乳腺癌改良根治术后调强放疗的精细化调整

Refined intensity-modulated radiotherapy planning after modified radical mastectomy for breast cancer

摘要:

目的 探讨乳腺癌改良根治术后调强放疗计划系统（TPS）参数设置的影响。方法 回顾性分析2022年8月—2023年5月在中山市小榄人民医院行左侧乳腺癌改良根治术后调强放疗的14例患者。在放疗TPS中，对同一患者放疗计划的3个参数即最小子野面积（MSA）、最小机器跳数（MMU）和最大子野数（MNOS）先后设置不同数值，比较数值改变引起的剂量学参数［计划靶区的100%处方剂量覆盖体积（V_100%）和110%处方剂量覆盖体积（V_110%）、适形度指数（CI）、均匀性指数，危及器官中左肺接受5 Gy的肺体积、左肺接受20 Gy的肺体积（LV₂₀）、左肺接受30 Gy的肺体积、左肺平均剂量，右肺接受5 Gy的肺体积（RV₅）、右肺平均剂量，心脏接受30 Gy的组织体积、心脏平均剂量，脊髓最高值Cord］及执行参数计划执行时长的变化。结果 与初始计划（MSA=4 cm²）相比，MSA≥9 cm²时总机器跳数（OMU）降低（P <0.05）；MSA≥16 cm²时计划执行时长降低（P <0.05）；MSA≥49 cm²时ONOS降低（P <0.05）；MSA≥64 cm²时V_100%降低（P <0.05）。与初始计划（MMU=5）相比，MMU≥12时ONOS降低（P <0.05）；MMU≥15时V_110%和RV₅升高（P <0.05），计划执行时长降低（P <0.05）；MMU≥20时LV₂₀升高（P <0.05），V_100%和OMU降低（P <0.05）；MMU≥25时CI降低（P <0.05），Cord升高（P <0.05）。其他MNOS与初始计划（MNOS=56）的ONOS和计划执行时长比较，差异均有统计学意义（P <0.05）；ONOS和计划执行时长的变化与MNOS的大小变化一致。结论 在满足计划评估的前提下，乳腺癌改良根治术后调强放疗时适当调整TPS的参数值有利于提高执行效率。MSA最高可达49 cm²，MMU最高可达12，MNOS与执行时长密切相关，应谨慎设置。

Abstract:

Objective To study the influence of treatment planning system (TPS) parameters on intensity-modulated radiotherapy (IMRT) after modified radical mastectomy for breast cancer.Methods A retrospective analysis was conducted on 14 patients receiving IMRT after modified radical mastectomy for left breast cancer at our hospital from August 2022 to May 2023. For each patient, three parameters in the radiotherapy TPS, including minimum segment area (MSA), minimum monitor unit (MMU), and maximum number of segments (MNOS), were sequentially set to different values. The changes in dosimetric parameters resulting from these adjustments were compared, including the volume receiving 100% of the prescribed dose (V_100%), the volume receiving 110% of the prescribed dose (V_110%), the conformity index (CI), and the homogeneity index (HI) of the planning target, the left lung volume receiving 5 Gy (LV₅), 20 Gy (LV₂₀), and 30 Gy (LV₃₀), the mean left lung dose (LD_mean), the right lung volume receiving 5 Gy (RV₅), the mean right lung dose (RD_mean), the heart volume receiving 30 Gy (HV₃₀), the mean heart dose (HD_mean), and the maximum spinal cord dose (Cord). Additionally, changes in the plan execution time were evaluated.Results Compared with the initial plan (MSA = 4 cm²), the overall monitor units (OMU) decreased with MSA ≥ 9 cm² (P < 0.05), plan execution time decreased with MSA ≥ 16 cm² (P < 0.05), the overall number of segments (ONOS) decreased with MSA ≥ 49 cm² (P < 0.05), and V100% decreased with MSA ≥ 64 cm² (P < 0.05). Compared with the initial plan (MMU = 5), ONOS decreased with MMU ≥ 12 (P < 0.05), V110% and RV₅ increased and plan execution time decreased with MMU ≥ 15 (P < 0.05), LV₂₀ increased and V_100% and OMU decreased with MMU ≥ 20 (P < 0.05), CI decreased and Cord increased with MMU ≥ 25 (P < 0.05). Compared with the initial plan (MNOS = 56), changes in ONOS and plan execution time for other MNOS settings were all statistically significant (P < 0.05). The variations in ONOS and plan execution time were consistent with the changes in MNOS values.Conclusion Within the constraints of acceptable plan evaluation, appropriately adjusting TPS parameters during IMRT after modified radical mastectomy for breast cancer can improve plan execution efficiency. The maximum values for MSA and MMU can reach 49 and 12, respectively, while MNOS is closely correlated with plan execution time and should be set cautiously.