ESTRO 2024 - Abstract Book

S1516

Clinical - Lower GI

ESTRO 2024

1550

Digital Poster

Dose escalation in neoadjuvant radiotherapy of locally advanced rectal cancer

Olivera Ivanov 1,2 , Milijana Rakin 1 , Nataša Aničić 1 , Marko Bojović 1,2 , Jelena Ličina 1,2 , Borislava Petrović 1,3

1 Oncology Institute of Vojvodina, Radiation oncology Department, Sr.Kamenica, Serbia. 2 Faculty of medicine, University of Novi Sad, Department for Oncology, Novi Sad, Serbia. 3 Faculty of Sciences, University of Novi Sad,, Department for physics, Novi Sad, Serbia

Purpose/Objective:

Chemoradiation therapy (CRT) is golden standard for locally advanced rectal cancer (LARC). Neoadjuvant therapy intensification via Total Neoadjuvant Therapy (TNT) has resulted in better response rates and excellent long-term oncological outcomes. However, the role of radiotherapy dose escalation itself in terms of toxicity and treatment outcome is still unclear. The aim of the study was to investigate the contribution of dose escalation in LARC radiotherapy to local control, survival and to assess treatment toxicity.

Material/Methods:

In retrospective analyses we assessed the outcome of two arms of radiotherapy treatments of LARC patients, treated between 2017 -2023: VMAT of 57.5Gy : 46 Gy in 23 fractions with simultaneous integrated boost- SIB administered to primary tumor and lymph nodes, compared to 3DCRT of 50.4-50Gy : 45Gy CRT + 5.4-9 Gy boost to primary tumor. Complete clinical response (cCR) rate, treatment toxicity, disease free survival (DFS) and overall survival (OS) were analyzed for each arm.

Results:

Sixty-one patients were enrolled. Median follow-up was 30 months. VMAT – SIB technique was administried to 30 patients and 31 of patients underwent 3DCRT. In the VMAT-SIB group 10 (33.3%) patients achieved cCR compared to 1 (3.22%) patient in the 3DCRT group (p<0.05). There was significant difference in acute urinary and rectal toxicity ≥grade 2 in favour of VMAT-SIB group (p<0.05). Late toxicity was similar in the both groups (p=0.134). Interestingly, DFS was signicificantly worse in the VMAT-SIB group (p=0.009) with no difference in overall survival (p=0.454).

Conclusion:

Radiotherapy dose escalation results with increased cCR rates and more patients become eligible for organ- preservation. VMAT-SIB technique provides less acute toxicity. However, dose escalation itself seems to be not enough to provide better local control without escalation in systemic therapy.

Keywords: Rectal cancer, dose escalation, radiotherapy