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

Translational Frontiers and Clinical Opportunities of Immunologically Fitted Radiotherapy

Ionizing radiation can have a wide range of impacts on tumor-immune interactions, which are being studied with the greatest interest and at an accelerating pace by the medical community. Despite its undeniable immunostimulatory potential, it clearly appears that radiotherapy as it is prescribed and delivered nowadays often alters the host's immunity toward a suboptimal state. This may impair the full recovery of a sustained and efficient antitumor immunosurveillance posttreatment. An emerging concept is arising from this awareness and consists of reconsidering the way of designing radiation treatment planning, notably by taking into account the individualized risks of deleterious radio-induced immune alteration that can be deciphered from the planned beam trajectory through lymphocyte-rich organs. In this review, we critically appraise key aspects to consider while planning immunologically fitted radiotherapy, including the challenges linked to the identification of new dose constraints to immune-rich structures. We also discuss how pharmacologic immunomodulation could be advantageously used in combination with radiotherapy to compensate for the radio-induced loss, for example, with (i) agonists of interleukin (IL)2, IL4, IL7, IL9, IL15, or IL21, similarly to G-CSF being used for the prophylaxis of severe chemo-induced neutropenia, or with (ii) myeloid-derived suppressive cell blockers.

Dosimetric impact of bone marrow sparing for robustly optimized IMPT for locally advanced cervical cancer

BACKGROUND AND PURPOSE

To investigate the trade-off between bone marrow sparing (BMS) and dose to organs at risk (OARs) for intensity modulated proton therapy (IMPT) for women with locally advanced cervical cancer (LACC).

MATERIALS AND METHODS

Twenty LACC patients were retrospectively included. IMPT plans were created for each patient using automated treatment planning. These plans progressively reduced bone marrow mean doses by steps of 1 GyRBE, while constraining target coverage and conformality. The relation between bone marrow dose and bladder, small bowel, rectum, and sigmoid doses was evaluated.

RESULTS

A total of 140 IMPT plans were created. Plans without BMS had an average [range] bone marrow mean dose of 17.3 [14.7-21.6] GyRBE , which reduced to 12.0 [10.0-14.0] GyRBE with maximum BMS. The mean OAR dose [range] increased modestly for 1 GyRBE BMS: 0.2 [0.0 - 0.6] GyRBE for bladder, 0.3 [-0.2 - 0.7] GyRBE for rectum, 0.4 [0.1 - 0.8] GyRBE for small bowel, and 0.2 [-0.2 - 0.4] GyRBE for sigmoid. Moreover, for maximum BMS, mean OAR doses [range] escalated by 3.3 [0.1 - 6.7] GyRBE for bladder, 5.8 [1.8 - 12.4] GyRBE for rectum, 3.9 [1.6 - 5.9] GyRBE for small bowel, and 2.7 [0.6 - 5.9] GyRBE for sigmoid.

CONCLUSION

Achieving 1 GyRBE BMS for IMPT is feasible for LACC patients with limited dosimetric impact on other OARs. While further bone marrow dose reduction is possible for some patients, it may increase OAR doses substantially for others. Hence, we recommend a personalized approach when introducing BMS into clinical IMPT treatment planning to carefully assess individual patient benefits and risks.

The relationship between splenic dose and radiation-induced lymphopenia

Lymphocytes, which are highly sensitive to radiation, play a crucial role in the body's defense against tumors. Radiation-induced lymphopenia has been associated with poorer outcomes in different cancer types. Despite being the largest secondary lymphoid organ, the spleen has not been officially designated as an organ at risk. This study hypothesizes a connection between spleen irradiation and lymphopenia and seeks to establish evidence-based dosage limits for the spleen. We retrospectively analyzed data from 96 patients with locally advanced gastric cancer who received postoperative chemoradiotherapy (CRT) between May 2010 and May 2017. Complete blood counts were collected before, during and after CRT. We established a model for predicting the minimum absolute lymphocyte count (Min ALC) and to investigate potential associations between spleen dosimetric variables and Min ALC. The median follow-up was 60 months. The 5-year overall survival (OS) and disease-free survival (DFS) were 65.2% and 56.8%, respectively. The median values of pre-treatment ALC, Min ALC and post-treatment ALC were 1.40 × 109, 0.23 × 109 and 0.28 × 109/L, respectively. Regression analysis confirmed that the primary tumor location, number of fractions and spleen V5 were significant predictors of Min ALC during radiation therapy. Changes in ALC (ΔALC) were identified as an independent predictor of both OS and DFS. Spleen V5 is an independent predictor for Min ALC, and the maximum dose of the spleen is associated with an increased risk of severe lymphopenia. Therefore, these doses should be restricted in clinical practice. Additionally, ΔALC can serve as a prognostic indicator for adjuvant radiotherapy in gastric cancer.

Hypofractionated Radiotherapy-Related Lymphopenia Is Associated With Worse Survival in Unresectable Intrahepatic Cholangiocarcinoma

OBJECTIVE

The aim of this study was to evaluate the incidence of radiotherapy (RT)-related lymphopenia, its predictors, and association with survival in unresectable intrahepatic cholangiocarcinoma (ICC) treated with hypofractionated-RT (HF-RT).

METHODS

Retrospective analysis of 96 patients with unresectable ICC who underwent HF-RT (median 58.05 Gy in 15 fractions) between 2009 and 2022 was performed. Absolute lymphocyte count (ALC) nadir within 12 weeks of RT was analyzed. Primary variable of interest was severe lymphopenia, defined as Grade 3+ (ALC <0.5 k/μL) per CTCAE v5.0. Primary outcome of interest was overall survival (OS) from RT.

RESULTS

Median follow-up was 16 months. Fifty-two percent of patients had chemotherapy pre-RT, 23% during RT, and 40% post-RT. Pre-RT, median ALC was 1.1 k/μL and 5% had severe lymphopenia. Post-RT, 68% developed RT-related severe lymphopenia. Patients who developed severe lymphopenia had a significantly lower pre-RT ALC (median 1.1 vs. 1.5 k/μL, P=0.01) and larger target tumor volume (median 125 vs. 62 cm3, P=0.02). In our multivariable Cox model, severe lymphopenia was associated with a 1.7-fold increased risk of death (P=0.04); 1-year OS rates were 63% vs 77% (P=0.03). Receipt of photon versus proton-based RT (OR=3.50, P=0.02), higher mean liver dose (OR=1.19, P<0.01), and longer RT duration (OR=1.49, P=0.02) predicted severe lymphopenia.

CONCLUSIONS

HF-RT-related lymphopenia is an independent prognostic factor for survival in patients with unresectable ICC. Patients with lower baseline ALC and larger tumor volume may be at increased risk, and use of proton therapy, minimizing mean liver dose, and avoiding treatment breaks may reduce RT-related lymphopenia.

Survival outcomes and toxicity of adjuvant immunotherapy after definitive concurrent chemotherapy with proton beam radiation therapy for patients with inoperable locally advanced non-small cell lung carcinoma

INTRODUCTION

Adjuvant immunotherapy (IO) following concurrent chemotherapy and photon radiation therapy confers an overall survival (OS) benefit for patients with inoperable locally advanced non-small cell lung carcinoma (LA-NSCLC); however, outcomes of adjuvant IO after concurrent chemotherapy with proton beam therapy (CPBT) are unknown. We investigated OS and toxicity after CPBT with adjuvant IO versus CPBT alone for inoperable LA-NSCLC.

MATERIALS AND METHODS

We analyzed 354 patients with LA-NSCLC who were prospectively treated with CPBT with or without adjuvant IO from 2009 to 2021. Optimal variable ratio propensity score matching (PSM) matched CPBT with CPBT + IO patients. Survival was estimated with the Kaplan-Meier method and compared with log-rank tests. Multivariable Cox proportional hazards regression evaluated the effect of IO on disease outcomes.

RESULTS

Median age was 70 years; 71 (20%) received CPBT + IO and 283 (80%) received CPBT only. After PSM, 71 CPBT patients were matched with 71 CPBT + IO patients. Three-year survival rates for CPBT + IO vs CPBT were: OS 67% vs 30% (P < 0.001) and PFS 59% vs 35% (P = 0.017). Three-year LRFS (P = 0.137) and DMFS (P = 0.086) did not differ. Receipt of adjuvant IO was a strong predictor of OS (HR 0.40, P = 0.001) and PFS (HR 0.56, P = 0.030), but not LRFS (HR 0.61, P = 0.121) or DMFS (HR 0.61, P = 0.136). There was an increased incidence of grade ≥3 esophagitis in the CPBT-only group (6% CPBT + IO vs 17% CPBT, P = 0.037).

CONCLUSION

This study, one of the first to investigate CPBT followed by IO for inoperable LA-NSCLC, showed that IO conferred survival benefits with no increased rates of toxicity.

Systematic review and pooled analysis of the impact of treatment-induced lymphopenia on survival of glioblastoma patients

PURPOSE/OBJECTIVE(S)

Treatment related lymphopenia is a known toxicity for glioblastoma (GBM) patients and several single-institution studies have linked lymphopenia with poor survival outcomes. We performed a systematic review and pooled analysis to evaluate the association between lymphopenia and overall survival (OS) for GBM patients undergoing chemotherapy and radiation therapy (RT).

