基于TOMO保护海马的全脑放疗计划的多参数分析与剂量学研究

Multi-parameter analysis and dosimetric study of the whole brain radiotherapy plan based on TOMO for hippocampus sparing

目的探索螺旋断层放射治疗(TOMO)保护海马的全脑放疗计划(WBRT)的参数设置,在满足临床评估指标的条件下进行多参数分析与剂量学研究,获取放疗计划的基本参数设置的最佳值和范围.方法回顾性分析2017年1月至2022年11月于陕西省肿瘤医院行WBRT的10例脑肿瘤患者的临床资料,其中男性4例、女性6例,年龄(60.0±8.1)岁,范围42~74岁.所有患者均进行保护海马的放疗计划设计,计划需满足海马最大剂量(D_(max))、危及器官D_(max)、机架旋转周期、出束时间等指标均在限定范围内.按照TOMO机的参数要求,分别设置调制因子(MF)为2.0、2.3、2.5、2.7、3.0、4.0,射野宽度(FW)为2.5、5.0 cm,螺距为0.143、0.287、0.430进行计划设计,分析MF、FW、螺距对海马保护计划的影响.FW对应各项指标的比较采用配对样本t检验,MF、螺距对应各项指标的比较采用方差分析.结果螺距=0.287、MF=2.7时,FW=2.5、5.0 cm对应的出束时间[(508.90±34.44)s对(281.47±19.77)s]、计划靶区(PTV)-D_(max)[(32.90±1.28)Gy对(34.14±1.20)Gy]、左侧海马D_(max)[(15.21±0.53)Gy对(15.88±0.94)Gy]、脑干D_(max)[(33.69±0.23)Gy对(35.09±0.43)Gy]的差异均有统计学意义(t=39.756、11.226、2.467、11.269,均P<0.05).FW=2.5 cm能够更好地保护海马.FW=2.5 cm、螺距=0.287时,MF=2.0、2.3、2.5、2.7、3.0、4.0对应的TOMO机架旋转周期[(17.91±0.96)、(20.18±0.70)、(21.61±0.73)、(23.28±0.63)、(25.82±1.20)、(34.54±1.22)s]、出束时间[(376.77±26.53)、(432.58±27.73)、(466.64±31.42)、(508.90±34.44)、(554.10±44.70)、(750.63±50.91)s]的差异均有统计学意义(F=677.482、209.716,均P<0.001).MF=2.0、2.3、2.5、3.0、4.0时,1例患者右侧海马的D_(max)为18.19、18.35、18.83、18.75、18.80 Gy,均超出剂量限量范围.MF=4.0时,TOMO机架旋转周期为(34.54±1.22)s,超过了TOMO机架的最佳旋转周期.MF=2.0时,1例患者左、右眼晶状体D_(max)为9.07、10.30 Gy,均超出剂量限量范围.最终选取2.7作为MF最佳值.MF=2.7、FW=2.5cm时,螺距=0.143、0.287、0.430对应的机架旋转周期为(11.81±0.03)、(23.28±0.63)、(29.59±0.47)s,差异有统计学意义(F=3935.056,P<0.001).螺距=0.143时,机架旋转周期为(11.81±0.03)s,并非最佳转速.出束时间为(518.80±26.09)、(508.90±34.44)、(431.37±25.44)s,差异有统计学意义(F=26.889,P<0.001).螺距为0.143和0.430时,均有部分患者海马的D_(max)超出剂量限量范围,螺距=0.287更合适保护海马的TOMO计划.结论在保护海马的TOMO计划设计中,推荐MF=2.7、FW=2.5cm、螺距=0.287.

Objective To explore the parameter setting of whole brain radiotherapy(WBRT)plan using a helical tomotherapy(TOMO)machine to protect the hippocampus.To meet the clinical evaluation index,multi parameter analysis and dosimetric research were conducted to obtain the optimal value and range of the basic parameter setting of a radiotherapy plan.Methods The clinical data of 10 brain tumor patients who underwent WBRT at Shanxi Provincial Cancer Hospital from January 2017 to November 2022 were retrospectively analyzed.Among them,four males and six females were identified with an average age of(60.0±8.1)years and an age range of 42–74 years.Radiotherapy plans for protecting the hippocampus were designed for all patients,within the limited range of the maximum dose(D_(max))to the hippocampus,D_(max) of critical organs,gantry period,and beam on time.In accordance with the parameter requirements of TOMO machine,a modulation factor(MF)of 2.0,2.3,2.5,2.7,3.0,and 4.0;field widths(FW)of 2.5 and 5.0 cm;and pitch of 0.143,0.287,and 0.430 were selected for planning.The effects of MF,FW,and pitch on the hippocampus sparing plans were analysised.A paired sample t-test was used to compare the corresponding indicators of FW,and analysis of variance was used to compare the corresponding indicators of MF and pitch.Results MF=2.7,and pitch=0.287,in addition,FW was set to 2.5 and 5.0 cm.Statistically significant differences in beam on time((508.90±34.44)s vs.(281.47±19.77)s),planned target volume(PTV)-D_(max)((32.90±1.28)Gy vs.(34.14±1.20)Gy),left hippocampus D_(max)((15.21±0.53)Gy vs.(15.88±0.94)Gy),and brainstem D_(max)((33.69±0.23)Gy vs.(35.09±0.43)Gy)were found(t=39.756,11.226,2.467,11.269;all P<0.05).The FW=2.5 cm is better at protecting the hippocampus.FW=2.5 cm,and pitch=0.287,MF was set to 2.0,2.3,2.5,2.7,3.0,4.0.Statistically significant differences in gantry period((17.91±0.96),(20.18±0.70),(21.61±0.73),(23.28±0.63),(25.82±1.20),and(34.54±1.22)s)and beam on time((376.77±26.53),(432.58±27.73),(466.64±31.42),(508.90±34.44),(554.10±44.70),and(750.63±50.91)s)of TOMO were found(F=677.482,209.716;both P<0.001).MF was set to 2.0,2.3,2.5,3.0,and 4.0.D_(max) of the right hippocampus(18.19,18.35,18.83,18.75,and 18.80 Gy)of one patient was exceeded the limit.The gantry period was(34.54±1.22)s at MF=4.0,which exceeds the optimal gantry period of TOMO.At MF=2.0,the left and right lens D_(max) of another patient were 9.07 and 10.30 Gy,respectively,which exceeded the limit.Therefore,the best MF value is 2.7.MF=2.7,FW=2.5 cm,pitch=0.143,0.287 and 0.430,the gantry period is(11.81±0.03),(23.28±0.63)and(29.59±0.47)s,the difference in corresponding gantry period is statistically significant(F=3939.056,P<0.001).At pitch=0.143,the gantry period is(11.81±0.03)s,which is not the best gantry period.The difference in beam on time((518.80±26.09),(508.90±34.44),and(431.37±25.44)s)corresponding to different pitches was statistically significant(F=26.889,P<0.001).Some patients with pitch of 0.143 and 0.430 exceeded the limit of hippocampus D_(max).Overall,pitch=0.287 is more appropriate for the TOMO hippocampus sparing plans.Conclusion The recommended parameters are MF=2.7,FW=2.5 cm,and pitch=0.287 in TOMO for hippocampus sparing.