[Quality assurance of a virtual simulation software: application to IMAgo and SIMAgo (ISOgray)]

Risk Factors for Heart Failure Among Pan-European Childhood Cancer Survivors: A PanCareSurFup and ProCardio Cohort and Nested Case-Control Study

PURPOSE

Heart failure (HF) is a potentially life-threatening complication of treatment for childhood cancer. We evaluated the risk and risk factors for HF in a large European study of long-term survivors. Little is known of the effects of low doses of treatment, which is needed to improve current treatment protocols and surveillance guidelines.

METHODS

This study includes the PanCareSurFup and ProCardio cohort of ≥ 5-year childhood cancer survivors diagnosed between 1940 and 2009 in seven European countries (N = 42,361). We calculated the cumulative incidence of HF and conducted a nested case-control study to evaluate detailed treatment-related risk factors.

RESULTS

The cumulative incidence of HF was 2% (95% CI, 1.7 to 2.2) by age 50 years. The case-control study (n = 1,000) showed that survivors who received a mean heart radiation therapy (RT) dose of 5 to < 15 Gy have an increased risk of HF (odds ratio, 5.5; 95% CI, 2.5 to 12.3), when compared with no heart RT. The risk associated with doses 5 to < 15 Gy increased with exposure of a larger heart volume. In addition, the HF risk increased in a linear fashion with higher mean heart RT doses. Regarding total cumulative anthracycline dose, survivors who received ≥ 100 mg/m² had a substantially increased risk of HF and survivors treated with a lower dose showed no significantly increased risk of HF. The dose-response relationship appeared quadratic with higher anthracycline doses.

CONCLUSION

Survivors who received a mean heart RT dose of ≥ 5 Gy have an increased risk of HF. The risk associated with RT increases with larger volumes exposed. Survivors treated with < 100 mg/m² total cumulative anthracycline dose have no significantly increased risk of HF. These new findings might have consequences for new treatment protocols for children with cancer and for cardiomyopathy surveillance guidelines.

The role of irradiated heart and left ventricular volumes in heart failure occurrence after childhood cancer

BACKGROUND

Paediatric cancer survivors have a high risk of developing cardiac diseases, and the most frequent cardiac disease is heart failure (HF). The radiation dose-volume effects in the heart and cardiac substructures have not been explored in childhood cancer survivors (CCS). Therefore, the role of irradiated heart volume in the occurrence of HF among this population remains unclear. The aims of this study were to determine the doses and irradiated volumes of the heart and left ventricle (LV) related to the risk of HF in CCS and to investigate the impact of anthracycline exposure on this risk.

METHODS AND RESULTS

A case-control study nested in the French Childhood Cancer Survivors Study cohort. The mean heart and left ventricular doses and volumes indicators were estimated by reconstruction of individual treatments. A total of 239 HF cases and 1042 matched controls were included. The median age of HF diagnosis was 25.1 years. The median volume of the heart that received ≥ 30 Gy was 61.1% for cases and 16.9% for controls. In patients who did not receive anthracycline, the risk of HF was increased 3.6-fold when less than 10% of the LV received ≥ 30 Gy when compared to patients who were not exposed to any cardiac radiation and anthracycline.

CONCLUSIONS

Small irradiated volumes of the heart or LV were significantly associated with HF risk. To the author's knowledge, this is the first study to report a dose-response relationship based on dose-volume indicators in CCS, which can be translated efficiently into current clinical practice.

A review of uncertainties in radiotherapy dose reconstruction and their impacts on dose-response relationships

Proper understanding of the risk of radiation-induced late effects for patients receiving external photon beam radiotherapy requires the determination of reliable dose-response relationships. Although significant efforts have been devoted to improving dose estimates for the study of late effects, the most often questioned explanatory variable is still the dose. In this work, based on a literature review, we provide an in-depth description of the radiotherapy dose reconstruction process for the study of late effects. In particular, we focus on the identification of the main sources of dose uncertainty involved in this process and summarise their impacts on the dose-response relationship for radiotherapy late effects. We provide a number of recommendations for making progress in estimating the uncertainties in current studies of radiotherapy late effects and reducing these uncertainties in future studies.

Comparison of organs' shapes with geometric and Zernike 3D moments

The morphological similarity of organs is studied with feature vectors based on geometric and Zernike 3D moments. It is particularly investigated if outliers and average models can be identified. For this purpose, the relative proximity to the mean feature vector is defined, principal coordinate and clustering analyses are also performed. To study the consistency and usefulness of this approach, 17 livers and 76 hearts voxel models from several sources are considered. In the liver case, models with similar morphological feature are identified. For the limited amount of studied cases, the liver of the ICRP male voxel model is identified as a better surrogate than the female one. For hearts, the clustering analysis shows that three heart shapes represent about 80% of the morphological variations. The relative proximity and clustering analysis rather consistently identify outliers and average models. For the two cases, identification of outliers and surrogate of average models is rather robust. However, deeper classification of morphological feature is subject to caution and can only be performed after cross analysis of at least two kinds of feature vectors. Finally, the Zernike moments contain all the information needed to re-construct the studied objects and thus appear as a promising tool to derive statistical organ shapes.

