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[P294] Dose rate dosimetric effects during 6 MV flattening filter free RapidArc-based on stereotactic body radiation therapy on lung
Abstracts / Physica Medica 52 (2018) 99–187
Methods. 3D-CRT plans for 27 patients with localized rectal cancer were included in this study. The dose to the bladder was compared and analyzed for two treatment techniques (1) 3-field Box with wedges and (2) 3-field Box with Field in a Field technique (FIF) without wedges. The median, maximum and minimum dose to the bladder was extracted from dose volume histograms (DVH). The prescribed radiation dose to the PTV was 45 Gy in 25 fractions of 1.8 Gy. Results. In 3D conformal with wedges technique the max dose for bladder is 40.901 ± 0.19 Gy and mean dose 10.2427 ± 0.16 Gy compared to the corresponding max dose for bladder, which is 34.7837 ± 0.44 Gy and mean dose 9.1960 ± 0.123 Gy in 3D conformal with FIF. The mean time is 0.993 ± 0.057 min in 3D-CRT with wedges and for 3D-CRT with FIF is 0.582 ± 0.028 min. The mean MU in 3DCRT with wedges is 397.25 ± 23.138 and in 3D-CRT with FIF is 233.07 ± 11.416. Therefore, the FIF method seems to be more effective than that with wedges treatment planning. Conclusions. The comparison of median and maximum doses to the bladder from the two techniques shows that in the second technique, due to the fact that wedge is not used with the FIF, the collimator angle can be such in order to have the best conformance of PTV and therefore better bladder sparing. During the 2nd technique, where better bladder sparing is achieved, especially for the ELEKTA Linacs usage, the number of MU is smaller because wedge is not used. Consequently, the comparison of median and maximum dose is both efficient for PTV radiation and bladder sparing, and time efficient because of short delivery. https://doi.org/10.1016/j.ejmp.2018.06.567
[P294] Dose rate dosimetric effects during 6 MV flattening filter free RapidArc-based on stereotactic body radiation therapy on lung Nicolae Dumitru a,*, Mukunda Pudasaini a, Silvia Pella b, Theodora Leventouri a a
Florida Atlantic University, Medical Physics, Boca Raton, United States South Florida Radiation Oncology, Florida Atlantic University, Medical Physics, Boca Raton, United States ⇑ Corresponding author. b
Purpose. As the technology advanced we are able, now to develop treatment plans using 6X Flattening Filter Free (FFF) for RapidArc. We noticed that the dose rate has high fluctuations in value during the treatment delivery for 6X FFF. This prompted us to start monitoring the dose delivered using portal dosimetry. We wish to develop protocols for developing arc treatment plans when using dose rates above 600 MU/min. Methods. A retrospective study was performed on 25 patients treated using a Varian TrueBeam machine. The SBRT plans were made using RapidArc technique in Varian’s Eclipse. For 25 treatment plans we measured the dose using the Electronic Portal Imaging Dosimetry (EPID) and the diode detectors via Mapcheck. We also recorded the dose rate variance during the treatment delivery and the dose conformality index. We evaluated the biological effective dose (BED), normal tissue complications probability (NTCP) and tumor control probability (TCP). Results. For every treatment delivered the dose rate varies between 100 MU/min and the prescribed rate (600–1400 MU/min). The dosimetric measurements are correlating very well with the dose rate variance. There is also a correlation between the dose rate, the width of the treated fields and the arc’s size. The larger the field the higher the dose rate variance. We also noticed difficulties in passing the complex RapidArc QA measuring plans consistency with
185
the range of the dose rate variation. Biological effectiveness is also affected by the dose rate variance in a percentage between 0.75% and 2.73%. Conclusion. We found optimum dose rate for RapidArc with a value of 622 MU/min that allow a minimum dose rate variance of 36 MU/min during the treatment delivery and an optimum field size that in combination with the correct dose rate will generate plans that will deliver the calculated dose rate with a minimum variance and will not depend to the arc’s degrees range. https://doi.org/10.1016/j.ejmp.2018.06.568
[P295] Reliability of planning dose distribution for assessment of dose distribution in rectum for prostate cancer Anna Treter a, Paweł Franciszek Kukołowicz b,* a
