100% peer review in radiation oncology: is it feasible?

PURPOSE: Peer review has been proposed as a strategy to ensure patient safety and plan quality in radiation oncology. Despite its potential benefits, barriers commonly exist to its optimal implementation in daily clinical routine. Our purpose is to analyze peer-review process at our institution. METHODS AND MATERIALS: Based on our group peer-review process, we quantified the rate of plan changes, time and resources needed for this process. Prospectively, data on cases presented at our institutional peer-review conference attended by physicians, resident physicians and physicists were collected. Items such as time to present per case, type of patient (adult or pediatric), treatment intent, dose, aimed technique, disease location and receipt of previous radiation were gathered. Cases were then analyzed to determine the rate of major change, minor change and plan rejection after presentation as well as the median time per session. RESULTS: Over a period of 4 weeks, 148 cases were reviewed. Median of attendants was six physicians, three in-training-physicians and one physicist. Median time per session was 38 (4-72) minutes. 59.5% of cases presented in 1-4 min, 32.4% in 5-9 min and 8.1% in ≥ 10 min. 79.1% of cases were accepted without changes, 11.5% with minor changes, 6% with major changes and 3.4% were rejected with indication of new presentation. Most frequent reason of change was contouring corrections (53.8%) followed by dose or fractionation (26.9%). CONCLUSION: Everyday group consensus peer review is an efficient manner to recollect clinical and technical data of cases presented to ensure quality radiation care before initiation of treatment as well as ensuring department quality in a feedback team environment. This model is feasible within the normal operation of every radiation oncology Department.

Evaluation of lens absorbed dose with Cone Beam IGRT procedures.

The purpose of this work is to evaluate the absorbed dose to the eye lenses due to the cone beam computed tomography (CBCT) system used to accurately position the patient during head-and-neck image guided procedures. The on-board imaging (OBI) systems (v.1.5) of Clinac iX and TrueBeam (Varian) accelerators were used to evaluate the imparted dose to the eye lenses and some additional points of the head. All CBCT scans were acquired with the Standard-Dose Head protocol from Varian. Doses were measured using thermoluminescence dosimeters (TLDs) placed in an anthropomorphic phantom. TLDs were calibrated at the beam quality used to reduce their energy dependence. Average dose to the lens due to the OBI systems of the Clinac iX and the TrueBeam were 0.71 ± 0.07 mGy/CBCT and 0.70 ± 0.08 mGy/CBCT, respectively. The extra absorbed dose received by the eye lenses due to one CBCT acquisition with the studied protocol is far below the 500 mGy threshold established by ICRP for cataract formation (ICRP 2011 Statement on Tissue Reactions). However, the incremental effect of several CBCT acquisitions during the whole treatment should be taken into account.

Fetal dose measurements and shielding efficiency assessment in a custom setup of (192)Ir brachytherapy for a pregnant woman with breast cancer.

PURPOSE: To assess the radiation dose to the fetus of a pregnant patient undergoing high-dose-rate (HDR) (192)Ir interstitial breast brachytherapy, and to design a new patient setup and lead shielding technique that minimizes the fetal dose. METHODS: Radiochromic films were placed between the slices of an anthropomorphic phantom modeling the patient. The pregnant woman was seated in a chair with the breast over a table and inside a leaded box. Dose variation as a function of distance from the implant volume as well as dose homogeneity within a representative slice of the fetal position was evaluated without and with shielding. RESULTS: With shielding, the peripheral dose after a complete treatment ranged from 50 cGy at 5 cm from the caudal edge of the breast to <0.1 cGy at 30 cm. The shielding reduces absorbed dose by a factor of two near the breast and more than an order of magnitude beyond 20 cm. The dose is heterogeneous within a given axial plane, with variations from the central region within 50%. Interstitial HDR (192)Ir brachytherapy with breast shielding can be more advantageous than external-beam radiotherapy (EBRT) from a radiation protection point of view, as long as the distance to the uterine fundus is higher than about 10 cm. Furthermore, the weight of the shielding here proposed is notably lower than that needed in EBRT. CONCLUSIONS: Shielded breast brachytherapy may benefit pregnant patients needing localized radiotherapy, especially during the early gestational ages when the fetus is more sensitive to ionizing radiation.

