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Inter-operator variability in organs at risk delineation: Their effects on dose-volume histograms
Abstracts of the SFPM Annual Meeting 2013 / Physica Medica 29 (2013) e1–e46
with film is about 3% higher in the bone. In the junction region, inhomogeneity is less than ±2.5% for the ‘‘Full Tomo” method and inferior to ±3.5% for the ‘‘Linac-Tomo” method. Difference between in vivo measurements and calculated dose is inferior to 5%. Conclusion: The feasibility study is conclusive, treatment planning objectives are achievable, presence of heterogeneities are well taken into account, in vivo and junction methods are validated. http://dx.doi.org/10.1016/j.ejmp.2013.08.120
115 COMPARISON OF DOSE DISTRIBUTION BETWEEN INTENSITY MODULATED RADIATION THERAPY AND DYNAMIC ARC THERAPY IN AND OUT-OF-FIELD FOR PROSTATE CANCER TREATMENT PLAN A. Ben Abdennebi 1,2,3,5, G. Auzac 1, J. Chavaudra 1, M. Besbes 5, D. Llanas 1,2,3, R. Allodji 2,3, Y. Tao 1, P. Blanchard 1, A. Veres 4, A. Bridier 1, D. Lefkopoulos 1, F. de Vathaire 1,2,3, I. Diallo 1,2,3. 1 Institut Gustave Roussy, Villejuif, France, 2 Inserm, CESP – U1018, Radiation Epidemiology Team, Villejuif, France, 3 Université Paris XI, Villejuif, France, 4 EQUAL Measuring Laboratory, Service de Physique, Institut Gustave-Roussy, Villejuif, France, 5 Université de Tunis El Manar Faculté des Sciences de Tunis, El Manar, Tunis Introduction: The aim of this study is to compare intensity modulated radiation therapy (IMRT) and dynamic conformal arc therapy (DAT) for prostate cancer treatments. Doses received by in-field and out-of-field organs were estimated for both techniques. Materials and methods: We selected five patients with a prostate cancer and we simulated their treatment by IMRT and DAT A 6-beam (6MV) ballistic was used for the IMRT treatment whereas a 4-arc (6MV) ballistic was used for the DAT. Dose volume histograms (DVHs), were computed OARs and Remaining Volume at Risk (RVR) for both techniques, and estimates of the dose out-of-field for twelve anatomical sites were analyzed and compared between the two techniques. The out-of-field dose was performed using experimental data from previous work. Results: The mean increase for the RVR included between 2–45 Gy for IMRT was about 1434 cm3 as compared to DAT. On the other hand, IMRT significantly increased the irradiated volume of the rectum wall in the dose range of 2–60 Gy and also significantly increased the irradiated volume of bladder wall. However the IMRT significantly reduced the dose to the femoral heads compared to the DAT. For both techniques, the dose to the PTV remained similar. For the twelve out-of-field anatomical sites evaluated, ratio between the estimated doses for both techniques varies between 1.01 and 1.1, DAT leading to the lower doses. Conclusion: DAT improves the treatment of the prostate cancer by reducing the doses not only to the OARs but also to the RVR. http://dx.doi.org/10.1016/j.ejmp.2013.08.121
116 INTER-OPERATOR VARIABILITY IN ORGANS AT RISK DELINEATION: THEIR EFFECTS ON DOSE-VOLUME HISTOGRAMS D. Llanas 1,2,3, J. Bézin 1,2,3, A. Ben Abdennebi 1,2,3, C. Veres 1,2,3, D. Lefkopoulos 1, F. de Vathaire 1,2,3, I. Diallo 1,2,3. 1 Institut Gustave Roussy, Villejuif, France, 2 Inserm, CESP – U1018, Equipe d’épidémiologie des Irradiations, Villejuif, France, 3 Université Paris XI, Villejuif, France Introduction: As recommended by the ICRU report 83, while planning treatment in radiotherapy (RT), organs at risk (OAR) must be systematically delineated. As several studies have shown, interoperator variability implies differences in volume once rebuilt from
e39
computed tomography images. This work aims to evaluate the impact of this variability on dose-volume histograms (DVH). Materials and methods: Using a treatment planning system (TPS) Isogray (DosisoftÒ), three typical treatment plans, for 3 different pathologies, were performed: a case of carcinoma of the prostate in 3D conformational radiotherapy (3DCRT), one case of Hodgkin lymphoma Involved Field and in a case of breast carcinoma 3DCRT. To model changes in volumes of organs at risk induced by delineation, margins, implemented by the TPS were defined around reference delineations. These margins have been defined using results of several authors who have studied inter-operator variability in delineation. In addition, reference delineations were validated by two radiation oncologists from the Gustave Roussy Institute. The resulting DVH were analyzed to compare the dose-volume metrics for all treatment plans and all organs. Results: Preliminary results relate to the D98%, D50% and D2%. Whatever the position of the OAR from the irradiated volume, defined by the 50% isodose of the prescribed