| Objective:Because of the transrectal ultrasound and template guidance,prostate cancer iodine-125 seeds implantation has been used as a standard first-line treatment for many years.The introducing of pre-operation and intra-operation plan can make the dose parameters of post-plan match that in pre-plan[1-4].Iodine-125 radioactive seed implantation has been used widely in head and neck tumor,lung cancer,digestive tract tumor,pelvic tumor and bone sarcoma in China[5-10].Although we got very good results in some kind of tumors,because of lacking standard implant procedure,it is difficult to make the dose parameters in post-plan the same compared to pre-plan.The good results of iodine-125 seeds implantation are difficult to repeat and the treatment method cannot be generalized.Treatment planning system?TPS?based dose calculation is the standard dose verification method till now.But disadvantages do exist.Only by knowing the seed number and activity can the dose be calculated in an image-based post-operative plan.At the same time,there are some other drawbacks such as difficulty in identifying seeds in TPS,errors in the seed number,activity inaccuracy,seed location identification imprecision,and artificial errors.This study aimed to do some research to provide some new methods to implant the seed and verify the dose after the implantation.For seeds implantation,3D printed template guidance can insert the needles accurately to the target with arbitrary angle and at the same time avoiding blood vessels,bones,and other organs at risks.The error of the seeds'location is smaller,the dose distribution is more conformal and the dose consistency between pre-and post-plan is better compared to traditional implant method.For dose verification,the disadvantages of the TPS are very difficult to improve by the technique used now.SPECT/CT based radiation detection and imaging method may resolve the problems completely.Methods:Based on the background above,this study focused on 3D printed template guided iodine-125 seed implantation and the feasibility and accuracy of SPECT/CT based iodine-125 seed dose verification.In the first part,we analyzed 64 patients who underwent 3D printed template guided iodine-125 seed implantation retrospectively.The result showed that this new implant method has many advantages compared to traditional implant method.In the second part,70 seeds with different activity were scanned and the relationship between radioactive count values around the seeds and the dose were revealed.In part three,two patients with prostate cancer underwent iodine-125 seed implantation was scanned by SPECT/CT.The patients were followed up to observe the feasibility of SPECT/CT based dose verification for clinical use.Results:1.In the 3D template group,35 patients underwent 3D printed template–guided seed implantation successfully.One patient underwent CT-guided brachytherapy because of the shifting of mediastinum caused by pneumothorax.In the traditional group,all 28 patients underwent CT-guided brachytherapy successfully.The mean D90 values pre-and post-operation in the template group were?90.32±25?Gy and?89±24.83?Gy,respectively,with no statistically significant difference.The mean D90 values pre-and post-operation in the traditional group were?85.66±30.42?Gy and?73.28±41.61?Gy,respectively,with a statistically significant difference.The mean V90 values post-operation in the template and traditional groups were?92.38%±4.64%?and?83.5%±12.62%?,respectively,with a statistically significant difference.The local control rate of the template and traditional groups at 4 months were 82.86%and 60.71%,with a statistically significant difference.The response rate of the template and traditional groups at 4months were 51.43%and 32.14%,with no statistically significant difference.2.There was an exponential relationship between the dose around iodine-125 seed and the radioactive count value detected by SPECT/CT.The formula of 1.48×107Bq,1.85×107Bq,2.22×107Bq,2.59×107Bq,2.96×107Bq,3.33×107Bq and 3.7×107Bq seeds were Y=2.442×1.006x,Y=2.460×1.006x,Y=2.361×1.006x,Y=1.586×1.006x,Y=2.657×1.006x,Y=3.929×1.006x,Y=1.817×1.006x respectively.The formula of seeds with all activity was Y=2.489×1.006x.3.The count value matched 145Gy isodose line in the first patient was200.The count value matched 217.5Gy isodose line in the first patient was300.The 200-count value line in the second patient covered the target completely and part of the anterior wall of the rectum was involved.The300-count value line in the second patient covered part of the urethra.The second patient was followed up for three months.PSA declined to 0.003?g/L and no complications of rectum and urethra were observed.Conclusion:For immobilized malignant tumors,3D-printed template can be used reproducibly.The dose parameters in pre-plan can be achieved easily and satisfactorily by 3D-printed template guided brachytherapy.The local control rate in template group is higher than traditional group.3D-printed template guided seed implantation may become an easily reproducible standardized procedure in the future.The count value around the iodine-125seed can be detected accurately by SPECT/CT,and then can be quantified.This study provided useful experiment data for the precision measurement of iodine-125 seed implantation.Radiation detection-based dose measurement may become a new noninvasive technology for the dosimetry verification method after brachytherapy. |
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