Room: AAPM ePoster Library
Purpose: For head and neck cancer patients treated with carbon-ion radiotherapy (CIRT), normal tissues such as brain and optic nerve are close to the irradiation field such that those may receive radiation damage. In order to estimate their clinical results, a dose-averaged LET (LETd) calculation tool was developed. We focused on the usefulness of LETd as a clinical analytical parameter.
Methods: In-house Heavy Ion Plan (HIPLAN) treatment planning system was used in the CIRT with a wobbler-scattering method. We developed the LETd and its standard deviation (LETdSD) calculation tool, and implemented in the HIPLAN. 33 head and neck patients treated with CIRT, who had follow-up more than 3 years and did not receive additional radiotherapy, were selected in order to evaluate local control and optic neuropathy. LETd and LETdSD for these 33 patients were calculated using the analysis tool.
Results: By implementing the clinical analysis tool in HIPLAN, it was possible to efficiently calculate and analyze the LETd and LETdSD for each patient. Of the 33 patients, 13 had local recurrences and 8 had optic neuropathies. Among 33 with and without recurrence cases, the mean LETd values in the PTV were 58.7±5.4 for with recurrence and 61.7±6.9 keV/µm for without recurrence, respectively. On the other hand, the mean LETd values were 45.6±12.8 for with optic neuropathy and 29.0±19.0 keV/µm for without optic neuropathy (p-value=0.046).
Conclusion: We developed the LETd and LETdSD calculation tool and analyzed 33 patients of head and neck cancer for local control and optic neuropathy. Although the mean LETd in the PTV were similar values between cases with and without recurrence, we could observe the usefulness of the LETd analysis for optic neuropathy cases. We will continue to analyze more patients in the future.
Funding Support, Disclosures, and Conflict of Interest: This study was supported by JSPS KAKENHI Grant Number JP19K08188.
Heavy Ions, LET, Treatment Verification
TH- External Beam- Particle/high LET therapy: Carbon ion therapy – computational dosimetry-deterministic