Dosimetric Considerations for Ytterbium-169, Selenium-75, and Iridium-192 Radioisotopes in High-Dose-Rate Endorectal Brachytherapy

Shoemaker, Tristan; Vuong, T.; Glickman, Harry; Kaifi, Samar; Famulari, Gabriel; Enger, Shirin A.

doi:10.1016/j.ijrobp.2019.07.003

Cited by 8 publications

(8 citation statements)

References 45 publications

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“…However, Shoemaker et al showed in a previous study that when performing MRI-based planning, the loss of CT-density data will not have a clinically significant effect on dosimetry, as long as material elemental compositions and nominal mass densities are correctly assigned to each contoured structure and implanted objects such as shields and applicators. 14 Treatment times with 192 Ir-based IMBT would increase by a factor of 1.7, from 6.0 to 10.3 min. For 75 Se and 169 Yb, treatments would be delivered in 19.9 and 14.0 mins, respectively, due to the high-specific activity of these sources despite their lower energies.…”

Section: Discussionmentioning

confidence: 99%

“…MRI‐based dosimetry was used in this study. However, Shoemaker et al showed in a previous study that when performing MRI‐based planning, the loss of CT‐density data will not have a clinically significant effect on dosimetry, as long as material elemental compositions and nominal mass densities are correctly assigned to each contoured structure and implanted objects such as shields and applicators 14 …”

Section: Discussionmentioning

confidence: 99%

“…7 An additional limitation of the aforementioned IMBT investigation is that the dose calculations were based on dose to water, an assumption which leads to dosimetric inaccuracies due to the non-water equivalence of mass energy absorption coefficient for metal and different tissues. 13,14 The inaccuracies increase with decreasing photon energy where photoelectric interactions dominate. 15 75 Se and 169 Yb have been hypothesized for HDR BT use for decades due to their high practical specific activities of 5.8 and 8.0 kCi/g, respectively, compared to 3.9 kCi/g for 192 Ir.…”

Section: Introductionmentioning

confidence: 99%

“…However due to the low specific activity of 153 Gd, 20 simultaneous HDR sources were required and treatment times were on the order of 2 h. Electronic BT‐based IMBT for cervical cancer uses a 50 kVp source, which is more easily shielded, yet has limited penetration depth and require a larger tandem with a diameter of 9.4 mm 7 . An additional limitation of the aforementioned IMBT investigation is that the dose calculations were based on dose to water, an assumption which leads to dosimetric inaccuracies due to the non‐water equivalence of mass energy absorption coefficient for metal and different tissues 13,14 . The inaccuracies increase with decreasing photon energy where photoelectric interactions dominate 15 .…”

Section: Introductionmentioning

confidence: 99%

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A novel minimally invasive dynamic‐shield, intensity‐modulated brachytherapy system for the treatment of cervical cancer

et al. 2020

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Purpose To present a novel, MRI‐compatible dynamicshield intensity modulated brachytherapy (IMBT) applicator and delivery system using 192Ir, 75Se, and 169Yb radioisotopes for the treatment of locally advanced cervical cancer. Needle‐free IMBT is a promising technique for improving target coverage and organs at risk (OAR) sparing. Methods and materials The IMBT delivery system dynamically controls the rotation of a novel tungsten shield placed inside an MRI‐compatible, 6‐mm wide intrauterine tandem. Using 36 cervical cancer cases, conventional intracavitary brachytherapy (IC‐BT) and intracavitary/interstitial brachytherapy (IC/IS‐BT) (10Ci 192Ir) plans were compared to IMBT (10Ci 192Ir; 11.5Ci 75Se; 44Ci 169Yb). All plans were generated using the Geant4‐based Monte Carlo dose calculation engine, RapidBrachyMC. Treatment plans were optimized then normalized to the same high‐risk clinical target volume (HR‐CTV) D90 and the D2cc for bladder, rectum, and sigmoid in the research brachytherapy planning system, RapidBrachyMCTPS. Plans were renormalized until either of the three OAR reached dose limits to calculate the maximum achievable HR‐CTV D90 and D98. Results Compared to IC‐BT, IMBT with either of the three radionuclides significantly improves the HR‐CTV D90 and D98 by up to 5.2% ± 0.3% (P < 0.001) and 6.7% ± 0.5% (P < 0.001), respectively, with the largest dosimetric enhancement when using 169Yb followed by 75Se and then 192Ir. Similarly, D2cc for all OAR improved with IMBT by up to 7.7% ± 0.6% (P < 0.001). For IC/IS‐BT cases, needle‐free IMBT achieved clinically acceptable plans with 169Yb‐based IMBT further improving HR‐CTV D98 by 1.5% ± 0.2% (P = 0.034) and decreasing sigmoid D2cc by 1.9% ± 0.4% (P = 0.048). Delivery times for IMBT are increased by a factor of 1.7, 3.3, and 2.3 for 192Ir, 75Se, and 169Yb, respectively, relative to conventional 192Ir BT. Conclusions Dynamic shield IMBT provides a promising alternative to conventional IC‐ and IC/IS‐BT techniques with significant dosimetric enhancements and even greater improvements with intermediate energy radionuclides. The ability to deliver a highly conformal, OAR‐sparing dose without IS needles provides a simplified method for improving the therapeutic ratio less invasively and in a less resource intensive manner.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A novel minimally invasive dynamic‐shield, intensity‐modulated brachytherapy system for the treatment of cervical cancer

et al. 2020

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“…This is in contrast with static shielding techniques used in endorectal brachytherapy where calculating D w,w to the CTV and ignoring the contralateral tungsten shield leads to only 4% difference relative to and D w,w-App . 29 Taking the applicator into account, the effect of ignoring the patient heterogeneities was studied by looking at the percent difference between D m,m ( ρ CT) and D w,w-App . The effect of scoring dose to a small mass of water as opposed to medium was quantified by taking the percent difference between D w,m ( ρ CT) and D m,m ( ρ CT) .…”

