巨块型NSCLC质子部分立体定向消融推量放疗的剂量学优势

Partial stereotactic ablative boost radiotherapy in bulky non-small cell lung cancer:a dosimetric comparison between proton and photon

目的探索肿瘤长径>8 cm的巨块非小细胞肺癌(NSCLC)放疗中质子部分立体定向消融推量放疗(P-SABR)的剂量学优势。方法收集既往应用光子P-SABR治疗的9例巨块NSCLC的定位影像。在光子肿瘤推量靶区(光子GTVb)基础上逐步外扩,直到重要危及器官受量达3.0 Gy/次时停止,形成质子肿瘤推量靶区(质子GTVb),质子GTV、CTV范围同光子,分别制订光子固定野调强放疗(光子FF-IMRT)、光子容积调强弧形治疗(光子VMAT)、质子调强放疗(IMPT)计划。对比不同治疗技术的剂量学参数。结果光子GTVb和质子GTVb占GTV体积比分别为25.4%±13.4%和69.7%±30.0%(P<0.001)。光子IMRT、光子VMAT、IMPT的CTV平均剂量分别为(76.1±4.9)Gy、(78.2±3.6)Gy、(84.7±4.9)Gy,生物有效剂量(BED)≥90 Gy所包含肿瘤占GTV体积的百分比分别为70.7%±21.7%、76.8%±22.1%、97.9%±4.0%,质子较光子P-SABR计划显著提高了靶区剂量及BED(P<0.05)。质子较光子计划还降低了危及器官受量,其中光子FF-IMRT、光子VMAT和IMPT的双肺V5 Gy分别为49.2%±22.0%、56.8%±19.0%和16.1%±6.3%(P<0.001)。结论质子P-SABR较光子可在降低危及器官受量情况下,扩大肿瘤推量靶区范围并提高肿瘤内BED,有望进一步提高巨块NSCLC的局部控制率。

Objective Partial stereotactic ablative boost radiotherapy(P-SABR)is a method to deliver SABR boost to the gross tumor boost volume(GTVb),followed by conventionally fractionated radiotherapy to the whole tumor area(GTV).GTVb is the max volume receiving SABR while ensuring the critical organ-at-risk(OAR)falloff to 3 GyE/f.We investigated the potential advantage of proton therapy in treating bulky non-small cell lung cancer(the tumor length greater than 8 cm).Methods Nine patients with bulky NSCLC treated with photon P-SABR in our institute were selected.For the treatment planning of proton therapy,the GTVb target area was gradually outwardly expanded based on the photon GTVb target area until the dose to critical OARs reached 3 GyE/f.The GTV and CTV areas remained the same as photon plan.A proton intensity-modulated radiation treatment plan(proton-IMPT),a photon intensity-modulated radiation treatment plan(photon-IMRT)and a photon volumetric modulated arc therapy(photon-VMAT)were created for each patient,respectively.The dosimetric parameters of different treatment plans were compared.Results The volume ratio of GTVb-photon and GTVb-proton to GTV was(25.4±13.4)%and(69.7±30.0)%,respectively(P<0.001).In photon-IMRT,photon-VMAT,and proton-IMPT plan groups,the mean dose of CTV was(76.1±4.9)Gy,(78.2±3.6)Gy,and(84.7±4.9)Gy,respectively;the ratio of tumor volume with Biologic Effective Dose(BED)≥90 Gy to GTV volume was(70.7±21.7)%,(76.8±22.1)%,and(97.9±4.0)%,respectively.The actual dose and BED to the tumor area of the proton-IMPT plan group were significantly higher than those of the photon plan group(both P<0.05).Besides,the OARs dose was significantly decreased in the proton-IMPT group,with(49.2±22.0)%,(56.8±19.0)%and(16.1±6.3)%of the whole lung V5 for photon-IMRT,photon-VMAT and proton-IMPT,respectively(all P<0.001).Conclusions Larger GTV boost target volume,higher BED and reduced OARs dose can be achieved in proton plans compared with photon plans.Proton P-SABR is expected to further improve the local control rate of bulky NSCLC with fewer adverse effects.