Effects of minimum monitor unit threshold on spot scanning proton plan quality
Effects of minimum monitor unit threshold on spot scanning proton plan quality
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DOI：
10.1118/1.4892057
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发表时间：
2014-09-01
期刊：
影响因子：
3.8
通讯作者：
Herman, Michael G.
中科院分区：
文献类型：
--
作者：
Howard, Michelle;Beltran, Chris;Herman, Michael G.
目的：调查的最小监测单元（MU）的扫描质子therapy.Methods的临床治疗计划的质量的影响：输送系统的特点限制了质子的最小数量，可以提供每个斑点，导致最小MU限制。计划质量可能受到最小MU限制的影响。两个研究中心用于研究min-MU对治疗计划的影响：5-10 cm深度的儿科脑肿瘤; 1-20 cm深度的头颈部肿瘤。为每个部位创建了三个磁场，强度调制点扫描质子计划，参数变化如下：最小MU限值范围为0.0000-0.0060;点间距范围为2-8 mm。比较基于靶均匀性和正常组织保留。对于小儿脑，还比较了两个版本的治疗计划系统，以根据最小MU限值在优化过程中的时间来判断其影响（Eclipse v.10和v.13，Varian Medical Systems，Palo Alto，CA）。在固定光斑间距的情况下，最小MU限制的增加降低了均匀目标覆盖和避免关键结构的计划质量。当比较0.0000和0.0060的最小MU限值与4 mm的固定光斑间距时，头部和颈部以及小儿脑部计划均显示CTV中热点的相对剂量增加20%，关键关键结构的相对剂量增加10%。0.0000和0.0010的MU限值产生相似的计划质量，并且随着最小MU限值增加到0.0020以上，质量降低。当光斑间距接近8 mm时，当没有施加最小MU限制时，观察到计划质量下降。
Purpose: To investigate the influence of the minimum monitor unit (MU) on the quality of clinical treatment plans for scanned proton therapy.Methods: Delivery system characteristics limit the minimum number of protons that can be delivered per spot, resulting in a min-MU limit. Plan quality can be impacted by the min-MU limit. Two sites were used to investigate the impact of min-MU on treatment plans: pediatric brain tumor at a depth of 5-10 cm; a head and neck tumor at a depth of 1-20 cm. Three-field, intensity modulated spot scanning proton plans were created for each site with the following parameter variations: min-MU limit range of 0.0000-0.0060; and spot spacing range of 2-8 mm. Comparisons were based on target homogeneity and normal tissue sparing. For the pediatric brain, two versions of the treatment planning system were also compared to judge the effects of the min-MU limit based on when it is accounted for in the optimization process (Eclipse v. 10 and v. 13, Varian Medical Systems, Palo Alto, CA).Results: The increase of the min-MU limit with a fixed spot spacing decreases plan quality both in homogeneous target coverage and in the avoidance of critical structures. Both head and neck and pediatric brain plans show a 20% increase in relative dose for the hot spot in the CTV and 10% increase in key critical structures when comparing min-MU limits of 0.0000 and 0.0060 with a fixed spot spacing of 4 mm. The DVHs of CTVs show min-MU limits of 0.0000 and 0.0010 produce similar plan quality and quality decreases as the min-MU limit increases beyond 0.0020. As spot spacing approaches 8 mm, degradation in plan quality is observed when no min-MU limit is imposed.Conclusions: Given a fixed spot spacing of