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.
Abstract
Background
Multiple approaches are under development for delivering temporary intensity modulated brachytherapy (IMBT) using partially shielded applicators wherein the delivered dose ...distributions are sensitive to spatial uncertainties in both the applicator position and shield orientation, rather than only applicator position as with conventional high‐dose‐rate brachytherapy (HDR‐BT). Sensitivity analyses to spatial uncertainties have been reported as components of publications on these emerging technologies, however, a generalized framework for the rigorous determination of the spatial uncertainty tolerances of dose‐volume parameters is needed.
Purpose
To derive and present the population percentile allowance (PPA) method, a generalized mathematical and statistical framework to evaluate the tolerance of temporary IMBT approaches to spatial uncertainties in applicator position and shield orientation.
Methods
A mathematical formalism describing geometric applicator position and shield orientation shifts was derived that supports straight and curved applicators and applies to serial and helical rotating shield brachytherapy (RSBT) and direction modulated brachytherapy (DMBT). The PPA method entails defining the percentage of a patient population receiving a given therapy that is, allowed to receive dose‐volume errors in the target volume and specified organs at risk of a defined percentage or less, then determining what combinations of applicator position and shield orientation systematic errors would be expected to produce that outcome in the population. The PPA method was applied to the use case of multi‐shield helical
169
Yb‐based RSBT for cervical cancer, with 45° and 180° shield emission angles. A total of 37 cervical cancer patients were considered in the population, with average (± 1 standard deviation) HR‐CTV volumes of 79 cm
3
± 37 cm
3
and optimized baseline treatment plans (no spatial uncertainties applied) created for each patient to meet dose‐volume requirements of 85 Gy
EQD2
(equivalent uniform dose in 2 Gy fraction), with
D
2cc
tolerance doses of 90 Gy
EQD2
, 75 Gy
EQD2
, and 75 Gy
EQD2
for bladder, rectum, and sigmoid colon, respectively.
Results
For the PPA requirement that 90% of cervical cancer patients receiving multi‐shield helical RSBT could have a maximum dose‐volume uncertainty of 10% for high‐risk clinical target volume (HR‐CTV)
D
90
(minimum dose to hottest 90%) and bladder, rectum, and sigmoid colon
D
2cc
(minimum dose to hottest 2 cm
3
), the tolerance systematic applicator position and shield orientation uncertainties were approximately ± 1.0 mm and ± 4.25°, respectively. For ± 1.5 mm and ± 5° systematic applicator position and shield orientation tolerances, 90% of the patients considered would have a maximum dose‐volume uncertainty of 12.8% or less.
Conclusion
The PPA method was formalized to determine the temporary IMBT spatial uncertainty tolerances that would be expected to result in an allowed percentage of a population of patients receiving relative dose‐volume errors above a defined percentage. Multi‐shield, helical
169
Yb‐based RSBT for cervical cancer was evaluated and tolerances determined, which, if applied on each treatment fraction, would represent an extreme situation. The PPA method is applicable to a variety of temporary IMBT approaches and can be used to rigorously determine the design parameters for the delivery systems such as mechanical driver motor accuracy, shield angle backlash, applicator rotation, and applicator fixation stability.
Brachytherapy: An overview for clinicians Chargari, Cyrus; Deutsch, Eric; Blanchard, Pierre ...
CA: a cancer journal for clinicians,
September/October 2019, Volume:
69, Issue:
5
Journal Article
Peer reviewed
Open access
Brachytherapy is a specific form of radiotherapy consisting of the precise placement of radioactive sources directly into or next to the tumor. This technique is indicated for patients affected by ...various types of cancers. It is an optimal tool for delivering very high doses to the tumor focally while minimizing the probability of normal tissue complications. Physicians from a wide range of specialties may be involved in either the referral to or the placement of brachytherapy. Many patients require brachytherapy as either primary treatment or as part of their oncologic care. On the basis of high‐level evidence from randomized controlled trials, brachytherapy is mainly indicated: 1) as standard in combination with chemoradiation in patients with locally advanced cervical cancer; 2) in surgically treated patients with uterine endometrial cancer for decreasing the risk of vaginal vault recurrence; 3) in patients with high‐risk prostate cancer to perform dose escalation and improve progression‐free survival; and 4) in patients with breast cancer as adjuvant, accelerated partial breast irradiation or to boost the tumor bed. In this review, the authors discuss the clinical relevance of brachytherapy with a focus on indications, levels of evidence, and results in the overall context of radiation use for patients with cancer.
To determine the trends in brachytherapy use in cervical cancer in the United States and to identify factors and survival benefits associated with brachytherapy treatment.
