Assessment of the radiotherapy treatment plans of Three-dimensional conformal radiation therapy, intensity modulated radiation therapy and tomotherapy in prostate cancer using dosimetric and radiobiological indices

Objective: New radiation therapy techniques have been developed in recent years for prostate cancer. The quality of treatment is influenced by the type of treatment technique in terms of dose distribution techniques and also its radiobiological indicators, including the Tumor Control Probability (TCP) and Normal Tissue Complication Probability (NTCP). This research was done with the aim of finding an adequate technique for treating prostate cancer by dosimetric and radiobiological comparison of three-dimensional conformal radiation therapy (۳D-CRT) techniques and two new techniques of dynamic intensity modulated radiation therapy (Dynamic-IMRT) and tomotherapy.Methods: In this study, ten patients with high-risk prostate cancer treated with radiation therapy in Madani Hospital of Tabriz were selected. Prostate tumoral tissue as a target and rectum, bladder and femoral head as normal tissues at risk were contoured according to the criteria of RTOG protocol. For each patient, three separate treatment plans were created for all three techniques. Prescribed dose of ۷۰ Gy in ۳۵ fractions was used for all three techniques. Monaco and Precision Accuray treatment planning systems were used for treatment planning. The dosimetric indicators of each treatment plan, including the heterogeneity index, irradiation time, and the minimum, maximum, and mean doses for each patient and each technique were extracted from the dose-volume histogram (DVH) curves. Then, by using the Biosuite software, using DVH data and radiobiological factors, the TCP and the NTCP were calculated based on LKB and RS models. Results: In ۳D-CRT technique, the mean dose values of bladder, rectum and head of right and left femoral bones were showed a significant difference compared to the other two techniques. The heterogeneity index of the ۳D-CRT was higher than the other two techniques. The NTCP in the LKB model of the ۳D-CRT technique was about ۱۰% (range ۳-۱۱%) in the rectum, respectively, compared to IMRT and tomotherapy techniques. These numbers for the RS model was about ۲۴% in the bladder and up to ۱۷% in the rectum in ۳D-CRT. The TCP parameter in all three techniques was ۱۰۰%. Conclusion: In ۳D-CRT compared to other two techniques and in D-IMRT to tomotherapy, the absorbed dose was higher and as a result the probability of damage and complications of healthy organs was higher. This point was also confirmed by radiobiological models.

Keywords:

TCP , NTCP , ۳D-CRT , IMRT , Tomotherapy , Prostate cancer