Concordant F-18 FDG PET and Y-90 Bremsstrahlung scans depict selective delivery of Y-90-microspheres to liver tumors: confirmation with histopathology

99mTc-radiolabeled composites enabling in vivo imaging of arterial dispersal and retention of microspheres in the vascular network of rabbit lungs, liver, and liver tumors

Purpose

Selective internal radiation therapy (SIRT) is an effective treatment option for liver tumors, using Y-90-loaded polymer microspheres that are delivered via catheterization of the hepatic artery. Since Y-90 is a beta emitter and not conveniently imaged by standard clinical instrumentation, dosimetry is currently evaluated in each patient using a surrogate particle, ^99mTechnetium-labeled macroaggregated albumin (^99mTc-MAA). We report a new composite consisting of ^99mTc-labeled nanoparticles attached to the same polymer microspheres as used for SIRT, which can be imaged with standard SPECT.

Methods

Carbon nanoparticles with an encapsulated core of ^99mTc were coated with the polycation protamine sulfate to provide electrostatic attachment to anionic polystyrene sulfonate microspheres of different sizes (30, 12, and 8 µm). The in vivo stability of these composites was determined via intravenous injection and entrapment in the capillary network of normal rabbit lungs for up to 3 hours. Furthermore, we evaluated their biodistribution in normal rabbit livers, and livers implanted with VX2 tumors, following intrahepatic artery instillation.

Results

We report distribution tests for three different sizes of radiolabeled microspheres and compare the results with those obtained using ^99mTc-MAA. Lung retention of the radiolabeled microspheres ranged from 72.8% to 92.9%, with the smaller diameter microspheres showing the lowest retention. Liver retention of the microspheres was higher, with retention in normal livers ranging from 99.2% to 99.8%, and in livers with VX2 tumors from 98.2% to 99.2%. The radiolabeled microspheres clearly demonstrated preferential uptake at tumor sites due to the increased arterial perfusion produced by angiogenesis.

Conclusion

We describe a novel use of radiolabeled carbon nanoparticles to generate an imageable microsphere that is stable in vivo under the shear stress conditions of arterial networks. Following intra-arterial instillation in the normal rabbit liver, they distribute in a distinct segmented pattern, with the smaller microspheres extending throughout the organ in finer detail, while still being well retained within the liver. Furthermore, in livers hosting an implanted VX2 tumor, they reveal the increased arterial perfusion of tumor tissue resulting from angiogenesis. These novel composites may have potential as a more representative mimic of the vascular distribution of therapeutic microspheres in patients undergoing SIRT.

Other non-surgical treatments for liver cancer

Interventional radiology plays a major role in the modern management of liver cancers, in primary hepatic malignancies or metastases and in palliative or curative situations. Radiological treatments are divided in two categories based on their approach: endovascular treatment and direct transcapsular access. Endovascular treatments include mainly three applications: transarterial chemoembolization (TACE), transarterial radioembolization (TARE) and portal vein embolization (PVE). TACE and TARE share an endovascular arterial approach, consisting of a selective catheterization of the hepatic artery or its branches. Subsequently, either a chemotherapy (TACE) or radioembolic (TARE) agent is injected in the target vessel to act on the tumor. PVE raises the volume of the future liver remnant in extended hepatectomy by embolizing a portal vein territory which results in hepatic regeneration. Direct transcapsular access treatments involve mainly three techniques: radiofrequency thermal ablation (RFA), microwave thermal ablation (MWA) and percutaneous ethanol injection (PEI). RFA and MWA procedures are almost identical, their clinical applications are similar. A probe is deployed directly into the tumor to generate heat and coagulation necrosis. PEI has known implications based on the chemical toxicity of intra-tumoral injection with highly concentrated alcohol by a thin needle.

90Y Digital PET/CT Imaging Following Radioembolization

Imaging of Y internal pair production with conventional photomultiplier detector PET technology has been previously reported for patients with malignant/metastatic liver lesions treated with Y radioembolization (RE). We present a 54-year-old man with unresectable liver metastases from rectal carcinoma (involving the right and left lobes) who was referred for Y RE and subsequently imaged using new solid-state digital photon counting technology (Vereos 64 Time-of-Flight PET/CT; Philips, Cleveland, OH). Despite imaging at 26 hours following RE, digital PET/CT provides improved image quality and Y-to-background contrast as well as accurate visualization of Y biodistribution when compared with Bremsstrahlung SPECT/CT.

