Department of Radiation Oncology Works

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Superimposition of beams to vary shot size in gamma knife stereotactic radiosurgery
(American Association of Physicists in Medicine, 2002) Bank, Morris I.; Timmerman, Robert; Radiation Oncology, School of Medicine
The Leksell Gamma Knife [Elekta Corp] uses helmets as collimators to produce four standard beam sizes. The nominal beam diameters are 18, 14, 8, and 4 mm. During computer treatment planning for gamma knife stereotactic radiosurgery, the size of the treated volume may differ from the standard beam sizes. To maintain conformality of the isodose curves to the treated volume, beam sizes may be superimposed during computer treatment planning to produce beam diameters that are intermediate to the standard beams. A study of superimposed gamma knife beams was performed to confirm the accuracy of this method and to verify the accuracy of the GammaPlan treatment planning computer. Superimposed beams were simulated on the Elekta treatment planning computer, GammaPlan, version 4.12, and tested by film measurements of beam profiles for single helmet sizes and superimposed shots with various beam weightings. The weighting for each beam size is varied to attain the beam size diameter desired. The beams were defined at the 50% isodose line. The profiles of the superimposed beams were obtained and compared with the single helmet shots. The uniformity of the resulting beams was measured. The results show a linear relationship between beam size and beam weighting for the superimposed beams. The film measurements confirm the computer calculations.
Ion chamber measurements of transverse gamma knife beam profiles
(American Association of Physicists in Medicine, 2002) Bank, Morris I.; Radiation Oncology, School of Medicine
A microchamber, PTW Pinpoint 31006, was used to measure transverse beam profiles for an Elekta Gamma Knife, Model B, and compared with profiles measured with film dosimetry. The microchamber sensitive volume has a diameter of 2 mm, which is smaller than the gamma knife beams, and a length of 5 mm. The chamber was mounted in a custom cassette in a spherical plastic phantom, supplied by Elekta, and oriented in a sagittal plane with the 2-mm dimension at right angles to the transverse plane. The phantom was manually moved across the beam, using the gamma knife x-coordinate trunnions, to measure the profiles. Profiles were also measured with V-film placed in a cassette mounted in the spherical plastic phantom. The films were scanned with a Scanditronix film scanner and converted to dose with a density to dose calibration curve. The results were superimposed for comparison. The beam width at the 50% intensity was measured from the film profiles to give the dimensions of the beams in the orthagonal planes. The ion chamber measurements are compared with the film results for the transverse, x profiles. Good agreement between the film and ion chamber transverse profiles is observed.
Response to “Radiation Therapeutic Gain and Asian Botanicals,” by Stephen Sagar
(SAGE Publications, 2010-03-21) Lawenda, Brian D.; Radiation Oncology, School of Medicine
Numerous botanical agents, many of which are used in whole medical system practices (i.e. traditional Chinese medicine, Ayurvedic medicine, etc.), have been shown to exhibit radiomodifying effects on tumors and normal tissues in-vitro and invivo studies. Some of these agents can enhance the therapeutic gain of radiation therapy by either acting as a radiosensitizer to tumor cells and/or as a radioprotector to normal cells. Botanical agents are comprised of multiple phytochemical compounds that may work individually or synergistically to not only improve radiation therapy outcomes, but may also exhibit a variety of anti-cancer effects as well. It will be important to evaluate these botanicals for efficacy, tumor specificity, and safety profiles before they can be recommended during radiation therapy.
