Comparison of clinical, tumour-related and dosimetric factors in grade 0-1, grade 2 and grade 3 radiation pneumonitis after stereotactic body radiotherapy for lung tumours

Prediction of Acute Radiation-Induced Lung Toxicity After Stereotactic Body Radiation Therapy Using Dose-Volume Parameters From Functional Mapping on Gallium 68 Perfusion Positron Emission Tomography/Computed Tomography

PURPOSE

The aim of this work was to compare anatomic and functional dose-volume parameters as predictors of acute radiation-induced lung toxicity (RILT) in patients with lung tumors treated with stereotactic body radiation therapy.

METHODS AND MATERIALS

Fifty-nine patients treated with stereotactic body radiation therapy were prospectively included. All patients underwent gallium 68 lung perfusion positron emission tomography (PET)/computed tomography (CT) imaging before treatment. Mean lung dose (MLD) and volumes receiving x Gy (VxGy, 5-30 Gy) were calculated in 5 lung volumes: the conventional anatomic volume (AV) delineated on CT images, 3 lung functional volumes (FVs) defined on lung perfusion PET imaging (FV50%, FV70%, and FV90%; ie, the minimal volume containing 50%, 70%, and 90% of the total activity within the AV), and a low FV (LFV; LFV = AV - FV90%). The primary endpoint of this analysis was grade ≥2 acute RILT at 3 months as assessed with National Cancer Institute Common Terminology Criteria for Adverse Events version 5. Dose-volume parameters in patients with and without acute RILT were compared. Receiver operating characteristic curves assessing the ability of dose-volume parameters to discriminate between patients with and without acute RILT were generated, and area under the curve (AUC) values were calculated.

RESULTS

Of the 59 patients, 10 (17%) had grade ≥2 acute RILT. The MLD and the VxGy in the AV and LFV were not statistically different between patients with and without acute RILT (P > .05). All functional parameters were significantly higher in acute RILT patients (P < .05). AUC values (95% CI) for MLD AV, LFV, FV50%, FV70%, and FV90% were 0.66 (0.46-0.85), 0.60 (0.39-0.80), 0.77 (0.63-0.91), 0.77 (0.64-0.91), and 0.75 (0.58-0.91), respectively. AUC values for V20Gy AV, LFV, FV50%, FV70%, and FV90% were 0.65 (0.44-0.87), 0.64 (0.46-0.83), 0.82 (0.69-0.95), 0.81 (0.67-0.96), and 0.75 (0.57-0.94), respectively.

CONCLUSIONS

The predictive value of PET perfusion-based functional parameters outperforms the standard CT-based dose-volume parameters for the risk of grade ≥2 acute RILT. Functional parameters could be useful for guiding radiation therapy planning and reducing the risk of acute RILT.

Optimizing lung cancer radiation therapy: A systematic review of multifactorial risk assessment for radiation-induced lung toxicity

BACKGROUND

Radiation therapy (RT) is essential in treating advanced lung cancer, but may lead to radiation pneumonitis (RP). This systematic review investigates the use of pulmonary function tests (PFT) and other parameters to predict and mitigate RP, thereby improving RT planning.

METHODS

A systematic review sifted through PubMed and on BioMed Central, targeting articles from September 2005 to December 2022 containing the keywords: Lung Cancer, Radiotherapy, and pulmonary function test.

RESULTS

From 1153 articles, 80 were included. RP was assessed using CTCAEv.4 in 30 % of these. Six studies evaluated post-RT quality of life in lung cancer patients, reporting no decline. Patients with RP and chronic obstructive pulmonary disease (COPD) generally exhibited poorer overall survival. Notably, forced expiratory volume in one second (FEV1) and diffusing capacity of the lung for carbon monoxide (DLCO) declined 24 months post-RT, while forced vital capacity (FVC) stayed stable. In the majority of studies, age over 60, tumors located in the lower part of the lung, and low FEV1 before RT were associated with a higher risk of RP. Dosimetric factors (V5, V20, MLD) and metabolic imaging emerged as significant predictors of RP risk. A clinical checklist blending patient and tumor characteristics, PFT results, and dosimetric criteria was proposed for assessing RP risk before RT.

CONCLUSION

The review reveals the multifactorial nature of RP development following RT in lung cancer. This approach should guide individualized management and calls for a prospective study to validate these findings and enhance RP prevention strategies.

And Yet It Moves: Clinical Outcomes and Motion Management in Stereotactic Body Radiation Therapy (SBRT) of Centrally Located Non-Small Cell Lung Cancer (NSCLC): Shedding Light on the Internal Organ at Risk Volume (IRV) Concept

The internal organ at risk volume (IRV) concept might improve toxicity profiles in stereotactic body radiation therapy (SBRT) for non-small cell lung cancer (NSCLC). We studied (1) clinical aspects in central vs. peripheral tumors, (2) the IRV concept in central tumors, (3) organ motion, and (4) associated normal tissue complication probabilities (NTCPs). We analyzed patients who received SBRT for NSCLC (clinical aspects, n = 78; motion management, n = 35). We found lower biologically effective doses, larger planning target volume sizes, higher lung doses, and worse locoregional control for central vs. peripheral tumors. Organ motion was greater in males and tall patients (bronchial tree), whereas volume changes were lower in patients with a high body mass index (BMI) (esophagus). Applying the IRV concept (retrospectively, without new optimization), we found an absolute increase of >10% in NTCPs for the bronchial tree in three patients. This study emphasizes the need to optimize methods to balance dose escalation with toxicities in central tumors. There is evidence that organ motion/volume changes could be more pronounced in males and tall patients, and less pronounced in patients with higher BMI. Since recent studies have made efforts to further subclassify central tumors to refine treatment, the IRV concept should be considered for optimal risk assessment.

