The Role of MRSI in Target Volume Definition for Radiation Therapy of Prostate Cancer

Introduction: Recently, magnetic resonance spectroscopic imaging (MRSI), as a functional imaging method, has been used for clinical target volume definition. In this study, we used this method to define the target volume in prostate radiotherapy. Material and Method: In this study, we used images of 20 prostate cancer cases. MRSI and MRI images were fused with CT images. Then, treatment planning was preformed for each patient using three methods: CT, CT+MRI and CT+MRSI planning. Results: The volumes of MRICTV and MRIPTV were on average 12.83% and 8.97% lower than the corresponding CTCTV and CTPTV volumes, respectively. For MRSI, the CTV and PTV volumes were 21% and 27.41% greater than the corresponding CT-based volumes. Maximum dose to rectum showed a 0.58% increase in MRSI relative to CT, and 1.09% reduction in MRI relative to CT. Maximum dose variation in femoral heads showed a 5.4% increase in MRSI relative to CT and 0.67% reduction in MRI relative to CT. Discussion and Conclusion: Application of MRSI for target volume definition of prostate cancer leads to an increase in this volume in comparison to CT planning alone. In this imaging technique, protocol and resolution should be considered to determine the target volume exactly.