A quality assurance phantom for electronic portal imaging devices
(American Association of Physicists in Medicine, 2011) Das, Indra J.; Cao, Minsong; Cheng, Chee-Wai; Misic, Vladimir; Scheuring, Klaus; Schüle, Edmund; Johnstone, Peter A.S.; Radiation Oncology, School of Medicine
Electronic portal imaging device (EPID) plays an important role in radiation therapy portal imaging, geometric and dosimetric verification. Consistent image quality and stable radiation response is necessary for proper utilization that requires routine quality assurance (QA). A commercial ‘EPID QC’ phantom weighing 3.8 kg with a dimension of 25 × 25 × 4.8 cm3 is used for EPID QA. This device has five essential tools to measure the geometric accuracy, signal‐to‐noise ratio (SNR), dose linearity, and the low‐ and the high‐contrast resolutions. It is aligned with beam divergence to measure the imaging and geometric parameters in both X and Y directions, and can be used as a baseline check for routine QA. The low‐contrast tool consists of a series of holes with various diameters and depths in an aluminum slab, very similar to the Las Vegas phantom. The high‐resolution contrast tool provides the modulation transfer function (MTF) in both the x‐ and y‐dimensions to measure the focal spot of linear accelerator that is important for imaging and small field dosimetry. The device is tested in different institutions with various amorphous silicon imagers including Elekta, Siemens and Varian units. Images of the QA phantom were acquired at 95.2 cm source‐skin‐distance (SSD) in the range 1–15 MU for a 26 × 26 cm2 field and phantom surface is set normal to the beam direction when gantry is at 0° and 90°. The epidSoft is a software program provided with the EPID QA phantom for analysis of the data. The preliminary results using the phantom on the tested EPID showed very good low‐contrast resolution and high resolution, and an MTF (0.5) in the range of 0.3–0.4 lp/mm. All imagers also exhibit satisfactory geometric accuracy, dose linearity and SNR, and are independent of MU and spatial orientations. The epidSoft maintains an image analysis record and provides a graph of the temporal variations in imaging parameters. In conclusion, this device is simple to use and provides testing on basic and advanced imaging parameters for daily QA on any imager used in clinical practices
A semi-empirical model for the therapeutic range shift estimation caused by inhomogeneities in proton beam therapy
(American Association of Physicists in Medicine, 2012-03-08) Moskvin, Vadim; Cheng, Chee-Wai; Fanelli, Leia; Zhao, Li; Das, Indra J.; Radiation Oncology, School of Medicine
The purpose of this study was to devise a simple semi-empirical model to estimate the range shift in clinical practices with high-Z inhomogeneity in proton beam. A semi-empirical model utilizing the logarithmic dependence on Z in stopping power from Bohr's classical approach has been developed to calculate the range shift due to the presence of inhomogeneity. Range shift from metallic plates of atomic number Z of various thicknesses were measured in water using a parallel plate ionization chamber and calculated with the FLUKA Monte Carlo code. The proton range shifts for bone and polymethyl methacrylate (PMMA) were estimated using the semi-empirical model and compared with Monte Carlo calculation. The semi-empirical equation to determine range shift and water equivalent thickness is presented. The model predicts a shift of the therapeutic range to within 2.5% accuracy for initial proton energies of 50 to 250 MeV and atomic numbers from 3.3 (effective Z for water) to 82. This equation is independent of beam energy, and thus provides range shift from high-Z materials without the knowledge of proton energy. The proposed method of calculating the therapeutic range shift accurately requires only knowledge of the effective or actual atomic number of the inhomogeneity and the thickness of the inhomogeneity along the beam direction. The model generalizes the range shift calculation for any material based on its effective atomic number, and permits reliable prediction of the range shift for material combinations where no data is currently available. The proposed model can be readily implemented in routine clinical practice for proton range shift estimation and quality assurance on the treatment planning.
