In order to facilitate a smooth transition for brachytherapy dose calculations from the American Association of Physicists in Medicine (AAPM) Task Group No. 43 (TG-43) formalism to model-based dose ...calculation algorithms (MBDCAs), treatment planning systems (TPSs) using a MBDCA require a set of well-defined test case plans characterized by Monte Carlo (MC) methods. This also permits direct dose comparison to TG-43 reference data. Such test case plans should be made available for use in the software commissioning process performed by clinical end users. To this end, a hypothetical, generic high-dose rate (HDR) (192)Ir source and a virtual water phantom were designed, which can be imported into a TPS.
A hypothetical, generic HDR (192)Ir source was designed based on commercially available sources as well as a virtual, cubic water phantom that can be imported into any TPS in DICOM format. The dose distribution of the generic (192)Ir source when placed at the center of the cubic phantom, and away from the center under altered scatter conditions, was evaluated using two commercial MBDCAs Oncentra(®) Brachy with advanced collapsed-cone engine (ACE) and BrachyVision ACUROS™ . Dose comparisons were performed using state-of-the-art MC codes for radiation transport, including ALGEBRA, BrachyDose, GEANT4, MCNP5, MCNP6, and PENELOPE2008. The methodologies adhered to recommendations in the AAPM TG-229 report on high-energy brachytherapy source dosimetry. TG-43 dosimetry parameters, an along-away dose-rate table, and primary and scatter separated (PSS) data were obtained. The virtual water phantom of (201)(3) voxels (1 mm sides) was used to evaluate the calculated dose distributions. Two test case plans involving a single position of the generic HDR (192)Ir source in this phantom were prepared: (i) source centered in the phantom and (ii) source displaced 7 cm laterally from the center. Datasets were independently produced by different investigators. MC results were then compared against dose calculated using TG-43 and MBDCA methods.
TG-43 and PSS datasets were generated for the generic source, the PSS data for use with the ace algorithm. The dose-rate constant values obtained from seven MC simulations, performed independently using different codes, were in excellent agreement, yielding an average of 1.1109 ± 0.0004 cGy/(h U) (k = 1, Type A uncertainty). MC calculated dose-rate distributions for the two plans were also found to be in excellent agreement, with differences within type A uncertainties. Differences between commercial MBDCA and MC results were test, position, and calculation parameter dependent. On average, however, these differences were within 1% for ACUROS and 2% for ace at clinically relevant distances.
A hypothetical, generic HDR (192)Ir source was designed and implemented in two commercially available TPSs employing different MBDCAs. Reference dose distributions for this source were benchmarked and used for the evaluation of MBDCA calculations employing a virtual, cubic water phantom in the form of a CT DICOM image series. The implementation of a generic source of identical design in all TPSs using MBDCAs is an important step toward supporting univocal commissioning procedures and direct comparisons between TPSs.
Purpose: In order to facilitate a smooth transition for brachytherapy dose calculations from the American Association of Physicists in Medicine (AAPM) Task Group No. 43 (TG-43) formalism to ...model-based dose calculation algorithms (MBDCAs), treatment planning systems (TPSs) using a MBDCA require a set of well-defined test case plans characterized by Monte Carlo (MC) methods. This also permits direct dose comparison to TG-43 reference data. Such test case plans should be made available for use in the software commissioning process performed by clinical end users. To this end, a hypothetical, generic high-dose rate (HDR) Ir-192 source and a virtual water phantom were designed, which can be imported into a TPS. Methods: A hypothetical, generic HDR Ir-192 source was designed based on commercially available sources as well as a virtual, cubic water phantom that can be imported into any TPS in DICOM format. The dose distribution of the generic Ir-192 source when placed at the center of the cubic phantom, and away from the center under altered scatter conditions, was evaluated using two commercial MBDCAs Oncentra (R) Brachy with advanced collapsed-cone engine (ACE) and BrachyVision AcuRos (TM). Dose comparisons were performed using state-of-the-art MC codes for radiation transport, including ALGEBRA, BrachyDose, GEANT4, MCNP5, MCNP6, and pENELopE2008. The methodologies adhered to recommendations in the AAPM TG-229 report on high-energy brachytherapy source dosimetry. TG-43 dosimetry parameters, an along-away dose-rate table, and primary and scatter separated (PSS) data were obtained. The virtual water phantom of (201)(3) voxels (1 mm sides) was used to evaluate the calculated dose distributions. Two test case plans involving a single position of the generic HDR Ir-192 source in this phantom were prepared: (i) source centered in the phantom and (ii) source displaced 7 cm laterally from the center. Datasets were independently produced by different investigators. MC results were then compared against dose calculated using TG-43 and MBDCA methods. Results: TG-43 and PSS datasets were generated for the generic source, the PSS data for use with the ACE algorithm. The dose-rate constant values obtained from seven MC simulations, performed independently using different codes, were in excellent agreement, yielding an average of 1.1109 +/- 0.0004 cGy/(h U) (k = 1, Type A uncertainty). MC calculated dose-rate distributions for the two plans were also found to be in excellent agreement, with differences within type A uncertainties. Differences between commercial MBDCA and MC results were test, position, and calculation parameter dependent. On average, however, these differences were within 1% for ACUROS and 2% for ACE at clinically relevant distances. Conclusions: A hypothetical, generic HDR Ir-192 source was designed and implemented in two commercially available TPSs employing different MBDCAs. Reference dose distributions for this source were benchmarked and used for the evaluation of MBDCA calculations employing a virtual, cubic water phantom in the form of a CT DICOM image series. The implementation of a generic source of identical design in all TPSs using MBDCAs is an important step toward supporting univocal commissioning procedures and direct comparisons between TPSs. (C) 2015 American Association of Physicists in Medicine.
