The Relationship between the Different Prostate Intensity Modulated Radiation Therapy Techniques and Patient’s Anatomical Parameters

Introduction: Intensity Modulated Radiotherapy (IMRT) is a common method for treating prostate cancers. Different IMRT methods can apply for irradiating the prostate, but there is not clear that which of these methods can provide better dose distribution for each patient individually. Therefore, the aim of this study was to evaluate the relationship between the different prostate IMRT techniques and Patients anatomical parameters for determining the appropriate IMRT method for each patient regarding to his anatomical parameters. Materials and Methods: 50 patients with low to high risk prostate cancer were considered for hypo fractionated IMRT (70.2Gy in 26 fractions). CT and MRI (T2 weighted) scans were obtained and imported to the treatment planning system (Eclipse version 11, Varian corporation, USA). Planning tumor volume (PTV) and organs at risk (OARs) were contoured on these images. 4 different IMRT plans including 9 fields, 7 fields, 5 fields and beam angle optimization were created for each patient. Furthermore, the dose distributions of these techniques were evaluated using cost function value that determined the differences between the ideal dose distribution and calculated one. anatomical parameters including OARs volume, joint volumes between OAR and PTV, prostate volume, PTV volume, width and height in the central slice of prostate and femur distance was measured. The relationship between the cost function values with the anatomical parameters were assessed in this study. Results: 9 and 7 fields IMRT had lower cost function values compared to other techniques with increasing the prostate volume, PTV volume and joint volumes between the PTV and OARs. Increasing the OAR volumes, patient’s width and height in the central slice of prostate and femur distance had not any effect in creating differences between the above 4 mentioned IMRT techniques. Conclusion: Prostate IMRT with 9 and 7 fields can be used interchangeably because of their close value of cost function in all patients, especially they can provide better dose distribution in patients with large PTVs (more than 350cc) and large joint volumes between the OARs and PTV (25 cc for rectum and 50 cc for bladder) compared to 5 fields and beam angle optimization IMRT. All of the mentioned IMRT techniques provided relatively the same dose distributions in patients with small PTV and joint volumes and all range of the other mentioned anatomical parameters.