Analysis of the Measured FDG Uptake from the First-in-Human Clinical Trial of Biology-Guided Radiotherapy

PURPOSE/OBJECTIVE(S)

The RefleXion X1 system is a novel linear accelerator equipped with dual 90° PET arcs incorporated into its architecture to capture emissions from tumors and designed to respond by directing the radiation beam towards target. This study reports on the measured FDG uptake from the first in human multi-institutional clinical trial (BIOGUIDE-X) evaluating the performance and safety of the RefleXion X1 PET-LINAC.

MATERIALS/METHODS

A total of nine patients treated with stereotactic body radiotherapy (SBRT) for lung (5) and bone (4) tumors were enrolled in the Cohort II of this study after screening their pre-study diagnostic PET/CT, acquired up to 60 days prior to enrollment, to ensure their tumor size between 2 to 5 cm and SUVmax >6. After CT simulation, the tumor and OARs were delineated, and patients had a 4-pass Imaging-only (BgRT Modeling) PET/CT acquisition on the X1 system to generate biology-guided radiotherapy (BgRT) plans. Before the patients' first and last SBRT fractions, they were injected with FDG, and short PET pre-scan (1-pass) was performed on the X1 followed by a long-PET acquisition (4-pass) to emulate the expected BgRT dose distribution without firing beam. Patients were also imaged on a third-party diagnostic PET/CT scanner after the last-fraction X1 scan. This study compares the SUVmax from the screening PET/CT, X1 Imaging-only scan, X1 PET pre-scan and long scan before the first and last-fractions, and final diagnostic PET/CT.

RESULTS

The median time from injection to PET imaging was 84 ± 15.4 mins for X1 Imaging-only (used for generating BgRT plans), 77 ± 21.6 mins for X1 pre-scan (safety check before treatment start), 108+/- 22 mins for X1 long-PET (used to emulate treatment delivery), and 161 ± 23 mins for final diagnostic PET. For a nominal 10 mCi injection, the mean SUVmax for screening imaging performed on the diagnostic PET/CT was 10.8 ± 4.3. For a 15 mCi nominal injection, the mean SUVmax calculated on the X1 was 5.3 ± 2.6, 5.4 ± 2.0, 5.5 ± 2.6, 5.2 ± 1.8 and 5.4 ± 2.2 for the Imaging-only, first-fraction PET pre-scan, first-fraction long PET scan, last-fraction PET pre-scan, and last-fraction long PET scan, respectively. The overall median SUVmax for all patients across all timepoints and scans with X1 was calculated to be 4.8 with a range of 2.4 to 9.8. The median SUVmax for the diagnostic PET/CT scan after the last fraction X1 scan was 15.8 with a range of 8.5 to 27.7.

CONCLUSION

The dual PET arcs and limited axial extent of the X1 PET subsystem results in lower system sensitivity in comparison to diagnostic PET scanners equipped with full ring and larger axial extent, as expected. With the same FDG injection, the RefleXion X1 produced SUVmax values that were 30.4 % of the diagnostic PET/CT scanners' values. Nevertheless, the X1 collected sufficient emission data to enable successful completion of emulated BgRT deliveries that met dose accuracy criteria in a clinical setting.

Imaging Performance of the PET Scan on a Novel Ring Gantry-Based PET/CT Linear Accelerator System in the First-in-Human Study of Biology-Guided Radiotherapy

PURPOSE/OBJECTIVE(S)

Biology-guided radiotherapy (BgRT) is a novel tracked dose delivery modality using real-time positron emission tomography (PET) to guide radiotherapy beamlets. The present study was performed with sequential cohorts of participants to evaluate the performance and safety of BgRT. Primary endpoints were previously reported. We hereby report on one of the secondary endpoints assessing a novel treatment planning machine with integrated dual kVCT/PET imaging ("novel device") performance in comparison to a third-party diagnostic PET/CT scan.

MATERIALS/METHODS

This single-arm, open-label, prospective study included participants with at least 1 FDG-avid targetable primary or metastatic tumor (≥2cm and ≤5cm) in the lung or bone. PET imaging data were collected on the novel device and on a third-party diagnostic PET/CT performed in sequence once at the planning timepoint in Cohort I, and immediately before the last fraction among patients undergoing stereotactic radiotherapy in Cohort II. Three central read radiation oncologists (CRRO) provided an interpretation of the novel device PET scans which were compared to an agreement standard based on 3 central radiologists' review of the paired diagnostic PET/CT scan. Positive percent agreement for localization of the target tumor within the biology-tracking zone (BTZ) was the key metric because it reflects whether advancing patients to subsequent steps in the BgRT workflow based on the novel device's imaging was ultimately appropriate.

RESULTS

In Cohort 1, 6 image comparisons were performed. The positive (%) agreement for the aggregate radiation oncologist review was 100% (5/5), reflecting that in all 5 cases where the aggregate radiation oncologists deemed the tumor to fall within the BTZ based upon the novel device PET images, the central radiologists came to the same conclusion upon review of the paired diagnostic PET/CT images. The overall (%) agreement for the aggregate radiation oncologist review was 83.3% (5/6): localization was not established on the novel device in 1 case, even though it was established on the diagnostic PET/CT. This would not pose risk in real world practice as BgRT candidacy would be aborted for tumors not visible on the novel device. In Cohort II, among the 7 image comparisons, there was 100% positive percent agreement between the aggregate CRRO and the agreement standard as the localization criteria was met in both scans for all 7 patients. This was concordant with a 100% overall percent agreement.

