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Image-guided radiotherapy: Is it necessary to adapt?
Abstracts of the SFPM Annual Meeting 2013 / Physica Medica 29 (2013) e1–e46
Used in clinical routine, those new imaging protocols have contributed to define a new patient management in the radiotherapy service (IGRT) of the Institut Paoli-Calmettes. http://dx.doi.org/10.1016/j.ejmp.2013.08.009
7 IMAGE-GUIDED RADIOTHERAPY: IS IT NECESSARY TO ADAPT? S. Yartsev. London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada Introduction: Image guidance usage is growing in clinical practice of radiation therapy aiming to make the necessary corrections in the treatment plan in order to compensate for changes in patient’s anatomy. In theory, these changes should improve the treatment, but any modifications of the initial plan require additional time, resources and more QA procedures. Materials and methods: Several examples of typical patients with head and neck, prostate, and lung cancer were analyzed by simulations of different scenarios of adaptive radiotherapy. Daily MVCT images were used to construct hybrid MV/kV images using the Planned Adaptive software of TomoTherapy Inc. (Madison, WI). Initial planning contours were modified in the hybrid images in order to take into account anatomical changes of the target and organs of risk. Results: Calculations of dose-volume histograms for the adapted structures were used for evaluation of the changes significance. A decision to re-plan is taken by the treating physician based on the extent of the anatomical changes with respect to initial anatomy. Adapted plans were prepared for different moments during treatment course. Conclusion: Dose summations for the tumours and main organs at risk were used for evaluation of the plan quality. Action level for a re-planning is proposed. http://dx.doi.org/10.1016/j.ejmp.2013.08.010
8 PHANTOM BASED KV-CBCT DOSE PLAN CALCULATIONS FOR RE-PLANNING DECISION: COMPARISON WITH CT-BASED DOSE PLANS A. Dubouloz, P. Nouet, G. Dipasquale, M. Rouzaud. Radiation Oncology, Geneva University Hospitals, Switzerland Objective: Kilovoltage cone-beam computed tomography scans (kVCBCT) are helpful for patients positioning and viewing anatomical changes. This study investigates, on an anthropomorphic phantom, with no movement and anatomical changes, the possibility and accuracy of using CBCT-based dosimetry for re-planning decision. Materials and method: Rando phantom’s brain, Head and Neck (H&N), thorax and pelvis were scanned. Targets and main organ at risks (OAR) were contoured. IMRT was used for H&N and VMAT for brain, lung and pelvis. Dose distributions were calculated using Eclipse 10.0 AAA Algorithm (Varian Medical System). CBCT scans were acquired per region on a Novalis Tx. After registration with the reference CT, structures were copied and dosimetric plans were recalculated on the CBCT. The dose volume histograms (HVH) for targets and OAR and 2D dose maps were compared. Furthermore the Hounsfield units to electron density (HU to ED) curves for the different CBCT protocols were obtained using a CatphanÒ 504 phantom. To end examples of patients with anatomical changes are presented. Results: PTV and OAR average mean dose differences for the brain, H&N, lungs and pelvic region were 1.1 ± 0.7%, 0.6 ± 0.4%,
e3
0.9 ± 1.0% and 0.1 ± 0.5% respectively. Passing rate superior than 98% was achieved (gamma index criteria of 2%/1 mm) for absolute 2D CBCT and CT-based dose distributions. CBCT HU to ED curves were within ±30 HU compared with the reference HU of the materials contained inside phantom, amply inside requested CT tolerance values. Conclusion: Decision to re-plan VMAT or IMRT treatments seems feasible using CBCT data. Future investigations on the HU to ED curve and curve stability will be done with the help of a CBCT electron density phantom (CIRS). http://dx.doi.org/10.1016/j.ejmp.2013.08.011