MATERIALS/METHODS

Following PRISMA guidelines, a systematic literature review of the MEDLINE database and abstracts from ASTRO, ASCO, and SNO annual meetings was conducted. A pooled analysis was performed using inverse variance-weighted random effects to generate a pooled estimate of the hazard ratio of association between lymphopenia and OS.

RESULTS

Ten of 104 identified studies met inclusion criteria, representing 1,718 patients. The lymphopenia cutoff value varied (400-1100 cells/uL) and as well as the timing of its onset. Studies were grouped as time-point (i.e., lymphopenia at approximately 2-months post-RT) or time-range (any lymphopenia occurrence from treatment-start to approximately 2-months post-RT. The mean overall pooled incidence of lymphopenia for all studies was 31.8%, and 11.8% vs. 39.9% for time-point vs. time-range studies, respectively. Lymphopenia was associated with increased risk of death, with a pooled HR of 1.78 (95% CI 1.46-2.17, P < 0.00001) for the time-point studies, and a pooled HR of 1.38 (95% CI 1.24-1.55, P < 0.00001) for the time-point studies. There was no significant heterogeneity between studies.

CONCLUSION

These results strengthen observations from previous individual single-institution studies and better defines the magnitude of the association between lymphopenia with OS in GBM patients, highlighting lymphopenia as a poor prognostic factor.

Kaplan lecture 2023: lymphopenia in particle therapy

PURPOSE

Lymphopenia is now generally recognized as a negative prognostic factor in radiotherapy. Already at the beginning of the century we demonstrated that high-energy carbon ions induce less damage to the lymphocytes of radiotherapy patients than X-rays, even if heavy ions are more effective per unit dose in the induction of chromosomal aberrations in blood cells irradiated ex-vivo. The explanation was based on the volume effect, i.e. the sparing of larger volumes of normal tissue in Bragg peak therapy. Here we will review the current knowledge about the difference in lymphopenia between particle and photon therapy and the consequences.

CONCLUSIONS

There is nowadays an overwhelming evidence that particle therapy reduces significantly the radiotherapy-induced lymphopenia in several tumor sites. Because lymphopenia turns down the immune response to checkpoint inhibitors, it can be predicted that particle therapy may be the ideal partner for combined radiation and immunotherapy treatment and should be selected for patients where severe lymphopenia is expected after X-rays.

The need for paradigm shift: prognostic significance and implications of standard therapy-related systemic immunosuppression in glioblastoma for immunotherapy and oncolytic virotherapy

Despite significant advances in our knowledge regarding the genetics and molecular biology of gliomas over the past two decades and hundreds of clinical trials, no effective therapeutic approach has been identified for adult patients with newly diagnosed glioblastoma, and overall survival remains dismal. Great hopes are now placed on combination immunotherapy. In clinical trials, immunotherapeutics are generally tested after standard therapy (radiation, temozolomide, and steroid dexamethasone) or concurrently with temozolomide and/or steroids. Only a minor subset of patients with progressive/recurrent glioblastoma have benefited from immunotherapies. In this review, we comprehensively discuss standard therapy-related systemic immunosuppression and lymphopenia, their prognostic significance, and the implications for immunotherapy/oncolytic virotherapy. The effectiveness of immunotherapy and oncolytic virotherapy (viro-immunotherapy) critically depends on the activity of the host immune cells. The absolute counts, ratios, and functional states of different circulating and tumor-infiltrating immune cell subsets determine the net immune fitness of patients with cancer and may have various effects on tumor progression, therapeutic response, and survival outcomes. Although different immunosuppressive mechanisms operate in patients with glioblastoma/gliomas at presentation, the immunological competence of patients may be significantly compromised by standard therapy, exacerbating tumor-related systemic immunosuppression. Standard therapy affects diverse immune cell subsets, including dendritic, CD4+, CD8+, natural killer (NK), NKT, macrophage, neutrophil, and myeloid-derived suppressor cell (MDSC). Systemic immunosuppression and lymphopenia limit the immune system's ability to target glioblastoma. Changes in the standard therapy are required to increase the success of immunotherapies. Steroid use, high neutrophil-to-lymphocyte ratio (NLR), and low post-treatment total lymphocyte count (TLC) are significant prognostic factors for shorter survival in patients with glioblastoma in retrospective studies; however, these clinically relevant variables are rarely reported and correlated with response and survival in immunotherapy studies (e.g., immune checkpoint inhibitors, vaccines, and oncolytic viruses). Our analysis should help in the development of a more rational clinical trial design and decision-making regarding the treatment to potentially improve the efficacy of immunotherapy or oncolytic virotherapy.

Severe Lymphopenia During Chemoradiation Therapy for Esophageal Cancer: Comprehensive Analysis of Randomized Phase 2B Trial of Proton Beam Therapy Versus Intensity Modulated Radiation Therapy

PURPOSE

Lymphocytes play an important role in antitumor immunity; however, they are also especially vulnerable to depletion during chemoradiation therapy (CRT). The purpose of this study was to compare the incidence of grade 4 lymphopenia (G4L) between proton beam therapy (PBT) and intensity modulated photon radiation therapy (IMRT) in patients with esophageal cancer treated with CRT in a completed randomized trial and to ascertain patient heterogeneity to G4L risk based on treatment and established prognostic factors.

METHODS AND MATERIALS

Between April 2012 and March 2019, a single-institution, open-label, nonblinded, phase 2 randomized trial (NCT01512589) was conducted at the University of Texas MD Anderson Cancer Center. Patients were randomly assigned to IMRT or PBT, either definitively or preoperatively. This secondary analysis of the randomized trial was G4L during concurrent CRT according to Common Terminology Criteria for Adverse Events version 5.0.

RESULTS

Among 105 patients evaluable for analysis, 44 patients (42%) experienced G4L at a median of 28 days after the start date of concurrent CRT. Induction chemotherapy (P = .003), baseline absolute lymphocyte count (P < .001), radiation therapy modality (P = .002), and planning treatment volume (P = .033) were found to be significantly associated with G4L. Multivariate classification analysis partitioned patients into 5 subgroups for whom the incidence of G4L was observed in 0%, 14%, 35%, 70%, and 100% of patients. The benefit of PBT over IMRT was most pronounced in patients with an intermediate baseline absolute lymphocyte count and large planning treatment volume (P = .011).

CONCLUSIONS

This is the first prospective evidence that limiting dose scatter by PBT significantly reduced the incidence of G4L, especially in the intermediate-risk patients. The implication of this immune-sparing effect of PBT, especially in the context of standard adjuvant immunotherapy, needs further examination in the current phase 3 randomized trials.

The Correlation Between Low-Dose Radiotherapy Area of the Mediastinum and CD8+T Cells and the Efficacy of Radiotherapy for Non-Small Cell Lung Cancer

Background

Radiation therapy (RT) can cause changes in peripheral blood immune cells. The relationship between the efficacy of radiation therapy for non-small cell lung cancer (NSCLC) and immune cell changes and the study of how mediastinal radiation dose parameters affect immune cell changes is still unclear. This study aims to analyze the relationship between immune cell changes induced by radiotherapy and the efficacy of NSCLC radiotherapy, as well as the relationship between radiotherapy dose parameters and immune cell changes.

Materials and Methods

We retrospectively analyzed the data of NSCLC patients receiving mediastinal radiation therapy from 2020 to 2022. Collect lymphocytes and circulating immune cells within one week before and after radiotherapy and collect the dose-volume parameters of the whole mediastinum in the patient's RT planning system. Analyze the changes in lymphocytes and radiotherapy effects after radiotherapy, and explore the relationship between radiotherapy dose parameters and immune cell changes.

Results

A total of 72 patients were enrolled. Compared with before radiotherapy, the proportion of CD3+T cells, CD8+T cells, and CD8/Treg in peripheral blood significantly increased after radiotherapy (P<0.05). The increase in CD8+T cells and CD8/Treg after radiotherapy was correlated with Objective response rate (ORR) (P<0.05). Based on binary logistic univariate and multivariate regression analysis, an increase in CD8+T cells after radiotherapy is an independent predictor of objective tumor response after radiotherapy (OR=12.71, 95% CI=3.64-44.64, P=0.01), and Volume of 200 cGy irradiation (V2) is an independent positive predictor of an increase in CD8+T lymphocyte ratio after radiotherapy (high group, OR=3.40, 95% CI=1.13-10.36, P=0.03).

Conclusion

The increase in CD8+T cells after radiotherapy can positively predict the short-term efficacy of radiotherapy. Mediastinal low-dose radiation therapy can increase CD8+T cells, thereby improving the short-term efficacy of radiotherapy. These potentially related mechanisms are worth further verification and exploration.

Severe radiation-induced lymphopenia during concurrent chemoradiotherapy for stage III non-small cell lung cancer: external validation of two prediction models

Background

Severe radiation-induced lymphopenia (RIL) in patients undergoing chemoradiotherapy (CRT) for non-small cell lung cancer (NSCLC) is associated with decreased immunotherapy efficacy and survival. At The Christie and MD Anderson Cancer Center (MDACC), prediction models for lymphopenia were developed in lung and esophageal cancer patients, respectively. The aim of this study was to externally validate both models in patients with stage III NSCLC.

