Methods of Accurate 106Ru and 125I Eye Plaque Dosimetry Using Radiochromic Film in a Solid Water “Eye” Phantom and a Small Silicon Diode in a Water Tank

Purpose: The use of 106Ru eye plaques for the treatment of intraocular malignancies has produced inconsistent clinical outcomes and has even resulted in treatment failures. I hypothesized that inconsistent clinical results were attributable to high uncertainties in 106Ru eye plaque dosimetry. Furthermore, I hypothesized that more accurate methods for assessing radiation dose from eye plaques would lead to more reliable treatment planning and therefore better overall clinical outcomes. Methods: A Solid Water “eye” phantom with several novel features was developed for radiochromic film eye plaque dosimetry. Films perpendicular to the central axis of the eye plaques were sandwiched between inserts in the phantom. Small holes in the inserts enabled the film to be marked with respect to the eye plaques, assuring exact geometrical co-registration. In cooperation with the manufacturer, special thin radiochromic films were developed and utilized to permit dosimetric measurements almost at the eye plaque surface. Precise film punches were developed for the purpose of cutting films with diameters as small as 8.5 mm and making cutouts in films without damaging the cut edges. Findings from a secondary dosimetry system, utilizing a small silicon diode in a water tank, were compared to film data. In addition to testing the new dosimetry methods with 106Ru eye plaques, which utilize high energy (MeV) β emissions, this approach was also applied to 125I containing eye plaques, which due to their inherently lower energy (keV) γ emission spectrum, raised additional dosimetric complications. In the latter case dosimetry, films and the diode were calibrated for absolute dosimetry using calibrated 125I seeds in Solid Water and water, respectively, applying the TG-43 formalism. A novel calibration method of radiochromic film for low-energy photon dosimetry was introduced. Monte Carlo simulations were used to convert the results measured in Solid Water to liquid water, and to compare measured and simulated dosimetric results. Results: Dosimetric characterization of both 106Ru eye plaques and a novel concept 125I eye plaque are described. Furthermore, dosimetry of a 20 mm 125I Collaborative Ocular Melanoma Study (COMS) eye plaque validated the presumed substantial dose reduction resulting from its gold alloy backing and seed carrier insert predicted by Monte Carlo simulations. Dose distributions measured with radiochromic film were in good agreement with diode measurements and Monte Carlo simulations. Replicate film results were reproducible from 0.9% to 5.5%. As little as 4% non-uniformities in planar dose rates were easily detected using 106Ru eye plaques. The novel 125I eye plaques had uniform dose distributions. Dosimetric characterization of the 20 mm COMS plaque demonstrated that the plaque’s dose rate was 15% lower than that predicted by homogenous TG-43 calculations. Lastly, Monte Carlo simulations indicated dose conversion factors between water and film in Solid Water compared to water and Solid Water alone differed by as much as 16.8%. Change in the calcium content of Solid Water from 2.3% to 1.7% resulted in a 3.3% calculated difference in dose to film and in an 8.7% difference in dose to Solid Water. Conclusions: Precise and reproducible 106Ru and 125I eye plaque dosimetry was achieved utilizing radiochromic film in a water equivalent phantom and a small semiconductor diode in water. Co-registration of eye plaques and films permitted not only precise treatment planning calculations along the central axis of the plaque, but also made it possible to account for dosimetric non-uniformities using 2D or 3D methodologies. A calibrated 125I seed enabled calibration of the film and the diode for absolute dosimetry of 125I containing eye plaques. Dose measurements on the inner surface of the plaques provided precise assessment of the scleral dose, its homogeneity, and of the active area of the plaques for coverage determination. Monte Carlo simulations facilitated conversion of doses measured in various media to liquid water

Feasibility and safety of GliaSite brachytherapy in treatment of CNS tumors following neurosurgical resection

