3200 - Beating the Clock: An Audit of Time Taken to Deliver Swallowing Sparing IMRT for Head and Neck Carcinoma

Y. I. K N¹, T. Choden², A. Aashita³, A. Ghosh³, A. Dagar³, S. Hazarika³, J. Raj³, A. R⁴, K. Kamboj³, S. Mallick⁵, D. Sharma⁶, and A. Sharma³; ¹National Cancer Institute-All India Institute of Medical Sciences, Haryana, India, ²All India Institute of Medical Sciences, New Delhi, India, ³National Cancer Institute, All India Institute of Medical Sciences, New Delhi, India, ⁴National Cancer Institute, Haryana, India, ⁵National Cancer Institute, Jhajjar, Haryana, India, ⁶All India Institute of Medical Sciences, New Delhi, New Delhi, India

Purpose/Objective(s): At present there is a paucity of literature regarding the time taken to complete target and organ-at-risk (OAR) delineation to start swallowing sparing IMRT (Sw-IMRT). To our knowledge, this is the first study in the world to evaluate workflow of time taken to deliver Sw_IMRT. Materials/

Methods: All HNC treated with radical CRT/RT from August 2020 - December 2023 were included. Gross tumour volume (GTV=GTV_primary+GTV_Nodes) delineation included clinically/radiologically (including PET scan) apparent disease. For primary tumor (GTV_P) margin of 0.5 cm generated CTV_P1 and 1 cm margin generated CTV_P2. CTV_LN encompassed microscopic disease to regional lymphatics at risk. A 5 mm margin generated the planning target volume. The dysphagia & aspiration related structures (DARS) delineated included superior, middle, inferior constrictor muscles, base of tongue, supraglottic larynx, larynx, cricopharyngeus muscle, esophageal inlet and cervical esophagus. All patients received SIB IMRT of 70 Gy (for N3 nodes), 66Gy, 54Gy in 30 fractions. Sw_ IMRT was delivered by double arc VMAT using 6 MV photons (dose rate 600MU/min) (Acuros-XB algorithm version 15.6.05). At our department we aimed to start Sw_IMRT within 7 days of CT simulation. To evaluate the time factor to deliver Sw_IMRT following parameters were noted CT simulation date, contouring approval/prescription date, time taken to planning Sw_IMRT & plan approval date. Overall all treatment time (OTT) was calculated from start to end of Sw_IMRT in all patients.
Results: The study included 316 patients. Majority (59.2%) of patients had oropharyngeal primary. Seventy-three per cent of patients (Stages IV=49.8% & Stage III=34%) presented in loco-regionally advanced disease. Target coverage aim was to cover 95% of prescribed dose (PD) to at least 95% of PTV. Table 1 summarizes target volumes and DARS doses. Median time from CT-simulation to completion of target & OAR delineation was 8 days (IQR 5-14 days). Median time to Sw_IMRT planning was 2 days (IQR 1-6 days), and to plan approval was ‹ 1 day (median 0 IQR 0-1). Median OTT was 43 days (IQR 41-46 days).
Conclusion: In the audit median of 10 days was taken to deliver Sw-IMRT (8 days for contouring & 2 days for planning). This exceeded 3 days from intended time frame. The study identified target & OAR delineation as the rate-limiting step in delivery of Sw_IMRT & was 4 times more time-consuming than Sw_IMRT planning. A conscious effort to reduce delineation times will further refine Sw-IMRT practice for HNC.

Abstract 3200 - Table 1: Doses to DARS, PTV coverage & GTV volumes

DARS	MEAN DOSE (Gy)	IQR
Superior Constrictor	47.6	38.0-58.1
Middle constrictor	50.4	41.2-62.1
Inferior constrictor	41.1	27.9-57.2
Cricopharyngeus	37.0	27.5-33.3
Esophageal-inlet	33.2	24.3-41.9
Cervical esophagus	27.7	18.8-35.1
Supra glottis larynx	49.6	35.1-63.5
Larynx	35.7	22.5-47.4
Base of tongue	48.6	39.7-53
PTV_66 coverage (95%)	97.2 of PD	96.5-98.8
PTV_54 coverage (95%)	98.1 of PD	96.8-99
GTV_P (cc)	27.07	11.12-37.95
GTV_N (cc)	5.3	2.1-12.6