Methods

Patients who underwent concurrent CRT for stage III NSCLC in 2019-2021 were studied. Outcomes were grade ≥3 and grade 4 lymphopenia during CRT. The Christie model predictors for grade ≥3 lymphopenia included age, baseline lymphocyte count, radiotherapy duration, chemotherapy, mean heart and lung doses, and thoracic vertebrae V20Gy. MDACC predictors for grade 4 lymphopenia were age, baseline lymphocyte count, planning target volume (PTV), and BMI. The external performance of both models was assessed.

Results

Among 100 patients, 78 patients (78%) developed grade ≥3 lymphopenia, with grade 4 lymphopenia in 17 (17%). For predicting grade ≥3 lymphopenia, the Christie and MDACC models yielded c-statistics of 0.77 and 0.79, respectively. For predicting grade 4 lymphopenia, c-statistics were 0.69 and 0.80, respectively. Calibration for the Christie and MDACC models demonstrated moderate and good agreement, respectively.

Conclusion

The PTV-based MDACC prediction model for severe RIL demonstrated superior external performance in NSCLC patients compared to the dosimetry-based Christie model. As such, the MDACC model can aid in identifying patients at high risk for severe lymphopenia. However, to optimize radiotherapy planning, further improvement and external validation of dosimetry-based models is desired.

Dosimetric Effect of Thymus and Thoracic Duct on Radiation-Induced Lymphopenia in Patients With Primary Lung Cancer Who Received Thoracic Radiation

Purpose

Radiation-induced lymphopenia is a well-recognized factor for tumor control and survival in patients with cancer. This study aimed to determine the role of radiation dose to the thymus and thoracic duct on radiation-induced lymphopenia.

Methods and Materials

Patients with primary lung cancer treated with thoracic radiation therapy between May 2015 and February 2020 with whole blood count data were eligible. Clinical characteristics, including age, gender, histology, stage, chemotherapy regimen, radiation dosimetry, and absolute lymphocyte count (ALC) were collected. The thymus and thoracic duct were contoured by one investigator for consistency and checked by one senior physician. The primary endpoint was radiation-induced decrease in lymphocytes, defined as the difference in ALC (DALC) before and after radiation therapy.

Results

The data of a total of 116 consecutive patients were retrospectively retrieved. Significant correlations were found between DALC and several clinical factors. These factors include stage, chemotherapy or concurrent chemoradiation, biologically effective dose (BED), mean lung dose, mean body dose, effective dose to immune cells (EDIC), mean thymus dose (MTD), and mean thoracic duct dose (MTDD) (all P < .05). Ridge regression showed that DALC = 0.0063 × BED + 0.0172 × EDIC + 0.0002 × MTD + 0.0147 × MTDD + 0.2510 (overall P = .00025 and F = 5.85). The combination model has the highest area under the curve of 0.77 (P < .001) when fitting the logistic regression model on DALC categorized as binary endpoint. The sensitivity and specificity of the combined model were 89% and 58%, respectively.

Conclusions

This study demonstrated for the first time that radiation doses to the thymus and thoracic duct are strongly associated with radiation-induced lymphopenia patients with lung cancer. Further validation studies are needed to implement thymus and thoracic duct as organs at risk.

Concurrent chemoradiotherapy using proton beams can reduce cardiopulmonary morbidity in esophageal cancer patients: a systematic review

This systematic review was performed to investigate the superiority of proton beam therapy (PBT) to photon-based radiotherapy (RT) in treating esophageal cancer patients, especially those with poor cardiopulmonary function. The MEDLINE (PubMed) and ICHUSHI (Japana Centra Revuo Medicina) databases were searched from January 2000 to August 2020 for studies evaluating one end point at least as follows; overall survival, progression-free survival, grade ≥ 3 cardiopulmonary toxicities, dose-volume histograms, or lymphopenia or absolute lymphocyte counts (ALCs) in esophageal cancer patients treated with PBT or photon-based RT. Of 286 selected studies, 23 including 1 randomized control study, 2 propensity matched analyses, and 20 cohort studies were eligible for qualitative review. Overall survival and progression-free survival were better after PBT than after photon-based RT, but the difference was significant in only one of seven studies. The rate of grade 3 cardiopulmonary toxicities was lower after PBT (0-13%) than after photon-based RT (7.1-30.3%). Dose-volume histograms revealed better results for PBT than photon-based RT. Three of four reports evaluating the ALC demonstrated a significantly higher ALC after PBT than after photon-based RT. Our review found that PBT resulted in a favorable trend in the survival rate and had an excellent dose distribution, contributing to reduced cardiopulmonary toxicities and a maintained number of lymphocytes. These results warrant novel prospective trials to validate the clinical evidence.

Cardiac Dose Predicts the Response to Concurrent Chemoradiotherapy in Esophageal Squamous Cell Carcinoma

Definitive concurrent chemoradiation (CCRT) is the standard treatment for cervical esophageal cancer and non-surgical candidates. Initial treatment response affects survival; however, few validated markers are available for prediction. This study evaluated the clinical variables and chemoradiation parameters associated with treatment response. Between May 2010 and April 2016, 86 completed CCRT patients' clinical, dosimetric, and laboratory data at baseline and during treatment were collected. Cox regression analysis assessed the risk factors for overall survival (OS). A receiver operating characteristic curve with Youden's index was chosen to obtain the optimal cut-off value of each parameter. Treatment response was defined per Response Evaluation Criteria in Solid Tumors v.1.1 at the first post-CCRT computed tomography scan. Responders had complete and partial responses; non-responders had stable and progressive diseases. Logistic regression (LR) was used to evaluate the variables associated with responders. The Cox regression model confirmed the presence of responders (n = 50) vs. non-responders (n = 36) with a significant difference in OS. In multivariate LR, cardiac dose-volume received ≥10 Gy; the baseline hemoglobin level, highest neutrophil to lymphocyte ratio during CCRT, and cumulative cisplatin dose were significantly associated with the responders. The initial clinical treatment response significantly determines disease outcome. Cardiac irradiation may affect the treatment response.

A review on lymphocyte radiosensitivity and its impact on radiotherapy

It is well known that radiation therapy causes lymphopenia in patients and that this is correlated with a negative outcome. The mechanism is not well understood because radiation can have both immunostimulatory and immunosuppressive effects. How tumor dose conformation, dose fractionation, and selective lymph node irradiation in radiation therapy does affect lymphopenia and immune response is an active area of research. In addition, understanding the impact of radiation on the immune system is important for the design and interpretation of clinical trials combining radiation with immune checkpoint inhibitors, both in terms of radiation dose and treatment schedules. Although only a few percent of the total lymphocyte population are circulating, it has been speculated that their increased radiosensitivity may contribute to, or even be the primary cause of, lymphopenia. This review summarizes published data on lymphocyte radiosensitivity based on human, small animal, and in vitro studies. The data indicate differences in radiosensitivity among lymphocyte subpopulations that affect their relative contribution and thus the dynamics of the immune response. In general, B cells appear to be more radiosensitive than T cells and NK cells appear to be the most resistant. However, the reported dose-response data suggest that in the context of lymphopenia in patients, aspects other than cell death must also be considered. Not only absolute lymphocyte counts, but also lymphocyte diversity and activity are likely to be affected by radiation. Taken together, the reviewed data suggest that it is unlikely that radiation-induced cell death in lymphocytes is the sole factor in radiation-induced lymphopenia.

Efficacy and Safety in Proton Therapy and Photon Therapy for Patients With Esophageal Cancer: A Meta-Analysis

Importance

Radiotherapy plays an important role in the treatment of esophageal cancer. Proton therapy has unique physical properties and higher relative biological effectiveness. However, whether proton therapy has greater benefit than photon therapy is still unclear.

Objective

To evaluate whether proton was associated with better efficacy and safety outcomes, including dosimetric, prognosis, and toxic effects outcomes, compared with photon therapy and to evaluate the efficacy and safety of proton therapy singly.

Data Sources

A systematic search of PubMed, Embase, the Cochrane Library, Web of Science, SinoMed, and China National Knowledge Infrastructure databases was conducted for articles published through November 25, 2021, and updated to March 25, 2023.

Study Selection

For the comparison of proton and photon therapy, studies including dosimetric, prognosis, and associated toxic effects outcomes were included. The separate evaluation of proton therapy evaluated the same metrics.

Data Extraction and Synthesis

Data on study design, individual characteristics, and outcomes were extracted. If I2 was greater than 50%, the random-effects model was selected. This meta-analysis is reported following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline.

Main Outcomes and Measures

The main outcomes were organs at risk (OARs) dosimetric outcomes, prognosis (overall survival [OS], progression-free survival [PFS], and objective response rate [ORR]), and radiation-related toxic effects.

