Radiation-Associated Lymphopenia and Outcomes of Patients with Unresectable Hepatocellular Carcinoma Treated with Radiotherapy

Late-onset lymphopenia during radiation is associated with an increased risk of tumor recurrence in newly diagnosed pediatric medulloblastoma

BACKGROUND

Recent data found a correlation between lymphopenia occurring early during craniospinal radiation therapy (RT) and risk of disease recurrence in newly diagnosed childhood medulloblastoma. However, the population included patients who received chemotherapy prior to or during RT. Here, we investigate the effect of lymphopenia during RT in patients with newly diagnosed pediatric medulloblastoma who were chemotherapy-naïve.

PROCEDURE

We analyzed 79 patients with newly diagnosed medulloblastoma (ages 2-21 years) treated between 1997 and 2013 with craniospinal RT. Log-rank tests were used to determine survival differences, and Cox proportional hazards regression was used to assess associations between patient characteristics and lymphopenia with disease recurrence risk.

RESULTS

Eighty-three percent of patients (62/75) had grade ≥3 lymphopenia by RT Week 3, with 95% developing grade ≥3 lymphopenia at some point during therapy. There was no difference in incidence of lymphopenia between those who received proton beam RT (93%) versus photon (97%). Twenty-four of 79 (30%) patients developed disease recurrence at an average 27.0 months after diagnosis. There was higher risk of disease recurrence in patients with grade ≥3 lymphopenia during RT Week 4 (log-rank p = .016; Cox p = .03) and Week 5 (log-rank p = .024; Cox p = .032); after adjusting for clinical risk group, only grade ≥3 lymphopenia at Week 4 remained prognostic (Cox p = .04). No correlation was found between risk of tumor recurrence and early lymphopenia (RT Weeks 0-3) or absolute lymphocyte count (ALC) below the median at any time during RT.

CONCLUSIONS

Lymphopenia during RT Weeks 4 and 5 correlates with increased risk of tumor recurrence in pediatric patients with newly diagnosed medulloblastoma.

Acute hospitalizations after proton therapy versus intensity-modulated radiotherapy for locally advanced non-small cell lung cancer in the durvalumab era

INTRODUCTION

It was hypothesized that use of proton beam therapy (PBT) in patients with locally advanced non-small cell lung cancer treated with concurrent chemoradiation and consolidative immune checkpoint inhibition is associated with fewer unplanned hospitalizations compared with intensity-modulated radiotherapy (IMRT).

METHODS

Patients with locally advanced non-small cell lung cancer treated between October 2017 and December 2021 with concurrent chemoradiation with either IMRT or PBT ± consolidative immune checkpoint inhibition were retrospectively identified. Logistic regression was used to assess the association of radiation therapy technique with 90-day hospitalization and grade 3 (G3+) lymphopenia. Competing risk regression was used to compare G3+ pneumonitis, G3+ esophagitis, and G3+ cardiac events. Kaplan-Meier method was used for progression-free survival and overall survival. Inverse probability treatment weighting was applied to adjust for differences in PBT and IMRT groups.

RESULTS

Of 316 patients, 117 (37%) received PBT and 199 (63%) received IMRT. The PBT group was older (p < .001) and had higher Charlson Comorbidity Index scores (p = .02). The PBT group received a lower mean heart dose (p < .0001), left anterior descending artery V15 Gy (p = .001), mean lung dose (p = .008), and effective dose to immune circulating cells (p < .001). On inverse probability treatment weighting analysis, PBT was associated with fewer unplanned hospitalizations (adjusted odds ratio, 0.55; 95% CI, 0.38-0.81; p = .002) and less G3+ lymphopenia (adjusted odds ratio, 0.55; 95% CI, 0.37-0.81; p = .003). There was no difference in other G3+ toxicities, progression-free survival, or overall survival.

CONCLUSIONS

PBT is associated with fewer unplanned hospitalizations, lower effective dose to immune circulating cells and less G3+ lymphopenia compared with IMRT. Minimizing dose to lymphocytes may be warranted, but prospective data are needed.

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.