CONCLUSION

This investigation demonstrated a 100% positive percent agreement between central review of this novel device images by radiation oncologists and central review of the accompanying third-party PET/CT images by radiologists. There were no cases where a positive localization by the aggregate CRRO was not confirmed by the third-party PET/CT standard, providing evidence against the likelihood of falsely positive localizations on the novel device that would inappropriately advance patients in the workflow.

Workflow Considerations for Biology-Guided Radiotherapy (BgRT) Implementation

PURPOSE/OBJECTIVE(S)

Biology-guided radiotherapy (BgRT) is a novel platform that combines real-time PET imaging with a 6MV Linac to target tumors. The performance and safety of BgRT was assessed in the BIOGUIDE-X clinical trial. This study aims to report on the BgRT workflow steps and assess the time required for each step of the BgRT process during this trial.

MATERIALS/METHODS

A total of nine patients were enrolled in the second Cohort of the BIOGUIDE-X study which included patients treated with stereotactic body radiotherapy (SBRT) for lung tumors (5) and bone tumors (4). The pre-treatment BgRT workflow includes CT simulation, contouring, imaging-only (BgRT Modeling) PET acquisition, BgRT planning, patient specific QA and plan approval. The imaging-only PET acquisition on the X1 collects a representative PET volumetric 3D image and is an input to develop the BgRT treatment plan. The steps during the BgRT delivery session are kVCT localization, PET pre-scan, PET evaluation and BgRT delivery. The PET PreScan is a 1-pass short-duration PET acquisition that is used to confirm that the PET biodistribution on the day of treatment is consistent with that of the imaging-only PET. During BIOGUIDE-X, the BgRT delivery step was replaced by a 4-pass long-PET acquisition that was used to emulate the expected BgRT dose distribution without turning the beam on. To assess BgRT workflow, times from 18F-FDG injection to image-only PET acquisition, 18F-FDG injection to PET pre-scan, Pre-scan to PET evaluation, and PET evaluation to BgRT delivery (long PET acquisition) were recorded.

RESULTS

Time between the 18F-FDG injection and the X1 imaging-only PET scan was 84 ± 19 minutes which includes time for 18F-FDG update. Average time to perform imaging-only PET scan was 26 ± 4 minutes. During the BgRT 'delivery' session, the mean time between the kVCT acquisition and PET pre-scan acquisition was 7 ± 3 minutes. The mean time to acquire a 1-pass PET pre-scan was 6 ± 1 then followed by 6 ± 1 minutes for the PET pre-scan dose calculation to estimate the BgRT doses that it would have delivered for this fraction. On average, the PET reconstruction, the PET signal localization verification and the evaluation of safety metrics took 11 ± 4 minutes. The mean time for BgRT 'delivery' was 27 ± 5 minutes based on the 4-pass long PET acquisition. Time from the start of the BgRT session to the end of the BgRT 'delivery' with this version of the investigative product release was 65 ± 9 minutes.

CONCLUSION

The new processes introduced by the BgRT technology were evaluated and found clinically feasible. Improvements are being undertaken to shorten the time required for each step and to increase patient comfort ahead of BgRT clinical implementation.

Prognostic Significance of Positron Emission Tomography Delta Radiomics Following Bridging Therapy in Patients with Large B-Cell Lymphoma Undergoing CAR T-Cell Therapy

PURPOSE/OBJECTIVE(S)

CAR T-cell therapy is routinely used as a treatment option for relapsed/refractory large B-cell lymphoma (LBCL). Bridging therapy radiation therapy (bRT) is increasingly being utilized prior to chimeric antigen receptor (CAR) T-cell therapy for large B-cell lymphoma (LBCL). It is unknown how the extent of debulking as a result of bRT impacts outcomes following CAR T-cell infusion. We hypothesized that the extent of debulking is prognostic of overall response to therapy.

MATERIALS/METHODS

We reviewed patients with LBCL treated with bRT followed by commercially available CAR T-cell therapy between 2017 and 2022. Patients required a F-fluorodeoxyglucose (FDG) positron emission tomography (PET) scan prior to bRT and between completion of bRT and CAR T-cell infusion. On each scan, metabolic tumor volume (MTV), maximum standardized uptake value (SUVmax), SUVmean, and total lesion glycolysis (TLG) were determined. Delta-radiomics based on changes of these values between scans in patients overall and irradiated sites were then calculated. Optimal cut points were determined using maximally selected log-rank. The primary endpoints were progression-free survival (PFS) and local control (LC), measured from CAR T-cell infusion by Kaplan-Meier and Fine-Gray competing risk survival analyses, respectively.