Using the Surveillance, ...Epidemiology, and End Results (SEER) database, we identified 7359 patients with stages IB2-IVA cervical cancer treated with external beam radiation therapy (EBRT) between 1988 and 2009. Propensity score matching was used to adjust for differences between patients who received brachytherapy and those who did not from 2000 onward (after the National Cancer Institute alert recommending concurrent chemotherapy).
Sixty-three percent of the 7359 women received brachytherapy in combination with EBRT, and 37% received EBRT alone. The brachytherapy utilization rate has decreased from 83% in 1988 to 58% in 2009 (P<.001), with a sharp decline of 23% in 2003 to 43%. Factors associated with higher odds of brachytherapy use include younger age, married (vs single) patients, earlier years of diagnosis, earlier stage and certain SEER regions. In the propensity score-matched cohort, brachytherapy treatment was associated with higher 4-year cause-specific survival (CSS; 64.3% vs 51.5%, P<.001) and overall survival (OS; 58.2% vs 46.2%, P<.001). Brachytherapy treatment was independently associated with better CSS (hazard ratio HR, 0.64; 95% confidence interval CI, 0.57-0.71), and OS (HR 0.66; 95% CI, 0.60 to 0.74).
This population-based analysis reveals a concerning decline in brachytherapy utilization and significant geographic disparities in the delivery of brachytherapy in the United States. Brachytherapy use is independently associated with significantly higher CSS and OS and should be implemented in all feasible cases.
Purpose:
To present a novel brachytherapy technique, called multihelix rotating shield brachytherapy (H‐RSBT), for the precise angular and linear positioning of a partial shield in a curved ...applicator. H‐RSBT mechanically enables the dose delivery using only linear translational motion of the radiation source/shield combination. The previously proposed approach of serial rotating shield brachytherapy (S‐RSBT), in which the partial shield is rotated to several angular positions at each source dwell position W. Yang et al., “Rotating‐shield brachytherapy for cervical cancer,” Phys. Med. Biol. 58, 3931–3941 (2013), is mechanically challenging to implement in a curved applicator, and H‐RSBT is proposed as a feasible solution.
Methods:
A Henschke‐type applicator, designed for an electronic brachytherapy source (Xoft Axxent™) and a 0.5 mm thick tungsten partial shield with 180° or 45° azimuthal emission angles and 116° asymmetric zenith angle, is proposed. The interior wall of the applicator contains six evenly spaced helical keyways that rigidly define the emission direction of the partial radiation shield as a function of depth in the applicator. The shield contains three uniformly distributed protruding keys on its exterior wall and is attached to the source such that it rotates freely, thus longitudinal translational motion of the source is transferred to rotational motion of the shield. S‐RSBT and H‐RSBT treatment plans with 180° and 45° azimuthal emission angles were generated for five cervical cancer patients with a diverse range of high‐risk target volume (HR‐CTV) shapes and applicator positions. For each patient, the total number of emission angles was held nearly constant for S‐RSBT and H‐RSBT by using dwell positions separated by 5 and 1.7 mm, respectively, and emission directions separated by 22.5° and 60°, respectively. Treatment delivery time and tumor coverage (D90 of HR‐CTV) were the two metrics used as the basis for evaluation and comparison. For all the generated treatment plans, the D90 of the HR‐CTV in units of equivalent dose in 2 Gy fractions (EQD2) was escalated until the D2cc (minimum dose to hottest 2 cm3) tolerance of either the bladder (90 Gy3), rectum (75 Gy3), or sigmoid colon (75 Gy3) was reached.
Results:
Treatment time changed for H‐RSBT versus S‐RSBT by −7.62% to 1.17% with an average change of −2.8%, thus H‐RSBT treatments times tended to be shorter than for S‐RSBT. The HR‐CTV D90 also changed by −2.7% to 2.38% with an average of −0.65%.
Conclusions:
H‐RSBT is a mechanically feasible delivery technique for use in the curved applicators needed for cervical cancer brachytherapy. S‐RSBT and H‐RSBT were clinically equivalent for all patients considered, with the H‐RSBT technique tending to require less time for delivery.
Background
Applicator conspicuity in ultrasound‐guided brachytherapy procedures is commonly impaired by imaging artifacts or non‐ideal imaging geometry, which can slow down applicator position ...digitization and increase the geometric uncertainty of the delivered dose distribution.
Purpose
The purpose of this study was to improve the conspicuity of high‐dose rate (HDR) brachytherapy needles under B‐mode ultrasound imaging by applying an echogenic surface coating. Our hypothesis was that an echogenic coating would reduce artifacts and improve needle visualization within regions of signal degradation.