Commissioning and initial experience with a commercial software for in vivo volumetric dosimetry.

INTRODUCTION AND PURPOSE: Dosimetry Check (DC) (Math Resolutions) is a commercial EPID-based dosimetry software, which allows performing pre-treatment and transit dosimetry. DC provides an independent verification of the treatment, being potentially of great interest due to the high benefits of the in vivo volumetric dosimetry, which guarantee the treatment delivery and anatomy constancy. The aim of this work is to study the differences in dose between DC and the Treatment Planning System (TPS) to establish an accuracy level of the system. MATERIAL AND METHODS: DC v.3.8 was used along with Varian Clinac iX accelerator equipped with EPID aS1000 and Eclipse v.10.0 with AAA and Acuros XB calculation algorithms. The DC evaluated version is based on a pencil beam calculation algorithm. Various plans were generated over several homogeneous and heterogeneous phantoms. Isocentre point doses and gamma analysis were evaluated. RESULTS: Total dose differences at the isocentre between DC and TPS for the studied plans are less than 2%, but single field contributions achieve greater values. In the presence of heterogeneities, the discrepancies can reach up to 15%. In transit mode, DC does not consider properly the couch attenuation, especially when there is an air gap between phantom and couch. CONCLUSIONS: The possibility of this in vivo evaluation and the potentiality of this new system have a very positive impact on improving patient QA. But improvements are required in both calculation algorithm and integration with the record and verify system.

Organ contouring for prostate cancer: interobserver and internal organ motion variability.

The purpose of this study is to assess the uncertainties that arise in locating the boundaries of anatomical structures, such as the prostate and the bladder, due to interobserver variability in the delineation of the structures and to internal organ motion. The variabilities are computed in all the radial directions and this information is used to obtain the margins, following the techniques and limitations imposed by medical practice. The margins obtained from the organ motions are significantly greater than those arising from interobserver variability. The developed tools, allow us to obtain the required margins in an efficient way.

Technical note: fitted dosimetric parameters of high dose-rate 192Ir sources according to the AAPM TG43 formalism.

Functional fits for the anisotrophy function and the radial dose function, have been studied, in a previous work, in order to characterize dose-rate distributions around some of the high-intensity 192Ir sources. The purpose of the present work is to complete the previous one in order to include all the existing HDR and PDR 192Ir sources. The sources addressed here are: the Buchler source from Amersham, the 12i and Plus PDR sources and the 12i and Plus HDR sources from GammaMed, and the new VariSource HDR source wire model VS2000 from Varian Oncology Systems.

A monte carlo study of dose rate distribution around the specially asymmetric CSM3-a 137Cs source.

The CSM3 137Cs type stainless-steel encapsulated source is widely used in manually afterloaded low dose rate brachytherapy. A specially asymmetric source, CSM3-a, has been designed by CIS Bio International (France) substituting the eyelet side seed with an inactive material in the CSM3 source. This modification has been done in order to allow a uniform dose level over the upper vaginal surface when this 'linear' source is inserted at the top of the dome vaginal applicators. In this study the Monte Carlo GEANT3 simulation code, incorporating the source geometry in detail, was used to investigate the dosimetric characteristics of this special CSM3-a 137Cs brachytherapy source. The absolute dose rate distribution in water around this source was calculated and is presented in the form of an along-away table. Comparison of Sievert integral type calculations with Monte Carlo results are discussed.

Fitted dosimetric parameters of high dose-rate 192Ir sources according to the AAPM TG43 formalism.