Does shortening the duration of radiotherapy treatment in breast cancer increase the risk of radiation pneumonia: A retrospective study

Randomized studies evaluating hypofractionation and conventional fractionation radiotherapy treatments (RT) in patients with breast cancer have shown that hypofractionation achieves similar results to conventional fractionation in terms of survival and local control rates. It has also been shown that their long-term toxicities are similar. This study aimed to evaluate the effects of hypofractionated radiotherapy (H-RT) and conventional radiotherapy (C-RT) on lung toxicity and identify factors affecting this toxicity in patients with breast cancer. The study included 118 patients who underwent adjuvant RT following breast-conserving surgery (BCS). Out of these, 63 patients were assigned to receive C-RT, while the remaining 55 were assigned to receive H-RT. To clarify, we treated 63 patients with C-RT and 55 patients with H-RT. 60 patients were treated using 3-dimensional conformal radiotherapy (3DCRT) and 58 patients were treated using intensity modulated radiotherapy (IMRT). The patients were evaluated weekly for toxicity during radiotherapy (RT) treatment and were called every 3 months for routine controls after the treatment. The first control was performed 1 month after the treatment. Statistical analysis was performed using the SPSS20 program, and a P value of <.005 was considered statistically significant. The study found that the median age of the participants was 54.9 years and tomographic findings were observed in 70 patients. Radiological findings were detected at a median of 5 months after RT. The mean lung dose (MLD) on the treated breast side (referred to as ipsilateral lung or OAR) was 10.4 Gy for the entire group. Among patients who received 18 MV energy in RT, those with an area volume (V20) of the lung on the treated breast side >18.5%, those with a mean dose of the treated breast side lung (ipsilateral lung) >10.5 Gy, and those who received concurrent hormone therapy had significantly more tomographic findings. However, patients treated with YART had fewer tomographic findings. No symptomatic patients were observed during the follow-up period. Our findings show that the risk of lung toxicity is similar with H-RT and C-RT, and H-RT can be considered an effective and safe treatment option for breast cancer. The key factors affecting the development of lung toxicity were found to be the type of RT energy used, RT to the side breast, volume receiving 20 Gy in the side lung, side lung mean dose, and simultaneous hormonal therapy.

Volumetric modulated arc therapy (VMAT) comparison to 3D-conformal technique in lung stereotactic ablative radiotherapy (SABR)

INTRODUCTION

Stereotactic ablative radiotherapy (SABR) can be a curative option for non-small cell lung cancer (NSCLC) and oligometastatic lung disease. Volumetric modulated arc therapy (VMAT) has offered further advancements in terms of radiation dose shaping without compromising treatment times however there is potential for greater low-dose exposure to the lung. This study was to assess whether VMAT lung SABR would result in any increase to the dosimetry parameters compared with three-dimensional conformal radiotherapy (3D-CRT) that could confer increased risk of radiation pneumonitis.

METHODS

A total of 53 and 30 3D-CRT treatment plans of patients treated with 48 Gy in 4 fractions were compared.

RESULTS

No statistically significant difference in planning target volumes between the VMAT 29.9 cc (range 12.4-58.5 cc) and 3D-CRT 31.2 cc (range 12.3-58.3 cc) P = 0.79. The mean of total lung V5, ipsilateral lung V5 and contralateral lung V5 all showed a trend of being smaller in the VMAT treatment group- 14% versus 15.8%, 25.6% versus 30.4% and 1.6% versus 2.2%, respectively, but all were not statistically significant differences. Mean of the mean lung dose MLD, again showed a trend of being lower in the VMAT treatments but was also non-significant, 2.6 Gy versus 3.0 Gy, P = 1.0. Mean V20 was the same in both cohorts, 3.3%.

CONCLUSIONS

The dosimetry for 3D-CRT and VMAT plans were not significantly different including V5, and therefore we conclude that VMAT treatment is unlikely to be associated with an increased risk of radiation pneumonitis.

Research Progress on Radiotherapy Combined with Immunotherapy for Associated Pneumonitis During Treatment of Non-Small Cell Lung Cancer

Radiation pneumonitis is a common and serious complication of radiotherapy for thoracic tumours. Although radiotherapy technology is constantly improving, the incidence of radiation pneumonitis is still not low, and severe cases can be life-threatening. Once radiation pneumonitis develops into radiation fibrosis (RF), it will have irreversible consequences, so it is particularly important to prevent the occurrence and development of radiation pneumonitis. Immune checkpoint inhibitors (ICIs) have rapidly altered the treatment landscape for multiple tumour types, providing unprecedented survival in some patients, especially for the treatment of non-small cell lung cancer (NSCLC). However, in addition to its remarkable curative effect, ICls may cause immune-related adverse events. The incidence of checkpoint inhibitor pneumonitis (CIP) is 3% to 5%, and its mortality rate is 10% to 17%. In addition, the incidence of CIP in NSCLC is higher than in other tumour types, reaching 7%–13%. With the increasing use of immune checkpoint inhibitors (ICls) and thoracic radiotherapy in the treatment of patients with NSCLC, ICIs may induce delayed radiation pneumonitis in patients previously treated with radiation therapy, or radiation activation of the systemic immune system increases the toxicity of adverse reactions, which may lead to increased pulmonary toxicity and the incidence of pneumonitis. In this paper, the data about the occurrence of radiation pneumonitis, immune pneumonitis, and combined treatment and the latest related research results will be reviewed.

Lung Function After Stereotactic Body Radiation Therapy for Early-Stage Non-Small Cell Lung Cancer, Changes and Predictive Markers

Introduction

The present study explores changes in pulmonary function, symptoms and radiological signs of pneumonitis after curatively intended stereotactic body radiation therapy (SBRT).

Methods

All inoperable, early-stage non-small cell lung cancer patients treated with stereotactic body radiation therapy (SBRT) from 2014-2017 were included in this single-centre study. They were followed regularly for 12 months after treatment. The patients were classified into three groups based on radiology and symptomatology: no radiation pneumonitis, asymptomatic and symptomatic radiation pneumonitis.

Results

Forty-four patients with stage IA-IIB disease were treated with 45–56 Gy in 3–8 fractions. The median age was 75 years, 43% of the patients were female; 60% of the patients had a COPD in GOLD grade of 2-4, and 95.5% were active or former smokers. Symptomatic radiation pneumonitis occurred in 18% of the patients and asymptomatic pneumonitis as defined by radiology, in 39%. The mean of forced expiratory volume in 1 second (FEV1) and diffusion capacity for carbon monoxide (DLCO) decreases for all patients during the first years were higher than one would expect from physiologic ageing. FEV1 and DLCO in percent decrease 7-8% at 1-1.5 months in the symptomatic radiation pneumonitis group. CT scan findings consistent with radiation pneumonitis occurred after a median of 2.9 months in the symptomatic and 5.4 months in the asymptomatic radiation pneumonitis groups. In the group with symptomatic radiation pneumonitis, symptoms, as measured by the Clinical COPD questionnaire score, significantly increased at 3 and 6 months. Significant higher maximum doses to the critical lung volumes DC1000cm³ (1000 cm³ of lung receiving a given dose or less) and DC 1500cm³ (1500 cm³ of lung receiving a given dose or less) were observed in patients who developed radiation pneumonitis.

