Evaluating equity of access and predictors of minimally invasive hysterectomy for endometrial and cervical cancer from 2000 to 2017 in Ontario, Canada: A population-based cohort study.

INTRODUCTION: We sought to assess the uptake of minimally invasive hysterectomy among patients with endometrial and cervical cancer in Ontario, Canada, and assess the equity of access to minimally invasive surgery (MIS) by evaluating associations with patient, disease, institutional, and provider factors. METHODS: This is a retrospective population-based cohort study of hysterectomy for endometrial and cervical cancer in Ontario (2000-2017). Surgical approach, clinicopathologic, sociodemographic, institutional, and provider factors were identified through administrative databases. Fisher's exact, χ2 , Wilcoxon rank sum, logistic regression, and Cox proportional hazards modeling were used to explore factors associated with MIS. RESULTS: A total of 27 652 patients were included. In total, 6199/24 264 (26%) endometrial and 842/3388 (25%) cervical cancer patients received MIS. The proportion of MIS to open surgeries increased from <0.1% in 2000 to over 55% in 2017 (odds ratio [OR] = 1.31, confidence interval [CI] = 1.28-1.34). Low-income quintile, rurality, low hospital volume, nonacademic hospital, nongynecologic oncology surgeon, and earlier year of surgeon graduation were associated with reduced odds of MIS (OR < 1). CONCLUSIONS: The uptake of MIS hysterectomy increased steadily over the time period. Receipt of MIS is dependent upon multiple social determinants, provider variables, and systems factors. These disparities raise concern for health equity in Ontario and have significant implications for health systems planning and resource allocation.

Disease control outcomes of stereotactic body radiation therapy or moderate hypo-fractionation for prostate cancer: Real-world experience at two Canadian centers.

BACKGROUND: Advantages of using stereotactic body radiation therapy to treat prostate cancer include short treatment times, decreased costs, and limited toxicity. Randomized trial outcomes comparing 5-fraction stereotactic body radiation therapy to conventionally fractionated radiotherapy or hypo-fractionated radiation therapy are pending. OBJECTIVE: We report the 10-year experience with 5-fraction stereotactic body radiation therapy and hypo-fractionated radiation therapy at two Canadian centers. MATERIAL AND METHODS: Patients with low- or intermediate-risk prostate cancer treated with stereotactic body radiation therapy alone (35-40 Gy in 5 fractions) or hypo-fractionated radiation therapy alone (60-62 Gy in 20 fractions) in the period of July 2010 and June 2020. The biochemical relapse-free survival, PSA nadir, interval time to PSA nadir, time to biochemical recurrence (2 ng/ml above PSA nadir) and overall survival were reviewed. Outcomes between treatment groups were compared after propensity-matching by patient baseline characteristics. Kaplan-Meier curves were used to assess biochemical relapse-free survival and overall survival. RESULTS: We identified 205 and 513 patients with low or intermediate-risk prostate cancer who were treated with stereotactic body radiation therapy or hypo-fractionation, respectively. Intermediate-risk category composed 81% and 95% of the stereotactic body radiation therapy and hypo-fractionated radiation therapy cohorts, respectively. After a median follow up of 58.6 months for the stereotactic body radiation therapy cohort and 45.0 months for the hypo-fractionated cohort, biochemical relapse-free survival and overall survival were not significantly different between treatment groups. The 5-year biochemical relapse-free survival rates were 92.1% and 93.6% and overall survival rates were 96.4% and 95.0% for the stereotactic body radiation therapy and hypo-fractionated cohorts, respectively, after propensity-matching. Stereotactic body radiation therapy resulted in a significantly lower PSA nadir (0.18 ng/ml) compared to hypo-fractionated radiation therapy (0.48 ng/ml) in patients with low-risk prostate cancer. Mean time to biochemical recurrence was not different between treatment groups. CONCLUSIONS: Stereotactic body radiation therapy is an effective treatment option for low and intermediate-risk prostate cancer with encouraging biochemical relapse-free survival and overall survival rates comparable with hypo-fractionated radiation therapy.

