ESTRO 2021 Abstract Book

S791

ESTRO 2021

remained: for late dysphagia no dose metrics were significantly associated with outcome while HPV status always was; for early dysphagia the same four dose metrics were significantly associated with outcome even when in a model with age, sex, and HPV status. Conclusion While HPV is a known contributing factor for tumor prognosis in oropharyngeal cancers, its role in normal tissue toxicities for head and neck cancers has never been evaluated. Our results indicate HPV-negative status may increase a patient’s risk of high-grade late dysphagia. As a result, it could be a useful biomarker for novel treatment plan personalization or changes in post-treatment follow-up for these patients.

PO-0949 Comparison between simultaneous integrated boost IMRT and sequential IMRT in head and neck cancers P. Ahlawat 1 , M. Gairola 1 , M.I. Sharief 1 , S. Tandon 1 , S. Purohit 1 , N. Sachdeva 1 , T. Singh 1 , K. Dobriyal 1 , A. Krishnan 1 1 Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, Radiation Oncology, New Delhi, India Purpose or Objective Intensity Modulated Radiotherapy (IMRT) is currently considered the preferred technique of radiotherapy for head and neck cancers (HNC). The two common strategies to deliver IMRT are simultaneous integrated boost IMRT (SIB-IMRT) and sequential IMRT (Seq-IMRT). In Seq-IMRT same fraction size of 2 Gy as a single fraction per day is delivered to initially treat the gross disease as well as elective volume, and then to finally treat the boost volume in sequential manner. In SIB-IMRT different dose levels (2 or 3) are treated simultaneously with different doses per fraction. The superiority of one technique over the other has not been proved. The current study aimed to compare these two techniques with regard to treatment outcomes and toxicities. Materials and Methods One hundred patients with locally advanced HNC were randomized equally into Seq-IMRT and SIB-IMRT with 50 patients in each group. The Seq-IMRT was planned in 3 phases, phase I (low-risk region) with 44 Gy in 22 fractions; phase II (intermediate-risk region) with 12 Gy in 6 fractions; and phase III (high-risk region) with 14 Gy in 7 fractions in sequence. The SIB-IMRT was planned with 70 Gy for high-risk region, 63 Gy for intermediate-risk region, and 56 Gy for low-risk region, all in 35 fractions thus prescribing 2 Gy, 1.8 Gy and 1.6 Gy respectively. Concurrent weekly cisplatin 40mg/m 2 was given to all patients if found fit for it. The end points for this study were loco-regional control (LRC), overall survival (OS), acute toxicities and late toxicities. LRC and OS were computed with Kaplan-Meier curve with log-rank test for comparison between the two groups. Univariate analysis and Multivariate Cox proportional hazards regression analysis was performed to estimate the impact of known relevant prognostic factors on LRC and OS. Results The median follow up was 26.20 months in Seq-IMRT group and 33.20 months in SIB-IMRT group. The median LRC was statistically non-significant (33.12 in Seq-IMRT vs 52.44 months in SIB-IMRT; p 0.128). The difference in 3 years LRC was non-significant (39.5 in Seq-IMRT vs 54.1% in SIB-IMRT; p = 0.101). The median OS was 36.12 months in Seq-IMRT and 55.90 months in SIB-IMRT group, a statistically non-significant difference in OS distribution, χ 2 (2) = 2.09, p =0.241 respectively. The difference in 3 years OS was non-significant (77.18 vs 52.08%; p =0.102). In univariate cox regression model, the two treatment techniques were not found to be associated significantly with LRC (HR 1.25, 95% CI, 0.65–4.66) and OS (HR 1.44, 95% CI, 0.78–3.01 respectively). There were no significant differences between the two techniques with respect to acute toxicities of grades ≥3 and late toxicities of grades ≥3. Conclusion Seq-IMRT is comparable with SIB-IMRT with regard to LRC, OS, acute toxicities and late toxicities. Hence, SIB- IMRT given its potential dosimetric advantages in past studies and less time consuming technique may be preferred over Seq-IMRT for HNC. PO-0950 Comparison between two-dose levels versus three-dose levels IMRT in head and neck cancers P. Ahlawat 1 , S. Tiwari 2 , M. Gairola 1 , S. Tandon 1 , S. Purohit 1 , K. Dobriyal 1 , T. Singh 1 , A. Krishnan 3 1 Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, Radiation Oncology, New Delhi, India; 2 Sri Balaji Action Medical Institute, New Delhi, Oncology, New Delhi, India; 3 Rajiv Gandhi Cancer Institute and