Conclusion

Early decrease in measured FEV1 and DLCO occurred before imaging changes and symptoms and might indicate the development of symptomatic radiation pneumonitis. The dose to critical lung volumes of DC1000 cm³ and DC1500 cm³ may predict the risk for the development of symptomatic radiation pneumonitis.

Radiographic findings after stereotactic body radiation therapy for stage I non-small cell lung carcinomas: retrospective analysis of 90 patients

Aim:

Stereotactic body radiation therapy for lung tumours can expose patients to radiation pneumonitis (RP) (<6 months after irradiation) and lung fibrosis (beyond 6 months). The aim of this study was to describe post-irradiation radiographics appearances.

Materials and methods:

This retrospective study of 90 patients with a stage I non-small cell lung carcinoma reports a detailed description of the computed tomography (CT) or positron emission tomography/CT changes that can be observed after treatment, according to modified Kimura score for RP and Koenig’s classification for fibrosis. This evaluation was realised at 1 month and then every 3–4 months, with a median follow-up of 35 months.

Results:

The most common radiological RP pattern was diffuse consolidation. It appears in a mean time of 4 months and reaches its maximum at 9 months after radiotherapy. Seventy-three per cent of the RP evolved to fibrosis. Most of these findings were encompassed in the 35 Gy isodose.

Findings:

Radiological parenchymal changes are frequent in the treatment region, which renders the tumour response monitoring by tumour size, particularly by response evaluation criteria in solid tumours, unsuitable.

Correlation of dosimetric factors with the development of symptomatic radiation pneumonitis in stereotactic body radiotherapy

BACKGROUND

The development of radiation pneumonitis (RP) after Stereotactic Body Radiotherapy (SBRT) is known to be associated with many different factors, although historical analyses of RP have commonly utilized heterogeneous fractionation schemes and methods of reporting. This study aims to correlate dosimetric values and their association with the development of Symptomatic RP according to recent reporting standards as recommended by the American Association of Physicists in Medicine.

METHODS

We performed a single-institution retrospective review for patients who received SBRT to the lung from 2010 to 2017. Inclusion criteria required near-homogeneous tumoricidal (α/β = 10 Gy) biological effective dose (BED10) of 100-105 Gy (e.g., 50/5, 48/4, 60/8), one or two synchronously treated lesions, and at least 6 months of follow up or documented evidence of pneumonitis. Symptomatic RP was determined clinically by treating radiation oncologists, requiring radiographic evidence and the administration of steroids. Dosimetric parameters and patient factors were recorded. Lung volumes subtracted gross tumor volume(s). Wilcoxon Rank Sums tests were used for nonparametric comparison of dosimetric data between patients with and without RP; p-values were Bonferroni adjusted when applicable. Logistic regressions were conducted to predict probabilities of symptomatic RP using univariable models for each radiation dosimetric parameter.

RESULTS

The final cohort included 103 treated lesions in 93 patients, eight of whom developed symptomatic RP (n = 8; 8.6%). The use of total mean lung dose (MLD) > 6 Gy alone captured five of the eight patients who developed symptomatic RP, while V20 > 10% captured two patients, both of whom demonstrated a MLD > 6 Gy. The remaining three patients who developed symptomatic RP without exceeding either metric were noted to have imaging evidence of moderate interstitial lung disease, inflammation of the lungs from recent concurrent chemoradiation therapy to the contralateral lung, or unique peri-tumoral inflammatory appearance at baseline before treatment.

CONCLUSIONS

This study is the largest dosimetric analysis of symptomatic RP in the literature, of which we are aware, that utilizes near-homogenous tumoricidal BED fractionation schemes. Mean lung dose and V20 are the most consistently reported of the various dosimetric parameters associated with symptomatic RP. MLD should be considered alongside V20 in the treatment planning process.

TRIAL REGISTRATION

Retrospectively registered on IRB 398-17-EP.

Lung Cancer in Women: A Modern Epidemic

Lung cancer in women is a modern epidemic and a major health crisis. Cigarette smoking remains the most important risk factor for lung cancer, and unfortunately smoking rates are either stabilized or continue to increase among women. Women may not be more susceptible to the carcinogenic effects of tobacco, but the biology of lung cancer differs between the sexes. This paper summarizes the biological sex differences in lung cancer, including molecular abnormalities, growth factor receptors, hormonal influences, DNA repair capacity, as well as differences in the histology and treatment outcomes of lung cancer in women.

Organs at Risk Considerations for Thoracic Stereotactic Body Radiation Therapy: What Is Safe for Lung Parenchyma?

PURPOSE

Stereotactic body radiation therapy (SBRT) has become the standard of care for inoperable early-stage non-small cell lung cancer and is often used for recurrent lung cancer and pulmonary metastases. Radiation-induced lung toxicity (RILT), including radiation pneumonitis and pulmonary fibrosis, is a major concern for which it is important to understand dosimetric and clinical predictors.

METHODS AND MATERIALS

This study was undertaken through the American Association of Physicists in Medicine's Working Group on Biological Effects of Stereotactic Body Radiotherapy. Data from studies of lung SBRT published through the summer of 2016 that provided detailed information about RILT were analyzed.

RESULTS

Ninety-seven studies were ultimately considered. Definitions of the risk organ and complication endpoints as well as dose-volume information presented varied among studies. The risk of RILT, including radiation pneumonitis and pulmonary fibrosis, was reported to be associated with the size and location of the tumor. Patients with interstitial lung disease appear to be especially susceptible to severe RILT. A variety of dosimetric parameters were reported to be associated with RILT. There was no apparent threshold "tolerance dose-volume" level. However, most studies noted safe treatment with a rate of symptomatic RILT of <10% to 15% after lung SBRT with a mean lung dose (MLD) of the combined lungs ≤8 Gy in 3 to 5 fractions and the percent of total lung volume receiving more than 20 Gy (V₂₀) <10% to 15%.

CONCLUSIONS

To allow more rigorous analysis of this complication, future studies should standardize reporting by including standardized endpoint and volume definitions and providing dose-volume information for all patients, with and without RILT.

