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EP-1542: Can proton therapy for head and neck cancer reduce side effects while maintaining target robustness?
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markers during the treatment. These surrogates are used as an input parameter for a 4D motion model to predict CT volumes at arbitrary positions within the respiratory cycle. Daily CBCT images are used to calculate a baseline shift between the planning CT and the actual anatomy using deformable image registration. Treatment planning was done by the TPS Pinnacle³ v9.8 (Phillips Radiation Oncology Systems, Fitchburg, WI, USA). The motion model was used to estimate CT volumes in intervals of 100 ms that were imported into the TPS to calculate a partial delivered dose. The Vero system uses rotations of the LINAC head for DT, so the resulting images have to be rotated according to the pan/tilt motion since the TPS is not able to model a non-axial beam line. The partial doses were back-rotated and superposed resulting in the actually delivered 4D dose distribution. In addition, 4D dose-volume-histograms (DVH) were calculated by warping the reference contours onto every respiratory phase using the motion model. The resulting 4D dose distributions were evaluated and compared to phantom measurements using the ArcCheck (Sun Nuclear, Melbourne, FL, USA) in combination with a motion platform jointly developed with QRM, Möhrendorf, Germany. Results The accuracy of the motion model was validated for 20 patients with a geometrical uncertainty of < 3 mm. Dose comparison of the estimated volumes to clinical groundtruth CTs resulted in a pass rate above 98.9% for a γcriterion of 2% / 2 mm. 4D dose distributions could be reconstructed and were in good agreement to phantom measurements. The actually delivered dose for two liver patients was recalculated and additional patients are currently ongoing. Conclusion The presented approach is feasible to reconstruct 4D dose distributions for DT patients using a common TPS together with the presented motion model. External surrogates to calculate the breathing state are essential as well as daily CBCT or kV images to correct for baseline shifts.
index and normalised to CTV70 D98%. Four beams were used in an ‘x’ arrangement and a 4 cm range shifter was used where appropriate.The PTV was defined as 5 mm geometric expansion to CTV, identical to current photon plans in our clinic (VMAT). Robust optimisation settings were 5 mm isotropically and ±3% HU uncertainty. For each plan, robust evaluation was performed for a combination of ±5 mm translational, ±2⁰ rotational and ±3% HU errors (>50 scenarios per plan). The error scenario with the lowest target coverage (V95% to CTV70) is deemed the ‘worst-case’ scenario. Organ at risk (OAR) doses and NTCP values of the nominal proton plans and the clinical VMAT plan were compared. Results Robust evaluation showed CTV70 target coverage degraded significantly for PTV based plans, particularly using MFO (-15%) but also for SFO (-5.4%). Robustly optimised plans performed much better, particularly CTVMFO (-1.7%) which comes very close to matching the robustness of the clinical VMAT plan (-1.2%) (figure 1). CTV-SFO under-performed due to the beam arrangement and the high weighting on OAR dose reduction. OAR doses were significantly better in MFO plans, as this gave the optimiser the most freedom in per–beam dose distribution. In particular, CTV-MFO plans had the lowest OAR doses of all proton and photon plans. NTCP model calculations show that, compared to our clinical VMAT plans, reductions across all patients for xerostomia (5.9%), dysphagia (-7.0%) and tube feeding (-4.7%) can be expected, but these values varied widely among different tumour sites, stages and individual patients (table 1).
EP-1542 Can proton therapy for head and neck cancer reduce side effects while maintaining target robustness? D. Scandurra1, R.G.J. Kierkels1, M. Gelderman1, H.M. Credoe1, H.P. Bijl1, R.J.H.M. Steenbakkers1, J.G.M. Vemer - van de Hoek1, J.A. Langendijk1 1 University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands Purpose or Objective Head and neck cancer generally consists of targets requiring high doses of radiation in close proximity to vital healthy organs. Proton therapy leads to a reduction of integral dose and therefore can reduce normal tissue complication probabilities (NTCP). The proton range, however, depends on the material along its path and is therefore susceptible to uncertainties, potentially degrading target coverage. These uncertainties can be partially accounted for by conventional target margins (PTV) or robust-optimisation approaches. In this in-silico study, four variations of pencil beam scanning (PBS) proton therapy plans were designed for each patient and compared to the clinical photon plan in terms of robustness and NTCP reduction. Material and Methods Four PBS plans were made for each patient using RayStation (v4.99 RaySearch Laboratories AB, Sweden): 1) PTV based, multi-field optimisation (PTV-MFO), 2) PTV based, single field optimisation (PTV-SFO), 3) CTV robustly optimised MFO (CTV-MFO), and 4) CTV robustly optimised SFO (CTV-SFO). Each plan was designed to a similar target homogeneity
Conclusion Compared to photon VMAT plans, robustly optimised PBS proton therapy plans reduce OAR doses in head and neck cancer while maintaining a high degree of target coverage robustness. NTCP calculations show a clinical benefit can be expected for a significant proportion of patients. EP-1543 Dominant intraprostatic lesions boosting: comparison of tomotherapy, VMAT and IMPT P. Andrzejewski1, A. Jodda2, P. Kuess1, D. Georg1, J. Malicki3, T. Piotrowski3