The Next Chapter in Immunotherapy and Radiation Combination Therapy: Cancer-Specific Perspectives

Immunotherapeutic agents have revolutionized cancer treatment over the past decade. However, most patients fail to respond to immunotherapy alone. A growing body of preclinical studies highlights the potential for synergy between radiation therapy and immunotherapy, but the outcomes of clinical studies have been mixed. This review summarizes the current state of immunotherapy and radiation combination therapy across cancers, highlighting existing challenges and promising areas for future investigation.

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.

Clinical and Dosimetric Results of Proton or Photon Radiation Therapy for Large (>5 cm) Hepatocellular Carcinoma: A Retrospective Analysis

PURPOSE

Our purpose was to report the clinical and dosimetric attributes of patients with large unresectable hepatocellular carcinoma (HCC) undergoing proton or photon radiation therapy.

METHODS AND MATERIALS

We retrospectively analyzed the outcomes and dosimetric indices of 159 patients with >5 cm nonmetastatic HCC who underwent definitive radiation therapy using either protons (N = 105) or photons (N = 54) between 2014 and 2018. Additional photon plans were performed in the 105 proton-treated patients using the same dose prescription criteria for intragroup dosimetric comparison.

RESULTS

After a median follow-up of 47 months, patients with biologically effective dose (BED10) ≥ 75 Gy exhibited significantly better local control (LC; 2-year: 85.6% vs 20.5%; P < .001), progression-free survival (PFS; median, 7.4 vs 3.2 months; P < .001), and overall survival (OS; median, 18.1 vs 7.3 months; P < .001) compared with those with BED10 < 75 Gy. Notably, proton-treated patients had a significantly higher BED10 (96 vs 67 Gy; P < .001) and improved LC (2-year: 88.5% vs 33.8%; P < .001), PFS (median, 7.4 vs 3.3 months; P = .001), and OS (median, 18.9 vs 8.3 months; P < .001) than those undergoing photon radiation therapy. Furthermore, patients treated with protons had significantly lower V1 of the liver (P < .001), mean upper gastrointestinal tract dose (P < .001), and mean splenic dose (P < .001), with significantly decreased incidences of radiation-induced liver disease (P = .007), grade ≥3 upper gastrointestinal bleeding (P = .001), and grade ≥3 lymphopenia (P = .003). On multivariate analysis, proton radiation therapy consistently correlated with superior LC (P < .001), PFS (P < .001), and OS (P < .001). In intragroup dosimetric comparison, photon plans demonstrated significantly higher mean liver dose (P < .001) compared with actually delivered proton treatments, and 72 (69%) of them had mean liver dose exceeding 28 Gy, which necessitated target dose de-escalation.

CONCLUSIONS

In the context of large HCC radiation therapy, a higher target BED10 was associated with improved outcomes. Notably, proton therapy has demonstrated the capability to deliver ablative doses while also being accompanied by fewer instances of severe toxicity.

Lineage-specific regulation of PD-1 expression in early-stage hepatocellular carcinoma following 90yttrium transarterial radioembolization - Implications in treatment outcomes

BACKGROUND

Hepatocellular carcinoma (HCC) remains one of the leading causes of cancer-related deaths in the world. Liver-directed therapies, including 90Yttrium (90Y) radioembolization, play an integral role in the management of HCC with excellent response rates. This has led to clinical trials of immunotherapy in combination with 90Y. Elevated PD-1 expression and lymphopenia were recently shown as risk factors for disease progression in early-stage HCC treated with liver-directed therapies. The aim of this study was to investigate PD-1 expression dynamics in bridge/downstage to transplant in HCC patients receiving first-cycle 90Y and evaluate the impact of these changes on response rates and time-to-progression (TTP).

METHODS

Patients with HCC receiving first-cycle 90Y as a bridge to liver transplantation (n = 99) were prospectively enrolled. Blood specimens were collected before 90Y and again during routine imagining follow-up to analyze PD-1 expression via flow cytometry. Complete and objective response rates (CR and ORR) were determined using mRECIST.

RESULTS

In 84/88 patients with available follow-up imaging, 83% had a localized ORR with 63% having localized CR. For overall response, 71% and 54% experienced ORR and CR, respectively. Post-90Y PD-1 upregulation in CD8 + associated with HCC progression and decreased TTP. Treatment with 90Y was associated with an anticipated significant post-treatment drop in lymphocytes (P < 0.001) that was independent of PD-1 expression for either CD4+ or CD8+ T cells (P = 0.751 and P = 0.375) and not associated with TTP risk. The change in lymphocytes was not correlated with PD-1 expression following treatment nor TTP.

