Calibration system correction factor for measuring the reference air kerma rate (RAKR) applied to high dose rate192Ir sources (HDR).

The aim of this study was to use computer simulation to analyze the impact of the aluminum fixing support on the Reference Air Kerma (RAK), a physical quantity obtained in a calibration system that was experimentally developed in the Laboratory of Radiological Sciences of the University of the State of Rio de Janeiro (LCR-UERJ). Correction factors due to scattered radiation and the geometry of the192Ir sources were also sought to be determined. The computational simulation was validated by comparing some parameters of the experimental results with the computational results. These parameters were: verification of the inverse square law of distance, determination of (RAKR), analysis of the source spectrum with and without encapsulation, and the sensitivity curve of the Sourcecheck 4PI ionization chamber response, as a function of the distance from the source along the axial axis, using the microSelectron-v2 (mSv2) and GammaMedplus (GMp) sources. Kerma was determined by activity in the Reference air, with calculated values of 1.725 × 10-3U. Bq-1and 1.710 × 10-3U. Bq-1for the ionization chamber NE 2571 and TN 30001, respectively. The expanded uncertainty for these values was 0.932% and 0.919%, respectively, for a coverage factor (k = 2). The correction factor due to the influence of the aluminum fixing support for measurements at 1 cm and 10 cm from the source was 0.978 and 0.969, respectively. The geometric correction factor of the sources was ksg= 1.005 with an expanded uncertainty of 0.7% for a coverage factor (k = 2). This value has a difference of approximately 0.2% compared to the experimental values.

High dose rate 192Ir brachytherapy source model Monte Carlo dosimetry: mHDR-v2 and mHDR-v2r.

After 2010, the source model of the microSelectron HDR Afterloader System was slightly modified from the previous model. Granero et al. named the modified source model "mHDR-v2r (revised model mHDR-v2)" and the previous model "mHDR-v2". They concluded that the dosimetric differences arising from the dimensional changes between the mHDR-v2 and mHDR-v2r designs were negligible at almost all locations (within 0.5% for r ≥ 0.25 cm), the two-dimensional anisotropy function difference between the two sources is found 2.1% at r = 1.0 cm when compared with the results of the other experimental group. To confirm this difference, we performed a full Monte Carlo simulation without energy-fluence approximation. This is useful near the radiation source where charged-particle equilibrium does not hold. The two-dimensional anisotropy function of the TG-43U1 dataset showed a few percent difference between the mHDR-v2r and mHDR-v2 sources. There was no agreement in the immediate vicinity of the source (0.10 cm and 0.25 cm), when compared to Granero et al. in mHDR-v2r sources. The differences in these two-dimensional anisotropy functions were identified.

The effect of vaginal cylinder inhomogeneity on the HDR brachytherapy dose calculations using Monte Carlo simulations.

PURPOSE: To analytically assess the heterogeneity effect of vaginal cylinders (VC) made of high-density plastics on dose calculations, considering the prescription point (surface or 5 mm beyond the surface), and benchmark the accuracy of a commercial model-based dose calculation (MBDC) algorithm using Monte Carlo (MC) simulations. METHODS AND MATERIALS: The GEANT4 MC code was used to simulate a commercial 192 Ir HDR source and VC, with diameters ranging from 20 to 35 mm, inside a virtual water phantom. Standard plans were generated from a commercial treatment planning system [TPS-BrachyVision ACUROS (BV)] optimized for a treatment length of 5 cm through two dose calculation approaches: (1) assuming all the environment as water (i.e., Dw,w-MC & Dw,w-TG43 ) and (2) accounting for the heterogeneity of VC applicators (i.e., Dw,w-App-MC & Dw,w-App-MBDC ). The compared isodose lines, and dose & energy difference maps were extracted for analysis. In addition, the dose difference on the peripheral surface, along the applicator and at middle of treatment length, as well as apical tip was evaluated. RESULTS: The Dw,w-App-MC results indicated that the VC heterogeneity can cause a dose reduction of (up to) % 6.8 on average (for all sizes) on the peripheral surface, translating to 1 mm shrinkage of the isodose lines compared to Dw,w-MC . In addition, the results denoted that BV overestimates the dose on the peripheral surface and apical tip of about 3.7% and 17.9%, respectively, (i.e., Dw,w-App-MBDC vs Dw,w-App-MC ) when prescribing to the surface. However, the difference between the two were negligible at the prescription point when prescribing to 5 mm beyond the surface. CONCLUSION: The VCs' heterogeneity could cause dose reduction when prescribing dose to the surface of the applicator, and hence increases the level of uncertainty. Thus, reviewing the TG43 results, in addition to ACUROS, becomes prudent, when evaluating the surface coverage at the apex.

