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Dynamic rotating‐shield brachytherapy
Author(s) -
Liu Yunlong,
Flynn Ryan T.,
Kim Yusung,
Yang Wenjun,
Wu Xiaodong
Publication year - 2013
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4828778
Subject(s) - brachytherapy , dosimetry , nuclear medicine , radiation treatment planning , radiation therapy , medicine , radiology
Purpose: To present dynamic rotating shield brachytherapy (D‐RSBT), a novel form of high‐dose‐rate brachytherapy (HDR‐BT) with electronic brachytherapy source, where the radiation shield is capable of changing emission angles during the radiation delivery process.Methods: A D‐RSBT system uses two layers of independently rotating tungsten alloy shields, each with a 180° azimuthal emission angle. The D‐RSBT planning is separated into two stages: anchor plan optimization and optimal sequencing. In the anchor plan optimization, anchor plans are generated by maximizing the D 90 for the high‐risk clinical‐tumor‐volume (HR‐CTV) assuming a fixed azimuthal emission angle of 11.25°. In the optimal sequencing, treatment plans that most closely approximate the anchor plans under the delivery‐time constraint will be efficiently computed. Treatment plans for five cervical cancer patients were generated for D‐RSBT, single‐shield RSBT (S‐RSBT), and 192 Ir‐based intracavitary brachytherapy with supplementary interstitial brachytherapy (IS + ICBT) assuming five treatment fractions. External beam radiotherapy doses of 45 Gy in 25 fractions of 1.8 Gy each were accounted for. The high‐risk clinical target volume (HR‐CTV) doses were escalated such that the D 2cc of the rectum, sigmoid colon, or bladder reached its tolerance equivalent dose in 2 Gy fractions (EQD2 with α / β = 3 Gy) of 75 Gy, 75 Gy, or 90 Gy, respectively.Results: For the patients considered, IS + ICBT had an average total dwell time of 5.7 minutes/fraction (min/fx) assuming a 10 Ci 192 Ir source, and the average HR‐CTV D 90 was 78.9 Gy. In order to match the HR‐CTV D 90 of IS + ICBT, D‐RSBT required an average of 10.1 min/fx more delivery time, and S‐RSBT required 6.7 min/fx more. If an additional 20 min/fx of delivery time is allowed beyond that of the IS + ICBT case, D‐RSBT and S‐RSBT increased the HR‐CTV D 90 above IS + ICBT by an average of 16.3 Gy and 9.1 Gy, respectively.Conclusions: For cervical cancer patients, D‐RSBT can boost HR‐CTV D 90 over IS + ICBT and S‐RSBT without violating the tolerance doses to the bladder, rectum, or sigmoid. The D 90 improvements from D‐RSBT depend on the patient, the delivery time budget, and the applicator structure.