CONCLUSIONS

Elevated PD-1 expression on peripheral T cells is associated with increased risk of HCC progression and shorter time to progression in bridging/downstaging to transplant HCC patients undergoing first-cycle 90Y. Treatment-induced lymphopenia was not associated with treatment response, or increased progression risk, suggesting this anticipated adverse event does not impact short-term HCC outcomes.

Neoadjuvant chemoradiotherapy induced lymphopenia in gastric cancer and associations with spleen dosimetry and survival outcomes

Background

Few studies concentrate on spleen dosimetry of radiotherapy for gastric cancer (GC). Although there is no consensus on the spleen dose-volume threshold for lymphopenia, several studies indicated that the higher the spleen dose, the higher the risk of lymphopenia. This study aimed to identify the appropriate spleen dosimetric parameters for predicting grade 4 + lymphopenia in patients with locally advanced GC.

Material and methods

A total of 295 patients treated with nCRT and nChT from June 2013 to December 2021 at two major centers were included, of whom 220 were assigned to the training cohort and 75 to the external validation cohort.

Results

Grade 4 + lymphopenia was more common in the nCRT than in the nChT group (49.5% vs. 0, P < 0.001 in the training cohort; 25.0% vs. 0, P = 0.001 in the external validation cohort). Age ≥ 60 years (P = 0.006), lower pretreatment absolute lymphocyte count (P = 0.001), higher spleen volume (SPV) (P = 0.001), and higher V₂₀ (P = 0.003) were significant risk factors of grade 4 + lymphopenia for patients treated with nCRT. Patients with grade 4 + lymphopenia had significantly worse PFS (P = 0.043) and showed a negative correlation trend with OS (P = 0.07). Limiting V₂₀ to < 84.5% could decrease the incidence of grade 4 + lymphopenia by 35.7%. The predictive effectiveness of the multivariable model in the training and external validation cohorts was 0.880 and 0.737, respectively.

Conclusion

Grade 4 + lymphopenia during nCRT was more common than nChT, and was associated with a worse PFS in GC patients. Constraining the spleen V₂₀ to < 84.5% may indirectly improve outcomes through lymphocyte preservation.

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.

Combination of Preoperative Circulating Tumor Cell Count and Neutrophil-Lymphocyte Ratio for Prognostic Prediction in Hepatocellular Carcinoma Patients after Curative Hepatectomy

Background

Both the preoperative neutrophil-lymphocyte ratio (NLR) and circulating tumor cell count (CTC) are associated with poor prognosis in hepatocellular carcinoma (HCC). The purpose of this study was to explore the prognostic value of these two indices (CTC-NLR) in HCC.

Methods

We retrospectively collected demographic and clinical data, including NLR and CTC, from 97 patients with HCC who underwent curative hepatectomy at our institution from March 2014 to May 2017. X-Tile software was used to confirm the optimal cut-off value of NLR and CTC for predicting overall survival (OS) in this study. OS were also analyzed using Kaplan-Meier and Cox regression methods. Based on preoperative CTC and NLR, patients were divided into three groups: CTC-NLR (0), CTC-NLR (1), and CTC-NLR (2). Relationships of CTC-NLR with clinicopathological factors and survival were evaluated.

Results

Preoperatively, CTC positively correlated with NLR. Patients with NLR and CTC higher than the cut-offs had shorter OS than patients with low NLR and CTC. Kaplan-Meier analysis, and log-rank tests revealed significantly lower OS among patients with CTC-NLR scores of 0, 1, and 2. Uni- and multivariate analyses showed that CTC-NLR (hazard ratio 2.050, P = 0.005), CTC (hazard ratio 2.285, P = 0.032), and NLR (hazard ratio 1.902, P = 0.048) were independent predictor of OS. A time-dependent ROC curve indicated that the prognostic efficacy of the CTC-NLR at 1 year (0.714) was better than that of NLR (0.687) and CTC (0.590); the prognostic efficacy of the CTC-NLR at 2 years (0.746) was better than that of NLR (0.711) and CTC (0.601); the prognostic efficacy of the CTC-NLR at 3 years (0.742) was better than that of NLR (0.694) and CTC (0.629).

