Lung perfusion imaging can risk stratify lung cancer patients for the development of pulmonary complications after chemoradiation

MRI-based ventilation and perfusion imaging to predict radiation-induced pneumonitis in lung tumor patients at a 0.35T MR-Linac

BACKGROUND AND PURPOSE

Radiation-induced pneumonitis (RP), diagnosed 6-12 weeks after treatment, is a complication of lung tumor radiotherapy. So far, clinical and dosimetric parameters have not been reliable in predicting RP. We propose using non-contrast enhanced magnetic resonance imaging (MRI) based functional parameters acquired over the treatment course for patient stratification for improved follow-up.

MATERIALS AND METHODS

23 lung tumor patients received MR-guided hypofractionated stereotactic body radiation therapy at a 0.35T MR-Linac. Ventilation- and perfusion-maps were generated from 2D-cine MRI-scans acquired after the first and last treatment fraction (Fx) using non-uniform Fourier decomposition. The relative differences in ventilation and perfusion between last and first Fx in three regions (planning target volume (PTV), lung volume receiving more than 20Gy (V20) excluding PTV, whole tumor-bearing lung excluding PTV) and three dosimetric parameters (mean lung dose, V20, mean dose to the gross tumor volume) were investigated. Univariate receiver operating characteristic curve - area under the curve (ROC-AUC) analysis was performed (endpoint RP grade≥1) using 5000 bootstrapping samples. Differences between RP and non-RP patients were tested for statistical significance with the non-parametric Mann-Whitney U test (α=0.05).

RESULTS

14/23 patients developed RP of grade≥1 within 3 months. The dosimetric parameters showed no significant differences between RP and non-RP patients. In contrast, the functional parameters, especially the relative ventilation difference in the PTV, achieved a p-value<0.05 and an AUC value of 0.84.

CONCLUSION

MRI-based functional parameters extracted from 2D-cine MRI-scans were found to be predictive of RP development in lung tumor patients.

Incorporation of Functional Lung Imaging Into Radiation Therapy Planning in Patients With Lung Cancer: A Systematic Review and Meta-Analysis

Our purpose was to provide an understanding of current functional lung imaging (FLI) techniques and their potential to improve dosimetry and outcomes for patients with lung cancer receiving radiation therapy (RT). Excerpta Medica dataBASE (EMBASE), PubMed, and Cochrane Library were searched from 1990 until April 2023. Articles were included if they reported on FLI in one of: techniques, incorporation into RT planning for lung cancer, or quantification of RT-related outcomes for patients with lung cancer. Studies involving all RT modalities, including stereotactic body RT and particle therapy, were included. Meta-analyses were conducted to investigate differences in dose-function parameters between anatomic and functional RT planning techniques, as well as to investigate correlations of dose-function parameters with grade 2+ radiation pneumonitis (RP). One hundred seventy-eight studies were included in the narrative synthesis. We report on FLI modalities, dose-response quantification, functional lung (FL) definitions, FL avoidance techniques, and correlations between FL irradiation and toxicity. Meta-analysis results show that FL avoidance planning gives statistically significant absolute reductions of 3.22% to the fraction of well-ventilated lung receiving 20 Gy or more, 3.52% to the fraction of well-perfused lung receiving 20 Gy or more, 1.3 Gy to the mean dose to the well-ventilated lung, and 2.41 Gy to the mean dose to the well-perfused lung. Increases in the threshold value for defining FL are associated with decreases in functional parameters. For intensity modulated RT and volumetric modulated arc therapy, avoidance planning results in a 13% rate of grade 2+ RP, which is reduced compared with results from conventional planning cohorts. A trend of increased predictive ability for grade 2+ RP was seen in models using FL information but was not statistically significant. FLI shows promise as a method to spare FL during thoracic RT, but interventional trials related to FL avoidance planning are sparse. Such trials are critical to understanding the effect of FL avoidance planning on toxicity reduction and patient outcomes.

Comparison of dual-energy CT with positron emission tomography for lung perfusion imaging in patients with non-small cell lung cancer

