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Title: SU-F-T-485: Independent Remote Audits for TG51 NonCompliant Photon Beams Performed by the IROC Houston QA Center

Abstract

Purpose: IROC-H conducts external audits for output check verification of photon and electron beams. Many of these beams can meet the geometric requirements of the TG 51 calibration protocol. For those photon beams that are non TG 51 compliant like Elekta GammaKnife, Accuray CyberKnife and TomoTherapy, IROC-H has specific audit tools to monitor the reference calibration. Methods: IROC-H used its TLD and OSLD remote monitoring systems to verify the output of machines with TG 51 non compliant beams. Acrylic OSLD miniphantoms are used for the CyberKnife. Special TLD phantoms are used for TomoTherapy and GammaKnife machines to accommodate the specific geometry of each machine. These remote audit tools are sent to institutions to be irradiated and returned to IROC-H for analysis. Results: The average IROC-H/institution ratios for 480 GammaKnife, 660 CyberKnife and 907 rotational TomoTherapy beams are 1.000±0.021, 1.008±0.019, 0.974±0.023, respectively. In the particular case of TomoTherapy, the overall ratio is 0.977±0.022 for HD units. The standard deviations of all results are consistent with values determined for TG 51 compliant photon beams. These ratios have shown some changes compared to values presented in 2008. The GammaKnife results were corrected by an experimentally determined scatter factor of 1.025 in 2013. Themore » TomoTherapy helical beam results are now from a rotational beam whereas in 2008 the results were from a static beam. The decision to change modality was based on recommendations from the users. Conclusion: External audits of beam outputs is a valuable tool to confirm the calibrations of photon beams regardless of whether the machine is TG 51 or TG 51 non compliant. The difference found for TomoTherapy units is under investigation. This investigation was supported by IROC grant CA180803 awarded by the NCI.« less

Authors:
; ; ; ; ;  [1]
  1. UT MD Anderson Cancer Center, Houston, TX (United States)
Publication Date:
OSTI Identifier:
22649072
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
61 RADIATION PROTECTION AND DOSIMETRY; 60 APPLIED LIFE SCIENCES; AUDITS; CALIBRATION; COMPUTERIZED TOMOGRAPHY; CT-GUIDED RADIOTHERAPY; ELECTRON BEAMS; PHOTON BEAMS