Thyroid volume measurement in external beam radiotherapy patients using CT imaging: correlation with clinical and anthropometric characteristics

The aim of this study is to define criteria for accurate representation of the thyroid in human models used to represent external beam radiotherapy (EBRT) patients and evaluate the relationship between the volume of this organ and clinical and anthropometric characteristics. From CT images, we segmented the thyroid gland and calculated its volume for a population of 188 EBRT patients of both sexes, with ages ranging from 1 to 89 years. To evaluate uncertainties linked to measured volumes, experimental studies on the Livermore anthropomorphic phantom were performed. For our population of EBRT patients, we observed that in children, thyroid volume increased rapidly with age, from about 3 cm(3) at 2 years to about 16 cm(3) at 20. In adults, the mean thyroid gland volume was 23.5 ± 9 cm(3) for males and 17.5 ± 8 cm(3) for females. According to anthropometric parameters, the best fit for children was obtained by modeling the log of thyroid volume as a linear function of body surface area (BSA) (p < 0.0001) and age (p = 0.04) and for adults, as a linear function of BSA (p < 0.0001) and gender (p = 0.01). This work enabled us to demonstrate that BSA was the best indicator of thyroid volume for both males and females. These results should be taken into account when modeling the volume of the thyroid in human models used to represent EBRT patients for dosimetry in retrospective studies of the relationship between the estimated dose to the thyroid and long-term follow-up data on EBRT patients.

Determination of the optimal statistical uncertainty to perform electron-beam Monte Carlo absorbed dose estimation in the target volume

PURPOSE OF STUDY

Monte Carlo based treatment planning system are known to be more accurate than analytical methods for performing absorbed dose estimation, particularly in and near heterogeneities. However, the required computation time can still be an issue. The present study focused on the determination of the optimum statistical uncertainty in order to minimise computation time while keeping the reliability of the absorbed dose estimation in treatments planned with electron-beams.

MATERIALS AND METHODS

Three radiotherapy plans (medulloblastoma, breast and gynaecological) were used to investigate the influence of the statistical uncertainty of the absorbed dose on the target volume dose-volume histograms (spinal cord, intramammary nodes and pelvic lymph nodes, respectively).

RESULTS

The study of the dose-volume histograms showed that for statistical uncertainty levels (1 S.D.) above 2 to 3%, the standard deviation of the mean dose in the target volume calculated from the dose-volume histograms increases by at least 6%, reflecting the gradual flattening of the dose-volume histograms.

CONCLUSIONS

This work suggests that, in clinical context, Monte Carlo based absorbed dose estimations should be performed with a maximum statistical uncertainty of 2 to 3%.

[Quality assurance of enhanced dynamic wedge using the aS500-II, EPID]

PURPOSE

The work presented herein rests on the study of the Varian EPID aS500-II and the Image Acquisition system IAS3. We assessed the dosimetric performance of this EPID for measurements and quality assurance of enhanced dynamic wedge profiles and wedge factors.

MATERIALS AND METHODS

We evaluated the dosimeter properties using the integrated asynchronous mode of acquisition in treatments with enhanced dynamic wedges (EDW). We studied the performance, stability and the reproducibility in measurements of the transmission factors and profiles of the fields with dynamic wedges. EPID profiles were compared to the "Profiler Sun Nuclear" diode array and PTW ion chamber. Analytical functions were developed in order to correct EDW profiles. The dependence of EPID measurements on wedge direction, beam dimensions and source to EPID distance was assessed.

RESULTS

The backscatter produced by the "exact arm" was evaluated; EPID profiles depended on the EDW direction and on the detector source distance. Wedge factors were determined using this detector and compared to the ion chamber response, differences were all within 1 %. Two empirical correction functions were developed to produce EPID wedge profiles that correspond to diode for all wedge angles and energies depending on the wedge direction.

CONCLUSION

The EPID is highly suited to regular measurement of EDW due to the reproducibility of the EPID-measured wedge factors and profiles.

Application of a 3D volumetric display for radiation therapy treatment planning I: quality assurance procedures

To design and implement a set of quality assurance tests for an innovative 3D volumetric display for radiation treatment planning applications. A genuine 3D display (Perspecta Spatial 3D, Actuality‐Systems Inc., Bedford, MA) has been integrated with the Pinnacle TPS (Philips Medical Systems, Madison WI), for treatment planning. The Perspecta 3D display renders a 25 cm diameter volume that is viewable from any side, floating within a translucent dome. In addition to displaying all 3D data exported from Pinnacle, the system provides a 3D mouse to define beam angles and apertures and to measure distance. The focus of this work is the design and implementation of a quality assurance program for 3D displays and specific 3D planning issues as guided by AAPM Task Group Report 53. A series of acceptance and quality assurance tests have been designed to evaluate the accuracy of CT images, contours, beams, and dose distributions as displayed on Perspecta. Three‐dimensional matrices, rulers and phantoms with known spatial dimensions were used to check Perspecta's absolute spatial accuracy. In addition, a system of tests was designed to confirm Perspecta's ability to import and display Pinnacle data consistently. CT scans of phantoms were used to confirm beam field size, divergence, and gantry and couch angular accuracy as displayed on Perspecta. Beam angles were verified through Cartesian coordinate system measurements and by CT scans of phantoms rotated at known angles. Beams designed on Perspecta were exported to Pinnacle and checked for accuracy. Dose at sampled points were checked for consistency with Pinnacle and agreed within 1% or 1 mm. All data exported from Pinnacle to Perspecta was displayed consistently. The 3D spatial display of images, contours, and dose distributions were consistent with Pinnacle display. When measured by the 3D ruler, the distances between any two points calculated using Perspecta agreed with Pinnacle within the measurement error

PACS number: 07.07.Hj, 87.55.Qr, 87.56.Da, 87.55.D‐; Radiation Treatment Planning