2243 - TCP and NTCP for the Next Generation in Modulated Arc Therapy for Nasopharyngeal Carcinoma

02:30pm - 04:00pm PT

Hall F

Screen: 24

POSTER

Presenter(s)

Kenton Thompson, - Peter MacCallum Cancer Centre, Melbourne, VIC

K. Thompson^1,2, C. Laferlita^1,2, V. Panettieri^1,2, T. Fua^1,2, C. P. Daniels^1,2, N. Hardcastle^1,2, T. Devereux^1,2, T. Kron^1,2, P. Lim¹, K. Woodford^1,2, and S. Porceddu^1,2; ¹Peter MacCallum Cancer Centre, Melbourne, VIC, Australia, ²Sir Peter MacCallum Department of Oncology, The University of Melbourne, Melbourne, VIC, Australia

Purpose/Objective(s):

A new optimization algorithm within a commercial system uniquely leverages dynamic collimation and combines VMAT with the modulation of IMRT-like static angle modulated ports (STAMPs) in a single continuous delivery (VMATp). This comparative study evaluates the difference in Tumor Control Probability (TCP) and Normal Tissue Complication Probability (NTCP) and clinical acceptability of VMATp plans to conventional VMAT for a cohort of curative NPC cases.

Materials/Methods:

Twenty patients with T3-4, any N, M0 NPC patients treated at our institution with curative intent between 1 July 2019 and 1 July 2023 were included. These were treated with two or more VMAT arcs (‘clinical plans’). Two VMATp approaches were developed:

1) Single arc with 5 STAMPs - VMATpA

2) 2 arcs with 4 STAMPs per arc - VMATpB

VMATp optimization, blinded from the clinical plan, aimed to adhere to maximum clinical goals whilst prioritizing target coverage and serial organs (late effects) over parallel organs (acute effects).

TCP was calculated with the Marsden model(a=0.3(Gy^-1), sa=0.09, a/b=10Gy) and NTCP for Xerostomia, Dysphagia and Mucositis were calculated with published LKB, Multivariate Logistic regression and Logistic regression models respectively. TCP and NTCP for VMATpA and VMATpB were compared with the clinical plan (deltas) using the Wilcoxon signed-rank test (p = 0.05).

To determine the clinical acceptability, the VMATp plans, and the approved clinical plans were presented to two practicing head and neck specialists for blinded review. The reviewers were given a clinical summary and asked to confirm that each plan was acceptable (Y/N) and rank the plans from 1 (best) to 3 (worst).

Results:

Median deltas for TCP were higher for the VMATp plans. Median TCP delta increase for VMATpA and VMATpB were 0.7% and 0.8% respectively. Median deltas for NTCP decreased for VMATp plans. Xerostomia, Dysphagia and Mucositis median deltas decreased by 2.2%, 1.5% and 1.1% and 2.3%, 1.7% and 1.5% for VMATpA and VMATpB respectively. Table 1. summarises the TCP and NTCP results.

VMATpA and VMATpB approaches were both assessed as acceptable 32/40 compared to only 20/40 clinical plans, and 32/40 highest ranked plans were one of the two VMATp approaches.

Conclusion:

The evaluation of VMATp suggests that this next generation arc therapy can improve target coverage and OAR sparing, potentially influencing TCP and NTCP to support higher quality treatment plans compared to current practice. Additionally, VMATp was favored in a blinded physician review.

Abstract 2243 - Table 1: TCP and NTCP deltas for VMATpA and VMATpB compared to clinical plan

	VMATpA		VMATpB
	Median ? to Clinical (? range) (%)	P Value	Median ? to Clinical (? range) (%)	P Value
TCP	0.7 (-2.2 - 2.0)	0.009	0.8 (-1.1 - 1.8)	<0.001
NTCP Xerostomia	-2.2 (-18.5 - 6.4)	0.005	-2.3 (-18.3 - 6.5)	0.008
NTCP Dysphagia	-1.5 (-3.7 - 2.4)	0.007	-1.7 (-3.8 - 0.6)	<0.001
NTCP Mucositis	-1.1 (-7.6 – 3.0)	0.065	-1.5 (-7.9 – 5.6)	0.005