dose, D50% of each organ at risk does not vary significantly with the volume in the volume range defined. D98% decreases of about 9% when delineation tends to overestimate the volume of interest at the maximum. However D2% increases of about 7% when delineation tends to overestimate volume of interest at the maximum. Conclusion: Except for D50%, inter-operator variability in OAR delineation may induce a different interpretation of the DVH in the treatment planning process. These results have to be taken into account during the validation of a clinical treatment plan. In addition, to reduce inter-operator variability, this work recommends to define standardized protocols of delineation for each organ. http://dx.doi.org/10.1016/j.ejmp.2013.08.122
117 UNCERTAINTIES DOSE EVALUATION INDUCED BY NON-EXHAUSTIVITY DATA J. Tranel, I. Diallo. Equipe d’Epidémiologie des Radiations, Centre d’Etudes en Santé des Populations (CESP), UMR 1018 INSERM Institut de Cancérologie Gustave Roussy, Villejuif, France Introduction: The individual dose estimation to organs at risk has known important evolution last years, with new tools whose permits to obtain histogram dose-volume. However, dose reconstruction based on retrospective epidemiology studies are often realized dozens of years after initial radiotherapy, based sometimes on nonexhaustive data, both on patient anatomy as the beams. The aim is to establish the link between the missing data rate and the uncertainties induced on out-of-field dose by the non-exhaustivity of the data. Methods and materials: Statistics are used for evaluating the missing data rate in patient radiotherapy files from french, british, italian and dutch cohorts. The around twenty variables contributing to the patient anatomy modelisation and dose calculation are evaluated. Statistics methods (multiples imputation) are used to complete the missing data. For uncertainties dose calculation, the formalism defined in TRS 384 is applied, variances are deducted from the statistical study. Results: The primary results indicate that, according to the considered parameter, missing data rate is very inconstant and strongly linked to the year of treatment and the institution. The dose uncertainties induced is very linked to the considered parameter. Conclusion: The results of the study should allow a better knowledge of the uncertainties in retrospective dose estimations used for long term studies of effects of radiotherapy. http://dx.doi.org/10.1016/j.ejmp.2013.08.123
with film is about 3% higher in the bone. In the junction region, inhomogeneity is less than ±2.5% for the ‘‘Full Tomo” method and inferior to ±3.5% for the ‘‘Linac-Tomo” method. Difference between in vivo measurements and calculated dose is inferior to 5%. Conclusion: The feasibility study is conclusive, treatment planning objectives are achievable, presence of heterogeneities are well taken into account, in vivo and junction methods are validated. http://dx.doi.org/10.1016/j.ejmp.2013.08.120
115 COMPARISON OF DOSE DISTRIBUTION BETWEEN INTENSITY MODULATED RADIATION THERAPY AND DYNAMIC ARC THERAPY IN AND OUT-OF-FIELD FOR PROSTATE CANCER TREATMENT PLAN A. Ben Abdennebi 1,2,3,5, G. Auzac 1, J. Chavaudra 1, M. Besbes 5, D. Llanas 1,2,3, R. Allodji 2,3, Y. Tao 1, P. Blanchard 1, A. Veres 4, A. Bridier 1, D. Lefkopoulos 1, F. de Vathaire 1,2,3, I. Diallo 1,2,3. 1 Institut Gustave Roussy, Villejuif, France, 2 Inserm, CESP – U1018, Radiation Epidemiology Team, Villejuif, France, 3 Université Paris XI, Villejuif, France, 4 EQUAL Measuring Laboratory, Service de Physique, Institut Gustave-Roussy, Villejuif, France, 5 Université de Tunis El Manar Faculté des Sciences de Tunis, El Manar, Tunis Introduction: The aim of this study is to compare intensity modulated radiation therapy (IMRT) and dynamic conformal arc therapy (DAT) for prostate cancer treatments. Doses received by in-field and out-of-field organs were estimated for both techniques. Materials and methods: We selected five patients with a prostate cancer and we simulated their treatment by IMRT and DAT A 6-beam (6MV) ballistic was used for the IMRT treatment whereas a 4-arc (6MV) ballistic was used for the DAT. Dose volume histograms (DVHs), were computed OARs and Remaining Volume at Risk (RVR) for both techniques, and estimates of the dose out-of-field for twelve anatomical sites were analyzed and compared between the two techniques. The out-of-field dose was performed using experimental data from previous work. Results: The mean increase for the RVR included between 2–45 Gy for IMRT was about 1434 cm3 as compared to DAT. On the other hand, IMRT significantly increased the irradiated volume of the rectum wall in the dose range of 2–60 Gy and also significantly increased the irradiated volume of bladder wall. However the IMRT significantly reduced the dose to the femoral heads compared to the DAT. For both techniques, the dose to the PTV remained similar. For the twelve out-of-field anatomical sites evaluated, ratio between the estimated doses for both techniques varies between 1.01 and 1.1, DAT leading to the lower doses. Conclusion: DAT improves the treatment of the prostate cancer by reducing the doses not only to the OARs but also to the RVR. http://dx.doi.org/10.1016/j.ejmp.2013.08.121