Conclusions

HCC patients with higher NLR and CTC tend to show shorter OS. Preoperative CTC-NLR may be associated with poor survival and might be a reliable prognostic predictor in HCC after curative hepatectomy.

Proton Therapy in the Management of Pancreatic Cancer

Simple Summary

Radiation treatment plays a pivotal a role in the management of pancreatic cancer, mainly in the neoadjuvant setting for borderline resectable tumors and in the definitive setting for unresectable localized disease. Most of the studies on pancreatic cancer use photon-based radiation therapy modalities. However, there is a growing interest in the application of protons therapy for gastrointestinal cancers. This review summarizes the literature on the use of proton therapy in the management of pancreatic cancer.

Abstract

Radiation therapy plays a central role in the treatment of pancreatic cancer. While generally shown to be feasible, proton irradiation, particularly when an ablative dose is planned, remains a challenge, especially due to tumor motion and the proximity to organs at risk, like the stomach, duodenum, and bowel. Clinically, standard doses of proton radiation treatment have not been shown to be statistically different from photon radiation treatment in terms of oncologic outcomes and toxicity rates as per non-randomized comparative studies. Fractionation schedules and concurrent chemotherapy combinations are yet to be optimized for proton therapy and are the subject of ongoing trials.

Outcomes and Toxicities of Modern Combined Modality Therapy with Atezolizumab Plus Bevacizumab and Radiation Therapy for Hepatocellular Carcinoma

Atezolizumab plus bevacizumab has become frontline therapy for unresectable HCC. The compatibility of atezolizumab/bevacizumab with liver-directed RT has not been reported. Methods: HCC patients treated with liver-directed RT and atezolizumab/bevacizumab between 1/2020−11/2021 were included. Toxicity and outcomes were retrospectively recorded. For ALCs, we matched the analysis to a previously cohort of RT-treated HCC patients who did not receive atezolizumab/bevacizumab. Survival and time-to-liver-failure were analyzed using Kaplan−Meier. Results: Of 21 patients, with a median follow-up of 9.5 months, the median OS was 16.1 months. Post-RT, all patients had reduced tumors or treatment response. There were no ≥Grade 3 RT-related toxicities. Autoimmune complications occurred in two patients (9.5%), and GI bleeding in three patients (14.3%). Liver function remained stable post-RT. There was a marked decrease in ALCs immediately post-RT (post-RT/pre-RT ratio 47.3%, p < 0.0001), restored by 1 month to pre-treatment baseline (1-month post-RT/pre-RT ratio 95.1%, n.s.). Compared to HCC patients treated with RT alone, post-RT ALC recovery was faster with atezolizumab/bevacizumab (p = 0.009). Conclusion: In this first reported experience of RT with modern systemic therapy for HCC, combination therapy is safe and well-tolerated. As a favorable prognosticator, there appears to be faster recovery of ALC among patients who received RT with atezolizumab/bevacizumab.

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.

Leveraging Blood-Based Diagnostics to Predict Tumor Biology and Extend the Application and Personalization of Radiotherapy in Liver Cancers

While the incidence of primary liver cancers has been increasing worldwide over the last few decades, the mortality has remained consistently high. Most patients present with underlying liver disease and have limited treatment options. In recent years, radiotherapy has emerged as a promising approach for some patients; however, the risk of radiation induced liver disease (RILD) remains a limiting factor for some patients. Thus, the discovery and validation of biomarkers to measure treatment response and toxicity is critical to make progress in personalizing radiotherapy for liver cancers. While tissue biomarkers are optimal, hepatocellular carcinoma (HCC) is typically diagnosed radiographically, making tumor tissue not readily available. Alternatively, blood-based diagnostics may be a more practical option as blood draws are minimally invasive, widely availability and may be performed serially during treatment. Possible blood-based diagnostics include indocyanine green test, plasma or serum levels of HGF or cytokines, circulating blood cells and genomic biomarkers. The albumin–bilirubin (ALBI) score incorporates albumin and bilirubin to subdivide patients with well-compensated underlying liver dysfunction (Child–Pugh score A) into two distinct groups. This review provides an overview of the current knowledge on circulating biomarkers and blood-based scores in patients with malignant liver disease undergoing radiotherapy and outlines potential future directions.