Holycross Cancer Center, Medical Physics Department, Kielce, Poland Maria Skłodowska-Curie Memorial Cancer Center and Institute of Oncology, Kukolowicz, Warszaw, Poland ⇑ Corresponding author. b
Purpose. To assess the influence of changes of the rectum during radiotherapy on the dose distribution in rectum. Methods. For 9 patients computerized 3D/IMRT CT plans were prepared. Before each session of radiotherapy the actual CT performed with the CT on rails was made. Due to technical problems on some days the CT was not made. In total, they were made 213 CTs. The lacking CTs were generated with the bootstrap method. The contour of rectum were was delineated according to RTOG recommendations. Total dose of 78 Gy in 2 Gy fraction dose was delivered. The actual CT images were transferred to Pinnacle treatment planning system. After fusion (on prostate) of actual and planning CT the actual dose distribution for each fraction was calculated. Next cumulative DVH and DVH for planning and the planning and actual no 1, 1-2, 1-3 CTs were calculated. For each set of data the NTCP was calculated. The model proposed by Defraene (Red, 2012) was used. The cumulative, the planning and actual no 1, 1-2, 1-3 and the planning DVHs were compared. Also we compared the planning volume and the cumulative rectum volume and the NTCPs. Results. For some patients quite small changes of volume were observed, for some other quite large, e.g. the planning volume was 35.9 cm3, while cumulative one was 149.0 cm3. In 6 cases the cumulative NTCP was larger than the planning one. For two patients the differences were 0.11, 0.10 (NTCPcum-NTCPplan). For other patients the differences were smaller than ±0.05. Using the CTs made in the first few fractions enabled better estimation of the cumulative DVH but the improvements is not spectacular. Conclusions. The changes of the rectum volume and position for some patients may influence quite large on DVH in rectum and as a result of this on NTCP. It is not clear for which patients such large differences may be expected. https://doi.org/10.1016/j.ejmp.2018.06.569
[P296] Use of statistical interference for tolerance determination in dose measurements Irena Koniarova a,*, Lukas Kotik b a
National Radiation Protection Institute, Department of Radiotherapy and X-Ray Laboratory, Praha 4, Czech Republic b National Radiation Protection Institute, Radiation Risk Assessment Department, Praha 4, Czech Republic ⇑ Corresponding author.
Methods. 3D-CRT plans for 27 patients with localized rectal cancer were included in this study. The dose to the bladder was compared and analyzed for two treatment techniques (1) 3-field Box with wedges and (2) 3-field Box with Field in a Field technique (FIF) without wedges. The median, maximum and minimum dose to the bladder was extracted from dose volume histograms (DVH). The prescribed radiation dose to the PTV was 45 Gy in 25 fractions of 1.8 Gy. Results. In 3D conformal with wedges technique the max dose for bladder is 40.901 ± 0.19 Gy and mean dose 10.2427 ± 0.16 Gy compared to the corresponding max dose for bladder, which is 34.7837 ± 0.44 Gy and mean dose 9.1960 ± 0.123 Gy in 3D conformal with FIF. The mean time is 0.993 ± 0.057 min in 3D-CRT with wedges and for 3D-CRT with FIF is 0.582 ± 0.028 min. The mean MU in 3DCRT with wedges is 397.25 ± 23.138 and in 3D-CRT with FIF is 233.07 ± 11.416. Therefore, the FIF method seems to be more effective than that with wedges treatment planning. Conclusions. The comparison of median and maximum doses to the bladder from the two techniques shows that in the second technique, due to the fact that wedge is not used with the FIF, the collimator angle can be such in order to have the best conformance of PTV and therefore better bladder sparing. During the 2nd technique, where better bladder sparing is achieved, especially for the ELEKTA Linacs usage, the number of MU is smaller because wedge is not used. Consequently, the comparison of median and maximum dose is both efficient for PTV radiation and bladder sparing, and time efficient because of short delivery. https://doi.org/10.1016/j.ejmp.2018.06.567
[P294] Dose rate dosimetric effects during 6 MV flattening filter free RapidArc-based on stereotactic body radiation therapy on lung Nicolae Dumitru a,*, Mukunda Pudasaini a, Silvia Pella b, Theodora Leventouri a a
Florida Atlantic University, Medical Physics, Boca Raton, United States South Florida Radiation Oncology, Florida Atlantic University, Medical Physics, Boca Raton, United States ⇑ Corresponding author. b
