Li Winnie, Winter Jeff, Padayachee Jerusha, Dang Jennifer, Kong Vickie, Chung Peter
Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, ON, Canada.
Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada.
Front Oncol. 2022 Apr 14;12:877452. doi: 10.3389/fonc.2022.877452. eCollection 2022.
A magnetic resonance linear accelerator (MR-Linac) provides superior soft tissue contrast to evaluate inter- and intra-fraction motion and facilitate online adaptive radiation therapy (ART). We present here an unusual case of locally advanced castrate-resistant prostate cancer treated with high-dose palliative ultra-hypofractionated radiation therapy on the MR-Linac with significant inter-fraction tumor regression.
The patient was a 65-year-old man diagnosed with metastatic prostate cancer to bone and pelvic lymph nodes 7 years prior. At diagnosis, he presented with a PSA of 23 ng/ml and was commenced on a luteinizing hormone-releasing hormone agonist, achieving a PSA nadir of 4.68 ng/ml at 12 months. The patient subsequently had progressive lower urinary tract symptoms, his PSA increased to 47 ng/ml, and there was a markedly enlarged pelvic mass involving the prostate with gross extra-capsular disease and invasion into the posterior bladder wall. The patient was referred for palliative radiation to the pelvic mass due to urinary symptoms, pain, and lower limb paraesthesia. Treatment was planned to be delivered on the MR-Linac with a schedule of 36 Gy over 6 weekly factions allowing for maximal target dose delivery while minimizing surrounding organs at risk (OARs) radiation exposure. Unexpectedly, the target volume had a marked 49% (453 cc to 233 cc) reduction that was accounted for in the online adaptive process. A new reference plan was generated after 3 fractions to add sacral plexus as an OAR, previously not visible due to mass encroachment. The patient reported ongoing reduction in urinary symptoms, pelvic pain, and lower limb paresthesia by the end of treatment.
Using daily MR-guided ART, improved visualization of the changing target and OARs ensured safe dose escalation. The unexpected positive response of the target and improved patient outcomes demonstrated the added value of the MR-Linac for online adaptive radiotherapy in this setting.
磁共振直线加速器（MR-Linac）能提供卓越的软组织对比度，以评估分次间和分次内的运动，并有助于在线自适应放射治疗（ART）。我们在此介绍一例局部晚期去势抵抗性前列腺癌的特殊病例，该患者在MR-Linac上接受了高剂量姑息性超分割放射治疗，分次间肿瘤有显著消退。
该患者为一名65岁男性，7年前被诊断为骨和盆腔淋巴结转移性前列腺癌。诊断时，他的前列腺特异性抗原（PSA）为23 ng/ml，并开始使用促黄体生成素释放激素激动剂，12个月时PSA最低降至4.68 ng/ml。患者随后出现进行性下尿路症状，PSA升至47 ng/ml，盆腔有一个明显增大的肿块，累及前列腺，有明显的包膜外病变并侵犯膀胱后壁。由于尿路症状、疼痛和下肢感觉异常，患者被转诊接受盆腔肿块的姑息性放疗。计划在MR-Linac上进行治疗，方案为每周6次，每次36 Gy，以在最大限度减少周围危及器官（OARs）辐射暴露的同时实现最大靶剂量照射。出乎意料的是，靶体积有显著的49%（从453 cc降至233 cc）缩小，这在在线自适应过程中得到了解释。在3次分割后生成了一个新的参考计划，将骶丛作为一个OAR添加进去，该部位之前因肿块侵犯而不可见。到治疗结束时，患者报告尿路症状、盆腔疼痛和下肢感觉异常持续减轻。
使用每日MR引导的ART，改善了对变化的靶区和OARs的可视化，确保了安全的剂量递增。靶区意外的积极反应和患者预后的改善证明了MR-Linac在这种情况下用于在线自适应放疗的附加价值。