Results

A total of 45 studies were included in the meta-analysis. For dosimetric analysis, proton therapy was associated with significantly reduced OARs dose. Meta-analysis showed that photon therapy was associated with poor OS (hazard ratio [HR], 1.31; 95% CI, 1.07-1.61; I2 = 11%), but no difference in PFS was observed. Subgroup analysis showed worse OS (HR, 1.42; 95% CI, 1.14-1.78; I2 = 34%) and PFS (HR, 1.48; 95% CI, 1.06-2.08; I2 = 7%) in the radical therapy group with photon therapy. The pathological complete response rate was similar between groups. Proton therapy was associated with significantly decreased grade 2 or higher radiation pneumonitis and pericardial effusion, and grade 4 or higher lymphocytopenia. Single-rate analysis of proton therapy found 89% OS and 65% PFS at 1 year, 71% OS and 56% PFS at 2 years, 63% OS and 48% PFS at 3 years, and 56% OS and 42% PFS at 5 years. The incidence of grade 2 or higher radiation esophagitis was 50%, grade 2 or higher radiation pneumonitis was 2%, grade 2 or higher pleural effusion was 4%, grade 2 or higher pericardial effusion was 3%, grade 3 or higher radiation esophagitis was 8%, and grade 4 or higher lymphocytopenia was 17%.

Conclusions and Relevance

In this meta-analysis, proton therapy was associated with reduced OARs doses and toxic effects and improved prognosis compared with photon therapy for esophageal cancer, but caution is warranted. In the future, these findings should be further validated in randomized clinical trials.

A Review of Advances in Radiotherapy in the Setting of Esophageal Cancers

Esophageal cancer is the eighth most common cancer worldwide and is the sixth most common cause of cancer-related mortality. The paradigm has shifted to include a multimodality approach with surgery, chemotherapy, targeted therapy (including immunotherapy), and radiation therapy. Advances in radiotherapy through techniques such as intensity modulated radiotherapy and proton beam therapy have allowed for the more dose homogeneity and improved organ sparing. In addition, recent studies of targeted therapies and predictive approaches in patients with locally advanced disease provide clinicians with new approaches to modify multimodality treatment to improve clinical outcomes.

Can lymphocytes serve as a predictor of response to preoperative chemoradiation therapy for locally advanced rectal cancer?

Introduction

The aim of this study is to identify factors that may predict the response of locally advanced rectal cancer tumors (LARC) to neoadjuvant chemoradiotherapy (CRT) and to evaluate the effect of circulating lymphocytes on pathological tumor response.

Methods

This retrospective study included neoadjuvant CRT-treated, LARC-diagnosed patients at the Rambam Health Care Campus in Haifa, Israel. CHAID analysis, t-test, χ2 test, and ROC curve analyses were performed to explore the association between pathological complete response (pCR) and several factors including patient demographics, tumor characteristics, type of treatment, and levels of circulating lymphocytes measured on a weekly basis.

Results

Out of 198 patients enrolled in the study, pCR was achieved in 50 patients (25%). ROC curve and CHAID analyses showed that absolute lymphopenia was significantly associated with lower pCR rates (p=0.046 and p=0.001, respectively). Other factors that were found to have a significant impact were radiation therapy type (p=0.033) and tumor distance from the anal verge (p= 0.041).

Conclusion

An absolute decrease in the level of circulating lymphocytes during preoperative CRT to LARC is associated with poorer tumor response to treatment and thus may serve as a predictive biomarker for treatment resistance.

Proton versus photon radiation therapy: A clinical review

While proton radiation therapy offers substantially better dose distribution characteristics than photon radiation therapy in certain clinical applications, data demonstrating a quantifiable clinical advantage is still needed for many treatment sites. Unfortunately, the number of patients treated with proton radiation therapy is still comparatively small, in some part due to the lack of evidence of clear benefits over lower-cost photon-based treatments. This review is designed to present the comparative clinical outcomes between proton and photon therapies, and to provide an overview of the current state of knowledge regarding the effectiveness of proton radiation therapy.

Effects of lymphopenia on survival in proton therapy with chemotherapy for non-small cell lung cancer

Lymphocytes play an important role in the cancer immune system. In the present study, we aimed to evaluate the associations of lymphopenia during proton beam therapy (PBT) and concurrent chemotherapy with clinical outcomes and to determine whether lung or bone is more influential on lymphopenia during PBT. Data from 41 patients with stage III non-small cell lung cancer (NSCLC) who received PBT of 74 GyE with concurrent chemotherapy between 2007 and 2017 were reviewed retrospectively. The correlation between dosimetry parameters obtained from dose-volume histograms of the bone and lung and lymphopenia during PBT were analyzed. Minimum absolute lymphocyte count (ALCmin) and maximum neutrophil/lymphocyte ratio (NLRmax) were used as indicators of lymphopenia. Bone V5-20 and lung V5-50 were significantly correlated with the ALCmin and NLRmax during PBT. Multivariable analysis showed that the NLRmax, but not the ALCmin, was associated with overall survival (OS), progression-free survival (PFS) and distant metastasis-free survival (DMFS). The 3-year rates of OS, PFS and DMFS of patients with a low (≤ 6.3) versus high (> 6.3) NLRmax were 73.9% vs 44.4% (P = 0.042), 26.1% vs 5.6% (P = 0.022) and 39.1% vs 5.6% (P < 0.001), respectively. Lung V20 was significantly associated with DMFS on multivariable analyses (hazard ratio: 1.094, P = 0.008), whereas bone V5 had no impact on survival outcomes. We concluded that the NLRmax was a better prognostic indicator than the ALCmin, and the lung dose had more influence than the bone dose on the main survival outcomes in stage III NSCLC patients treated with PBT combined with concurrent chemotherapy.

Hypofractionation and SABR: 25 years of evolution in medical physics and a glimpse of the future

As we were invited to write an article for celebrating the 50^th Anniversary of Medical Physics journal, on something historically significant, commemorative, and exciting happening in the past decades, the first idea came to our mind is the fascinating radiotherapy paradigm shift from conventional fractionation to hypofractionation and stereotactic ablative radiotherapy (SABR). It is historically and clinically significant since as we all know this RT treatment revolution not only reduces treatment duration for patients, but also improves tumor control and cancer treatment outcomes. It is also commemorative and exciting for us medical physicists since the technology development in medical physics has been the main driver for the success of this treatment regimen which requires high precision and accuracy throughout the entire treatment planning and delivery. This article provides an overview of the technological development and clinical trials evolvement in the past 25 years for hypofractionation and SABR, with an outlook to the future improvement.

Proton and Carbon Ion Radiation Therapy Decreased Severe Lymphopenia by Reducing Thoracic Vertebra and Aortic Doses in Non-small Cell Lung Cancer Versus Intensity Modulated Radiation Therapy

PURPOSE

Lymphopenia is a common adverse effect of radiation therapy (RT). Little is known about the difference in lymphopenia between intensity modulated (photon) radiation therapy (IMRT) and proton and carbon ion radiation therapy (PCIRT). This study aimed to investigate lymphopenia differences between IMRT and PCIRT in non-small cell lung cancer (NSCLC).

METHODS AND MATERIALS

Clinical and dosimetric parameters were collected from 343 patients who received definitive IMRT or PCIRT for NSCLC. Severe lymphopenia (SRL) was defined as an absolute lymphocyte count (ALC) ≤0.5 × 10³ cells/μL. Overall survival (OS) was analyzed using the Kaplan-Meier method. Propensity score matching was performed between the IMRT and PCIRT groups. Least absolute shrinkage and selection operator analysis was used to select appropriate dosimetric parameters. Univariate and multivariate logistic regression analyses were conducted to identify the predictors of SRL.

RESULTS

Compared with the IMRT group, the PCIRT group was less likely to develop SRL (P < .001). Compared with the non-SRL group, the SRL group showed significant association with poorer OS, with a median survival time of 29.2 versus 15.0 months (P = .046). IMRT was an independent risk factor of SRL (P = .004). A lower ALC before RT (P = .030) and larger planning target volume (PTV) (P = .002) were also significant independent risk factors for SRL. Moreover, the majority of dosimetric parameters of organs at risk in PCIRT were lower than those in IMRT (P < .001). Thoracic vertebra V5 (P = .002) and aorta V5 (P = .026) were identified as independent risk predictors of SRL after adding dosimetric parameters to the regression model.

CONCLUSIONS

Compared with IMRT, PCIRT could reduce SRL incidence, possibly by limiting thoracic vertebra and aortic doses, and SRL was associated with poor outcomes in patients with NSCLC.

Proton Therapy With Concurrent Chemotherapy for Thoracic Esophageal Cancer: Toxicity, Disease Control, and Survival Outcomes

Purpose

When treating esophageal cancer with radiation therapy, it is critical to limit the dose to surrounding structures, such as the lung and/or heart, as much as possible. Proton radiation therapy allows a reduced radiation dose to both the heart and lungs, potentially reducing the risk of cardiopulmonary toxicity. Here, we report disease control, survival, and toxicity outcomes among patients with esophageal cancer treated with proton radiation therapy and concurrent chemotherapy (chemoradiation therapy; CRT) with or without surgery.

