Tumour status prediction by means of carbon-ion beam irradiation: comparison of washout rates between in-beam PET and DCE-MRI in rats.

Tumour response to radiation therapy appears as changes in tumour vascular condition. There are several methods for analysing tumour blood circulatory changes one of which is dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), but there is no method that can observe the tumour vascular condition and physiological changes at the site of radiation therapy. Positron emission tomography (PET) has been applied for treatment verification in charged particle therapy, which is based on the detection of positron emitters produced through nuclear fragmentation reactions in a patient's body.

Predictors of Adverse Gastrointestinal Events After Stereotactic Body Radiation Therapy for Liver Tumors.

Background/aim: To identify predictors of adverse gastrointestinal (GI) events related to stereotactic body radiation therapy (SBRT) for liver tumors.

Patients And Methods: We retrospectively analyzed 56 patients who underwent SBRT for liver tumors at our institution between 2016 and 2021. The α/β ratio of the GI tract (stomach, duodenum, and large intestine) was assumed to be 3 Gy in the Linear-Quadratic model (LQ model).

Measurement of biological washout rates depending on tumor vascular status inO in-beam rat-PET.

The biological washout of positron emitters should be modeled and corrected in order to achieve quantitative dose range verification in charged particle therapy based on positron emission tomography (PET). This biological washout effect is affected by physiological environmental conditions such as blood perfusion and metabolism, but the correlation to tumour pathology has not been studied yet.The aim of this study was to investigate the dependence of the biological washout rate on tumour vascular status in rat irradiation.

Assessment of the confidence interval in the multivariable normal tissue complication probability model for predicting radiation-induced liver disease in primary liver cancer.

We developed a confidence interval-(CI) assessing model in multivariable normal tissue complication probability (NTCP) modeling for predicting radiation-induced liver disease (RILD) in primary liver cancer patients using clinical and dosimetric data. Both the mean NTCP and difference in the mean NTCP (ΔNTCP) between two treatment plans of different radiotherapy modalities were further evaluated and their CIs were assessed. Clinical data were retrospectively reviewed in 322 patients with hepatocellular carcinoma (n = 215) and intrahepatic cholangiocarcinoma (n = 107) treated with photon therapy.

Biological washout modelling for in-beam PET: rabbit brain irradiation by C and O ion beams.

Positron emission tomography (PET) has been used for dose verification in charged particle therapy. The causes of washout of positron emitters by physiological functions should be clarified for accurate dose verification. In this study, we visualized the distribution of irradiated radioactive beams, C and O beams, in the rabbit whole-body using our original depth-of-interaction (DOI)-PET prototype to add basic data for biological washout effect correction.

The normal tissue complication probability model-based approach considering uncertainties for the selective use of radiation modality in primary liver cancer patients.

Purpose: To predict the probability of radiation-induced liver toxicity (RILT) and implement the normal tissue complication probability (NTCP) model-based approach considering confidence intervals (CIs) to select patients for new treatment techniques, such as proton beam therapy, based on a certain NTCP reduction (ΔNTCP) threshold for primary liver cancer patients.

Methods And Materials: Common Toxicity Criteria for Adverse Events (CTCAE) grade ≥2 RILT was scored. The Lyman NTCP models predicting the probability of CTCAE grade ≥2 RILT as a function of the fraction-size adjusted mean liver dose (MLD), using reference fraction size = 2 Gy/fraction and α/β ratio = 2 Gy, were fitted using the maximum likelihood method.

Assessing the uncertainty in a normal tissue complication probability difference (∆NTCP): radiation-induced liver disease (RILD) in liver tumour patients treated with proton vs X-ray therapy.

Modern radiotherapy technologies such as proton beam therapy (PBT) permit dose escalation to the tumour and minimize unnecessary doses to normal tissues. To achieve appropriate patient selection for PBT, a normal tissue complication probability (NTCP) model can be applied to estimate the risk of treatment-related toxicity relative to X-ray therapy (XRT). A methodology for estimating the difference in NTCP (∆NTCP), including its uncertainty as a function of dose to normal tissue, is described in this study using the Delta method, a statistical method for evaluating the variance of functions, considering the variance-covariance matrix.