The significance of bremsstrahlung SPECT/CT after yttrium-90 radioembolization treatment in the prediction of extrahepatic side effects

Purpose Unwanted deposition of 90Y microspheres in organs other than the liver during radioembolization of liver tumours may cause severe side effects such as duodenal ulcer. The aim of this study was to evaluate the significance of posttherapy bremsstrahlung (BS) SPECT/CT images of the liver in comparison to planar and SPECT images in the prediction of radioembolization-induced extrahepatic side effects.Methods A total of 188 radioembolization procedures were performed in 123 patients (50 women, 73 men) over a 2-year period. Planar, whole-body and BS SPECT/CT imaging were performed 24 h after treatment as a part of therapy work-up.Any focally increased extrahepatic accumulation was evaluated as suspicious. Clinical follow-up and gastroduodenoscopy served as reference standards. The studies were reviewed to evaluate whether BS SPECT/CT imaging was of benefit.Results In the light of anatomic data obtained from SPECT/CT, apparent extrahepatic BS in 43% of planar and in 52% of SPECT images proved to be in the liver and hence false positive.The results of planar scintigraphy could not be analysed further since 12 images were not assessable due to high scatter artefacts. On the basis of the gastrointestinal (GI)complications and the results of gastroduodenoscopy, true positive,true-negative, false-positive and false-negative results of BS SPECT and SPECT/CT imaging in the prediction of GI ulcers were determined. The sensitivity, specificity, positive and negative predictive values and the accuracy of SPECT and SPECT/CT in the prediction of GI ulcers were 13%, 88%, 8%,92% and 82%, and 87%, 100%, 100%, 99% and 99%,respectively.Conclusion Despite the low quality of BS images, BSSPECT/CT can be used as a reliable method to confirm the safe distribution of 90Y microspheres and in the prediction of GI side effects.

SPIO-labeled Yttrium Microspheres for MR Imaging Quantification of Transcatheter Intrahepatic Delivery in a Rodent Model

PURPOSE

To investigate the qualitative and quantitative impacts of labeling yttrium microspheres with increasing amounts of superparamagnetic iron oxide (SPIO) material for magnetic resonance (MR) imaging in phantom and rodent models.

MATERIALS AND METHODS

Animal model studies were approved by the institutional Animal Care and Use Committee. The r2* relaxivity for each of four microsphere SPIO compositions was determined from 32 phantoms constructed with agarose gel and in eight concentrations from each of the four compositions. Intrahepatic transcatheter infusion procedures were performed in rats by using each of the four compositions before MR imaging to visualize distributions within the liver. For quantitative studies, doses of 5, 10, 15, or 20 mg 2% SPIO-labeled yttrium microspheres were infused into 24 rats (six rats per group). MR imaging R2* measurements were used to quantify the dose delivered to each liver. Pearson correlation, analysis of variance, and intraclass correlation analyses were performed to compare MR imaging measurements in phantoms and animal models.

RESULTS

Increased r2* relaxivity was observed with incremental increases of SPIO microsphere content. R2* measurements of the 2% SPIO-labeled yttrium microsphere concentration were well correlated with known phantom concentrations (R(2) = 1.00, P < .001) over a broader linear range than observed for the other three compositions. Microspheres were heterogeneously distributed within each liver; increasing microsphere SPIO content produced marked signal voids. R2*-based measurements of 2% SPIO-labeled yttrium microsphere delivery were well correlated with infused dose (intraclass correlation coefficient, 0.98; P < .001).

CONCLUSION

MR imaging R2* measurements of yttrium microspheres labeled with 2% SPIO can quantitatively depict in vivo intrahepatic biodistribution in a rat model.

Theranostic Imaging of Yttrium-90

This paper overviews Yttrium-90 ((90)Y) as a theranostic and nuclear medicine imaging of (90)Y radioactivity with bremsstrahlung imaging and positron emission tomography. In addition, detection and optical imaging of (90)Y radioactivity using Cerenkov luminescence will also be reviewed. Methods and approaches for qualitative and quantitative (90)Y imaging will be briefly discussed. Although challenges remain for (90)Y imaging, continued clinical demand for predictive imaging response assessment and target/nontarget dosimetry will drive research and technical innovation to provide greater clinical utility of (90)Y as a theranostic agent.

