Stoker Joshua, Vora Sujay, Patel Ameet, Grosshans David, Brown Paul D, Vern-Gross Tamara, Bues Martin, Daniels Thomas, Allred Bryce, Uejo Arielle, Kosiorek Heidi, Bruso Marlene, Keole Sameer
Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, AZ, USA.
Department of Radiology, Division of Neuroradiology, Mayo Clinic Arizona, Phoenix, AZ, USA.
Phys Imaging Radiat Oncol. 2018 Nov 27;8:28-32. doi: 10.1016/j.phro.2018.11.001. eCollection 2018 Oct.
Intensity modulated proton therapy (IMPT) allows for modulation parameterized for individual beamlets by position, intensity, and depth. This modulation capability is ideally suited for sparing organs at risk intermediate of the radiation target, such as hippocampal volumes within the whole brain. This work compared IMPT relative to volumetric modulated arc therapy (VMAT) during hippocampal avoidance whole brain radiation therapy (HA WBRT).
Ten adult and ten pediatric patients previously treated for central nervous system malignancies were identified. IMPT and VMAT treatment plans employing HA WBRT were generated for each patient, delivering 30 GyE (Gray Equivalent) in 10 fractions for adults and 36 GyE in 20 fractions for pediatrics. Dose indices, including dose volume histogram metrics and homogeneity index HI = [D5% - D95%]/[D] × 100, were used to assess plan quality and describe target coverage and normal-tissue sparing.
IMPT offered significant benefits relative to VMAT for hippocampal sparing. Hippocampal mean dose was reduced from 13.7 ± 0.8 Gy with VMAT to 5.4 ± 0.3 GyE using IMPT for pediatrics, and was reduced from 11.7 ± 0.9 Gy with VMAT to 4.4 ± 0.2 GyE using IMPT for adults. IMPT similarly lowered left hippocampal mean dose. Dose to 95% of the clinical target volume was statistically equivalent for both groups; however IMPT reduced the homogeneity index by roughly half.
This manuscript demonstrates that HA IMPT can match or exceed dosimetric benefits offered with modulated X-rays. Inclusion of IMPT in future prospective studies is warranted.
调强质子治疗（IMPT）允许通过位置、强度和深度对各个子野的调制参数进行调整。这种调制能力非常适合于在放疗靶区中间保护危及器官，比如全脑内的海马体积。本研究比较了在海马回避全脑放疗（HA WBRT）期间IMPT与容积调强弧形放疗（VMAT）的效果。
确定了10例曾接受中枢神经系统恶性肿瘤治疗的成年患者和10例儿科患者。为每位患者生成采用HA WBRT的IMPT和VMAT治疗计划，成年患者分10次给予30 GyE（戈瑞当量），儿科患者分20次给予36 GyE。使用剂量指数，包括剂量体积直方图指标和均匀性指数HI = [D5% - D95%]/[D]×100，来评估计划质量并描述靶区覆盖和正常组织保护情况。
相对于VMAT，IMPT在保护海马方面具有显著优势。儿科患者海马平均剂量从VMAT的13.7±0.8 Gy降至IMPT的5.4±0.3 GyE，成年患者从VMAT的11.7±0.9 Gy降至IMPT的4.4±0.2 GyE。IMPT同样降低了左侧海马平均剂量。两组临床靶区体积95%的剂量在统计学上相当；然而，IMPT使均匀性指数降低了约一半。
本研究表明HA IMPT能够达到或超过调强X射线的剂量学优势。未来的前瞻性研究有必要纳入IMPT。
