Program Information
The Impact of Deviations Between Accumulated and Planned Dose in Luminal NTCP Models
M McCulloch1,3,7*, D Muenz2 , M Schipper 2,3 , M Velec4,6 , L Dawson4,5,6 , K Brock7 , 1Department of Nuclear Engineering and Radiological Sciences, 2Department of Biostatistics, and 3Department of Radiation Oncology, University of Michigan, Ann Arbor, MI; 4Radiation Medicine Program, Princess Margaret Hospital, University Health Network, Toronto, ON, Canada; 5Department of Radiation Oncology and the 6Institute of Medical Science, University of Toronto, Toronto, ON, Canada; 7Department of Imaging Physics, The University of Texas MD Anderson Cancer Center
Presentations
WE-RAM3-GePD-TT-5 (Wednesday, August 2, 2017) 10:30 AM - 11:00 AM Room: Therapy ePoster Theater
Purpose: Analyze the clinical impact of differences between planned and accumulated dose on the development and use of normal tissue complication probability (NTCP) models.
Methods: Thirty patients previously treated with SBRT for liver disease and for whom accumulated dose was computed, were assessed retrospectively. The linear quadratic equivalent dose at 2Gy per fraction (LQED2) and generalized equivalent uniform dose (gEUD) were calculated for planned and accumulated dose. New duodenal Lyman-Kutcher-Burman (LKB) NTCP models (α/β=2.5, n=0.09) were developed based on planned and accumulated gEUD to find the probability of toxicity that more accurately reflects the delivered dose. NTCP models based on the accumulated dose enables better understanding of the radiation-toxicity risk, however the delivered dose is not known at the time of planning. Therefor the error in using the new NTCP model developed from the accumulated dose was also evaluated for improvement in accuracy when used with the planning dose.
Results: For doses of 22 Gy and below, when using standard planned-dose NTCP models, the probability of duodenal toxicity was overestimated by up to 45%. For a protocol fixing a 10% toxicity risk to the duodenum, a 15 Gy max dose constraint would be necessary when using standard NTCP models based on planned dose, while an 18 Gy max dose would be allowed when using NTCP models based on accumulated dose. Evaluation of the duodenal toxicity risk using the accumulated-dose NTCP model at the time of planning provides a more accurate assessment of risk (average error 7.0%, SD 5.6) compared to using the standard, planned-dose model (average error 42.6%, SD 28.5).
Conclusion: Evaluation of the duodenal toxicity risk using the NTCP model developed from the accumulated dose at the time of planning provides a more accurate assessment of risk and can improve the understanding of radiation toxicity for normal tissues.
Funding Support, Disclosures, and Conflict of Interest: This work is supported by NIH P01Ca059827 and Grant No. 5RO1CA124714-02 from the U.S. National Institutes of Health.
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