Citation Formats

Alvarez, P, Molineu, A, Lowenstein, J, Taylor, P, Kry, S, and Followill, D. SU-F-T-485: Independent Remote Audits for TG51 NonCompliant Photon Beams Performed by the IROC Houston QA Center. United States: N. p., 2016. Web. doi:10.1118/1.4956670.
Alvarez, P, Molineu, A, Lowenstein, J, Taylor, P, Kry, S, & Followill, D. SU-F-T-485: Independent Remote Audits for TG51 NonCompliant Photon Beams Performed by the IROC Houston QA Center. United States. doi:10.1118/1.4956670.
Alvarez, P, Molineu, A, Lowenstein, J, Taylor, P, Kry, S, and Followill, D. Wed . "SU-F-T-485: Independent Remote Audits for TG51 NonCompliant Photon Beams Performed by the IROC Houston QA Center". United States. doi:10.1118/1.4956670.
@article{osti_22649072,
title = {SU-F-T-485: Independent Remote Audits for TG51 NonCompliant Photon Beams Performed by the IROC Houston QA Center},
author = {Alvarez, P and Molineu, A and Lowenstein, J and Taylor, P and Kry, S and Followill, D},
abstractNote = {Purpose: IROC-H conducts external audits for output check verification of photon and electron beams. Many of these beams can meet the geometric requirements of the TG 51 calibration protocol. For those photon beams that are non TG 51 compliant like Elekta GammaKnife, Accuray CyberKnife and TomoTherapy, IROC-H has specific audit tools to monitor the reference calibration. Methods: IROC-H used its TLD and OSLD remote monitoring systems to verify the output of machines with TG 51 non compliant beams. Acrylic OSLD miniphantoms are used for the CyberKnife. Special TLD phantoms are used for TomoTherapy and GammaKnife machines to accommodate the specific geometry of each machine. These remote audit tools are sent to institutions to be irradiated and returned to IROC-H for analysis. Results: The average IROC-H/institution ratios for 480 GammaKnife, 660 CyberKnife and 907 rotational TomoTherapy beams are 1.000±0.021, 1.008±0.019, 0.974±0.023, respectively. In the particular case of TomoTherapy, the overall ratio is 0.977±0.022 for HD units. The standard deviations of all results are consistent with values determined for TG 51 compliant photon beams. These ratios have shown some changes compared to values presented in 2008. The GammaKnife results were corrected by an experimentally determined scatter factor of 1.025 in 2013. The TomoTherapy helical beam results are now from a rotational beam whereas in 2008 the results were from a static beam. The decision to change modality was based on recommendations from the users. Conclusion: External audits of beam outputs is a valuable tool to confirm the calibrations of photon beams regardless of whether the machine is TG 51 or TG 51 non compliant. The difference found for TomoTherapy units is under investigation. This investigation was supported by IROC grant CA180803 awarded by the NCI.},
doi = {10.1118/1.4956670},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = {Wed Jun 15 00:00:00 EDT 2016},
month = {Wed Jun 15 00:00:00 EDT 2016}
}
  • Purpose: Analyze the results from irradiations of an anthropomorphic liver phantom based on irradiation technique and number of isocenters used for the SBRT delivery. Methods: The phantom consists of a water-fillable plastic shell that has a polystyrene insert, representing the liver which includes two Solid WaterTM targets (PTV1 and PTV2) mimicking liver metastases. The two targets, PTV1 and PTV2 are non-coplanar and are an ovoid 2 cm in diameter and 2.5 cm long and a 3 cm diameter sphere, respectively. Each PTV houses one TLD and 2 planes of radiochromic film. The phantom and a motion table to simulate respiratorymore » motion is sent to institutions sthat are instructed to design and deliver a stereotactic treatment plan that delivers 6 Gy to ≥ 95% of each PTV. The maximum motion of the phantom on the motion table was 1 cm in the superior-inferior direction. Results: Irradiations from 93 institutions have been analyzed. The acceptance criteria are ±7% for the TLD and 85% of the pixels in a region surrounding each PTV passing a ±7%/4 mm global gamma analysis. Sixty-seven (71%) irradiations meet this criteria. The majority, 74 (80%), of the irradiations were performed with IMRT. 73% of the IMRT deliveries were within criteria and 68% of the 3D CRT delivery were within criteria. 32 of the irradiations had a single isocenter plan, 50 were performed with two isocenters and 11 irradiations were performed with CyberKnife and TomoTherapy units where the concept of isocenter is not applicable. The pass rate for the single, dual and no isocenter irradiations were 69%, 74% and 73%, respectively and are not statistically different. Conclusion: The pass rate for the anthropomorphic liver phantom is approximately 70%. There does not seem to be any correlation with number of isocenters used or irradiation technique used for the delivery. This work was supported by PHS CA180803 awarded by NCI, DHHS.« less
  • Purpose: To describe the results of IROC Houston’s international and domestic end-to-end QA phantom irradiations. Methods: IROC Houston has anthropomorphic lung, liver, head and neck, prostate, SRS and spine phantoms that are used for credentialing and quality assurance purposes. The phantoms include structures that closely mimic targets and organs at risk and are made from tissue equivalent materials: high impact polystyrene, solid water, cork and acrylic. Motion tables are used to mimic breathing motion for some lung and liver phantoms. Dose is measured with TLD and radiochromic film in various planes within the target of the phantoms. Results: The mostmore » common phantom requested is the head and neck followed by the lung phantom. The head and neck phantom was sent to 800 domestic and 148 international sites between 2011 and 2015, with average pass rates of 89% and 92%, respectively. During the past five years, a general upward trend exists regarding demand for the lung phantom for both international and domestic sites with international sites more than tripling from 5 (2011) to 16 (2015) and domestic sites doubling from 66 (2011) to 152 (2015). The pass rate for lung phantoms has been consistent from year to year despite this large increase in the number of phantoms irradiated with an average pass rate of 85% (domestic) and 95% (international) sites. The percentage of lung phantoms used in combination with motions tables increased from 38% to 79% over the 5 year time span. Conclusion: The number of domestic and international sites irradiating the head and neck and lung phantoms continues to increase and the pass rates remained constant. These end-to-end QA tests continue to be a crucial part of clinical trial credentialing and institution quality assurance. This investigation was supported by IROC grant CA180803 awarded by the NCI.« less
