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Yttrium-90 microsphere brachytherapy of the liver exploits the distinctive features of the liver anatomy to treat liver malignancies with beta radiation and is gaining more wide spread clinical use. This report provides a general overview of microsphere liver brachytherapy and assists the treatment team in creating local treatment practices to provide safe and efficient patient treatment. Suggestions for future improvements are incorporated with the basic rationale for the therapy and currently used procedures. Imaging modalities utilized and their respective quality assurance are discussed. General as well as vendor specific delivery procedures are reviewed. The current dosimetry models are reviewed and suggestions for dosimetry advancement are made. Beta activity standards are reviewed and vendor implementation strategies are discussed. Radioactive material licensing and radiation safety are discussed given the unique requirements of microsphere brachytherapy. A general, team-based quality assurance program is reviewed to provide guidance for the creation of the local procedures. Finally, recommendations are given on how to deliver the current state of the art treatments and directions for future improvements in the therapy.

We have implemented a three-dimensional dose calculation technique accounting for dose inhomogeneity within the liver and tumor of a patient treated with 90 Y microspheres. Single-photon emission computed tomography(SPECT)images were used to derive the activity distribution within liver. A Monte Carlo calculation was performed to create a voxel dose kernel for the 90 Y source. The activity distribution was convolved with the voxel dose kernel to obtain the three-dimensional (3D) radiation absorbed dose distribution. An automated technique was developed to accurately register the computed tomography(CT) and SPECT scans in order to display the 3D dose distribution on the CT scans. In addition, dose-volume histograms were generated to fully analyze the tumor and liver doses. The calculated dose-volume histogram indicated that although the patient was treated to the nominal whole liver dose of 110 Gy, only 16% of the liver and 83% of the tumor received a dose higher than 110 Gy. The mean tumor and liver doses were 163 and 58 Gy, respectively.

A quality assurance method is developed for measuring, verifying and analyzing intensity modulated radiation fields. It is applicable for rotational and fixed-beam intensity modulated radiation therapy(IMRT)treatments. A gantry-mount device was constructed to measure the transmission dose of an IMRT field using radiographicfilms. A double-exposure technique with optimal kernel estimate method was developed to minimize the errors from measurements. A χ 2 confidence level test method was developed to detect the discrepancies between measured and prescribed IMRT fluence distributions. Our method was tested for rotational and fixed-beam IMRTtreatment verifications. The method was found insensitive to the hardware-related parameters for rotational and fixed-beam IMRTdeliveries. The χ 2 confidence level test was found to be more sensitive than linear correlation method in detecting relative small errors for cases with a few segments or narrow regions of interest. In conclusion, we demonstrated a quantitative method for verifying and analyzing IMRTtreatmentdeliveries.

Administration of yttrium-90 microspheres via the hepatic artery is an attractive approach to selectively delivertherapeuticdoses of radiation to livermalignancies. This procedure allows deliveringradiation absorbed doses in excess of 100 Gy to the tumors without significant liver toxicity. The microsphere therapy involves different specialties including medicaloncology,radiationoncology, nuclear medicine, interventional radiology, medical physics, and radiation safety. We have treated 80 patients with nonresectable hepatic tumors with yttrium-90 microspheres during the past two years on an institutional study protocol. The nominal radiation absorbed dose to the tumor in this study was 150 Gy. Required activity was calculated based on the nominal radiation absorbed dose and patient’s liver volume obtained from the CT scan, assuming a uniform distribution of the microspheres within the liver. Microspheres were administered via a catheter placed into the hepatic artery. The actual radiation absorbed doses to tumors and normal liver tissue were calculated retrospectively based on the patient’s 99 m Tc-MAA study and CT scans. As expected, the activity uptake within the liver was found to be highly nonuniform and multifold tumor to nontumor uptake was observed. A partition model was used to calculate the radiation absorbed dose within each region. For a typical patient the calculated radiation absorbed doses to the tumor and liver were 402 and 118 Gy, respectively. The radiation safety procedure involves confinement of the source and proper disposal of the contaminated materials. The average exposure rates at 1 m from the patients and on contact just anterior to the liver were 6 and 135 uSv/h, respectively. The special physics and dosimetry protocol developed for this procedure is presented.

