Kainz Kristofer, Firat Selim, Wilson J Frank, Schultz Christopher, Siker Malika, Wang Andrew, Olson Dan, Li X Allen
Department of Radiation Oncology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, Wisconsin 53226, USA.
Phys Med Biol. 2015 Mar 21;60(6):2167-77. doi: 10.1088/0031-9155/60/6/2167. Epub 2015 Feb 16.
We compare the quality of photon IMRT (helical tomotherapy) with classic proton plans for brain, head and neck tumors, in terms of target dose uniformity and conformity along with organ-at-risk (OAR) sparing. Plans were created for twelve target volumes among eight cases. All patients were originally planned and treated using helical tomotherapy. Proton plans were generated using a passively-scattered beam model with a maximum range of 32 g cm(-2) (225 MeV), range modulation in 0.5 g cm(-2) increments and range compensators with 4.8 mm milling tool diameters. All proton plans were limited to two to four beams. Plan quality was compared using uniformity index (UI), conformation number (CN) and a EUD-based plan quality index (fEUD). For 11 of the 12 targets, UI was improved for the proton plan; on average, UI was 1.05 for protons versus 1.08 for tomotherapy. For 7 of the 12 targets, the tomotherapy plan exhibited more favorable CN. For proximal OARs, the improved dose conformity to the target volume from tomotherapy led to a lower maximum dose. For distal OARs, the maximum dose was much lower for proton plans. For 6 of the 8 cases, near-total avoidance for distal OARs provided by protons leads to improved fEUD. However, if distal OARs are excluded in the fEUD calculation, the proton plans exhibit better fEUD in only 3 of the 8 cases. The distal OAR sparing and target dose uniformity are generally better with passive-scatter proton planning than with photon tomotherapy; proton therapy may be preferred if the clinician deems those attributes critical. However, tomotherapy may serve equally as well as protons for cases where superior target dose conformity from tomotherapy leads to plan quality nearly identical to or better than protons and for cases where distal OAR sparing is not concerning.
我们在靶区剂量均匀性、适形性以及危及器官（OAR）保护方面，比较了光子调强放疗（螺旋断层放疗）与经典质子计划用于脑、头颈部肿瘤的质量。针对8例病例中的12个靶区体积制定了计划。所有患者最初均采用螺旋断层放疗进行计划制定和治疗。质子计划使用被动散射束模型生成，最大射程为32 g cm(-2)（225 MeV），射程调制以0.5 g cm(-2)为增量，射程补偿器的铣刀直径为4.8 mm。所有质子计划限制在两到四个射野。使用均匀性指数（UI）、适形数（CN）和基于等效均匀剂量（EUD）的计划质量指数（fEUD）来比较计划质量。在12个靶区中的11个，质子计划的UI有所改善；平均而言，质子计划的UI为1.05，而断层放疗为1.08。在12个靶区中的7个，断层放疗计划显示出更有利的CN。对于近端OARs，断层放疗对靶区体积更好的剂量适形性导致最大剂量更低。对于远端OARs，质子计划的最大剂量要低得多。在8例病例中的6例，质子对远端OARs的近乎完全回避导致fEUD得到改善。然而，如果在fEUD计算中排除远端OARs，质子计划仅在8例病例中的3例显示出更好的fEUD。与光子断层放疗相比，被动散射质子计划在远端OARs保护和靶区剂量均匀性方面通常更好；如果临床医生认为这些属性至关重要，质子治疗可能更受青睐。然而，对于断层放疗具有更好的靶区剂量适形性从而导致计划质量与质子计划几乎相同或更好的情况，以及对于远端OARs保护不相关的情况，断层放疗可能与质子治疗效果相当。
