Analytical HDR prostate brachytherapy planning with automatic catheter and isotope selection

• Published in: Medical physics (Lancaster) 2023-10, Vol.50 (10), p.6525-6534
• Main Authors: Frank, Catherine Holly, Ramesh, Pavitra, Lyu, Qihui, Ruan, Dan, Park, Sang-June, Chang, Albert J, Venkat, Puja S, Kishan, Amar U, Sheng, Ke
• Format: Article
• Language: English
• Subjects: Brachytherapy - methods; Catheters; Humans; Iridium Radioisotopes - therapeutic use; Male; Prostate; Prostatic Neoplasms - drug therapy; Prostatic Neoplasms - radiotherapy; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Retrospective Studies
• ISSN: 0094-2405; 2473-4209; 2473-4209
• DOI: 10.1002/mp.16677

High dose rate (HDR) brachytherapy is commonly used to treat prostate cancer. Existing HDR planning systems solve the dwell time problem for predetermined catheters and a single energy source. Additional degrees of freedom can be obtained by relaxing the catheters' pre-designation and introducing more source types, and may have a dosimetric benefit, particularly in improving conformality to spare the urethra. This study presents a novel analytical approach to solving the corresponding HDR planning problem. The catheter and dual-energy source selection problem was formulated as a constrained optimization problem with a non-convex group sparsity regularization. The optimization problem was solved using the fast-iterative shrinkage-thresholding algorithm (FISTA). Two isotopes were considered. The dose rates for the HDR 4140 Ytterbium (Yb-169) source and the Elekta Iridium (Ir-192) HDR Flexisource were modeled according to the TG-43U1 formalism and benchmarked accordingly. Twenty-two retrospective HDR prostate brachytherapy patients treated with Ir-192 were considered. An Ir-192 only (IRO), Yb-169 only (YBO), and dual-source (DS) plan with optimized catheter location was created for each patient with N catheters, where N is the number of catheters used in the clinically delivered plans. The DS plans jointly optimized Yb-169 and Ir-192 dwell times. All plans and the clinical plans were normalized to deliver a 15 Gy prescription (Rx) dose to 95% of the clinical treatment volume (CTV) and evaluated for the CTV D90%, V150%, and V200%, urethra D0.1cc and D1cc, bladder V75%, and rectum V75%. Dose-volume histograms (DVHs) were generated for each structure. The DS plans ubiquitously selected Ir-192 as the only treatment source. IRO outperformed YBO in organ at risk (OARs) OAR sparing, reducing the urethra D0.1cc and D1cc by 0.98% ( ) and 1.09% ( ) of the Rx dose, respectively, and reducing the bladder and rectum V75% by 0.09 ( ) and 0.13 cubic centimeters (cc) ( ), respectively. The YBO plans delivered a more homogenous dose to the CTV, with a smaller V150% and V200% by 3.20 ( ) and 1.91 cc ( ), respectively, and a lower CTV D90% by 0.49% ( ) of the prescription dose. The IRO plans reduce the urethral D1cc by 2.82% ( ) of the Rx dose compared to the clinical plans, at the cost of increased bladder and rectal V75% by 0.57 ( ) and 0.21 cc ( ), respectively, and increased CTV V150% by a mean of 1.46 cc ( ) and CTV D90% by an average of 1.40% of the Rx dose ( ). While the