Estimation of Conditional Neurocognitive Function Failure (NCFF) Incidence in Patients Receiving Whole Brain Radiation Therapy (WBRT) for Brain Metastases (BM): Secondary Analysis of NRG CC001

PURPOSE/OBJECTIVE(S)

NRG CC001 was a trial that demonstrated a significantly lower risk of neurocognitive function failure (NCFF) with the use of hippocampal avoidant whole brain radiotherapy (HA-WBRT) as compared to conventional WBRT in patients with brain metastases (BM). Although a sizeable proportion of patients ultimately still did develop NCFF, the utility of this data from time of radiation treatment diminishes over time. Conditional survival analyses can provide better estimates especially for patients who demonstrate longer term neurocognitive protection. We sought to use clinical trial data to estimate the conditional risk of development of NCFF for short and longer-term survivors and to evaluate if factors prognostic of NCFF at diagnosis remained relevant over time.

MATERIALS/METHODS

We performed a post hoc analysis of 518 patients enrolled in NRG CC001, a phase III trial in which patients with BM were randomly assigned to WBRT plus memantine or HA-WBRT plus memantine, using data obtained from the NCI NCTN Data Archive. In this secondary analysis, cumulative incidence function and Gray's test were used to estimate conditional NCFF incidence for the entire cohort and between arms at various time points of survivorship without neurocognitive dysfunction. Risk factors were analyzed using cause-specific multivariable Cox proportional hazards modeling analysis (MVA).

RESULTS

Overall, the cumulative risk of development NCFF by 6 months was 64.5%. Following 2- (n = 259), 4- (n = 74), 6- (n = 43), and 8-month (n = 26) survivorship without NCFF, the conditional probability of developing neurocognitive impairment within the next 2 months were 70.1%, 27.7%, 12.7%, and 3.8%, and within the next 4 months were 78.1%, 35.4%, 15.6%, and 3.8%, respectively. For those who retained intact neurocognitive function at 2 months, only receipt of HA-WBRT (HR = 0.743, P = 0.033) and age ≤61 (HR = 0.620, P = 0.003) were predictive on MVA for decreased risk of NCFF. Prognostic factors predictive of NCFF at diagnosis were no longer associated with decreased risk of NCFF following 4 months of survivorship without cognitive impairment. Patients who achieved survivorship of ≥4 months had similar conditional risk of cognitive dysfunction between treatment arms (Gray's test, P = 0.219), and this trend persisted for patients free of NCFF at ≥6 and 8 months.

CONCLUSION

Our data highlight that the greatest risk for development of NCFF after WBRT is in within the first 4 months after treatment. Conditional risk of NCFF for patients who have survived ≥4-, 6-, and 8- months without NCFF steadily decreases the longer survivorship is; this risk also appears to plateau. HA-WBRT confers reduced risk of NCFF at time of diagnosis and for short-term survivors without NCFF. Most importantly, these data can be used to counsel patients about their conditional risk of neurocognitive dysfunction over time, and suggest that those who are able to remain free of cognitive impairment may have lower risks of developing NCFF in the future.

Conditional Survival Estimates for Malignant Glioma Patients by RPA Class: Secondary Analysis of RTOG 9006

PURPOSE/OBJECTIVE(S)

The RTOG recursive partitioning analysis (RPA) for malignant glioma patients is a key prognostic factor correlated with survival for patients with a malignant glioma, which was established using data from RTOG 9006. While such data is useful when counseling patients on survival outcomes at the time of diagnosis, the utility of such data diminishes over time. Conditional survival (CS) is a way to provide 'real-time' estimates of how survival changes over time. The primary objective of this secondary analysis is to report conditional survival estimates for patients with malignant gliomas enrolled on RTOG 9006 stratified by RPA class.

MATERIALS/METHODS

RTOG 9006 was a phase III trial of patients diagnosed with malignant gliomas randomized to BCNU and hyper-fractionated radiation therapy (RT) vs. BCNU and conventionally fractionated RT that showed no significant differences in toxicities or oncologic outcomes. We performed a post-hoc analysis of RTOG 9006 using data obtained from the NCI NCTN Data Archive to evaluate conditional survival estimates for different RPA subgroups. Eligible patients included those with a known RPA class who were enrolled on RTOG 9006 (n = 632). Conditional survival estimates from the time of diagnosis and following 1-, 3-, and 5-y of survival were calculated using the Kaplan-Meier method. Cox proportional hazards modeling was performed to evaluate the prognostic significance of treatment arm, histology, extent of surgical resection, and RPA class following 1-, 3-, and 5-y of survival.