[Radiation-induced lung toxicity predictors after stereotactic radiation therapy for non-small cell lung carcinoma stage I]

In case of refusal or contraindication for surgical management of a stage I non-small cell lung carcinoma, the validated alternative therapy is stereotactic irradiation. This technique reaches an equivalent tumour control rate than surgery and significantly higher than conventional radiotherapy. One of the dreaded complications is radiation induced lung toxicity (radiation pneumonitis and lung fibrosis), especially when it is symptomatic, occurring in about 10 % of cases. This article is a literature review of this complication's predictive factors.

Clarithromycin mitigates radiation pneumonitis in patients with lung cancer treated with stereotactic body radiotherapy

Background

Radiation pneumonitis is a critical pulmonary toxicity after irradiation of the lung. Macrolides including clarithromycin (CAM) are antibiotics. They also have immunomodulatory properties and are used to treat respiratory inflammatory diseases. Radiation pneumonitis has similar pathology to them. Adverse reactions to macrolides are few and self-limited. We thus administered CAM to patients with high-risk factors for radiation pneumonitis, and retrospectively investigated whether CAM mitigated radiation pneumonitis following stereotactic body radiotherapy (SBRT).

Methods

Among consecutive patients treated with SBRT, we retrospectively examined lung cancer patients treated with a total dose of 40-60 Gy in 5-10 fractions and followed ≥6 months. Since January 2014, CAM has been administered in patients with pretreatment predictable radiation pneumonitis high-risk factors, including idiopathic interstitial pneumonias (IIPs), and elevated Krebs von den Lungen-6 (KL-6) and/or surfactant protein D (SP-D), and in patients developing early onset radiation pneumonitis.

Results

Five hundred and eighty eligible patients were identified and divided into 445 patients during the non-CAM-administration era (non-CAM-era) (before December 2013) and 136 patients during the CAM-administration era (CAM-era) (after January 2014). Median follow-up durations were 38.0 and 13.9 months, respectively. The rates of radiation pneumonitis ≥ grade 2 and ≥ grade 3 were significantly lower in CAM-era (grade ≥2, 16% vs. 9.6%, P=0.047; grade ≥3, 3.8% vs. 0.73%, P=0.037). For patients with the pretreatment predictable high-risk factors, the rate of radiation pneumonitis ≥ grade 3 was significantly lower, and that of grade ≥2 had a lower tendency (grade ≥3, 7.2% vs. 0%, P=0.011; grade ≥2, 21% vs. 9.6%, P=0.061). For patients developing early onset radiation pneumonitis, the rate of radiation pneumonitis ≥ grade 3 was also significantly lower (23% vs. 0%, P<0.05). Multivariate analysis revealed that dose-volumetric factor, the pretreatment predictable high-risk factors and non-CAM-administration era were significantly associated with or trended toward radiation pneumonitis ≥ grade 2 and ≥ grade 3.

Conclusions

CAM mitigated radiation pneumonitis following SBRT. The efficacy of CAM should be confirmed in prospective studies.

Organs at risk in lung SBRT

Lung stereotactic body radiotherapy (SBRT) is an accurate and precise technique to treat lung tumors with high 'ablative' doses. Given the encouraging data in terms of local control and toxicity profile, SBRT has currently become a treatment option for both early stage lung cancer and lung oligometastatic disease in patients who are medically inoperable or refuse surgical resection. Dose-adapted fractionation schedules and ongoing prospective trials should provide further evidence of SBRT safety trying to reduce toxicities and complications. In this heterogeneous scenario, a non-systematic review of dose constraints for lung SBRT was performed, including the main organs at risk in the thorax.

Risk Factors Associated With Symptomatic Radiation Pneumonitis After Stereotactic Body Radiation Therapy for Stage I Non-Small Cell Lung Cancer

Radiation pneumonitis is the most frequent acute pulmonary toxicity following stereotactic body radiation therapy for lung cancer. Here, we investigate clinical and dosimetric factors associated with symptomatic radiation pneumonitis in patients with stage I non-small cell lung cancer treated with stereotactic body radiation therapy. A total of 67 patients with stage I non-small cell lung cancer who received stereotactic body radiation therapy at our institution were enrolled, and their clinicopathological parameters and dosimetric parameters were recorded and analyzed. The median follow-up period was 26.4 months (range: 7-48 months). In univariate analysis, tumor size ( P = .041), mean lung dose ( P = .028), V2.5 ( P = .024), V5 ( P = .014), V10 ( P = .004), V20 ( P = .024), V30 ( P = .020), V40 ( P = .040), and V50 ( P = 0.040) were associated with symptomatic radiation pneumonitis. In multivariable logistic regression analysis, V10 ( P = .049) was significantly associated with symptomatic radiation pneumonitis. In conclusion, this study found that tumor size, mean lung dose, and V2.5 to V50 were risk factors markedly associated with symptomatic radiation pneumonitis. Our data suggested that lung V10 was the most significant factor, and optimizing lung V10 may reduce the risk of symptomatic radiation pneumonitis. For both central and peripheral stage I lung cancer, rate of radiation pneumonitis ≥grade 2 was low after stereotactic body radiation therapy with appropriate fraction dose.

Predicting risk factors for radiation pneumonitis after stereotactic body radiation therapy for primary or metastatic lung tumours

OBJECTIVE

To investigate risk factors for radiation-induced pneumonitis (RP) after hypofractionated stereotactic body radiotherapy (SBRT) in patients with lung tumours.

METHODS

From May 2004 to January 2016, 66 patients with 71 primary or metastatic lung tumours were treated with SBRT; these 71 cases were retrospectively analyzed for RP. To explore the risk factors for RP, the following factors were investigated: age, sex, performance status, operability, number of treatments, respiratory gating, pulmonary emphysema, tumour location and subclinical interstitial lung disease (ILD). Irradiated underlying lung volumes of more than 5 Gy, 10 Gy, 20 Gy and 30 Gy (Lung V5, V10, V20 and V30), mean lung dose and volumes of gross tumour volume (in cubic centimetre) and planning target volume were calculated for possible risk factors of RP.

RESULTS

The median follow-up period was 32 months. RP of Grade 2 or more, according to the Common Terminology Criteria for Adverse Events v. 4.0, was detected in 6 (8.4%) of the 71 cases. Grade 5 RP was identified in two cases. Of the risk factors of RP, subclinical ILD was the only factor significantly associated with the occurrence of RP of Grade 2 or more (p < 0.001). Both cases with Grade 5 RP had ILD with a honeycombing image.

