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[P163] Dosimetric effects from high density markers for prostate cancer treatments
Abstracts / Physica Medica 52 (2018) 99–187
[P160] From anisotropical analytical algorithm to acuros XB: Clinical implications in vmat technique for lung, head&neck and prostate treatments Ana Aparicio *, Iban Conles, Elena Cenizo, María Jesús Cesteros Complejo Asistencial Universitario de León, Medical Physics and Radiological Potection, León, Spain ⇑ Corresponding author. Purpose. To determine the dose differences and clinical implications of using a high accuracy algorithm, AcurosXB (AXB), instead of the Anisotropic Analytical Algorithm (AAA), for three different treatment sites with VMAT technique, in order to use AXB as routine algorithm. Methods. We selected fifteen prostate and head&neck cancer patients, and seventeen lung cancer patients. All of them had been optimized with the Photon Optimizer algorithm and calculated with AAA. These plans were recalculated with AXB to quantify dose differences in significant points of the DVH: coverage and maximum dose criteria for the PTV, and several dose-volume constraints for the involved Organs at Risk (OAR). All data were statistically treated. For the PTV, we analyzed clinical consequences in terms of coverage and homogeneity. For the OAR, it is well known that classic dose tolerances have been stated based on AAA or even simpler algorithms. In our study, we identified those dose-volume points in which AXB provides lower calculated doses than AAA. In these cases, it wouldn’t be safe to plan with AXB according to classic dose tolerances, since it might imply that these criteria weren’t met with AAA. To prevent this, an additional statistically derived restriction to tolerance constrains is proposed when using AXB. Results. PTV: For lung and head&neck patients, due to the high heterogeneity involved, we observe a worse coverage and homogeneity in plans recalculated with AXB. Consequently, if we use AXB in our practice, a more demanding optimization is needed to meet objectives, implying a better local control disease. OAR: for most of the dose-volume points studied the differences found are statistically significant. Some of them might lead to clinical consequences for serial OAR. In these cases, we encourage to restrict Dmax tolerance when AXB is used, as discussed above. Conclusions. The results obtained with AXB differ from those obtained with AAA. Since AXB is more accurate, we propose using it in clinical practice. Nevertheless, we strongly recommend being cautious about OAR tolerances, setting an additional restriction to the tolerance criteria when required, until these are reviewed and an international consensus is adopted taking into account the new algorithms. https://doi.org/10.1016/j.ejmp.2018.06.462
[P162] Postal TLD dosimetry audits in radiotherapy in poland – Results of 2017 Wiola Slusarczyk-kacprzyk, Wojciech Bulski *, Piotr Ulkowski, Krzysztof Chelminski The Maria Sklodowska-Curie Memorial Cancer Centre and Institute of Oncology, Medical Physics Department, Warsaw, Poland ⇑ Corresponding author. Purpose. The regulation of Ministry of Health on safe use of ionizing radiation for medical exposures (18.02.2011) forces all radiotherapy centers in Poland to participate in external dosimetric audits. First external dosimetric audit in Poland was organized by the Secondary Standard Dosimetric Laboratory (SSDL) of the Institute of Oncology in Warsaw in 1991. Since 1999 the postal audits have been carried out yearly.
145
Methods. In 2017, 37 radiotherapy centers participated in the audit. Most of them requested an audit for more than one beam quality. Totally, 143 radiation beams were audited, including 131 photon beams and 12 electron beams. Thermoluminescent dosimeters (TLD) of Li-F MT-F type (Institute of Nuclear Physics, Cracow, Poland) were mailed to each participant. The participants were instructed to irradiate three TL detectors for each beam with a dose of 2 Gy in reference conditions. After irradiation the detectors were sent back to the SSDL. At the same time, set of reference detectors was irradiated with known doses at the SSDL. All detectors were read out at the SSDL with a Fimel PCL 3 TLD reader. Finally, delta factor was calculated for each audited beam: delta = 100 (DP – DSSDL Þ=DSSDL [%] where: DP – the dose reported by the participant; DSSDL – the dose determined by the SSDL. The results were classified in three categories: delta 6 ± 3,5% - correct result; 3,5% < jdeltaj 65% – reason of deviation has to be explained; delta > ± 5% – reason of deviation has to be explained, and then the audit should be repeated. Results. The results were correct for vast majority of cases. Deviations larger than 3.5% were observed for fife beams in fife radiotherapy centers. For one photon beam the deviations were between 3.5% and 5%, while for four photon beam they were larger than 5% (from 5,3% to 30,1%). In all radiotherapy centers, we explained the reasons for the negative results obtained. A repeated audit gave correct results. Conclusions. Postal dosimetry audits are important tools for assuring safe and effective radiotherapy in a country. https://doi.org/10.1016/j.ejmp.2018.06.463
[P163] Dosimetric effects from high density markers for prostate cancer treatments Marcus Krantz a,*, Angela Lund a, Roumiana Chakarova a a Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden ⇑ Corresponding author.
