Weber Damien C, Trofimov Alexei V, Delaney Thomas F, Bortfeld Thomas
Department of Radiation Medicine, Paul Scherrer Institute, Villigen-PSI, Switzerland.
Int J Radiat Oncol Biol Phys. 2004 Apr 1;58(5):1596-606. doi: 10.1016/j.ijrobp.2003.11.028.
A comparative treatment planning study has been undertaken between intensity modulated (IM) photon therapy and IM proton therapy (IMPT) in paraspinal sarcomas, so as to assess the potential benefits and limitations of these treatment modalities. In the case of IM proton therapy, plans were compared also for two different sizes of the pencil beam. Finally, a 10% and 20% dose escalation with IM protons was planned, and the consequential organ at risk (OAR) irradiation was evaluated.
Plans for 5 patients were computed for IM photons (7 coplanar fields) and protons (3 coplanar beams), using the KonRad inverse treatment planning system (developed at the German Cancer Research Center). IMPT planning was performed assuming 2 different sizes of the pencil beam: IMPT with a beam of full width at half-maximum of 20 mm, and IMPT with a "mini-beam" (IMPT(M), full width at half-maximum = 12 mm). Prescribed dose was 77.4 Gy or cobalt Gray equivalent (CGE) for protons to the gross tumor volume (GTV). Surface and center spinal cord dose constraint for all techniques was 64 and 53 Gy/CGE, respectively. Tumor and OAR dose-volume histograms were calculated. Results were analyzed using dose-volume histogram parameters, inhomogeneity coefficient, and conformity index.
Gross tumor volume coverage was optimal and equally homogeneous with both IM photon and IM proton plans. Compared to the IM photon plans, the use of IM proton beam therapy leads to a substantial reduction of the OAR total integral dose in the low-level to mid-dose level. Median heart, lung, kidney, stomach, and liver mean dose and dose at the 50% volume level were consistently reduced by a factor of 1.3 to 25. Tumor dose homogeneity in IMPT(M) plans was always better than with IMPT planning (median inhomogeneity coefficient, 0.19 vs. 0.25). IMPT dose escalation (to 92.9 CGE to the GTV) was possible in all patients without exceeding the normal-tissue dose limits.
These results suggest that the use of IM photon therapy, when compared to IM protons, can result in similar levels of tumor conformation. IM proton therapy, however, reduces the OAR integral dose substantially, compared to IM photon radiation therapy. As a result, tumor dose escalation was always possible with IM proton planning, within the maximal OAR dose constraints. In IM proton planning, reducing the size of the proton pencil beam (using the "mini-beam") improved the dose homogeneity, but it did not have a significant effect on the dose conformity.
开展一项针对脊柱旁肉瘤的调强（IM）光子治疗与调强质子治疗（IMPT）的对比治疗计划研究，以评估这些治疗方式的潜在益处和局限性。对于IM质子治疗，还比较了两种不同尺寸笔形束的计划。最后，计划将IM质子剂量提高10%和20%，并评估相应的危及器官（OAR）照射情况。
使用KonRad逆向治疗计划系统（由德国癌症研究中心开发），为5例患者计算了IM光子（7个共面野）和质子（3个共面射束）的计划。IMPT计划是在假设两种不同尺寸笔形束的情况下进行的：半高宽为20 mm射束的IMPT，以及“迷你束”（IMPT(M)，半高宽 = 12 mm）的IMPT。质子对大体肿瘤体积（GTV）的处方剂量为77.4 Gy或钴灰当量（CGE）。所有技术的脊髓表面和中心剂量约束分别为64和53 Gy/CGE。计算肿瘤和OAR的剂量体积直方图。使用剂量体积直方图参数、不均匀性系数和适形指数对结果进行分析。
IM光子计划和IM质子计划对大体肿瘤体积的覆盖均最佳且均匀性相同。与IM光子计划相比，使用IM质子束治疗可使低剂量至中剂量水平的OAR总积分剂量大幅降低。心脏、肺、肾、胃和肝脏的中位平均剂量以及50%体积水平处的剂量持续降低了1.3至25倍。IMPT(M)计划中的肿瘤剂量均匀性始终优于IMPT计划（中位不均匀性系数，0.19对0.25）。所有患者均有可能将IMPT剂量提高（至GTV为92.9 CGE）而不超过正常组织剂量限制。
这些结果表明，与IM质子治疗相比，IM光子治疗可产生相似水平的肿瘤适形性。然而，与IM光子放射治疗相比，IM质子治疗可大幅降低OAR积分剂量。因此，在最大OAR剂量约束范围内，IM质子计划始终可以提高肿瘤剂量。在IM质子计划中，减小质子笔形束的尺寸（使用“迷你束”）可改善剂量均匀性，但对剂量适形性没有显著影响。
