Normal tissue complication probability: Does simultaneous integrated boost intensity-modulated radiotherapy score over other techniques in treatment of prostate adenocarcinoma

Aim: The main objective of this study was to analyze the radiobiological effect of different treatment strategies on high-risk prostate adenocarcinoma.
Materials and Methods: Ten cases of high-risk prostate adenocarcinoma were selected for this dosimetric study. Four different treatment strategies used for treating prostate cancer were compared. Conventional four-field box technique covering prostate and nodal volumes followed by three-field conformal boost (3D + 3DCRT), four-field box technique followed by intensity-modulated radiotherapy (IMRT) boost (3D + IMRT), IMRT followed by IMRT boost (IMRT + IMRT), and simultaneous integrated boost IMRT (SIBIMRT) were compared in terms of tumor control probability (TCP) and normal tissue complication probability (NTCP). The dose prescription except for SIBIMRT was 45 Gy in 25 fractions for the prostate and nodal volumes in the initial phase and 27 Gy in 15 fractions for the prostate in the boost phase. For SIBIMRT, equivalent doses were calculated using biologically equivalent dose assuming the α/β ratio of 1.5 Gy with a dose prescription of 60.75 Gy for the gross tumor volume (GTV) and 45 Gy for the clinical target volume in 25 fractions. IMRT plans were made with 15-MV equispaced seven coplanar fields. NTCP was calculated using the Lyman-Kutcher-Burman (LKB) model.
Results: An NTCP of 10.7 ± 0.99%, 8.36 ± 0.66%, 6.72 ± 0.85%, and 1.45 ± 0.11% for the bladder and 14.9 ± 0.99%, 14.04 ± 0.66%, 11.38 ± 0.85%, 5.12 ± 0.11% for the rectum was seen with 3D + 3DCRT, 3D + IMRT, IMRT + IMRT, and SIBIMRT respectively.
Conclusions: SIBIMRT had the least NTCP over all other strategies with a reduced treatment time (3 weeks less). It should be the technique of choice for dose escalation in prostate carcinoma.

Keywords
Intensity-modulated radiotherapy, normal tissue complication probability, prostate