Palliative care utilization across health sectors for patients with gynecologic malignancies in Ontario, Canada from 2006 to 2018.

OBJECTIVE: Early palliative care (PC) is associated with improved patient quality of life, less aggressive end-of-life care, and prolonged survival. We evaluated patterns of PC delivery in gynecologic oncology. METHODS: We conducted a population-based, retrospective cohort study of gynecologic cancer decedents in Ontario from 2006 to 2018 using linked administrative health care data. RESULTS: The cohort included 16,237 decedents; 51.1% died of ovarian cancer, 30.3% uterine cancer, 12.1% cervical cancer, and 6.5% vulvar/vaginal cancers. Palliative care was most often delivered in the hospital inpatient setting in 81%, and 53% received specialist PC. PC was first received during hospital admission in 53%, and by outpatient physician care in only 23%. Palliative care was initiated a median 193 days prior to death, with the lowest two quintiles initiating care ≤70 days before death. The average user of PC resources (third quintile) received 68 days of PC. While cumulative use of community PC gradually increased over the final year of life, institutional palliative care use exponentially rose from 12 weeks until death. On multivariable analyses, predictors of initiating palliative care during a hospital admission included age ≥70 years at death, ≤3 month cancer survival, having cervical or uterine cancer, not having a primary care provider, or being in the lowest 3 income quintiles. CONCLUSION: Most palliative care is initiated and delivered during hospital admission, and is initiated late in a significant proportion. Strategies to increase access to anticipatory and integrated palliative care may improve the quality of the disease course and the end of life.

A two-center experience: The impact of COVID-19 on two brachytherapy programs in Ontario - virtual care, service suspension and radiation therapy workflow.

INTRODUCTION: Most brachytherapy (BT) procedures require general anesthesia and are therefore considered aerosol generating medical procedures (AGMPs). The COVID-19 pandemic impacted BT as services were prioritized by balancing the harm associated with COVID-19 infection versus the effect of delay of potentially curative treatment. This article summarizes the impact of the pandemic on BT programs in two cancer centers in a Canadian province. METHODS: As part of a quality assurance project, a retrospective study was conducted for the first five months of the pandemic (March 1 to July 31, 2020). Chart review and COVID-19 related mitigation strategies were identified by BT Clinical Specialist Radiation Therapists (bCSRT) in each center using electronic medical records, departmental reports, policies and procedures. RESULTS: Impact included start of virtual care (VC), shortened fractionation, suspension of services and workflow changes.  Both centers implemented VC strategies to reduce clinic visits: "same-day size and treat" strategy for post-operative endometrial cancer patients and virtual patient education for all patients. BT services that were suspended were low-dose-rate and high-dose-rate (HDR) prostate treatments (Center 1), lung and esophagus HDR treatments (Center 2).  Workflow changes that affected staff and patients in both centers included COVID-19 screening and the use of personal protective equipment. The centers were marginally different in workflow adjustments for AGMP procedures.  Those considered high-risk AGMP and low-risk cancer were suspended temporarily with alternate treatment strategies sought for some patients. Others had temporizing treatment such as androgen deprivation therapy to facilitate oncological safe deferral of procedures. CONCLUSION: Both BT programs delivered treatment to most patients with minimal delays and cancellations, where feasible. Some of the pandemic workflow changes continued to the current state of the pandemic. Long-term follow-up is needed to assess the impact of COVID-19 and treatment interruptions on oncologic outcomes.

Disparities in the survival of endometrial cancer patients in a public healthcare system: A population-based cohort study.

