Measuring liver radioembolization dose with positron emission tomography

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Background: There is no established way to measure radiation dose deposition during liver radioembolization to help quantify the shortcomings of prescription calculations, which do not consider size, shape, and location of tumors. We aimed to establish a standardized method of radioembolization dose measurement though a novel technique using Positron Emission Tomography and Computed Tomography (PET-CT). Methods: Patients who were recommended for liver radioembolization treatment were enrolled in a prospective single-arm registry study. Index lesions were contoured on the patients’ CT simulation scans. Immediate post-treatment PET/CTs were used to measure the deposited radiation dose by capturing the positron emission from the Yttrium-90’s daughter nuclei. The CT simulation scans were fused to the post-treatment PET/CT scans using rigid registration around the index lesions. The primary dosimetric outcomes were mean dose and dose to 70% of the tumor volume (D70). The optimal mean dose and D70 were > 100 Gy and > 70 Gy, respectively. Results: From November 2014 to November 2015, fifteen consecutive patients with either hepatocellular carcinoma (n = 4) or liver metastases (n = 11) were enrolled in the study. A total of 43 index lesions were contoured with a mean and median size of 18.2 cc and 5.4 cc, respectively. The average mean dose to the index lesions was 99.9 Gy (mean dose range: 2 – 298 Gy; Table). The mean and median D70 were 66.9 Gy and 71 Gy, respectively (range: 1.4 – 211 Gy; standard deviation [SD]: 40.3 Gy). The mean and median D90s were 43 Gy and 41 Gy, respectively. A total of 20 (46.5%) lesions received optimal mean dose and 23 (53.5%) lesions received optimal D70 dose. Conclusions: We established a successful standardized procedure utilizing PET/CT scans to measure the radiation dose delivered during liver radioembolization. The range of the doses received by the tumors underlines the need to collect dosimetric data for future treatment optimization. Dosimetric parameters. Clinical trial information: NCT02088775. [Table: see text]

3D inpatient dose reconstruction from the PET-CT imaging of 90Y microspheres for metastatic cancer to the liver: feasibility study

PURPOSE

The introduction of radioembolization with microspheres represents a significant step forward in the treatment of patients with metastatic disease to the liver. This technique uses semiempirical formulae based on body surface area or liver and target volumes to calculate the required total activity for a given patient. However, this treatment modality lacks extremely important information, which is the three-dimensional (3D) dose delivered by microspheres to different organs after their administration. The absence of this information dramatically limits the clinical efficacy of this modality, specifically the predictive power of the treatment. Therefore, the aim of this study is to develop a 3D dose calculation technique that is based on the PET imaging of the infused microspheres.

METHODS

The Fluka Monte Carlo code was used to calculate the voxel dose kernel for 90Y source with voxel size equal to that of the PET scan. The measured PET activity distribution was converted to total activity distribution for the subsequent convolution with the voxel dose kernel to obtain the 3D dose distribution. In addition, dose-volume histograms were generated to analyze the dose to the tumor and critical structures.

RESULTS

The 3D inpatient dose distribution can be reconstructed from the PET data of a patient scanned after the infusion of microspheres. A total of seven patients have been analyzed so far using the proposed reconstruction method. Four patients underwent treatment with SIR-Spheres for liver metastases from colorectal cancer and three patients were treated with Therasphere for hepatocellular cancer. A total of 14 target tumors were contoured on post-treatment PET-CT scans for dosimetric evaluation. Mean prescription activity was 1.7 GBq (range: 0.58-3.8 GBq). The resulting mean maximum measured dose to targets was 167 Gy (range: 71-311 Gy). Mean minimum dose to 70% of target (D70) was 68 Gy (range: 25-155 Gy). Mean minimum dose to 90% of target (D90) was 53 Gy (range: 13-125 Gy).

CONCLUSIONS

A three-dimensional inpatient dose reconstruction method has been developed that is based on the PET/CT data of a patient treated with 90Y microspheres. It allows for a complete description of the absorbed dose by the tumor and critical structures. It represents the first step in building predictive models for treatment outcomes for patients receiving this therapeutic modality as well as it allows for better analysis of patients' dose response and will ultimately improve future treatment administration.

An evidence based review of proton beam therapy: the report of ASTRO's emerging technology committee

Proton beam therapy (PBT) is a novel method for treating malignant disease with radiotherapy. The purpose of this work was to evaluate the state of the science of PBT and arrive at a recommendation for the use of PBT. The emerging technology committee of the American Society of Radiation Oncology (ASTRO) routinely evaluates new modalities in radiotherapy and assesses the published evidence to determine recommendations for the society as a whole. In 2007, a Proton Task Force was assembled to evaluate the state of the art of PBT. This report reflects evidence collected up to November 2009. Data was reviewed for PBT in central nervous system tumors, gastrointestinal malignancies, lung, head and neck, prostate, and pediatric tumors. Current data do not provide sufficient evidence to recommend PBT in lung cancer, head and neck cancer, GI malignancies, and pediatric non-CNS malignancies. In hepatocellular carcinoma and prostate cancer and there is evidence for the efficacy of PBT but no suggestion that it is superior to photon based approaches. In pediatric CNS malignancies PBT appears superior to photon approaches but more data is needed. In large ocular melanomas and chordomas, we believe that there is evidence for a benefit of PBT over photon approaches. PBT is an important new technology in radiotherapy. Current evidence provides a limited indication for PBT. More robust prospective clinical trials are needed to determine the appropriate clinical setting for PBT.

Shielding design for a laser-accelerated proton therapy system

In this paper, we present the shielding analysis to determine the necessary neutron and photon shielding for a laser-accelerated proton therapy system. Laser-accelerated protons coming out of a solid high-density target have broad energy and angular spectra leading to dose distributions that cannot be directly used for therapeutic applications. A special particle selection and collimation device is needed to generate desired proton beams for energy- and intensity-modulated proton therapy. A great number of unwanted protons and even more electrons as a side-product of laser acceleration have to be stopped by collimation devices and shielding walls, posing a challenge in radiation shielding. Parameters of primary particles resulting from the laser-target interaction have been investigated by particle-in-cell simulations, which predicted energy spectra with 300 MeV maximum energy for protons and 270 MeV for electrons at a laser intensity of 2 x 10(21) W cm(-2). Monte Carlo simulations using FLUKA have been performed to design the collimators and shielding walls inside the treatment gantry, which consist of stainless steel, tungsten, polyethylene and lead. A composite primary collimator was designed to effectively reduce high-energy neutron production since their highly penetrating nature makes shielding very difficult. The necessary shielding for the treatment gantry was carefully studied to meet the criteria of head leakage <0.1% of therapeutic absorbed dose. A layer of polyethylene enclosing the whole particle selection and collimation device was used to shield neutrons and an outer layer of lead was used to reduce photon dose from neutron capture and electron bremsstrahlung. It is shown that the two-layer shielding design with 10-12 cm thick polyethylene and 4 cm thick lead can effectively absorb the unwanted particles to meet the shielding requirements.