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EP-1559 IS THERE A BEST PRACTISE USING INDICES IN THE PROCESS OF TREATMENT PLANNING?
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EP-1557 RADIOTHERAPY OF SOFT-TISSUE SARCOMA OF LOWER EXTREMITY WITH HIGH BONE SPARING WITH RAPIDARC AND PROTONS A. Fogliata1, M. Scorsetti2, P. Navarria2, M. Catalano2, A. Clivio1, F. Lobefalo2, C. Pellegrini2, F. Alongi2, S. Pentimalli2, P. Mancosu2 1 Oncology Institute of Southern Switzerland, Medical Physics, Bellinzona, Switzerland 2 Istituto Clinico Humanitas, Radio-Oncology, Rozzano-Milan, Italy Purpose/Objective: To investigate the advanced radiotherapy treatments of soft-tissue sarcoma with adequate target coverage and bone high sparing with volumetric modulated arc therapy (RapidArc) and proton beams. Materials and Methods: Ten patients presenting soft tissue sarcoma of the leg, and treated with RapidArc in author’s institutions were collected for the study. Dose was prescribed to 66.5 Gy in 25 fractions to mean planning target volume (PTV), and significant maximum dose to the bone was limited to 50 Gy. Plans were prepared using RapidArc with flattened 6 MV (6X) and unflattened 10 MV (10FFF) photon beams from a Varian TrueBeam facility, and using proton beams up to 250 MeV. RapidArc photon plans were computed with AAA and Acuros XB in the two options of dose to medium and dose to water. Proton plans were prepared using intensity modulated spot scanned proton beams. Plan evaluation was assessed by dose volume histogram analysis, comparing different dose distributions and different dose calculation algorithms (and dose to medium or to water option). Results: All plans acceptably met the criteria of target coverage (V95%>90-95%) and bone sparing (D1cm3<50 Gy). Better coverage was shown for proton plans with respect to 6X RapidArc photon plans, at 95% of the prescription dose (V95% about 5% higher for protons, p<0.05). Dose was more homogeneously distributed in the proton cases: Standard Deviation 2.3Gy for protons, 3.0-3.3Gy for photons, p<0.05. A small difference tending to be significant was found between 6X and 10FFF plans, in favor of using flattened beams. Bone significant maximum dose objective of 50Gy was met in all cases, photon RapidArc and protons, with no significant differences. The largest difference between proton and photon plans in Bone tissue is reflected in the medium/low doses. Similar results were found for surrounding normal tissue. For Healthy Tissue, the low dose bath is minimized with protons, where the Dose Integral is about halved with respect to all photon plans. Interesting result is the significant (p<<0.01) lower Dose Integral when FFF photon beams are used in place of more conventional flattened beams. Dose to water calculations resulted in bone doses of about 5% higher than for dose to medium calculations. A deep understanding of the two calculation options would lead the user to properly choose between the two modalities of dose to water, or the dose to medium (that better reflects the physical dose to the specific tissue). Conclusions: A substantial equivalence between RapidArc technique for photon beams and proton plans for the management of soft-tissue sarcoma of the lower extremity was here presented, yielding good target coverage to 66.5 Gy prescription, while keeping the maximum significant dose to the bone below the 50 Gy minimizing the risk of bone fractures. EP-1558 CHEST WALL RADIOTHERAPY WITH VOLUMETRIC MODULATED ARCS AND THE POTENTIAL ROLE OF FLATTENING FILTER FREE PHOTON BEAMS L. Cozzi1, S. Subramanian2, S. Thirumalaiswamy2, S. Chilukuri2, A. Gandhi2, M. Babaiah2, A. Clivio1, E. Vanetti1, G. Nicolini1, A. Fogliata1 1 IOSI, Medical Physics, Bellinzona, Switzerland; 2 Yashoda Super Speciality Hospital, Radiation oncology, Hyderabad, India Purpose/Objective: To assess the role RapidArc treatments in chest wall irradiation after mastectomy and the potential benefit of flattening filter free beams. Materials and Methods: Planning CTs of 10 women after mastectomy and requiring chest wall radiotherapy were included in the study. A dose of 50 Gy in 2 Gy fractions was prescribed. Organs at risk (OAR) were: heart, lungs, contralateral breast, spinal cord. Dose-volume metrics were defined to quantify the quality of concurrent treatment plans assessing target coverage and sparing of OAR. Plans were designed for conformal 3D therapy (3DCRT) or for RapidArc with double partial arcs (RA). RapidArc plans were optimized for both conventional beams as well as for unflattened beams (RA_FFF). The goal for this planning effort was to cover 100% of the PTV with ≥ 90% of the prescribed dose and to minimize the volume inside the PTV