OBJECTIVE: Social determinants of health (SDH) have been shown to correlate with adverse cancer outcomes. It is unclear if their impact goes beyond behavioral risk or healthcare access. We aimed to evaluate the association of SDH with endometrial cancer outcomes in a public healthcare system. METHODS: A retrospective cohort study of endometrial cancer patients diagnosed between 2009 and 2017 in Ontario, Canada. Clinical and sociodemographic variables were extracted from administrative databases. Validated multifactorial marginalization scores for domains of material deprivation, residential instability and ethnic concentration were used. Associations between marginalization and survival were evaluated using log-rank testing and Cox proportional hazards regression. RESULTS: 20228 women with endometrial cancer were identified. Fewer patients in marginalized communities presented with early disease (70% vs. 76%, p < 0.001) and received surgery (89% vs. 93%, p < 0.001). Overall survival was shorter among marginalized patients (p < 0.001). On multivariable analysis adjusted for patient and disease factors, overall marginalization (HR = 1.22, 95% CI 1.03-1.08), material deprivation (HR = 1.22, 95% CI 1.10-1.35) and residential instability (HR = 1.32, 95% CI 1.19-1.46) were associated with increased risk of death (p < 0.001). CONCLUSIONS: Socioeconomic marginalization is associated with an increased risk of death in endometrial cancer patients. Targetable events in the cancer care pathway should be identified to improve health equity. FUNDING: This study was supported by a grant (#RD-196) from the Hamilton Health Sciences Juravinski Hospital and Cancer Center Foundation.

Desmoplastic small round cell tumor involving the uterine cervix: The first reported case in the literature, and brief review of gynecologic presentations.

Background: Desmoplastic small round cell tumors are exceedingly rare, usually involve abdominal organs and predominantly affect male patients. We describe the first reported case arising from the uterine cervix and provide a summary of 20 previously reported cases involving gynecologic organs. Case: A 54 year-old was diagnosed with a rapidly growing 13 cm desmoplastic small round cell tumor of the cervix. She was treated through a multimodal approach involving neoadjuvant chemotherapy and surgery. She subsequently recurred, and this was successfully treated with radiation therapy. She is well and without evidence of disease 22 months after initial diagnosis. Conclusion: We report successful treatment through multidisciplinary and multimodal management. This can guide management of future patients as no gold-standard treatment has yet been described.

Trends in quality indicators of end-of-life care for women with gynecologic malignancies in Ontario, Canada.

OBJECTIVE: A large body of research has validated several quality indicators of end-of-life (EOL) cancer care, but few have examined these in gynecologic cancer at a population-level. We examined patterns of EOL care quality in patients with gynecologic cancers across 13 years in Ontario, Canada. METHODS: We conducted a population-based, retrospective cohort study of gynecologic cancer decedents in Ontario from 2006 to 2018 using linked administrative health care databases. Proportions of quality indices were calculated, including: emergency department (ED) use, hospital or intensive care unit (ICU) admission, chemotherapy ≤14 days of death, cancer-related surgery, tube or intravenous feeds, palliative home visits, and hospital death. We used multivariable logistic regression to examine factors associated with receipt of aggressive and supportive care. RESULTS: There were 16,237 included decedents over the study period; hospital death rates decreased from 47% to 37%, supportive care use rose from 65% to 74%, and aggressive care remained stable (16%). Within 30 days of death, 50% were hospitalized, 5% admitted to ICU, and 67% accessed palliative homecare. Within 14 days of death, 31% visited the ED and 4% received chemotherapy. Patients with vulvovaginal cancers received the lowest rates of aggressive and supportive care. Using multivariable analyses, factors associated with increased aggressive EOL care use included younger age, shorter disease duration, lower income quintiles, and rural residence. CONCLUSIONS: Over time, less women dying with gynecologic cancers in Ontario experienced death in hospital, and more accessed supportive care. However, the majority were still hospitalized and a significant proportion received aggressive care in the final 30 days of life.

Impact of stereotactic body radiotherapy (SBRT) in oligoprogressive metastatic disease.