Purpose
A joint working group was created by the American Association of Physicists in Medicine (AAPM), the European Society for Radiotherapy and Oncology (ESTRO), and the Australasian Brachytherapy ...Group (ABG) with the charge, among others, to develop a set of well‐defined test case plans and perform calculations and comparisons with model‐based dose calculation algorithms (MBDCAs). Its main goal is to facilitate a smooth transition from the AAPM Task Group No. 43 (TG‐43) dose calculation formalism, widely being used in clinical practice for brachytherapy, to the one proposed by Task Group No. 186 (TG‐186) for MBDCAs. To do so, in this work a hypothetical, generic high‐dose rate (HDR) 192Ir shielded applicator has been designed and benchmarked.
Methods
A generic HDR 192Ir shielded applicator was designed based on three commercially available gynecological applicators as well as a virtual cubic water phantom that can be imported into any DICOM‐RT compatible treatment planning system (TPS). The absorbed dose distribution around the applicator with the TG‐186 192Ir source located at one dwell position at its center was computed using two commercial TPSs incorporating MBDCAs (Oncentra® Brachy with Advanced Collapsed‐cone Engine, ACE™, and BrachyVision ACUROS™) and state‐of‐the‐art Monte Carlo (MC) codes, including ALGEBRA, BrachyDose, egs_brachy, Geant4, MCNP6, and Penelope2008. TPS‐based volumetric dose distributions for the previously reported “source centered in water” and “source displaced” test cases, and the new “source centered in applicator” test case, were analyzed here using the MCNP6 dose distribution as a reference. Volumetric dose comparisons of TPS results against results for the other MC codes were also performed. Distributions of local and global dose difference ratios are reported.
Results
The local dose differences among MC codes are comparable to the statistical uncertainties of the reference datasets for the “source centered in water” and “source displaced” test cases and for the clinically relevant part of the unshielded volume in the “source centered in applicator” case. Larger local differences appear in the shielded volume or at large distances. Considering clinically relevant regions, global dose differences are smaller than the local ones. The most disadvantageous case for the MBDCAs is the one including the shielded applicator. In this case, ACUROS agrees with MC within −4.2%, +4.2% for the majority of voxels (95%) while presenting dose differences within −0.12%, +0.12% of the dose at a clinically relevant reference point. For ACE, 95% of the total volume presents differences with respect to MC in the range −1.7%, +0.4% of the dose at the reference point.
Conclusions
The combination of the generic source and generic shielded applicator, together with the previously developed test cases and reference datasets (available in the Brachytherapy Source Registry), lay a solid foundation in supporting uniform commissioning procedures and direct comparisons among treatment planning systems for HDR 192Ir brachytherapy.
