Very Early Post-Treatment PET/CT Scan Performed One Week after First Chemotherapy Course Compared Against the Standard PET after Third Course in Histologically Aggressive Lymphoma (NHL).
Authors: Cabanillas Fernando , Toro Jorge , Perdomo Jorge W. , Liboy Idalia , Pavia Orestes , Maldonado Norman , Rivera Ezequiel 
Published: October 2019

The FDG-PET/CT scan has become a standard tool in the management of NHL. Failure to achieve an early metabolic CR (mCR) is associated with a poor outcome and this information can be used to modify subsequent management. However, several issues still need to be resolved, including: 1-What is the best time to perform a post-treatment PET scan? Is very early (i.e. 1 week) after the first chemotherapy superior to the traditional 3rd course PET scan? 2-What criteria can we use to define mCR? Is there an SUV threshold on the very early PET scan that best defines mCR? In order to answer these questions we designed a study in which patients with histologically aggressive NHLs had 3 sequential PET scans: 1st one at baseline, a 2nd one on week 1 after the 1st course of chemotherapy (W1 PET) and the 3rd one after course 3 of chemotherapy (C3 PET). We have entered 32 patients of which 30 are currently assessable. Histologies were: DLCL=26, FLCL=4. IPI was ≥2 in 69%. At baseline, median SUVmax=17.14 (range 5.6–47.1). In the 30 cases who had a W1 PET, the mean SUVmax dropped to 4.4 (0.7–21.3, corrected for background). In the 24 who have completed their C3 PET the mean SUVmax was 1.55 (0–15.2) and only 6 patients had an SUV >0: 0.9, 3.7, 3.9, 5.1, 8.3, 15.2. We then examined the correlation between the SUVmax of W1 PET with SUVmax of C3 PET. 24 cases have already had both a W1 PET and a C3 PET. Table 1 shows that the W1 PET correlated well with 17 (71%) of the 24 C3 PETs. All 14 who achieved SUVmax <4.0 on W1 PET had an SUVmax <4.0 on C3 PET (all of the latter achieved SUVs <1.0). However, of 10 cases who failed to attain SUVmax <4.0 on W1 PET, 7 went on to achieve SUVmax <4.0 on C3 PET, and 2 of these 7 relapsed. For the purpose of determining the best SUV cut-off that can be used to define mCR, we examined the failure free survival (FFS) at various cut-offs ranging from 0 to 8.0 for both W1 PETs and C3 PETs. The best cut-off for both W1 PET and C3 PET was observed at 4.0 (table 2). We thus defined mCR as a post-treatment SUVmax <4.0. Those who achieved mCR on the W1 PET had a significantly superior FFS (Kaplan-Meier method) than those who didn’t reach mCR (table 2). The results for the C3 PET didn’t reach statistical significance (table 2).

Conclusions: 1- Striking improvements in the PET scan are seen as early as 1 week after the first chemotherapy course. 2-The results of the W1 PET anticipated correctly 71% of C3 PET results. 3- Patients who attained an SUVmax <4.0 on the W1 PET had a remarkably superior outcome than those with SUV max ≥4.0 and was associated with a 91% FFS. Thus an SUV cut-off of <4.0 at W1 PET can be used to define mCR. This finding should be confirmed in an independent set of patients. 4- The W1 PET is more sensitive and specific than the C3 PET and is preferable to the C3 PET in predicting clinical outcome.

Correlation of W1PET SUVmax With C3PET SUVmax W1PET SUVmax N C3PET SUVmax<4.0 C3PET SUVmax≥4.0 <4.0 14 14 0 ≥4.0 10 7 3 Correlation of W1PET SUVmax and C3PET SUVmax With Outcome W1PET SUVmax N %FFS 8 mos. P value <4.0 18 91% ≥4.0 12 0% .01 C3PET SUVmax <4.0 21 73% ≥4.0 3 67% .19