CONCLUSION

Subclinical ILD was the only significant factor for Grade 2-5 RP. In addition, the cases with honeycombing had a high potential for fatality related to severe RP. Patients with subclinical ILD should be carefully monitored for the occurrence of severe RP after SBRT. Advances in knowledge: Hypofractionated SBRT for primary or metastatic lung tumours provides a high local control rate and safe treatment.

Dosimetric factors predicting radiation pneumonitis after CyberKnife stereotactic body radiotherapy for peripheral lung cancer

Objective:

The aims of this study were to investigate the frequency of symptomatic radiation pneumonitis (RP) after CyberKnife lung stereotactic body radiotherapy (SBRT) and to evaluate predictive factors of symptomatic RP.

Methods:

56 patients with peripheral non-small-cell lung cancer were treated using the CyberKnife^® VSI^™ System (Accuracy Inc., Sunnyvale, CA) between May 2013 and September 2015. Total radiation doses ranged from 48 to 56 Gy, as delivered in four equal fractions. Symptomatic RP was defined as a grade of ≥2. Predictive factors for symptomatic RP were evaluated using univariate and multivariate analyses.

Results:

With a median follow-up duration of 12.5 months (range, 3–27 months), symptomatic RP was observed in 6 (10.7%) of the 56 patients. In the univariate analysis, percent vital capacity (p < 0.05), maximum tumour diameter (p < 0.05), gross tumour volume (p < 0.05), planning target volume (p < 0.01), mean lung dose (p < 0.01) and a normal lung volume receiving 5–50 Gy of radiation (V_5–50) (p < 0.01) were identified as significant predictive factors for symptomatic RP. In the multivariate analysis, only a V₂₅ >3.4% (p = 0.011) was identified as a significant predictive factor of symptomatic RP.

Conclusion:

The incidence of symptomatic RP after CyberKnife SBRT was almost identical to the incidences reported in the linear accelerator-based SBRT. A significant association was observed between a V₂₅ >3.4% and the risk of developing symptomatic RP.

Advances in knowledge:

This is the first report that has investigated prognostic factors for symptomatic RP after CyberKnife SBRT for lung cancer. The newly developed scoring system may help to predict symptomatic RP.

A survey of changing trends in modelling radiation lung injury in mice: bringing out the good, the bad, and the uncertain

Within this millennium there has been resurgence in funding and research dealing with animal models of radiation-induced lung injury to identify and establish predictive biomarkers and effective mitigating agents that are applicable to humans. Most have been performed on mice but there needs to be assurance that the emphasis on such models is not misplaced. We therefore considered it timely to perform a comprehensive appraisal of the literature dealing with radiation lung injury of mice and to critically evaluate the validity and clinical relevance of the research. A total of 357 research papers covering the period of 1970-2015 were extensively reviewed. Whole thorax irradiation (WTI) has become the most common treatment for studying lung injury in mice and distinct trends were seen with regard to the murine strain, radiation dose, intended pathology investigated, length of study, and assays. Recently, the C57BL/6 strain has been increasingly used in the majority of these studies with the notion that they are susceptible to pulmonary fibrosis. Nonetheless, many of these investigations depend on animal survival as the primary end point and neglect the importance of radiation pneumonitis and the anomaly of lethal pleural effusions. A relatively large variation in survival times of C5BL/6 mice is also seen among different institutions pointing to the need for standardization of radiation treatments and environmental conditions. An analysis of mitigating drug treatments is complicated by the fact that the majority of studies are limited to the C57BL/6 strain with a premature termination of the experiments and do not establish whether the treatment actually prevents or simply delays the progression of radiation injury. This survey of the literature has pointed to several improvements that need to be considered in establishing a reliable preclinical murine model of radiation lung injury. The lethality end point should also be used cautiously and with greater emphasis on other assays such as non-invasive lung functional and imaging monitoring in order to quantify specific pulmonary injury that can be better extrapolated to radiation toxicity encountered in our own species.

Simple Factors Associated With Radiation-Induced Lung Toxicity After Stereotactic Body Radiation Therapy of the Thorax: A Pooled Analysis of 88 Studies

PURPOSE

To study the risk factors for radiation-induced lung toxicity (RILT) after stereotactic body radiation therapy (SBRT) of the thorax.

METHODS AND MATERIALS

Published studies on lung toxicity in patients with early-stage non-small cell lung cancer (NSCLC) or metastatic lung tumors treated with SBRT were pooled and analyzed. The primary endpoint was RILT, including pneumonitis and fibrosis. Data of RILT and risk factors were extracted from each study, and rates of grade 2 to 5 (G2+) and grade 3 to 5 (G3+) RILT were computed. Patient, tumor, and dosimetric factors were analyzed for their correlation with RILT.

RESULTS

Eighty-eight studies (7752 patients) that reported RILT incidence were eligible. The pooled rates of G2+ and G3+ RILT from all 88 studies were 9.1% (95% confidence interval [CI]: 7.15-11.4) and 1.8% (95% CI: 1.3-2.5), respectively. The median of median tumor sizes was 2.3 (range, 1.4-4.1) cm. Among the factors analyzed, older patient age (P=.044) and larger tumor size (the greatest diameter) were significantly correlated with higher rates of G2+ (P=.049) and G3+ RILT (P=.001). Patients with stage IA versus stage IB NSCLC had significantly lower risks of G2+ RILT (8.3% vs 17.1%, odds ratio = 0.43, 95% CI: 0.29-0.64, P<.0001). Among studies that provided detailed dosimetric data, the pooled analysis demonstrated a significantly higher mean lung dose (MLD) (P=.027) and V20 (P=.019) in patients with G2+ RILT than in those with grade 0 to 1 RILT.

CONCLUSIONS

The overall rate of RILT is relatively low after thoracic SBRT. Older age and larger tumor size are significant adverse risk factors for RILT. Lung dosimetry, specifically lung V20 and MLD, also significantly affect RILT risk.

Simple Factors Associated With Radiation-Induced Lung Toxicity After Stereotactic Body Radiation Therapy of the Thorax: A Pooled Analysis of 88 Studies

PURPOSE

To study the risk factors for radiation-induced lung toxicity (RILT) after stereotactic body radiation therapy (SBRT) of the thorax.

