A Pilot Study of Stereotactic Body Radiotherapy and 177Lu-PSMA-617 for Oligometastatic Hormone Sensitive Prostate Cancer

PURPOSE/OBJECTIVE(S)

Stereotactic body radiotherapy (SBRT) is increasingly used for oligorecurrent prostate cancer (OPC). Despite excellent local control, distant metastasis free survival rates are more modest. We hypothesized SBRT outcomes could be optimized with improved staging imaging and integration of a well-tolerated targeted radiopharmaceutical therapy (RLT) for microscopic disease. We report initial results of a prospective, single-institution pilot (NCT05079698) of a novel, PSMA-based theranostic strategy for OPC.

MATERIALS/METHODS

Men with castrate sensitive OPC and 1-3 sites of PSMA PET avid disease ("index lesions") and no PSMA non-avid sites were eligible. No androgen deprivation therapy was permitted. Subjects first received 2 cycles of 177Lu-PSMA-617 RLT (7.47±0.14 GBq) spaced 6 weeks apart. In vivo dosimetry was performed during cycle 1. Four weeks post-cycle 2, patients were restaged with 68Ga-PSMA PET for an interim (post-RLT) response assessment. Index lesions were then consolidated with SBRT (9 Gy x 3) irrespective of post-RLT PET response. The primary outcome was feasibility defined as successful completion of protocol-mandated therapy without intercurrent distant failure on post-RLT PET.

RESULTS

Six men were treated with nine total index lesions (5 nodal, 3 osseous, 1 visceral). The study met its primary endpoint; all completed required interventions and no distant progression was seen on interim PSMA PET. Treatment was well tolerated; no grade 3+ toxicities, 2/6 had grade 2 toxicities (transient anemia and hyperbilirubinemia) and 5/6 had grade 1 toxicities. Median baseline lesion-level PSMA SUVmax was 16.8±8.7. Median interim SUVmax was 6.2±2.5 and declined for all but one lesion post-RLT (median -65%). Median SUVmax at 3-mos post-SBRT was 3.3±2.5 and decreased for all evaluable lesions (median -80%). Median baseline PSA was 2.01 ng/mL (range: 0.72-4.56) which declined in 5/6 post-RLT. The 6th patient experienced biochemical rise with interim PET showing only greater avidity in the known index lesion and SBRT was completed per protocol. All 4 evaluable patients with at least one post-SBRT follow-up have improved PSA at last visit (range 5.5-12 mos from cycle 1), and 2/4 have undetectable PSA. Composite dosimetry, correlatives and quality of life studies are forthcoming.

CONCLUSION

Our pilot study demonstrates the feasibility of a novel PSMA anchored theranostic strategy combining SBRT with targeted RLT for OPC. Preliminary data suggests promising outcomes, including the possibility of achieving an undetectable biochemical disease state without hormone therapy.

Abstract P1-19-03: A phase I trial of sorafenib with whole brain radiotherapy (WBRT) in breast cancer patients with brain metastases and a correlative study of FLT-PET brain imaging in patients receiving WBRT with or without sorafenib