Section: D Dosimetric Evaluationmentioning

confidence: 99%

On the impact of absorbed dose specification, tissue heterogeneities, and applicator heterogeneities on Monte Carlo‐based dosimetry of Ir‐192, Se‐75, and Yb‐169 in conventional and intensity‐modulated brachytherapy for the treatment of cervical cancer

2021

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The purpose of this study was to evaluate the impact of dose reporting schemes and tissue/ applicator heterogeneities for 192 Ir-, 75 Se-, and 169 Yb-based MRI-guided conventional and intensitymodulated brachytherapy. Methods and Materials: Treatment plans using a variety of dose reporting and tissue/applicator segmentation schemes were generated for a cohort (n = 10) of cervical cancer patients treated with 192 Ir-based Venezia brachytherapy. Dose calculations were performed using RapidBrachyMCTPS, a Geant4-based research Monte Carlo treatment planning system. Ultimately, five dose calculation scenarios were evaluated: (a) dose to water in water (D w,w ); (b) D w,w taking the applicator material into consideration (D w,wApp ); (c) dose to water in medium (D w,m ); (d and e) dose to medium in medium with mass densities assigned either nominally per structure (D m,m (Nom) ) or voxel-by-voxel (D m,m ).Results: Ignoring the plastic Venezia applicator (D w,wApp ) overestimates D m,m by up to 1% (average) with high energy source ( 192 Ir and 75 Se) and up to 2% with 169 Yb. Scoring dose to water (D w,wApp or D w,m ) generally overestimates dose and this effect increases with decreasing photon energy. Reporting dose other than D m,m (or D m,m Nom ) for 169 Yb-based conventional and intensity-modulated brachytherapy leads to a simultaneous overestimation (up to 4%) of CTV HR D 90 and underestimation (up to 2%) of bladder D 2cc due to a significant dip in the mass-energy absorption ratios at the depths of nearby targets and OARs. Using a nominal mass-density assignment per structure, rather than a CT-derived voxel-by-voxel assignment for MRI-guided brachytherapy, amounts to a dose error up to 1% for all radionuclides considered. Conclusions: The effects of the considered dose reporting schemes trend correspondingly between conventional and intensity-modulated brachytherapy. In the absence of CT-derived mass densities, MRI-only-based dosimetry can adequately approximate D m,m by assigning nominal mass densities to structures. Tissue and applicator heterogeneities do not significantly impact dosimetry for 192 Ir and 75 Se, but do for 169 Yb; dose reporting must be explicitly defined since D w,m and D w,w may overstate the dosimetric benefits.

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Dosimetric impact of a robust optimization approach to mitigate effects from rotational uncertainty in prostate intensity‐modulated brachytherapy

et al. 2022

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Background: Intensity-modulated brachytherapy (IMBT) is an emerging technology for cancer treatment, in which radiation sources are shielded to shape the dose distribution. The rotatable shields provide an additional degree of freedom, but also introduce an additional, directional, type of uncertainty, compared to conventional high-dose-rate brachytherapy (HDR BT). Purpose: We propose and evaluate a robust optimization approach to mitigate the effects of rotational uncertainty in the shields with respect to planning criteria. Methods: A previously suggested prototype for platinum-shielded prostate 169 Yb-based dynamic IMBT is considered. We study a retrospective patient data set (anatomical contours and catheter placement) from two clinics, consisting of six patients that had previously undergone conventional 192 Ir HDR BT treatment. The Monte Carlo-based treatment planning software RapidBrachyMCTPS is used for dose calculations. In our computational experiments, we investigate systematic rotational shield errors of ±10 • and ±20 • , and the same systematic error is applied to all dwell positions in each scenario. This gives us three scenarios, one nominal and two with errors. The robust optimization approach finds a compromise between the average and worst-case scenario outcomes. Results: We compare dose plans obtained from standard models and their robust counterparts. With dwell times obtained from a linear penalty model (LPM), for 10 • errors, the dose to urethra (D 0.1cc ) and rectum (D 0.1cc and D 1cc ) increase with up to 5% and 7%, respectively, in the worst-case scenario, while with the robust counterpart, the corresponding increases were 3% and 3%. For all patients and all evaluated criteria, the worst-case scenario outcome with the robust approach had lower deviation compared to the standard model, without compromising target coverage. We also evaluated shield errors up to 20 • and while the deviations increased to a large extent with the standard models, the robust models were capable of handling even such large errors. Conclusions: We conclude that robust optimization can be used to mitigate the effects from rotational uncertainty and to ensure the treatment plan quality of IMBT.

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Dosimetric Considerations for Ytterbium-169, Selenium-75, and Iridium-192 Radioisotopes in High-Dose-Rate Endorectal Brachytherapy

Cited by 8 publications

References 45 publications

A novel minimally invasive dynamic‐shield, intensity‐modulated brachytherapy system for the treatment of cervical cancer

A novel minimally invasive dynamic‐shield, intensity‐modulated brachytherapy system for the treatment of cervical cancer

On the impact of absorbed dose specification, tissue heterogeneities, and applicator heterogeneities on Monte Carlo‐based dosimetry of Ir‐192, Se‐75, and Yb‐169 in conventional and intensity‐modulated brachytherapy for the treatment of cervical cancer

Dosimetric impact of a robust optimization approach to mitigate effects from rotational uncertainty in prostate intensity‐modulated brachytherapy

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