METHODS AND MATERIALS

Published studies on lung toxicity in patients with early-stage non-small cell lung cancer (NSCLC) or metastatic lung tumors treated with SBRT were pooled and analyzed. The primary endpoint was RILT, including pneumonitis and fibrosis. Data of RILT and risk factors were extracted from each study, and rates of grade 2 to 5 (G2+) and grade 3 to 5 (G3+) RILT were computed. Patient, tumor, and dosimetric factors were analyzed for their correlation with RILT.

RESULTS

Eighty-eight studies (7752 patients) that reported RILT incidence were eligible. The pooled rates of G2+ and G3+ RILT from all 88 studies were 9.1% (95% confidence interval [CI]: 7.15-11.4) and 1.8% (95% CI: 1.3-2.5), respectively. The median of median tumor sizes was 2.3 (range, 1.4-4.1) cm. Among the factors analyzed, older patient age (P=.044) and larger tumor size (the greatest diameter) were significantly correlated with higher rates of G2+ (P=.049) and G3+ RILT (P=.001). Patients with stage IA versus stage IB NSCLC had significantly lower risks of G2+ RILT (8.3% vs 17.1%, odds ratio = 0.43, 95% CI: 0.29-0.64, P<.0001). Among studies that provided detailed dosimetric data, the pooled analysis demonstrated a significantly higher mean lung dose (MLD) (P=.027) and V20 (P=.019) in patients with G2+ RILT than in those with grade 0 to 1 RILT.

CONCLUSIONS

The overall rate of RILT is relatively low after thoracic SBRT. Older age and larger tumor size are significant adverse risk factors for RILT. Lung dosimetry, specifically lung V20 and MLD, also significantly affect RILT risk.

Pulmonary dose-volume predictors of radiation pneumonitis following stereotactic body radiation therapy

PURPOSE

Radiation pneumonitis (RP) may be severe after stereotactic body radiation therapy. Our purpose was to identify pulmonary and cardiac dosimetric parameters that predicted for post-stereotactic body radiation therapy grade ≥2 RP.

METHODS AND MATERIALS

A total of 335 patients with ≥3 months' follow-up were included. Normal pulmonary volume was total lungs minus gross tumor volume. Pulmonary maximum dose, mean lung dose (MLD), and the percent of lung receiving ≥x Gy for 5 to 50 Gy in 5-Gy increments were collected. Cardiac maximum dose, mean dose, volume of lung receiving ≥0.1 Gy (V0.1), V0.25 to V1, and V2.5 to V12.5 were recorded. Multivariable logistic regression with manual backward stepwise elimination was used to identify the best dosimetric predictors of toxicity. Optimal dose-volume cutoffs were isolated with recursive partitioning analysis (RPA).

RESULTS

The grade ≥2 RP rate was 18.8%. Pulmonary V5 to V50, MLD, and cardiac V0.1 to V2.5 were significantly associated with toxicity on univariate analysis. On multivariable logistic regression, V10 was the strongest dosimetric predictor of grade ≥2 RP (odds ratio, 1.052; 95% confidence interval, 1.014-1.092; P = .007). RPA identified a 21.6% risk of grade ≥2 RP with V10 ≥6.14% (vs 3.8% with <6.14). MLD was the most significant predictor of grade ≥3 RP (odds ratio, 1.002; 95% confidence interval, 1.000-1.003; P = .031). RPA identified a 25.0% risk of grade ≥3 RP with MLD ≥7.84 Gy (vs 8.0% when <7.84 Gy).

CONCLUSIONS

With a grade ≥2 RP rate of 18.8%, lung V10 was the best predictor of grade ≥2 toxicity. MLD was the best predictor of grade ≥3 RP.

Impact of Preexisting Interstitial Lung Disease on Acute, Extensive Radiation Pneumonitis: Retrospective Analysis of Patients with Lung Cancer

INTRODUCTION

This study investigated the clinical characteristics and predictive factors for developing acute extended radiation pneumonitis with a focus on the presence and radiological characteristics of preexisting interstitial lung disease.

METHODS

Of 1429 irradiations for lung cancer from May 2006 to August 2013, we reviewed 651 irradiations involving the lung field. The presence, compatibility with usual interstitial pneumonia, and occupying area of preexisting interstitial lung disease were retrospectively evaluated by pretreatment computed tomography. Cases of non-infectious, non-cardiogenic, acute respiratory failure with an extended bilateral shadow developing within 30 days after the last irradiation were defined as acute extended radiation pneumonitis.

RESULTS

Nine (1.4%) patients developed acute extended radiation pneumonitis a mean of 6.7 days after the last irradiation. Although preexisting interstitial lung disease was found in 13% of patients (84 patients), 78% of patients (7 patients) with acute extended radiation pneumonitis cases had preexisting interstitial lung disease, which resulted in incidences of acute extended radiation pneumonitis of 0.35 and 8.3% in patients without and with preexisting interstitial lung disease, respectively. Multivariate logistic analysis indicated that the presence of preexisting interstitial lung disease (odds ratio = 22.6; 95% confidence interval = 5.29-155; p < 0.001) and performance status (≥2; odds ratio = 4.22; 95% confidence interval = 1.06-20.8; p = 0.049) were significant predictive factors. Further analysis of the 84 patients with preexisting interstitial lung disease revealed that involvement of more than 10% of the lung field was the only independent predictive factor associated with the risk of acute extended radiation pneumonitis (odds ratio = 6.14; 95% confidence interval = 1.0-37.4); p = 0.038).

CONCLUSIONS

Pretreatment computed tomography evaluations of the presence of and area size occupied by preexisting interstitial lung disease should be assessed for safer irradiation of areas involving the lung field.

Renin-Angiotensin System Inhibitors Might Help to Reduce the Development of Symptomatic Radiation Pneumonitis After Stereotactic Body Radiotherapy for Lung Cancer

INTRODUCTION

The purpose of the present study was to evaluate the role of renin-angiotensin system (RAS) inhibitors in preventing symptomatic radiation pneumonitis (RP) after stereotactic body radiotherapy (SBRT).

MATERIALS AND METHODS

The data from 158 patients with a solitary lung lesion treated with 1 to 3 fractions of SBRT from December 2008 to July 2014 were retrospectively analyzed. The incidence of RP was evaluated according to the Common Toxicity Criteria for Adverse Events, version 4. The use of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) was analyzed to assess for possible correlations with the development of grade ≥ 2 RP. The patient and dosimetric variables were also assessed.