Methods
In this study, 17‐gauge, 25‐cm long titanium HDR brachytherapy needles were coated with acoustically reflective microspheres over a 2.5 cm region starting from the needle tip. Three coating thicknesses (27 μm, 40 μm, 64 μm) were compared against an uncoated control needle. The coated and uncoated needles were imaged using B‐mode ultrasound in a tissue‐equivalent prostate phantom and in a cadaverous male pelvis using a transrectal probe. Needle conspicuity was assessed under multiple conditions: a single needle implant, an implant with multiple needles between the probe and the needle of interest, and an angled needle implant. All images were assessed qualitatively for needle conspicuity and the presence of artifacts and quantitatively using grey‐scale image intensity values.
Results
The 64 μm echogenic coating reduced the magnitude of reverberation artifacts by 31 ± 14% and comet tail artifacts by 40%–70%. The echogenic coating also improved needle contrast, measured by the relative differences in signal intensity compared with the adjacent environment, when needles were angled up to 30° with respect to the transducer probe in the cadaver. The improvements in conspicuity and artifact reduction increased with increasing coating thickness. The performance of the needles coated with the 64 μm thickness was qualitatively superior and yielded high‐contrast, well‐circumscribed signals in the cadaverous male pelvis, even under situations where a needle was acoustically shadowed by multiple other needles.
Conclusions
An echogenic surface coating reduced imaging artifacts and improved needle conspicuity under realistic clinical conditions for ultrasound‐based prostate or gynecological brachytherapy. The improved conspicuity has the potential to improve the efficiency of needle placement and the accuracy of needle position digitization during brachytherapy procedures.
Paddle‐based rotating‐shield brachytherapy Liu, Yunlong; Flynn, Ryan T.; Kim, Yusung ...
Medical physics (Lancaster),
October 2015, Volume:
42, Issue:
10
Journal Article
Peer reviewed
Open access
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™). 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 cm3 (D2cm3) of either the rectum, sigmoid colon, or bladder reached their tolerance doses of 75, 75, and 90 Gy3, respectively, expressed as equivalent doses in 2 Gy fractions (EQD2 with α/β = 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°, the average D90 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 Gy10, respectively, with delivery times of 10, 15, 20, 25, and 30 min/fx. The increases in HR‐CTV D90, compared to D‐RSBT, were 16.6, 12.9, 7.2, 3.7, and 1.7 Gy10, respectively. P‐RSBT HR‐CTV D90‐values were insensitive to the paddle size for paddles angled at less than 60°. Increasing the paddle angle from 5° to 60° resulted in only a 0.6 Gy10 decrease in HR‐CTV D90 on average for five cases when the delivery times were set to 15 min/fx. The HR‐CTV D90 decreased to 2.5 and 11.9 Gy10 with paddle angles of 90° and 120°, 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.
Radiation therapy is an integral component in the multimodality management of many gastrointestinal (GI) cancers at all stages of clinical presentation. With recent advances in technology and ...radiation delivery, external beam radiation therapy (EBRT) can be delivered with reduced toxicity. However, despite these advances, EBRT doses are still limited by the presence of radiosensitive serial structures near clinical targets in the GI tract. Relative to EBRT techniques, brachytherapy techniques have a lower integral dose and more rapid fall-off, allowing for high-dose delivery with little normal tissue exposure. Given the unique characteristics of brachytherapy, it is an attractive strategy to treat GI malignancies. This review addresses the application of both high-dose rate brachytherapy (HDRBT) and low-dose rate brachytherapy (LDRBT) to multiple GI malignancies for both definitive and palliative management.
Purpose
The purpose of this study was to evaluate the impact of dose reporting schemes and tissue/applicator heterogeneities for 192Ir‐, 75Se‐, and 169Yb‐based MRI‐guided conventional and ...intensity‐modulated 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 192Ir‐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 (Dw,w); (b) Dw,w taking the applicator material into consideration (Dw,wApp); (c) dose to water in medium (Dw,m); (d and e) dose to medium in medium with mass densities assigned either nominally per structure (Dm,m (Nom)) or voxel‐by‐voxel (Dm,m).
Results
Ignoring the plastic Venezia applicator (Dw,wApp) overestimates Dm,m by up to 1% (average) with high energy source (192Ir and 75Se) and up to 2% with 169Yb. Scoring dose to water (Dw,wApp or Dw,m) generally overestimates dose and this effect increases with decreasing photon energy. Reporting dose other than Dm,m (or Dm,m Nom) for 169Yb‐based conventional and intensity‐modulated brachytherapy leads to a simultaneous overestimation (up to 4%) of CTVHR D90 and underestimation (up to 2%) of bladder D2cc 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 Dm,m by assigning nominal mass densities to structures. Tissue and applicator heterogeneities do not significantly impact dosimetry for 192Ir and 75Se, but do for 169Yb; dose reporting must be explicitly defined since Dw,m and Dw,w may overstate the dosimetric benefits.
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