Analytical HDR prostate brachytherapy planning with automatic catheter and isotope selection.

BACKGROUND: 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. PURPOSE: 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. METHODS: 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. RESULTS: 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% ( p = 2.22 ∗ 10 - 9 $p\ = \ 2.22*{10^{ - 9}}$ ) and 1.09% ( p = 1.22 ∗ 10 - 10 $p\ = \ 1.22*{10^{ - 10}}$ ) of the Rx dose, respectively, and reducing the bladder and rectum V75% by 0.09 ( p = 0.0023 $p\ = \ 0.0023$ ) and 0.13 cubic centimeters (cc) ( p = 0.033 $p\ = \ 0.033$ ), respectively. The YBO plans delivered a more homogenous dose to the CTV, with a smaller V150% and V200% by 3.20 ( p = 4.67 ∗ 10 - 10 $p\ = \ 4.67*{10^{ - 10}}$ ) and 1.91 cc ( p = 5.79 ∗ 10 - 10 $p\ = \ 5.79*{10^{ - 10}}$ ), respectively, and a lower CTV D90% by 0.49% ( p = 0.0056 $p\ = \ 0.0056$ ) of the prescription dose. The IRO plans reduce the urethral D1cc by 2.82% ( p = 1.38 ∗ 10 - 4 $p\ = \ 1.38*{10^{ - 4}}$ ) of the Rx dose compared to the clinical plans, at the cost of increased bladder and rectal V75% by 0.57 ( p = 0.0022 $p\ = \ 0.0022$ ) and 0.21 cc ( p = 0.019 $p\ = \ 0.019$ ), respectively, and increased CTV V150% by a mean of 1.46 cc ( p = 0.010 $p\ = \ 0.010$ ) and CTV D90% by an average of 1.40% of the Rx dose ( p = 8.80 ∗ 10 - 8 $p\ = \ 8.80*{10^{ - 8}}$ ). While these differences are statistically significant, the clinical differences between the plans are minimal. CONCLUSIONS: The proposed analytical HDR planning algorithm integrates catheter and isotope selection with dwell time optimization for varying clinical goals, including urethra sparing. The planning method can guide HDR implants and identify promising isotopes for specific HDR clinical goals, such as target conformality or OAR sparing.

Use of Thermoluminescence Dosimetry for QA in High-Dose-Rate Skin Surface Brachytherapy with Custom-Flap Applicator.

Surface brachytherapy (BT) lacks standard quality assurance (QA) protocols. Commercially available treatment planning systems (TPSs) are based on a dose calculation formalism that assumes the patient is made of water, resulting in potential deviations between planned and delivered doses. Here, a method for treatment plan verification for skin surface BT is reported. Chips of thermoluminescent dosimeters (TLDs) were used for dose point measurements. High-dose-rate treatments were simulated and delivered through a custom-flap applicator provided with four fixed catheters to guide the Iridium-192 (Ir-192) source by way of a remote afterloading system. A flat water-equivalent phantom was used to simulate patient skin. Elekta TPS Oncentra Brachy was used for planning. TLDs were calibrated to Ir-192 through an indirect method of linear interpolation between calibration factors (CFs) measured for 250 kV X-rays, Cesium-137, and Cobalt-60. Subsequently, plans were designed and delivered to test the reproducibility of the irradiation set-up and to make comparisons between planned and delivered dose. The obtained CF for Ir-192 was (4.96 ± 0.25) µC/Gy. Deviations between measured and TPS calculated doses for multi-catheter treatment configuration ranged from -8.4% to 13.3% with an average of 0.6%. TLDs could be included in clinical practice for QA in skin BT with a customized flap applicator.

Dose perturbation effects by metal hip prosthesis in gynaecological 192Ir HDR brachytherapy.

