Comparison of Radiation Treatment Volumes for Borderline Resectable Pancreatic Cancer in Contemporary Clinical Trials

Moving From the Background Toward the Spotlight: A Critical Review of Radiation Therapy for Locally Advanced Pancreas Cancer

Radiation therapy (RT) for locally advanced pancreatic cancer (LAPC) continues to be controversial. Advances in both systemic therapy and RT techniques have changed the landscape of LAPC management in recent years. Clinical outcomes of ablative RT have been encouraging, and randomized clinical trials may clarify the role of RT for LAPC. We present a contemporary critical review of key aspects regarding optimal patient selection, radiation dose escalation techniques, novel radiosensitizers and radioprotectors, and treatment response assessment for LAPC.

Patterns of Locoregional Pancreatic Cancer Recurrence After Total Neoadjuvant Therapy and Implications on Optimal Neoadjuvant Radiation Treatment Volumes

PURPOSE

This study aimed to generate a map of local recurrences after neoadjuvant chemotherapy and radiation (total neoadjuvant therapy [TNT]) followed by surgical resection for pancreatic ductal adenocarcinoma (PDAC). Such recurrence patterns will serve to inform radiation treatment planning volumes that should be given in the neoadjuvant setting.

METHODS AND MATERIALS

Locoregional recurrences after TNT followed by surgery treated between 2009 and 2022 were radiologically identified. Recurrences were individually segmented using MIM software and complied in a single base scan. All contour compilations were used to create a threshold contour encompassing 80% of recurrences among all patients, head only, and body/tail only. The distance between organs at risk and the threshold contour were measured to design an optimal clinical target volume contour for patients treated with TNT. Recurrence patterns were also compared with existing adjuvant guidelines to assess coverage.

RESULTS

A database of 474 patients managed with TNT for PDAC was queried. While locoregional recurrences were rare in this cohort, we identified 80 patients with either isolated locoregional or simultaneous local and distant recurrences. Patients with diagnostic imaging at the time of recurrence were identified. The majority of recurrences were partially in the field of published contouring guidelines or volumetric expansions off of vessels, and volumetric coverage was low for all. Common areas of recurrence include the aorticodiaphragmatic junction, retropancreatic duodenal nodal basin, and the region to the right of the superior mesenteric artery. A novel set of proposed neoadjuvant contours was designed to cover the central-most 80% of recurrences.

CONCLUSIONS

This is the largest collection of local/regional PDAC recurrences from a cohort of patients treated exclusively with TNT. Patterns of local/regional recurrence using TNT in PDAC vary significantly from those patients with PDAC treated with a surgery-first approach. Novel contouring guidelines presented in this study can help to ensure optimal coverage of high risk regions and avoid reliance on the current adjuvant guidelines to guide treatment planning.

Indications for Radiation in Pancreatic Adenocarcinoma: A Review

Pancreatic adenocarcinoma remains a deadly disease with 5 year overall survival of 10% among all stages. Standard of care for resectable disease remains surgical resection and adjuvant systemic therapy, but paradigms for borderline resectable and unresectable cases remain more nuanced. Radiation has been explored in the neoadjuvant, adjuvant, and definitive settings in a variety of randomized and non-randomized trials with mixed results. There is strong evidence to support the use of neoadjuvant radiation for borderline resectable pancreatic cancer. Utilization of radiation in the adjuvant setting remains unclear while the results of radiation therapy oncology group (RTOG) 0848 are pending.

Neoadjuvant treatment for pancreatic cancer: Controversies and advances

Despite the advancements in the treatment of localized pancreatic cancer, several unresolved issues persist in clinical practice, especially in the neoadjuvant setting. These include determining the criteria for selecting patients for treatment, identifying the most effective chemotherapy regimens, understanding the role of radiotherapy, and accurately assessing how patients respond to treatment. Current strategies for assessing patients before surgery involve thoroughly evaluating their overall health status, analyzing tumor markers, and using advanced imaging techniques. However, existing methods for staging the disease still have limitations when it comes to accurately detecting metastatic cancer. The ongoing debate between performing surgery upfront or administering neoadjuvant therapy highlights the need for robust clinical evidence to guide treatment decisions effectively. This review analyzes the evidence regarding controversial topics in neoadjuvant pancreatic cancer treatment and discusses further research efforts to enhance patient outcomes. To improve the outcomes found with surgery alone, multimodal treatment with chemotherapy.

Relationship of dose to vascular target volumes and local failure in pancreatic cancer patients undergoing neoadjuvant chemoradiation

Objective

The objectives of this study were to evaluate whether dose to the vasculature is associated with local control after surgery in patients with borderline resectable (BLR) and resectable pancreatic cancer (PCA) receiving neoadjuvant radiation therapy (RT) and to identify a dose threshold for clinical use.