markers during the treatment. These surrogates are used as an input parameter for a 4D motion model to predict CT volumes at arbitrary positions within the respiratory cycle. Daily CBCT images are used to calculate a baseline shift between the planning CT and the actual anatomy using deformable image registration. Treatment planning was done by the TPS Pinnacle³ v9.8 (Phillips Radiation Oncology Systems, Fitchburg, WI, USA). The motion model was used to estimate CT volumes in intervals of 100 ms that were imported into the TPS to calculate a partial delivered dose. The Vero system uses rotations of the LINAC head for DT, so the resulting images have to be rotated according to the pan/tilt motion since the TPS is not able to model a non-axial beam line. The partial doses were back-rotated and superposed resulting in the actually delivered 4D dose distribution. In addition, 4D dose-volume-histograms (DVH) were calculated by warping the reference contours onto every respiratory phase using the motion model. The resulting 4D dose distributions were evaluated and compared to phantom measurements using the ArcCheck (Sun Nuclear, Melbourne, FL, USA) in combination with a motion platform jointly developed with QRM, Möhrendorf, Germany. Results The accuracy of the motion model was validated for 20 patients with a geometrical uncertainty of < 3 mm. Dose comparison of the estimated volumes to clinical groundtruth CTs resulted in a pass rate above 98.9% for a γcriterion of 2% / 2 mm. 4D dose distributions could be reconstructed and were in good agreement to phantom measurements. The actually delivered dose for two liver patients was recalculated and additional patients are currently ongoing. Conclusion The presented approach is feasible to reconstruct 4D dose distributions for DT patients using a common TPS together with the presented motion model. External surrogates to calculate the breathing state are essential as well as daily CBCT or kV images to correct for baseline shifts.
index and normalised to CTV70 D98%. Four beams were used in an ‘x’ arrangement and a 4 cm range shifter was used where appropriate.The PTV was defined as 5 mm geometric expansion to CTV, identical to current photon plans in our clinic (VMAT). Robust optimisation settings were 5 mm isotropically and ±3% HU uncertainty. For each plan, robust evaluation was performed for a combination of ±5 mm translational, ±2⁰ rotational and ±3% HU errors (>50 scenarios per plan). The error scenario with the lowest target coverage (V95% to CTV70) is deemed the ‘worst-case’ scenario. Organ at risk (OAR) doses and NTCP values of the nominal proton plans and the clinical VMAT plan were compared. Results Robust evaluation showed CTV70 target coverage degraded significantly for PTV based plans, particularly using MFO (-15%) but also for SFO (-5.4%). Robustly optimised plans performed much better, particularly CTVMFO (-1.7%) which comes very close to matching the robustness of the clinical VMAT plan (-1.2%) (figure 1). CTV-SFO under-performed due to the beam arrangement and the high weighting on OAR dose reduction. OAR doses were significantly better in MFO plans, as this gave the optimiser the most freedom in per–beam dose distribution. In particular, CTV-MFO plans had the lowest OAR doses of all proton and photon plans. NTCP model calculations show that, compared to our clinical VMAT plans, reductions across all patients for xerostomia (5.9%), dysphagia (-7.0%) and tube feeding (-4.7%) can be expected, but these values varied widely among different tumour sites, stages and individual patients (table 1).
EP-1542 Can proton therapy for head and neck cancer reduce side effects while maintaining target robustness? D. Scandurra1, R.G.J. Kierkels1, M. Gelderman1, H.M. Credoe1, H.P. Bijl1, R.J.H.M. Steenbakkers1, J.G.M. Vemer - van de Hoek1, J.A. Langendijk1 1 University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands Purpose or Objective Head and neck cancer generally consists of targets requiring high doses of radiation in close proximity to vital healthy organs. Proton therapy leads to a reduction of integral dose and therefore can reduce normal tissue complication probabilities (NTCP). The proton range, however, depends on the material along its path and is therefore susceptible to uncertainties, potentially degrading target coverage. These uncertainties can be partially accounted for by conventional target margins (PTV) or robust-optimisation approaches. In this in-silico study, four variations of pencil beam scanning (PBS) proton therapy plans were designed for each patient and compared to the clinical photon plan in terms of robustness and NTCP reduction. Material and Methods Four PBS plans were made for each patient using RayStation (v4.99 RaySearch Laboratories AB, Sweden): 1) PTV based, multi-field optimisation (PTV-MFO), 2) PTV based, single field optimisation (PTV-SFO), 3) CTV robustly optimised MFO (CTV-MFO), and 4) CTV robustly optimised SFO (CTV-SFO). Each plan was designed to a similar target homogeneity
Conclusion Compared to photon VMAT plans, robustly optimised PBS proton therapy plans reduce OAR doses in head and neck cancer while maintaining a high degree of target coverage robustness. NTCP calculations show a clinical benefit can be expected for a significant proportion of patients. EP-1543 Dominant intraprostatic lesions boosting: comparison of tomotherapy, VMAT and IMPT P. Andrzejewski1, A. Jodda2, P. Kuess1, D. Georg1, J. Malicki3, T. Piotrowski3