Hippocampal avoidance prophylactic cranial irradiation (HA-PCI) for small cell lung cancer reduces hippocampal atrophy compared to conventional PCI

Perihippocampal failure after hippocampal-avoidance brain radiotherapy in small cell lung cancer patients: Cases report and literature review

RATIONALE

Brain metastasis is a major concern, and may occur in roughly 50% of patients during the clinical course of small cell lung cancer (SCLC). Because prophylactic cranial irradiation reduces the incidence of brain metastases and improves overall survival, prophylactic cranial irradiation is recommended for SCLC patients without distant metastases or an extensive stage and have responded well to systemic therapy. Hippocampal-avoidance whole-brain radiotherapy (HA-WBRT) is preferred to preserve hippocampal function while minimizing negative cognitive effects.

PATIENT CONCERNS

Reducing the dose delivered to the hippocampus below the therapeutic brain dose may increase the risk of hippocampal progression; thus, HA-WBRT may be associated with a risk of perihippocampal recurrence.

DIAGNOSIS

Three patients with SCLC received HA-WBRT and developed intracranial failure during clinical follow-up; 3 relapsed with intracranial failure in the perihippocampal region after 12, 13, and 7 months, respectively.

INTERVENTION AND OUTCOMES

Compared to the therapeutic brain dose of cases and the underdose region around the HA region, we matched MRI scans of intracranial failure and previous planning scans of simulation and found a deviation of the underdosed region within the perihippocampal failure of approximately 55% to 63%.

LESSONS

Perihippocampal failure is a rare clinical outcome in SCLC patients following HA-WBRT. Perihippocampal failure could be caused by an underdose of radiation or by the aggressiveness of the cancer itself. More research into this topic is encouraged.

Big Decisions on Small Cell Lung Cancer: A Focus on Clinical Care Updates and Patient Perspectives

Small cell lung cancer (SCLC) is an uncommon, aggressive high-grade neuroendocrine carcinoma, associated with tobacco use. It is a highly chemosensitive disease that initially responds quickly to systemic therapy, although patients with SCLC tend to develop relapse. Although the landscape of SCLC treatment has remained stagnant for many decades, the field has seen notable advances in the past few years, including the use of immunotherapy, the development of further lines of systemic therapy, the refinement of thoracic and intracranial radiotherapy, and-most recently-the promise of more targeted therapies. Patients with SCLC also must face unique psychosocial burdens in their experience with their cancer, distinct from patients with other lung cancer. In this article, we review the latest literature and future directions in the management and investigation of SCLC, as well as the critical decisions that providers and patients must navigate in the current landscape. We also present the perspectives of several patients with SCLC in conjunction with this summary, to spotlight their individual journeys in the context of this challenging disease.

Predicting overall survival and prophylactic cranial irradiation benefit in small-cell lung cancer with CT-based deep learning: A retrospective multicenter study

BACKGROUND AND PURPOSE

To develop a computed tomography (CT)-based deep learning model to predict overall survival (OS) among small-cell lung cancer (SCLC) patients and identify patients who could benefit from prophylactic cranial irradiation (PCI) based on OS signature risk stratification.

MATERIALS AND METHODS

This study retrospectively included 556 SCLC patients from three medical centers. The training, internal validation, and external validation cohorts comprised 309, 133, and 114 patients, respectively. The OS signature was built using a unified fully connected neural network. A deep learning model was developed based on the OS signature. Clinical and combined models were developed and compared with a deep learning model. Additionally, the benefits of PCI were evaluated after stratification using an OS signature.

RESULTS

Within the internal and external validation cohorts, the deep learning model (concordance index [C-index] 0.745, 0.733) was far superior to the clinical model (C-index: 0.635, 0.630) in predicting OS, but slightly worse than the combined model (C-index: 0.771, 0.770). Additionally, the deep learning model had excellent calibration, clinical usefulness, and improved accuracy in classifying survival outcomes. Remarkably, patients at high risk had a survival benefit from PCI in both the limited and extensive stages (all P < 0.05), whereas no significant association was observed in patients at low risk.

CONCLUSIONS

The CT-based deep learning model exhibited promising performance in predicting the OS of SCLC patients. The OS signature may aid in individualized treatment planning to select patients who may benefit from PCI.