Objective.Functional lung avoidance (FLA) radiotherapy treatment aims to spare lung regions identified as functional from imaging. Perfusion contributes to lung function and can be measured from the determination of pulmonary blood volume (PBV). An advantageous alternative to the current determination of PBV from positron emission tomography (PET) may be from dual energy CT (DECT), due to shorter examination time and widespread availability. This study aims to determine the correlation between PBV determined from DECT and PET in the context of FLA radiotherapy.Approach.DECT and PET acquisitions at baseline of patients enrolled in the HI-FIVE clinical trial (ID: NCT03569072) were reviewed. Determination of PBV from PET imaging (PBVPET), from DECT imaging generated from a commercial software (Syngo.via, Siemens Healthineers, Forchheim, Germany) with its lowest (PBVsyngoR=1) and highest (PBVsyngoR=10) smoothing level parameter value (R), and from a two-material decomposition (TMD) method (PBVTMDL) with variable median filter kernel size (L) were compared. Deformable image registration between DECT images and the CT component of the PET/CT was applied to PBV maps before resampling to the PET resolution. The Spearman correlation coefficient (r_s) between PBV determinations was calculated voxel-wise in lung subvolumes.Main results.Of this cohort of 19 patients, 17 had a DECT acquisition at baseline. PBV maps determined from the commercial software and the TMD method were very strongly correlated [r_s(PBVsyngoR=1,PBVTMDL=1) = 0.94 ± 0.01 andr_s(PBVsyngoR=10,PBVTMDL=9) = 0.94 ± 0.02].PBVPETwas strongly correlated withPBVTMDL[r_s(PBVPET,PBVTMDL=28) = 0.67 ± 0.11]. Perfusion patterns differed along the posterior-anterior direction [r_s(PBVPET,PBVTMDL=28) = 0.77 ± 0.13/0.57 ± 0.16 in the anterior/posterior region].Significance. A strong correlation between DECT and PET determination of PBV was observed. Streak and smoothing effects in DECT and gravitational artefacts and misregistration in PET reduced the correlation posteriorly.

Functional lung volume mapping with perfusion Single-Photon Emission Computed Tomography scan for radiotherapy planning in patients with locally advanced nonsmall cell lung cancer

OBJECTIVES

Radical chemotherapy-radiotherapy represents the standard treatment for locally-advanced nonsmall cell lung cancer (NSCLC). Conventional radiotherapy achieves limited local tumor control, but dose escalation to the primary tumor is prevented by radiotherapy-induced toxicity. The aim of this study was to evaluate feasibility of tailored intensity-modulated radiotherapy (IMRT) planning based on lung single-photon emission computed tomography (SPECT) perfusion data and to compare functional and conventional dose-volume parameters.

METHODS

A total of 21 patients were prospectively enrolled. Patients underwent IMRT treatment with 2 Gy/fraction (median total dose of 60 Gy). Lung perfusion SPECT images were acquired before radiotherapy and 3 and 6 months after radiotherapy completion. SPECT and planning computed tomography images were co-registered using MIM-MAESTRO software with 3D-PET Edge algorithm. Lung volumes were defined anatomically as total lung and functionally as total not functional lung and total functional lung. Dose-volume histograms were calculated using QUANTEC constraints [mean lung dose (MLD)<20 Gy, V20<20%]. For each patient, conventional and functional radiotherapy plans were generated and compared.

RESULTS

A total of 19 of 21 patients with NSCLC were included (mean age 66 years, 11 stage IIIA, 8 stage IIIB), 12/19 patients completed the 6-months follow-up. A significant reduction of mean V20 was observed in functional radiotherapy planning compared to conventional plan (405.9 cc, P < 0.001). Mean MLD was also lower in the SPECT-based plans, but the difference was not statistically relevant (0.8 Gy, P = 0.299). G2 radiation pneumonitis was observed in two patients.

CONCLUSIONS

Functional radiotherapy planning allowed to decrease functional lung irradiation compared to conventional planning. The possibility to limit radiotherapy-induced toxicity could allow us to perform an effective dose-escalation to target volume.

The increasing potential of nuclear medicine imaging for the evaluation and reduction of normal tissue toxicity from radiation treatments

Radiation therapy is an effective treatment modality for a variety of cancers. Despite several advances in delivery techniques, its main drawback remains the deposition of dose in normal tissues which can result in toxicity. Common practices of evaluating toxicity, using questionnaires and grading systems, provide little underlying information beyond subjective scores, and this can limit further optimization of treatment strategies. Nuclear medicine imaging techniques can be utilised to directly measure regional baseline function and function loss from internal/external radiation therapy within normal tissues in an in vivo setting with high spatial resolution. This can be correlated with dose delivered by radiotherapy techniques to establish objective dose-effect relationships, and can also be used in the treatment planning step to spare normal tissues more efficiently. Toxicity in radionuclide therapy typically occurs due to undesired off-target uptake in normal tissues. Molecular imaging using diagnostic analogues of therapeutic radionuclides can be used to test various interventional protective strategies that can potentially reduce this normal tissue uptake without compromising tumour uptake. We provide an overview of the existing literature on these applications of nuclear medicine imaging in diverse normal tissue types utilising various tracers, and discuss its future potential.