The present study was conducted to elucidate the effects of hip prostheses in 192Ir HDR brachytherapy and determine dose uncertainties introduced by the treatment planning. A gynaecological phantom irradiated using Nucletron 192Ir microSelectron HDR source was modeled using MCNP5 code. Three hip materials considered in this study were water, bone, and metal prosthesis. According to the obtained results, a dose perturbation was observed within the medium with a higher atomic number, which reduced the dose to the nearby region.

Efficacy of Nanoparticles in dose enhancement with high dose rate of Iridium-192 and Cobalt-60 radionuclide sources in the Treatment of Cancer: A systematic review.

ABSTRACTS: A key challenge in radiation therapy is to maximize the radiation dose to cancer cells while minimizing damage to healthy tissues. In recent years, the introduction of remote after-loading technology such as high-dose-rate (HDR) brachytherapy becomes the safest and more precise way of radiation delivery compared to classical low-dose-rate (LDR) brachytherapy. However, the axially symmetric dose distribution of HDR with single channel cylindrical applicator, the physical "dead-space" with multichannel applicators, and shielding material heterogeneities are the main challenges of HDR brachytherapy. Thus, this review aimed to quantitatively evaluate the dose enhancement factor (DEF) produced by high atomic number nanoparticles (NPs) which increases the interaction probability of photons mainly through the photoelectric effect induced in the great number of atoms contained in each nanoparticle. The NPs loaded to the target volume create a local intensification effect on the target tissue that allows imparting the prescribed therapeutic dose using lower fluxes of irradiation and spare the surrounding healthy tissues. An electronic database such as PubMed/Medline, Embase, Scopus, and Google Scholar was searched to retrieve the required articles. Unpublished articles were also reached by hand from available sources. The dose is increased using the high atomic number of nanoparticle elements under the high dose iridium radionuclide whereas the cobalt-60 radionuclide source did not. However, much work is required to determine the dose distribution outside the target organ or tumor to spare the surrounding healthy tissues for the iridium source and make compressive work to have more data for the cobalt source.

Radiobiological and dosimetric comparison of 60Co versus 192Ir high-dose-rate intracavitary-interstitial brachytherapy for cervical cancer.

BACKGROUND: High-dose-rate (HDR) intracavitary-interstitial brachytherapy (IC-ISBT) is an effective treatment for bulky, middle, and advanced cervical cancer. In this study, we compared the differences between 60Co and 192Ir HDR IC-ISBT plans in terms of radiobiological and dosimetric parameters, providing a reference for clinical workers in brachytherapy. METHODS: A total of 30 patients with cervical cancer receiving HDR IC-ISBT were included in this study, and IC-ISBT plans for each individual were designed with both 60Co and 192Ir at a prescribed dose of CTV D90 = 6 Gy while keeping the dose to OARs as low as possible. Physical dose and dose-volume parameters of CTV and OARs were extracted from TPS. The EQD2, EUBED, EUD, TCP, and NTCP were calculated using corresponding formulas. The differences between the 60Co and 192Ir IC-ISBT plans were compared using the paired t-test. RESULTS: In each patient's 60Co and 192Ir IC-ISBT plan, the average physical dose and EQD2 of 60Co were lower than those of 192Ir, and there were statistically significant differences in D2cc and D1cc for the OARs (p < 0.05); there were statistically significant differences in D0.1 cc for the bladder (p < 0.05) and no significant differences in D0.1 cc for the rectum or intestines (p > 0.05). The EUBED ratio (60Co/192Ir) at the CTV was mostly close to 1 when neither 60Co or 192Ir passed their half-lives or when both passed two half-lives, and the difference between them was not significant; at the OARs, the mean value of 60Co was lower than that of 192Ir. There was no statistical difference between 60Co and 192Ir in the EUD (93.93 versus 93.92 Gy, p > 0.05) and TCP (97.07% versus 97.08%, p > 0.05) of the tumors. The mean NTCP value of 60Co was lower than that of 192Ir. CONCLUSIONS: Considering the CTV and OARs, the dosimetric parameters of 60Co and 192Ir are comparable. Compared with 192Ir, the use of 60Co for HDR IC-ISBT can ensure a similar tumor control probability while providing better protection to the OARs. In addition, 60Co has obvious economic advantages and can be promoted as a good alternative to 192Ir.

