国产医用直线加速器在早期乳腺癌术后放疗的剂量学特性分析∗

摘要

Objective To evaluate the characteristics of dosimetry and clinical efficiencies of domestic medical linear acceler⁃ator, and provide dosimetry basis for the clinical application of domestic linac. Methods Eleven patients were selected after breast conserving surgery who need to adjuvant radiotherapy, including 5 right breast cancer patients and 6 left breast cancer patients. The prescription dose was 50Gy/25f. Each patient performed dynamic intensity modulated radio⁃therapy ( dIMRT) and three⁃dimensional conformal radiotherapy(3D⁃CRT) by TIGRT TPS. The dose volume histograms (DVHs) were used to analyze the characteristics of do⁃simetry on target volume and the organs at risk ( OARs) , and the conformity index ( CI) and homogeneity index ( HI) were calculated. The monitor unit ( MU) and performing time was recorded. Results There was similar coverage of target dose between dIMRT and 3D⁃CRT. D95 and V100 of dIMRT and 3D⁃CRT plan were (5009�73±12�70)cGy, (95�41±0�54)% and (5005�47±7�30)cGy, (95�18± 0�28)%. D2, CI and HI of dIMRT and 3D⁃CRT plan were (5551�66±89�21)cGy, 0�83±0�01,1�10±0�02 and (5819�20±111�19) cGy, 0�52±0�05, 1�14±0�02,with significant differences(P<0�05). V5, V10 and V20 of patients with ipsilateral lung of dIMRT was (65�32±5�88)%, (38�99±14�42)% and (17�76±0�43)%, which was significantly higher than that of 3D⁃CRT plan(P<0�05). V30of patients with ipsilateral lung of dIMRT plan was(5�59±1�52)%,which was significantly lower than that of 3D⁃CRT plan,with significant differences(P<0�05). Dmeanof left breast cancer patient�s heart in dIMRT plan was(814�59±154�82)cGy, which was higher than that in 3D⁃CRT plan, with significant differences(P<0�05);Dmaxof left breast cancer patient�s heart in dIMRT plan was(4067�93 ±441�39)cGy, which was lower than that in 3D⁃CRT plan, with significant differences(P<0�05). Dmax and Dmeanof right breast cancer patient�s heart in 3D⁃CRT plan were(56�34±15�56)cGy and(393�00±94�95)cGy,which were lower than those in dIMRT plan, with significant differences(P<0�05). MU and treatment delivery time of dIMRT plan was 593�17±39�27 and (124�57±8�25)s,while that in 3D⁃CRT plan was 639�50±49�81 and (134�30±10�46)s. Conclusion Domestic linac can be perform well in rediotherapy for early stage cancer after breast⁃conserving surgery, and dIMRT with good at CI and HI, 3D⁃CRT has lower sparing at OARs.%目的：探讨国产医用直线加速器在乳腺癌保乳术后放疗的剂量学特性与治疗实施效率，为其临床应用提供剂量学依据。方法选取11例早期保乳术后需辅助放疗的患者影像资料，左侧患者6例，右侧患者5例，处方剂量为50 Gy／25次。采用TIGRT计划系统分别设计固定野动态调强（ dIMRT）与三维适形（3D⁃CRT）放疗计划，根据剂量体积直方图（DVH）统计靶区、危及器官（OARs）的剂量，并计算靶区适形指数（CI）与均匀指数（HI），最后统计机器跳数（MU）和治疗时间（ t）。结果 dIMRT 与3D⁃CRT 计划靶区剂量覆盖度相似， D95与 V100分别为（5009�73±12�70） cGy、（95�41±0�54）％与（5005�47±7�30）cGy、（95�18±0�28）％；两种计划靶区最大剂量（D2）、CI与HI分别为（5551�66±89�21）cGy、0�83±0�01、1�10±0�02与（5819�20±111�19）cGy、0�52±0�05、1�14±0�02，差异具有统计学意义（P＜0�05）。 dIMRT组患侧肺的V5、V10和V20分别为（65�32±5�88）％、（38�99±14�42）％和（17�76±0�43）％，均高于3D⁃CRT的（21�77±2�08）％、（16�88±1�80）％和（14�79±1�90）％，而V30为（5�59±1�52）％，低于3D⁃CRT组的（13�52±1�86）％，差异具有统计学意义（P＜0�05）。 dIMRT组左侧患者心脏Dmean为（814�59±154�82）cGy高于3D⁃CRT组的（347�88±57�29）cGy；dIMRT组左侧患者心脏Dmax为（4067�93±441�39）cGy低于3D⁃CRT组的（5355�75±337�41）cGy，差异具有统计学意义（P＜0�05）。3D⁃CRT组右侧患者心脏的 Dmean、Dmax分别为（56�34±15�56）cGy、（393�00±94�95）cGy，均低于dIMRT组的（349�31±50�92）cGy、（1647�49±419�65）cGy，差异具有统计学意义（P＜0�05）。 dIMRT组平均 MU 为593�17±39�27，平均出束时间为（124�57±8�25） s，3D⁃CRT 组平均 MU 为639�50±49�81，平均时间为（134�30±10�46）s，差异无统计学意义（P＞0�05）。结论国产加速器能够实现早期乳腺癌保乳术后患者放疗的靶区剂量与危及器官的剂量学要求，并且dIMRT靶区剂量分布更加均匀，适形度更好，而3D⁃CRT组在危及器官低剂量区域中体现出更好的优越性。