PURPOSE: There is increasing interest in using stereotactic body radiation therapy (SBRT) in areas of oligoprogressive metastatic disease (OPD). Our main objective was to investigate the impact of SBRT on overall survival (OS) and the incidence of systemic therapy treatment switches in this population. METHODS: A retrospective institutional review of patients treated with SBRT for OPD was performed. Patients were included if they received SBRT for 1-3 discrete progressing metastases, using a dose of at least 5 Gy per fraction. The study aimed to calculate progression-free survival (PFS), overall survival (OS), local control (LC), and incidence of treatment switch (TS). PFS and OS were calculated using the Kaplan-Meier methodology, while LC and TS were determined using cumulative incidence. RESULTS: Eighty-one patients with a total of 118 lesions were treated with SBRT from July 2014 to November 2020. The Median SBRT dose was 40 (18-60) Gy in 5 (2-8) fractions. Patients had primarily kidney, lung, or breast cancer. Most patients were treated with a tyrosine kinase inhibitor (TKI) (30.9%) or chemotherapy (29.6%) before OPD. The median follow-up post-SBRT was 14 months. Median OS and PFS were 25.1 (95% CI 11.2-39.1) months and 7.8 (95% CI 4.6-10.9) months, respectively. The cumulative incidence of local progression of treated lesions was 5% at 1 year and 7.3% at 2 years. Sixty patients progressed after SBRT and 17 underwent additional SBRT. Thirty-eight patients (47%) changed systemic therapy following SBRT; the cumulative incidence of TS was 28.5% at 6 months, 37.4% at 1 year, and 43.9% at 2 years. CONCLUSIONS: SBRT effectively controls locally progressing lesions but distant progression still occurs frequently. A sizeable number of patients can be salvaged by further SBRT or have minimally progressing diseases that may not warrant an immediate initiation/switch in systemic therapy. Further prospective studies are needed to validate this benefit.

The impact of preoperative imaging on wait times, surgical approach and overall survival in endometrioid endometrial cancers.

OBJECTIVES: Routine preoperative axial imaging studies (CT/MRI) are not recommended for endometrioid endometrial cancer as they are unlikely to change management and may delay surgery. This study evaluated the association of receiving preoperative imaging on various outcomes. METHODS: A population-based cohort of Endometrioid Endometrial Cancer cases from 2006 to 2016 were identified from the Cancer Registry in Ontario, Canada. Wait time to surgery, type of surgery and overall survival were evaluated in patients with and without preoperative imaging. Predictive factors for wait time > 56 days and aggressive surgery (radical hysterectomy / lymphadenectomy) were determined using multivariable regression analysis. RESULTS: 13,050 cases were included. 22.6% of patients received preoperative imaging, mainly CT scans. Most patients (95.9%) received no neoadjuvant treatment. Patients with preoperative imaging were more likely to have neoadjuvant treatment (11.7% vs. 1.8%) and less likely to have surgery at 180 days post diagnosis (87.9% vs 94.6%). Patients with preoperative imaging had median wait time to surgery of 64 days (47-87), compared to 53 days (36-74) than those without imaging (p < 0.001). Multivariable modeling showed preoperative imaging was associated with decreased odds of having surgery within 56 days (OR = 0.68, 95% CI = 0.62-0.75), and increased odds (OR = 1.73, 95% CI = 1.53-1.95) of having aggressive surgery. The 5-year overall survival for patients with imaging was 84.8% versus 91.1% for patients without preoperative imaging. CONCLUSIONS: Preoperative imaging was associated with longer wait times to surgery, more aggressive surgery, surgery with a gynecologic oncologist and increased use of neoadjuvant and adjuvant treatment. In early-stage disease there was no observed improvement in overall survival for patients with preoperative imaging. Further research on potential benefits of preoperative imaging in higher risk patients is required.

Salvage radiotherapy following HiFU: An institutional series and literature review.