Background: WBRT is a standard therapy for metastatic breast cancer (MBC) patients (pts) with brain metastases (BM), but disease progression in the brain is common. Sorafenib, a tyrosine kinase inhibitor with anti-VEGF activity, has demonstrated anti-tumor efficacy in MBC and radiosensitizing activity preclinically. [18F] 3'deoxy-3'-fluorothymidine (FLT) is a new PET tracer which correlates with cellular proliferation and may improve response assessment in the brain. Methods: A phase I trial of sorafenib with WBRT in MBC pts with BM was conducted using a 3+3 design. Sorafenib was given orally daily at the start of WBRT for a total of 21 days with 3 doses levels: 200mg, 400mg, and 600mg. The primary endpoints were to determine a maximum tolerated dose (MTD) and to evaluate safety and toxicity. The secondary endpoint was central nervous system progression-free survival (CNS-PFS). Macdonald Criteria were used for response assessment with serial MRI brain imaging. Key eligibility criteria include MBC with new or progressive ≥ 1cm BM, ECOG PS 0-2, non-escalating corticosteroid dose, and no other concurrent anti-tumor therapy except trastuzumab. In parallel, we conducted a correlative FLT-PET imaging study (baseline, 7-10 days (FU1), and 10-12 weeks (FU2) after the WBRT) to assess radiographic changes among pts receiving WBRT + sorafenib and in a separate WBRT only cohort. FLT standard uptake value (SUV) and kinetic parameter data were obtained. Results: 13 pts were treated in the dose escalation phase and evaluable for dose-limiting toxicity (DLT). The median age was 56 years (range: 43-77). There were 4 HER2 positive (31%) and 3 triple negative (23%) pts. 2 pts had prior stereotactic radiosurgery. DLTs were: Grade (G) 4 increased lipase at 200mg (1 pt) and G3 rash at 400mg (3 pts) level. MTD was determined to be 200mg. 10 pts were evaluable for response (at least 1 follow up brain imaging). The overall response rate was 70%: 4 complete responses (CR) + 3 partial responses. All 13 pts were evaluated for CNS PFS with a median follow up of 29.7 months (min 19.6, max 57.4mo). Median CNS-PFS was 8.2 months (95%CI: 3.4-31.8). Median OS was 15.4 months (95% CI: 3.4-NR). A total of 10 pts with WBRT and sorafenib and 5 pts with WBRT only were enrolled in the FLT-PET study: all 15 pts had baseline FLT PET, 14 with FU1, and 9 with FU2. 55 baseline lesions, 38 at FU1 and 15 at FU2 were observed and analyzed. All lesions with FLT uptake had MRI correlates. Decline in average SUVmax of ≥25% was seen in 9/10 (90%) of WBRT+sorafenib and 2/4(50%) of WBRT only pts at FU1. A complete disappearance of FLT uptake was noted in 1 pt at FU1 and 2 more pts at FU2. Conclusions: Concurrent WBRT with sorafenib appears safe at 200mg daily dose with a higher rate of CR compared to historical WBRT data. We are currently enrolling patients in the safety-expansion cohort. This combination should be considered for further efficacy evaluation. Additional analysis of FLT-PET as a complementary imaging modality to MRI is currently ongoing. Clinical trial registry: NCT01724606 and NCT01621906. Support: Bayer, Susan G Komen, ASCO Gianni Bonadonna Breast Cancer Award

Citation Format: Morikawa A, Jhaveri K, Grkovski M, Tang K, Humm JL, Holodny A, Beal K, Schoder H, Seidman AD. A phase I trial of sorafenib with whole brain radiotherapy (WBRT) in breast cancer patients with brain metastases and a correlative study of FLT-PET brain imaging in patients receiving WBRT with or without sorafenib [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-19-03.

International Working Group consensus response evaluation criteria in lymphoma (RECIL 2017)

In recent years, the number of approved and investigational agents that can be safely administered for the treatment of lymphoma patients for a prolonged period of time has substantially increased. Many of these novel agents are evaluated in early-phase clinical trials in patients with a wide range of malignancies, including solid tumors and lymphoma. Furthermore, with the advances in genome sequencing, new "basket" clinical trial designs have emerged that select patients based on the presence of specific genetic alterations across different types of solid tumors and lymphoma. The standard response criteria currently in use for lymphoma are the Lugano Criteria which are based on [18F]2-fluoro-2-deoxy-D-glucose positron emission tomography or bidimensional tumor measurements on computerized tomography scans. These differ from the RECIST criteria used in solid tumors, which use unidimensional measurements. The RECIL group hypothesized that single-dimension measurement could be used to assess response to therapy in lymphoma patients, producing results similar to the standard criteria. We tested this hypothesis by analyzing 47 828 imaging measurements from 2983 individual adult and pediatric lymphoma patients enrolled on 10 multicenter clinical trials and developed new lymphoma response criteria (RECIL 2017). We demonstrate that assessment of tumor burden in lymphoma clinical trials can use the sum of longest diameters of a maximum of three target lesions. Furthermore, we introduced a new provisional category of a minor response. We also clarified response assessment in patients receiving novel immune therapy and targeted agents that generate unique imaging situations.