Purpose. Implanted high density gold markers are used in radiotherapy of prostate cancer for a more accurate delivery of planned target dose. However, the presence of high density objects inside the prostate causes artefacts in the computed tomography (CT) images from which the dose calculations are based on. The interpretation of the tissues made by the different dose calculation algorithms becomes uncertain and this uncertainty may propagate to the final dose distribution. The aim of this work was to quantify the dosimetric effects from high density markers on dose distributions for prostate cancer treatments using three different algorithms. Methods. About 200 patients treated with volumetric modulated arc therapy (VMAT) for prostate cancer were included. Dose calculations (dose to water) were executed using the treatment planning system (TPS) algorithms, anisotropic analytical algorithm (AAA), Acuros XB (AXB) and by an automated Monte Carlo (MC) system based on the EGSnrc code package with modifications. In order to quantify the effect of high density markers, dose distributions for prostate plans (post-operative and with gold markers) were compared. Dose volume histogram (DVH) estimates such as the mean dose to the clinical target volume (CTV), the planning target volume (PTV), D98% PTV and D2% PTV (dose to xx% of the PTV) were evaluated. Further analysis was performed by modifying the artefact areas in the CT images by setting the material in the PTV to water.
146
Abstracts / Physica Medica 52 (2018) 99–187
Results. The mean difference between AAA, AXB and MC estimations of the mean dose to the CTV and PTV was within 0.5% for all cases. Also, mean dose deviations up to 2% were observed for individual plans, especially for plans with gold markers. Dose deviations up to 5%, related to the shape of the DVH, were detected for D98% PTV and D2% PTV. The size of the CTV showed no impact on dose deviations for prostate plans with gold markers. Conclusions. The presence of gold markers increases the variation between CTV and PTV dosimetry parameters obtained by different algorithms. However, no clinically relevant dosimetric effects arise from artefacts caused by high density markers. https://doi.org/10.1016/j.ejmp.2018.06.464
[P164] Dosimetric comparison between CyberKnife and VMAT treatment plans for radiosurgery Alba Díaz-Martín *, Irene Fernández, Ana María Tornero-López, Luis Luque-Japón, Celia Madan-Rodríguez, Iago González-Vecín, Artemi Morera-Molina, Eugenio Ruiz-Egea, Margarita Melián-Jiménez Hospital Universitario Gran Canaria Dr. Negrín, Medical Physics, Las Palmas de Gran Canaria, Spain ⇑ Corresponding author. Purpose. Two advanced modalities for radiosurgery treatment in selected patients with brain lesions are CyberKnife (CK) and volumetric arc therapy (VMAT) through a TrueBeam Linac. We aim to evaluate and compare multiple radiosurgery metrics between both modalities to establish the benefits when treating with each one. Methods. 13 patients having single brain lesions were used to create plans on each system, which were performed according to their usual methodologies, meaning stronger maximum dose restriction for VMAT. The comparison was performed by means of Pearson and Wilcoxon tests of various representative parameters distributions, such as: Conformity Index, Paddick Conformity Index, Homogeneity Index, Gradient Index, tissue volume receiving more than 12 and 10 Gy, beam-on time (BOT), Monitor Units (MU), as well as the V10%, V25%, V50% and V80% isodose volumes. Also, maximum and mean doses were taken for several organs at risk (OARs). Results. Being both systems set to have the same coverage, the tumor volume received significantly more dose in CK plans, which agrees with the better homogeneity achieved in VMAT plans (l ± r = 1.25 ± 0.06 (CK) vs. 1.09 ± 0.03 (VMAT), p < 0.001). Both systems showed comparable results in terms of conformity (p = 0.388). Maximum dose for skin was significantly smaller for CK (l ± r = 5.0 ± 2.6 (CK) vs. 6.6 ± 3.4 (VMAT) Gy, p < 