Variations Between Dose-Ventilation and Dose-Perfusion Metrics in Radiation Therapy Planning for Lung Cancer

Purpose

Currently, several active clinical trials of functional lung avoidance radiation therapy using different imaging modalities for ventilation or perfusion are underway. Patients with lung cancer often show ventilation-perfusion mismatch, whereas the significance of dose-function metric remains unclear. The aim of the present study was to compare dose-ventilation metrics with dose-perfusion metrics for radiation therapy plan evaluation.

Methods and Materials

Pretreatment 4-dimensional computed tomography and ^99mTc-macroaggregated albumin single-photon emission computed tomography perfusion images of 60 patients with lung cancer treated with radiation therapy were analyzed. Ventilation images were created using the deformable image registration of 4-dimensional computed tomography image sets and image analysis for regional volume changes as a surrogate for ventilation. Ventilation and perfusion images were converted into percentile distribution images. Analyses included Pearson’s correlation coefficient and comparison of agreements between the following dose-ventilation and dose-perfusion metrics: functional mean lung dose and functional percent lung function receiving 5, 10, 20, 30, and 40 Gy (fV₅, fV₁₀, fV₂₀, fV₃₀, and fV₄₀, respectively).

Results

Overall, the dose-ventilation metrics were greater than the dose-perfusion metrics (ie, fV₂₀, 26.3% ± 9.9% vs 23.9% ± 9.8%). Correlations between the dose-ventilation and dose-perfusion metrics were strong (range, r = 0.94-0.97), whereas the agreements widely varied among patients, with differences as large as 6.6 Gy for functional mean lung dose and 11.1% for fV₂₀. Paired t test indicated that the dose-ventilation and dose-perfusion metrics were significantly different.

Conclusions

Strong correlations were present between the dose-ventilation and dose-perfusion metrics. However, the agreement between the dose-ventilation and dose-perfusion metrics widely varied among patients, suggesting that ventilation-based radiation therapy plan evaluation may not be comparable to that based on perfusion. Future studies should elucidate the correlation of dose-function metrics with clinical pulmonary toxicity metrics.

Comparison of regional lung perfusion response on longitudinal MAA SPECT/CT in lung cancer patients treated with and without functional tissue-avoidance radiation therapy

OBJECTIVE

The effect of functional lung avoidance planning on radiation dose-dependent changes in regional lung perfusion is unknown. We characterized dose-perfusion response on longitudinal perfusion single photon emission computed tomography (SPECT)/CT in two cohorts of lung cancer patients treated with and without functional lung avoidance techniques.

METHODS

The study included 28 primary lung cancer patients: 20 from interventional (NCT02773238) (FLARE-RT) and eight from observational (NCT01982123) (LUNG-RT) clinical trials. FLARE-RT treatment plans included perfused lung dose constraints while LUNG-RT plans adhered to clinical standards. Pre- and 3 month post-treatment macro-aggregated albumin (MAA) SPECT/CT scans were rigidly co-registered to planning four-dimensional CT scans. Tumour-subtracted lung dose was converted to EQD2 and sorted into 5 Gy bins. Mean dose and percent change between pre/post-RT MAA-SPECT uptake (%ΔPERF), normalized to total tumour-subtracted lung uptake, were calculated in each binned dose region. Perfusion frequency histograms of pre/post-RT MAA-SPECT were analyzed. Dose-response data were parameterized by sigmoid logistic functions to estimate maximum perfusion increase (%ΔPERFmaxincrease), maximum perfusion decrease (%ΔPERFmaxdecrease), dose midpoint (Dmid), and dose-response slope (k).

RESULTS

Differences in MAA perfusion frequency distribution shape between time points were observed in 11/20 (55%) FLARE-RT and 2/8 (25%) LUNG-RT patients (p < 0.05). FLARE-RT dose response was characterized by >10% perfusion increase in the 0-5 Gy dose bin for 8/20 patients (%ΔPERFmaxincrease = 10-40%), which was not observed in any LUNG-RT patients (p = 0.03). The dose midpoint Dmid at which relative perfusion declined by 50% trended higher in FLARE-RT compared to LUNG-RT cohorts (35 GyEQD2 vs 21 GyEQD2, p = 0.09), while the dose-response slope k was similar between FLARE-RT and LUNG-RT cohorts (3.1-3.2, p = 0.86).

CONCLUSION

Functional lung avoidance planning may promote increased post-treatment perfusion in low dose regions for select patients, though inter-patient variability remains high in unbalanced cohorts. These preliminary findings form testable hypotheses that warrant subsequent validation in larger cohorts within randomized or case-matched control investigations.

ADVANCES IN KNOWLEDGE

This novel preliminary study reports differences in dose-response relationships between patients receiving functional lung avoidance radiation therapy (FLARE-RT) and those receiving conventionally planned radiation therapy (LUNG-RT). Following further validation and testing of these effects in larger patient populations, individualized estimation of regional lung perfusion dose-response may help refine future risk-adaptive strategies to minimize lung function deficits and toxicity incidence.

