¹⁶⁹Yb‐based rotating shield brachytherapy for prostate cancer

Abstract

Purpose To present a system for the treatment of prostate cancer in a single‐fraction regimen using 169Yb‐based rotating shield brachytherapy (RSBT) with a single‐catheter robotic delivery system. The proposed system is innovative because it can deliver RSBT through multiple implanted needles independently, in serial, using flexible catheters, with no inter‐needle shielding effects and without the need to rotate multiple shielded catheters inside the needles simultaneously, resulting in a simple, mechanically robust, delivery approach. RSBT was compared to conventional 192Ir‐based high‐dose‐rate brachytherapy (HDR‐BT) in a treatment planning study with dose escalation and urethral sparing goals, representing single‐fraction brachytherapy monotherapy and brachytherapy as a boost to external beam radiotherapy, respectively. A prototype mechanical delivery system was constructed and quantitatively evaluated as a proof of concept. Methods Treatment plans for twenty‐six patients with single fraction prescriptions of 20.5 and 15 Gy, were created for dose escalation and urethral sparing, respectively. The RSBT and HDR‐BT delivery systems were modeled with one partially shielded 999 GBq (27 Ci) 169Yb source and one 370 GBq (10 Ci) 192Ir source, respectively. A prototype angular drive system for helical source delivery was constructed. Mechanical accuracy measurements of source translational position and angular orientation in a simulated treatment delivery setup were obtained using the prototype system. Results For dose escalation, with equivalent urethra D10%, PTV D90% for RSBT vs HDR‐BT increased from 22.6 ± 0.0 Gy (average ± standard deviation) to 29.3 ± 0.9 Gy, or 29.9 % ± 3.0%, with treatment times of 51.4 ± 6.1 min for RSBT and 15.8 ± 2.3 min for 10 Ci 192Ir‐based HDR‐BT. For urethra sparing, with equivalent PTV D90%, urethra D10% for RSBT vs HDR‐BT decreased for RSBT vs HDR‐BT from 15.6 ± 0.4 Gy to 12.0 ± 0.4 Gy, or 23.1% ± 3.5%, with treatment times of 30.0 ± 3.7 min for RSBT and 12.3 ± 1.8 min for HDR‐BT. Differences between measured vs predicted rotating catheter positions (corresponding to source position) were within 0.18 mm ± 0.12 mm longitudinally and 0.07° ± 0.78°. Conclusion 169Yb‐based RSBT can increase PTV D90% or decrease urethral D10% relative to HDR‐BT with treatment times of less than 1 h using a single‐source robotic delivery system with treatment delivered in a single fraction. The prototype helical delivery system was able to demonstrate adequate mechanical accuracy.

Analytical HDR prostate brachytherapy planning with automatic catheter and isotope selection

“…The current study provides further evidence to suggest a minimal benefit‐cost ratio to adopt isotropic Yb‐169 for prostate radiotherapy. Therefore, research focus related to Yb‐169 should be focused on directionally shielded sources for intensity‐modulated brachytherapy 45–47 …”

The population percentile allowance method for determining systematic spatial error tolerances for temporary intensity modulated brachytherapy

“…For helical RSBT 10–12 the pitch, p [mm rot −1 ], is the distance the source and shield translate along the applicator axis for every full shield rotation, thus $$p/2\pi $$ [mm rad −1 ] is the distance translated for every radian the shield rotates. Assuming the shield rotates about the vector $$\Delta {\overset{\scriptscriptstyle\rightharpoonup}{s}_j}$$ while it travels between dwell positions j and $$j + 1$$, it follows that $$\Delta {\varphi _j} = \ 2\pi \|\Delta {\overset{\scriptscriptstyle\rightharpoonup}{s}_j}\|/p$$ [rad] is the angle the shield rotates between points $${\overset{\scriptscriptstyle\rightharpoonup}{s}_j}$$ and $${\overset{\scriptscriptstyle\rightharpoonup}{s}_{j + 1}}$$ along the channel in the applicator.…”

“…For helical RSBT [10][11][12] the pitch, p [mm rot −1 ], is the distance the source and shield translate along the applicator axis for every full shield rotation, thus p∕2𝜋 [mm rad −1 ] is the distance translated for every radian the shield rotates. Assuming the shield rotates about the vector Δ ⇀ s j while it travels between dwell positions j and beginning at dwell position j, are transformed to the "primed" unit vectors m′ j (h) and n′ j (h), respectively.…”

“…Multiple approaches are under development for delivering temporary intensity modulated brachytherapy (IMBT) [1][2][3][4] using partially shielded applicators including serial rotating shield brachytherapy (RSBT), [5][6][7][8][9] helical RSBT, [10][11][12] and direction modulated brachytherapy (DMBT). [13][14][15][16] These techniques have been proposed to reduce the need for interstitial brachytherapy for cervical cancer patients in favor of an intracavitary approach, 6,[8][9][10][11][14][15][16] improving tumor dose conformity for prostate cancer, 7,12 and improving tumor dose conformity for rectal cancer.…”

“…Multiple approaches are under development for delivering temporary intensity modulated brachytherapy (IMBT) [1][2][3][4] using partially shielded applicators including serial rotating shield brachytherapy (RSBT), [5][6][7][8][9] helical RSBT, [10][11][12] and direction modulated brachytherapy (DMBT). [13][14][15][16] These techniques have been proposed to reduce the need for interstitial brachytherapy for cervical cancer patients in favor of an intracavitary approach, 6,[8][9][10][11][14][15][16] improving tumor dose conformity for prostate cancer, 7,12 and improving tumor dose conformity for rectal cancer. 5,13 For each IMBT approach, partial shields are used within the applicators which are either static (DMBT) or that dynamically (RSBT) rotate throughout delivery, making the delivered dose distributions sensitive to spatial uncertainties in both the applicator position and shield orientation, rather than just applicator position as with conventional high-doserate brachytherapy (HDR-BT).…”