116 INTER-OPERATOR VARIABILITY IN ORGANS AT RISK DELINEATION: THEIR EFFECTS ON DOSE-VOLUME HISTOGRAMS D. Llanas 1,2,3, J. Bézin 1,2,3, A. Ben Abdennebi 1,2,3, C. Veres 1,2,3, D. Lefkopoulos 1, F. de Vathaire 1,2,3, I. Diallo 1,2,3. 1 Institut Gustave Roussy, Villejuif, France, 2 Inserm, CESP – U1018, Equipe d’épidémiologie des Irradiations, Villejuif, France, 3 Université Paris XI, Villejuif, France Introduction: As recommended by the ICRU report 83, while planning treatment in radiotherapy (RT), organs at risk (OAR) must be systematically delineated. As several studies have shown, interoperator variability implies differences in volume once rebuilt from
e39
computed tomography images. This work aims to evaluate the impact of this variability on dose-volume histograms (DVH). Materials and methods: Using a treatment planning system (TPS) Isogray (DosisoftÒ), three typical treatment plans, for 3 different pathologies, were performed: a case of carcinoma of the prostate in 3D conformational radiotherapy (3DCRT), one case of Hodgkin lymphoma Involved Field and in a case of breast carcinoma 3DCRT. To model changes in volumes of organs at risk induced by delineation, margins, implemented by the TPS were defined around reference delineations. These margins have been defined using results of several authors who have studied inter-operator variability in delineation. In addition, reference delineations were validated by two radiation oncologists from the Gustave Roussy Institute. The resulting DVH were analyzed to compare the dose-volume metrics for all treatment plans and all organs. Results: Preliminary results relate to the D98%, D50% and D2%. Whatever the position of the OAR from the irradiated volume, defined by the 50% isodose of the prescribed dose, D50% of each organ at risk does not vary significantly with the volume in the volume range defined. D98% decreases of about 9% when delineation tends to overestimate the volume of interest at the maximum. However D2% increases of about 7% when delineation tends to overestimate volume of interest at the maximum. Conclusion: Except for D50%, inter-operator variability in OAR delineation may induce a different interpretation of the DVH in the treatment planning process. These results have to be taken into account during the validation of a clinical treatment plan. In addition, to reduce inter-operator variability, this work recommends to define standardized protocols of delineation for each organ. http://dx.doi.org/10.1016/j.ejmp.2013.08.122
117 UNCERTAINTIES DOSE EVALUATION INDUCED BY NON-EXHAUSTIVITY DATA J. Tranel, I. Diallo. Equipe d’Epidémiologie des Radiations, Centre d’Etudes en Santé des Populations (CESP), UMR 1018 INSERM Institut de Cancérologie Gustave Roussy, Villejuif, France Introduction: The individual dose estimation to organs at risk has known important evolution last years, with new tools whose permits to obtain histogram dose-volume. However, dose reconstruction based on retrospective epidemiology studies are often realized dozens of years after initial radiotherapy, based sometimes on nonexhaustive data, both on patient anatomy as the beams. The aim is to establish the link between the missing data rate and the uncertainties induced on out-of-field dose by the non-exhaustivity of the data. Methods and materials: Statistics are used for evaluating the missing data rate in patient radiotherapy files from french, british, italian and dutch cohorts. The around twenty variables contributing to the patient anatomy modelisation and dose calculation are evaluated. Statistics methods (multiples imputation) are used to complete the missing data. For uncertainties dose calculation, the formalism defined in TRS 384 is applied, variances are deducted from the statistical study. Results: The primary results indicate that, according to the considered parameter, missing data rate is very inconstant and strongly linked to the year of treatment and the institution. The dose uncertainties induced is very linked to the considered parameter. Conclusion: The results of the study should allow a better knowledge of the uncertainties in retrospective dose estimations used for long term studies of effects of radiotherapy. http://dx.doi.org/10.1016/j.ejmp.2013.08.123