Predictive Modeling of Survival and Toxicity in Patients With Hepatocellular Carcinoma After Radiotherapy

PURPOSE

To stratify patients and aid clinical decision making, we developed machine learning models to predict treatment failure and radiation-induced toxicities after radiotherapy (RT) in patients with hepatocellular carcinoma across institutions.

MATERIALS AND METHODS

The models were developed using linear and nonlinear algorithms, predicting survival, nonlocal failure, radiation-induced liver disease, and lymphopenia from baseline patient and treatment parameters. The models were trained on 207 patients from Massachusetts General Hospital. Performance was quantified using Harrell's c-index, area under the curve (AUC), and accuracy in high-risk populations. Models' structures were optimized in a nested cross-validation approach to prevent overfitting. A study analysis plan was registered before external validation using 143 patients from MD Anderson Cancer Center. Clinical utility was assessed using net-benefit analysis.

RESULTS

The survival model stratified high-risk versus low-risk patients well in the external validation cohort (c-index = 0.75), better than existing risk scores. Predictions of 1-year survival and nonlocal failure were excellent (external AUC = 0.74 and 0.80, respectively), especially in the high-risk group (accuracy > 90%). Cause-of-death analysis showed differential modes of treatment failure in these cohorts and indicated that these models could be used to stratify RT patients for liver-sparing treatment regimen or combination approaches with systemic agents. Predictions of liver disease and lymphopenia were good but less robust (external AUC = 0.68 and 0.7, respectively), suggesting the need for more comprehensive consideration of dosimetry and better predictive biomarkers. The liver disease model showed excellent accuracy in the high-risk group (92%) and revealed possible interactions of platelet count with initial liver function.

CONCLUSION

Machine learning approaches can provide reliable outcome predictions in patients with hepatocellular carcinoma after RT in diverse cohorts across institutions. The excellent performance, particularly in high-risk patients, suggests novel strategies for patient stratification and treatment selection.

Particle radiotherapy and molecular therapies: mechanisms and strategies towards clinical applications

Immunotherapy and targeted therapy are now commonly used in clinical trials in combination with radiotherapy for several cancers. While results are promising and encouraging, the molecular mechanisms of the interaction between the drugs and radiation remain largely unknown. This is especially important when switching from conventional photon therapy to particle therapy using protons or heavier ions. Different dose deposition patterns and molecular radiobiology can in fact modify the interaction with drugs and their effectiveness. We will show here that whilst the main molecular players are the same after low and high linear energy transfer radiation exposure, significant differences are observed in post-exposure signalling pathways that may lead to different effects of the drugs. We will also emphasise that the problem of the timing between drug administration and radiation and the fractionation regime are critical issues that need to be addressed urgently to achieve optimal results in combined treatments with particle therapy.

Mechanisms and Review of Clinical Evidence of Variations in Relative Biological Effectiveness in Proton Therapy

Proton therapy is increasingly being used as a radiation therapy modality. There is uncertainty about the biological effectiveness of protons relative to photon therapies as it depends on several physical and biological parameters. Radiation oncology currently applies a constant and generic value for the relative biological effectiveness (RBE) of 1.1, which was chosen conservatively to ensure tumor coverage. The use of a constant value has been challenged particularly when considering normal tissue constraints. Potential variations in RBE have been assessed in several published reviews but have mostly focused on data from clonogenic cell survival experiments with unclear relevance for clinical proton therapy. The goal of this review is to put in vitro findings in relation to clinical observations. Relevant in vivo pathways determining RBE for tumors and normal tissues are outlined, including not only damage to tumor cells and parenchyma but also vascular damage and immune response. Furthermore, the current clinical evidence of varying RBE is reviewed. The assessment can serve as guidance for treatment planning, personalized dose prescriptions, and outcome analysis.

