Kalff Victor, Ware Robert, Heriot Alexander, Chao Michael, Drummond Elizabeth, Hicks Rodney J
Centre for Molecular Imaging, the Peter MacCallum Cancer Centre, Melbourne Australia.
Int J Radiat Oncol Biol Phys. 2009 May 1;74(1):60-6. doi: 10.1016/j.ijrobp.2008.06.1944. Epub 2008 Oct 14.
Changes in F-18 fluorodeoxyglucose (FDG) uptake in normal tissues after chemoradiation therapy (CRT) potentially limit the ability of positron emission tomography (PET) to provide early assessment of therapeutic response. This study evaluated whether such changes negatively impact interpretation of posttherapy PET performed within 6 weeks of CRT completion and before definitive surgery in patients with locally advanced rectal cancer. The positive predictive value (PPV) and specificity of post-CRT PET, read clinically, was determined in 63 consecutive rectal cancer patients who had undergone preoperative CRT.
A schema for identifying and scoring postradiation effects on PET was prospectively defined and applied in a blinded manner. This was compared with initial clinical reporting of response. Histologic assessment of the operative specimens was used as the reference standard. Correlation between clinical proctitis during CRT and radiation changes on subsequent PET was also assessed.
Clinical reporting of post-CRT PET yielded a high PPV (94%; 95% confidence interval, 89--100%) but may have been exaggerated by the low prevalence of complete tumor clearance (16%). The specificity was 80% with only two false-positive results. On blinded reading, significant post-CRT effects on PET were recorded in 4 of 63 patients (6% 95% confidence interval, 0-13%), but pattern recognition converted both false-positive PET results to a complete metabolic response. Clinical CRT proctitis was not correlated with PET findings.
Postradiation effects do not appear to significantly compromise the interpretation of PET for therapeutic response assessment. The proposed PET pattern of response may further improve the specificity of PET.
放化疗（CRT）后正常组织中F-18氟脱氧葡萄糖（FDG）摄取的变化可能会限制正电子发射断层扫描（PET）对治疗反应进行早期评估的能力。本研究评估了这种变化是否会对局部晚期直肠癌患者在CRT完成后6周内且在确定性手术前进行的治疗后PET解读产生负面影响。对63例接受术前CRT的连续直肠癌患者进行了临床解读的CRT后PET的阳性预测值（PPV）和特异性测定。
前瞻性地定义了一种识别和评估PET辐射后效应的方案，并以盲法应用。将其与最初的临床反应报告进行比较。手术标本的组织学评估用作参考标准。还评估了CRT期间临床直肠炎与后续PET上的放射变化之间的相关性。
CRT后PET的临床报告产生了较高的PPV（94%；95%置信区间，89-100%），但可能因完全肿瘤清除率较低（16%）而被夸大。特异性为80%，仅有两个假阳性结果。在盲法解读中，63例患者中有4例（6%；95%置信区间，0-13%）记录到CRT后对PET有显著影响，但模式识别将两个假阳性PET结果均转换为完全代谢反应。临床CRT直肠炎与PET结果无关。
辐射后效应似乎不会显著影响PET对治疗反应评估的解读。所提出的PET反应模式可能会进一步提高PET的特异性。