Purpose. As the technology advanced we are able, now to develop treatment plans using 6X Flattening Filter Free (FFF) for RapidArc. We noticed that the dose rate has high fluctuations in value during the treatment delivery for 6X FFF. This prompted us to start monitoring the dose delivered using portal dosimetry. We wish to develop protocols for developing arc treatment plans when using dose rates above 600 MU/min. Methods. A retrospective study was performed on 25 patients treated using a Varian TrueBeam machine. The SBRT plans were made using RapidArc technique in Varian’s Eclipse. For 25 treatment plans we measured the dose using the Electronic Portal Imaging Dosimetry (EPID) and the diode detectors via Mapcheck. We also recorded the dose rate variance during the treatment delivery and the dose conformality index. We evaluated the biological effective dose (BED), normal tissue complications probability (NTCP) and tumor control probability (TCP). Results. For every treatment delivered the dose rate varies between 100 MU/min and the prescribed rate (600–1400 MU/min). The dosimetric measurements are correlating very well with the dose rate variance. There is also a correlation between the dose rate, the width of the treated fields and the arc’s size. The larger the field the higher the dose rate variance. We also noticed difficulties in passing the complex RapidArc QA measuring plans consistency with
185
the range of the dose rate variation. Biological effectiveness is also affected by the dose rate variance in a percentage between 0.75% and 2.73%. Conclusion. We found optimum dose rate for RapidArc with a value of 622 MU/min that allow a minimum dose rate variance of 36 MU/min during the treatment delivery and an optimum field size that in combination with the correct dose rate will generate plans that will deliver the calculated dose rate with a minimum variance and will not depend to the arc’s degrees range. https://doi.org/10.1016/j.ejmp.2018.06.568
[P295] Reliability of planning dose distribution for assessment of dose distribution in rectum for prostate cancer Anna Treter a, Paweł Franciszek Kukołowicz b,* a
Holycross Cancer Center, Medical Physics Department, Kielce, Poland Maria Skłodowska-Curie Memorial Cancer Center and Institute of Oncology, Kukolowicz, Warszaw, Poland ⇑ Corresponding author. b
Purpose. To assess the influence of changes of the rectum during radiotherapy on the dose distribution in rectum. Methods. For 9 patients computerized 3D/IMRT CT plans were prepared. Before each session of radiotherapy the actual CT performed with the CT on rails was made. Due to technical problems on some days the CT was not made. In total, they were made 213 CTs. The lacking CTs were generated with the bootstrap method. The contour of rectum were was delineated according to RTOG recommendations. Total dose of 78 Gy in 2 Gy fraction dose was delivered. The actual CT images were transferred to Pinnacle treatment planning system. After fusion (on prostate) of actual and planning CT the actual dose distribution for each fraction was calculated. Next cumulative DVH and DVH for planning and the planning and actual no 1, 1-2, 1-3 CTs were calculated. For each set of data the NTCP was calculated. The model proposed by Defraene (Red, 2012) was used. The cumulative, the planning and actual no 1, 1-2, 1-3 and the planning DVHs were compared. Also we compared the planning volume and the cumulative rectum volume and the NTCPs. Results. For some patients quite small changes of volume were observed, for some other quite large, e.g. the planning volume was 35.9 cm3, while cumulative one was 149.0 cm3. In 6 cases the cumulative NTCP was larger than the planning one. For two patients the differences were 0.11, 0.10 (NTCPcum-NTCPplan). For other patients the differences were smaller than ±0.05. Using the CTs made in the first few fractions enabled better estimation of the cumulative DVH but the improvements is not spectacular. Conclusions. The changes of the rectum volume and position for some patients may influence quite large on DVH in rectum and as a result of this on NTCP. It is not clear for which patients such large differences may be expected. https://doi.org/10.1016/j.ejmp.2018.06.569
[P296] Use of statistical interference for tolerance determination in dose measurements Irena Koniarova a,*, Lukas Kotik b a
National Radiation Protection Institute, Department of Radiotherapy and X-Ray Laboratory, Praha 4, Czech Republic b National Radiation Protection Institute, Radiation Risk Assessment Department, Praha 4, Czech Republic ⇑ Corresponding author.