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receiving >105% of the dose. Mean ipsilateral lung dose was required to be lower than 15 Gy and V20Gy Results: All techniques basically met planning objectives for PTV and for lung (3DCRT marginally failed for V20Gy). RA plans showed a net superiority compared to 3DCRT in the medium to high dose region of the lungs. Heart irradiation was minimized by RA_FFF plans with ~4.5Gy and ~15Gy reduction in maximum dose compared to RA or 3DCRT. RA_FFF resulted superior to RA in protecting contralateral breast and lung with a further reduction of ~1.7Gy and 1.0Gy in the respective mean doses. Conclusions: RapidArc resulted to provide acceptable plan quality with superior ipsilateral tissue sparing compared to traditional techniques. Flattening filter free beams, recently made available for clinical use, might provide further healthy tissue sparing, particularly in contralateral organs, suggesting their applicability also for large targets. EP-1559 IS THERE A BEST PRACTISE USING INDICES IN THE PROCESS OF TREATMENT PLANNING ? U. Haverkamp1, M. Löbbel2, A. Miller3, D. Norkus3, B. Prümer4, H. Eich1 1 University Münster, Department of Radiotherapy, Münster, Germany 2 Clemens Hospital, Department of Radiology and Radiotherapy, Münster, Germany 3 Vilnius University, Oncology Institute, Münster, Lithuania 4 Herz-Jesu-Krankenhaus, Radiology, Münster, Germany Purpose/Objective: Physical treatment planning provides a pool of data describing dose distributions. In order to enable quicker evaluation, it is often useful to define specific parameters like conformal and homogeneity indices. The approach in this study was to check the indices’ sensitivity, to evaluate mean values and ranges and to find best practice using indices in the clinical routine. Materials and Methods: 21 indices were tested, based on PTV, TV, partial volume of the PTV enclosed by the prescribed isodose, H2, H98 and Dmean. 154 patients were involved, treated with external beam radiation (3DCRT, radiosurgery, tomotherapy, RapidArc, Vmat). The data were analyzed according to treatment modality and tumor entity. The planning procedure followed ICRU-Reports 50 and 83. Additionally, the indices were analyzed in extreme situations (small coverage of the PTV, TV inside PTV, TV outside PTV) in order to evaluate the sensitivity. Results: As expected the 3CDRT and radiosurgery (RS) showed the lowest mean values and largest ranges, the best results can be seen in IMRT, dynamic IMRT and Tomotherapy (e.g. CN; RS: 0.60, 3DCRT: 0.64, IMRT: 0.81, dyn.IMRT: 0.9, TOMO: 0.86). Except in 3DCRT and RS typical ranges can be defined. For the group of IMRT techniques the results are influenced by the tumor entity rather than by the modality. The sensitivity check shows positive, false positive, and negative, but no false negative results. Different combinations of indices were tested to find two indices, whose common completion of given specifications indicates a satisfactory conformation. We found Cdelta and HI as recommendable. Conclusions: A conformal index should indicate underdosages within the PTV and overdosages within the normal tissue. But not all indices reflect the situation in a correct way. This study recommends typical ranges and a favourable combination of a conformity and homogeneity index, e.g. Cdelta and HI as best practise. EP-1560 DOSIMETRIC ANALYSIS OF THE BRACHIAL PLEXUS USING MONTE CARLO BASED IMRT FOR HEAD AND NECK CANCER J.J. Lee1, M. Lei1, S. Connor1, A. Siddiqui1, R. Lynn1, D. Convery1, T. Guerrero Urbano1 1 Guy's and St. Thomas' NHS Foundation Trust, Oncology, London, United Kingdom Purpose/Objective: To evaluate the radiation doses received by the brachial plexus (BP) during radical image-guided intensity-modulated radiation therapy (IG-IMRT) in head and neck cancer (HNC) treatment and assess the association between radiation dose delivered to different neck node levels and maximum BP dose. Materials and Methods: Anonymised datasets for twenty patients who had completed radical IG-IMRT for HNC were identified retrospectively. Right and left BPs were retrospectively contoured for each patient by the same observer and reviewed by two specialist HN radiologists using a modified version of the Radiation Therapy Oncology Group (RTOG)-endorsed atlas (in our protocol BP visible but lying outside the scalene muscles was included). BP were labeled as