CONTEMPORARY APPROACHES TO PROGNOSTICATION AND MANAGEMENT OF PELVIC RADIATION INJURIES IN GYNECOLOGICAL CANCER PATIENTS. / SUChASNI PIDKhODY DO PROGNOZUVANNIa TA LIKUVANNIa PROMENEVYKh UShKODZhEN' ORGANIV MALOGO TAZU PISLIa RADIOTERAPIÏ KhVORYKh ONKOGINEKOLOGIChNOGO PROFILIu.

BACKGROUND: Rapid development of radiotherapeutic techniques and implementation of radiation therapy (RT) nanotechnologies in practice, taking into account principles of radiobiology, ensures that the planned dose will bedelivered to the target volume with minimal irradiation of healthy tissues while maintaining the guaranteed RTquality. Therefore, further advance of RT involves not only implementation of the new technologies in radiationpractice, but also the intensive developments in fields of radiation medicine and clinical radiobiology. OBJECTIVE: search for optimal models of the high-energy (HDR - high dose rate) brachytherapy (BT) using the 192Irsource in comparison with effects of the reference gamma radiation from 60Co, thereby, to increase the effectivenessof chemoradiation therapy (CRT) of gynecological cancer patients (GCPs) with minimal radiation loads on criticalorgans and tissues in the tumor environment. The radiobiological study was aimed to determine the feasibility ofusing the transmembrane potential (TMP) and intensity of reactive oxygen species (ROS) production in peripheralblood lymphocytes (PBL) as predictors of radiosensitivity of non-malignant cells from the tumor environment or itsbed in order to minimize the RT complications in GCPs. MATERIALS AND METHODS: Patients (n = 115) with cancer stages II-III, T2-3N0-1M0 were managed with comprehensiveconservative treatment. Three groups of patients were selected depending on the applied HDR BT method against abackground of the administered chemosensitizing agents. Blood samples of GCPs (n = 24) before the RT initiationand of apparently healthy individuals (AHIs, i.e. the control group, n = 18) were taken for the radiobiologicalresearch. RESULTS: Review of the direct results of 60Co or 192Ir sources use in HDR BT and of the follow-up data showed theincreased tumor positive response in the main study groups after CRT course by respectively 16.6 % and 20.1 % incomparison with 60Со HDR BT administration. Concerning local reactions it was noted that grade II radiation reactions were almost absent in the main groups. According to the results of radiobiological studies, it was establishedthat TMP level in PBL of GCPs was 1.36 times higher than in AHIs. CONCLUSIONS: Thus, the emerging of late radiation injuries depended on the accuracy of of individual computer planning and correct reproduction of the planned RT course, timely correction of treatment programs, use of a complexof rational medical prophylaxis, severity of tumor process and concomitant disorders, as well as on the used type ofHDR radiation sources (192Ir and 60Co). Changes in TMP values and intensity of ROS production in PBL of GCPs in comparison with AHIs, and the high values of these parameters in PBL of individual patients are a rationale to specifythem as additional indicators characterizing the possibility of radiation complications before the RT planning.

Optimization of the energy window setting in Ir-192 source imaging for high-dose-rate brachytherapy using a YAP(Ce) gamma camera.

PURPOSE: Although real-time imaging of the high-activity iridium-192 (Ir-192) source position during high-dose-rate (HDR) brachytherapy using a high-energy gamma camera system is a promising approach, the energy window was not optimized for spatial resolution or scatter fraction. METHODS: By using a list-mode data-acquisition system that can acquire energy information of a cerium-doped yttrium aluminum perovskite (YA1O3: YAP(Ce)) gamma camera, we tried to optimize the energy window's setting to improve the spatial resolution and reduce scatter fraction. RESULTS: The spatial resolution was highest for the central energy of the window at ∼300 keV. The scatter fraction was also smallest for the central energy of the window at ∼300 keV, and the scatter fraction was more than 48 % smaller than that for the full energy window. CONCLUSIONS: We clarified that the spatial resolution can be improved and the scatter fraction can be reduced through optimizing the energy window of the YAP(Ce) gamma camera by setting the central energy of the window to ∼300 keV for HDR brachytherapy.

Technical note: Short-time sequential high-energy gamma photon imaging using list-mode data acquisition system for high-dose-rate brachytherapy.