0.007). CK showed significantly steeper gradients (l ± r = 4.3 ± 1.1 (CK) vs. 5.8 ± 2.3 (VMAT) cc, p = 0.002), significantly more MU (l ± r = 22,177 ± 11,295 (CK) vs 3405 ± 1093 (VMAT), p < 0.001) and therefore, longer beam-on times (l ± r = 22.2 ± 11.3 (CK) vs. 2.4 ± 0.8 (VMAT) min, p < 0.001). Regarding dose spread, V10% indicated no significant difference, unlike V20%, V50% and V80% that showed progressively smaller values for CK (50%, 35% and 19% respectively, p < 0.006). The mean volume of brain receiving 12 Gy achieved better results for CK (l ± r = 6.5 ± 11.6 (CK) vs. 10.1 ± 18.5 (VMAT) cc, p < 0.001). Similar results were obtained at 10 Gy. Conclusions. Considering different planning methodologies, preliminary results show that in general equivalent quality can be achieved using both modalities, with the distinctive feature that in cases OARs are adjacent to the target, CK would be a better option
since steeper gradients can be achieved. On the other hand, VMAT could benefit from the reduced MUs and BOT. Further studies are being held where the methodology used for CK is performed for VMAT, regarding optimization objectives and beam geometry, expecting to improve gradient when planning with VMAT. https://doi.org/10.1016/j.ejmp.2018.06.465
[P165] Analysis of dose deposition in lung lesions: A modified PTV for a robust optimization Angelo Filippo Monti a,*, David Antonio Brito b, Maria Grazia Brambilla c, Claudia Carbonini c, Maria Bernadetta Ferrari c, Daniela Zanni c, Hae Song Mainardi c, Alberto Torresin a a
Asst Ospedale Niguarda, Struttura Complessa DI Fisica Sanitaria, Milan, Italy b Hospital Metropolitano, Dept. Medical Physics, Quito, Ecuador c Asst Ospedale Niguarda, Medical Physics, Milan, Italy ⇑ Corresponding author. Purpose. SBRT in lung cancer delivers high doses to a small dense nodule (GTV) moving into a low density tissue. If an IMRT-VMAT technique is used, an apparently homogeneous dose is delivered, but an high photon fluence is generated inside the PTV-GTV shell due to its low electron density (ED). This gives the paradox that the dose distribution seems uniform, but the GTV, which moves into the PTV, will receive a dose depending on its position. Methods. A TPS ”Monaco” (MC algorithm) was used to simulate a dummy patient (55 Gy in 5 fractions). In step 1, in order to evaluate the dose discrepancy on the target when the motion of the GTV is considered, the photon fluence was optimized for the original PTV ED (EDo) and thus used to calculate the dose on a ‘‘forced” PTV ED (EDf), in which the ED of the PTV was forced to the mean ED of the GTV. In step 2, the photon fluence was optimized for PTV EDf and then used for dose calculation on PTV EDo to evaluate the dose variation on the lower ED region of the PTV and inside the GTV. Dosimetric comparisons between the original and the recalculated dose distribution for PTV-GTV were made in terms of: dose profiles, Dmean, D98% and D2%. Results. In step 1 dose profiles differ up to 6.6%, 3.4% and 3.8% on longitudinal, sagittal and transversal axes along the isocenter. Increments of 1.6% for D98%, 2.5% for Dmean and 5% for D2% were obtained for PTV-GTV. In step 2 differences between dose profiles were 3% for all. A reductions of 1.5% for D98%, 1.5% for Dmean and 1.4% for D2% were achieved for PTV-GTV. Conclusions. Step 1 shows that the dose delivered to GTV, when it moves where the photon fluence is optimized for lower ED, is higher than what estimated on the original EDo. The GTV is irradiated in a more homogeneous way in step 2 in which the fluence is optimized for EDf. We propose to modify the PTV electron density thus considering the GTV mobility, and evaluating more effectively the actual GTV dose. https://doi.org/10.1016/j.ejmp.2018.06.466
[P166] Analysis of dose distribution in HDR endobronchial brachytherapy in 2D and 3D methods with the use of threedimensional images Marcin Sawicki *, Jarosław Łyczek, Łukasz Kowalik, Damian Kazalski Subcarpathian Cancer Center, Brachytherapy, Brzozów, Poland Corresponding author.
