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SU‐E‐T‐564: Multi‐Helix Rotating Shield Brachytherapy for Cervical Cancer
Author(s) -
Dadkhah H,
Flynn R,
Wu X,
Kim Y
Publication year - 2015
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 - 10.1118/1.4924926
Subject(s) - brachytherapy , shield , dosimetry , nuclear medicine , radiation treatment planning , physics , cervical cancer , optics , radiation therapy , medicine , geology , cancer , surgery , petrology
Purpose: To present a novel and practical brachytherapy technique, called multi‐helix rotating shield brachytherapy (H‐RSBT), for the precise positioning of a partial shield in a curved applicator. H‐RSBT enables RSBT delivery using only translational motion of the radiation source/shield combination. H‐RSBT overcomes the challenges associated with previously proposed RSBT approaches based on a serial (S‐RSBT) step‐and‐shoot delivery technique, which required independent translational and rotational motion. Methods: A Fletcher‐type applicator, compatible with the combination of a Xoft Axxent™ electronic brachytherapy source and a 0.5 mm thick tungsten shield, is proposed. The wall of the applicator contains six evenly‐spaced helical keyways that rigidly define the emission direction of the shield as a function of depth. The shield contains three protruding keys and is attached to the source such that it rotates freely. S‐RSBT and H‐RSBT treatment plans with 180° and 45° azimuthal emission angles were generated for five cervical cancer patients representative of a wide range of high‐risk clinical target volume (HR‐CTV) shapes and applicator positions. The number of beamlets used in the treatment planning process was nearly constant for S‐RSBT and H‐RSBT by using dwell positions separated by 5 and 1.7 mm, respectively, and emission directions separated by 22.5° and 60°, respectively. For all the treatment plans the EQD2 of the HR‐CTV was escalated until the EQD 2cc tolerance of either the bladder, rectum, or sigmoid colon was reached. Results: Treatment times for H‐RSBT tended to be shorter than for S‐RSBT, with changes of −38.47% to 1.12% with an average of −8.34%. The HR‐CTV D 90 changed by −8.81% to 2.08% with an average of −2.46%. Conclusion: H‐RSBT is a mechanically feasible technique in the curved applicators needed for cervical cancer brachytherapy. S‐RSBT and H‐RSBT dose distributions were clinically equivalent for all patients considered, with the H‐RSBT deliveries tending to be faster. Ryan Flynn has ownership interest in pxAlpha, LLC, which is a startup company developing a rotating shield brachytherapy system.