Materials and Methods

We enrolled 17 patients with thoracic esophageal carcinoma on a prospective registry between 2010 and 2021. Patients received proton therapy to a median dose of 50.4-GyRBE (range, 50.4-64.8) in 1.8-Gy fractions.Acute and late toxicities were graded per the Common Terminology Criteria for Adverse Events, version 4.0 (US National Cancer Institute, Bethesda, Maryland). In addition, disease control, patterns of failure, and survival outcomes were collected.

Results

Nine patients received preoperative CRT, and 8 received definitive CRT. Overall, 88% of patients had adenocarcinoma, and 12% had squamous cell carcinoma. With a median follow-up of 2.1 years (range, 0.5-9.4), the 3-year local progression-free, disease-free, and overall survival rates were 85%, 66%, and 55%, respectively. Two patients (1 with adenocarcinoma and 1 with squamous cell carcinoma) recurred at the primary site after refusing surgery after a complete clinical response to CRT. The most common acute nonhematologic and hematologic toxicities, respectively, were grades 1 to 3 esophagitis and grades 1 to 4 leukopenia, both affecting 82% of patients. No acute cardiopulmonary toxicities were observed in the absence of surgical resection. Reagarding surgical complications, 3 postoperative cardiopulmonary complications occurred as follows: 1 grade 1 pleural effusion, 1 grade 3 pleural effusion, and 1 grade 2 anastomotic leak. Two severe late CRT toxicities occurred: 1 grade 5 tracheoesophageal fistula and 1 grade 3 esophageal stenosis requiring a feeding tube.

Conclusion

Proton radiation therapy is a safe, effective treatment for esophageal cancer with increasing evidence supporting its role in reducing cardiopulmonary toxicity.

Robustness assessment of clinical adaptive proton and photon radiotherapy for oesophageal cancer in the model-based approach

PURPOSE

In the Netherlands, oesophageal cancer (EC) patients are selected for intensity modulated proton therapy (IMPT) using the expected normal tissue complication probability reduction (ΔNTCP) when treating with IMPT compared to volumetric modulated arc therapy (VMAT). In this study, we evaluate the robustness of the first EC patients treated with IMPT in our clinic in terms of target and organs-at-risk (OAR) dose with corresponding NTCP, as compared to VMAT.

MATERIALS AND METHODS

For 20 consecutive EC patients, clinical IMPT and VMAT plans were created on the average planning 4DCT. Both plans were robustly evaluated on weekly repeated 4DCTs and if target coverage degraded, replanning was performed. Target coverage was evaluated for complete treatment trajectories with and without replanning. The planned and accumulated mean lung dose (MLD) and mean heart dose (MHD) were additionally evaluated and translated into NTCP.

RESULTS

Replanning in the clinic was performed more often for IMPT (15x) than would have been needed for VMAT (8x) (p = 0.11). Both adaptive treatments would have resulted in adequate accumulated target dose coverage. Replanning in the first week of treatment had most clinical impact, as anatomical changes resulting in insufficient accumulated target coverage were already observed at this stage. No differences were found in MLD between the planned dose and the accumulated dose. Accumulated MHD differed from the planned dose (p < 0.001), but since these differences were similar for VMAT and IMPT (1.0 and 1.5 Gy, respectively), the ΔNTCP remained unchanged.

CONCLUSION

Following an adaptive clinical workflow, adequate target dose coverage and stable OAR doses with corresponding NTCPs was assured for both IMPT and VMAT.

Current landscape of radiation oncology in esophageal cancer: a narrative review

Background and Objective

Esophageal cancer is an aggressive disease that is the sixth leading cause of cancer-related death worldwide. The overall treatment paradigm for esophageal cancer has changed considerably over the past decade. This narrative review aims to summarize the current landscape of radiation oncology for esophageal cancer.

Methods

A systematic search of the MEDLINE/PubMed database and Clinicaltrials.gov was performed, focusing on studies published within the last 10 years. Our search queried "esophageal cancer [AND] neoadjuvant radiation" as well as "locally advanced esophageal cancer [AND] definitive radiation". Our search resulted in 298 total references. These were manually reviewed, and only 58 references were within our scope of interest ranging from 2012-2022.

Key Content and Findings

For resectable esophageal cancer, neoadjuvant chemoradiation followed by surgery has been defined as the standard of care over the past decade. In patients with incomplete response to neoadjuvant chemoradiation, the benefit of immunotherapy in the adjuvant setting has recently been established. Ongoing studies are examining whether perioperative chemotherapy may be equivalent to neoadjuvant chemoradiation in resectable esophageal adenocarcinoma. For locally advanced esophageal cancer, recent studies have failed to show a benefit with radiation dose escalation in an unselected population, although the use of early positron emission tomography (PET) response to guide dose escalation is currently being studied. Other ongoing studies aiming to improve outcomes in locally advanced esophageal cancer involve using proton beam therapy to reduce toxicity and combining immunotherapy or targeted therapies with chemoradiation to amplify response.

Conclusions

Recent advances in radiation oncology may continue to improve outcomes for patients with esophageal cancer.

Severe radiation-induced lymphopenia during postoperative radiotherapy or chemoradiotherapy has poor prognosis in patients with stage IIB-III after radical esophagectomy: A post hoc analysis of a randomized controlled trial

Objective

To investigate whether radiation-induced lymphopenia (RIL) affects survival and identify the predictors of RIL in postoperative esophageal cancer.

Materials and methods

Post hoc analysis was conducted on data from 116 patients with esophageal cancer from a randomized controlled trial comparing adjuvant therapy with surgery alone. Doses of 54 Gy in 27 fractions was delivered in the postoperative radiotherapy (PORT) group and 50.4 Gy in 28 fractions combined with chemotherapy was delivered in postoperative concurrent chemoradiotherapy (POCRT) group. Blood counts were obtained before, during, and at first follow-up after treatment. Lymphopenia was graded per version 4.03 of the Common Terminology Criteria for Adverse Events. Disease-free survival (DFS) and overall survival (OS) were analyzed using the Kaplan-Meier method, and compared between groups using the log-rank test. Receiver operating characteristic curves identified thresholds for preventing grade 4 (G4) lymphopenia.

Results

Median follow-up duration was 56.0 months. During treatment, 16 patients (13.8%) had G4 lymphopenia. All cases of G4 lymphopenia occurred in group PORT (30.2% vs 0.0%, p<0.001). Baseline absolute lymphocyte count was comparable between G1-3 and G4 patients (2.0 ± 0.8 *10⁹/L vs 1.7 ± 0.5 *10⁹/L; p=0.101). The 3-year DFS was significantly lower in group G4 lymphopenia than that in group G1-3 (31.3% vs 57.6%, p=0.036). The 3-year OS was comparable between both groups (50.0% vs 66.5%, p=0.095). Logistic regression analysis revealed that exposed more thoracic marrow (TM V20 ≥75%; TVB V20 ≥71%), heart (V15 ≥40%) and PTV (volume ≥507 ml) were associated with G4 lymphopenia (p<0.05).

Conclusions

G4 RIL had poor disease-free survival, which may be related to more dose exposure of thoracic marrow and heart due to larger PTV. Reasonably reducing the radiation field combined with concurrent chemotherapy, or radiation dose constraints for these normal tissues may be sufficient to decrease the incidence of G4 lymphopenia, but further prospective trials are needed to verify the results.

Clinical Trial Registration

clinicaltrials.gov, identifier NCT02279134

Radiation-induced lymphopenia does not impact treatment efficacy in a mouse tumor model

Radiation-induced lymphopenia is a common occurrence in radiation oncology and an established negative prognostic factor, however the mechanisms underlying the relationship between lymphopenia and inferior survival remain elusive. The relevance of lymphocyte co-irradiation as critical normal tissue component at risk is an emerging topic of high clinical relevance, even more so in the context of potentially synergistic radiotherapy-immunotherapy combinations. The impact of the radiotherapy treatment volume on the lymphocytes of healthy and tumor-bearing mice was investigated in a novel mouse model of radiation-induced lymphopenia. Using an image-guided small-animal radiotherapy treatment platform, translationally relevant tumor-oriented volumes of irradiation with an anatomically defined increasing amount of normal tissue were irradiated, with a focus on the circulating blood and lymph nodes. In healthy mice, the influence of irradiation with increasing radiotherapy treatment volumes was quantified on the level of circulating blood cells and in the spleen. A significant decrease in the lymphocytes was observed in response to irradiation, including the minimally irradiated putative tumor area. The extent of lymphopenia correlated with the increasing volumes of irradiation. In tumor-bearing mice, differential radiotherapy treatment volumes did not influence the overall therapeutic response to radiotherapy alone. Intriguingly, an improved treatment efficacy in mice treated with draining-lymph node co-irradiation was observed in combination with an immune checkpoint inhibitor. Taken together, our study reveals compelling data on the importance of radiotherapy treatment volume in the context of lymphocytes as critical components of normal tissue co-irradiation and highlights emerging challenges at the interface of radiotherapy and immunotherapy.

Severe Radiation-Induced Lymphopenia Attenuates the Benefit of Durvalumab After Concurrent Chemoradiotherapy for NSCLC

Introduction

Durvalumab after concurrent chemoradiation (CCRT) for NSCLC improves survival, but only in a subset of patients. We investigated the effect of severe radiation-induced lymphopenia (sRIL) on survival in these patients.

