胃癌放射治疗中静态调强计划射野和子野的优化研究

Optimization of beam sets and segments number in static intensity-modulated radiation therapy plans in radiotherapy of gastric cancer

目的比较胃癌术后不同布野方案及子野数设置的静态调强计划质量差异,研究胃癌术后调强放射治疗(放疗)计划设计中较优的射野及子野数设置。方法采用随机抽样法选择四川大学华西医院2013年2月1日—8月30日接受胃癌术后辅助放疗的15例患者入组研究,在每例患者原有的个体化5野调强计划的基础上,在相同的放疗计划系统Pinnacle 9.2中重新对每例患者进行4种不同共面布野方案的静态调强计划设计:布野方案一为7野等角度均分静态调强计划;方案二为5野等角度均分静态调强计划;方案三为4野静态调强计划,射野方向为310、20、90、180°;方案四为3野静态调强计划,射野方向为310、65、180°。对于4种不同布野方案的静态调强计划,设置最大子野数为65。对于布野方案三,改变最大子野数65的设置为45和25,另得2个不同的静态调强计划。分析对比15×7个静态调强计划结果中靶区和危及器官的剂量体积参数、机器跳数和治疗时间。结果当最大子野数为65时,使用4野调强计划相对于临床5野调强计划在靶区适形度方面稍有提高(0.74±0.04 vs.0.73±0.05,P<0.01),在对危及器官肝脏[如受到30 Gy照射的百分体积V30:(22.71±6.10)%vs.(24.03±6.84)%,P<0.01]和肾脏[如右肾V20:(14.97±6.72)%vs.(19.41±6.14)%,P<0.01]的保护上优势明显。与最大子野数为65的4野调强计划相比,最大子野数为45和25的4野调强计划靶区适形度有所降低(0.74±0.04 vs.0.73±0.04 vs.0.71±0.04,P<0.05),但仍在临床可接受的范围内,且继续保持了对危及器官肝脏和肾脏的保护优势;治疗时间分别平均减少了1.8、4.3 min[(494.66±26.79)vs.(384.26±14.99)vs.(235.00±9.21)s,P<0.01];治疗效率分别提高了22.3%和52.4%,且该结果具有统计学意义(P<0.05)。结论在胃癌辅助放疗中,使用较少射野和子野数的4野静态调强技术在保证计划质量的同时,更好地保护了危及器官,尤其是肝脏和肾脏,并且减少了照射时间,提高了治疗效率。

Objective To compare the static intensity-modulated radiation therapy （IMRT） plans using different beams sets and segments number, and find the better static IMRT plan sets on beams and segments in gastric surgical adjuvant radiotherapy. Methods Fifteen patients who underwent adjuvant radiotherapy for gastric cancer between February 1 st and August 30th, 2013 were chosen as subjects through random sampling. Based on the 5 beams static IMRT plans already used in clinical practice, four different static IMRT plans used diverse beams sets for each patient were designed in the same treatment planning system （Pinnacle 9.2）. The beams sets of static IMRT plans were as follows： 7 coplanar equal beams; 5 coplanar equal beams; 4 coplanar beams of 310, 20, 90 and 180% 3 coplanar beams of 310, 65 and 180°. Sufficient segments 65 was set as the max segments number in order to compare the plans＇ difference just resulting from beams. In the second step, the max segments number was changed from 65 to 45 and 25 to design two different static IMRT plans for the 4 coplanar beams static IMRT plans. The dosimetric parameters were compared for the planning target volume （PTV） and organs at risk （OARs）. The monitor units and treatment times of the different static IMRT plans were also evaluated. Results When the max segments number was set to 65, the 4 coplanar beams static IMRT plans were a little better on PTV conformability than the 5 coplanar beams static IMRT plans used in clinical practice （0.74±0.04 vs. 0.73±0.05, P〈0.01）. Meanwhile, better OARs dose sparing especially for liver and kidneys were gained by the 4 coplanar beams static IMRT plans, for example, the percent volume gained 30 Gy for liver [（22.71 ±6.10）% vs. （24.03±6.84）%, P〈0.01] and the percent volume gained 20 Gy for the right kidney [（14.97±6.72）% vs. （19.41±6.14）%, P〈0.01]. The PTV conformability of the 4 coplanar beams static IMRT plans reduced as the max segments number became smaller （0.74±0.04 vs. 0.73±0.04 vs. 0.71±0.04, P〈0.05）. However, they were still acceptable in clinical practice. And the better dose sparing for liver and kidneys were retained. The average reductions of 1.8 and 4.3 minutes on the irradiation time were get by the 4 coplanar beams static IMRT plans with the max segments number 45 and 25 compared to that with the max segments number 65 [（494.66±26.79） vs. （384.26±14.99） vs. （235.00±9.21） s, P〈0.01]. And the raises of treatment efficiency were 22.3% and 52.4%, respectively （P〈0.05）. Conclusions The 4 coplanar beams static IMRT plans with fewer segments could ensure plan quality, and protect the OARs better in the meanwhile, especially for liver and kidneys. The treatment time is reduced as well. The 4 coplanar beams static IMRT plans could improve the treatment efficiency.