PURPOSE: Measurement of the dwell time and moving speed of a high-activity iridium-192 (Ir-192) source used for high-dose-rate (HDR) brachytherapy is important for estimating the precise dose delivery to a tumor. For this purpose, we used a cerium-doped yttrium aluminum perovskite (YA1O3 :YAP(Ce)) gamma camera system, combined with a list-mode data acquisition system that can acquire short-time sequential images, and measured the dwell times and moving speeds of the Ir-192 source. METHODS: Gamma photon imaging was conducted using the gamma camera in list mode for the Ir-192 source of HDR brachytherapy with fixed dwell times and positions. The acquired list-mode images were sorted to millisecond-order interval time sequential images to evaluate the dwell time at each position. Time count rate curves were derived to calculate the dwell time at each source position and moving speed of the source. RESULTS: We could measure the millisecond-order time sequential images for the Ir-192 source. The measured times for the preset dwell times of 2 s and 10 s were 1.98 to 2.00 s full width at half maximum (FWHM) and 10.0 s FWHM, respectively. The dwell times at the first dwell position were larger than those at other positions. We also measured the moving speeds of the source after the dwells while moving back to the afterloader and found the speed increased with the distance from the edge of the field of view to the last dwell position. CONCLUSION: We conclude that millisecond-order time sequential imaging of the Ir-192 source is possible by using a gamma camera and is useful for evaluating the dwell times and moving speeds of the Ir-192 source.

The inverse square law: A basic principle in brachytherapy.

The purpose of this article is to remind the importance of the inverse square law in radiotherapy and especially in brachytherapy. Indeed, beyond the impact in radiation therapy with high energy beam, there is the use of radionuclides and low energy photons with short FSD where it is still more important. Comparisons between Iridium Brachytherapy and low energy X-rays brachytherapy show equivalent dose distributions in the first few centimeters. If the inverse square law is not the only element influencing the dose distributions calculations, it must not be forgotten. And it is playing a major role in brachytherapy with short FSD (<6cm).

Investigation the effect of a magnetic field on the dose distribution of I-125, Ir-192, Yb-169, and Co-60 brachytherapy sources by Monte Carlo simulation.

Magnetic resonance imaging (MRI) during brachytherapy may alter the dose distribution of radioactive sources implanted in the tumor. This study investigates the impact of a magnetic field of 1.5 T, 3 T, and 7 T strengths on the dose distribution of high dose rate Co-60, Ir-192, and Yb-169, and low dose rate I-125 sources, using Geant4 Monte Carlo toolkit. After validating the simulation results by calculating the AAPM-TG43 dosimetric parameters, seven sources of each radioisotope were simulated in a water phantom, and their dose distributions were compared under the influence of a magnetic field. The simulation results indicate that using Co-60 brachytherapy under the MRI guidance is not recommended. Furthermore, the impact of a magnetic field of up to 7 T strength on the dose distribution of Ir-192, Yb-169, and I-125 sources is negligible, provided that there is no air pocket near brachytherapy sources.

Comparing Iridium-192 with Cobalt-60 sources in high-dose-rate brachytherapy boost for localized prostate cancer.

BACKGROUND: Dosimetric and clinical comparison of two cohorts of Iridium-192 (Ir-192) and Cobalt-60 (Co-60) high-dose-rate brachytherapy (DR-BT) boost for localized prostate cancer. MATERIAL AND METHODS: Patients with localized prostate cancer receiving either Ir-192 or Co-60 high-dose-rate brachytherapy (HDR-BT) boost in combination with external beam radiotherapy (EBRT) in the period of 2002-2019 were evaluated for dosimetric differences, side effects, biochemical relapse-free survival (bRFS), metastasis-free survival (MFS), and overall survival (OS). EBRT, delivered in 46 Gy (DMean) in conventional fractionation, was followed by two fractions HDR-BT boost with 9 Gy (D90%) 2 and 4 weeks after EBRT. Genitourinary (GU)/gastrointestinal (GI) toxicity were evaluated utilizing the Common Toxicity Criteria for Adverse Events version 5.0 and biochemical failure was defined according to the Phoenix definition. RESULTS: A total of 338 patients with a median follow-up of 101.8 (IQR 65.7-143.0) months were evaluated. At 10 years the estimated bRFS, MFS, and OS in our patient sample were 81.1%/71.2% (p=.073), 87.0%/85.7% (p=.862), and 70.1%/69.7% (p=.998) for Ir-192/Co-60, respectively. Cumulative 5-year late grade ≥2 GU toxicity was 20% for Ir-192 and 18.3% for Co-60 (p=.771). Cumulative 5-year late grade ≥2 GI toxicity was 5.8% for Ir-192 and 4.6% for Co-60 (p=.610). Grade 3 late GU side effects were pronounced in the Ir-192 cohort with 8.1% versus 1.4% in the Co-60 cohort (p=.01), which was associated with significantly lower dose to the organs at risk in the Co-60 cohort. PTV D90% was 9.3 ± 0.8 Gy versus 9.0 ± 1.1 Gy (p=.027) for Ir-192 versus Co-60. PTV V100% and PTV V150% were not significantly different between both cohorts. CONCLUSION: Co-60 brachytherapy sources are an effective alternative to Ir-192 in combined prostate HDR-BT boost + EBRT.

