Author of

• 12544

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  P3.08 - Poster Session 3 - Radiotherapy (ID 199)

  • Event: WCLC 2013
  • Type: Poster Session
  • Track: Radiation Oncology + Radiotherapy
  • Presentations: 1
  • Moderators:
  • Coordinates: 10/30/2013, 09:30 - 16:30, Exhibit Hall, Ground Level

  • 12565

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    P3.08-021 - Patient Specific Quality Assurance for Lung Cancer Stereotactic Ablative Body Radiotherapy (ID 2559)

    09:30 - 09:30  |  Author(s): N. Clements
    • Abstract

    Background
    Hypofractionated image guided radiotherapy of extracranial targets has become increasingly popular as a treatment modality for inoperable patients with one or more small lesions, often referred to as Stereotactic Ablative Body Radiotherapy (SABR). Our institution is using SABR for lung, liver, spine and kidney tumours and is the lead in a multicentre clinical trial of radical SABR for early stage lung cancer. Current and future trends in patient safety and quality assurance (QA) programs are towards ensuring patient safety using the most efficient methods. There is limited published work on patient specific QA for lung SABR treatments on which to base risk management QA programs. Thus, we have performed a review of the first two years of lung SABR patient specific QA process with the aims of highlighting specific areas of uncertainty in lung SABR delivery with the aims of improving efficiency and effectiveness of our QA program. This presentation will detail the results of the review and the evolution of the QA program to a risk-management based approach.

    Methods
    SABR involves one or few fractions of high radiation dose typically delivered in many small fields or arcs. Tight margins are often applied to mobile targets through heterogeneous tissue density with non-coplanar beams. We have conducted thorough QA for individual patients similar to the more common IMRT QA with particular reference to motion management. Individual patient QA was performed in a Perspex phantom (Modus Medical) using a point dose verification and radiochromic film for verification of the dose distribution. The results for the first 33 plans were analysed with the aim of revising QA procedures for future lung SABR plans. The results from these plans were then used to highlight particular areas of delivery uncertainty which require attention during patient specific QA.

    Results
    While individual beams could vary by up to 7%, the total dose in the target was found to be within ±2% of the prescribed dose for all 33 plans. The QA process verified all aspects of the plan delivery including non-coplanar geometry, isocentre accuracy under couch rotation and internal target volume construction. The QA process highlighted the importance of accounting for couch transmission and demonstrated the need for accurate motion management strategies. The review of the first 33 plans lead to the creation of a risk-management based approach to QA of subsequent treatment plans. Particular emphasis is now placed on verification of small field dosimetry and motion management strategies for lesions with large motion.

    Conclusion
    QA is essential for complex radiotherapy deliveries such as SABR. We found individual patient QA helpful in setting up the technique and understanding weak points in the process chain. Ongoing review of the patient specific QA results has lead to improvements in efficiency in the process, facilitating a risk-management based approach to patient specific QA for SABR.