Non-invasive molecular imaging for preclinical cancer therapeutic development

Molecular and non-invasive imaging are rapidly emerging fields in preclinical cancer drug discovery. This is driven by the need to develop more efficacious and safer treatments, the advent of molecular-targeted therapeutics, and the requirements to reduce and refine current preclinical in vivo models. Such bioimaging strategies include MRI, PET, single positron emission computed tomography, ultrasound, and optical approaches such as bioluminescence and fluorescence imaging. These molecular imaging modalities have several advantages over traditional screening methods, not least the ability to quantitatively monitor pharmacodynamic changes at the cellular and molecular level in living animals non-invasively in real time. This review aims to provide an overview of non-invasive molecular imaging techniques, highlighting the strengths, limitations and versatility of these approaches in preclinical cancer drug discovery and development.

Technical Considerations of Phosphorous-32 Bremsstrahlung SPECT Imaging after Radioembolization of Hepatic Tumors: A Clinical Assessment with a Review of Imaging Parameters

Background. Bremsstrahlung (BS) imaging during radioembolization (RE) confirms the deposition of radiotracer in hepatic/extrahepatic tumors. The aim of this study is to demonstrate (32)P images and to optimize the imaging parameters. Materials and Methods. Thirty-nine patients with variable types of hepatic tumors, treated with the intra-arterial injection of (32)P, were included. All patients underwent BS SPECT imaging 24-72 h after tracer administration, using low energy high resolution (LEHR) (18 patients) or medium energy general purpose (MEGP) (21 patients) collimators. A grading scale from 1 to 4 was used to express the compatibility of the (32)P images with those obtained from CT/MRI. Results. Although the image quality obtained with the MEGP collimator was visually and quantitatively better than with the LEHR (76% concordance score versus 71%, resp.), there was no statistically significant difference between them. Conclusion. The MEGP collimator is the first choice for BS SPECT imaging. However, if the collimator change is time consuming (as in a busy center) or an MEGP collimator is not available, the LEHR collimator could be practical with acceptable images, especially in a SPECT study. In addition, BS imaging is a useful method to confirm the proper distribution of radiotherapeutic agents and has good correlation with anatomical findings.

Optimization of energy window for 90Y bremsstrahlung SPECT imaging for detection tasks using the ideal observer with model-mismatch

PURPOSE

In yttrium-90 ((90)Y) microsphere brachytherapy (radioembolization) of unresectable liver cancer, posttherapy (90)Y bremsstrahlung single photon emission computed tomography (SPECT) has been used to document the distribution of microspheres in the patient and to help predict potential side effects. The energy window used during projection acquisition can have a significant effect on image quality. Thus, using an optimal energy window is desirable. However, there has been great variability in the choice of energy window due to the continuous and broad energy distribution of (90)Y bremsstrahlung photons. The area under the receiver operating characteristic curve (AUC) for the ideal observer (IO) is a widely used figure of merit (FOM) for optimizing the imaging system for detection tasks. The IO implicitly assumes a perfect model of the image formation process. However, for (90)Y bremsstrahlung SPECT there can be substantial model-mismatch (i.e., difference between the actual image formation process and the model of it assumed in reconstruction), and the amount of the model-mismatch depends on the energy window. It is thus important to account for the degradation of the observer performance due to model-mismatch in the optimization of the energy window. The purpose of this paper is to optimize the energy window for (90)Y bremsstrahlung SPECT for a detection task while taking into account the effects of the model-mismatch.

METHODS

An observer, termed the ideal observer with model-mismatch (IO-MM), has been proposed previously to account for the effects of the model-mismatch on IO performance. In this work, the AUC for the IO-MM was used as the FOM for the optimization. To provide a clinically realistic object model and imaging simulation, the authors used a background-known-statistically and signal-known-statistically task. The background was modeled as multiple compartments in the liver with activity parameters independently following a Gaussian distribution; the signal was modeled as a tumor with a Gaussian-distributed activity parameter located randomly with equal probability at one of three positions. The IO test statistics (i.e., likelihood ratios) were estimated using Markov-chain Monte Carlo methods. The authors realistically modeled human anatomy using a digital phantom code, and realistically simulated (90)Y bremsstrahlung SPECT imaging with a clinical SPECT system and typical imaging parameters using a previously validated Monte Carlo bremsstrahlung simulation method. Model-mismatch was included by modeling image formation process in the calculation of IO test statistics using an analytic modeling method previously developed for quantitative (90)Y bremsstrahlung SPECT. To demonstrate the effects of the model-mismatch on the detection task, the authors optimized the energy window both with and without model-mismatch included in the IO.