Monte Carlo characterization of high atomic number inorganic scintillators for in vivo dosimetry in 192 Ir brachytherapy.

BACKGROUND: There is increased interest in in vivo dosimetry for 192 Ir brachytherapy (BT) treatments using high atomic number (Z) inorganic scintillators. Their high light output enables construction of small detectors with negligible stem effect and simple readout electronics. Experimental determination of absorbed-dose energy dependence of detectors relative to water is prevalent, but it can be prone to high detector positioning uncertainties and does not allow for decoupling of absorbed-dose energy dependence from other factors affecting detector response . PURPOSE: To investigate which measurement conditions and detector properties could affect their absorbed-dose energy dependence in BT in vivo dosimetry. METHODS: We used a general-purpose Monte Carlo (MC) code PENELOPE for the characterization of high-Z inorganic scintillators with the focus on ZnSe ( Z ¯ = 32 $\bar{Z}=32$ ) Z. Two other promising media CsI ( Z ¯ = 54 $\bar{Z}=54$ ) and Al2 O3 ( Z ¯ = 11 $\bar{Z}=11$ ) were included for comparison in selected scenarios. We determined absorbed-dose energy dependence of crystals relative to water under different scatter conditions (calibration phantom 12 × 12 × 30 cm3 , characterization phantoms 20 × 20 × 20 cm3 , 30 × 30 × 30 cm3 , 40 × 40 × 40 cm3 , and patient-like elliptic phantom 40 × 30 × 25 cm3 ). To mimic irradiation conditions during prostate treatments, we evaluated whether the presence of pelvic bones and calcifications affect ZnSe response. ZnSe detector design influence was also investigated. RESULTS: In contrast to low-Z organic and medium-Z inorganic scintillators, ZnSe and CsI media have substantially greater absorbed-dose energy dependence relative to water. The response was phantom-size dependent and changed by 11% between limited- and full-scatter conditions for ZnSe, but not for Al2 O3 . For a given phantom size, a part of the absorbed-dose energy dependence of ZnSe is caused not due to in-phantom scatter but due to source anisotropy. Thus, the absorbed-dose energy dependence of high-Z scintillators is a function of not only the radial distance but also the polar angle. Pelvic bones did not affect ZnSe response, whereas large and intermediate size calcifications reduced it by 9% and 5%, respectively, when placed midway between the source and the detector. CONCLUSIONS: Unlike currently prevalent low- and medium-Z scintillators, high-Z crystals are sensitive to characterization and in vivo measurement conditions. However, good agreement between MC data for ZnSe in the present study and experimental data for ZnSe:O by Jørgensen et al. (2021) suggests that detector signal is proportional to the average absorbed dose to the detector cavity. This enables an easy correction for non-TG43-like scenarios (e.g., patient sizes and calcifications) through MC simulations. Such information should be provided to the clinic by the detector vendors.

The design of a novel direction modulated brachytherapy vaginal cylinder applicator for optimizing coverage of the apex.