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[P160] From anisotropical analytical algorithm to acuros XB: Clinical implications in vmat technique for lung, head&neck and prostate treatments Ana Aparicio *, Iban Conles, Elena Cenizo, María Jesús Cesteros Complejo Asistencial Universitario de León, Medical Physics and Radiological Potection, León, Spain ⇑ Corresponding author. Purpose. To determine the dose differences and clinical implications of using a high accuracy algorithm, AcurosXB (AXB), instead of the Anisotropic Analytical Algorithm (AAA), for three different treatment sites with VMAT technique, in order to use AXB as routine algorithm. Methods. We selected fifteen prostate and head&neck cancer patients, and seventeen lung cancer patients. All of them had been optimized with the Photon Optimizer algorithm and calculated with AAA. These plans were recalculated with AXB to quantify dose differences in significant points of the DVH: coverage and maximum dose criteria for the PTV, and several dose-volume constraints for the involved Organs at Risk (OAR). All data were statistically treated. For the PTV, we analyzed clinical consequences in terms of coverage and homogeneity. For the OAR, it is well known that classic dose tolerances have been stated based on AAA or even simpler algorithms. In our study, we identified those dose-volume points in which AXB provides lower calculated doses than AAA. In these cases, it wouldn’t be safe to plan with AXB according to classic dose tolerances, since it might imply that these criteria weren’t met with AAA. To prevent this, an additional statistically derived restriction to tolerance constrains is proposed when using AXB. Results. PTV: For lung and head&neck patients, due to the high heterogeneity involved, we observe a worse coverage and homogeneity in plans recalculated with AXB. Consequently, if we use AXB in our practice, a more demanding optimization is needed to meet objectives, implying a better local control disease. OAR: for most of the dose-volume points studied the differences found are statistically significant. Some of them might lead to clinical consequences for serial OAR. In these cases, we encourage to restrict Dmax tolerance when AXB is used, as discussed above. Conclusions. The results obtained with AXB differ from those obtained with AAA. Since AXB is more accurate, we propose using it in clinical practice. Nevertheless, we strongly recommend being cautious about OAR tolerances, setting an additional restriction to the tolerance criteria when required, until these are reviewed and an international consensus is adopted taking into account the new algorithms. https://doi.org/10.1016/j.ejmp.2018.06.462
[P162] Postal TLD dosimetry audits in radiotherapy in poland – Results of 2017 Wiola Slusarczyk-kacprzyk, Wojciech Bulski *, Piotr Ulkowski, Krzysztof Chelminski The Maria Sklodowska-Curie Memorial Cancer Centre and Institute of Oncology, Medical Physics Department, Warsaw, Poland ⇑ Corresponding author. Purpose. The regulation of Ministry of Health on safe use of ionizing radiation for medical exposures (18.02.2011) forces all radiotherapy centers in Poland to participate in external dosimetric audits. First external dosimetric audit in Poland was organized by the Secondary Standard Dosimetric Laboratory (SSDL) of the Institute of Oncology in Warsaw in 1991. Since 1999 the postal audits have been carried out yearly.
145
Methods. In 2017, 37 radiotherapy centers participated in the audit. Most of them requested an audit for more than one beam quality. Totally, 143 radiation beams were audited, including 131 photon beams and 12 electron beams. Thermoluminescent dosimeters (TLD) of Li-F MT-F type (Institute of Nuclear Physics, Cracow, Poland) were mailed to each participant. The participants were instructed to irradiate three TL detectors for each beam with a dose of 2 Gy in reference conditions. After irradiation the detectors were sent back to the SSDL. At the same time, set of reference detectors was irradiated with known doses at the SSDL. All detectors were read out at the SSDL with a Fimel PCL 3 TLD reader. Finally, delta factor was calculated for each audited beam: delta = 100 (DP – DSSDL Þ=DSSDL [%] where: DP – the dose reported by the participant; DSSDL – the dose determined by the SSDL. The results were classified in three categories: delta 6 ± 3,5% - correct result; 3,5% < jdeltaj 65% – reason of deviation has to be explained; delta > ± 5% – reason of deviation has to be explained, and then the audit should be repeated. Results. The results were correct for vast majority of cases. Deviations larger than 3.5% were observed for fife beams in fife radiotherapy centers. For one photon beam the deviations were between 3.5% and 5%, while for four photon beam they were larger than 5% (from 5,3% to 30,1%). In all radiotherapy centers, we explained the reasons for the negative results obtained. A repeated audit gave correct results. Conclusions. Postal dosimetry audits are important tools for assuring safe and effective radiotherapy in a country. https://doi.org/10.1016/j.ejmp.2018.06.463
[P163] Dosimetric effects from high density markers for prostate cancer treatments Marcus Krantz a,*, Angela Lund a, Roumiana Chakarova a a Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden ⇑ Corresponding author.
