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EP-1871: Image guided radiotherapy using daily vs weekly cone beam CT for intensity modulated radiotherapy of head and neck
ESTRO 33, 2014 Conclusions: The significant difference in the field size, minimality of errors in positioning, decrease in the number of radiation reactions and time of their occurrence admits the use of the PTV margin ≤ 1 cm. EP-1871 Image guided radiotherapy using daily vs weekly cone beam CT for intensity modulated radiotherapy of head and neck Z. Mulla1, M.E. El Sayed2, T. Boubakra3, V.J. Arputharaj4 1 King Faisal Specialist Hospital& Research Centre-Jeddah, Oncology Department-Radiation Oncology Section, Jeddah, Saudi Arabia 2 King Faisal Specialist Hospital & Research Center -Oncology Department- Radiation Oncology Section-Jeddah-KSA-and National Cancer Institute-Radiation Oncology and Nuclear Medicine DepartmentCairo University- Cairo-Egypt, Oncology Department, Jeddah, S 3 King Faisal Specialist Hospital & Research Center, Oncology Department-Radiation Oncology Section-, Jeddah, Saudi Arabia 4 King abdulaziz University Hospital, Radiology Department, Jeddah, Saudi Arabia Purpose/Objective: To prospectively compare daily CBCT (DCBCT) Vs. weekly CBCT (WCBCT) as a verification methods for delivery of the intensity modulated radiotherapy (IMRT) for head and neck cancer patients(HNC) . Materials and Methods: The readings of DCBCT images of 25 head and neck cancer(HNC) patients treated with IMRT between the periods of October 2010 till April 2013 were reviewed .The mean(M) and standard variation(SD) of the systematic(S) and random(R) setup errors of the DCBCT and WCBCT in the three directions , anterior-posterior(AP), medial-Lateral(ML) and superior- inferior(SI )were compared and analyzed . Results: From the 25 patients, 843 images and 2394 reading were recorded and reviewed. The mean of the overall population systematic setup errors were 0.4±0.7, 0.0 ±0.6 and 0.0±0.9mm for DCBCT Vs. 0.5±0.7, -0.1± 1 and 0.0±0.8 mm for the WCBCT : in the AP, ML and SI directions respectively. The mean of the overall population random setup errors for the were 1.2±0.3, 1.4 ±0.5 and 1.3±0.5mm for the DCBCT Vs. 1.3±0.5, 1.2± 0.5 and1.3±0.5 mm in the AP, ML and SI directions respectively. There was no significant differences between mean of the systematic errors for the DCBCT Vs WCBCT readings for all the 3 directions ,the same for the random errors except in the ML directions were the difference was significant (p=.013) in favor of DCBCT .The frequency of recorded shifts more than 3mm were reported in 1% of the readings and between 2 and 3mm in 14% of the reading sand about 85%of the readings are less than the 2mm . Using the Van Herk's formula the suggested clinical target volume (CTV) to planning target volume (PTV) margin in our patients in the AP, ML. and SI. directions is 2, 1 and 1 mm for DCBCT & 2.2, 1.1 and 1 mm for WCBCT data respectively , with no significant difference ,similar suggested margins were proposed when using the Stroom's and ICRU 62 formulas. An average of 2-3mm appears to be adequate. Conclusions: The results of our study showed that the use of image guided radiotherapy using CBCT is effective, it allow reduction of the PTV margins used by 50% (compare to use of EPIDs in our pervious study ). In this study there was no significant difference as regard the degree of shifts when using daily CBCT Vs. weekly CBCT if other parameters (registration, fixation, etc.) were applied properly .In busy departments, weekly CBCT can be used for head and neck cancer patients treated with IMRT, with a CTV to PTV margin of 3mm EP-1872 OAR¥s dose distribution evaluation before and after on-line corrections through CBCT in prostate cancer patients V. Salvador1, A.L. Soares1, L.T. Cunha2, C. Castro1, A.G. Dias2 1 Instituto Português de Oncologia do Porto Francisco Gentil (IPOPFG, E.P.E.) – Serviço de Radioterapia Externa, Porto, Portugal 2 Instituto Português de Oncologia do Porto Francisco Gentil (IPOPFG, E.P.E.) – Serviço de Física Médica, Porto, Portugal Purpose/Objective: Prostate carcinoma is nowadays the most incident cancer in Portugal male population. RadiationTherapy (RT) is part of this pathology´s treatment. During RT treatment, geometric uncertainties occur associated with the delineation of the target volume, the setup errors and the physiological changes of the patient. Thus, different strategies should be applied, namely image guidedradiotherapy (IGRT), in order to minimize this kind of uncertainty ensuring target volume control. The aim of this study was resorting to the use of cone beam CT (CBCT) images acquired on the treatment course, to evaluate the organs at risk (OAR) volume changes (rectum and bladder) and compare it with the delineated volumes in the planning CT and finally evaluate the dose