PURPOSE: High-dose-rate (HDR) vaginal cuff brachytherapy is an effective adjuvant therapy for women with stage I endometrial cancer. Although infrequent, failures do occur, most frequently at the vaginal vault. A potential cause of failure is insufficient dosimetric coverage at the vaginal apex due to cold spots from the anisotropic dose distribution of the source. Here, we propose a novel direction modulated brachytherapy (DMBT)-concept vaginal cylinder (VC) applicator that resolves this dosimetric issue. METHODS AND MATERIALS: The novel DMBT-VC applicator was designed and simulated with the GEANT4 Monte Carlo code. The outer cylinder material chosen was polyphenylsulfone (PPSU) plastic, and the central part was a detachable rod, housing a single lumen made of either polyether ether ketone (PEEK) plastic or an MR-compatible tungsten alloy. The PPSU-based outer cylinder, together with the inner PEEK rod provides the dose distribution of a conventional VC applicator. The PEEK rod is then replaced with an MR-compatible tungsten alloy rod of the same dimensions to generate directional "pencil-like" beams to compensate for the anisotropic cold spots. Two widely used 192 Ir HDR sources, VS2000 and GammaMedPlus, were also simulated. RESULTS: The novel DMBT-VC applicator was able to remove the underdosage at the apex due to the anisotropy effect regardless of the HDR sources without unnecessarily increasing the dose to the periphery of the applicator. Also, further directional modulation to reach deeper in the apex by up to 14 mm beyond the VC surface was achievable, again without increasing the peripheral doses. Total treatment dwell times increased only by 7-13%. CONCLUSIONS: The novel DMBT-VC applicator provides improved dose coverage at the vaginal apex by overcoming the classical anisotropy issue ubiquitous to all HDR brachytherapy sources. The next step in development of the device is manufacturing a prototype for clinical testing.

On the potential of 2D ion chamber arrays for high-dose rate remote afterloading brachytherapy quality assurance.

Objective. To investigate the potential of 2D ion chamber arrays to serve as a standalone tool for the verification of source strength, positioning and dwell time, within the framework of192Ir high-dose rate brachytherapy device quality assurance (QA).Approach.A commercially available ion chamber array was used. Fitting of a 2D Lorentzian peak function to experimental data from a multiple source dwell position irradiation on a frame-by-frame basis, facilitated tracking of the source center orthogonal projection on the array plane. For source air kerma strength verification, Monte Carlo simulation was employed to obtain a chamber array- and source-specific correction factor of calibration with a 6 MV photon beam. This factor converted the signal measured by each ion chamber element to air kerma in free space. A source positioning correction was also applied to lift potential geometry mismatch between experiment and Monte Carlo simulation.Main results.Spatial and temporal accuracy of source movement was verified within 0.5 mm and 0.02 s, respectively, in compliance with the test endpoints recommended by international professional societies. The source air kerma strength was verified experimentally within method uncertainties estimated as 1.44% (k = 1). The source positioning correction method employed did not introduce bias to experimental results of irradiations where source positioning was accurate. Development of a custom jig attachable to the chamber array for accurate and reproducible experimental set up would improve testing accuracy and obviate the need for source positioning correction in air kerma strength verification.Significance.Delivery of a single irradiation plan, optimized based on results of this work, to a 2D ion chamber array can be used for concurrent testing of source position, dwell time and air kerma strength, and the procedure can be expedited through automation. Chamber arrays merit further study in treatment planning QA and real time,in vivodose verification.

Image-Guided Brachytherapy a Comparison Between 192Ir and 60Co Sources in Carcinoma Uterine Cervix.