INTRODUCTION: Algorithms for the treatment of prostate cancer (PrCa) rely on risk grouping, and those who fall into low (LR) and favourable intermediate risk (FIR) categories have multiple options for treatment. High-intensity focused ultrasound (HiFU) is a local treatment modality that uses ultrasound waves to ablate prostate cancer. In case of treatment failure, optimal salvage modality after HiFU remains unclear. METHODS: Here, we describe a retrospective review of our regional cancer database for men who underwent salvage radiotherapy after failure of HiFU treatment for prostate cancer. Oncologic and toxicity outcomes of the men identified in our database are discussed. RESULTS: We identified 14 men in our regional database who received salvage radiotherapy (70-74 Gy with or without androgen deprivation therapy (ADT) after primary HiFU, in the period of 2009-2017. No cases of any grade 3 or higher toxicity were observed. In our cohort, 50% (7/14) of patients developed secondary biochemical failure at a median follow-up of 54 months post-radiotherapy, with a mean time to biochemical failure of 39 months. We compare our data to other available reports to date consisting mostly of small, non-randomized studies. Our biochemical control rates are noticeably lower compared with those reported by other studies but our length of follow-up is longer, compared with other studies. CONCLUSION: The available data to date suggest that salvage radiotherapy after HiFU failure is well-tolerated albeit with only modest efficacy.

The use of imaging in endometrial cancer prior to potential surgery: Are guidelines being followed?

OBJECTIVES: Clinical practice guidelines recommend against routine preoperative axial imaging studies (CT/MRI) for endometrial cancer, except for cases of locally advanced disease or aggressive histologies. This study utilized population-based data to evaluate the use of preoperative imaging and factors associated with its use. METHODS: A population-based cohort of women diagnosed with endometrial cancer from 2006 to 2016 were identified from the Ontario Cancer Registry in Ontario, Canada. Patients were excluded if they had: hysterectomy prior to the date of diagnosis, non-epithelial histology or a prior cancer diagnosis within 5 years. Preoperative imaging (CT or MRI) rates were calculated over time. Predictive factors for preoperative imaging use were determined using multi-variable regression analysis. RESULTS: 17,718 cases were eligible for analysis. From 2006 to 2016, the proportion of patients receiving preoperative imaging increased from 22.2% to 39.3%. In a subgroup of patients with low-risk disease (stage 1, endometrioid adenocarcinoma), imaging increased from 16.3% to 29.5%. Multivariate analysis showed an association between preoperative imaging and advanced stage, advanced grade, non-endometrioid morphology, surgery with a gynecologic oncologist, surgery at a teaching hospital and a later year of diagnosis. From 2006 to 2016, the yearly incidence of endometrial cancer increased from 22.3/100,000 to 36.1/100,000, representing a mean annual increase of 3.6% per year. CONCLUSIONS: Endometrial cancer incidence and the use of preoperative imaging are increasing. Factors most associated with preoperative imaging are high-risk features. However, preoperative imaging is still being performed in low-risk patients, indicating non-adherence to guidelines, which has implications for constrained healthcare resources.

A pilot study of stereotactic boost for malignant epidural spinal cord compression: clinical significance and initial dosimetric evaluation.

PURPOSE: Metastatic epidural spinal cord compression (MESCC) is a devastating complication of advanced malignancy, which can result in neurologic complications and significant deterioration in overall function and quality of life. Most patients are not candidates for optimal surgical decompression and as a result, receive urgent 3D conformal radiotherapy (3DCRT) to prevent or attempt to reverse neurologic progression. Multiple trials indicate that response and ambulatory rates after 3DCRT are inferior to surgery. The advent of stereotactic body radiation therapy (SBRT) has created a method with which a "radiosurgical decompression" boost may facilitate improve outcomes for MESCC patients. METHODS: We are conducting a pilot study to investigate SBRT boost after urgent 3D CRT for patients with MESCC. The aim of the study is to establish feasibility of this two-phase treatment regimen, and secondarily to characterize post-treatment ambulation status, motor response, pain control, quality of life and survival. DISCUSSION: We describe the study protocol and present a case report of one patient. A quality assurance review was conducted after the first seven patients, and resultant dose-constraints were revised to improve safety and feasibility of planning through more conservative organ at risk constraints. There have been no severe adverse events (grade 3-5) to date. We have illustrated clinical and dosimetric data of an example case, where a patient regained full strength and ambulatory capacity. CONCLUSIONS: Our study aims to determine if SBRT is a feasible option in addition to standard 3DCRT for MESCC patients, with the goal to consider future randomized trials if successful. Having a robust quality assurance process in this study ensures translatability going forward if future trials with multicenter and increased patient representation are to be considered. TRIAL REGISTRATION: clinicaltrials.gov; registration no. NCT03529708; https://clinicaltrials.gov/ct2/show/NCT03529708 ; First posted May 18, 2018.