Purpose. Implanted high density gold markers are used in radiotherapy of prostate cancer for a more accurate delivery of planned target dose. However, the presence of high density objects inside the prostate causes artefacts in the computed tomography (CT) images from which the dose calculations are based on. The interpretation of the tissues made by the different dose calculation algorithms becomes uncertain and this uncertainty may propagate to the final dose distribution. The aim of this work was to quantify the dosimetric effects from high density markers on dose distributions for prostate cancer treatments using three different algorithms. Methods. About 200 patients treated with volumetric modulated arc therapy (VMAT) for prostate cancer were included. Dose calculations (dose to water) were executed using the treatment planning system (TPS) algorithms, anisotropic analytical algorithm (AAA), Acuros XB (AXB) and by an automated Monte Carlo (MC) system based on the EGSnrc code package with modifications. In order to quantify the effect of high density markers, dose distributions for prostate plans (post-operative and with gold markers) were compared. Dose volume histogram (DVH) estimates such as the mean dose to the clinical target volume (CTV), the planning target volume (PTV), D98% PTV and D2% PTV (dose to xx% of the PTV) were evaluated. Further analysis was performed by modifying the artefact areas in the CT images by setting the material in the PTV to water.
146
Abstracts / Physica Medica 52 (2018) 99–187
Results. The mean difference between AAA, AXB and MC estimations of the mean dose to the CTV and PTV was within 0.5% for all cases. Also, mean dose deviations up to 2% were observed for individual plans, especially for plans with gold markers. Dose deviations up to 5%, related to the shape of the DVH, were detected for D98% PTV and D2% PTV. The size of the CTV showed no impact on dose deviations for prostate plans with gold markers. Conclusions. The presence of gold markers increases the variation between CTV and PTV dosimetry parameters obtained by different algorithms. However, no clinically relevant dosimetric effects arise from artefacts caused by high density markers. https://doi.org/10.1016/j.ejmp.2018.06.464
[P164] Dosimetric comparison between CyberKnife and VMAT treatment plans for radiosurgery Alba Díaz-Martín *, Irene Fernández, Ana María Tornero-López, Luis Luque-Japón, Celia Madan-Rodríguez, Iago González-Vecín, Artemi Morera-Molina, Eugenio Ruiz-Egea, Margarita Melián-Jiménez Hospital Universitario Gran Canaria Dr. Negrín, Medical Physics, Las Palmas de Gran Canaria, Spain ⇑ Corresponding author. Purpose. Two advanced modalities for radiosurgery treatment in selected patients with brain lesions are CyberKnife (CK) and volumetric arc therapy (VMAT) through a TrueBeam Linac. We aim to evaluate and compare multiple radiosurgery metrics between both modalities to establish the benefits when treating with each one. Methods. 13 patients having single brain lesions were used to create plans on each system, which were performed according to their usual methodologies, meaning stronger maximum dose restriction for VMAT. The comparison was performed by means of Pearson and Wilcoxon tests of various representative parameters distributions, such as: Conformity Index, Paddick Conformity Index, Homogeneity Index, Gradient Index, tissue volume receiving more than 12 and 10 Gy, beam-on time (BOT), Monitor Units (MU), as well as the V10%, V25%, V50% and V80% isodose volumes. Also, maximum and mean doses were taken for several organs at risk (OARs). Results. Being both systems set to have the same coverage, the tumor volume received significantly more dose in CK plans, which agrees with the better homogeneity achieved in VMAT plans (l ± r = 1.25 ± 0.06 (CK) vs. 1.09 ± 0.03 (VMAT), p < 0.001). Both systems showed comparable results in terms of conformity (p = 0.388). Maximum dose for skin was significantly smaller for CK (l ± r = 5.0 ± 2.6 (CK) vs. 6.6 ± 3.4 (VMAT) Gy, p < 0.007). CK showed significantly