Background/Objectives: The current standard treatment for locally advanced rectal cancer (LARC) is neoadjuvant chemoradiotherapy, or total neoadjuvant therapy (TNT), followed by total mesorectal excision (TME). If the neoadjuvant treatment results in a clinical complete response (cCR), non-operative management of LARC might be possible. It is hypothesized that cCR rates will increase with increasing radiotherapy doses. By using proton therapy, doses to organs at risk (OAR) may be decreased. In preparation for a clinical trial on dose-escalated proton therapy for LARC, the purpose of this study is to establish the feasibility of proton therapy for dose-escalated hypofractionated radiotherapy of LARC.Methods: Ten patients, having previously received short course radiotherapy (SCRT) for LARC, were included in this planning study. Two photon plans and two proton plans were created for each patient: one with a standard 5 × 5 Gy fractionation and one dose-escalated up to 5 × 7 Gy. Proton plans were robustly optimized. For all plans the integral dose (ID) was computed, and for the proton plans relative biological effectiveness (RBE) distributions were calculated. Feasibility was assessed in terms of target coverage and OAR doses.Results: All treatment plans satisfied target coverage criteria. Three of the photon and two of the proton dose-escalated plans exceeded recommended OAR objectives. Proton IDs were on average lower by a factor of 1.97 compared to photon IDs. Mean doses to OAR were, in general, lower for protons. All proton RBE values in the escalated target volumes were between 1.09 and 1.16.Conclusions: The proposed dose escalation was found to be feasible. Protons can reduce the integral dose and mean doses to OARs compared to photons in both the dose-escalated and non-escalated cases. Differences in RBE between escalated and standard fractionation were small.
背景/目的：局部进展期直肠癌（LARC）目前的标准治疗模式为新辅助放化疗或全程新辅助治疗（TNT）后行全直肠系膜切除术（TME）。若新辅助治疗达到临床完全缓解（cCR），则LARC存在非手术治疗的可能性。理论上，随着放疗剂量提升，cCR率将相应提高。质子治疗可降低危及器官（OAR）的受照剂量。本研究旨在为开展LARC剂量递增质子治疗临床试验进行前期准备，重点评估质子治疗在LARC大分割剂量递增放疗中的可行性。 方法：本计划研究纳入10例既往接受过LARC短程放疗（SCRT）的患者。为每例患者制定两种光子计划和两种质子计划：一组采用标准5×5 Gy分割方案，另一组采用剂量递增至5×7 Gy方案。质子计划均经过稳健性优化。计算所有计划的积分剂量（ID），并对质子计划计算相对生物效应（RBE）分布。通过靶区覆盖度和危及器官剂量评估可行性。 结果：所有治疗计划均满足靶区覆盖标准。光子剂量递增计划中有3例、质子剂量递增计划中有2例超出推荐的危及器官剂量限值。质子计划的积分剂量平均比光子计划低1.97倍。质子治疗对危及器官的平均剂量普遍较低。所有递增靶区内的质子RBE值介于1.09至1.16之间。 结论：研究证实所提出的剂量递增方案具有可行性。在剂量递增与非递增情况下，相较于光子治疗，质子治疗均能降低积分剂量及危及器官平均剂量。递增方案与标准分割方案间的RBE差异较小。
An In Silico Feasibility Study of Dose-Escalated Hypofractionated Proton Therapy for Rectal Cancer
肿瘤(癌症)患者之家