EP-1557 RADIOTHERAPY OF SOFT-TISSUE SARCOMA OF LOWER EXTREMITY WITH HIGH BONE SPARING WITH RAPIDARC AND PROTONS A. Fogliata1, M. Scorsetti2, P. Navarria2, M. Catalano2, A. Clivio1, F. Lobefalo2, C. Pellegrini2, F. Alongi2, S. Pentimalli2, P. Mancosu2 1 Oncology Institute of Southern Switzerland, Medical Physics, Bellinzona, Switzerland 2 Istituto Clinico Humanitas, Radio-Oncology, Rozzano-Milan, Italy Purpose/Objective: To investigate the advanced radiotherapy treatments of soft-tissue sarcoma with adequate target coverage and bone high sparing with volumetric modulated arc therapy (RapidArc) and proton beams. Materials and Methods: Ten patients presenting soft tissue sarcoma of the leg, and treated with RapidArc in author’s institutions were collected for the study. Dose was prescribed to 66.5 Gy in 25 fractions to mean planning target volume (PTV), and significant maximum dose to the bone was limited to 50 Gy. Plans were prepared using RapidArc with flattened 6 MV (6X) and unflattened 10 MV (10FFF) photon beams from a Varian TrueBeam facility, and using proton beams up to 250 MeV. RapidArc photon plans were computed with AAA and Acuros XB in the two options of dose to medium and dose to water. Proton plans were prepared using intensity modulated spot scanned proton beams. Plan evaluation was assessed by dose volume histogram analysis, comparing different dose distributions and different dose calculation algorithms (and dose to medium or to water option). Results: All plans acceptably met the criteria of target coverage (V95%>90-95%) and bone sparing (D1cm3<50 Gy). Better coverage was shown for proton plans with respect to 6X RapidArc photon plans, at 95% of the prescription dose (V95% about 5% higher for protons, p<0.05). Dose was more homogeneously distributed in the proton cases: Standard Deviation 2.3Gy for protons, 3.0-3.3Gy for photons, p<0.05. A small difference tending to be significant was found between 6X and 10FFF plans, in favor of using flattened beams. Bone significant maximum dose objective of 50Gy was met in all cases, photon RapidArc and protons, with no significant differences. The largest difference between proton and photon plans in Bone tissue is reflected in the medium/low doses. Similar results were found for surrounding normal tissue. For Healthy Tissue, the low dose bath is minimized with protons, where the Dose Integral is about halved with respect to all photon plans. Interesting result is the significant (p<<0.01) lower Dose Integral when FFF photon beams are used in place of more conventional flattened beams. Dose to water calculations resulted in bone doses of about 5% higher than for dose to medium calculations. A deep understanding of the two calculation options would lead the user to properly choose between the two modalities of dose to water, or the dose to medium (that better reflects the physical dose to the specific tissue). Conclusions: A substantial equivalence between RapidArc technique for photon beams and proton plans for the management of soft-tissue sarcoma of the lower extremity was here presented, yielding good target coverage to 66.5 Gy prescription, while keeping the maximum significant dose to the bone below the 50 Gy minimizing the risk of bone fractures. EP-1558 CHEST WALL RADIOTHERAPY WITH VOLUMETRIC MODULATED ARCS AND THE POTENTIAL ROLE OF FLATTENING FILTER FREE PHOTON BEAMS L. Cozzi1, S. Subramanian2, S. Thirumalaiswamy2, S. Chilukuri2, A. Gandhi2, M. Babaiah2, A. Clivio1, E. Vanetti1, G. Nicolini1, A. Fogliata1 1 IOSI, Medical Physics, Bellinzona, Switzerland; 2 Yashoda Super Speciality Hospital, Radiation oncology, Hyderabad, India Purpose/Objective: To assess the role RapidArc treatments in chest wall irradiation after mastectomy and the potential benefit of flattening filter free beams. Materials and Methods: Planning CTs of 10 women after mastectomy and requiring chest wall radiotherapy were included in the study. A dose of 50 Gy in 2 Gy fractions was prescribed. Organs at risk (OAR) were: heart, lungs, contralateral breast, spinal cord. Dose-volume metrics were defined to quantify the quality of concurrent treatment plans assessing target coverage and sparing of OAR. Plans were designed for conformal 3D therapy (3DCRT) or for RapidArc with double partial arcs (RA). RapidArc plans were optimized for both conventional beams as well as for unflattened beams (RA_FFF). The goal for this planning effort was to cover 100% of the PTV with ≥ 90% of the prescribed dose and to minimize the volume inside the PTV