RESULTS

For all the energy windows, the AUC values for the IO-MM were smaller than that for the IO. The optimal windows for the IO-MM and the IO were 80-180 and 60-400 keV, respectively.

CONCLUSIONS

The authors have demonstrated the degradation of the ideal performance due to model-mismatch and optimized the energy window for (90)Y bremsstrahlung SPECT for detection tasks by accounting for the effects of the model-mismatch. The obtained optimal window was much narrower when taking into account the model-mismatch and similar to that obtained previously for estimation tasks.

Radioembolisation with Yttrium-90 microspheres: an effective treatment modality for unresectable liver metastases

PURPOSE

To compare the outcomes (survival and adverse events) of the authors' use of (90) Y microsphere radioembolisation in patients with chemotherapy-refractory liver metastases with published data from other groups using radioembolisation. To retrospectively evaluate the efficiency, in particular survival benefits, of radioembolisation in the treatment of liver metastases.

METHODS AND MATERIALS

Over 5 years, 339 patients underwent (90) Y microsphere radioembolisation for unresectable liver metastases and were evaluated for adverse events at the time of treatment and 1 and 3 months after treatment. Overall survival (OS) was calculated by the Kaplan-Meier method. The results from the present retrospective study were compared with a number of prospective and retrospective clinical trials which have addressed the use of (90) Y microspheres as a salvage treatment for liver metastases.

RESULTS

The OS time of the present study (12.0 months) compares favourably with survival times reported by other groups. The incidence of late grade 2 adverse events (e.g. duodenal or gastric ulceration, radiation-induced liver disease, gall bladder complications) is comparable to previous studies, with a lower prevalence of grade 2/3 ulcerations (3.7%) at our centre.

CONCLUSIONS

The survival results, together with the low acute and late toxicity observed in our data and previous studies, support the use of radioembolisation to aid in the local control of unresectable liver metastases in the salvage setting. The present study contributes to the growing evidence for efficiency, in particular survival gains, of radioembolisation in the treatment of liver metastases.

Development and evaluation of an improved quantitative (90)Y bremsstrahlung SPECT method

PURPOSE

Yttrium-90 ((90)Y) is one of the most commonly used radionuclides in targeted radionuclide therapy (TRT). Since it decays with essentially no gamma photon emissions, surrogate radionuclides (e.g., (111)In) or imaging agents (e.g., (99m)Tc MAA) are typically used for treatment planning. It would, however, be useful to image (90)Y directly in order to confirm that the distributions measured with these other radionuclides or agents are the same as for the (90)Y labeled agents. As a result, there has been a great deal of interest in quantitative imaging of (90)Y bremsstrahlung photons using single photon emission computed tomography (SPECT) imaging. The continuous and broad energy distribution of bremsstrahlung photons, however, imposes substantial challenges on accurate quantification of the activity distribution. The aim of this work was to develop and evaluate an improved quantitative (90)Y bremsstrahlung SPECT reconstruction method appropriate for these imaging applications.

METHODS

Accurate modeling of image degrading factors such as object attenuation and scatter and the collimator-detector response is essential to obtain quantitatively accurate images. All of the image degrading factors are energy dependent. Thus, the authors separated the modeling of the bremsstrahlung photons into multiple categories and energy ranges. To improve the accuracy, the authors used a bremsstrahlung energy spectrum previously estimated from experimental measurements and incorporated a model of the distance between (90)Y decay location and bremsstrahlung emission location into the SIMIND code used to generate the response functions and kernels used in the model. This improved Monte Carlo bremsstrahlung simulation was validated by comparison to experimentally measured projection data of a (90)Y line source. The authors validated the accuracy of the forward projection model for photons in the various categories and energy ranges using the validated Monte Carlo (MC) simulation method. The forward projection model was incorporated into an iterative ordered subsets-expectation maximization (OS-EM) reconstruction code to allow for quantitative SPECT reconstruction. The resulting code was validated using both a physical phantom experiment with spherical objects in a warm background and a realistic anatomical phantom simulation. In the physical phantom study, the authors evaluated the method in terms of quantitative accuracy of activity estimates in the spheres; in the simulation study, the authors evaluated the accuracy and precision of activity estimates from various organs and compared them to results from a previously proposed method.

RESULTS

The authors demonstrated excellent agreement between the experimental measurement and Monte Carlo simulation. In the XCAT phantom simulation, the proposed method achieved much better accuracy in the modeling (error in photon counts was -1.1 %) compared to a previously proposed method (errors were more than 20  %); the quantitative accuracy of activity estimates was excellent for all organs (errors were from -1.6 % to 11.9 %) and comparable to previously published results for (131)I using the same collimator.