Evaluation of lung toxicity risk with computed tomography ventilation image for thoracic cancer patients

Background

Four-dimensional computed tomography (4D-CT) ventilation is an emerging imaging modality. Functional avoidance of regions according to 4D-CT ventilation may reduce lung toxicity after radiation therapy. This study evaluated associations between 4D-CT ventilation-based dosimetric parameters and clinical outcomes.

Methods

Pre-treatment 4D-CT data were used to retrospectively construct ventilation images for 40 thoracic cancer patients retrospectively. Fifteen patients were treated with conventional radiation therapy, 6 patients with hyperfractionated radiation therapy and 19 patients with stereotactic body radiation therapy (SBRT). Ventilation images were calculated from 4D-CT data using a deformable image registration and Jacobian-based algorithm. Each ventilation map was normalized by converting it to percentile images. Ventilation-based dosimetric parameters (Mean Dose, V5 [percent lung volume receiving ≥5 Gy], and V20 [percent lung volume receiving ≥20 Gy]) were calculated for highly and poorly ventilated regions. To test whether the ventilation-based dosimetric parameters could be used predict radiation pneumonitis of ≥Grade 2, the area under the curve (AUC) was determined from the receiver operating characteristic analysis.

Results

For Mean Dose, poorly ventilated lung regions in the 0–30% range showed the highest AUC value (0.809; 95% confidence interval [CI], 0.663–0.955). For V20, poorly ventilated lung regions in the 0–20% range had the highest AUC value (0.774; 95% [CI], 0.598–0.915), and for V5, poorly ventilated lung regions in the 0–30% range had the highest AUC value (0.843; 95% [CI], 0.732–0.954). The highest AUC values for Mean Dose, V20, and V5 were obtained in poorly ventilated regions. There were significant differences in all dosimetric parameters between radiation pneumonitis of Grade 1 and Grade ≥2.

Conclusions

Poorly ventilated lung regions identified on 4D-CT had higher AUC values than highly ventilated regions, suggesting that functional planning based on poorly ventilated regions may reduce the risk of lung toxicity in radiation therapy.

Quantitation of Perfused Lung Volume Using Hybrid SPECT/CT Allows Refining the Assessment of Lung Perfusion and Estimating Disease Extent in Chronic Thromboembolic Pulmonary Hypertension

BACKGROUND

We evaluated the feasibility of perfusion SPECT/CT for providing quantitative data for estimation of perfusion defect extent in chronic thromboembolic pulmonary hypertension (CTEPH).

METHODS

Thirty patients with CTEPH underwent Tc-human serum albumin lung perfusion SPECT/CT. Perfusion defects were quantified using 3 different methods: (1) visual, semiquantitative scoring of perfusion defect extent in each lung segment, (2) threshold-based segmentation of perfused lung volumes, and (3) threshold-based segmentation of perfused lung volumes divided by segmented lung volumes at CT (perfusion index). Imaging findings were correlated with right-sided heart catheterization results and N-terminal pro-B-type natriuretic peptide. Receiver operating characteristic analysis was performed to identify SPECT thresholds for mean pulmonary arterial pressure (PAPm) greater than 50 mm Hg.

RESULTS

Assessment of lung perfusion provided similar results using all 3 methods. The perfusion defect score correlated with PAPm (rs = 0.60, P = 0.0005) and was associated with serum levels of N-terminal pro-B-type natriuretic peptide (rs = 0.37, P = 0.04). Perfused lung volume (40% threshold, rs = -0.48, P = 0.007) and perfusion index (40% threshold, rs = -0.50, P = 0.005) decreased as PAPm increased. Receiver operating characteristic analysis showed that perfusion defect score (sensitivity, 88%; specificity, 77%; area under the curve [AUC] = 0.89, P = 0.001), perfused lung volume (sensitivity, 88%; specificity, 64%; AUC = 0.80, P = 0.01), and perfusion index (sensitivity, 88%; specificity, 64%; AUC = 0.82, P = 0.009) could identify patients with PAPm of greater than 50 mm Hg.

CONCLUSIONS

Quantitative analysis of perfusion defects at SPECT is feasible, provides a measure of disease severity, and correlates with established clinical parameters. Quantitation of perfusion SPECT may refine the diagnostic approach in CTEPH providing a quantitative imaging biomarker, for example, for therapy monitoring.

Functional lung imaging in radiation therapy for lung cancer: A systematic review and meta-analysis

RATIONALE

Advanced imaging techniques allow functional information to be derived and integrated into treatment planning.

METHODS

A systematic review was conducted with the primary objective to evaluate the ability of functional lung imaging to predict risk of radiation pneumonitis. Secondary objectives were to evaluate dose-response relationships on post treatment functional imaging and assess the utility in including functional lung information into treatment planning. A structured search for publications was performed following PRISMA guidelines and registered on PROSPERO.

