Towards Biology-Guided Radiotherapy Planning and Delivery on a Novel O-Ring PET-Linac Platform: Extended Beyond Bone and Lung Lesions

PURPOSE/OBJECTIVE(S)

Biology-guided radiotherapy (BgRT) with FDG signal collected via an on-board positron emission tomography (PET) system integrated in an O-ring gantry Linac was recently cleared by the FDA for lung and bone lesions. This study aims to determine if BgRT plans, guided via PET signal, are clinically acceptable for FDG-avid lesions in disease sites beyond bone and lung.

MATERIALS/METHODS

Ten patients previously treated for lesions in the liver, head and neck (HN), pancreas, renal and pelvic-abdominal lymph nodes were identified. Diagnostic PET/CT images of these treatment sites were first collected and processed/converted to mimic PET images that are acquired on PET-Linac and would be used to guide the delivery. For BgRT planning, the PTV was generated with 5 mm margin from GTV and a Biology Tracking Zone was generated including the anticipated full range of target motion. BgRT plans, guided by the emulated PET signal, were generated with 46Gy in 3 fractions for liver and 40Gy in 5 fractions for all other sites. BgRT plan deliverability was first assessed by evaluating the Activity Concentration (AC) and Normalized Target Signals (NTS) on converted PET images with the goal to meet NTS >2 (hard constraint) and AC >5kBq/ml (goal). BgRT plan quality was then evaluated with institutional guidelines on PTV coverage, OAR doses, conformity index (CI) and Heterogeneity index (HI).

RESULTS

BgRT plans were successfully generated for 11 target lesions among ten patients. The average diagnostic PET SUV, derived NTS and AC on converted PET images were 12.62, 9.33 and 12.10 kBq/ml, respectively. All images met the NTS constraints, and 8/11 plans met the AC goal for deliverability. All plans met the OAR hard constraints such as max dose on duodenum, small bowel, large bowel and spinal cord. Five of 11 plans had a limiting GI structure that resulted in an expected reduction in PTV coverage with an average PTV V100% = 77.9%, CI of 1.4, HI of 1.36 and max dose of 133.8%. The other 6 of 11 cases met the PTV V100% = 95%, had an average CI of 1.1, HI of 1.28 and Dmax of 127.67%. The estimated average time for BgRT delivery was 17 mins 25 secs. Although these plan parameters are deemed to be clinically acceptable, heterogeneity was detected inside the target region and suboptimal dose fall off was observed in some cases that may be caused by current implementation.

CONCLUSION

This preliminary study showed that BgRT plans were generated successfully with emulated PET images on 11 treatment sites covering HN, abdominal and pelvic regions. All plans met NTS constraints and 8 out of 11 met AC goals for deliverability. The plan quality of all BgRT plans were clinically acceptable based on institutional constraints. Further investigations are required to test more patients/sites for BgRT plan feasibility. Dosimetric benefit from margin reduction of BgRT target should also be investigated in future study.

Pancreas Cancer Learning Health Network Established to Share Best Practice Across 14 Centers and Improve Patient Outcomes

PURPOSE/OBJECTIVE(S)

Pancreas cancer (PC) survival is among the lowest of all malignancies. Clinical trials have failed to significantly improve outcomes. Individual and institutional biases in care result in significant variation in practice, further hindering progress. Learning health networks (LHNs) prospectively collect real world data across centers and test improvements that can rapidly be expanded across centers if deemed successful. Herein, we report preliminary progress from the Pancreas Cancer Canopy Cancer Collective (PC-CCC), the first oncology LHN, established to improve duration and quality of survival in PC.

MATERIALS/METHODS

In 2019, we established the PC-CCC with six care centers who engaged in a collaborative design process to create a set of improvement aims, change ideas, and outcome measures. Center team members receive training and coaching in collaborative quality improvement methods, applied to local improvement efforts. Eight more centers joined in 2021, and a shared Canopy outcomes database was built and implemented to inform center-specific and network-wide improvement efforts and allow the LHN to undertake research using real-world data. Current improvement efforts are focused on proactively screening new PC patients for: (1) Clinical trials, (2) pancreas enzymes, (3) palliative care needs, and (4) goals of care conversations.

RESULTS

Currently, 14 care centers are active participants in the PC-CCC LHN. Data on a total of 2,002 PC patients are available to date. At presentation to the care center, most patients are female (51%) and have biopsy proven PC (83.9%). Average age is 68 years, and presenting disease status is metastatic (14.5%), resectable (11.4%), locally advanced (10.9%), borderline resectable (8.1%), or not yet staged (40%). For those who received radiation, 75.8% received stereotactic body radiation therapy. Among patients whose chemotherapy regimen was documented, most received 5-fluorouracilbased treatment (52%). Descriptive follow up data (including treatment and outcomes) are being actively updated, to be reported at time of presentation.

