Feasibility of Simultaneous Integrated Boost Intensity Modulated Radiotherapy treatment plans in patients with localized carcinoma prostate

Abstract

Aim: To dosimeterically analyze Simultaneous Integrated Boost Intensity Modulated Radiotherapy (SIB-IMRT) treatment plan in prostate cancer patients, in terms of target coverage and dose to organs at risk. To determine radiobiological effect of this technique on target and normal tissues using Tumor Control Probability (TCP) and Normal Tissue Complication Probability (NTCP). Materials and Methods: Twenty patients with localized prostate cancer were enrolled. In all, the target consisted of PTV P + SV (Prostate and seminal vesicles) and PTV LN (lymph nodes) where PTV refers to planning target volume and the critical structures included: bladder, rectum, small bowel, penile bulb and bilateral femoral heads. For all patients, SIB IMRT plan was created. The prescription dose to the PTV P + SV is 74 Gy delivered in 27 fractions over 5.5 weeks and the dose to PTV LN is 54 Gy delivered in 27 fractions over 5.5 weeks. The treatment plan was analyzed in terms of their dose-volume histograms, target volume covered by 95% of the prescription dose (V 95%), and maximum and mean structure doses (Dmax and Dmean). Also an analysis was done on TCP and NTCP obtained with the plan. NTCP was calculated by Lyman Kutcher Burman (LKB) model. Results: All the critical structures received doses within the dose constraints specified for the SIB IMRT plan. The volume of rectum and bladder receiving 65 Gy or more ( V > 65 Gy) was 18.23% and 24.05%. The mean doses to both bladder and rectum were 59 ± 3 Gy and 57 ± 4 Gy respectively. NTCP of 0.01 ± 0.02% for bladder, 4.31 ± 2.61% for rectum and 8.25 ± 7.98% for small bowel was achieved with SIB-IMRT plans. Conclusions: SIB-IMRT is dosimetrically and radiobiologically feasible treatment technique for prostate cancer IMRT.