RESULTS

814 articles were screened against review criteria and 114 publications met criteria. Methods of identifying functional lung included using CT, MRI, SPECT and PET to image ventilation or perfusion. Six studies compared differences between functional and anatomical lung imaging at predicting radiation pneumonitis. These found higher predictive values using functional lung imaging. Twenty-one studies identified a dose-response relationship on post-treatment functional lung imaging. Nineteen planning studies demonstrated the ability of functional lung optimised planning techniques to spare regions of functional lung. Meta-analysis of these studies found that mean (95% CI) functional volume receiving 20 Gy was reduced by 4.2% [95% CI: 2.3: 6.0] and mean lung dose by 2.2 Gy [95% CI: 1.2: 3.3] when plans were optimised to spare functional lung. There was significant variation between publications in the definition of functional lung.

CONCLUSION

Functional lung imaging may have potential utility in radiation therapy planning and delivery, although significant heterogeneity was identified in approaches and reporting. Recommendations have been made based on the available evidence for future functional lung trials.

Assessing lung function using contrast-enhanced dual-energy computed tomography for potential applications in radiation therapy

PURPOSE

There is an increasing interest in the evaluation of lung function from physiological images in radiation therapy treatment planning to reduce the extent of postradiation toxicities. The purpose of this work was to retrieve reliable functional information from contrast-enhanced dual-energy computed tomography (DECT) for new applications in radiation therapy. The functional information obtained by DECT is also compared with other methods using single-energy CT (SECT) and single-photon emission computed tomography (SPECT) with CT. The differential function between left and right lung, as well as between lobes is computed for all methods.

METHODS

Five lung cancer patients were retrospectively selected for this study; each underwent a SPECT/CT scan and a contrast-injected DECT scan, using 100 and 140 Sn kVp. The DECT images are postprocessed into iodine concentration maps, which are further used to determine the perfused blood volume. These maps are calculated in two steps: (a) a DECT stoichiometric calibration adapted to the presence of iodine and followed by (b) a two-material decomposition technique. The functional information from SECT is assumed proportional to the HU numbers from a mixed CT image. The functional data from SPECT/CT are considered proportional to the number of counts. A radiation oncologist segmented the entire lung volume into five lobes on both mixed CT images and low-dose CT images from SPECT/CT to allow a regional comparison. The differential function for each subvolume is computed relative to the entire lung volume.

RESULTS

The differential function per lobe derived from SPECT/CT correlates strongly with DECT (Pearson's coefficient r = 0.91) and moderately with SECT (r = 0.46). The differential function for the left lung shows a mean difference of 7% between SPECT/CT and DECT; and 17% between SPECT/CT and SECT. The presence of nonfunctional areas, such as localized emphysema or a lung tumor, is reflected by an intensity drop in the iodine concentration maps. Functional dose volume histograms (fDVH) are also generated for two patients as a proof of concept.

CONCLUSION

The extraction of iodine concentration maps from a contrast-enhanced DECT scan is achieved to compute the differential function for each lung subvolume and good agreement is found in respect to SPECT/CT. One promising avenue in radiation therapy is to include such functional information during treatment planning dose optimization to spare functional lung tissues.

Single-energy computed tomography-based pulmonary perfusion imaging: Proof-of-principle in a canine model

Purpose:

Radiotherapy (RT) that selectively avoids irradiating highly functional lung regions may reduce pulmonary toxicity, which is substantial in lung cancer RT. Single-energy computed tomography (CT) pulmonary perfusion imaging has several advantages (e.g., higher resolution) over other modalities and has great potential for widespread clinical implementation, particularly in RT. The purpose of this study was to establish proof-of-principle for single-energy CT perfusion imaging.

Methods:

Single-energy CT perfusion imaging is based on the following: (1) acquisition of end-inspiratory breath-hold CT scans before and after intravenous injection of iodinated contrast agents, (2) deformable image registration (DIR) for spatial mapping of those two CT image data sets, and (3) subtraction of the precontrast image data set from the postcontrast image data set, yielding a map of regional Hounsfield unit (HU) enhancement, a surrogate for regional perfusion. In a protocol approved by the institutional animal care and use committee, the authors acquired CT scans in the prone position for a total of 14 anesthetized canines (seven canines with normal lungs and seven canines with diseased lungs). The elastix algorithm was used for DIR. The accuracy of DIR was evaluated based on the target registration error (TRE) of 50 anatomic pulmonary landmarks per subject for 10 randomly selected subjects as well as on singularities (i.e., regions where the displacement vector field is not bijective). Prior to perfusion computation, HUs of the precontrast end-inspiratory image were corrected for variation in the lung inflation level between the precontrast and postcontrast end-inspiratory CT scans, using a model built from two additional precontrast CT scans at end-expiration and midinspiration. The authors also assessed spatial heterogeneity and gravitationally directed gradients of regional perfusion for normal lung subjects and diseased lung subjects using a two-sample two-tailed t-test.