Effective radioimmunotherapy may depend on a priori knowledge of the radiation absorbed dose distribution obtained by trace imaging activities administered to a patient before treatment. A new, fast, and effective treatment planning approach is developed to deal with a heterogeneous activity distribution. Calculation of the three-dimensional absorbed dose distribution requires convolution of a cumulated activity distribution matrix with a point-source kernel; both are represented by large matrices (64 x 64 x 64). To reduce the computation time required for these calculations, an implementation of convolution using three-dimensional (3-D) fast Hartley transform (FHT) is realized. Using the 3-D FHT convolution, absorbed dose calculation time was reduced over 1000 times. With this system, fast and accurate absorbed dose calculations are possible in radioimmunotherapy. This approach was validated in simple geometries and then was used to calculate the absorbed dose distribution for a patient's tumor and a bone marrow sample.

Yttrium-90 microsphere brachytherapy of the liver exploits the distinctive features of the liver anatomy to treat liver malignancies with beta radiation and is gaining more wide spread clinical use. This report provides a general overview of microsphere liver brachytherapy and assists the treatment team in creating local treatment practices to provide safe and efficient patient treatment. Suggestions for future improvements are incorporated with the basic rationale for the therapy and currently used procedures. Imaging modalities utilized and their respective quality assurance are discussed. General as well as vendor specific delivery procedures are reviewed. The current dosimetry models are reviewed and suggestions for dosimetry advancement are made. Beta activity standards are reviewed and vendor implementation strategies are discussed. Radioactive material licensing and radiation safety are discussed given the unique requirements of microsphere brachytherapy. A general, team-based quality assurance program is reviewed to provide guidance for the creation of the local procedures. Finally, recommendations are given on how to deliver the current state of the art treatments and directions for future improvements in the therapy.

Treatment verification has been a weak link in external beam radiation therapy. As new and more complicated treatment techniques, such as intensity-modulated radiation therapy (IMRT), are implemented into clinical practice, verifying the accuracy of treatment delivery becomes increasingly important. Existing methods for treatment verification are highly labor intensive. We have developed a method for verifying the delivery of external beam radiotherapy and implemented the methodology into a system consisting of both hardware and software components. The system uses grayscale images acquired on the treatment machine from the planned treatment beams. From these images, the photon fluence distribution of each beam is derived. These measured photon fluence maps are then used as input to a separate dose calculation engine to compute the delivered absolute dose and the dose distribution in the same patient, assuming that the patient is set up as required by the treatment plan. The dose distribution generated from the measured fluence maps can then be compared to that of the treatment plan. Software tools, such as overlaying isodose curves generated with this method on those imported from the plan, dose difference maps, dose difference volume histograms, and three-dimensional perspective views of the dose differences, have also been developed. The system thus provides a means to verify the dose, the dose prescription, and the monitor units applied. The potential exists with a suitable electronic portal imaging system to reduce the quality assurance efforts, especially for IMRT.

Purpose: Total body irradiation (TBI) with moving couch technique has been used in our clinic for years. Moving couch TMR for a field size has been acquired by multiplying TMR for a stationary beam and the ‘m factor’ defined as the ratio between moving phantom dose to stationary beam dose for same setup. The ‘m factor’ has been known to be field size dependent and not depth dependent. In order to replace lung and kidney blocks and achieve better dose uniformity using dynamic MLC, comprehensive understanding on the TMR for variable field sizes for an MLC leaf sequence is required. Method and Materials: A thorough measurement on the moving TMR has been performed. TMR's for field sizes of 5cm×40cm, 10cm×40cm, 15cm×40cm, 20cm×40cm and 30cm×40cm were measured both for the stationary and for the moving phantoms. Field sizes are defined at SAD 100cm and TMR's were measured at SCD 170cm for depths dmax to 34cm in 50cm×50cm×50cm water phantom with 6MV photon (21EX, Varian, Palo Alto, CA). Results: TMR's in moving phantom for different field sizes showed not more than 1% difference, while those of stationary phantom showed up to 34.8% difference for different sizes. The m factor which has been known to be a constant for a given field size rapidly increases after 15cm depth. Analysis of the data allowed us to understand the phenomena of measuring a point dose in a moving phantom. The key to the understanding was that both the phantom scatter and primary dose seen at the measurement position does not vary with field size when normalized to the reference condition. Conclusion: TMR's are independent to field size when couch is moving. This suggests that TMR variation does not need to be considered when designing the dose compensator with dynamic MLC for moving couch TBI.