RESULTS

After a median follow-up period of 13.8 months (range, 3.2-55.0 months), 22 patients had developed grade ≥ 2 RP. Patients with peripheral lesions, favorable dosimetric data, and ACEI and/or ARB use had a reduced risk of symptomatic RP. In unadjusted and adjusted multivariate analyses, ACEI and/or ARB intake and the dosimetric variables were statistically significant factors. In a secondary analysis, the use of ACEIs and ARBs among patients with a greater planning target volume and higher dosimetric values correlated with a reduced risk of symptomatic RP.

CONCLUSION

The use of a RAS inhibitor was associated with a decreased incidence of symptomatic RP among patients undergoing SBRT for lung lesions. Patients with higher dosimetric values had a reduced risk of grade ≥ 2 RP with ACEI and ARB use.

Angiotensin-converting enzyme inhibitors decrease the risk of radiation pneumonitis after stereotactic body radiation therapy

PURPOSE

Although angiotensin-converting enzyme (ACE) inhibitor use during conventionally fractionated radiation therapy has been associated with a decreased risk of radiation pneumonitis (RP), a similar effect has not been demonstrated in stereotactic body radiation therapy (SBRT). The purpose of this study was to examine the impact of ACE inhibitor use during SBRT on the risk of symptomatic (grade ≥2) RP.

METHODS AND MATERIALS

Patients with at least 1 follow-up treated with SBRT for primary lung cancer were included. ACE inhibitors, angiotensin receptor blockers, statins, nonsteroidal anti-inflammatory drugs, and glucocorticoids were examined. RP was determined from all available medical records, including follow-up appointments with radiation oncology, pulmonology, medical oncology, and hospitalizations. It was scored with the Common Terminology Criteria for Adverse Events, version 4.0. Analysis was performed with Kaplan-Meier and Cox proportional hazards modeling.

RESULTS

A total of 257 patients met inclusion criteria. Seventy (27.2%) used an ACE inhibitor during SBRT. The overall rates of grade ≥2 and ≥3 RP were 19.1% (n = 49) and 7.0% (n = 18), respectively. ACE inhibitor users experienced greater freedom from symptomatic RP on univariate (vs nonusers, 89.8% vs 76.3% at 12 months, P = .029) and multivariate analysis (hazard ratio 0.373, 95% confidence interval 0.156-0.891, P =.026). The volume of normal lung tissue receiving ≥5 Gy, %, ≥10 Gy, ≥20 Gy, and mean lung dose were also significantly associated with RP on univariate and multivariate analysis. ACE inhibitor use was not associated with overall survival. Angiotensin receptor blockers, nonsteroidal anti-inflammatory drugs, glucocorticoids, and statin administration were not associated with symptomatic RP or survival.

CONCLUSIONS

ACE inhibitor use during SBRT was associated with significantly greater freedom from grade ≥2 RP, even after adjusting for pulmonary dose. Given the data on their protective effect in human and animal models, a prospective evaluation is warranted.

Complications from Stereotactic Body Radiotherapy for Lung Cancer

Stereotactic body radiotherapy (SBRT) has become a standard treatment option for early stage, node negative non-small cell lung cancer (NSCLC) in patients who are either medically inoperable or refuse surgical resection. SBRT has high local control rates and a favorable toxicity profile relative to other surgical and non-surgical approaches. Given the excellent tumor control rates and increasing utilization of SBRT, recent efforts have focused on limiting toxicity while expanding treatment to increasingly complex patients. We review toxicities from SBRT for lung cancer, including central airway, esophageal, vascular (e.g., aorta), lung parenchyma (e.g., radiation pneumonitis), and chest wall toxicities, as well as radiation-induced neuropathies (e.g., brachial plexus, vagus nerve and recurrent laryngeal nerve). We summarize patient-related, tumor-related, dosimetric characteristics of these toxicities, review published dose constraints, and propose strategies to reduce such complications.

Influence of liver toxicities on prognosis after stereotactic body radiation therapy for hepatocellular carcinoma

AIM

To better define clinically relevant non-classic radiation-induced liver disease (RILD) following stereotactic body radiotherapy (SBRT) in patients with small hepatocellular carcinoma (HCC).

METHODS

We retrospectively evaluated the influence of acute liver toxicities on fatal hepatic failure in HCC patients treated with SBRT. Between April 2006 and February 2012, 194 HCC were treated with SBRT. Among them, patients followed up for more than 6 months were eligible. Laboratory results and Child-Pugh (CP) scores were obtained before treatment and at monthly follow-up visits. Toxicities were evaluated by the Common Terminology Criteria for Adverse Events version 4.0. Possible definitions of RILD were evaluated with respect to fatal hepatic failure within 12 months.

RESULTS

One hundred and eighty HCC were evaluated with a median follow-up of 28.2 months. Fatal hepatic failure within 12 months occurred in eight patients (4%). On univariate analysis, grade 3 or more elevated transaminases, CP score of 8 or more, and/or grade 3 or more decreased platelet count significantly predicted fatal hepatic failure within 12 months. Combinations of these factors (i.e. having at least one criterion) also predicted fatal hepatic failure within 12 months (16% with criteria vs 1% without criteria). Two-year overall survival rates for patients with and without RILD was 64.9% and 83.8% (P < 0.001), respectively.

CONCLUSION

We identified three criteria that affected overall survival in HCC patients treated with SBRT. Further prospective studies are warranted to validate the safety and effect of SBRT for HCC.

Stereotactic body radiotherapy with helical TomoTherapy for medically inoperable early stage primary and second-primary non-small-cell lung neoplasm: 1-year outcome and toxicity analysis

OBJECTIVE

This study investigated the effectiveness of stereotactic body radiotherapy with helical TomoTherapy (T-SBRT) for treating medically inoperable primary and second-primary early stage non-small-cell lung neoplasm (SPLN) and evaluated whether the movement of organizing pneumonia (OP) within the irradiation field (IF) can be detected via analysis of radiological changes.

METHODS

Patients (n = 16) treated for 1 year (2011-12) at our hospital by T-SBRT at a total dose of 60 Gy in five fractions were examined retrospectively. Outcome and toxicity were recorded and were separately described for SPLN. CT scans were reviewed by a single radiologist.