Results:

The mean TRE (and standard deviation) was 0.6 ± 0.7 mm (smaller than the voxel dimension) for DIR between pre contrast and postcontrast end-inspiratory CT image data sets. No singularities were observed in the displacement vector fields. The mean HU enhancement (and standard deviation) was 37.3 ± 10.5 HU for normal lung subjects and 30.7 ± 13.5 HU for diseased lung subjects. Spatial heterogeneity of regional perfusion was found to be higher for diseased lung subjects than for normal lung subjects, i.e., a mean coefficient of variation of 2.06 vs 1.59 (p = 0.07). The average gravitationally directed gradient was strong and significant (R² = 0.99, p < 0.01) for normal lung dogs, whereas it was moderate and nonsignificant (R² = 0.61, p = 0.12) for diseased lung dogs.

Conclusions:

This canine study demonstrated the accuracy of DIR with subvoxel TREs on average, higher spatial heterogeneity of regional perfusion for diseased lung subjects than for normal lung subjects, and a strong gravitationally directed gradient for normal lung subjects, providing proof-of-principle for single-energy CT pulmonary perfusion imaging. Further studies such as comparison with other perfusion imaging modalities will be necessary to validate the physiological significance.

Priority-driven plan optimization in locally advanced lung patients based on perfusion SPECT imaging

Purpose

Limits on mean lung dose (MLD) allow for individualization of radiation doses at safe levels for patients with lung tumors. However, MLD does not account for individual differences in the extent or spatial distribution of pulmonary dysfunction among patients, which leads to toxicity variability at the same MLD. We investigated dose rearrangement to minimize the radiation dose to the functional lung as assessed by perfusion single photon emission computed tomography (SPECT) and maximize the target coverage to maintain conventional normal tissue limits.

Methods and materials

Retrospective plans were optimized for 15 patients with locally advanced non-small cell lung cancer who were enrolled in a prospective imaging trial. A staged, priority-based optimization system was used. The baseline priorities were to meet physical MLD and other dose constraints for organs at risk, and to maximize the target generalized equivalent uniform dose (gEUD). To determine the benefit of dose rearrangement with perfusion SPECT, plans were reoptimized to minimize the generalized equivalent uniform functional dose (gEUfD) to the lung as the subsequent priority.

Results

When only physical MLD is minimized, lung gEUfD was 12.6 ± 4.9 Gy (6.3-21.7 Gy). When the dose is rearranged to minimize gEUfD directly in the optimization objective function, 10 of 15 cases showed a decrease in lung gEUfD of >20% (lung gEUfD mean 9.9 ± 4.3 Gy, range 2.1-16.2 Gy) while maintaining equivalent planning target volume coverage. Although all dose-limiting constraints remained unviolated, the dose rearrangement resulted in slight gEUD increases to the cord (5.4 ± 3.9 Gy), esophagus (3.0 ± 3.7 Gy), and heart (2.3 ± 2.6 Gy).

Conclusions

Priority-driven optimization in conjunction with perfusion SPECT permits image guided spatial dose redistribution within the lung and allows for a reduced dose to the functional lung without compromising target coverage or exceeding conventional limits for organs at risk.

Changes in functional lung regions during the course of radiation therapy and their potential impact on lung dosimetry for non-small cell lung cancer

PURPOSE

To study changes in functional activity on ventilation (V)/perfusion (Q) single-photon emission computed tomography (SPECT) during radiation therapy (RT) and explore the impact of such changes on lung dosimetry in patients with non-small cell lung cancer (NSCLC).

METHODS AND MATERIALS

Fifteen NSCLC patients with centrally located tumors were enrolled. All patients were treated with definitive RT dose of ≥60 Gy. V/Q SPECT-CT scans were performed prior to and after delivery of 45 Gy of fractionated RT. SPECT images were used to define temporarily dysfunctional regions of lung caused by tumor or other potentially reversible conditions as B3. The functional lung (FL) was defined on SPECT by 2 separate approaches: FL1, a threshold of 30% of the maximum uptake of the patient's lung; and FL2, FL1 plus B3 region. The impact of changes in FL between initiation of RT and delivery of 45 Gy on lung dosimetry were analyzed.

RESULTS

Fourteen patients (93%) had larger FL2 volumes than FL1 pre-RT (P<.001). Dysfunctional lung became functional in 11 patients (73%) on V SPECT and in 10 patients (67%) on Q SPECT. The dosimetric parameters generated from CT-based anatomical lung had significantly lower values in FL1 than FL2, with a median reduction in the volume of lung receiving a dose of at least 20 Gy (V20) of 3%, 5.6%, and mean lung dose of 0.95 and 1.55 on V and Q SPECT respectively.

