62/Are standard quality parameters useful in comparison of conventional and IMSRT plans?

ObjectiveIntensity modulated radiation therapy (IMRT) is the technique, which has a potential to improve conformity in dose distributions and to increase the protection of organs at risk (OARs) at the same time, compared to conventional conformal technique. IMRT may also improve the dose distribution in stereotactic radiotherapy (SRT). The combination of these two techniques was called (IMSRT). This study presents a comparison of dose distribution in conformal stereotactic radiotherapy versus IMSRT for lesions located in base of scull. The aim of this study is to evaluate the quality of conformal and IMSRT treatment plans and to assess the usefulness of several quality factors in planning evaluation.Material and methodsFour patients with meningeoma and one with pituitary adenoma have been selected for analysis. For each case ten different plans were created and compared. The first one (TP) was the plan used for patient treatment. The second conformal plan (SP) was created using invariable beam arrangement, the same for all patients. Eight IMSRT plans were generated with different OARs prioritization, on the base of TP and SP beams arrangement, using “step and shoot” delivery method. The results were evaluated by analysis of consecutive factors: PTV minimum and maximum dose, homogeneity index (HI), coverage index (Covl), conformity index (CI) as well as tumor control probability (TCP) and normal tissue complication probability (NTCP). These quantities were incorporated into ten degrees scale of ranking factors and assigned for each plan.ResultsHI shows better homogeneity in conformal plans and IMSRT plans with high PTV priority in optimization process and consequently higher probability of tumor control. CI and coverage index are higher with higher importance of PTV too. Better protection of OARs, thereby lower normal tissue complication probability is achieved in plans with their increased weighting.ConclusionsThe test carried out for five patients showed efficiency as well as some limitation of IMSRT techniques. The use of number of quality factors allowed to assess dose distribution in more depth. It was also confirmed that decision about the best treatment plan depends largely on the means chosen for the evaluation process in the sense that all means employed during plans evaluation consider different aspects of plan quality