There is an acknowledged need for the design and implementation of physical phantoms appropriate for the experimental validation of model-based dose calculation algorithms (MBDCA) introduced recently ...in
Ir brachytherapy treatment planning systems (TPS), and this work investigates whether it can be met. A PMMA phantom was prepared to accommodate material inhomogeneities (air and Teflon), four plastic brachytherapy catheters, as well as 84 LiF TLD dosimeters (MTS-100M 1 × 1 × 1 mm
microcubes), two radiochromic films (Gafchromic EBT3) and a plastic 3D dosimeter (PRESAGE). An irradiation plan consisting of 53 source dwell positions was prepared on phantom CT images using a commercially available TPS and taking into account the calibration dose range of each detector. Irradiation was performed using an
Ir high dose rate (HDR) source. Dose to medium in medium, Formula: see text, was calculated using the MBDCA option of the same TPS as well as Monte Carlo (MC) simulation with the MCNP code and a benchmarked methodology. Measured and calculated dose distributions were spatially registered and compared. The total standard (k = 1) spatial uncertainties for TLD, film and PRESAGE were: 0.71, 1.58 and 2.55 mm. Corresponding percentage total dosimetric uncertainties were: 5.4-6.4, 2.5-6.4 and 4.85, owing mainly to the absorbed dose sensitivity correction and the relative energy dependence correction (position dependent) for TLD, the film sensitivity calibration (dose dependent) and the dependencies of PRESAGE sensitivity. Results imply a LiF over-response due to a relative intrinsic energy dependence between
Ir and megavoltage calibration energies, and a dose rate dependence of PRESAGE sensitivity at low dose rates (<1 Gy min
). Calculations were experimentally validated within uncertainties except for MBDCA results for points in the phantom periphery and dose levels <20%. Experimental MBDCA validation is laborious, yet feasible. Further work is required for the full characterization of dosimeter response for
Ir and the reduction of experimental uncertainties.
A source model is a prerequisite of all model based dose calculation algorithms. Besides direct simulation, the use of pre-calculated phase space files (phsp source models) and parameterized phsp ...source models has been proposed for Monte Carlo (MC) to promote efficiency and ease of implementation in obtaining photon energy, position and direction. In this work, a phsp file for a generic (192)Ir source design (Ballester et al 2015) is obtained from MC simulation. This is used to configure a parameterized phsp source model comprising appropriate probability density functions (PDFs) and a sampling procedure. According to phsp data analysis 15.6% of the generated photons are absorbed within the source, and 90.4% of the emergent photons are primary. The PDFs for sampling photon energy and direction relative to the source long axis, depend on the position of photon emergence. Photons emerge mainly from the cylindrical source surface with a constant probability over ±0.1 cm from the center of the 0.35 cm long source core, and only 1.7% and 0.2% emerge from the source tip and drive wire, respectively. Based on these findings, an analytical parameterized source model is prepared for the calculation of the PDFs from data of source geometry and materials, without the need for a phsp file. The PDFs from the analytical parameterized source model are in close agreement with those employed in the parameterized phsp source model. This agreement prompted the proposal of a purely analytical source model based on isotropic emission of photons generated homogeneously within the source core with energy sampled from the (192)Ir spectrum, and the assignment of a weight according to attenuation within the source. Comparison of single source dosimetry data obtained from detailed MC simulation and the proposed analytical source model show agreement better than 2% except for points lying close to the source longitudinal axis.
Dosimetry audits (DA) are useful for the evaluation of the dosimetric quality, planned dose accuracy, treatment complexity and deliverability of radiotherapy (RT) procedures, aiming to consult on ...detected discrepancies and improve standards and reliability of the RT centers. Since 2002, Greek Atomic Energy Commission (EEAE) provides dosimetry auditing services of level I and II and recently III, IV in MV photon and electron beams in all RT centers of the country.
DAs were conducted by means of on-site visits. The audit levels applied in sequence were: Mechanical and functional tests of the RT machine, absolute and relative dosimetry, beam and treatment planning system (TPS) output measurements under reference and non-reference conditions, end-to-end tests for the assessment of the TPS dose calculations, in basic and advanced radiotherapy techniques through 1D, 2D and 3D dosimetry. Measurements were compared to the stated by the RT center values according to acceptance and tolerance criteria. Uncertainties were estimated according to GUM.
98% for photons and 95% for electrons beams fulfilled dosimetry accuracy acceptance criteria (±3%) under reference conditions, improving gradually for the latter. The assessment of TPS output for 1134 beams (790 open, 344 wedged) was satisfactory in 95% and 84% of open and wedged beams, respectively. Non-acceptable results decreased progressively through time. End-to-end dosimetry tests, applied in 727 beams, exhibited acceptable, tolerated and non-acceptable results in 94%, 3% and 3% cases, respectively. Results for IMRT, VMAT and SRS were acceptable in all cases, stressing the need for systematic review of procedures for the whole chain of the clinical practice.
Dosimetry audit was proved to be a valuable tool for the improvement of quality in radiotherapy. Dosimetry accuracy is verified in the gross majority of RT centers. Discrepancies and bad practices were detected, presenting a decreasing incidence over the years. Guidance and recommendations provided, improved dosimetry practices and verified that the quality assurance of procedures in an institution is essential for achieving the required accuracy and safe operation. Results of this study imply challenges in TPS commissioning, especially for small fields, and challenges in multicenter comparison for complex dose distributions.
