Can intermediate-energy sources lead to elevated bone doses for prostate and head &amp; neck high-dose-rate brachytherapy?

Famulari, Gabriel; Alfieri, Joanne; Duclos, Marie; Vuong, T.; Enger, Shirin A.

doi:10.1016/j.brachy.2019.12.004

Cited by 9 publications

(9 citation statements)

References 55 publications

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“…In the intermediate‐to‐high brachytherapy source photon energy range investigated in this study, D w,m underestimates bone by approximately 8% (6%), 29% (25%), and 63% (59%) for conventional brachytherapy (IMBT) with 192 Ir, 75 Se, and 169 Yb, respectively. These results are consistent with AAPM TG‐186 and TG‐286, 1,19 and more recently, reported in a recent prostate planning study, which also investigated 169 Yb 34 . Pelvic insufficiency fractures have been observed in gynecologic cancer patients after pelvic irradiation 35 .…”

Section: Discussionsupporting

confidence: 91%

“…These results are consistent with AAPM TG-186 and TG-286, 1,19 and more recently, reported in a recent prostate planning study, which also investigated 169 Yb. 34 Pelvic insufficiency fractures have been observed in gynecologic cancer patients after pelvic irradiation. 35 Based on the results obtained in this study, when 169 Yb or 75 Se is used for cervical cancer brachytherapy, dose to bone should be considered.…”

Section: Discussionmentioning

confidence: 99%

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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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Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

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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“…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%

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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“…However, comparative studies have shown similarity (albeit not identity) of physical dose distributions in many disease sites including the cervix for both these sources. [17][18][19][20][21][22] But the clinical outcomes including tumor control or normal tissue toxicity are more directly linked to the biological dose distributions rather than the physical dose distributions. The biological dose is in turn influenced by not only the physical dose but also the relative biological effectiveness (RBE) and the repair of sublethal damages during irradiation, which depend on the source energy spectrum and dose rate, respectively.…”

Section: Introductionmentioning

confidence: 99%

Radiobiological comparison between Cobalt‐60 and Iridium‐192 high‐dose‐rate brachytherapy sources: Part I—cervical cancer

et al. 2021

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This study aimed to compare the biological effective doses (BEDs) to clinical target volume (CTV) and organs at risk (OARs) for cervical cancer patients treated with high-dose-rate (HDR) or Cobalt-60 ( 60 Co) brachytherapy (BT) boost and to determine if the radiobiological differences between the two isotopes are clinically relevant. Methods: Considering all radiosensitivity parameters and their reported variations, the BEDs to CTV and OARs during HDR 60 Co/ 192 Ir BT boost were evaluated at the voxel level. The anatomical differences between individuals were also taken into account by retrospectively considering 25 cervical cancer patients. The intrafraction repair, proliferation, hypoxia-induced radiosensitivity heterogeneity, relative biological effectiveness (RBE), and source aging doserate variation were also taken into account. The comparisons in CTV were performed based on equivalent uniform BED (EUBED). Results: Considering nominal parameters with no RBE correction, the CTV EUBEDs were almost similar with a median ratio of ∼1.00 (p < 0.00001), whereas RBE correction resulted in 3.9%-5.5% (p = 0.005, median = 4.8%) decrease for 60 Co with respect to 192 Ir. For OARs, the median values of D 2cc (in EQD2 3 ) for 60 Co were lower than that of 192 Ir up to 9.2% and 11.3% (p < 0.00001) for nominal parameters and fast repair conditions, respectively. In addition, for a nominal value (reported range) of radiosensitive parameters, the CTV EUBED differences of up to 6% (5%-10%) were assessed for HDR-BT component. Conclusion:The RBE values are the most important cause of discrepancies between the two sources. By comparing BED/EUBEDs to CTV and OARs between 60 Co and 192 Ir sources,this numerical study suggests that a dose escalation to ∼4% is feasible and safe while sparing well the surrounding normal tissues. This 4% dose escalation should be benchmarked with clinical evidences (such as the results of clinical trials) before it can be used in clinical practice.

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Can intermediate-energy sources lead to elevated bone doses for prostate and head & neck high-dose-rate brachytherapy?

Cited by 9 publications

References 55 publications

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

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

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

Radiobiological comparison between Cobalt‐60 and Iridium‐192 high‐dose‐rate brachytherapy sources: Part I—cervical cancer

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