RESULTS

Twenty-three patients with LBCL with 33 irradiated sites were reviewed. All metabolically active disease was treated in 10 patients. Median equivalent dose in 2 Gy fractions (EQD2) was 26 Gy (14-44). Median interval from bRT to PET was 9 days (2-30). Following bRT, 2 patients achieved complete responses, 16 had partial responses, and 5 had progressive disease. Five irradiated sites progressed through bRT. No local failures were observed when EQD2>32.5 Gy was given. LC was improved with EQD2>20 Gy (24 mo LC: 94.5% vs 68.6%; p = 0.075). Following BRT, median overall decreases in MTV, SUVmax, SUVmean, and TLG were 22.2 cc (63.1%), 8.9 (36.8%), 3.4 (31.1%), and 297.9 cc (75.8%), respectively. Median decreases in MTV, SUVmax, SUVmean, and TLG in irradiated sites were 15.6 cc (91.1%), 17.0 (74.6%), 6.8 (55.3%), and 157.0 cc (94.6%), respectively. PFS was significantly improved in patients with reductions of MTV of at least 36 cc (24 mo PFS: 69.2% vs 0%; p = 0.047) or SUVmax of at least 15 (24-mo PFS: 80.0% vs 28.1%; p < 0.001). LC was significantly improved in lesions with reductions of SUVmax of at least 14 (24-mo LC: 100% vs 67.3%; p < 0.001) or SUVmean of at least 7 (24-mo LC: 100% vs 74.4%; p < 0.001).

CONCLUSION

bRT led to significant reductions in MTV, SUVmax, SUVmean, and TLG. The extent of these decreases correlated with improved PFS and LC. There appears to be a dose-response relationship. Larger cohorts should validate the value of interim PET following bRT, and associated changes in disease burden as a means of prognosticating patients. Future work might evaluate whether escalation of BT in patients with suboptimal response, using either systemic therapy or higher radiation doses, has an impact on outcomes.

Abstract S3-07: Complication and economic burden of local therapy options for early breast cancer

Background: Guideline-concordant local therapy options for early breast cancer include lumpectomy plus whole breast irradiation (lump+WBI), lumpectomy plus brachytherapy (lump+brachy), mastectomy without reconstruction or radiation (mast alone), mastectomy with reconstruction without radiation (mast+recon), and, in older women, lumpectomy without radiation (lump alone). Little is known regarding the comparative complication and economic burden of these options in the general population.

Methods: We used the MarketScan database which includes younger women with private insurance and the SEER-Medicare database which includes older women with Medicare. Women were included if they had early stage disease (T1/2 N0/1 M0) diagnosed in 2000-2011, no prior cancer, and complete insurance coverage from 12 months prior through 24 months after diagnosis. A complication from local therapy was defined as a diagnosis or procedure code for any of the following within 24 months of diagnosis: wound complication, local infection, seroma/hematoma, fat necrosis, breast pain, pneumonitis, rib fracture, and implant removal. Total costs and complication-related costs within 24 months of diagnosis were calculated from a payer's perspective and are reported in 2014 dollars. Logistic regression compared complications by local therapy and generalized linear regression (log link function, gamma distribution) compared complication-related and total costs by local therapy; all models adjusted for relevant covariables.

Results: We selected 44,344 patients from the MarketScan cohort, median age of 53, and 50,562 patients from the SEER-Medicare cohort, median age of 75. For the MarketScan cohort, risk of complications varied as follows: 29% risk in patients treated with lump+WBI (referent), 44% with lump+brachy (adjusted odds ratio [AOR]=2.00;P&lt;.001), 25% with mast alone (AOR=0.85;P&lt;.001), and 54% with mast+recon (AOR=2.89;P&lt;.001). For the SEER-Medicare cohort, risk of complications varied as follows: 37% with lump+WBI (referent), 52% with lump+brachy (AOR=1.91;P&lt;.001), 37% with mast alone (AOR=0.97;P=.17), 65% with mast+recon (AOR=3.17; P&lt;.001), and 30% with lump alone (AOR=0.81; P&lt;.001). Compared to lump+WBI, mean adjusted complication-related cost was $8,085 higher per patient with mast+recon in the MarketScan cohort and $3,711 higher per patient with mast+recon in the SEER-Medicare cohort. In contrast, complication-related costs were similar (+/- $750) for all other local therapy options relative to lump+WBI in both cohorts. For total cost, mast+recon was the most expensive local therapy in the MarketScan cohort, with mean adjusted total cost of $77,321, which was $15,181 more expensive than lump+WBI. In the SEER-Medicare cohort, lump+brachy was the most expensive option ($39,534), followed by mast+recon ($35,269), lump+WBI ($32,562), mast alone ($26,401), and lump alone ($24,455).

Conclusion: Mast+recon results in the highest complication rate and complication-related cost in both younger women and older women with early breast cancer. These findings are relevant to defining which local therapies offer the highest value to patients, payers, and society, and are relevant to patients when evaluating their local therapy options.

Citation Format: Smith BD, Jiang J, Shih Y-CT, Giordano SH, Huo J, Jagsi R, Caudle AS, Hunt KK, Shaitelman SF, Buchholz TA, Shirvani SM. Complication and economic burden of local therapy options for early breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr S3-07.