ESTRO 31
receiving >105% of the dose. Mean ipsilateral lung dose was required to be lower than 15 Gy and V20Gy Results: All techniques basically met planning objectives for PTV and for lung (3DCRT marginally failed for V20Gy). RA plans showed a net superiority compared to 3DCRT in the medium to high dose region of the lungs. Heart irradiation was minimized by RA_FFF plans with ~4.5Gy and ~15Gy reduction in maximum dose compared to RA or 3DCRT. RA_FFF resulted superior to RA in protecting contralateral breast and lung with a further reduction of ~1.7Gy and 1.0Gy in the respective mean doses. Conclusions: RapidArc resulted to provide acceptable plan quality with superior ipsilateral tissue sparing compared to traditional techniques. Flattening filter free beams, recently made available for clinical use, might provide further healthy tissue sparing, particularly in contralateral organs, suggesting their applicability also for large targets. EP-1559 IS THERE A BEST PRACTISE USING INDICES IN THE PROCESS OF TREATMENT PLANNING ? U. Haverkamp1, M. Löbbel2, A. Miller3, D. Norkus3, B. Prümer4, H. Eich1 1 University Münster, Department of Radiotherapy, Münster, Germany 2 Clemens Hospital, Department of Radiology and Radiotherapy, Münster, Germany 3 Vilnius University, Oncology Institute, Münster, Lithuania 4 Herz-Jesu-Krankenhaus, Radiology, Münster, Germany Purpose/Objective: Physical treatment planning provides a pool of data describing dose distributions. In order to enable quicker evaluation, it is often useful to define specific parameters like conformal and homogeneity indices. The approach in this study was to check the indices’ sensitivity, to evaluate mean values and ranges and to find best practice using indices in the clinical routine. Materials and Methods: 21 indices were tested, based on PTV, TV, partial volume of the PTV enclosed by the prescribed isodose, H2, H98 and Dmean. 154 patients were involved, treated with external beam radiation (3DCRT, radiosurgery, tomotherapy, RapidArc, Vmat). The data were analyzed according to treatment modality and tumor entity. The planning procedure followed ICRU-Reports 50 and 83. Additionally, the indices were analyzed in extreme situations (small coverage of the PTV, TV inside PTV, TV outside PTV) in order to evaluate the sensitivity. Results: As expected the 3CDRT and radiosurgery (RS) showed the lowest mean values and largest ranges, the best results can be seen in IMRT, dynamic IMRT and Tomotherapy (e.g. CN; RS: 0.60, 3DCRT: 0.64, IMRT: 0.81, dyn.IMRT: 0.9, TOMO: 0.86). Except in 3DCRT and RS typical ranges can be defined. For the group of IMRT techniques the results are influenced by the tumor entity rather than by the modality. The sensitivity check shows positive, false positive, and negative, but no false negative results. Different combinations of indices were tested to find two indices, whose common completion of given specifications indicates a satisfactory conformation. We found Cdelta and HI as recommendable. Conclusions: A conformal index should indicate underdosages within the PTV and overdosages within the normal tissue. But not all indices reflect the situation in a correct way. This study recommends typical ranges and a favourable combination of a conformity and homogeneity index, e.g. Cdelta and HI as best practise. EP-1560 DOSIMETRIC ANALYSIS OF THE BRACHIAL PLEXUS USING MONTE CARLO BASED IMRT FOR HEAD AND NECK CANCER J.J. Lee1, M. Lei1, S. Connor1, A. Siddiqui1, R. Lynn1, D. Convery1, T. Guerrero Urbano1 1 Guy's and St. Thomas' NHS Foundation Trust, Oncology, London, United Kingdom Purpose/Objective: To evaluate the radiation doses received by the brachial plexus (BP) during radical image-guided intensity-modulated radiation therapy (IG-IMRT) in head and neck cancer (HNC) treatment and assess the association between radiation dose delivered to different neck node levels and maximum BP dose. Materials and Methods: Anonymised datasets for twenty patients who had completed radical IG-IMRT for HNC were identified retrospectively. Right and left BPs were retrospectively contoured for each patient by the same observer and reviewed by two specialist HN radiologists using a modified version of the Radiation Therapy Oncology Group (RTOG)-endorsed atlas (in our protocol BP visible but lying outside the scalene muscles was included). BP were labeled as