RESULTS

Of the 16 patients, 5 (31.3%) had primary lung malignancies, 10 (62.5%) had SPLN, and 1 case (6.3%) had isolated mediastinal metastasis of lung neoplasm. Pathological evidence was obtained for 72.2% of all lesions. The median radiological follow-up was 11 months (10.5 months for SPLN). For all cases, the 6- and 12-month survival rates were 100% and 77.7% (100% and 71.4%, respectively, for SPLN), and the 6- and 12-month locoregional control rates were 100% in all cases. 2 (12.5%) of 16 patients developed grade 3 late transient radiation pneumonitis following steroid therapy and 1 (6.3%) presented asymptomatic infiltrates comparable to OP opacities.

CONCLUSION

T-SBRT seems to be safe and effective.

ADVANCES IN KNOWLEDGE

Mild OP is likely associated with radiation-induced anomalies in the IF, identification of migrating opacities can help discern relapse of radiation-induced opacities.

Outcomes of stereotactic body radiotherapy (SBRT) treatment of multiple synchronous and recurrent lung nodules

Background

Stereotactic body radiotherapy (SBRT) is evolving into a standard of care for unresectable lung nodules. Local control has been shown to be in excess of 90% at 3 years. However, some patients present with synchronous lung nodules in the ipsilateral or contralateral lobe or metasynchronous disease. In these cases, patients may receive multiple courses of lung SBRT or a single course for synchronous nodules. The toxicity of such treatment is currently unknown.

Methods

Between 2006 and 2012, 63 subjects with 128 metasynchronous and synchronous lung nodules were treated at the Mayo Clinic with SBRT. Demographic patient data and dosimetric data regarding SBRT treatments were collected. Acute toxicity (defined as toxicity < 90 days) and late toxicity (defined as toxicity > = 90 days) were reported and graded as per standardized CTCAE 4.0 criteria. Local control, progression free survival and overall survival were also described.

Results

The median age of patients treated was 73 years. Sixty five percent were primary or recurrent lung cancers with the remainder metastatic lung nodules of varying histologies. Of 63 patients, 18 had prior high dose external beam radiation to the mediastinum or chest. Dose and fractionation varied but the most common prescriptions were 48 Gy/4 fractions, 54 Gy/3 fractions, and 50 Gy/5 fractions. Only 6 patients demonstrated local recurrence. With a median follow up of 12.6 months, median SBRT specific overall survival and progression free survival were 35.7 months and 10.7 months respectively. Fifty one percent (32/63 patients) experienced acute toxicity, predominantly grade 1 and 2 fatigue. One patient developed acute grade 3 radiation pneumonitis at 75 days. Forty six percent (29/63 patients) developed late effects. Most were grade 1 dyspnea. There was one patient with grade 5 pneumonitis.

Conclusion

Multiple courses of SBRT and SBRT delivery after external beam radiotherapy appear to be feasible and safe. Most toxicity was grade 1 and 2 but the risk was approximately 50% for both acute and late effects.

Feasibility study of stereotactic body radiotherapy for peripheral lung tumors with a maximum dose of 100 Gy in five fractions and a heterogeneous dose distribution in the planning target volume

We evaluated toxicity and outcomes for patients with peripheral lung tumors treated with stereotactic body radiation therapy (SBRT) in a dose-escalation and dose-convergence study. A total of 15 patients were enrolled. SBRT was performed with 60 Gy in 5 fractions (fr.) prescribed to the 60% isodose line of maximum dose, which was 100 Gy in 5 fr., covering the planning target volume (PTV) surface (60 Gy/5 fr. - (60%-isodose)) using dynamic conformal multiple arc therapy (DCMAT). The primary endpoint was radiation pneumonitis (RP) ≥ Grade 2 within 6 months. Toxicities were graded according to the Common Terminology Criteria for Adverse Events, version 4.0. Using dose-volumetric analysis, the trial regimen of 60 Gy/5 fr. - (60%-isodose) was compared with our institutional conventional regimen of 50 Gy/5 fr. - (80%-isodose). The enrolled consecutive patients had either a solitary peripheral tumor or two ipsilateral tumors. The median follow-up duration was 22.0 (12.0-27.0) months. After 6 months post-SBRT, the respective number of RP Grade 0, 1 and 2 cases was 5, 9 and 1. In the Grade 2 RP patient, the image showed an organizing pneumonia pattern at 6.0 months post-SBRT. No other toxicity was found. At last follow-up, there was no evidence of recurrence of the treated tumors. The target volumes of 60 Gy/ 5 fr. - (60%-isodose) were irradiated with a significantly higher dose than those of 50 Gy/5 fr. - (80%-isodose), while the former dosimetric parameters of normal lung were almost equivalent to the latter. SBRT with 60 Gy/5 fr. - (60%-isodose) using DCMAT allowed the delivery of very high and convergent doses to peripheral lung tumors with feasibility in the acute and subacute phases. Further follow-up is required to assess for late toxicity.

ATM polymorphisms predict severe radiation pneumonitis in patients with non-small cell lung cancer treated with definitive radiation therapy

PURPOSE

The ataxia telangiectasia mutated (ATM) gene mediates detection and repair of DNA damage. We investigated associations between ATM polymorphisms and severe radiation-induced pneumonitis (RP).

METHODS AND MATERIALS

We genotyped 3 potentially functional single nucleotide polymorphisms (SNPs) of ATM (rs1801516 [D1853N/5557G>A], rs189037 [-111G>A] and rs228590) in 362 patients with non-small cell lung cancer (NSCLC), who received definitive (chemo)radiation therapy. The cumulative severe RP probabilities by genotypes were evaluated using the Kaplan-Meier analysis. The associations between severe RP risk and genotypes were assessed by both logistic regression analysis and Cox proportional hazard model with time to event considered.

RESULTS

Of 362 patients (72.4% of non-Hispanic whites), 56 (15.5%) experienced grade ≥3 RP. Patients carrying ATM rs189037 AG/GG or rs228590 TT/CT genotypes or rs189037G/rs228590T/rs1801516G (G-T-G) haplotype had a lower risk of severe RP (rs189037: GG/AG vs AA, adjusted hazard ratio [HR] = 0.49, 95% confidence interval [CI], 0.29-0.83, P=.009; rs228590: TT/CT vs CC, HR=0.57, 95% CI, 0.33-0.97, P=.036; haplotype: G-T-G vs A-C-G, HR=0.52, 95% CI, 0.35-0.79, P=.002). Such positive findings remained in non-Hispanic whites.

CONCLUSIONS

ATM polymorphisms may serve as biomarkers for susceptibility to severe RP in non-Hispanic whites. Large prospective studies are required to confirm our findings.