A Randomized Phase II Trial of Prostate Boost Irradiation With Stereotactic Body Radiotherapy (SBRT) or Conventional Fractionation (CF) External Beam Radiotherapy (EBRT) in Locally Advanced Prostate Cancer: The PBS Trial (NCT03380806).

Standard therapy for high-risk (HR) prostate cancer (PrCa) involves androgen deprivation therapy (ADT) and pelvic conventional fractionation (CF) external beam radiotherapy (EBRT) followed by boost CF-EBRT treatment to prostate for a total of 78 to 80 Gy in 39 to 40 fractions. This is a long and inconvenient treatment for patients. Brachytherapy boost treatment studies indicate that escalation of biological dose of radiotherapy (RT) can improve outcomes in HR-PrCa. However, brachytherapy is an invasive treatment associated with increased toxicity and requires specialized resources. Stereotactic body radiotherapy (SBRT) is a promising, non-invasive alternative to brachytherapy. However, its impact on patient quality of life (QoL) and RT-associated toxicity has not been investigated in a randomized setting. In this study, we investigate SBRT as a boost treatment, following pelvic CF-EBRT, in patients with HR-PrCa treated with ADT. One hundred patients with locally advanced PrCa will be randomized to receive daily CF-EBRT of 45 to 46 Gy in 23 to 25 fractions followed by either daily CF-EBRT of 32 to 33 Gy in 15 to 16 fractions (control arm) or SBRT boost treatment of 19.5 to 21 Gy in 3 fractions (1 fraction per week) (experimental arm). The primary objective of the PBS trial is early bowel and urinary QoL (expanded prostate index composite [EPIC], up to 6 months after RT). This phase II randomized study (PBS) provides an appropriate setting to investigate effectively the impact of SBRT boost on QoL and toxicity in patients with HR-PrCa, before this modality can be compared against the current standard of care in larger phase III protocols.

Biological Response of Positron Emission Tomography Scan Exposure and Adaptive Response in Humans.

The biological effects of exposure to radioactive fluorodeoxyglucose ((18)F-FDG) were investigated in the lymphocytes of patients undergoing positron emission tomography (PET) procedures. Low-dose, radiation-induced cellular responses were measured using 3 different end points: (1) apoptosis; (2) chromosome aberrations; and (3) γH2AX foci formation. The results showed no significant change in lymphocyte apoptosis, or chromosome aberrations, as a result of in vivo (18)F-FDG exposure, and there was no evidence the PET scan modified the apoptotic response of lymphocytes to a subsequent 2 Gy in vitro challenge irradiation. However, lymphocytes sampled from patients following a PET scan showed an average of 22.86% fewer chromosome breaks and 39.16% fewer dicentrics after a subsequent 2 Gy in vitro challenge irradiation. The effect of (18)F-FDG exposure on phosphorylation of histone H2AX (γH2AX) in lymphocytes of patients showed a varied response between individuals. The relationship between γH2AX foci formation and increasing activity of (18)F-FDG was not directly proportional to dose. This variation is most likely attributed to differences in the factors that combine to constitute an individual's radiation response. In summary, the results of this study indicate(18)F-FDG PET scans may not be detrimental but can elicit variable responses between individuals and can modify cellular response to subsequent radiation exposures.

Radiation-induced lymphocyte apoptosis to predict radiation therapy late toxicity in prostate cancer patients.

