Parrella Giovanni, Magro Giuseppe, Chalaszczyk Agnieszka, Rotondi Marco, Ciocca Mario, Glimelius Lars, Fiore Maria R, Paganelli Chiara, Orlandi Ester, Molinelli Silvia, Baroni Guido
Department of Electronics, Information and Bioengineering, Politecnico di Milano, Via G.Ponzio 34/5, 20133 Milan, Italy.
Medical Physics Unit, National Center of Oncological Hadrontherapy (CNAO), Strada Campeggi, 53, 11 27100 Pavia, Italy.
Phys Imaging Radiat Oncol. 2024 Aug 8;31:100624. doi: 10.1016/j.phro.2024.100624. eCollection 2024 Jul.
A low linear energy transfer (LET) in the target can reduce the effectiveness of carbon ion radiotherapy (CIRT). This study aimed at exploring benefits and limitations of LET optimization for large sacral chordomas (SC) undergoing CIRT.
Seventeen cases were used to tune LET-based optimization, and seven to independently test interfraction plan robustness. For each patient, a reference plan was optimized on biologically-weighted dose cost functions. For the first group, 7 LET-optimized plans were obtained by increasing the gross tumor volume (GTV) minimum LET (minLET) in the range 37-55 keV/μm, in steps of 3 keV/μm. The optimal LET-optimized plan (LET) was the one maximizing LET while adhering to clinical acceptability criteria. Reference and LET plans were compared through dose and LETd metrics (D , L to x% volume) for the GTV, clinical target volume (CTV), and organs at risk (OARs). The 7 held-out cases were optimized setting minLET to the average GTV L of the investigation cohort. Both reference and LET plans were recalculated on re-evaluation CTs and compared.
GTV L increased from (31.8 ± 2.5)keV/μm to (47.6 ± 3.1)keV/μm on the LET plans, while the fraction of GTV receiving over 50 keV/μm increased on average by 36% (p < 0.001), without affecting target coverage goals, or impacting LET and dose to OARs. The interfraction analysis showed no significant worsening with minLET set to 48 keV/μm.
LET optimization for large SC could boost the LET in the GTV without significantly compromising plan quality, potentially improving the therapeutic effects of CIRT for large radioresistant tumors.
靶区低线性能量传递（LET）会降低碳离子放射治疗（CIRT）的疗效。本研究旨在探讨针对接受CIRT的大型骶骨脊索瘤（SC）进行LET优化的益处和局限性。
17例患者用于调整基于LET的优化方案，7例用于独立测试分次计划的稳健性。对于每位患者，在生物加权剂量成本函数上优化一个参考计划。对于第一组，通过将大体肿瘤体积（GTV）的最小LET（minLET）在37 - 55 keV/μm范围内以3 keV/μm的步长增加，获得7个LET优化计划。最佳LET优化计划（LET）是在符合临床可接受标准的同时使LET最大化的计划。通过GTV、临床靶体积（CTV）和危及器官（OARs）的剂量和LETd指标（D ，L 至x%体积）比较参考计划和LET计划。7例预留病例的minLET设置为研究队列的平均GTV L 进行优化。参考计划和LET计划均在重新评估CT上重新计算并比较。
LET计划中GTV L 从（31.8 ± 2.5）keV/μm增加到（47.6 ± 3.1）keV/μm，而接受超过50 keV/μm的GTV部分平均增加36%（p < 0.001），同时不影响靶区覆盖目标，也不影响OARs的LET和剂量。分次分析表明，当minLET设置为48 keV/μm时，无显著恶化。
大型SC的LET优化可提高GTV中的LET，而不会显著损害计划质量，可能改善CIRT对大型放射抗拒肿瘤的治疗效果。