Prognostic impact of lymphopenia and neutrophil-lymphocyte ratio for patients with anal squamous cell carcinoma

Background

Outcomes after definitive chemoradiation for squamous cell carcinoma are generally favorable. However, biomarkers to further yield prognostic information are desired. Treatment-related lymphopenia as well as an elevated baseline neutrophil-lymphocyte ratio have been associated with worse survival in several cancer types. We evaluated absolute lymphocyte count and neutrophil-lymphocyte ratio at baseline and at treatment-related nadir in patients with anal cancer for associations with oncologic endpoints.

Methods

We conducted a retrospective analysis of 428 consecutive patients with non-metastatic anal cancer treated with definitive, intensity-modulated radiation therapy-based chemoradiation. We analyzed absolute neutrophil and lymphocyte counts at several timepoints: pretreatment, weekly during treatment, and in the six weeks following treatment completion. Neutrophil-lymphocyte ratio was calculated at baseline and treatment-related nadir. We estimated oncologic endpoints using life tables and compared them using the log-rank test. We conducted univariate and multivariable time-to-event analyses using Cox proportional hazards.

Results

Median absolute lymphocyte count at baseline and nadir were 1.80 [interquartile range (IQR), 1.45-2.32] k/µL and 0.26 (IQR, 0.18-0.36) k/µL, respectively, and 31% developed treatment-related grade 4 lymphopenia. Median neutrophil-lymphocyte ratio at baseline and nadir were 2.34 (IQR, 1.68-3.30) and 8.80 (IQR, 5.86-12.68), respectively. Estimates of overall survival, local failure-free survival, distant metastasis-free survival (DMFS), and freedom from colostomy at 5 years were 87%, 86%, 82%, and 88%, respectively. Baseline and nadir absolute lymphocyte count were not associated with selected outcomes on univariate analysis. On multivariable analysis, factors independently associated with death included T3-T4 disease, HIV-positive status, treatment break, and baseline neutrophil-lymphocyte ratio >3. Baseline neutrophil-lymphocyte ratio showed a trend toward association with distant progression or death (P=0.07). The 5-year overall survival estimates for patients with baseline neutrophil-lymphocyte ratios ≤3 and >3 were 92.3% and 80.6%, respectively.

Conclusions

Lymphopenia during and after chemoradiation for anal cancer is common but does not appear to be associated with worse survival, recurrence, or metastases. However, elevated baseline neutrophil-lymphocyte ratio was independently associated with overall survival, local recurrence-free survival, and DMFS. Further studies are needed to determine the clinical utility of baseline neutrophil-lymphocyte ratio to guide treatment and follow-up.

HEDOS-a computational tool to assess radiation dose to circulating blood cells during external beam radiotherapy based on whole-body blood flow simulations

We have developed a time-dependent computational framework, hematological dose (HEDOS), to estimate dose to circulating blood cells from radiation therapy treatment fields for any treatment site. Two independent dynamic models were implemented in HEDOS: one describing the spatiotemporal distribution of blood particles (BPs) in organs and the second describing the time-dependent radiation field delivery. A whole-body blood flow network based on blood volumes and flow rates from ICRP Publication 89 was simulated to produce the spatiotemporal distribution of BPs in organs across the entire body using a discrete-time Markov process. Constant or time-varying transition probabilities were applied and their impact on transition time was investigated. The impact of treatment time and anatomical site were investigated using imaging data and dose distributions from a liver cancer and a brain cancer patient. The simulations revealed different dose levels to the circulating blood for brain irradiation compared to liver irradiation even for similar field sizes due to the different blood flow properties of the two organs. The volume of blood receiving any dose (V>0 Gy) after a single radiation fraction increases from 1.2% for a 1 s delivery time to 20.9% for 120 s delivery time for the brain cancer treatment, and from 10% (1 s) to 48.7% (120 s) for a liver cancer treatment. Other measures of the low-dose bath to the circulating blood such as the dose to small volumes of blood (D2%) decreases with longer delivery time. Furthermore, we demonstrate that the blood dose-volume histogram is highly sensitive to changes in the treatment time, indicating that dynamic modeling of blood flow and radiation fields is necessary to evaluate dose to circulating blood cells for the assessment of radiation-induced lymphopenia. HEDOS is publicly available and allows for the estimation of patient-specific dose to circulating blood cells based on organ DVHs, thus enabling the study of the impact of different treatment plans, dose rates, and fractionation schemes.