The purpose of this study is to find fitted functional forms to the anisotropy function, F(r, theta), and the radial dose function, g(r), in order to characterize dose-rate distributions around all the high-intensity 192Ir sources currently in use. Dosimetry data are at present available as tables for: the microSelectron HDR ("classic" and "new" design models), the PDR source, and the VariSource HDR source, expressed in terms of the AAPM Task Group No. 43 recommendations. There is only one paper out which introduces a functional form to fit the anisotropy function, but only for symmetric sources with respect to the transverse axis. However, dosimetric data of the HDR and PDR sources mentioned above cannot be reproduced with these functional forms. In our study F(r,theta) and g(r) published data are fitted with functional forms in such a way that appropriate limits are reached for both functions and the maximum fit error approaches the data uncertainty. The average fit error is less than 1% in all cases. These functional forms make handling data easier within the treatment planning system, avoiding the use of tabulated data.

Monte Carlo dosimetry of the Buchler high dose rate 192Ir source.

In this study a complete set of dosimetric data is presented for the high dose rate (HDR) source from Amersham used in the Buchler remote afterloading HDR unit. These data have been calculated by means of the Monte Carlo simulation code GEANT taking into account the detailed geometry of the source. Absolute dose rate distributions in water were calculated around this source and are presented as conventional 2D Cartesian look-up tables. All dosimetric quantities recommended by the AAPM Task Group 43 report have been calculated. Quantities determined are: dose rate constant, radial dose function, anisotropy function, anisotropy factor and anisotropy constant. The dose rate distributions of the Buchler HDR source are compared with those of other HDR sources used in brachytherapy, showing that the differences are large in zones near the long source axis due to oblique filtration. These Monte Carlo simulated data in water can be used for clinical applications.

A Monte Carlo investigation of the dosimetric characteristics of the CSM11 137Cs source from CIS.

The purpose of this study is to calculate basic dosimetry data for a CSM11 low dose rate 137Cs source in water. This source is widely used in afterloadable dome cylinders designed to homogeneously irradiate the vaginal cuff alone or additional areas of the vagina in hysterectomized patients. In this study, the Monte Carlo simulation code GEANT, incorporating in detail source geometry, is used to investigate the dosimetric characteristics of the source. The calculated data were analyzed using a fitting procedure that is described in detail. Absolute dose rate distributions in water were calculated around this source and are presented as conventional 2D Cartesian lookup tables (classically along-away tables). Also, the dose calculation formalism endorsed by the Interstitial Collaborative Working Group and the AAPM Task Group 43 have been calculated. The calculated dose rate constant for this source is lambda = 1.096 +/- 0.002 cGy h(-1) U(-1). The anisotropy function results in about 50% deviations from isotropy at positions near the long axis of the source. The radial dose function is given as a polynomial that reproduces the calculated data up to 20 cm. Best-fit values of attenuation coefficients suitable for use in Sievert integral calculations have been derived.

Monte Carlo calculations of dose rate distributions around the Amersham CDCS-M-type 137Cs source.

The Amersham CDCS-M-type 137Cs stainless-steel encapsulated source is widely used in low dose rate brachytherapy with manual afterloading. However there is a need for more accurate dosimetry data. In this study we present Monte Carlo calculations of absolute dose rate in water around this source using the Monte Carlo code GEANT, discuss dosimetric features of these data, and compare them with Krishnaswamy's results for 137Cs intracavitary sources. Dose rate distributions are presented in the form of along-away tables and in the TG43 formalism. Simulated absolute dose rate values can be used as benchmark data to verify the treatment planning system calculation results or directly as input data for treatment planning. Best-fit values of attenuation coefficients suitable for use in Sievert integral type calculations have been derived comparing dose rate distributions calculated using this algorithm with those obtained from Monte Carlo calculations.

Monte Carlo calculation of dose rate distributions around 192Ir wires.

Monte Carlo calculations of absolute dose rate in liquid water are presented in the form of away-along tables for 1 and 5 cm 192Ir wires of 0.3 mm diameter. Simulated absolute dose rate values can be used as benchmark data to verify the calculation results of treatment planning systems or directly as input data for treatment planning. Best fit value of attenuation coefficient suitable for use in Sievert-integrals-type calculations has been derived based on Monte Carlo calculation results. For the treatment planning systems that are based on TG43 formalism we have also calculated the required dosimetry parameters.