ESTRO 2022 - Abstract Book

S136

Abstract book

ESTRO 2022

The mandible's risk for osteoradionecrosis (ORN) is positively related to certain dose-volume histogram (DVH) parameters. This study aimed to determine the relationship between any DVH parameter of the mandible and ORN incidence in patients with head and neck (H&N) cancer treated with volumetric modulated arc therapy (VMAT). We performed this study for different algorithms and dose reporting modes. Materials and Methods We reviewed medical records to identify ORN of the mandible and its localization in a series of 106 patients diagnosed with H&N cancer, treated with a prescription dose of 70 Gy using dual-arc VMAT at our institution between October 2013 and May 2015. We only included patients with a minimum follow-up of 2 years. We calculated the mandible's mean Vx and Dx DVHs and performed heteroscedastic t-tests to evaluate the significance (p<0.01) of the differences between patients with and without ORN. We performed calculations with two algorithms implemented in the Eclipse treatment planning system (Varian Medical Systems; Palo Alto, CA, USA), namely the Analytical Anisotropic Algorithm (AAA) and Acuros XB (AXB) for both dose-to-medium (Dm) and dose-to-water (Dw) reporting modes. Results We observed ORN in 7 patients out of the 73 who had a minimum follow-up of 2 years (mean 5.2 years). Fig.1 shows that patients with ORN had higher Vx values, especially around 50 Gy, that Vx correlation with ORN was significant in the 45-55 Gy dose range, and that this range was shifted to higher and lower doses for AXB Dw and AXB Dm respectively compared to AAA. Fig. 2 shows that patients with ORN had higher Dx values, especially for low dose volumes, but that ORN significantly correlated with Dx corresponding to 40% or smaller volumes. Constraints in terms of Vx and Dx would depend on each algorithm and reporting mode.

Conclusion We observed ORN in 10% of H&N patients treated with VMAT. Vx and Dx values are higher for patients with ORN. Intermediate Vx and high Dx values significantly correlate with ORN. Although this is independent of the algorithm and reporting mode selected, they must be considered to specify constraints in terms of Vx and Dx.

PD-0161 Single-patient microbiota & inflammation profiles modulate dose-response curves for acute toxicity

E. Gioscio 1 , T. Rancati 1 , L. De Cecco 2 , A. Barbara 3 , B. Noris Chiorda 3 , F. Badenchini 4 , T. Giandini 5 , A. Cicchetti 4 , N. Zaffaroni 6 , V. Doldi 6 , E. Mancinelli 2 , M.S. Serafini 7 , A. Devecchi 7 , L. Andreoli 3 , E. Orlandi 8 , R. Valdagni 3 1 Fondazione IRCCS Istituto Nazionale Tumori , Prostate Cancer Program, Milan, Italy; 2 Fondazione IRCCS Istituto Nazionale Tumori, Department of Applied Research and Technology Development, Milan, Italy; 3 Fondazione IRCCS Istituto Nazionale Tumori, Division of Radiation Oncology 1, Milan, Italy; 4 Fondazione IRCCS Istituto Nazionale Tumori, Prostate Cancer Program, Milan, Italy; 5 Fondazione IRCCS Istituto Nazionale Tumori, Division of Medical Physics, Milan, Italy; 6 Fondazione IRCCS Istituto Nazionale Tumori, Division of Molecular Pharmacology, Milan, Italy; 7 Fondazione IRCCS Istituto Nazionale dei Tumori, Department of Applied Research and Technology Development, Milan, Italy; 8 Fondazione IRCCS Istituto Nazionale Tumori, Division of Radiation Oncology 2, Milan, Italy Purpose or Objective To investigate the role of gut microbiota (MB) and inflammation markers in driving toxicity (tox) after radiotherapy (RT) for prostate cancer (PC) and establish personalised Normal Tissue Complication Probability models (NTCP) for acute tox Materials and Methods We enrolled 135 consecutive patients (pts) receiving conventional (78Gy @2Gy/fr) or hypofractionated (65Gy @2.6Gy/fr) VMAT+IGRT.