CONCLUSIONS

The proposed (90)Y bremsstrahlung SPECT reconstruction method provided very accurate estimates of organ activities, with accuracies approaching those previously observed for (131)I. The method may be useful in verifying organ doses for targeted radionuclide therapy using (90)Y.

Yttrium-90-labeled microsphere tracking during liver selective internal radiotherapy by bremsstrahlung pinhole SPECT: feasibility study and evaluation in an abdominal phantom

BACKGROUND

The purpose of the study is to evaluate whether a pinhole collimator is better adapted to bremsstrahlung single photon emission computed tomography [SPECT] than parallel-hole collimators and in the affirmative, to evaluate whether pinhole bremsstrahlung SPECT, including a simple model of the scatter inside the patient, could provide a fast dosimetry assessment in liver selective internal radiotherapy [SIRT].

MATERIALS AND METHODS

Bremsstrahlung SPECT of an abdominal-shaped phantom including one cold and five hot spheres was performed using two long-bore parallel-hole collimators: a medium-energy general-purpose [MEGP] and a high-energy general-purpose [HEGP], and also using a medium-energy pinhole [MEPH] collimator. In addition, ten helical MEPH SPECTs (acquisition time 3.6 min) of a realistic liver-SIRT phantom were also acquired.

RESULTS

Without scatter correction for SPECT, MEPH SPECT provided a significantly better contrast recovery coefficient [CRC] than MEGP and HEGP SPECTs. The CRCs obtained with MEPH SPECT were still improved with the scatter correction and became comparable to those obtained with positron-emission tomography [PET] for the 36-, 30- (cold), 28-, and 24-mm-diameter spheres: CRC = 1.09, 0.59, 0.91, and 0.69, respectively, for SPECT and CRC = 1.07, 0.56, 0.84, and 0.63, respectively, for PET. However, MEPH SPECT gave the best CRC for the 19-mm-diameter sphere: CRC = 0.56 for SPECT and CRC = 0.01 for PET. The 3.6-min helical MEPH SPECT provided accurate and reproducible activity estimation for the liver-SIRT phantom: relative deviation = 10 ± 1%.

CONCLUSION

Bremsstrahlung SPECT using a pinhole collimator provided a better CRC than those obtained with parallel-hole collimators. The different designs and the better attenuating material used for the collimation (tungsten instead of lead) explain this result. Further, the addition of an analytical modeling of the scattering inside the phantom resulted in an almost fully recovered contrast. This fills the gap between the performance of90Y-PET and bremsstrahlung pinhole SPECT which is a more affordable technique and could even be used during the catheterization procedure in order to optimize the90Y activity to inject.

Usefulness of Bremsstrahlung Images after Intra-arterial Y-90 Resin Microphere Radioembolization for Hepatic Tumors

PURPOSE

Y-90 resin microsphere radioembolization is used to treat inoperable hepatic tumors. After injection of Y-90 resin microsphere, the only method to visualize the distribution of Y-90 is the scintigraphic imaging of bremsstrahlung radiation. The purpose of this study was to evaluate the characteristics and usefulness of bremsstrahlung imaging in Y-90 resin microsphere treatment.

METHODS

Twenty patients (22 administrations) underwent intra-arterial Y-90 resin microsphere treatment. For pre-treatment planning, images of Tc-99m albumin macroaggregate (MAA) arterial injection and hepatic contrast angiography were obtained. Post-treatment bremsstrahlung images were taken and compared with pre-treatment images. The extrahepatic activity was evaluated on bremsstrahlung images. To correlate the size and vascularity of the tumors with tumor visualization on bremsstrahlung images, the individual tumors were grouped according to visualization on each image and compared with one another by size and tumor-to-normal ratio.

RESULTS

All post-therapeutic bremsstrahlung images showed similar contours of the liver with pre-treatment angiography. No extrahepatic activity was seen in all cases. The visualized tumors on bremsstrahlung images were significantly larger than the non-visualized tumors. Tumor-to-normal ratios of the visualized tumors on bremsstrahlung images were significantly higher than those of the non-visualized tumors.

CONCLUSIONS

Bremsstrahlung images after intra-arterial Y-90 resin microsphere treatment are useful in evaluating the intrahepatic distribution of radioisotope and detecting possible extrahepatic activity.