RESULTS

For RPA Group I (n = 68), OS at 1-y from diagnosis was 95.58%. At 1- (n = 65), 3- (49) and 5-y (42) of survivorship, the chances of surviving an additional 1-y were 84.62, 91.84, 98.62% respectively (See Table 1). RPA class continued to be significantly correlated with survival following 1- and 3-y of survival irrespective of treatment arm. Treatment arm was not significantly correlated with conditional survival at any time point following treatment completion, and there was no interaction between treatment arm and RPA subgroups. Histology was significant at all time points.

CONCLUSION

Conditional risk of death for patients treated for malignant gliomas in RPA Group I remains low at levels similar to those at initial diagnosis. Conditional risk continuously improves for RPA Groups IV-V as patients live longer. In most groups, the lowest survival odds were found in patients who have already survived 1 year.

Relationship Between Spatial Distribution Tumor Location and Dosimetric Outcomes in Patients Receiving Definitive Proton Therapy for Locally Advanced Lung Cancer

PURPOSE/OBJECTIVE(S)

Intensity Modulated Proton Therapy with Pencil Beam Scanning (IMPT/PBS) has been postulated to have dosimetric benefits, especially for sparing of normal tissues in the treatment of thoracic malignancies. Distinguishing which patients may benefit most from IMPT/PBS treatment has important implications when counseling patients on optimal treatment modality, treatment approval turnaround time, and potential toxicities. We herein present a single institution experience assessing the relationship between spatial distribution of tumor location and dosimetric outcomes in patients receiving definitive IMPT/PBS for locally advanced lung cancer.

MATERIALS/METHODS

Consecutive patients treated with IMPT/PBS for locally advanced lung cancer from 2016-2022 at an academic proton center were retrospectively analyzed. Treatment, tumor volume, and patient characteristics were collected. Distance from the posterior pleura to the anterior-most portion of the clinical tumor volume (CTV) of the tumor was measured. A ratio of this distance to the pleura-to-pleura distance at that corresponding lung level was used to classify anterior (>0.7) versus posterior tumors. Dosimetric details including beam angles, dose-volume parameters for the ipsilateral, contralateral, total lung and heart for each patient were recorded. Statistical differences between groups were determined using Wilcoxon Signed Rank test. Pearson's correlation coefficient was used to determine impact of CTV volume and the anterior-most distance of CTV on dosimetric parameters.

RESULTS

Fifty-eight patients treated for Stage IIB-IIIC locally advanced lung cancer with a median CTV volume of 258 cc's were identified and included in this retrospective study. Median age was 68 years and there was an equal distribution of male (29, 50%) and female patients (29, 50%) as well as anterior (>0.7) and posterior lying tumors in this cohort. The majority of patients were white (42, 72%) Forty patients (69%) had right sided lung tumors. Median cumulative dose was 61.2 Gy (range 59.4-70 Gy) while median dose per fraction was 2 Gy (range 1.8-2 Gy). When compared to anterior tumors, posterior tumors had a lower Lung V20 (19.1% vs 21.6%, p = 0.1,), V5 (27.6% vs 32.4%, p = 0.03), Mean Lung (9.9 Gy vs 11.7 Gy, p = 0.04), Mean Heart (4.8 Gy vs 6.3 Gy, p = 0.1), and Heart V50 (3.1% vs. 4.6%, p = 0.15). Anterior-most distance of CTV from the posterior pleura was positively correlated with Lung V20 (r = .435, p = 0.001), Lung V5 (r = .390, p = 0.002), Mean Lung (r = .479, p = 0.001), Mean Heart (r = .304, p = 0.020), and Heart V50 (r = .322, p = 0.014). CTV volume was also significantly positively correlated (p <.01) with these parameters.

CONCLUSION

Spatial distribution and treatment volume size are predictive of dosimetric outcomes for locally advanced lung cancer. Posterior lying tumors may derive greater dosimetric advantage when compared to anterior lesions when utilizing IMPT/PBS.