CONCLUSIONS

Regional ventilation and perfusion function improve significantly during RT in centrally located NSCLC. Lung dosimetry values vary notably between different definitions of functional lung.

Prescribing radiation dose to lung cancer patients based on personalized toxicity estimates

INTRODUCTION

The lung radiosensitivity of the most sensitive patients limits doses that can be given to the majority of lung cancer patients. The purpose of the current study was to illustrate the concept of personalizing prescription dose by performing a retrospective study in which the prescription is determined using an individualized dose-volume constraint that is calculated from a toxicity prediction model. We test whether using a model-generated personalized lung-dose limit results in a clinically significant change to the prescription.

METHODS

A model consisting of a dose-volume component and a genetic component (single-nucleotide polymorphism information) was used to determine iso-risk mean lung-dose (MLD) limits for each patient. The prescription dose for each patient was scaled according to the individualized MLD constraint and population-based constraints for the cord, esophagus, and heart. The difference between the model-determined prescription dose and the prescription the patient was originally treated with was evaluated.

RESULTS

For 59% of the patients the change in prescription using the model-determined limit was greater than 5 Gy (either dose escalation or de-escalation). For 96% of the patients who developed radiation pneumonitis the model predicted that the prescription should have been lowered.

CONCLUSIONS

Our results indicate that using a model-generated personalized MLD results in a clinically different (≥ 5 Gy) prescription. A model used in the manner described by the study can help physicians further personalize radiation therapy and aid them in determining how much dose can safely be delivered to the tumor and normal tissues.

Reproducibility of four-dimensional computed tomography-based lung ventilation imaging

RATIONALE AND OBJECTIVES

A novel ventilation imaging method based on four-dimensional (4D) computed tomography (CT) has been applied to the field of radiation oncology. Understanding its reproducibility is a prerequisite for clinical applications. The purpose of this study was to quantify the reproducibility of 4D CT ventilation imaging over different days and the same session.

MATERIALS AND METHODS

Two ventilation images were created from repeat 4D CT scans acquired over the average time frames of 15 days for 6 lung cancer patients and 5 minutes for another 6 patients. The reproducibility was quantified using the voxel-based Spearman rank correlation coefficients for all lung voxels and Dice similarity coefficients (DSC) for the spatial overlap of segmented high-, moderate-, and low-functional lung volumes. Furthermore, the relationship between the variation in abdominal motion range as a measure of the depth of breathing and variation in ventilation was evaluated using linear regression.

RESULTS

The voxel-based correlation between the two ventilation images was moderate on average (0.50 ± 0.15). The DSCs were also moderate for the high- (0.60 ± 0.08), moderate- (0.46 ± 0.06), and low-functional lung (0.58 ± 0.09). No patients demonstrated strong correlations. The relationship between the motion range variation and ventilation variation was found to be moderate and significant.

CONCLUSIONS

We investigated the reproducibility of 4D CT ventilation imaging over the time frames of 15 days and 5 minutes and found that it was only moderately reproducible. Respiratory variation during 4D CT scans was found to deteriorate the reproducibility. Improvement of 4D CT imaging is necessary to increase the reproducibility of 4D CT ventilation imaging.

Changes in global function and regional ventilation and perfusion on SPECT during the course of radiotherapy in patients with non-small-cell lung cancer

PURPOSE

This study aimed to (1) examine changes in dyspnea, global pulmonary function test (PFT) results, and functional activity on ventilation (V)/perfusion (Q) single-photon emission computerized tomography (SPECT) scans during the course of radiation (RT), and (2) factors associated with the changes in patients with non-small-cell lung cancer (NSCLC).

METHODS AND MATERIALS

Fifty-six stage I to III NSCLC patients treated with definitive RT with or without chemotherapy were enrolled prospectively. Dyspnea was graded according to Common Terminology Criteria for Adverse Events version 3.0 prior to and weekly during RT. V/Q SPECT-computed tomography (CT) and PFTs were performed prior to and during RT at approximately 45 Gy. Functions of V and Q activities were assessed using a semiquantitative scoring of SPECT images.