Survival outcomes of a salvage patient population after radioembolization of hepatic metastases with yttrium-90 microspheres

PURPOSE

To determine in a retrospective study the potential benefit on survival outcomes of radioembolization using yttrium-90 ((90)Y) resin microspheres in a cohort of patients presenting with chemotherapy-refractory liver metastases, primarily from colorectal cancer (CRC).

MATERIALS AND METHODS

Over 3 years, 249 patients were referred to the authors' center to determine suitability for radioembolization as treatment for hepatic metastases. All patients were defined as salvage, having failed first-line and second-line chemotherapies. These patients were divided into group 1 (CRC) and group 2 (all other cancers, eg, breast, neuroendocrine) and assessed for overall survival (OS) as a whole and according to group.

RESULTS

Using (90)Y resin microspheres, 208 patients were treated, undergoing 223 radioembolization treatments. The median OS was 8.3 months for the whole cohort, 7.9 months for group 1, and 8.7 months for group 2. At the 3-month follow-up, there was an overall adverse event rate of 9%. At the end of the data collection period, 62 patients were still alive.

CONCLUSIONS

Radioembolization shows promise as an effective and safe treatment for patients with chemotherapy-refractory hepatic metastases providing an extension to survival in the salvage setting.

Dose delivery estimated by bremsstrahlung imaging and partition model correlated with response following intra-arterial radioembolization with 32P-glass microspheres for the treatment of hepatocellular carcinoma

RATIONALE

The objective of this study was to retrospectively evaluate the efficacy of a combination of (32)P-glass microsphere-mediated intra-arterial internal radiation and chemoembolization for the treatment of hepatocellular carcinoma.

METHODS

Twenty-five consecutive patients with primary hepatocellular carcinoma referred for radiation therapy were treated with intra-arterial infusion of (32)P-glass microspheres followed by chemoembolization. beta-bremsstrahlung imaging was performed to monitor microsphere distribution. A partition model and a radiation dose equation were used for determination of radiation exposure in various tissues. Clinical response was evaluated using computed axial tomography scans.

RESULTS

The mean estimated absorption dose in tumor tissue was 137.42 +/- 56.69 Gy. A receiver operating characteristic curve was used to establish 90.65 Gy as the cutoff absorption dose with the best sensitivity and specificity for predicting response. The overall tumor response rate was 92%, while response in patients with radiation doses >90.65 Gy was 100%. Overall median patient survival was 15 months.

CONCLUSION

beta-bremsstrahlung imaging following intra-arterial infusion of (32)P-glass microspheres and chemoembolization incorporates effective treatment with convenient dosimetry monitoring and manageable adverse events using a single surgical procedure. This approach is a safe and effective method for ameliorating hepatocellular carcinoma.

Incidence of radiation pneumonitis after hepatic intra-arterial radiotherapy with yttrium-90 microspheres assuming uniform lung distribution

OBJECTIVE

To assess the incidence of clinical and imaging radiation pneumonitis (RP) in a cohort of patients treated with >30 Gy cumulative lung dose (CLD) using Y90 microspheres.

MATERIALS AND METHODS

Four hundred three patients were treated with Y90 microspheres during a 4-year period. Of these, 58 patients received >30 Gy CLD. Patients were followed for toxicities suggestive of imaging or clinical RP. Toxicities were graded using the Radiation Therapy Oncology Group/European Organisation for Research and Treatment of Cancer Late Radiation Morbidity Scoring Schema. Patients were also followed for survival from time of first treatment.

RESULTS

There were 44 men and 14 women. Forty-three patients had hepatocellular carcinoma (HCC), whereas 15 had liver metastases. Mean and median follow-up were 7.3 and 6.0 months, respectively. Mean lung shunt fraction was slightly greater in the patients with HCC versus metastases (20% vs. 16.7%, P = 0.2308). The lifetime CLD for metastases and HCC groups were not statistically different (54.04 Gy vs. 48.44 Gy, P = 0.4303). Forty-three of 53 patients demonstrated no lung imaging findings suggestive of pneumonitis. Imaging findings in 10 patients included pleural effusions, atelectasis, and ground glass attenuation. There were no cases of clinical or imaging RP. Survival varied depending on stage as well as single and CLD. None of the patient deaths were attributed to respiratory compromise.

CONCLUSION

RP was not predicted using the currently used Y90 dosimetry models that assume uniform distribution in the lungs. Further investigation and dose escalation studies are required to more precisely define the radiation tolerance of lung parenchyma using this mode of therapy.