CONCLUSION

Creation of a cancer LHN for PC is feasible and has set the stage for improving patient and provider outcomes through iterative community-building, continuous improvement, and sharing of data and multidisciplinary best practices. Additionally, the data obtained from the CCC database can rapidly inform the network how variation in clinical practice across centers can influence outcomes.

Stereotactic Ablative Radiotherapy for the Treatment of Glandular Metastases from Renal Cell Carcinoma

PURPOSE/OBJECTIVE(S)

Glandular metastases including pancreatic and adrenal sites of disease are associated with renal cell carcinoma (RCC) of indolent biology. Adrenal and pancreatic metastases may develop in isolation or involve other organs and are associated with prolonged survival. Glandular metastases can be treated with systemic therapy, stereotactic ablative radiotherapy (SAbR) or surgical resection and the optimal management of these patients is unknown. There is paucity of data on SAbR for RCC glandular metastases. We hypothesize that ablative doses of radiation therapy utilizing SAbR are associated with high rates of local control greater than 90%, with minimal or no acute grade 3 toxicities or higher with this approach. Here, we report local control (LC), progression-free survival (PFS), overall survival (OS) rates as well as toxicities related to SAbR for RCC metastases to the pancreatic and adrenal glands.

MATERIALS/METHODS

This IRB-approved, single-institution, retrospective study included patients with RCC metastases to the adrenal glands and pancreas treated with SAbR. Data on patient demographics, functional status, tumor characteristics, International Metastatic RCC Database Consortium (IMDC) risk category, local and systemic treatments, toxicities, and outcomes were collected and analyzed. RECIST 1.1 principals were utilized to determine LC rates and PFS. PFS was determined from the initiation of SAbR to progression (at SAbR-treated or other sites), or death. OS was defined from the start of SAbR to death. Two independent reviewers assessed these measures and analyzed patient electronic health records for toxicities using CTCAE v5 and relatedness scores.

RESULTS

A total of 50 RCC patients were included in this study with 36 adrenal and 20 pancreatic metastases treated with SAbR. Median dose fractionation used was 40 Gray delivered in 5 fractions. Sixteen patients (32%) were treatment naïve with oligometastatic disease, and thirty-four (68%) were oligo-progressive on systemic therapy with 1-3 prior lines of systemic therapy. For treated adrenal metastatic lesions at 1 year, patients demonstrated a 75.3% OS, 46.7% PFS, and LC of 93.3%. For treated pancreatic metastatic lesions at 1 year, patients demonstrated a 100% OS, 48.6% PFS, and LC of 100%. At 1 year, there was an OS of 82.2%, PFS of 48.2%, and LC of 95.9 % in the combined cohort. The percentage of patients experiencing an acute grade 2 or 3 toxicity attributed to adrenal or pancreatic gland SAbR was 7.4%. There were no acute grade >3 toxicities. The percentage of patients experiencing a late grade 2 or 3 toxicity was 9.3%. Median time to late adverse events was 37.4 months.

CONCLUSION

SAbR of RCC metastases to the pancreas and adrenal glands is feasible, safe and appears to be effective. Median PFS and OS in this cohort compared favorably to those reported in historical cohorts and is consistent with indolent disease.

Phase I Trial of 'Re-Priming' Radiation Therapy for Relapsed/Refractory Non-Hodgkin Lymphoma Patients in Incomplete Response after Chimeric Antigen Receptor T-Cell (CAR-T) Therapy

PURPOSE/OBJECTIVE(S)

Inpatients with relapsed/refractory non-Hodgkin lymphoma (R/R NHL) treated with CD19-directed CAR-T, only ∼40% achieve complete response (CR) by day 30 PET/CT evaluation. Of those who do not, the large majority (∼70%) ultimately fail, providing an ideal target for early therapeutic intervention to 're-prime' CAR-T. Preclinical and early clinical studies suggest potential synergy and immune augmentation when combining RT with CAR-T. Here we report the phase I results of a prospective phase I/II clinical trial hypothesizing that early salvage focal RT to poor responding sites of disease after CAR-T in R/R NHL patients is safe (phase I) and will improve conversion to CR by day 90 post-CAR-T PET/CT from 29% (historical control) to 58% (phase II).

