Role of overall treatment time when estimating TCP & NTCP of head & neck radiotherapy treatment plans in altered fractionation

Document Type : Original Paper

Authors

1 RTRM Department, Institute of Medical Sciences, Banaras Hindu University, Varanasi-221005, INDIA

2 BANARAS HINDU UNIVERSITY

3 RTRM Department, Institute of Medical Sciences, BHU, Varanasi-221005

4 Department of Radiotherapy and Radiation Medicine Institute of Medical Sciences Banaras Hindu University VARANASI, Uttar Pradesh, INDIA.

Abstract

Purpose: Present study demonstrated role of overall treatment time when estimating tumor control probability (TCP) and normal tissue complication probability (NTCP) for moderately hypofractionated and accelerated fractionation schedules in head & neck treatment.

Methods: The proposed study separated into two parts. In first case, we assumed four moderately hypofractionated schedules for demonstration, conventional fractionation schedule (CFS) (70Gy/35 #), fractionation schedule (FS) 1 (66Gy/30#), FS2 (60Gy/24#), and FS3 (55Gy/20#). Four independent volumetric modulated arc treatment plans generated for four different fractionation schedules for 15 patients' data set and therefore total of 60 treatment plans. Treatment plan created for CFS is reference plan for calculated TCP & NTCP comparison amongst four plans. The rest three plans for each patient were created simply by changing the dose prescription for FS1, FS2 & FS3 means total dose and dose per fraction. In second scenario, conventional fractionation schedule (66Gy/33# with five fractions week) compared against accelerated fractionation schedule (66Gy/33# with six fractions per week). The cumulative dose-volume histogram for all treatment plans used for TCP/NTCP estimation by Niemierko, Poisson model, and LKB model. TCP/NTCP calculated two different ways for tumor & oral mucosa of head & neck sites.

Result: TCP calculated by Niemierko model with simple BED formula for PTV in CFS, FS1, FS2 & FS3 is 93,91,85.3 & 76.2% similarly calculated with time corrected BED formula TCP values are 70.4,73.4,72.4 &69.8%. For oral mucosa, NTCP calculated by LKB model for CFS,FS1,FS2 & FS3 with BED formula and values are 50.25,48,45.8 & 42.6% similarly calculated with time corrected BED NTCP values are 25.3,27.9,29.5 & 30%. There is a statistically significant difference (p<0.05) between calculated TCP and NTCP for four fractionation schedules.



Conclusion: OTT plays a significant role in radiobiological model-based plan evaluation of head & neck tumors and it should be considered while calculating TCP/NTCP.

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Articles in Press, Accepted Manuscript
Available Online from 31 January 2022
  • Receive Date: 26 September 2021
  • Revise Date: 28 January 2022
  • Accept Date: 31 January 2022
  • First Publish Date: 31 January 2022