Georg Dietmar, Hillbrand Martin, Stock Markus, Dieckmann Karin, Pötter Richard
Department of Radiotherapy, Medical University Vienna/AKH Vienna, Vienna, Austria.
Radiother Oncol. 2008 Sep;88(3):368-75. doi: 10.1016/j.radonc.2008.03.007. Epub 2008 Apr 9.
The aim of the present study was to investigate potential dosimetric benefits of proton therapy for hypofractionated stereotactic body radiotherapy (SBRT).
Twelve patients undergoing hypofractionated SBRT at the Medical University Vienna were selected. Passively scattered protons (PT) and intensity modulated proton therapy (IMPT) were evaluated against a conformal photon technique (3D-CRT), assuming a fractionation of 3x15Gy, prescribed to the 65% isodose. For all treatment techniques shallow breathing with abdominal compression (SB+AC) was compared with a deep inspiration breath hold technique (DIBH). Treatment planning was done with XiO (CMS, USA). Target conformity, dose-volume histograms (DVH) and various associated dosimetric parameters were considered for the planning target volume (PTV), lung, heart and esophagus.
For both breathing conditions conformity indices were very similar. They were between 0.75 and 0.78 for IMPT and 3D-CRT and around 0.55 for PT using 2-3 beams. Irrespective of treatment modality, DVHs for the ipsilateral lung were improved with the DIBH technique. For the PT technique, the 2Gy isodose (V2Gy) covered on average 7-9% less lung volume compared to 3D-CRT, for IMPT this reduction was more than 10%. Volumes covered the 4 and 6Gy isodoses were 2-4% smaller for IMPT, but very similar for PT and 3D-CRT. Both proton techniques achieved full sparing of the contralateral lung and superior sparing of the heart. Maximum doses to the heart and esophagus were on average around 3Gy for 3D-CRT and almost 0Gy for both proton techniques. For 3D-CRT average V2Gy values for the heart could be reduced from 64% in shallow breathing to 34% in DIBH. V2Gy for protons was negligible.
Only small dosimetric differences were found between photons and protons for SBRT of lung lesions. Whether these small dosimetric benefits translate in reduced side effects or have the potential to improve local control rates remains to be demonstrated in clinical studies.
本研究旨在探讨质子治疗在大分割立体定向体部放射治疗（SBRT）中的潜在剂量学优势。
选取了维也纳医科大学接受大分割SBRT的12例患者。将被动散射质子治疗（PT）和调强质子治疗（IMPT）与适形光子技术（3D-CRT）进行对比，假设分割方案为3×15Gy，处方剂量为65%等剂量线。对于所有治疗技术，比较了腹部压迫下的浅呼吸（SB+AC）与深吸气屏气技术（DIBH）。使用XiO（美国CMS公司）进行治疗计划。针对计划靶区（PTV）、肺、心脏和食管，考虑了靶区适形度、剂量体积直方图（DVH）以及各种相关的剂量学参数。
在两种呼吸条件下，适形指数非常相似。IMPT和3D-CRT的适形指数在0.75至0.78之间，使用2 - 3束射野的PT的适形指数约为0.55。无论治疗方式如何，DIBH技术均改善了同侧肺的DVH。对于PT技术，与3D-CRT相比，2Gy等剂量线（V2Gy）平均覆盖的肺体积减少了7 - 9%，IMPT的这种减少超过10%。IMPT覆盖4和6Gy等剂量线的体积小2 - 4%，但PT和3D-CRT非常相似。两种质子技术均实现了对侧肺的完全 sparing以及心脏的更好 sparing。3D-CRT对心脏和食管的最大剂量平均约为3Gy，两种质子技术的最大剂量几乎为0Gy。对于3D-CRT，心脏的平均V2Gy值可从浅呼吸时的64%降至DIBH时的34%。质子治疗的V2Gy可忽略不计。
在肺部病变的SBRT中，光子治疗和质子治疗之间仅发现了微小的剂量学差异。这些微小的剂量学优势是否能转化为副作用的减少或有改善局部控制率的潜力，仍有待临床研究证实。
