Severe lymphopenia during neoadjuvant chemoradiation for esophageal cancer: A propensity matched analysis of the relative risk of proton versus photon-based radiation therapy

Spleen Dose-Volume Parameters as a Predictor of Treatment-related Lymphopenia During Definitive Chemoradiotherapy for Esophageal Cancer

AIM

Our study sought to identify dosimetric predictors of treatment-related lymphopenia during chemoradiotherapy for esophageal cancer.

MATERIALS AND METHODS

Patients with esophageal cancer who had received definitive chemoradiotherapy at our Institution were retrospectively assessed. The absolute volume of the spleen, body, and bone marrow that had received 5, 10, 20, and 30 Gy and the mean splenic dose were recorded.

RESULTS

Multivariate linear regression analysis revealed that docetaxel use and spleen dose-volume parameters (V5, V10, V20, V30, and mean splenic dose) were significant independent factors negatively influencing the absolute lymphocyte count at nadir. An increase of 1 Gy in mean splenic dose predicted a 2.9% decrease in nadir absolute lymphocyte count. Univariable logistic regression analysis showed that the mean splenic dose was a significant predictor of grade 4 lymphopenia. None of the body or bone marrow dose-volume parameters significantly predicted lymphopenia.

CONCLUSION

Higher spleen dose-volume parameters were associated with severe lymphopenia during chemoradiotherapy.

A Comparison of Grade 4 Lymphopenia With Proton Versus Photon Radiation Therapy for Esophageal Cancer

Purpose

Grade 4 lymphopenia (G4L) during radiation therapy (RT) is associated with higher rates of distant metastasis and decreased overall survival in a number of malignancies, including esophageal cancer (EC). Through a reduction in integral radiation dose, proton RT (PRT) may reduce G4L relative to photon RT (XRT). The purpose of this study was to compare G4L in patients with EC undergoing PRT versus XRT.

Methods and materials

Patients receiving curative-intent RT and concurrent chemotherapy for EC were identified. Lymphocyte nadir was defined as the lowest lymphocyte count during RT. G4L was defined as absolute lymphocyte count <200/mm³. Univariate and multivariable logistic regression analyses (MVA) were performed to assess patient and treatment factors associated with lymphopenia. A propensity-matched (PM) cohort was created using logistic regression, including baseline covariates.

Results

A total of 144 patients met the inclusion criteria. The median age was 66 years (range, 32-85 years). Of these patients, 79 received XRT (27% 3-dimensional chemo-RT and 73% intensity modulated RT) and 65 received PRT (100% pencil-beam scanning). Chemotherapy consisted of weekly carboplatin and paclitaxel (99%). There were no significant differences in baseline characteristics between the groups, except for age (median 4 years older in the PRT cohort). G4L was significantly higher in patients who received XRT versus those who received PRT (56% vs 22%; P < .01). On MVA, XRT (odds ratio [OR]: 5.13; 95% confidence interval [CI], 2.35-11.18; P < .001) and stage III/IV (OR: 4.54; 95% CI, 1.87-11.00; P < .001) were associated with G4L. PM resulted in 50 PRT and 50 XRT patients. In the PM cohort, G4L occurred in 60% of patients who received XRT versus 24% of patients who received PRT. On MVA, XRT (OR: 5.28; 95% CI, 2.14-12.99; P < .001) and stage III/IV (OR: 3.77; 95% CI, 1.26-11.30; P = .02) were associated with G4L.

Conclusions

XRT was associated with a significantly higher risk of G4L in comparison with PRT. Further work is needed to evaluate a potential association between RT modality and antitumor immunity as well as long-term outcomes.

Field size effects on the risk and severity of treatment-induced lymphopenia in patients undergoing radiation therapy for solid tumors

Purpose

Radiation-induced lymphopenia (RIL) is the result of direct toxicity to circulating lymphocytes as they traverse the irradiated field, occurs in 40% to 70% of patients who undergo conventional external beam radiation therapy, and is associated with worse outcomes in multiple solid tumors. As immunotherapy strategies evolve, a better understanding of radiation's effects on the immune system is needed in order to develop rational methods of combining RT with immunotherapy.

Methods and materials

This paper is a review of the available literature on the clinical significance and dosimetric predictors of radiation-induced toxicity to the immune system.

Results

An association between severe RIL and inferior survival has been described in multiple solid tumors, including glioma, lung cancer, and pancreatic cancer. RIL risk is correlated with field size, dose per fraction, and fraction number. SBRT and proton therapy techniques are associated with lower RIL risk.

Conclusions

The immune system should be considered an organ at risk during RT, and absolute lymphocyte count is an important biomarker of RT-induced immunotoxicity. Radiation dose and technique affect the risk and severity of RIL. Further research is needed to accurately characterize RT-induced immunotoxicity and develop strategies to prevent or mitigate this clinically significant side effect.

"Radiobiology of Proton Therapy": Results of an international expert workshop

The physical properties of proton beams offer the potential to reduce toxicity in tumor-adjacent normal tissues. Toward this end, the number of proton radiotherapy facilities has steeply increased over the last 10-15 years to currently around 70 operational centers worldwide. However, taking full advantage of the opportunities offered by proton radiation for clinical radiotherapy requires a better understanding of the radiobiological effects of protons alone or combined with drugs or immunotherapy on normal tissues and tumors. This report summarizes the main results of the international expert workshop "Radiobiology of Proton Therapy" that was held in November 2016 in Dresden. It addresses the major topics (1) relative biological effectiveness (RBE) in proton beam therapy, (2) interaction of proton radiobiology with radiation physics in current treatment planning, (3) biological effects in proton therapy combined with systemic treatments, and (4) testing biological effects of protons in clinical trials. Finally, important research avenues for improvement of proton radiotherapy based on radiobiological knowledge are identified. The clinical distribution of radiobiological effectiveness of protons alone or in combination with systemic chemo- or immunotherapies as well as patient stratification based on biomarker expressions are key to reach the full potential of proton beam therapy. Dedicated preclinical experiments, innovative clinical trial designs, and large high-quality data repositories will be most important to achieve this goal.

Combining Immunotherapy and Radiotherapy for Cancer Treatment: Current Challenges and Future Directions

Since the approval of anti-CTLA4 therapy (ipilimumab) for late-stage melanoma in 2011, the development of anticancer immunotherapy agents has thrived. The success of many immune-checkpoint inhibitors has drastically changed the landscape of cancer treatment. For some types of cancer, monotherapy for targeting immune checkpoint pathways has proven more effective than traditional therapies, and combining immunotherapy with current treatment strategies may yield even better outcomes. Numerous preclinical studies have suggested that combining immunotherapy with radiotherapy could be a promising strategy for synergistic enhancement of treatment efficacy. Radiation delivered to the tumor site affects both tumor cells and surrounding stromal cells. Radiation-induced cancer cell damage exposes tumor-specific antigens that make them visible to immune surveillance and promotes the priming and activation of cytotoxic T cells. Radiation-induced modulation of the tumor microenvironment may also facilitate the recruitment and infiltration of immune cells. This unique relationship is the rationale for combining radiation with immune checkpoint blockade. Enhanced tumor recognition and immune cell targeting with checkpoint blockade may unleash the immune system to eliminate the cancer cells. However, challenges remain to be addressed to maximize the efficacy of this promising combination. Here we summarize the mechanisms of radiation and immune system interaction, and we discuss current challenges in radiation and immune checkpoint blockade therapy and possible future approaches to boost this combination.