Methods

Outcomes after CCRT (2010–2019) or CCRT followed by durvalumab (2018–2019) were reviewed. RIL was defined by absolute lymphocyte count (ALC) nadir in samples collected at end of CCRT; sRIL was defined as nadir ALC less than 0.23 × 10⁹/L (the lowest tertile). Progression-free survival (PFS) and overall survival (OS) were calculated by the Kaplan-Meier method. Cox proportional hazard modeling evaluated associations between clinical variables and survival.

Results

Of 309 patients, 192 (62%) received CCRT only and 117 (38%) CCRT plus durvalumab. Multivariable logistic regression analysis indicated that sRIL was associated with planning target volume (OR = 1.002, p = 0.001), stage IIIB disease (OR = 2.77, p = 0.04), and baseline ALC (OR = 0.36, p < 0.01). Durvalumab extended median PFS (23.3 versus 14.1 mo, p = 0.003) and OS (not reached versus 30.8 mo, p < 0.01). sRIL predicted poorer PFS and OS in both treatment groups. Among patients with sRIL, durvalumab did not improve survival (median = 24.6 mo versus 18.1 mo CCRT only, p = 0.079). On multivariable analyses, sRIL (OR = 1.81, p < 0.01) independently predicted poor survival.

Conclusions

Severe RIL compromises survival benefits from durvalumab after CCRT for NSCLC. Measures to mitigate RIL after CCRT may be warranted to enhance the benefit of consolidation durvalumab.

Proton Beam Therapy for Esophageal Cancer

Simple Summary

Early-stage esophageal cancer is managed surgically, with the addition of radiotherapy for locally advanced disease. Current photon-based radiotherapy results in a high treatment-related complications, due to proximal organ involvement. The anatomic location of the esophagus raises challenges due to the anatomical changes associated with diaphragmatic motion, weight loss, tumor changes, and set-up variability. These propelled the interest in proton beam therapy (PBT), which theoretically offers a reduction in the radiation exposure to healthy neighboring tissues with improvements in the therapeutic ratio. In this review, we present the role of PBT for esophageal cancer, including treatment planning, early clinical comparisons with photon-based techniques, ongoing trials, current challenges, toxicities, and issues of equity and health services.

Abstract

Early-stage esophageal cancer is often primarily managed surgically, with the addition of radiotherapy for locally advanced disease. However, current photon-based radiotherapy regimens and surgery results in a high incidence of treatment-related cardiac and pulmonary complications due to the involvement of proximal organs at risk. In addition, the anatomic location of the esophagus raises challenges for radiotherapy due to the anatomical changes associated with diaphragmatic motion, weight loss, tumor changes, and set-up variability. These challenges propelled the interest in proton beam therapy (PBT), which theoretically offers a reduction in the radiation exposure to healthy neighboring tissues with improvements in the therapeutic ratio. Several dosimetric studies support the potential advantages of PBT for esophageal cancer treatment however, translation of these results to improved clinical outcomes remains unclear with limited clinical data, especially in large populations. Studies on the effect on quality of life are likewise lacking. Here, we review the existing and emerging role of PBT for esophageal cancer, including treatment planning, early clinical comparisons of PBT with photon-based techniques, recently concluded and ongoing clinical trials, challenges and toxicities, effects on quality of life, and global inequities in the treatment of esophageal cancer.

Prediction and clinical impact of delayed lymphopenia after chemoradiotherapy in locally advanced non-small cell lung cancer

Introduction

The dosimetric factors of radiotherapy have an acute impact on the host immune system during chemoradiotherapy (CRT) in locally advanced non-small cell lung cancer (NSCLC). However, even after CRT, a substantial number of patients remain immunosuppressed with delayed lymphopenia. Therefore, we aimed to evaluate clinical and dose-volumetric predictors of delayed lymphopenia after CRT in locally advanced NSCLC.

Materials and methods

We retrospectively reviewed 272 patients with locally advanced NSCLC who received definitive CRT from January 2012 to August 2020. Differential blood count data, including serum albumin values, were obtained at baseline, during and at first follow up after CRT. Acute and delayed lymphopenia events were defined as grade III/IV lymphopenia developed during or 4-12 weeks after CRT completion, which accounted for 84% and 10% of cases, respectively. Dose-volume histogram parameters for planned target volume, whole body, heart, lung, great vessels, spleen, esophagus and thoracic vertebral bodies were evaluated.

Results

Multivariate analysis revealed that patients with delayed lymphopenia were associated with inferior overall survival (HR 2.53, P = 0.001) and progression-free survival (HR 1.98, P = 0.006). However, there was no significant survival difference between groups stratified by acute lymphopenia. On multivariable logistic regression models, lung V5, baseline ALC, during-CRT ALC, and albumin nadir were significant predictors for delayed lymphopenia. Furthermore, the nomogram for delayed lymphopenia based on these variables had good discrimination (area under the curve, 0.905).

Conclusions

In this study, we investigated the prognostic significance of delayed lymphopenia and identified clinico-dosimetric parameters to predict delayed lymphopenia.

The Key Clinical Questions of Neoadjuvant Chemoradiotherapy for Resectable Esophageal Cancer—A Review

Over 50% of individuals with esophageal cancer (EC) present with advanced stages of the disease; therefore, their outcome following surgery alone is poor, with only 25%–36% being alive 5 years post-surgery. Based on the evidence that the CROSS and NEOCRTEC5010 trials provided, neoadjuvant chemoradiotherapy (nCRT) is now the standard therapy for patients with locally advanced EC. However, there are still many concerning clinical questions that remain controversial such as radiation dose, appropriate patient selection, the design of the radiation field, the time interval between chemoradiotherapy (CRT) and surgery, and esophageal retention. With immune checkpoint inhibitors (ICIs) rapidly becoming a mainstay of cancer therapy, along with radiation, chemotherapy, and surgery, the combination mode of immunotherapy is also becoming a hot topic of discussion. Here, we try to provide constructive suggestions to answer the perplexing problems and clinical concerns for the progress of nCRT for EC in the future.

Reflections on beam configuration optimization for intensity-modulated proton therapy

Presumably, intensity-modulated proton radiotherapy (IMPT) is the most powerful form of proton radiotherapy. In the current state of the art, IMPT beam configurations (i.e. the number of beams and their directions) are, in general, chosen subjectively based on prior experience and practicality. Beam configuration optimization (BCO) for IMPT could, in theory, significantly enhance IMPT’s therapeutic potential. However, BCO is complex and highly computer resource-intensive. Some algorithms for BCO have been developed for intensity-modulated photon therapy (IMRT). They are rarely used clinically mainly because the large number of beams typically employed in IMRT renders BCO essentially unnecessary. Moreover, in the newer form of IMRT, volumetric modulated arc therapy, there are no individual static beams. BCO is of greater importance for IMPT because it typically employs a very small number of beams (2-4) and, when the number of beams is small, BCO is critical for improving plan quality. However, the unique properties and requirements of protons, particularly in IMPT, make BCO challenging. Protons are more sensitive than photons to anatomic changes, exhibit variable relative biological effectiveness along their paths, and, as recently discovered, may spare the immune system. Such factors must be considered in IMPT BCO, though doing so would make BCO more resource intensive and make it more challenging to extend BCO algorithms developed for IMRT to IMPT. A limited amount of research in IMPT BCO has been conducted; however, considerable additional work is needed for its further development to make it truly effective and computationally practical. This article aims to provide a review of existing BCO algorithms, most of which were developed for IMRT, and addresses important requirements specific to BCO for IMPT optimization that necessitate the modification of existing approaches or the development of new effective and efficient ones.

National Effort to Re-Establish Heavy Ion Cancer Therapy in the United States

In this review, we attempt to make a case for the establishment of a limited number of heavy ion cancer research and treatment facilities in the United States. Based on the basic physics and biology research, conducted largely in Japan and Germany, and early phase clinical trials involving a relatively small number of patients, we believe that heavy ions have a considerably greater potential to enhance the therapeutic ratio for many cancer types compared to conventional X-ray and proton radiotherapy. Moreover, with ongoing technological developments and with research in physical, biological, immunological, and clinical aspects, it is quite plausible that cost effectiveness of radiotherapy with heavier ions can be substantially improved.

Proton Therapy in the Management of Luminal Gastrointestinal Cancers: Esophagus, Stomach, and Anorectum

Simple Summary

Radiation treatment plays a major role in the management of luminal gastrointestinal cancers, mainly esophageal and anorectal cancers. There is a growing interest in the application of protons for gastrointestinal cancers, mainly owing to its dosimetric characteristics in decreasing dose to nearby organs at risk. We present here an up-to-date comprehensive review of the dosimetric and clinical literature on the use of proton therapy in the management of luminal gastrointestinal cancers.

