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

  • 12551

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    P3.08-007 - Stereotactic Ablative Radiotherapy (SABR) of Centrally Located Early Stage Lung Cancer Accrued to RTOG 0813: Novel Scoring System to Compare Plan Quality of Volumetric Modulated Arc Therapy (VMAT) versus Robotic Radiosurgery (ID 1068)

    09:30 - 09:30  |  Author(s): E. Henderson
    • Abstract

    Background
    Central lung tumours pose a challenge for stereotactic ablative radiotherapy (SABR) due to proximity to vital organs and risk of potentially fatal toxicity. RTOG 0813 is an attempt to determine a safe dose for these tumours in an era where many institutions have multiple technologies that can deliver lung SABR. The purpose of this study is to use a novel scoring system to compare two different SABR platforms, robotic radiosurgery (RRS) and linac-based volumetric modulated arc therapy (VMAT), in a cohort of patients actually treated on 0813. The comparison is limited to target coverage and organ-at-risk (OAR) sparing capability for this technically challenging group of patients.

    Methods
    All 5 patients from our institution accrued to RTOG 0813 were selected for this study. Eight planners (4 VMAT, 4 RRS) with combined experience of >500 lung SABR cases re-planned each case for 60 Gy in 5 fractions. Patient setup, contouring details, and planning constraints were as per 0813. Monte Carlo planning was performed on Monaco v3.20 (Elekta Inc., MI, USA) for VMAT and Multiplan v4.5.0 (Accuray Inc., Sunnyvale, USA) for RRS on CyberKnife. An objective scoring system was designed that included each dose-volume 0813 protocol criterion. For each target requirement or OAR constraint a “structure score” was assigned whereby [Actual Plan parameter /Expected 0813 parameter] X priority factor = structure score. Priority factors (high 0.9, intermediate 0.6, and low 0.3) were assigned by 3 experienced lung SABR radiation oncologists for each of the 5 patients given that different OARs were of greater concern depending on exact target location. A ‘final plan score’ was the sum of all structure scores, with a lower overall score indicating a plan that best achieved target coverage and OAR avoidance in keeping with radiation oncologist priority. To reduce inter-planner bias more than one plan was created for each of the 5 patients using both modalities and only the best plans were selected for comparison.

    Results
    A total of 15 VMAT and 10 RRS plans were submitted for analysis, each satisfying the minimum 0813 protocol requirements. Using the scoring system, a final plan score was obtained for all 25 plans with a median VMAT score of 8.02 (range 5.52 to 10.09) and RRS score of 7.1 (range 4.98 to 12.41). The lowest scoring VMAT plan was then compared with the lowest scoring RRS plan for each patient. Analysis of target coverage parameters showed that both modalities had similar scores, indicating an equivalent ability to conformally cover the target. RRS plans had lower OAR scores (mean reduction of 1.3) compared to VMAT plans. Overall the plan scores for each patient (RRS: VMAT) were: Patient 1 (6.74:9.2), Patient 2 (6.69:7.32), Patient 3 (4.98:5.94), Patient 4 (7.69:8.92), Patient 5 (5.78:7.36).

    Conclusion
    When using a scoring system based on RTOG 0813 planning criteria to compare patient plans from two different lung SABR delivery systems, 5 of 5 patients planned using a robotic radiosurgery system had more favourable overall scores compared to VMAT linac delivery for centrally located tumours.