Comparison of 16 mm OSU-Nag and COMS eye plaques
(American Association of Physicists in Medicine, 2012-05-10) Zhang, Hualin; Davidorf, Frederick; Qi, Yujin; Radiation Oncology, School of Medicine
OSU-NAG eye plaques use fewer sources than COMS-plaques of comparable size, and do not employ a Silastic seed carrier insert. Monte Carlo modeling was used to calculate 3D dose distributions for a 16 mm OSU-NAG eye plaque and a 16 mm COMS eye plaque loaded with either Iodine-125 or Cesium-131 brachytherapy sources. The OSU-NAG eye plaque was loaded with eight sources forming two squares, whereas the COMS eye plaque was loaded with thirteen sources approximating three isocentric circles. A spherical eyeball 24.6 mm in diameter and an ellipsoid-like tumor 6 mm in height and 12 mm in the major and minor axes were used to evaluate the doses delivered. To establish a fair comparison, a water seed carrier was used instead of the Silastic seed carrier designed for the traditional COMS eye plaque. Calculations were performed on the dose distributions along the eye plaque axis and the DVHs of the tumor, as well as the 3D distribution. Our results indicated that, to achieve a prescription dose of 85 Gy at 6 mm from the inner sclera edge for a six-day treatment, the OSU-NAG eye plaque will need 6.16 U/source and 6.82U/source for 125I and 131Cs, respectively. The COMS eye plaque will require 4.02 U/source and 4.43 U/source for the same source types. The dose profiles of the two types of eye plaques on their central axes are within 9% difference for all applicable distances. The OSU-NAG plaque delivers about 10% and 12% more dose than the COMS for 125I and 131Cs sources, respectively, at the inner sclera edge, but 6% and 3% less dose at the opposite retina. The DVHs of the tumor for two types of plaques were within 6% difference. In conclusion, the dosimetric quality of the OSU-NAG eye plaque used in eye plaque brachytherapy is comparable to the COMS eye plaque.
Impact of proton beam availability on patient treatment schedule in radiation oncology
(American Association of Physicists in Medicine, 2012-11-08) Miller, Eric D.; Derenchuk, Vladimir; Das, Indra J.; Johnstone, Peter A. S.; Radiation Oncology, School of Medicine
Proton beam therapy offers unique physical properties with potential for reduced toxicity and better patient care. There is an increased interest in radiation oncology centers to acquire proton therapy capabilities. The operation of a proton treatment center is quite different than a photon-based clinic because of the more complex technology involved, as well as the single proton beam source serving multiple treatment rooms with no backup source available. There is limited published data which investigates metrics that can be used to determine the performance of a proton facility. The purpose of this study is to evaluate performance metrics of Indiana University Cyclotron Operations (IUCO), including availability, mean time between failures, and mean time to repair, and to determine how changes in these metrics impact patient treatments. We utilized a computerized maintenance management system to log all downtime occurrences and servicing operations for the facility. These data were then used to calculate the availability as well as the mean time between failures and mean time to repair. Impact on patient treatments was determined by analyzing delayed and missed treatments, which were recorded in an electronic medical record and database maintained by the therapists. The availability of the IUCO proton beam has been increasing since beginning of operation in 2003 and averaged 96.9% for 2009 through 2011. The mean time between failures and mean time to repair were also determined and correlated with improvements in the maintenance and operating procedures of the facility, as well as environmental factors. It was found that events less than 15 minutes in duration have minimal impact on treatment delays, while events lasting longer than one hour may result in missed treatments. The availability of the proton beam was more closely correlated with delayed than with missed treatments, demonstrating the utility and limitations of the availability metric. In conclusion, we suggest that the availability metric and other performance parameters, such as the mean time between failures and the mean time to repair, should be used in combination with downtime impact on patient treatments in order to adequately evaluate the operational success of a proton therapy facility.
Radiation therapy in the last month of life
(Elsevier, 2013-10-16) Patel, Anand; Dunmore-Griffith, Jacquelyn; Lutz, Stephen; Johnstone, Peter A.S.; Department of Radiation Oncology, IU School of Medicine
Aim We sought to survey a large, multi-center patient sample to better characterize/quantify RT utilization at the end of life. Background Few objective data exist for radiation therapy (RT) delivery at end of life (EOL). Materials and methods Data were retrieved for all patients receiving RT in calendar year 2010 in the Department of Radiation Oncology at Indiana University (IU) and Howard University (HU) hospitals. Specific attention was made of the group of patients receiving RT in the last 30 days of life. Results A total of 852 patients received all or part of their RT during 2010 (HU: 139, IU: 713). At time of analysis in early 2012, 179 patients had died (21%). Fifty-four patients (6.3% of total; 30% of expired patients) died within 30 days of receiving their last treatment. Twenty patients (2.3% of total; 11.2% of expired patients) received RT within their last week of life. For both sites, the median time until death from completion of therapy was 12.5 days (range 2–30 days). Conclusions Radiation in the last month of life is likely to provide minimal palliation or survival benefit. This, coupled with the financial implications, time investment, and physical costs, suggests that physicians and patients should more strongly consider hospice, and minimize duration of palliative RT courses as far as possible. As with chemotherapy, RT utilization at EOL should be considered for collection as an overuse metric.
