Ruiz Brian, Feng Yuanming
Department of Radiation Oncology, Johnson City Medical Center, Johnson City, TN, USA.
Department of Physics, East Carolina University, Greenville, NC, USA.
Phys Imaging Radiat Oncol. 2018 Dec 7;8:51-56. doi: 10.1016/j.phro.2018.11.007. eCollection 2018 Oct.
Due to a smaller target volume when delineating prostate on magnetic resonance imaging (MRI), margins may be too tight as compared to computed tomography (CT) delineation, potentially reducing tumor control probability (TCP) in prostate radiotherapy. This study evaluated a clinically implemented MRI-based target expansion method to provide adequate margins yet limit organ-at-risk (OAR) dose as compared to CT-based delineation.
Patients in this study were treated to 79.2 Gy in 44 fractions via intensity modulated radiotherapy using an MRI-based expansion method, which excluded OARs when performing a 5 mm isotropic (except 4 mm posterior) expansion from gross tumor volume to clinical target volume (CTV), followed by an isotropic 5 mm expansion to generate the planning target volume (PTV). Ten cases were re-planned using CT-delineated prostate with CTV-to-PTV expansion of isotropic 8 mm, except for a 5 mm posterior expansion, with comparison of PTV volumes, TCP and normal tissue complication probability (NTCP) to the MRI-based method. Under IRB approved protocol, we retrospectively evaluated 51 patients treated with the MRI-based method for acute bladder and rectal toxicity with CTC-AE version 4.0 used for scoring.
MRI-based PTV volume differed by 4% compared to CT-based PTV volume. Radiobiological calculated TCP of the MRI-based method was found comparable to CT-based methods with an average equivalent uniform dose of 80.5 Gy and 80.1 Gy respectively. Statistically significant decrease in bladder NTCP (toxicity Grade 2 and above for 5% complications within 5 years post radiotherapy) was observed in the MRI-based method. Outcomes data collected showed 65% and 100% of patients studied experienced Grade 0/1 bladder and rectal acute toxicity respectively. Grade 2 bladder toxicity was indicated in the remaining 35% of patients studied with no Grade 3 toxicity reported.
Results showed comparable PTV volume with MRI-based method, and NTCP was reduced while maintaining TCP. Clinically, bladder and rectal toxicities were observed to be minimal.
在磁共振成像（MRI）上勾画前列腺时，由于靶区体积较小，与计算机断层扫描（CT）勾画相比，边界可能过紧，这可能会降低前列腺放疗中的肿瘤控制概率（TCP）。本研究评估了一种临床应用的基于MRI的靶区扩展方法，与基于CT的勾画相比，该方法可提供足够的边界，同时限制危及器官（OAR）的剂量。
本研究中的患者通过调强放疗接受44次分割、总量79.2 Gy的治疗，采用基于MRI的扩展方法，即从大体肿瘤体积向临床靶区体积（CTV）进行各向同性5 mm（后缘除外，为4 mm）扩展时排除OAR，然后进行各向同性5 mm扩展以生成计划靶区体积（PTV）。对10例患者使用CT勾画的前列腺进行重新计划，CTV到PTV的扩展为各向同性8 mm，后缘除外为5 mm，将PTV体积、TCP和正常组织并发症概率（NTCP）与基于MRI的方法进行比较。根据机构审查委员会批准的方案，我们回顾性评估了51例采用基于MRI方法治疗的患者的急性膀胱和直肠毒性，使用CTC-AE 4.0版进行评分。
基于MRI的PTV体积与基于CT的PTV体积相差4%。发现基于MRI方法的放射生物学计算TCP与基于CT的方法相当，平均等效均匀剂量分别为80.5 Gy和80.1 Gy。基于MRI的方法中观察到膀胱NTCP有统计学意义的降低（放疗后5年内5%并发症的2级及以上毒性）。收集的结果数据显示，65%和100%的研究患者分别经历了0/1级膀胱和直肠急性毒性。其余35%的研究患者出现2级膀胱毒性，未报告3级毒性。
结果表明基于MRI的方法的PTV体积相当，NTCP降低，同时维持TCP。临床上，观察到膀胱和直肠毒性最小。