Repeatability of SUV measurements in serial PET

PURPOSE

The standardized uptake value (SUV) is a quantitative measure of FDG tumor uptake frequently used as a tool to monitor therapeutic response. This study aims to (i) assess the reproducibility and uncertainty of SUV max and SUV mean, due to purely statistical, i.e., nonbiological, effects and (ii) to establish the minimum uncertainty below which changes in SUV cannot be expected to be an indicator of physiological changes.

METHODS

Three sets of measurements were made using a GE Discovery STE PET/CT Scanner in 3D mode: (1) A uniform 68Ge 20 cm diameter cylindrical phantom was imaged. Thirty serial frames were acquired for durations of 3, 6, 10, 15, and 30 min. (2) Esser flangeless phantom (Data Spectrum, approximately 6.1 L) with fillable thin-walled cylinders inserts (diameters: 8, 12, 16, and 25 mm; height: approximately 3.8 mm) was scanned for five consecutive 3 min runs. The cylinders were filled with 18FDG with a 37 kBq/cc concentration, and with a target-to-background ratio (T/BKG) of 3/1. (3) Eight cancer patients with healthy livers were scanned approximately 1.5 h post injection. Three sequential 3 min scans were performed for one bed position covering the liver, with the patient and bed remaining at the same position for the entire length of the scan. Volumes of interest were drawn on all images using the corresponding CT and then transferred to the PET images. For each study (1-3), the average percent change in SUV mean and SUV max were determined for each run pair. Moreover, the repeatability coefficient was calculated for both the SUV mean and SUV max for each pair of runs. Finally, the overall ROI repeatability coefficient was determined for each pair of runs.

RESULTS

For the 68Ge phantom the average percent change in SUV max and SUV mean decrease as a function of increasing acquisition time from 4.7 +/- 3.1 to 1.1 +/- 0.6%, and from 0.14 +/- 0.09 to 0.04 +/- 0.03%, respectively. Similarly, the coefficients of repeatability also decrease between the 3 and 30 min acquisition scans, in the range of 10.9 +/- 3.9% - 2.6 +/- 0.9%, and 0.3 +/- 0.1% - 0.10 +/- 0.04%, for the SUV max and SUV mean, respectively. The overall ROI repeatability decreased from 18.9 +/- 0.2 to 6.0 +/- 0.1% between the 3 and 30 min acquisition scans. For the l8FDG phantom, the average percent change in SUV max and SUV mean decreases with target diameter from 3.6 +/- 2.0 to 1.5 +/- 0.8% and 1.5 +/- 1.3 to 0.26 +/- 0.15%, respectively, for targets from 8-25 mm in diameter and for a region in the background (BKG). The coefficients of repeatability for SUV max and SUV mean also decrease as a function of target diameter from 7.1 +/- 2.5 to 2.4 +/- 0.9 and 4.2 +/- 1.5 to 0.6 +/- 0.2, respectively, for targets from 8 mm to BKG in diameter. Finally, overall ROI repeatability decreased from 12.0 +/- 4.1 to 13.4 +/- 0.5 targets from 8 mm to BKG in diameter. Finally, for the measurements in healthy livers the average percent change in SUVmax and SUV mean were in the range of 0.5 +/- 0.2% - 6.2 +/- 3.9% and 0.4 +/- 0.1 and 1.6 +/- 1%, respectively. The coefficients of repeatability for SUV max and SUV men are in the range of 0.6 +/- 0.7% - 9.5 +/- 12% and 0.6 +/- 0.7% - 2.9 +/- 3.6%, respectively. The overall target repeatability varied between 27.9 +/- 0.5% and 41.1 +/- 1.0%.

CONCLUSIONS

The statistical fluctuations of the SUV mean are half as large as those of the SUV max in the absence of biological or physiological effects. In addition, for clinically applicable scan durations (i.e., approximately 3 min) and FDG concentrations, the SUV max and SUV mean have similar amounts of statistical fluctuation for small regions. However, the statistical fluctuations of the SUVmean rapidly decrease with respect tothe SUVmax as the statistical power of the data grows either due to longer scanning times or as the target regions encompass a larger volume.