Beam angle selection incorporation of anatomical heterogeneities for pencil beam scanning charged-particle therapy.

In charged particle therapy with pencil beam scanning (PBS), localization of the dose in the Bragg peak makes dose distributions sensitive to lateral tissue heterogeneities. The sensitivity of a PBS plan to lateral tissue heterogeneities can be reduced by selecting appropriate beam angles. The purpose of this study is to develop a fast and accurate method of beam angle selection for PBS.

A motion-compensated image filter for low-dose fluoroscopy in a real-time tumor-tracking radiotherapy system.

In the real-time tumor-tracking radiotherapy system, a surrogate fiducial marker inserted in or near the tumor is detected by fluoroscopy to realize respiratory-gated radiotherapy. The imaging dose caused by fluoroscopy should be minimized. In this work, an image processing technique is proposed for tracing a moving marker in low-dose imaging.

Integration of a real-time tumor monitoring system into gated proton spot-scanning beam therapy: an initial phantom study using patient tumor trajectory data.

Purpose: In spot-scanning proton therapy, the interplay effect between tumor motion and beam delivery leads to deterioration of the dose distribution. To mitigate the impact of tumor motion, gating in combination with repainting is one of the most promising methods that have been proposed. This study focused on a synchrotron-based spot-scanning proton therapy system integrated with real-time tumor monitoring.

What is the appropriate size criterion for proton radiotherapy for hepatocellular carcinoma? A dosimetric comparison of spot-scanning proton therapy versus intensity-modulated radiation therapy.

Background: We performed a dosimetric comparison of spot-scanning proton therapy (SSPT) and intensity-modulated radiation therapy (IMRT) for hepatocellular carcinoma (HCC) to investigate the impact of tumor size on the risk of radiation induced liver disease (RILD).

Methods: A number of alternative plans were generated for 10 patients with HCC. The gross tumor volumes (GTV) varied from 20.

Biological effect of dose distortion by fiducial markers in spot-scanning proton therapy with a limited number of fields: a simulation study.

Purpose: In accurate proton spot-scanning therapy, continuous target tracking by fluoroscopic x ray during irradiation is beneficial not only for respiratory moving tumors of lung and liver but also for relatively stationary tumors of prostate. Implanted gold markers have been used with great effect for positioning the target volume by a fluoroscopy, especially for the cases of liver and prostate with the targets surrounded by water-equivalent tissues. However, recent studies have revealed that gold markers can cause a significant underdose in proton therapy.

Preliminary study on potential of the jPET-D4 human brain scanner for small animal imaging.

Objective: One trend in positron emission tomography (PET) instrumentation over the last decade has been the development of scanners dedicated to small animals such as rats and mice. Thicker crystals, which are necessary to obtain higher sensitivity, result in degraded spatial resolution in the peripheral field-of-view (FOV) owing to the parallax error. On the other hand, we are developing the jPET-D4, which is a dedicated human brain PET scanner that has a capability for depth-of-interaction (DOI) measurement.

Noninvasive and quantitative assessment of the function of multidrug resistance-associated protein 1 in the living brain.

Multidrug resistance-associated protein 1 (MRP1) acts as a defense mechanism by pumping xenobiotics and endogenous metabolites out of the brain. The currently available techniques for studying brain-to-blood efflux have significant limitations related to either their invasiveness or the qualitative assessment. Here, we describe an in vivo method, which overcomes these limitations for assessing MRP1 function, using positron emission tomography (PET) and a PET probe.

Feasibility studies of 4'-[methyl-(11)C]thiothymidine as a tumor proliferation imaging agent in mice.

This study reports on the radiosynthesis and feasibility studies of 4'-[methyl-(11)C]thiothymidine ([methyl-(11)C]S-dThd) as a tumor proliferation imaging agent. [Methyl-(11)C]S-dThd was synthesized by rapid methylation of corresponding 5-trimethylstannyl- or 5-tributylstannyl-precursor via a palladium-promoted Stille cross-coupling reaction with [(11)C]methyl iodide. The decay-corrected radiochemical yields of [methyl-(11)C]S-dThd synthesized by the corresponding 5-trimethylstannyl-precursor and 5-tributylstannyl-precursor based on [(11)C]CO(2) were 18.