INTRODUCTION: Combination of external beam radiotherapy (EBRT) and High Dose Rate (HDR) brachytherapy (BT) with concurrent chemotherapy (Cisplatin 40mg/m2/weekly) is the standard treatment of approach for the carcinoma of uterine cervix. In this study for image based HDR brachytherapy of intracavitary both 192Ir and 60Co sources were used for dosimetry and the dose distribution compared between point doses and volume doses as per the recommendation of ICRU89 and GEC-ESTRO on 3D image based planning. The dosimetry and clinical outcome will decide decisionmaking on choice of radionuclide for HDR brachytherapy of cervix in addition to economic reason. MATERIALS AND METHODS: The Study conducted for 27 patients of cancer cervix stage IIB or IIIB with vaginal involvement limited to the upper third of vagina. All patients underwent concurrent chemoradiation Cisplatin 40mg/m2 weekly throughout EBRT by 3D conformal therapy 46Gy in 23# followed by two fractions of HDR brachytherapy with 9Gy/1Fr. Post implants 3mm slice selection of pelvic CT scans performed with ring applicator in place followed by T2 weighted paracorpal or paracoronal section of MRI imaging. The solid ring applicator (AL13017000) from library used for applicator reconstruction. Initially all plan calculated with TG-43 formalism using 192Ir radionuclide (Varian, GammaMed HDR Plus source) and then modelled 60Co radionuclide (Eckert < Ziegler BEBIG GmbH, Co0. A86) used for dose computation. ICRU89 recommended points and volumes of targets and OARs evaluated and compared. RESULTS: The study concludes that 60Co based point-A, BICRU and RICRU doses showed a comparable result with that of 192Ir HDR source based dosimetry. The volume based criterion for the target such as GTV, CTVHR, CTVIR for D90, D98, V150%and V200% are all within 5% dose level comparing two sources. CONCLUSION: 60Co a viable alternate to 192Ir by taking into consideration frequency of source exchange and cost reserve with comparable dosimetry.

Evaluating dosimetric accuracy of the 6 MV calibration on EBT3 film in the use of Ir-192 high dose rate brachytherapy.

PURPOSE: To evaluate the dosimetric accuracy of EBT3 film calibrated with a 6 MV beam for high dose rate brachytherapy and propose a novel method for direct film calibration with an Ir-192 source. METHODS: The 6 MV calibration was performed in water on a linear accelerator (linac). The Ir-192 calibration was accomplished by irradiating the film wrapped around a cylinder applicator with an Ir-192 source. All films were scanned 1-day post-irradiation to acquire calibration curves for all three (red, blue, and green) channels. The Ir-192 calibration films were also used for single-dose comparison. Moreover, an independent test film under a H.A.M. applicator was irradiated and the 2D dose distribution was obtained separately for each calibration using the red channel data. Gamma analysis and point-by-point profile comparison were performed to evaluate the performance of both calibrations. The uncertainty budget for each calibration system was analyzed. RESULTS: The red channel had the best performance for both calibration systems in the single-dose comparison. We found a significant 4.89% difference from the reference for doses <250 cGy using the 6 MV calibration, while the difference was only 0.87% for doses >600 cGy. Gamma analysis of the 2D dose distribution showed the Ir-192 calibration had a higher passing rate of 91.9% for the 1 mm/2% criterion, compared to 83.5% for the 6 MV calibration. Most failing points were in the low-dose region (<200 cGy). The point-by-point profile comparison reported a discrepancy of 2%-3.6% between the Ir-192 and 6 MV calibrations in this low-dose region. The linac- and Ir-192-based dosimetry systems had an uncertainty of 4.1% (k = 2) and 5.66% (k = 2), respectively. CONCLUSIONS: Direct calibration of EBT3 films with an Ir-192 source is feasible and reliable, while the dosimetric accuracy of 6 MV calibration depends on the dose range. The Ir-192 calibration should be used when the measurement dose range is below 250 cGy.

Implantation of computed tomography-guided high-dose-rate 192Ir brachytherapy in oldest old patients with advanced non-small cell lung cancer: A case report and literature review.

BACKGROUND: With the increasing aging and the popularization of medical diagnosis, the growing number of oldest old with lung cancer needs to be focused on. Several medical and physiological challenges often accompanying the oldest old cancer patients make the choice of the optimal treatment daunting. The current research suggests that people who get adequate treatment can benefit, but it is worth discussing which treatment will benefit them more. High-dose-rate (HDR) 192Ir brachytherapy deserves attention in this context owing to its association with less trauma and reduced complications. CASE PRESENTATION: An 86-years-old woman with a right glandular lung carcinoma presented with progressive lesions 11 months after chemotherapy. Because of her old age and poor performance status (eastern cooperative oncology group performance status 3), she received HDR 192Ir brachytherapy for her right lung lesion without any common complications, such as pneumothorax and hemorrhage. She continued on 0.25 g oral gefitinib each day after received brachytherapy treatment. The right lung lesion keeps a partial response until 18 months later now. CONCLUSION: HDR 192Ir brachytherapy can potentially be used as a safe and effective choice for the oldest old with advanced non-small cell lung cancer. It can especially benefit cancer patients with concurrent chemotherapy or targeted therapy.