and dose escalation while respecting the dose to the organs at risk (OARs). Aim: To evaluate the benefit of adaptive radiotherapy in patients with advanced NSCLC treated with conformal technique. Methods: In this dosimetric planning study, we included computerized tomography data-sets from 10 patients with locally advanced NSCLC who responded to the first 22 fractions (44 Gy) and achieved ˃ 20% regression in gross tumor volume. We designed for each patient two plans. Plan 1 (conventional planning) in which the whole prescribed dose (64 Gy) was delivered to the planning target volume 1 (PTV1). Plan 2 (adaptive planning) was divided into plan 2A delivering 44 Gy to PTV1 and plan 2B delivering 20 Gy to PTV2. In plan 2B we re-delineated the PTV and all the target volumes on the repeated CT images to deliver the rest of the prescribed dose (20 Gy). Plan 2A and Plan 2B were summed to measure the accumulated dose delivered to OARs. Results: The mean PTV2 was significantly smaller than the mean PTV1 (p<0.001) with 53% reduction. Adaptive planning resulted in 13.2% mean reduction in the maximum dose to the spinal cord (p<0.001), 10.4% in esophagus V35 (p<0.001), 11.4% in esophagus V50 (p<0.001), 24.3% in mean lung dose (p=0.001) and 19.7% in lung V20 (p<0.001). The reduction in heart d-max and heart mean dose was not significant. Conclusion:The adaptive radiotherapy technique used in our study can reduce the irradiated volume and minimize the dose delivered to OARs. This simple applicable technique can be easily implemented in limited resources centers.