RESULTS

Breathing improved significantly at the third week (mean dyspnea grade, 0.8 vs. 0.6; paired t-test p = 0.011) and worsened during the later course of RT (p > 0.05). Global PFT results did not change significantly, while regional lung function on V/Q SPECT improved significantly after ∼45 Gy. The V defect score (DS) was 4.9 pre-RT versus 4.3 during RT (p = 0.01); Q DS was 4.3 pre-RT versus 4.0 during RT (p < 0.01). Improvements in V and Q functions were seen primarily in the ipsilateral lung (V DS, 1.9 pre-RT versus 1.4 during RT, p < 0.01; Q DS, 1.7 pre-RT versus 1.5 during RT, p < 0.01). Baseline primary tumor volume was significantly correlated with pre-RT V/Q DS (p < 0.01). Patients with central lung tumors had greater interval changes in V and Q than those with more peripheral tumors (p <0.05 for both V and Q DS).

CONCLUSIONS

Regional ventilation and perfusion improved during RT at 45 Gy. This suggests that adaptive planning based on V/Q SPECT during RT may allow sparing of functionally recoverable lung tissue.

Semiquantification and classification of local pulmonary function by V/Q single photon emission computed tomography in patients with non-small cell lung cancer: potential indication for radiotherapy planning

INTRODUCTION

Perfusion (Q) single photon emission computed tomography (SPECT) has been used to divert dose away from higher-functioning lung during radiation therapy (RT) planning. This study aimed to (1) study regional lung function through coregistered pulmonary ventilation/perfusion (V/Q)-SPECT-CT and (2) classify these defects for its potential value in radiation planning in patients with non-small cell lung cancer (NSCLC).

METHODS

Patients with stages I to III NSCLC requiring radiation-based therapy were eligible for this prospective study. V/Q-SPECT performed within 2 weeks before the start of radiation was interpreted by nuclear medicine physicians and then measured by a semiquantitative score. The potential mechanism of V and Q defects was analyzed; the potential impact of V/Q-SPECT over Q-SPECT alone was completed through classified applications (high-dose RT versus RT avoidance) during planning.

RESULTS

Images of 51 consecutive patients were analyzed. The V and Q defects were matched, reverse mismatched (V defect > Q defect), and mismatched (Q defect > V defect) in 61, 31, and 8% of patients, respectively. Tumor was the leading cause of the defects of ipsilateral lung in 73% of patients. The defect scores of the ipsilateral lung were greater in patients with central primaries than those with peripheral primaries for both V-SPECT (2.3 ± 1.1 versus 1.5 ± 0.8, p = 0.017) and Q-SPECT (2.2 ± 0.8 versus 1.4 ± 0.6, p = 0.000). The patients with chronic obstructive pulmonary disease had greater defect scores in contralateral lung for both V-SPECT (1.5 ± 0.7 versus 1.0 ± 0.8, p = 0.006) and Q-SPECT (1.4 ± 0.6 versus 1.0 ± 0.4, p = 0.010). On assessing the potential value of SPECT on RT plan, 39% of patients could have their RT plan when applying V/Q-SPECT rather than Q-SPECT alone.

CONCLUSIONS

V/Q-SPECT provides a more comprehensive functional assessment, may provide additional value over Q-SPECT alone in assessing local pulmonary function, and guide RT plan decisions in patients with NSCLC.

Detection of radiation-induced lung injury in non-small cell lung cancer patients using hyperpolarized helium-3 magnetic resonance imaging

PURPOSE

To compare hyperpolarized helium-3 magnetic resonance imaging ((3)He-MRI) acquired from non-small cell lung cancer (NSCLC) patients before and after external beam radiotherapy (EBRT).

METHODS AND MATERIALS

In an Ethics Committee-approved prospective study, five patients with histologically confirmed NSCLC gave written informed consent to undergo computed tomography (CT) and (3)He-MR ventilation imaging 1 week prior to and 3 months after radiotherapy. Images were registered to pre-treatment CT using anatomical landmark-based rigid registration to enable comparison. Emphysema was graded from examination of the CT. MRI-defined ventilation was calculated as the intersection of (3)He-MRI and CT lung volume as a percentage of the CT lung volume for the whole lung and regions of CT-defined pneumonitis.

RESULTS

On pre-treatment images, there was a significant correlation between the degree of CT-defined emphysema and (3)He-MRI whole lung ventilation (Spearman's rho=0.90, p=0.04). After radiation therapy, pneumonitis was evident on CT for 3/5 patients. For these cases, (3)He-MRI ventilation was significantly reduced within the regions of pneumonitis (pre: 94.1±2.2%, post: 73.7±4.7%; matched pairs Student's t-test, p=0.02, mean difference=20.4%, 95% confidence interval 6.3-34.6%).

CONCLUSIONS

This work demonstrates the feasibility of detecting ventilation changes between pre- and post-treatment using hyperpolarized helium-3 MRI for patients with NSCLC. Pre-treatment, the degree of emphysema and (3)He-MRI ventilation were correlated. For three cases of radiation pneumonitis, (3)He-MRI ventilation changes between pre- and post-treatment imaging were consistent with CT evidence of radiation-induced lung injury.