3-Dimensional conformal radiotherapy versus intensity modulated radiotherapy for localized prostate cancer: Dosimetric and radiobiologic analysis

 Background: To analyze the dosimetric and radio biologic advantages between intensity modulated radiotherapy (IMRT) and 3 dimensional conformal radiotherapy (3DCRT) and selection of optimal photon energy for IMRT treatments. Material and methods: 24 patients with localized prostate carcinoma were planned for 3DCRT and IMRT techniques. Radiation dose of 54 Gy with 2 Gy/fraction, was planned to Planning target volume (PTV1) (prostate + seminal vesicle + 1 cm margin) and 72 Gy to PTV2 (prostate + 1 cm margin) respectively. 3DCRT planning was done using 15 MV photon beam while IMRT plans were created using 6 MV and 15MV photons. Treatment plans were analyzed using mean, median, dose maximum and cumulative dose volume histogram for PTV1, PTV2, bladder, and rectum. Tumor control probability (TCP) was calculated for prostate. Normal tissue complication probability (NTCP) was calculated for bladder, rectum, and head of femur. Results: Mean dose to prostate was 72.79 ± 0.18 Gy for IMRT 15 MV, 72.16 ± 0.27 Gy for 3DCRT and 72.48 ± 0.19 Gy for IMRT 6 MV. TCP was greater for IMRT 15 MV followed by IMRT 6 MV. The mean value of NTCP was significantly lower (p = 0.0015) for IMRT 6 MV compared to 3DCRT for rectum while for bladder all were comparable.  Conclusion: IMRT techniques shows superiority in sparing surrounding critical organs, thus reducing normal tissue complication rates while maintaining the same or higher tumor control probability. No significant difference was observed between IMRT 6 MV and IMRT 15 MV techniques.