Defense Date

2022

Document Type

Thesis

Degree Name

Master of Science

Department

Medical Physics

First Advisor

Dr. William Y. Song

Abstract

Purpose: To evaluate and compare the performance of 9 experimental DMBT tandem models of varying physical dimensions in relation to 24 previously planned HDR cervical cancer treatment plans from multiple institutions that used conventional tandem and rings or ovoid applicators.

Methods and Materials: The DMBT tandem is designed to be used concurrently with IGABT and is made from an MRI-compatible tungsten-alloy rod with 6 channels grooved out of its periphery. 9 experimental DMBT tandem prototypes were provided. Each of the models was of equal lengths but varied in thickness, channel diameter size, and circle channel diameter size. Replanning was performed using our research TPS (BrachyVisionÒ v.16.1, Varian, Palo Alto, CA). Inverse optimization using Acuros was performed for 12 patient cases (24 plans) belonging to three institutions: Virginia Commonwealth University, University of Michigan, and University of California San Diego. Original plans used conventional tandem and ovoids or ring applicators. Each of the 9 DMBT tandem models replaced the location of the original tandem such that the new dwell positions were at the level of the original plan. The dwell positions of the ovoids or rings remained unchanged.

Results: The average relative reduction in D2cc using the thinnest DMBT tandem (model 1) were: -9.65% (∆EQD2 D2ccBladder = -3.6 Gy), -19.91% (∆EQD2 D2ccRectum = -3.87 Gy), and -14.55% (∆EQD2 D2ccSigmoid = -3.55 Gy), for the bladder, rectum, and sigmoid respectively. The average relative reduction in D2cc using the thickest DMBT tandem (model 9) were: -12.82% (∆EQD2 D2ccBladder = -4.05 Gy), -24.69% (∆EQD2 D2ccRectum = -4.05 Gy), and -18.42% (∆EQD2 D2ccSigmoid = -3.63 Gy), for the bladder, rectum, and sigmoid respectively. Conclusions: Significant reductions in OAR dose while maintaining identical target coverage (D90) can be achieved by the use of any of the 9 DMBT tandem models. As DMBT tandem thickness increases, OAR dose decreases; however, there is no significant differences in performance between models. Unless necessary to remain within an OAR’s total dose (EQD2) limit, we advise the use of a moderately thick DMBT tandem (model 5) for clinical use as its physical dimensions resemble that of already used clinically conventional tandems while offering enhanced modulating capabilities.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

5-19-2022

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