steeper gradients (l ± r = 4.3 ± 1.1 (CK) vs. 5.8 ± 2.3 (VMAT) cc, p = 0.002), significantly more MU (l ± r = 22,177 ± 11,295 (CK) vs 3405 ± 1093 (VMAT), p < 0.001) and therefore, longer beam-on times (l ± r = 22.2 ± 11.3 (CK) vs. 2.4 ± 0.8 (VMAT) min, p < 0.001). Regarding dose spread, V10% indicated no significant difference, unlike V20%, V50% and V80% that showed progressively smaller values for CK (50%, 35% and 19% respectively, p < 0.006). The mean volume of brain receiving 12 Gy achieved better results for CK (l ± r = 6.5 ± 11.6 (CK) vs. 10.1 ± 18.5 (VMAT) cc, p < 0.001). Similar results were obtained at 10 Gy. Conclusions. Considering different planning methodologies, preliminary results show that in general equivalent quality can be achieved using both modalities, with the distinctive feature that in cases OARs are adjacent to the target, CK would be a better option
since steeper gradients can be achieved. On the other hand, VMAT could benefit from the reduced MUs and BOT. Further studies are being held where the methodology used for CK is performed for VMAT, regarding optimization objectives and beam geometry, expecting to improve gradient when planning with VMAT. https://doi.org/10.1016/j.ejmp.2018.06.465
[P165] Analysis of dose deposition in lung lesions: A modified PTV for a robust optimization Angelo Filippo Monti a,*, David Antonio Brito b, Maria Grazia Brambilla c, Claudia Carbonini c, Maria Bernadetta Ferrari c, Daniela Zanni c, Hae Song Mainardi c, Alberto Torresin a a
Asst Ospedale Niguarda, Struttura Complessa DI Fisica Sanitaria, Milan, Italy b Hospital Metropolitano, Dept. Medical Physics, Quito, Ecuador c Asst Ospedale Niguarda, Medical Physics, Milan, Italy ⇑ Corresponding author. Purpose. SBRT in lung cancer delivers high doses to a small dense nodule (GTV) moving into a low density tissue. If an IMRT-VMAT technique is used, an apparently homogeneous dose is delivered, but an high photon fluence is generated inside the PTV-GTV shell due to its low electron density (ED). This gives the paradox that the dose distribution seems uniform, but the GTV, which moves into the PTV, will receive a dose depending on its position. Methods. A TPS ”Monaco” (MC algorithm) was used to simulate a dummy patient (55 Gy in 5 fractions). In step 1, in order to evaluate the dose discrepancy on the target when the motion of the GTV is considered, the photon fluence was optimized for the original PTV ED (EDo) and thus used to calculate the dose on a ‘‘forced” PTV ED (EDf), in which the ED of the PTV was forced to the mean ED of the GTV. In step 2, the photon fluence was optimized for PTV EDf and then used for dose calculation on PTV EDo to evaluate the dose variation on the lower ED region of the PTV and inside the GTV. Dosimetric comparisons between the original and the recalculated dose distribution for PTV-GTV were made in terms of: dose profiles, Dmean, D98% and D2%. Results. In step 1 dose profiles differ up to 6.6%, 3.4% and 3.8% on longitudinal, sagittal and transversal axes along the isocenter. Increments of 1.6% for D98%, 2.5% for Dmean and 5% for D2% were obtained for PTV-GTV. In step 2 differences between dose profiles were 3% for all. A reductions of 1.5% for D98%, 1.5% for Dmean and 1.4% for D2% were achieved for PTV-GTV. Conclusions. Step 1 shows that the dose delivered to GTV, when it moves where the photon fluence is optimized for lower ED, is higher than what estimated on the original EDo. The GTV is irradiated in a more homogeneous way in step 2 in which the fluence is optimized for EDf. We propose to modify the PTV electron density thus considering the GTV mobility, and evaluating more effectively the actual GTV dose. https://doi.org/10.1016/j.ejmp.2018.06.466
[P166] Analysis of dose distribution in HDR endobronchial brachytherapy in 2D and 3D methods with the use of threedimensional images Marcin Sawicki *, Jarosław Łyczek, Łukasz Kowalik, Damian Kazalski Subcarpathian Cancer Center, Brachytherapy, Brzozów, Poland Corresponding author.
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