S313 delivered to the OAR´s using CBCT images and compare with the dose calculation performed in the initial planning CT. Materials and Methods: Planning CT images from the 19 patients were obtained for dosimetric treatment planning in Eclipse® v8.9 system. The dosimetric plans were performed with Three-Dimensional Conformal Radiotherapy (3DCRT), RapidArc®,or with both techniques. After approval of the plans, the patients initiated the treatment in the accelerator (Varian Trilogy® with On-Board Imager® (OBI)), and 128 CBCT images were acquired for patient position evaluation. In the TPS the OAR´s were delineated in all CBCT images to allow assessment of the OAR´s volume changes and received dose. The dosimetric plans were calculate on the CBCT images either considering or not the on-line patient positioning corrections. The dosimetric plans were evaluated and compared taking into account the dosimetric parameters: V40Gy< 60% and V60Gy< 40%for OAR´s. A CBCT specific Hounsfield unit vs electronic density was obtained. Results: On average, the bladder and rectum volumes were greater in the planning CTs than in CBCTs acquired during the treatment course. The bladder volume obtained on CT scans was, on averaged 310.9 ±182.5 cm3 and 213.9 ± 102.2 cm3 for CBCTs. To rectum, the volume obtained on planning CTs was, on average 54.0 ± 19.1 cm3and 48.4 ± 18.3 cm3 in CBCT. OAR´s V40Gy and V60Gy evaluation before and after on-line corrections showed maximum deviation of 39.5 and 26.5 for bladder and 32.8 and 13.6 for rectum, respectively. Conclusions: Considering the obtained results, the IGRT using CBCT allows the evaluation of the bladder and rectum volume changes during the RT treatment, and the comparison with the defined on planning CT. The on-line CBCTcorrections shown to be a useful tool for treatment verification of the target volume, allowing corrections for the initial isocenter position marked in the CT. The values of V40Gy< 60% and V60Gy< 40% for bladder and rectum after corrections were, on average, achieved, highlighting the CBCT advantage on OAR´s dose evaluation also demonstrating the reproduction of the original dosimetric plan. EP-1873 Continuous verification during breast treatment to exclude dosimetric missings due to the chest respiratory motion G. Dinolfo1, F. Vazzano1, A. Di Giovanni1 1 Casa di Cura Macchiarella, Radioterapia, Palermo, Italy Purpose/Objective: Homogeneity in dose distribution of IMRT treatments justify the use of this technique in the treatment of breast cancer. Due to the hyperconformity of the IMRT treatment chest motion during the treatment could result in giving less dose to the target and overdosing lung or heart. We used the opportunity to film the single treatment for all the duration measuring all the motion of reference points in a two-dimensional setting. Materials and Methods: From July to September 2013 we verified the motion of the chest wall in 50 patients for a total of 250 verifications. For each verification we put a reference point on the skin of the patients measuring all the motions during the treatment. The verifications were for the tangential fields, so we measured motions in vertical and longitudinal directions. All the patients were not aware of the procedure right to have not any breath bias. Results: As predictable, the movements of the reference points were larger in the vertical direction but never more than 3 mm with a median value of 1,2 mm between the farther positions during treatment. In the longitudinal direction the median difference between the more distant reference points position for each patient was of less than 1 mm. Conclusions: Breast motion during treatment due to the patient breathing is negligible and is not a restriction to do hyperconformal treatments like IMRT. EP-1874 In determining the set-up margins for complex brain radiotherapy, is there a need to account for optic nerve motion? S. Moinuddin1, N. Fersht1, R. Lewis1, M. Boutros2, G. Royle3, I. Rosenberg2 1 University College Hospital, Radiotherapy UCH, London, United Kingdom 2 University College Hospital, Radiotherapy Physics UCH, London, United Kingdom 3 University College London, Department of Medical Physics, London, United Kingdom Purpose/Objective: Effective immobilisation in brain patients facilitates a possible reduction in set-up margins and offers the possibility of