Correlation of dynamic contrast enhanced magnetic resonance imaging (DCE MRI) with 18f-fluoromisonidazole positron emission and computed tomography (18F-FMISO PET/CT) in assessing tumor hypoxia in a series of head and neck cancer (HNC) patients with nodal metastases

6083

Background: 18F-FMISO PET/CT is a noninvasive hypoxia imaging modality. Hypoxia can develop within the tumor which typically corresponds to regions with poor blood perfusion. DCE-MRI can yield results on tumor perfusion. The present study compares hypoxic and perfusion status of HNC with nodal metastases using DCE-MRI and 18F-FMISO PET/CT imaging. Methods: 13 HNC (7 base of tongue, 5 tonsil, 1 larynx) patients with nodal metastases underwent both DCE-MRI and 18F-FMISO PET/CT scans prior to chemoradiotherapy. MRI was performed on a 1.5 Tesla GE Excite scanner. DCE-MRI studies were acquired using a fast multi-phase spoiled gradient echo sequence. Antecubital vein catheters delivered a bolus of 0.1 mmol/kg Gd-DTPA at 2 cc/s. For 18F-FMISO PET/CT,∼10.0 mCi of 18F-FMISO was administered IV and images were acquired ∼2 hours later. PET images were reconstructed; CT data were used for attenuation correction. Region of interests (ROIs) were manually drawn by a neuroradiologist. Quantitative DCE-MRI analyses were done using the 2-compartment Tofts model. The analyses calculated the pixel Ktrans(distribution rate constant), ve(extravascular-extra-cellular volume fraction), and kep(redistribution rate constant). 18F-FMISO PET/CT images were analyzed and the uptake by the tumor was scored as: no uptake (score 0); moderate-severe uptake (score 1). Semi-quantitative analysis included standardized uptake value (SUV) measurements. Statistical significance was calculated using a 2-sided Student's t-test, with p < 0.05. Results: A total of 17 nodes were analyzed. For the nodes that showed no hypoxia on PET imaging (n = 7), the mean (±SD) values were: 18F-MISO SUV (1.1 ± 03), Ktrans(0.33 ± 0.18), ve(0.53 ± 0.23), and kep(0.66 ± 0.25). For the nodes that showed moderate to severe 18F-MISO uptake (n = 10) the values were: 18F-FMISO SUV (2.8 ± 08), Ktrans(0.24 ± 0.07), ve(0.61 ± 0.13), and kep (0.43 ± 0.17). A significant lower kep for nodes with 18F-MISO uptake (p = 0.042). Conclusions: Preliminary result supports the hypothesis that the hypoxic nodes are poorly perfused nodes (lower kep values) versus nodes with no hypoxia.

No significant financial relationships to disclose.

New PET tracers for evaluation of solid tumor response to therapy

We take advantage of the special characteristics of human tumors to image tumor response including predicting susceptibility to specific cancer therapies. The metabolic phenotype of malignancy, includes increased glycolysis (2-[(18)F]fluoro-2-D-deoxyglucose [FDG]), increased proliferation (2-[(18)F]fluoro-L-thymidine [FLT]), increased amino acid transport, as well as other functions such as fatty acid synthesis which have yet to be fully exploited. The endocrine dependent malignancies offer rich opportunities for selective imaging, including radioligands that have high affinity for hormone receptors, like androgen receptor (AR) (16Beta-[(18)F]16beta-[(18)F]fluoro-5alpha-dihydrotestoste-rone [FDHT]) and estrogen receptor (ER) ([(18)F]fluoroestradiol [FES]) and tissue specific transporters such as sodium iodide symporter (NIS) ((124)I). As knowledge of cancer biology has grown, it has become possible to develop tracers which image the client proteins involved in response to specific drugs, e.g. Gallium-68-Fab'2 herceptin for HER 2 effected by HSP 90 inhibitor drugs. More and more radiolabeled drugs will be used to explore the pharmacology of anticancer therapies, such as [(18)F]Desatinib. These may or may not be excellent imaging agents, but as analogs or even true tracers for specific anti-cancer drugs, noninvasive imaging through positron emission tomography will provide highly useful information, relating cancer pharmacology within the local tumor, to treatment response.

