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Paddle-based rotating-shield brachytherapy
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DOI：10.1118/1.4930807.png)
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Abstract
En 中文
Purpose: The authors present a novel paddle-based rotating-shield brachytherapy (P-RSBT) method, whose radiation-attenuating shields are formed with a multileaf collimator (MLC), consisting of retractable paddles, to achieve intensity modulation in high-dose-rate brachytherapy. Methods: Five cervical cancer patients using an intrauterine tandem applicator were considered to assess the potential benefit of the P-RSBT method. The P-RSBT source used was a 50 kV electronic brachytherapy source (Xoft Axxent (TM)). The paddles can be retracted independently to form multiple emission windows around the source for radiation delivery. The MLC was assumed to be rotatable. P-RSBT treatment plans were generated using the asymmetric dose-volume optimization with smoothness control method [Liu et al., Med. Phys. 41(11), 111709 (11pp.) (2014)] with a delivery time constraint, different paddle sizes, and different rotation strides. The number of treatment fractions (fx) was assumed to be five. As brachytherapy is delivered as a boost for cervical cancer, the dose distribution for each case includes the dose from external beam radiotherapy as well, which is 45 Gy in 25 fx. The high-risk clinical target volume (HR-CTV) doses were escalated until the minimum dose to the hottest 2 cm(3) (D-2cm3) of either the rectum, sigmoid colon, or bladder reached their tolerance doses of 75, 75, and 90 Gy(3), respectively, expressed as equivalent doses in 2 Gy fractions (EQD2 with alpha/beta = 3 Gy). Results: P-RSBT outperformed the two other RSBT delivery techniques, single-shield RSBT (S-RSBT) and dynamic-shield RSBT (D-RSBT), with a properly selected paddle size. If the paddle size was angled at 60 degrees, the average D-90 increases for the delivery plans by P-RSBT on the five cases, compared to S-RSBT, were 2.2, 8.3, 12.6, 11.9, and 9.1 Gy(10), respectively, with delivery times of 10, 15, 20, 25, and 30 min/fx. The increases in HR-CTV D-90, compared to D-RSBT, were 16.6, 12.9, 7.2, 3.7, and 1.7 Gy(10), respectively. P-RSBT HR-CTV D-90-values were insensitive to the paddle size for paddles angled at less than 60 degrees. Increasing the paddle angle from 5 degrees to 60 degrees resulted in only a 0.6 Gy(10) decrease in HR-CTV D-90 on average for five cases when the delivery times were set to 15 min/fx. The HR-CTV D-90 decreased to 2.5 and 11.9 Gy(10) with paddle angles of 90 degrees and 120 degrees, respectively. Conclusions: P-RSBT produces treatment plans that are dosimetrically and temporally superior to those of S-RSBT and D-RSBT, although P-RSBT systems may be more mechanically challenging to develop than S-RSBT or D-RSBT. A P-RSBT implementation with 4-6 shield paddles would be sufficient to outperform S-RSBT and D-RSBT if delivery times are constrained to less than 15 min/fx. (C) 2015 American Association of Physicists in Medicine.
Keywords:
brachytherapy
intensity modulated brachytherapy
rotating-shield brachytherapy
cervical cancer
electronic brachytherapy
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