9 EVALUATION OF AN ULTRASOUND-BASED IMAGING SYSTEM FOR PELVIC CANCER LOCALIZATION IN RADIOTHERAPY M. Fargier-Voiron, B. Presles, A. Munoz, J. Debeaux, S. Rit, D. Sarrut, M.-C. Biston. CREATIS, Lyon, France Purpose: Improvement of prostate cancer treatment in radiotherapy requires reliable, non-invasive and if possible non-irradiating modalities to correct target position before each irradiation session. The goal of this study is to evaluate an ultrasound-based (US) verification system for prostate alignment (CLARITY-ELEKTA). Contrary to other systems based on a cross-modality registration (between reference CT and treatment US images), this system proposes an intra-modality registration that could potentially improve the inter-sessions repositioning quality [1]. Methods and materials: 14 patients with primary prostate cancer (P) and 9 patients with prostatectomy (post-P) were included in the first study. For each patient, a US image (US-ref) was acquired during the CT (CT-ref) stage. During the treatment session, a US image (US-T) was acquired just before performing a cone-beam computed tomography (CBCT). The shifts obtained with a US-ref/US-T registration were compared to those obtained with a CT-ref/CBCT registration. In the second study, 14 volunteers underwent three successive US acquisitions with increasing pressure in order to evaluate the impact of probe pressure on prostate localization with the Clarity system. Results: For the first study, the average registration differences between US-ref/US-T and CT-ref/CBCT were 2.8 ± 4.1 mm, 1.9 ± 5.8 mm and 3.5 ± 3.8 mm for the P group, and of 0.3 ± 4.4 mm, 2.9 ± 7.5 mm and 1.6 ± 6.7 mm for the post-P group in lateral, superior–inferior and anterior-posterior directions, respectively. The second study showed that probe pressure can imply a prostate displacement up to 4 mm. Conclusion: The first study pointed out significant standard deviations discrepancies between these two registration methods. However, both techniques have uncertainties. Soft tissue registration with CBCT imaging modality is not a ground truth, which needs to be considered in the analysis of the results[2,3]. Moreover, as highlighted with the second study, probe pressure can affect prostate localization and therefore can be one of uncertainty sources of US modality. Further studies are in progress to evaluate uncertainties of these two modalities in order to use this US system in clinical routine. References [1] Cury 2006, IJROBP. [2] Moseley 2007, IJROBP. [3] Barney 2011, IJROBP. http://dx.doi.org/10.1016/j.ejmp.2013.08.012
Used in clinical routine, those new imaging protocols have contributed to define a new patient management in the radiotherapy service (IGRT) of the Institut Paoli-Calmettes. http://dx.doi.org/10.1016/j.ejmp.2013.08.009
7 IMAGE-GUIDED RADIOTHERAPY: IS IT NECESSARY TO ADAPT? S. Yartsev. London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada Introduction: Image guidance usage is growing in clinical practice of radiation therapy aiming to make the necessary corrections in the treatment plan in order to compensate for changes in patient’s anatomy. In theory, these changes should improve the treatment, but any modifications of the initial plan require additional time, resources and more QA procedures. Materials and methods: Several examples of typical patients with head and neck, prostate, and lung cancer were analyzed by simulations of different scenarios of adaptive radiotherapy. Daily MVCT images were used to construct hybrid MV/kV images using the Planned Adaptive software of TomoTherapy Inc. (Madison, WI). Initial planning contours were modified in the hybrid images in order to take into account anatomical changes of the target and organs of risk. Results: Calculations of dose-volume histograms for the adapted structures were used for evaluation of the changes significance. A decision to re-plan is taken by the treating physician based on the extent of the anatomical changes with respect to initial anatomy. Adapted plans were prepared for different moments during treatment course. Conclusion: Dose summations for the tumours and main organs at risk were used for evaluation of the plan quality. Action level for a re-planning is proposed. http://dx.doi.org/10.1016/j.ejmp.2013.08.010