Abstract

While the role of proton therapy in gastric cancer is marginal, its role in esophageal and anorectal cancers is expanding. In esophageal cancer, protons are superior in sparing the organs at risk, as shown by multiple dosimetric studies. Literature is conflicting regarding clinical significance, but the preponderance of evidence suggests that protons yield similar or improved oncologic outcomes to photons at a decreased toxicity cost. Similarly, protons have improved sparing of the organs at risk in anorectal cancers, but clinical data is much more limited to date, and toxicity benefits have not yet been shown clinically. Large, randomized trials are currently underway for both disease sites.

Association of neutrophil-to-lymphocyte ratio, radiotherapy fractionation/technique, and risk of development of distant metastasis among patients with locally advanced rectal cancer

BACKGROUND

We investigated the prognostic impact of the neutrophil-to-lymphocyte ratio (NLR) in patients with locally advanced rectal cancer (LARC) and whether modifiable factors in radiotherapy (RT) influenced the NLR.

METHODS

Data of 1386 patients who were treated with neoadjuvant RT and concurrent or sequential chemotherapy for LARC between 2006 and 2019 were evaluated. Most patients (97.8%) were treated with long-course RT (LCRT; 50-50.4 Gy in 25-28 fractions) using three-dimensional conformal radiotherapy (3D-CRT) (n = 851) or helical tomotherapy (n = 504), and 30 patients underwent short-course RT (SCRT; 25 Gy in 5 fractions, followed by XELOX administration for 6 weeks). Absolute neutrophil and lymphocyte counts were obtained at initial diagnosis, before and during the preoperative RT course, and after preoperative concurrent chemoradiotherapy. The primary endpoint was distant metastasis-free survival (DMFS).

RESULTS

The median follow-up time was 61.3 (4.1-173.7) months; the 5-year DMFS was 80.1% and was significantly associated with the NLR after RT but not before. A post-RT NLR ≥ 4 independently correlated with worse DMFS (hazard ratio, 1.42; 95% confidence interval, 1.12-1.80), along with higher ypT and ypN stages. Post-RT NLR (≥ 4) more frequently increased following LCRT (vs. SCRT, odds ratio [OR] 2.77, p = 0.012) or helical tomotherapy (vs. 3D-CRT, OR 1.29, p < 0.001).

CONCLUSIONS

Increased NLR after neoadjuvant RT is associated with increased distant metastasis risk and poor survival outcome in patients with LARC. Moreover, high NLR following RT is directly related to RT fractionation, delivery modality, and tumor characteristics. These results are hypothesis-generating only, and confirmatory studies are required.

A Comparative Analysis of Photon versus Proton Beam Therapy in Neoadjuvant Concurrent Chemoradiotherapy for Intrathoracic Squamous Cell Carcinoma of the Esophagus at a Single Institute

BACKGROUND

Proton beam therapy (PBT), as a neoadjuvant chemoradiotherapy (nCRT) modality, is expected to result in better outcomes than photon-based radiotherapy (RT) for esophageal cancer, particularly adenocarcinoma. This study reports the results of nCRT for locally advanced esophageal squamous cell carcinoma (ESCC) using both modalities.

METHODS

We retrospectively reviewed the records of patients who underwent nCRT for ESCC between 2001 and 2020. A median of 41.4 Gy or cobalt gray equivalents of radiation was delivered using either photons or protons, with concurrent chemotherapy. Dosimetric and clinical parameters were compared between the two groups.

RESULTS

Of the 31 patients, the lungs and heart of the proton group (n = 15) were exposed to significantly less radiation compared to the photon group (n = 16). No significant differences in short-term postoperative outcomes or lymphocyte count were observed between the groups, and there were no significant differences between the photon and proton groups in 2-year overall survival (67.8% vs. 68.6%, p = 0.867) or 2-year disease-free survival (33.3% vs. 34.5%, p = 0.749), with a median follow-up of 17 months.

CONCLUSIONS

PBT provided a significant dosimetric benefit over photon-based RT during nCRT for ESCC; however, it did not improve clinical outcomes.

Lymphocyte depletion rate as a biomarker of radiation dose to circulating lymphocytes during fractionated partial-body radiotherapy

Purpose

Radiation causes exponential depletion of circulating lymphocyte populations; in turn, radiation-induced lymphopenia is associated with worse survival for many solid tumors, possibly owing to attenuated antitumor immune responses. Identifying reliable and reproducible methods of calculating the radiation dose to circulating immune cells may facilitate development of techniques to reduce the risk and severity of radiation-induced toxic effects to circulating lymphocytes.

Methods and Materials

Patient-specific lymphocyte loss rates were derived from a clinical data set including 684 adult patients with solid tumors. Multivariable linear regression was used to model the relationship between the lymphocyte loss rate and physical parameters of the radiation plan that determine circulating blood dose.

Results

During partial-body radiation, lymphocyte loss rates are determined by physical parameters of the radiation plan that reflect radiation exposure to circulating cells, including target volume size, dose per fraction squared, and anatomic site treated. Differences in observed versus predicted lymphocyte loss rates may be partly explained by variations in concurrent chemotherapy regimens.

Conclusions

We describe a novel method of using patient-specific lymphocyte loss kinetics to approximate the effective radiation dose to circulating lymphocytes during focal fractionated photon radiation therapy. Clinical applications of these findings include the early identification of patients at particularly high risk of severe radiation-induced lymphopenia based on physical parameters of the radiation therapy plan.

A hybrid deep learning model for forecasting lymphocyte depletion during radiation therapy

PURPOSE

Recent studies have shown that severe depletion of the absolute lymphocyte count (ALC) induced by radiation therapy (RT) has been associated with poor overall survival of patients with many solid tumors. In this paper, we aimed to predict radiation-induced lymphocyte depletion in esophageal cancer patients during the course of RT based on patient characteristics and dosimetric features.

METHODS

We proposed a hybrid deep learning model in a stacked structure to predict a trend toward ALC depletion based on the clinical information before or at the early stages of RT treatment. The proposed model consisted of four channels, one channel based on long short-term memory (LSTM) network and three channels based on neural networks, to process four categories of features followed by a dense layer to integrate the outputs of four channels and predict the weekly ALC values. Moreover, a discriminative kernel was developed to extract temporal features and assign different weights to each part of the input sequence which enabled the model to focus on the most relevant parts. The proposed model was trained and tested on a dataset of 860 esophageal cancer patients who received concurrent chemoradiotherapy.

RESULTS

The performance of the proposed model was evaluated based on several important prediction metrics and compared to other commonly used prediction models. The results showed that the proposed model outperformed off-the-shelf prediction methods with at least a 30% reduction in the mean squared error (MSE) of weekly ALC predictions based on pretreatment data.Moreover, using an extended model based on augmented first-week treatment data reduced the MSE of predictions by 70% compared to the model based on the pretreatment data.

CONCLUSIONS

In conclusion, our model performed well in predicting radiation-induced lymphocyte depletion for RT treatment planning. The ability to predict ALC will enable physicians to evaluate individual RT treatment plans for lymphopenia risk and to identify patients at high risk who would benefit from modified treatment approaches. This article is protected by copyright. All rights reserved.

A dynamic blood flow model to compute absorbed dose to circulating blood and lymphocytes in liver external beam radiotherapy

We have developed a novel 4D dynamic liver blood flow model, capable of accurate dose estimation to circulating blood cells during liver-directed external beam radiotherapy, accounting for blood recirculation and radiation delivery time structure. Adult male and adult female liver computational phantoms with detailed vascular trees were developed to include the hepatic arterial, hepatic portal venous, and hepatic venous trees. A discrete time Markov Chain approach was applied to determine the spatiotemporal distribution of 10⁵blood particles (BP) in the human body based on reference values for cardiac output and organ blood volumes. For BPs entering the liver, an explicit Monte Carlo simulation was implemented to track their propagation along ∼2000 distinct vascular pathways through the liver. The model tracks accumulated absorbed dose from time-dependent radiation fields with a 0.1 s time resolution. The computational model was then evaluated for 3 male and 3 female patients receiving photon (VMAT and IMRT) and proton (passive SOBP and active PBS) treatments. The dosimetric impact of treatment modality, delivery time, and fractionation on circulating blood cells was investigated and quantified using the mean dose (μdose,b),V_>0Gy,V_>0.125Gy,andD_2%. Average reductions inμdose,b,V_>0Gy,V_>0.125GyandD_2%of 45%, 6%, 53%, 19% respectively, were observed for proton treatments as compared to photon treatments. Our simulation also showed thatV_>0Gy,V_>0.125Gy, andD_2%were highly sensitive to the beam-on time. BothV_>0GyandV_>0.125Gyincreased with beam-on time, whereasD_2%decreased with increasing beam-on time, demonstrating the tradeoff between low dose to a large fraction of blood cells and high dose to a small fraction of blood cells. Consequently, proton treatments are not necessarily advantageous in terms of dose to the blood simply based on integral dose considerations. Instead, both integral dose and beam-on time can substantially impact relevant dosimetric indices.

Association between unintentional splenic radiation and lymphopenia and high neutrophil/lymphocyte ratio after radiotherapy in patients with esophageal cancer

Background

Unintentional irradiation of the spleen may reduce absolute lymphocyte count (ALC), which can affect tumor immunity. Therefore, in the present study, we evaluated spleen dose-volume parameters associated with ALC and neutrophil/lymphocyte ratio (NLR) in patients with esophageal cancer.