MATERIALS/METHODS

Weopened a single-arm open-label phase I/II prospective clinical trial at our institution for R/R NHL patients treated with CD19-directed CAR-T with incomplete response on day 30 post-CAR-T PET/CT scan (defined as Lugano > = 4). The phase I component used a 'Rolling 6' design with 6 patients enrolled concurrently at the "definitive" dose level (40-50 Gy EQD2 [i.e., 30 Gy in 5 fractions], with de-escalation to "palliative" dose level (20-32.5 Gy EQD2 [i.e., 20 Gy in 5 fractions]) if >2 dose-limiting toxicities (DLT) observed. Hypofractionated regimens (i.e., 5 fractions) directed only to residual FDG-avid disease were recommended to minimize lymphopenia and potentially result in a more favorable immune microenvironment. DLT rate was defined within 60 days of RT by CTCAE v5.0 grade 4+ hematologic, grade 3+ dermatitis/burn, pneumonitis, enteritis, or other toxicity attributable to RT, as well as new grade 3+ cytokine release syndrome (CRS) per ASTCT consensus guidelines or grade 3+ neurotoxicity per ASTCT ICANS consensus guidelines for adults.

RESULTS

BetweenApril 2021 and July 2022, 6 patients were enrolled. All 6 patients had diffuse large B-cell lymphoma (DLBCL), with 3/6 (50%) transformed from low-grade follicular lymphoma. 2/6 had primary refractory DLBL, while the other 4/6 had median 2.5 lines of treatment prior to CAR-T. No patient had prior RT to a site of residual FDG-avid disease on day 30 post-CAR-T PET/CT. 5/6 patients were treated to 30 Gy in 5 fractions, with the remainder patient treated to 36 Gy in 10 fractions. No grade 3+ DLTs related to RT were observed in the 60-day post-RT period. RT related toxicities included grad 1 alopecia, grade 1 radiation pneumonitis, grade 1 nausea & vomiting, and grade 2 skin infection.

CONCLUSION

Early salvage focal "definitive" dose RT to sites of incomplete response on day 30 post-CAR-T PET/CT for R/R/ NHL patients was safe with no de-escalation of dose needed. This dose will used in the subsequent phase II component of the trial.

Post-Progression Survival in Patients with Oligometastatic or Polymetastatic Pancreatic Adenocarcinoma

PURPOSE/OBJECTIVE(S)

Distant progression following surgical resection of stage I-III pancreatic ducal adenocarcinoma (PDAC) is a major cause of morbidity and mortality. Herein, we investigated the impact of tumor burden at the time of distant progression on survival. We hypothesize that patients with limited number of metastases (≤5) in a single organ will have improved survival post progression.

MATERIALS/METHODS

We queried our institutional database for patients with the following inclusion criteria: 1-Stage I-III PDAC who underwent curative resection, and 2-Metachronous single organ (liver or lung) distant failure >3 months from the date of surgery. Patients with serosal and/or multiple organ metastases were excluded. Single organ metastases other than liver or lung were also excluded. Patients were stratified into oligometastatic (≤5 tumors), and polymetastatic (>5 tumors). Primary endpoint was survival post failure, while secondary endpoints were distant failure free survival (DFFS) and overall survival. Reverse KM curve was used to calculate median follow up. KM curves were plotted for DFFS identified from date of surgery until date of distant failure, survival post failure was identified from date of distant failure until death/last follow up, and overall survival was identified from date of surgical resection until death/last follow up.

RESULTS

Out of 128 patients who developed metachronous distant progression following surgical resection, we identified 76 patients who met the inclusion criteria with a median follow up of 50 months. Among those, at the time of distant failure, 63% (n = 48) and 37% (n = 28) patients had ≤5 vs >5 metastases respectively. Median number of metastases was one (range 1-5) and eight (range 6-33), while 12 and 11 patients developed local failure in the oligometastatic and polymetastatic cohorts respectively. Among the 48 patients who developed oligometastases, 69% (n = 33) and 31% (n = 15) had liver and lung metastases respectively. On the other hand, 68% (n = 19) and 32% (n = 9) had liver and lung polymetastases respectively. Median DFFS was 11, and 9 months (HR = 1.59, 95 % CI 0.95-2.64, p value = 0.046), survival post distant failure was 17.8 and 5.3 months (HR = 3.03, 95 % CI 1.52-6.01, p value<0.0001), and median survival was 29.8, and 16.7 months (HR = 2.52, 95 % CI 1.31-4.86, p value = 0.0007) among patients with oligometastases and polymetastases respectively.

CONCLUSION

Within the surgically resected stage I-III PDAC who developed single organ liver or lung metachronous disease, oligometastases (one-five lesions) were more prevalent, had more durable DFFS, had improved survival post failure, and a longer median survival compared to patients with polymetastatic recurrence (>five metastases). Trials on treatment of metastatic PDAC should stratify by number of metastases, and the oligometastatic subset may derive survival benefit from ablative radiation therapy.

Spiers Memorial Lecture. Breeding and building molecular spies

To circumvent the limited spatial resolution of fluorescent protein imaging, we are developing genetically encoded tags for electron microscopy (EM).