Methods

Patients with BLR and resectable PCA treated with neoadjuvant RT were retrospectively reviewed. During this period, the institutional paradigm shifted from standard fractionation to hypofractionation/stereotactic body radiation therapy (SBRT). A vasculature clinical target volume (Vasc CTV) was contoured for each patient and defined as a 5-mm margin around the superior mesenteric artery (SMA) from its origin to the pancreatic head, the celiac artery from its origin to the level of the trifurcation and any involved vein. The Vasc CTV D95 was normalized to a 2-Gy equivalent dose to determine the optimal dose associated with optimal local failure-free survival (LFFS).

Results

Forty-seven patients were included in the analysis. A Vasc CTV D95 of 32.7 Gy was the optimal cutoff for LFFS. Patients with Vasc CTV D95 Equivalent dose in 2 Gy per fraction (EQD2) >32.7 Gy had significantly longer LFFS compared to patients with Vasc CTV D95 EQD2 ≤32.7 Gy at 12 months (91% vs. 51%, respectively) and 24 months (86% vs. 12%, respectively). The median disease-free survival (DFS) for patients with EQD2 >32.7 Gy was 30.4 months compared to 14.0 months in patients with EQD2 ≤32.7 Gy (p = 0.01). There was no significant difference in overall survival (OS) between the two groups.

Conclusions

During neoadjuvant treatment, dose to the Vasc CTV is associated with durability of local control (LC) after resection and should be intentionally included in the treatment volume with an EQD2 goal of 31–33 Gy.

Radiation therapy in borderline resectable pancreatic cancer: A review

BACKGROUND

Borderline resectable pancreatic cancer constitutes a complex clinical entity, presenting the clinician with a locally aggressive disease that has a proclivity for distant spread. The benefits of radiation therapy, such as improved local control and improved survival, have been questioned. In this review we seek to summarize the existing evidence on radiation therapy in borderline resectable pancreatic cancer and highlight future areas of research.

METHODS

A comprehensive review of PubMed for clinical studies reporting outcomes in borderline resectable pancreatic cancer was performed in June 2021, with an emphasis placed on prospective studies.

RESULTS

Radiologic "downstaging" in borderline resectable pancreatic cancer is a rare event, although some evidence shows increased clinical response to neoadjuvant chemotherapy over radiation therapy. Margin status seems to be equivalent between regimens that use neoadjuvant chemotherapy alone and regimens that include neoadjuvant radiation therapy. Local control in borderline resectable pancreatic cancer is likely improved with radiation therapy; however, the benefit of improved local control in a disease marked by systemic failure has been questioned. Although some studies have shown improved survival with radiation therapy, differences in the delivery and tolerance of chemotherapy between the neoadjuvant and adjuvant setting confound these results. When the evidence is evaluated as a whole, there is no clear survival benefit of radiation therapy in borderline resectable pancreatic cancer.

CONCLUSION

Once considered a staple of therapy, the role of radiation therapy in borderline resectable pancreatic cancer is evolving as systemic therapy regimens continues to improve. Increased clinical understanding of disease phenotype and response are needed to accurately tailor therapy for individual patients and to improve outcomes in this complex patient population.

Impact of neoadjuvant intensity-modulated radiation therapy on borderline resectable pancreatic cancer with arterial abutment; a prospective, open-label, phase II study in a single institution

Background

Borderline resectable pancreatic cancer (BRPC) is a category of pancreatic cancer that is anatomically widely spread, and curative resection is uncommon with upfront surgery. Intensity-modulated radiation therapy (IMRT) is a form of radiation therapy that delivers precise radiation to a tumor while minimizing the dose to surrounding normal tissues. Here, we conducted a phase 2 study to estimate the curability and efficacy of neoadjuvant chemoradiotherapy using IMRT (NACIMRT) for patients with BRPC with arterial abutment (BRPC-A).

Methods

A total of 49 BRPC-A patients were enrolled in this study and were treated at our hospital according to the study protocol between June 2013 and March 2021. The primary endpoint was microscopically margin-negative resection (R0) rates and we subsequently analyzed safety, histological effect of the treatment as well as survivals among patients with NACIMRT.

Results

Twenty-nine patients (59.2%) received pancreatectomy after NACIMRT. The R0 rate in resection patients was 93.1% and that in the whole cohort was 55.1%. No mortality was encountered. Local therapeutic effects as assessed by Evans classification showed good therapeutic effect (Grade 1, 3.4%; Grade 2a, 31.0%; Grade 2b, 48.3%; Grade 3, 3.4%; Grade 4, 3.4%). Median disease-free survival was 15.5 months. Median overall survival in the whole cohort was 35.1 months. The only independent prognostic pre-NACIMRT factor identified was serum carbohydrate antigen 19–9 (CA19-9) > 400 U/ml before NACIMRT.

Conclusions

NACIMRT showed preferable outcome without significant operative morbidity for BRPC-A patients. NACIMRT contributes to good local tumor control, but a high initial serum CA19-9 implies poor prognosis even after neoadjuvant treatment.

Trial Registration

UMIN-CTR Clinical Trial: https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000011776

Registration number: UMIN000010113.

Date of first registration: 01/03/2013,