2768 - Potential Utility of Interim PET CT as Predictive and Prognostic Marker is Locally Advanced Head and Neck Squamous Cell Carcinoma Patients Treated with Simultaneous Integrated Boost-IMRT- Can One Scan
P. S. Sridhar1, P. Anuradha1, D. Priyasha1, G. S. Sunayana1, K. Kallur1, M. Gupta1, M. Govindarajan2, K. Venkatachala1, B. J. Srinivas1, and G. Vineet3; 1Health Care Global Enterprises Ltd, Bangalore, India, 2Apollo Hospitals, Bangalore, India, 3Sakra World Hospital, Bangalore, India
Purpose/Objective(s):PET CT based RT planning has become standard for patients with locally advanced head and neck squamous cell carcinomas(LA-HNSCC) undergoing concurrent chemoradiation. Interim PETCT(IPET) has gained huge interest as a prognostic marker but the evidence is still debatable. Besides, the advantage of dose escalated Simultaneous integrated boost to the metabolic tumor volume to increase the therapeutic window is quite unexplored. Here we studied the efficacy of Interim PET CT as a marker(both prognostic and predictive) in LA-HNSCC treated with SIB-IMRT and its impact on disease control and survival outcomes.Materials/
Method: 61 patients with biopsy proven LA-HNSCC were prospectively analyzed from 2008 till 2023. All patients underwent baseline PETCT(BPET) and Interim PET(IPET) at 5 weeks of radiotherapy. Targets are delineated on CT/MR as per guidelines, GTVPET is marked separately. Doses prescribed were 70.95/66/59.4/56 in 33 fractions to GTVPET/CTV-HR/CTV-IR/CTV-LR respectively to both primary and nodal regions. Recontour was done after IPET only for GTVPET and planned accordingly. All patients received concurrent systemic therapy as advised. Followup PETCT was done for all patients and response was evaluated using PERCIST criteria. SUV-Max reduction ratios(SRR) has been calculated for primary/node and correlated with disease control and survival outcomes. Results: Of the total of 61 Head and Neck cases, 47.5% (n=29) were Oropharynx or Oral cavity and others were pharyngeal tumors. Stage III and IV tumors accounted for 31.1% and 59% of the sample respectively. Data not being normally distributed, Spearman’s correlation between SRR, VRR and survival outcomes showed a significant correlation of SRR with DFS (Rho=0.304, p=0.018) and OS (Rho=0.338, p=0.009). There was no statistically significant correlation between VRR and survival outcomes. Conclusion: With our study, we conclude that IPET has a significant correlation with treatment related outcomes. In the era of conformal radiotherapy, PET based SIB not only helps to predict the outcomes but also improves the therapeutic ratio with reduced acute/late toxicities. We would attempt to identify the predictability of SRR and VRR on survival upon continued data collection.