Oral and dental late effects in survivors of childhood cancer: a Children’s Oncology Group report
(Springer, 2014) Effinger, Karen E.; Migliorati, Cesar A.; Hudson, Melissa M.; McMullen, Kevin P.; Kaste, Sue C.; Ruble, Kathy; Guilcher, Gregory M. T.; Shah, Ami J.; Castellino, Sharon M.; Radiation Oncology, School of Medicine
Purpose: Multi-modality therapy has resulted in improved survival for childhood malignancies. The Children's Oncology Group Long-Term Follow-Up Guidelines for Survivors of Childhood, Adolescent, and Young Adult Cancers provide practitioners with exposure- and risk-based recommendations for the surveillance and management of asymptomatic survivors who are at least 2 years from completion of therapy. This review outlines the pathophysiology and risks for oral and dental late effects in pediatric cancer survivors and the rationale for oral and dental screening recommended by the Children's Oncology Group. Methods: An English literature search for oral and dental complications of childhood cancer treatment was undertaken via MEDLINE and encompassed January 1975 to January 2013. Proposed guideline content based on the literature review was approved by a multi-disciplinary panel of survivorship experts and scored according to a modified version of the National Comprehensive Cancer Network "Categories of Consensus" system. Results: The Children's Oncology Group oral-dental panel selected 85 relevant citations. Childhood cancer therapy may impact tooth development, salivary function, craniofacial development, and temporomandibular joint function placing some childhood cancer survivors at an increased risk for poor oral and dental health. Additionally, head and neck radiation and hematopoietic stem cell transplantation increase the risk of subsequent malignant neoplasms in the oral cavity. Survivors require routine dental care to evaluate for potential side effects and initiate early treatment. Conclusions: Certain childhood cancer survivors are at an increased risk for poor oral and dental health. Early identification of oral and dental morbidity and early interventions can optimize health and quality of life.
Correlation between target volume and electron transport effects affecting heterogeneity corrections in stereotactic body radiotherapy for lung cancer
(Oxford University Press, 2014) Akino, Yuichi; Das, Indra J.; Cardenes, Higinia R.; Desrosiers, Colleen M.; Radiation Oncology, School of Medicine
Recently, stereotactic body radiotherapy (SBRT) for lung cancer is conducted with heterogeneity-corrected treatment plans, as the correction greatly affects the dose delivery to the lung tumor. In this study, the correlation between the planning target volume (PTV) and the dose delivery is investigated by separation of the heterogeneity correction effects into photon attenuation and electron transport. Under Institutional Review Board exemption status, 74 patients with lung cancer who were treated with SBRT were retrospectively evaluated. All treatment plans were generated using an anisotropic analytical algorithm (AAA) of an Eclipse (Varian Medical Systems, Palo Alto, CA) treatment planning system. Two additional plans were created using the same treatment parameters (monitor units, beam angles and energy): a plan with no heterogeneity correction (NC), and a plan calculated with a pencil beam convolution algorithm (PBC). Compared with NC, AAA and PBC isocenter doses were on average 13.4% and 21.8% higher, respectively. The differences in the isocenter dose and the dose coverage for 95% of the PTV (D95%) between PBC and AAA were correlated logarithmically (ρ = 0.78 and ρ = 0.46, respectively) with PTV. Although D95% calculated with AAA was in general 2.9% larger than that for NC, patients with a small PTV showed a negative ΔD95% for AAA due to the significant effect of electron transport. The PTV volume shows logarithmic correlation with the effects of the lateral electron transport. These findings indicate that the dosimetric metrics and prescription, especially in clinical trials, should be clearly evaluated in the context of target volume characteristics and with proper heterogeneity correction.

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