Dosimetric Study Of Stereotactic Body Radiotherapy And Carbon Ion Radiotherapy For Prostate Cancer

Objective: To analyze the dosimetric advantages and heterogeneity in target volume and organs at risk when stereotactic radiotherapy（SBRT）and carbon ion radiotherapy（CIRT）were used for localized prostate cancer,and to provide theoretical support for clinical application.Methods: Total of 16 patients with localized prostate cancer were enrolled in this study at Department of Radiation Oncology,the 940 th Hospital of Joint Logistics Support Force of PLA in conjunction with the First Hospital of Lanzhou University,and the Second Hospital of Lanzhou University rom March 2014 to April 2021.The patients’ target volume and OARs as well as patient contours were delineated on the4 th generation treatment planning system Multi Plan4.0.Import the contours into the CIRT treatment plan system ci Plan.Patient was planned by using Cyberknife SBRT with 35.47 Gy in 5 fraction with daily dose of 7.09 Gy,5 days a week,while carbon ion radio-therapy（CIRT）was planned with 57.6Gy（RBE）in 16 fraction with daily dose of3.6 Gy（RBE）,5 days a week under the same biological effective dose（BED）of161.28Gy/Gy（RBE）.The results conducted were converted to EQD2 according to the L-Q model.The dosimetry characteristics and specification of planning target volume（PTV）was evaluated by Dmean,D98,D95,D90,D50,D5,D2,and HI;while Dmax,Dmean,D50 were evaluated for bladder and bowel;rectum were evaluated by Dmax,Dmean,D40,D20;Dmax,Dmean,D15,D5 were evaluated for femoral head.In the condition of different clinical stages,different sizes of primary tumor,different volumes of PTV/bladder/rectum,different PTV and relative sizes of bladder/rectum,and discuss the dosimetry characteristics and heterogeneity in two techniques.Using SPSS 22.0 for statistical analysis of the data.Results: 1.The result show there are higher CI,HI and larger area of medium and high dose region but lower V95 % and smaller area in low dose region of PTV for SBRT than CIRT.The Dmax of bladder and rectum is lower but higher in Dmean for SBRT than CIRT.The radiation dosage for bowel and the Dmax,Dmean of femur head are lower for CIRT than SBRT.2.The Dmax of bladder and rectum is lower but higher in Dmean for SBRT than CIRT in patients with specific primary tumor sizes or levels of risk,while Dmax and Dmean of bowel is lower for CIRT than SBRT.3.When the volume of PTV increases,the Dmean of bladder/rectum,femoral head,bowel increases in SBRT too.The Dmean of bladder/rectum,bowel and femoral head decreases when the volume of bladder/rectum increases in SBRT.4.When the relative size of PTV and bladder increases,both the Dmax of bowel in CIRT,and the Dmean of OARs and the Dmax of femoral head in SBRT increases too.Conclusion: 1.The target conformity and dose superiority of SBRT is better,while target dose coverage and uniformity is worse than CIRT.2.The dose distribution of CIRT is better for prostate cancer in middle and high risk with large tumor,while the dose distribution of SBRT with complex OARs around the target area is better than CIRT.3.The abundance control of bladder and rectum affects the dose performance of SBRT,and the filling degree should be well controlled;4.The dose distribution of SBRT and CIRT is a reciprocal of Dmax and Dmean for optimal plan decision making.