  • Purpose: To provide information pertaining to IROC Houston QA Center's (RPC) credentialing process for institutions participating in NCI-sponsored clinical trials. Methods: IROC Houston issues credentials for NCI sponsored study groups. Requirements for credentialing might include any combination of questionnaires, knowledge assessment forms, benchmarks, or phantom irradiations. Credentialing requirements for specific protocols can be found on IROC Houston's website (irochouston.mdanderson.org). The website also houses the credentialing status inquiry (CSI) form. Once an institution has reviewed the protocol's credentialing requirements, a CSI form should be completed and submitted to IROC Houston. This form is used both to request whether requirements have beenmore » met as well as to notify IROC Houston that the institution requests credentialing for a specific protocol. IROC Houston will contact the institution to discuss any delinquent requirements. Once the institution has met all requirements IROC Houston issues a credentialing letter to the institution and will inform study groups and other IROC offices of the credentials. Institutions can all phone the IROC Houston office to initiate credentialing or ask any credentialing related questions. Results: Since 2010 IROC has received 1313 credentialing status inquiry forms. We received 317 in 2010, 266 in 2011, 324 in 2012, and 406 in 2013. On average we receive 35 phone calls per week with multiple types of credentialing questions. Decisions regarding credentialing status are based on the protocol specifications and previous completed credentialing by the institution. In some cases, such as for general IMRT credentialing, up to 5 sites may be credentialed based on the credentialing of one main center. Each of these situations is handled individually. Conclusion: IROC Houston will issue radiation therapy credentials for the NCI trials in the National Clinical Trials Network. Credentialing requirements and the CSI form can be found online at the IROC Houston's website. Work supported by PHS grant CA10953 and CA081647 (NCI, DHHS)« less
  • Purpose: To understand the uncertainties in proton therapy treatment planning for the IROC- Houston proton phantom QA program due to variations in CT technique and proton energy. Methods: A CT phantom used by IROC-H during therapy site visits was scanned using three CT techniques (80, 120, 140kV) with a CT scanner used for proton therapy simulations and irradiated with a passively scattered beam at three energies (140, 200, 250 MeV) to measure, respectively, HU and Relative Linear Stopping Power (RLSP) in order to create HU to RLSP calibration curves for comparison with reference curves used by current proton treatment planningmore » systems. The phantom has proton equivalent materials with a wide variety of HU and RLSPs to allow for the creation of a calibration curve for common tissue equivalent materials. Treatment plans were created for a lung phantom using the various CT technique/ beam energy calibration curves to determine the differences in the dose distributions by performing a gamma analysis. Results: Comparison of the calibration curves created using the phantom materials showed a maximum difference of 12% for a given material between the custom curve and the reference curve currently used by the treatment planning system. The highest differences were a Result of using an 80 kV CT technique and a 250 MeV high proton energy. A comparison of the completed treatment plans will be presented. Conclusion: These results indicate the possibility of differences in proton HU to RLSP calibration curves caused by varying CT technique and proton energy that could manifest as differences in planned and delivered dose distributions, particularly at high proton energies and low kV CT techniques. These differences could Result in discrepancies not accounted for by IROC-Houston and could possibly affect proton institutions’ pass rate when irradiating the proton phantoms.« less
  • Purpose: To describe the proton phantoms that IROC Houston uses to approve and credential proton institutions to participate in NCI-sponsored clinical trials. Methods: Photon phantoms cannot necessarily be used for proton measurements because protons react differently than photons in some plastics. As such plastics that are tissue equivalent for protons were identified. Another required alteration is to ensure that the film dosimeters are housed in the phantom with no air gap to avoid proton streaming. Proton-equivalent plastics/materials used include RMI Solid Water, Techron HPV, blue water, RANDO soft tissue material, balsa wood, compressed cork and polyethylene. Institutions wishing to bemore » approved or credentialed request a phantom and are prioritized for delivery. At the institution, the phantom is imaged, a treatment plan is developed, positioned on the treatment couch and the treatment is delivered. The phantom is returned and the measured dose distributions are compared to the institution’s electronically submitted treatment plan dosimetry data. Results: IROC Houston has developed an extensive proton phantom approval/credentialing program consisting of five different phantoms designs: head, prostate, lung, liver and spine. The phantoms are made with proton equivalent plastics that have HU and relative stopping powers similar (within 5%) of human tissues. They also have imageable targets, avoidance structures, and heterogeneities. TLD and radiochromic film are contained in the target structures. There have been 13 head, 33 prostate, 18 lung, 2 liver and 16 spine irradiations with either passive scatter, or scanned proton beams. The pass rates have been: 100%, 69.7%, 72.2%, 50%, and 81.3%, respectively. Conclusion: IROC Houston has responded to the recent surge in proton facilities by developing a family of anthropomorphic phantoms that are able to be used for remote audits of proton beams. Work supported by PHS grant CA10953 and CA081647.« less