Quality assurance and safety of hippocampal avoidance prophylactic cranial irradiation in the multicenter randomized phase III trial (NCT01780675)

Objective

NCT01780675, a multicenter randomized phase III trial of prophylactic cranial irradiation (PCI) versus PCI with hippocampal sparing in small cell lung cancer (SCLC) investigated neurocognitive decline and safety. As part of quality assurance, we evaluated if hippocampal avoidance (HA)-PCI was performed according to the NCT01780675 trial protocol instructions, and performed a safety analysis to study the incidence and location of brain metastases for patients treated with HA-PCI.

Methods

This retrospective analysis evaluated the quality of the irradiation given in the randomized controlled trial (RCT) comparing SCLC patients receiving PCI with or without hippocampal avoidance, using intensity modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT). The dose distribution for each patient receiving HA-PCI was retrieved and analyzed to evaluate if the treatment dose constraints were met. A questionnaire was sent out to all participating sites, and data on radiotherapy technique, pre-treatment dummy runs, phantom measurements and treatment electronic portal imaging device (EPID) dosimetry were collected and analyzed. As part of the safety analysis, the follow-up magnetic resonance imaging (MRI) or computerized tomography (CT) scans on which cranial disease progression was first diagnosed were collected and matched to the radiotherapy planning dose distribution. The matched scans were reviewed to analyze the location of the brain metastases in relation to the prescribed dose.

Results

A total of 168 patients were randomized in the NCT01780675 trial in 10 centers in the Netherlands and Belgium from April 2013 until March 2018. Eighty two patients receiving HA-PCI without evidence of brain metastases were analyzed. All patients were treated with 25 Gy in 10 fractions. Dummy runs and phantom measurements were performed in all institutions prior to enrolling patients into the study. The radiotherapy (RT) plans showed a median mean bilateral hippocampal dose of 8.0 Gy, range 5.4-11.4 (constraint ≤ 8.5 Gy). In six patients (7.3%) there was a protocol violation of the mean dose in one or both hippocampi. In four of these six patients (4.9%) the mean dose to both hippocampi exceeded the constraint, in 1 patient (1.2%) only the left and in 1 patient (1.2%) only the right hippocampal mean dose was violated (average median dose left and right 8.9 Gy). All patients met the trial dose constraint of V 115% PTV ≤ 1%; however the D max PTV constraint of ≤ 28.75 Gy was violated in 22.0% of the patients. The safety analysis showed that 14 patients (17.1%) developed cranial progression. No solitary brain metastases in the underdosed region were found. Two out of 11 patients with multiple brain metastasis developed metastasis in the underdosed region(s).

Conclusions

The radiotherapy quality within the HA-PCI trial is performed according to the protocol guidelines. The dose constraints to the hippocampi are met in the vast majority of cases. In all patients, the volume of the brain for which a higher dose was accepted, is according to the trial. However, within this volume there are small areas with higher doses than advised.

Prophylactic cranial irradiation in small cell lung cancer: an update

PURPOSE OF REVIEW

The current review presents recent updates in the seminal literature of research on prophylactic cranial irradiation (PCI) in small cell lung cancer (SCLC).

RECENT FINDINGS

Brain MRI restaging before the administration of PCI reveals a substantial proportion of brain metastasis in baseline brain metastasis free extensive-stage SCLC (ES-SCLC) and limited-stage SCLC (LS-SCLC). Posthoc analyses from the CASPIAN and IMpower133 trials revealed decreases in brain metastasis rates in ES-SCLC treated with chemoimmunotherapy relative to the brain metastasis rates in ES-SCLC treated with chemotherapy alone. A recent meta-analysis of literature published after the landmark 1999 Auperin meta-analysis confirmed the survival benefit of PCI in LS-SCLC patients. A recent study employing PET before and after PCI demonstrated that hippocampal avoidance -PCI (HA-PCI) preserved the metabolic activity of the hippocampi compared with regular PCI. Two phase III trials evaluating neurocognitive functions after HA-PCI versus PCI have yielded conflicting results. Ongoing clinical trials (MAVERICK, PRIMALung, NRG CC003, NCT04535739, NCT04829708 and NCT03514849) regarding PCI versus MRI surveillance and HA-PCI versus PCI were also discussed.

SUMMARY

Currently, the indications for PCI in SCLC are under question in the modern MRI era. Result from prospective phase III, MRI staged and MRI monitored RCTs are expected to elucidate the role of PCI in LS-SCLC and ES-SCLC. Preliminary results indicated that adding immunotherapy to chemotherapy may reduce brain metastasis rate in SCLC. Further data to this aspect are warranted to determine the role of PCI in the immuno-chemotherapy era. The future direction for PCI should be the comprehensive integration of personalized patient selection, HA-PCI utilization and potential employment of other neurocognitive preservation strategies.