ESTRO 2023 - Abstract Book

S959

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ESTRO 2023

Table 1 shows a significant difference in xerostomia grade using these dose constraints. Clinical factors and other dosimetric factors (Volume and Dose maximum of parotid glands, dose received by submandibular gland) were not associated with persistent xerostomia grade ≥ 2.

Xerostomia G0-1 end of treatment

Xerostomia G2-3 end of treatment

Xerostomia G0-1 end at 3 monts

Xerostomia G2-3 end at 3 monts

p

p

Dmean 2parotids - PTV < 31Gy Dmean 2parotids - PTV ≥ 31Gy

56%

21%

36%

0%

0.019

0.036

44%

79%

64%

100%

D50 2parotids - PTV < 25Gy D50 2parotids - PTV ≥ 25Gy

69%

25%

44%

10%

0.005

0.11

31%

75%

56%

90%

Conclusion Xerostomia represents a common problem observed after IMRT of NPC. For all head and neck cancers, a dose constraint of Dmean of <26 Gy to at least 1 parotid gland is proposed. However, this dose is hard to achieve for NPC patients given the proximity of lymphadenopathy to parotid glands. Results of our study show that Dmean <31 Gy and D50 <25 Gy could be reasonable to respect for both parotids–PTV during dosimetric optimization of NRP IMRT to decrease the rate of persistent xerostomia.

PO-1198 SBRT can defer the need for systemic therapy in oligometastatic iodine-refractory thyroid cancer

G. SimontacchI 1 , E. Olmetto 1 , M. Mangoni 2 , M. Valzano 3 , V. Lorenzetti 2 , B. Bettazzi 2 , M. Casati 4 , C. Arilli 4 , M. Roghi 2 , C. Sparano 5 , L. Livi 2 1 Azienda Ospedaliero-Universitaria Careggi, SOD Radioterapia, Florence, Italy; 2 University of Florence, Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Florence, Italy; 3 University of Florence, Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Florence, Italy; 4 Azienda Ospedaliero-Universitaria Careggi, UO Fisica Medica, Florence, Italy; 5 University of Florence, Endocrinology, Florence, Italy Purpose or Objective Differentiated thyroid cancer is usually associated with a good prognosis, but the development of metastases in iodine refractory patients adversely affects quality of life and survival. The advent of tyrosine-kinase inhibitors drugs (TKI) allowed a great improvement of patients’ outcome in these cases but, in case of oligometastatic disease, a locoregional ablative approach such as Stereotactic Radiation Therapy (SRT) could effectively control tumor progression and possibly defer the need of systemic therapies. Materials and Methods We retrospectively analyzed patients with differentiated oligometastatic iodine refractory thyroid cancer treated with SRT in our Radiation Oncology Unit from 2011 to 2022. We collected demographics and treatment-related characteristics. Local Control (LC), Progression Free Survival (PFS), Overall Survival (OS) and the need for systemic therapy were evaluated. Patients with anaplastic histology, incomplete treatment or without follow-up information were excluded. Results We retrospective analyzed a cohort of 21 patients, aged between 47 and 84 years old (median 64,9). 11 (52,3%) patients were males and 10 (47,7%) were females. A total of 61 lesions were treated: 26 were located in bones (42,6%), 19 in lymph nodes (31,1%), 7 in the brain (11,4%), 6 in the lungs (9,8%) and 3 visceral (4,9%). SRT was delivered in 1-8 fractions, with a median dose of 30Gy (range 24-60Gy). Median follow-up was 41,1 months (range 5,7–128,2 months). After SRT we observed a complete response in 29 lesions (47,5%), partial response in 19 (31,1%), stable disease in 12 (19,6%) and only 1 progressive lesion (1,6%). We observed 10 local recurrences (16,3%) with an actuarial LC of 96,1% and 92,1% at 12 and 24 months respectively, while PFS was 62,0% and 55,1% at 12 and 24 months respectively. The OS at 24 and 48 months was 100% and 81,1% respectively. Patients with oligoprogressive disease were treated with further SRT, while patients with polimetastatic progression of disease or oligoprogression not suitable for ablative treatment received systemic therapy. A total number of 11 patients (52,4%) needed to start TKI treatment (6 Lenvatinib, 3 Sunitinib and 2 Sorafenib) for progressive disease: median time to first systemic treatment from SRT was 18,5 months (range 0,5-67 months). At the time of this analysis, 10 patients (47,6%) were still without systemic therapy, showing a good disease control after a median follow-up of 20,8 months (range 5,7-75). Freedom from systemic therapy rate from the time of SRT was 84,8% and 53,6% at 12 and 24 months respectively. Conclusion In our experience, SRT yields satisfying local control rates in oligometastatic Iodine-refractory thyroid cancer, allowing for a deferral of the need for systemic therapies.