Purpose To perform a comparative study of heterogeneities and finite patient dimension effects in 60Co and 192Ir high-dose-rate (HDR) brachytherapy. Material and methods Clinically equivalent plans ...were prepared for 19 cases (8 breast, 5 esophagus, 6 gynecologic) using the Ir2.A85-2 and the Co0.A86 HDR sources, with a TG-43 based treatment planning system (TPS). Phase space files were obtained for the two source designs using MCNP6, and validated through comparison to a single source dosimetry results in the literature. Dose to water, taking into account the patient specific anatomy and materials (Dw,m), was calculated for all plans using MCNP6, with input files prepared using the BrachyGuide software tool to analyze information from DICOM RT plan exports. Results A general TG-43 dose overestimation was observed, except for the lungs, with a greater magnitude for 192Ir. The distribution of percentage differences between TG-43 and Monte Carlo (MC) in dose volume histogram (DVH) indices for the planning target volume (PTV) presented small median values (about 2%) for both 60Co and 192Ir, with a greater dispersion for 192Ir. Regarding the organs at risk (OARs), median percentage differences for breast V50% were 3% (5%) for 60Co (192Ir). Differences in median skin D2cc were found comparable, with a larger dispersion for 192Ir, and the same applied to the lung D10cc and the aorta D2cc. TG-43 overestimates D2cc for the rectum and the sigmoid, with median differences from MC within 2% and a greater dispersion for 192Ir. For the bladder, the median of the difference is greater for 60Co (~2%) than for 192Ir (~0.75%), demonstrating however a greater dispersion again for 192Ir. Conclusions The magnitude of differences observed between TG-43 based and MC dosimetry and their smaller dispersion relative to 192Ir, suggest that 60Co HDR sources are more amenable to the TG-43 assumptions in clinical treatment planning dosimetry.
To perform a comparative study of heterogeneities and finite patient dimension effects in
Co and
Ir high-dose-rate (HDR) brachytherapy.
Clinically equivalent plans were prepared for 19 cases (8 ...breast, 5 esophagus, 6 gynecologic) using the Ir2.A85-2 and the Co0.A86 HDR sources, with a TG-43 based treatment planning system (TPS). Phase space files were obtained for the two source designs using MCNP6, and validated through comparison to a single source dosimetry results in the literature. Dose to water, taking into account the patient specific anatomy and materials (D
), was calculated for all plans using MCNP6, with input files prepared using the BrachyGuide software tool to analyze information from DICOM RT plan exports.
A general TG-43 dose overestimation was observed, except for the lungs, with a greater magnitude for
Ir. The distribution of percentage differences between TG-43 and Monte Carlo (MC) in dose volume histogram (DVH) indices for the planning target volume (PTV) presented small median values (about 2%) for both
Co and
Ir, with a greater dispersion for
Ir. Regarding the organs at risk (OARs), median percentage differences for breast V
were 3% (5%) for
Co (
Ir). Differences in median skin D
were found comparable, with a larger dispersion for
Ir, and the same applied to the lung D
and the aorta D
. TG-43 overestimates D
for the rectum and the sigmoid, with median differences from MC within 2% and a greater dispersion for
Ir. For the bladder, the median of the difference is greater for
Co (~2%) than for
Ir (~0.75%), demonstrating however a greater dispersion again for
Ir.
The magnitude of differences observed between TG-43 based and MC dosimetry and their smaller dispersion relative to
Ir, suggest that
Co HDR sources are more amenable to the TG-43 assumptions in clinical treatment planning dosimetry.
The Gamma Knife Icon allows the treatment of brain tumors mask‐based single‐fraction or fractionated treatment schemes. In clinic, uniform axial expansion of 1 mm around the gross tumor volume (GTV) ...and a 1.5 mm expansion in the superior and inferior directions are used to generate the planning target volume (PTV). The purpose of the study was to validate this margin scheme with two clinical scenarios: (a) the patient’s head remaining right below the high‐definition motion management (HDMM) threshold, and (b) frequent treatment interruptions followed by plan adaptation induced by large pitch head motion. A remote‐controlled head assembly was used to control the motion of a PseudoPatient® Prime head phantom; for dosimetric evaluations, an ionization chamber, EBT3 films, and polymer gels were used. These measurements were compared with those from the Gamma Knife plan. For the absolute dose measurements using an ionization chamber, the percentage differences for both targets were less than 3.0% for all scenarios, which was within the expected tolerance. For the film measurements, the two‐dimensional (2D) gamma index with a 2%/2 mm criterion showed the passing rates of ≥87% in all scenarios except the scenario 1. The results of Gel measurements showed that GTV (D100) was covered by the prescription dose and PTV (D95) was well above the planned dose by up to 5.6% and the largest geometric PTV offset was 0.8 mm for all scenarios. In conclusion, the current margin scheme with HDMM setting is adequate for a typical patient’s intrafractional motion.
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