Purpose: To investigate feasibility and safety of GliaSite brachytherapy for treatment of central nervous system (CNS) tumors following neurosurgical resection. We report mature results of long-term follow-up, outcomes and toxicity. Materials and Methods: In the period from 2004 to 2007, 10 consecutive adult patients with recurrent, newly diagnosed, and metastatic brain malignancies underwent GliaSite brachytherapy following maximally safe neurosurgical resection. While 6/10 (60%) patients were treated for recurrence, having previously been treated with external beam radiotherapy (EBRT), 4/10 (40%) received radiotherapy (RT) for the first time. A median dose of 52.0 Gy (range, 45.0 - 60.0 Gy) was prescribed to 0.5 cm - 1.0 cm from the balloon surface. Radiation Therapy Oncology Group (RTOG) criteria were used to assess toxicities associated with this technique. Follow-up was assessed with MRI scans and was available on all enrolled patients. Results: Median follow-up was 38 months (range, 18 - 57 months). Mean size of GliaSite balloon was 3.4 cm (range, 2.0 - 4.0 cm). Median survival was 14.0 months for the entire cohort after the treatment. The 17.6 and 16.0 months average survival for newly diagnosed and recurrent high grade gliomas (HGG), respectively, translated into a three-month improvement in survival in patients with newly diagnosed HGG compared to historical controls (P = 0.033). There were no RTOG grades 3 or 4 acute or late toxicities. Follow-up magnetic resonance imaging (MRI) imaging did not identify radiation necrosis. Conclusions: Our data indicate that treatment with GliaSite brachytherapy is feasible, safe and renders acceptable local control, acute and long-term toxicities. We are embarking on testing larger numbers of patients with this treatment modality

Feasibility and safety of GliaSite brachytherapy in treatment of CNS tumors following neurosurgical resection

Purpose: To investigate feasibility and safety of GliaSite brachytherapy for treatment of central nervous system (CNS) tumors following neurosurgical resection. We report mature results of long-term follow-up, outcomes and toxicity. Materials and Methods: In the period from 2004 to 2007, 10 consecutive adult patients with recurrent, newly diagnosed, and metastatic brain malignancies underwent GliaSite brachytherapy following maximally safe neurosurgical resection. While 6/10 (60%) patients were treated for recurrence, having previously been treated with external beam radiotherapy (EBRT), 4/10 (40%) received radiotherapy (RT) for the first time. A median dose of 52.0 Gy (range, 45.0 - 60.0 Gy) was prescribed to 0.5 cm - 1.0 cm from the balloon surface. Radiation Therapy Oncology Group (RTOG) criteria were used to assess toxicities associated with this technique. Follow-up was assessed with MRI scans and was available on all enrolled patients. Results: Median follow-up was 38 months (range, 18 - 57 months). Mean size of GliaSite balloon was 3.4 cm (range, 2.0 - 4.0 cm). Median survival was 14.0 months for the entire cohort after the treatment. The 17.6 and 16.0 months average survival for newly diagnosed and recurrent high grade gliomas (HGG), respectively, translated into a three-month improvement in survival in patients with newly diagnosed HGG compared to historical controls (P = 0.033). There were no RTOG grades 3 or 4 acute or late toxicities. Follow-up magnetic resonance imaging (MRI) imaging did not identify radiation necrosis. Conclusions: Our data indicate that treatment with GliaSite brachytherapy is feasible, safe and renders acceptable local control, acute and long-term toxicities. We are embarking on testing larger numbers of patients with this treatment modality

Report of AAPM Task Group 235 Radiochromic Film Dosimetry: An update to TG-55

The use of radiochromic film (RCF) dosimetry in radiation therapy is extensive due to its high level of achievable accuracy for a wide range of dose values and its suitability under a variety of measurement conditions. However, since the publication of the 1998 AAPM Task Group 55, Report No. 63 on RCF dosimetry, the chemistry, composition, and readout systems for RCFs have evolved steadily. There are several challenges in using the new RCFs, readout systems and validation of the results depending on their applications. Accurate RCF dosimetry requires understanding of RCF selection, handling and calibration methods, calibration curves, dose conversion methods, correction methodologies as well as selection, operation and quality assurance (QA) programs of the readout systems. Acquiring this level of knowledge is not straight forward, even for some experienced users. This Task Group report addresses these issues and provides a basic understanding of available RCF models, dosimetric characteristics and properties, advantages and limitations, configurations, and overall elemental compositions of the RCFs that have changed over the past 20 yr. In addition, this report provides specific guidelines for data processing and analysis schemes and correction methodologies for clinical applications in radiation therapy