Direction-Modulated Brachytherapy for High-Dose-Rate Treatment of Cervical Cancer. I: Theoretical Design

• Published in: International journal of radiation oncology, biology, physics Vol. 89; no. 3; pp. 666 - 673
• Main Authors: Han, Dae Yup, MSc, Webster, Matthew J., MSc, Scanderbeg, Daniel J., PhD, Yashar, Catheryn, MD, Choi, Dongju, PhD, Song, Bongyong, PhD, Devic, Slobodan, PhD, Ravi, Ananth, PhD, Song, William Y., PhD
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.2014
• Subjects: Adult; Algorithms; BIOMEDICAL RADIOGRAPHY; BLADDER; BRACHYTHERAPY; Brachytherapy - instrumentation; Brachytherapy - methods; Colon, Sigmoid - radiation effects; DOSE RATES; Equipment Design; Female; Hematology, Oncology and Palliative Medicine; Humans; IRIDIUM 192; Iridium Radioisotopes - therapeutic use; Magnetic Resonance Imaging; Middle Aged; Monte Carlo Method; NEOPLASMS; NMR IMAGING; OPTIMIZATION; Organs at Risk - radiation effects; PATIENTS; PLANNING; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES; Radiation Injuries - prevention & control; Radiology; RADIOLOGY AND NUCLEAR MEDICINE; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; RECTUM; Rectum - radiation effects; Tungsten; TUNGSTEN ALLOYS; Urinary Bladder - radiation effects; Uterine Cervical Neoplasms - radiotherapy; Young Adult
• ISSN: 0360-3016; 1879-355X
• DOI: 10.1016/j.ijrobp.2014.02.039

Purpose To demonstrate that utilization of the direction-modulated brachytherapy (DMBT) concept can significantly improve treatment plan quality in the setting of high-dose-rate (HDR) brachytherapy for cervical cancer. Methods and Materials The new, MRI-compatible, tandem design has 6 peripheral holes of 1.3-mm diameter, grooved along a nonmagnetic tungsten-alloy rod (ρ = 18.0 g/cm3 ), enclosed in Delrin tubing (polyoxymethylene, ρ = 1.41 g/cm3 ), with a total thickness of 6.4 mm. The Monte Carlo N-Particle code was used to calculate the anisotropic192 Ir dose distributions. An in-house-developed inverse planning platform, geared with simulated annealing and constrained-gradient optimization algorithms, was used to replan 15 patient cases (total 75 plans) treated with a conventional tandem and ovoids (T&O) applicator. Prescription dose was 6 Gy. For replanning, we replaced the conventional tandem with that of the new DMBT tandem for optimization but left the ovoids in place and kept the dwell positions as originally planned. All DMBT plans were normalized to match the high-risk clinical target volume V100 coverage of the T&O plans. Results In general there were marked improvements in plan quality for the DMBT plans. On average, D2cc for the bladder, rectum, and sigmoid were reduced by 0.59 ± 0.87 Gy (8.5% ± 28.7%), 0.48 ± 0.55 Gy (21.1% ± 27.2%), and 0.10 ± 0.38 Gy (40.6% ± 214.9%) among the 75 plans, with best single-plan reductions of 3.20 Gy (40.8%), 2.38 Gy (40.07%), and 1.26 Gy (27.5%), respectively. The high-risk clinical target volume D90 was similar, with 6.55 ± 0.96 Gy and 6.59 ± 1.06 Gy for T&O and DMBT, respectively. Conclusions Application of the DMBT concept to cervical cancer allowed for improved organ at risk sparing while achieving similar target coverage on a sizeable patient population, as intended, by maximally utilizing the anatomic information contained in 3-dimensional imaging. A series of mechanical and clinical validations are to be followed.