Dosimetric Comparison of Various Radiotherapeutic Treatment Plans Using Cobalt-60 and Linac for Prostate Cancer

Introduction: This study was designed to evaluate dosimetric parameters such as rectal dose, bladder dose, integral dose (ID), homogeneity index (HI) and conformity index (CI) in various treatment plans for prostate cancer. Materials and Methods: Pelvic computed tomography (CT) scans of 27 patients were acquired and transferred to the RTDosePLAN treatment planning system. For each patient, 8 conventional plans (3, 4, 5 and 6 fields) were planned for the cobalt-60 photon energy. Subsequently, the same plans were performed for 6 MV and 18 MV photon energies. Results: By increasing the energy of the beam relative to the cobalt-60 energy, the Dmean values for rectum and bladder were reduced from 3% to 4% and 4% to 6%, respectively, the dose received by the whole of the bladder volume decreased by 26% for 6 MV and by 58% for 18 MV. Increasing the photon beam energy decreased CI to 7% and 10%, ID was decreased by10% and 20% and Dmax was decreased by 3% and 4%, respectively. Discussion and Conclusion: A six-field treatment plan in comparison to the other plans offers the minimum dose to critical organs and sufficient dose to the prostate. Increasing the photon energy improves the treatment parameters of the bladder and the PTV.