(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: evaluate the dose distribution characteristics of early-stage glottic cancer by comparing the dose distribution between intensity-modulated radiation therapy (IMRT) and passive scattering proton therapy (PSPT) and to examine the usefulness of PSPT for early-stage glottic cancer.
Methods: tomography datasets of eight patients with T1–2 glottic cancer who had been treated by PSPT at our institution were used to create an IMRT plan in Eclipse with seven fields and a PSPT plan in XiO-M with two fields. Organs at risk (OARs) included the carotid arteries, arytenoids, inferior constrictor muscles, strap muscles, thyroid cartilage, cricoid cartilage, and spinal cord. The prescription dose was 66 Gy (RBE) in 33 fractions to the planning target volume (PTV). All plans were optimized such that 95% of the PTV received 90% of the prescription dose considering that the skin was slightly spared.
Results: distribution was very limited in the PSPT, while the middle- to low-dose range tended to spread with IMRT. In IMRT, the average maximum dose to the contralateral carotid artery was 18.1 Gy, and although the effect of reduction was observed, the PTV tended to have a small hot spot. By contrast, in the PSPT, the dose to the contralateral carotid artery and spinal cord, which is slightly distant from the PTV, were dramatically reduced while the dose distribution homogeneity of the PTV was maintained.
Conclusion: PSPT, the homogeneity of dose distribution in PTV was maintained, and the contralateral carotid artery was adequately spared without increasing the spinal cord dose, thus confirming its superiority. Although further investigation of the optimal dose fractionation must be necessary, the use of PT for early-stage glottic cancer is effective in reducing late effects, and it is expected that this will be particularly useful for young people.
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