S313 delivered to the OAR´s using CBCT images and compare with the dose calculation performed in the initial planning CT. Materials and Methods: Planning CT images from the 19 patients were obtained for dosimetric treatment planning in Eclipse® v8.9 system. The dosimetric plans were performed with Three-Dimensional Conformal Radiotherapy (3DCRT), RapidArc®,or with both techniques. After approval of the plans, the patients initiated the treatment in the accelerator (Varian Trilogy® with On-Board Imager® (OBI)), and 128 CBCT images were acquired for patient position evaluation. In the TPS the OAR´s were delineated in all CBCT images to allow assessment of the OAR´s volume changes and received dose. The dosimetric plans were calculate on the CBCT images either considering or not the on-line patient positioning corrections. The dosimetric plans were evaluated and compared taking into account the dosimetric parameters: V40Gy< 60% and V60Gy< 40%for OAR´s. A CBCT specific Hounsfield unit vs electronic density was obtained. Results: On average, the bladder and rectum volumes were greater in the planning CTs than in CBCTs acquired during the treatment course. The bladder volume obtained on CT scans was, on averaged 310.9 ±182.5 cm3 and 213.9 ± 102.2 cm3 for CBCTs. To rectum, the volume obtained on planning CTs was, on average 54.0 ± 19.1 cm3and 48.4 ± 18.3 cm3 in CBCT. OAR´s V40Gy and V60Gy evaluation before and after on-line corrections showed maximum deviation of 39.5 and 26.5 for bladder and 32.8 and 13.6 for rectum, respectively. Conclusions: Considering the obtained results, the IGRT using CBCT allows the evaluation of the bladder and rectum volume changes during the RT treatment, and the comparison with the defined on planning CT. The on-line CBCTcorrections shown to be a useful tool for treatment verification of the target volume, allowing corrections for the initial isocenter position marked in the CT. The values of V40Gy< 60% and V60Gy< 40% for bladder and rectum after corrections were, on average, achieved, highlighting the CBCT advantage on OAR´s dose evaluation also demonstrating the reproduction of the original dosimetric plan. EP-1873 Continuous verification during breast treatment to exclude dosimetric missings due to the chest respiratory motion G. Dinolfo1, F. Vazzano1, A. Di Giovanni1 1 Casa di Cura Macchiarella, Radioterapia, Palermo, Italy Purpose/Objective: Homogeneity in dose distribution of IMRT treatments justify the use of this technique in the treatment of breast cancer. Due to the hyperconformity of the IMRT treatment chest motion during the treatment could result in giving less dose to the target and overdosing lung or heart. We used the opportunity to film the single treatment for all the duration measuring all the motion of reference points in a two-dimensional setting. Materials and Methods: From July to September 2013 we verified the motion of the chest wall in 50 patients for a total of 250 verifications. For each verification we put a reference point on the skin of the patients measuring all the motions during the treatment. The verifications were for the tangential fields, so we measured motions in vertical and longitudinal directions. All the patients were not aware of the procedure right to have not any breath bias. Results: As predictable, the movements of the reference points were larger in the vertical direction but never more than 3 mm with a median value of 1,2 mm between the farther positions during treatment. In the longitudinal direction the median difference between the more distant reference points position for each patient was of less than 1 mm. Conclusions: Breast motion during treatment due to the patient breathing is negligible and is not a restriction to do hyperconformal treatments like IMRT. EP-1874 In determining the set-up margins for complex brain radiotherapy, is there a need to account for optic nerve motion? S. Moinuddin1, N. Fersht1, R. Lewis1, M. Boutros2, G. Royle3, I. Rosenberg2 1 University College Hospital, Radiotherapy UCH, London, United Kingdom 2 University College Hospital, Radiotherapy Physics UCH, London, United Kingdom 3 University College London, Department of Medical Physics, London, United Kingdom Purpose/Objective: Effective immobilisation in brain patients facilitates a possible reduction in set-up margins and offers the possibility of