PURPOSE: To examine a potential correlation between the in vitro apoptotic response of lymphocytes to radiation and the risk of developing late gastrointestinal (GI)/genitourinary (GU) toxicity from radiotherapy for prostate cancer. METHODS AND MATERIALS: Prostate cancer patients formerly enrolled in a randomized study were tested for radiosensitivity by using a radiation-induced lymphocyte apoptosis assay. Apoptosis was measured using flow cytometry-based Annexin-FITC/7AAD and DiOC(6)/7AAD assays in subpopulations of lymphocytes (total lymphocytes, CD4+, CD8+ and CD4-/CD8-) after exposure to an in vitro dose of 0, 2, 4, or 8 Gy. RESULTS: Patients with late toxicity after radiotherapy showed lower lymphocyte apoptotic responses to 8 Gy than patients who had not developed late toxicity (p = 0.01). All patients with late toxicity had apoptosis levels that were at or below the group mean. The negative predictive value in both apoptosis assays ranged from 95% to 100%, with sensitivity values of 83% to 100%. Apoptosis at lower dose points and in lymphocyte subpopulations had a weaker correlation with the occurrence of late toxicity. CONCLUSIONS: Lymphocyte apoptosis after 8 Gy of radiation has the potential to predict which patients will be spared late toxicity after radiation therapy. Further research should be performed to identify the specific subset of lymphocytes that correlates with late toxicity, followed by a corresponding prospective study.

Individual radiosensitivity and its relevance to health physics.

Radiation protection regulations have been established to reduce exposure of individuals to acceptable safe levels. These limits assume that people have similar responses to ionizing radiation and that there is no variation in individual radiation risk. The purpose of this research was to determine if apoptosis in lymphocytes can be used to assess individual sensitivity to ionizing radiation. Blood samples were taken from 54 males ranging in age from 19-85 years. Apoptosis was measured using modified flow cytometry based Annexin-FITC/7AAD and DiOC(6)/7AAD assays in different populations of lymphocytes (total mixed lymphocyte population, subset CD4+ or CD8+ lymphocytes) after exposure to in vitro doses of 0, 2, 4 or 8Gy (dose rate 0.1Gy/min). The variation in individual responses to radiation was large. The variation was the largest in the CD4+ lymphocyte sub-population. Radiation-induced apoptosis decreased with age of donor demonstrating that as people age their lymphocytes may become relatively more resistant to radiation. This research shows that individuals have marked differences in their sensitivity to radiation and protection policies may someday need to be tailored for some individuals.

Artificial neural network modeling of apoptosis in gamma irradiated human lymphocytes.

PURPOSE: To develop an artificial neural network (ANN) model of apoptotic response in gamma irradiated human lymphocytes. To assess the feasibility of training ANN radiobiological models using data collected with flow cytometry. MATERIALS AND METHODS: Irradiated isolated human lymphocytes were labelled with Annexin V-Fluorescein Isothiocyanate (FITC) and 7-Amino-Actinomycin D (7AAD) then analysed using flow cytometry. Twenty-four dose responses per donor from 14 donors were collected from a flow cytometer and used in model development as the training and cross-validation datasets. The general ANN model architecture was a multi-layer perceptron using the mean squared error of a cross validation dataset as the objective function. The ANN model was optimized by varying the number of hidden layers and the number of processing elements per layer. The optimized model constituted of three hidden layers with 80, 40, and 10 hidden layers in the first, second, and third layers respectively. RESULTS: The optimized model was used to simulate dose responses at the training doses of 0, 2, 4 and 8 Gray. A strong agreement between the model and measured dose responses was observed. The model was also used to simulate a dose response at 0.1 Gray and results were compared to the measured dose response from a donor not used in model development. Again, strong agreement between the model and the observed dose response was found. CONCLUSIONS: This study shows that artificial neural networks can be trained to provide high resolution, high accuracy models of multivariate radiobiological data collected by flow cytometry.