Author of

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  O14 - Radiotherapy - Toxicity and Clinical Trials (ID 105)

  • Event: WCLC 2013
  • Type: Oral Abstract Session
  • Track: Radiation Oncology + Radiotherapy
  • Presentations: 1
  • Moderators:G. Pratt, S.K. Vinod
  • Coordinates: 10/29/2013, 10:30 - 12:00, Parkside Ballroom A, Level 1

  • 12080

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    O14.03 - Using generalized equivalent uniform dose (gEUD) to model volume effects for brachial plexopathy after high-dose stereotactic body radiation therapy (SBRT) (ID 2835)

    10:30 - 12:00  |  Author(s): E.L. Williams
    • Abstract
    • Presentation
    • Slides

    Background
    Brachial plexopathy is a rare but important toxicity of radiation therapy because of its significant impact on quality of life. For standard fractionated raiation therapy, good models of brachial plexus (BP) tolerance exist. However, the tolerance of the BP to SBRT is not well understood. We combined data from SBRT for apical lung and metastatic lesions near the BP spanning a wide range of doses and hypofractionation schemes. We determined the clinical incidence of brachial plexopathy and modeled the correlation with generalized equivalent uniform dose (gEUD) for both physical and biologically effective doses (BED) using a range of fractionation-sensitivity parameters (α/β) and volume effect parameters (a).

    Methods
    Between 2004 and 2012, 180 lesions (76 lung lesions and 104 metastatic lesions) located above the aortic arch and below the level of C3 were treated with SBRT. Patients with prior radiation therapy to this region were excluded. Metastases were treated to 14-30 Gy in 1-5 fractions and lung tumors to 22-60 Gy in 1-5 fractions. The BP was contoured per RTOG atlas definitions. For 54 centrally located spine metastases, both left and right BP were contoured and analyzed separately for a total of 234 BPs in 180 patients. Brachial plexopathy of ≥grade 1 (CTCAE v4.0) was the primary endpoint. Maximum dose to the BP (Dmax), minimum dose to the hottest 5% of the BP (D05), and their respective BEDs were calculated using α/β= 3 Gy. The gEUD was also calculated with the volume effect parameter (a) ranging from log~10~a= -1.0 to +1.0 in log~10~a steps of 0.1. A logistic regression model (LR) was fit to the data as a function of a. Clinical dose recommendations were derived with logrank tests using median splits.

    Results
    With median follow-up of 15.1 months, brachial plexopathy due to SBRT occurred in 9/234 BPs. Severity of brachial plexopathy was grade 1 in two, grade 2 in five and grade 3 in two patients. Median time to onset of brachial plexopathy was 6.2 months and the 1-/2-year actuarial rates were 3.3%/5.6%. For all patients the median BED for BP Dmax was 117.5 Gy and for D05 was 89.3 Gy. Median BED Dmax for patients with and without brachial plexopathy was 234 Gy and 115.2 Gy respectively (p=0.002). Brachial plexopathy was significantly associated with BP BED Dmax (p=0.002), and D05 (p=0.015), but not with physical dose. Using LR, the strongest correlation of gEUD with brachial plexopathy occurred for log~10~a= 1.0 using BED (p=0.002), which is representative of the BED Dmax. LR models of BED Dmax versus brachial plexopathy for various α/β values showed that any α/β<25 was a significantly better predictor than physical dose.

    Conclusion
    Brachial plexopathy is significantly associated with BED Dmax ≥117.5 Gy (equivalent to a physical dose of 17 Gy x1, 9.3 Gy x3 or 7 Gy x5 fractions) and D05 ≥89.3 Gy. BED Dmax was the most important predictor of this rare but serious toxicity.

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