Methods

This retrospective study evaluated patients who were diagnosed with stage I–IV esophageal cancer and who received radiotherapy at Nihon University Itabashi Hospital between January 2015 and March 2020. Spleen V5, V10, V20, and V30 and mean spleen dose, which are dose-volume histogram parameters correlated with ALC and NLR, were analyzed.

Results

In total, 89 esophageal cancer patients with a median age of 72 years (range, 51–92 years) were included in this research. Results showed that spleen V5, V10, and V20 and mean splenic dose were significantly correlated with a low ALC. Meanwhile, a significant association was observed between spleen V5 and V10 and a high NLR (P<0.05). In the linear regression analysis, spleen V5 and V10 were remarkably associated with a low ALC (P=0.006 and 0.008). Further, a correlation was noted between spleen V5 and a high NLR (P=0.019). Spleen V5 and V10 were remarkably associated with greater than grade 3 lymphopenia (P=0.024 and P=0.031).

Conclusions

A correlation was observed between the irradiated volume of the spleen and ALC and NLR in patients with esophageal cancer. Furthermore, the spleen should be regarded as a high-risk organ, and the use of techniques in reducing spleen V5, V10 for the preservation of tumor immunity may be beneficial.

The impact of radiation induced lymphopenia in the prognosis of head and neck cancer: A systematic review and meta-analysis

OBJECTIVES

Radiotherapy is a key part of head and neck cancer (HNC) treatment. Radiation induced lymphopenia (RIL) is a severe complication of radiotherapy. The aim of this study was to evaluate the prognostic role of RIL in HNC patients.

METHOD

We conducted a PRISMA guideline based systemic review and meta-analysis. The studies were identified on the PubMed, Embase and Cochrane Library from 2007 to October 2021. The quality of each study was assessed by Newcastle-Ottawa Quality Assessment Form for Cohort Studies (NOS).

RESULTS

There were 8 studies with 2,733 samples finally included in current study. The meta-analysis showed that the odds ratio of developing grade 3-4 RIL was 13.49 (95%CI = 7.03-25.89, I² = 94%). The incidence rate of grade 3-4 RIL ranged from 73%-88%. Multivariate meta-analysis found that the RIL significantly decreased the overall survival (HR = 2.94, 95%CI = 1.83-4.74, I² = 0%) and distant metastasis free survival of HNC (HR = 3.79, 95%CI = 2.06-6.97, I² = 0%). After sensitivity analysis and excluding a potential study that caused heterogeneity, the new pooled multivariate meta-analysis showed RIL was a risk factor to the progression free survival of HNC patients (HR = 3.16, 95%CI = 1.77-5.63, I² = 0%).

CONCLUSION

This is the first meta-analysis which showed severe RIL decreased the overall survival and promoted the progression of HNC patients. Future large-scale prospective studies are required to evaluate the association between severe RIL and the prognosis of HNC.

Peripheral Lymphocyte Counts and Lymphocyte-Related Inflammation Indicators During Radiotherapy for Pelvic Malignancies: Temporal Characterization and Dosimetric Predictors

Purpose: To identify the dosimetric predictors of lymphocytopenia and retrospectively analyze the changing trend of peripheral lymphocyte counts and lymphocyte-related inflammatory indicators in patients with simple pelvic radiotherapy. Methods and Materials: We retrospectively reviewed the clinical data of 188 patients with pelvic malignancies undergoing pelvic radiotherapy. The absolute count of neutrophils, lymphocytes, monocytes, and platelets at each time point was collected, and lymphocyte-related inflammation indicators were obtained, including neutrophil-to-lymphocyte ratio (NLR), lymphocyte-to-monocyte ratio (LMR), platelet-to-lymphocyte ratio (PLR), and the systemic immune-inflammation index (SII). The total pelvic bone (TPB) and the body within the 5 Gy coverage were retrospectively delineated for each patient. Dose-volume histograms corresponding to the delivered volumetric arc therapy plan were used to assess the dose volumes received by the TPB and body. A paired-samples t-test or Wilcoxon signed-rank test for matched pairs was applied for pairwise comparisons. We also established a stepwise multiple linear regression model for the peripheral lymphocyte count (PLC) value at the end of radiotherapy. Results: The PLC and lymphocyte-related inflammatory indicators changed significantly after the start of radiotherapy and persisted for 3-6 months after radiotherapy. The nadirs of PLC occurred at RT-End, and the PLC was still significantly lower than the baseline value at RT-3 months and RT-6 months. NLR, PLR, and SII at RT-End are about 3.5 times the value at RT-Baseline, while LMR is one-fourth of the basal value. In a further multiple stepwise linear regression analysis, the basal PLC (β = 0.156, p ≤ .001), gender (β = 0.096, p = .005), and TPB-V5 (β = −0.016, p ≤ .001) turned out to be the predictor of the absolute value of lymphocytes at the end of radiotherapy. Conclusions: The impact of pelvic radiotherapy on PLC and lymphocyte-related inflammatory indicators is considerable and long-lasting. Minimizing pelvic bone radiation exposure dose (5 Gy) may help to avoid severe cases of lymphocytopenia.

Executive Summary of Clinical and Technical Guidelines for Esophageal Cancer Proton Beam Therapy From the Particle Therapy Co-Operative Group Thoracic and Gastrointestinal Subcommittees

Radiation therapy (RT) is an integral component of potentially curative management of esophageal cancer (EC). However, RT can cause significant acute and late morbidity due to excess radiation exposure to nearby critical organs, especially the heart and lungs. Sparing these organs from both low and high radiation dose has been demonstrated to achieve clinically meaningful reductions in toxicity and may improve long-term survival. Accruing dosimetry and clinical evidence support the consideration of proton beam therapy (PBT) for the management of EC. There are critical treatment planning and delivery uncertainties that should be considered when treating EC with PBT, especially as there may be substantial motion-related interplay effects. The Particle Therapy Co-operative Group Thoracic and Gastrointestinal Subcommittees jointly developed guidelines regarding patient selection, treatment planning, clinical trials, and future directions of PBT for EC.

Radiation-Induced Lymphopenia Risks of Photon Versus Proton Therapy for Esophageal Cancer Patients

Purpose

To assess possible differences in radiation-induced lymphocyte depletion for esophageal cancer patients being treated with the following 3 treatment modalities: intensity-modulated radiation therapy (IMRT), passive scattering proton therapy (PSPT), and intensity-modulated proton therapy (IMPT).

Methods and Materials

We used 2 prediction models to estimate lymphocyte depletion based on dose distributions. Model I used a piecewise linear relationship between lymphocyte survival and voxel-by-voxel dose. Model II assumes that lymphocytes deplete exponentially as a function of total delivered dose. The models can be fitted using the weekly absolute lymphocyte counts measurements collected throughout treatment. We randomly selected 45 esophageal cancer patients treated with IMRT, PSPT, or IMPT at our institution (15 per modality) to demonstrate the fitness of the 2 models. A different group of 10 esophageal cancer patients who had received PSPT were included in this study of in silico simulations of multiple modalities. One IMRT and one IMPT plan were created, using our standards of practice for each modality, as competing plans to the existing PSPT plan for each patient. We fitted the models by PSPT plans used in treatment and predicted absolute lymphocyte counts for IMRT and IMPT plans.

Results

Model validation on each modality group of patients showed good agreement between measured and predicted absolute lymphocyte counts nadirs with mean squared errors from 0.003 to 0.023 among the modalities and models. In the simulation study of IMRT and IMPT on the 10 PSPT patients, the average predicted absolute lymphocyte count (ALC) nadirs were 0.27, 0.35, and 0.37 K/μL after IMRT, PSPT, and IMPT treatments using Model I, respectively, and 0.14, 0.22, and 0.33 K/μL using Model II.

Conclusions

Proton plans carried a lower predicted risk of lymphopenia after the treatment course than did photon plans. Moreover, IMPT plans outperformed PSPT in terms of predicted lymphocyte preservation.

[The role of proton therapy in esophageal cancer]

Because of the physical properties of proton beam radiation therapy (PT), which allows energy to be deposited at a specific depth with a rapid energy fall-off beyond that depth, PT has several theoretical advantages over photon radiation therapy for esophageal cancer (EC). Protons have the potential to reduce the dose to healthy tissue and to more safely allow treatment of tumors near critical organs, dose escalation, trimodal treatment, and re-irradiation. In recent years, larger multicenter retrospective studies have been published showing excellent survival rates, lower than expected toxicities and even better outcomes with PT than with photon radiotherapy even using IMRT or VMAT techniques. Although PT was associated with reduced toxicities, postoperative complications, and hospital stays compared to photon radiation therapy, these studies all had inherent biases in relation with patient selection for PT. These observations were recently confirmed by a randomized phase II study in locally advanced EC that showed significantly reduced toxicities with protons compared with IMRT. Currently, two randomized phase III trials (NRG-GI006 in the US and PROTECT in Europe) are being conducted to confirm whether protons could become the standard of care in locally advanced and resectable esophageal cancers.