8 PHANTOM BASED KV-CBCT DOSE PLAN CALCULATIONS FOR RE-PLANNING DECISION: COMPARISON WITH CT-BASED DOSE PLANS A. Dubouloz, P. Nouet, G. Dipasquale, M. Rouzaud. Radiation Oncology, Geneva University Hospitals, Switzerland Objective: Kilovoltage cone-beam computed tomography scans (kVCBCT) are helpful for patients positioning and viewing anatomical changes. This study investigates, on an anthropomorphic phantom, with no movement and anatomical changes, the possibility and accuracy of using CBCT-based dosimetry for re-planning decision. Materials and method: Rando phantom’s brain, Head and Neck (H&N), thorax and pelvis were scanned. Targets and main organ at risks (OAR) were contoured. IMRT was used for H&N and VMAT for brain, lung and pelvis. Dose distributions were calculated using Eclipse 10.0 AAA Algorithm (Varian Medical System). CBCT scans were acquired per region on a Novalis Tx. After registration with the reference CT, structures were copied and dosimetric plans were recalculated on the CBCT. The dose volume histograms (HVH) for targets and OAR and 2D dose maps were compared. Furthermore the Hounsfield units to electron density (HU to ED) curves for the different CBCT protocols were obtained using a CatphanÒ 504 phantom. To end examples of patients with anatomical changes are presented. Results: PTV and OAR average mean dose differences for the brain, H&N, lungs and pelvic region were 1.1 ± 0.7%, 0.6 ± 0.4%,
e3
0.9 ± 1.0% and 0.1 ± 0.5% respectively. Passing rate superior than 98% was achieved (gamma index criteria of 2%/1 mm) for absolute 2D CBCT and CT-based dose distributions. CBCT HU to ED curves were within ±30 HU compared with the reference HU of the materials contained inside phantom, amply inside requested CT tolerance values. Conclusion: Decision to re-plan VMAT or IMRT treatments seems feasible using CBCT data. Future investigations on the HU to ED curve and curve stability will be done with the help of a CBCT electron density phantom (CIRS). http://dx.doi.org/10.1016/j.ejmp.2013.08.011
9 EVALUATION OF AN ULTRASOUND-BASED IMAGING SYSTEM FOR PELVIC CANCER LOCALIZATION IN RADIOTHERAPY M. Fargier-Voiron, B. Presles, A. Munoz, J. Debeaux, S. Rit, D. Sarrut, M.-C. Biston. CREATIS, Lyon, France Purpose: Improvement of prostate cancer treatment in radiotherapy requires reliable, non-invasive and if possible non-irradiating modalities to correct target position before each irradiation session. The goal of this study is to evaluate an ultrasound-based (US) verification system for prostate alignment (CLARITY-ELEKTA). Contrary to other systems based on a cross-modality registration (between reference CT and treatment US images), this system proposes an intra-modality registration that could potentially improve the inter-sessions repositioning quality [1]. Methods and materials: 14 patients with primary prostate cancer (P) and 9 patients with prostatectomy (post-P) were included in the first study. For each patient, a US image (US-ref) was acquired during the CT (CT-ref) stage. During the treatment session, a US image (US-T) was acquired just before performing a cone-beam computed tomography (CBCT). The shifts obtained with a US-ref/US-T registration were compared to those obtained with a CT-ref/CBCT registration. In the second study, 14 volunteers underwent three successive US acquisitions with increasing pressure in order to evaluate the impact of probe pressure on prostate localization with the Clarity system. Results: For the first study, the average registration differences between US-ref/US-T and CT-ref/CBCT were 2.8 ± 4.1 mm, 1.9 ± 5.8 mm and 3.5 ± 3.8 mm for the P group, and of 0.3 ± 4.4 mm, 2.9 ± 7.5 mm and 1.6 ± 6.7 mm for the post-P group in lateral, superior–inferior and anterior-posterior directions, respectively. The second study showed that probe pressure can imply a prostate displacement up to 4 mm. Conclusion: The first study pointed out significant standard deviations discrepancies between these two registration methods. However, both techniques have uncertainties. Soft tissue registration with CBCT imaging modality is not a ground truth, which needs to be considered in the analysis of the results[2,3]. Moreover, as highlighted with the second study, probe pressure can affect prostate localization and therefore can be one of uncertainty sources of US modality. Further studies are in progress to evaluate uncertainties of these two modalities in order to use this US system in clinical routine. References [1] Cury 2006, IJROBP. [2] Moseley 2007, IJROBP. [3] Barney 2011, IJROBP. http://dx.doi.org/10.1016/j.ejmp.2013.08.012