Quantitation of respiratory motion during 4D-PET/CT acquisition

We report on the variability of the respiratory motion during 4D-PET/CT acquisition. The respiratory motion for five lung cancer patients was monitored by tracking external markers placed on the abdomen. CT data were acquired over an entire respiratory cycle at each couch position. The x-ray tube status was recorded by the tracking system, for retrospective sorting of the CT data as a function of respiration phase. Each respiratory cycle was sampled in ten equal bins. 4D-PET data were acquired in gated mode, where each breathing cycle was divided into ten 500 ms bins. For both CT and PET acquisition, patients received audio prompting to regularize breathing. The 4D-CT and 4D-PET data were then correlated according to their respiratory phases. The respiratory periods, and average amplitude within each phase bin, acquired in both modality sessions were then analyzed. The average respiratory motion period during 4D-CT was within 18% from that in the 4D-PET sessions. This would reflect up to 1.8% fluctuation in the duration of each 4D-CT bin. This small uncertainty enabled good correlation between CT and PET data, on a phase-to-phase basis. Comparison of the average-amplitude within the respiration trace, between 4D-CT and 4D- PET, on a bin-by-bin basis show a maximum deviation of approximately 15%. This study has proved the feasibility of performing 4D-PET/CT acquisition. Respiratory motion was in most cases consistent between PET and CT sessions, thereby improving both the attenuation correction of PET images, and co-registration of PET and CT images. On the other hand, in two patients, there was an increased partial irregularity in their breathing motion, which would prevent accurately correlating the corresponding PET and CT images.

Four-dimensional (4D) PET/CT imaging of the thorax

We have reported in our previous studies on the methodology, and feasibility of 4D-PET (Gated PET) acquisition, to reduce respiratory motion artifact in PET imaging of the thorax. In this study, we expand our investigation to address the problem of respiration motion in PET/CT imaging. The respiratory motion of four lung cancer patients were monitored by tracking external markers placed on the thorax. A 4D-CT acquisition was performed using a "step-and-shoot" technique, in which computed tomography (CT) projection data were acquired over a complete respiratory cycle at each couch position. The period of each CT acquisition segment was time stamped with an "x-ray ON" signal, which was recorded by the tracking system. 4D-CT data were then sorted into 10 groups, according to their corresponding phase of the breathing cycle. 4D-PET data were acquired in the gated mode, where each breathing cycle was divided into ten 0.5 s bins. For both CT and PET acquisitions, patients received audio prompting to regularize breathing. The 4D-CT and 4D-PET data were then correlated according to respiratory phase. The effect of 4D acquisition on improving the co-registration of PET and CT images, reducing motion smearing, and consequently increase the quantitation of the SUV, were investigated. Also, quantitation of the tumor motions in PET, and CT, were studied and compared. 4D-PET with matching phase 4D-CTAC showed an improved accuracy in PET-CT image co-registration of up to 41%, compared to measurements from 4D-PET with clinical-CTAC. Gating PET data in correlation with respiratory motion reduced motion-induced smearing, thereby decreasing the observed tumor volume, by as much as 43%. 4D-PET lesions volumes showed a maximum deviation of 19% between clinical CT and phase- matched 4D-CT attenuation corrected PET images. In CT, 4D acquisition resulted in increasing the tumor volume in two patients by up to 79%, and decreasing it in the other two by up to 35%. Consequently, these corrections have yielded an increase in the measured SUV by up to 16% over the clinical measured SUV, and 36% over SUV's measured in 4D-PET with clinical-CT Attenuation Correction (CTAC) SUV's. Quantitation of the maximum tumor motion amplitude, using 4D-PET and 4D-CT, showed up to 30% discrepancy between the two modalities. We have shown that 4D PET/CT is clinically a feasible method, to correct for respiratory motion artifacts in PET/CT imaging of the thorax. 4D PET/CT acquisition can reduce smearing, improve the accuracy in PET-CT co-registration, and increase the measured SUV. This should result in an improved tumor assessment for patients with lung malignancies.