Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_13_3243 - Feasibility of Temporally Feathered Intensity Modulated Radiation Therapy Plans: Techniques to Reduce Normal Tissue Toxicity

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Feasibility of Temporally Feathered Intensity Modulated Radiation Therapy Plans: Techniques to Reduce Normal Tissue Toxicity
S. Parsai1, J. D. Donaghue2, J. C. L. Alfonso3, N. P. Joshi1, A. R. Godley1, J. J. Caudell4, C. D. Fuller5, H. Enderling4, S. Koyfman1, and J. G. Scott1; 1Department of Radiation Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH, 2Moll Cancer Center, Fairview Hospital, Cleveland Clinic, Cleveland, OH, 3Department of Systems Immunology and Braunschweig Integrated Centre of Systems Biology, Helmholtz Centre for Infection Research, Braunschweig, Germany, 4H. Lee Moffitt Cancer Center and Research Institute, Department of Radiation Oncology, Tampa, FL, 5Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX

Purpose/Objective(s): Intensity modulated radiation therapy (IMRT) has allowed optimization of 3D spatial dose distributions allowing target coverage while reducing toxicity. We propose the next logical step in the evolution of IMRT, optimizing the fourth dimension of time through which radiotherapy is delivered to further reduce toxicity by increased sublethal damage repair. We term this strategy “temporally feathered radiation therapy” (TFRT). Prior in silico modeling using a dynamic normal tissue complication probability (NTCP) model of tissue response, which accounts for recovery, has demonstrated NTCP reduction with TFRT plans compared to conventionally planned IMRT. Here we demonstrate the feasibility of generating TFRT plans using current treatment planning systems.

Materials/Methods: Four patients with oropharyngeal cancer treated with definitive chemoradiation to a dose of 70 Gy in 35 fractions were planned using conventional IMRT techniques and compared to the TFRT technique. TFRT plans were generated as a composite of 5 iso-curative plans each with altered constraints on particular OARs of interest. For each of these plans, a single OAR is deprioritized such that it receives a higher dose (dH) while the remaining 4 OARs receive a lower dose (dL) than the standard fractional dose (dS) delivered in a conventional IMRT plan. Each plan is delivered a specific day of the week, which in effect leads to a dH delivered to each OAR once weekly and dL that is delivered to that OAR on the other 4 days. The OARs chosen for feathering depends on its proximity to the PTV. The dose delivered to the PTV is not altered, and receives 2 Gy per day.

Results: In this feasibility study, the feathered OARs included the oral cavity, right or left parotid glands, right or left submandibular glands, pharyngeal constrictor muscles, and supraglottis. PTV coverage was not compromised in TFRT planning with all plans meeting goals of >95% PTV coverage. The mean PTV dose was 1% cooler (73 cGy) in the composite TFRT plans compared to IMRT. The mean composite dose delivered to the OARs with TFRT plans was 2% higher than that of conventionally planned IMRT. The mean difference between dH and dS was 6 cGy.

Conclusion: In this study we prove the feasibility of TFRT planning. With small variations in the total dose delivered, OARs can be safely and successfully temporally feathered. The magnitude of NTCP reduction despite greater doses delivered to the OAR can be determined using a dynamic NTCP model which accounts for normal tissue recovery. This model requires parameters of alpha, beta, and recovery rates for OARs, which are currently unknown. This study warrants further evaluation in a prospective clinical trial.

Author Disclosure: S. Parsai: None. J.D. Donaghue: None. J.L. Alfonso: None. N.P. Joshi: None. A.R. Godley: Honoraria; Elekta. C.D. Fuller: Research Grant; National Institutes of Health, National Science Foundation, Elekta AB. Grant funding; Elekta AB. Honoraria; Nederlandse Organisatie voor Wetenschappelijk Onde. Consultant; Elekta AB, Nederlandse Organisatie voor Wetenschappelijk Onde. Travel Expenses; Elekta AB, Nederlandse Organisatie voor Wetenschappelijk Onde. Reviewer; Radiological Society of North America. Associate Editor; Radiographics. Data Management Task Force Committee Member; MR-LinAc Consortium. Member; National Cancer Institute. Task Group Member; American Association of Physicists in Medicine. S. Koyfman: Research Grant; Merck.

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