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Multicenter evaluation of the dosimetric characterization of linac small beams using a plastic scintillator detector
Abstracts/Physica Medica 32 (2016) e1–e70
Conclusions: ART workflow, based on patients’ daily image and supported by hybrid algorithms, structures re-mapping and dose accumulation evaluations, could be integrated with novel predictive models to detect localized intra-organ displacements. Possible set-up errors could be localized during a specific treatment session. By using SIS epidemic model applied to RT, decision making process finalized to a re-planning strategy could be supported considering predicted PG variation and motion. http://dx.doi.org/10.1016/j.ejmp.2016.01.134 A.131 EVALUATION OF DOSE COMING FROM RADIOLOGICAL MONITOR IMAGES TO PACEMAKER IN PATIENT UNDERGOING CYBERKNIFE® TREATMENT S. Maffei *, L. Iadanza, V. Borzillo, L. D’Ambrosio, S. Imbimbo, M. Mormile, N. Villani, C. Zambella, V. Cerciello. Istituto Nazionale Tumori, Fondazione G. Pascale, Napoli, Italy Introduction: The aim of present work is showing a procedure to evaluate the radiological monitor dose to pacemaker of patient undergoing treatment with CyberKnife® (Accuray, Sunnyvale, CA). Radiological monitor dose is dose coming from radiological images that are generated by x-ray tubes to monitor patient positioning during radiotherapy dose delivering. The generation of such images gives patient total dose a contribution that is not accounted by treatment planning system (tps); tps in fact just takes into account radiotherapy dose and not even radiological monitor dose. In some situations this cannot be overlooked and it has to be accounted for; one of these may be a patient with a pacemaker. For this device manufacturer likely indicates a threshold dose value over witch functioning is compromised. Our patient to be treated with CyberKnife® has a pacemaker with a dose threshold value indicated by manufacturer as 2 Gy. Materials and Methods: To evaluate dose from radiological monitor images to the pacemaker we proceed with this tree step way: 1. measurement of dose in air in the same point pacemaker will be placed during patient treatment; 2. calculation in that same point of ratio between dose to pacemaker and dose in air; to do so we use Geant4 toolkit for the simulation of the passage of particles through matter; 3. evaluation of dose to pacemaker multiplying previous ratio by measurement of dose in air. Results: We get that dose in air is 0.650 mGy per image couple, and that the ratio between dose to pacemaker and dose in air is about 3.5; so multiplying 0.650 by 3.5 and by the total number of monitor image couples we obtain a estimation of dose to pacemaker. Conclusions: The sum of radiotherapy dose calculated by tps (1.4 Gy) and radiological monitor dose (0.4 Gy) is lower than threshold value of 2 Gy. The accuracy in evaluation of the dose to the pacemaker can be increased by knowing the real x-ray tubes emission spectra; we just used a rough estimation of it. http://dx.doi.org/10.1016/j.ejmp.2016.01.135 A.132 IS THE OUTCOME OF PROSTATE CANCER PATIENTS TREATED WITH 3D CONFORMAL RADIOTHERAPY INFLUENCED BY RECTAL/BLADDER PREPARATION? A. Maggio *,a, E. Garibaldi b, D. Gabriele c, S. Bresciani a, E. Delmastro b, A. Di Dia a, A. Miranti a, M. Poli a, P. Gabriele b, M. Stasi a. a Medical Physic Department, Candiolo Cancer Institute – FPO, IRCCS, Candiolo, Italy; b Radiotherapy Department, Candiolo Cancer Institute – FPO, IRCCS, Candiolo, Italy; c Neuroscience Department, Physiology Unit, University of Torino, Torino, Italy Purpose: To test the hypothesis that Cancer Specific Overall Survival (CSOS), Clinical Disease Free (CDFS) and Biochemical Disease free Survival (BDFS) are influenced by rectal/bladder preparation Material and Methods: From 1999 to 2012, 1080 prostate cancer patients (PCa) were treated with 3DCRT. 761 patients (pts) were treated with empty rectum and comfortable full bladder while for 319 pts no rectal/ bladder preparation (NRBP) protocol was adopted. The mean prescribed dose was 76 ± 2 Gy. The mean follow-up was 81 ± 39 months. Survival analysis was performed by Kaplan–Meier method. Comparison between groups
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was performed by the log–rank test. Cox proportional hazards model was applied for univariate (UVA) and multivariate analysis (MVA) while Hazard Ratio (HR) allowed to measure how rapidly an event occurs. Results: Pts with rectal/bladder preparation (RBP) have significantly lower risk of dying of PCa, lower biochemical and clinical failures rates respect to NRBP pts (p < 0.0001). At 140 months for RBP and NRPB, the CSOS was 95% vs 85%, the CDFS was 81% vs 71%, the BDFS was 64% vs 48%, respectively. In MVA, for CSOS the Gleason Score (GS) and RBP predicted for death from PCa; for CDSF and BDFS the GS, D’Amico Risk, PSA, dose > 75 Gy, clinical stage and RBP predicted for clinical and biochemical failures. MVA indicates that RBP is an independent risk factor for biochemical failure (p = 0.003, HR = 0.6) while it is the strongest risk factor for clinical failures and PCa deaths (p < 0.0001, HR < 0.5). No statistical significant difference in rectal volume between RBP (mean volume 62.4 ± 24.5 cc) and NRPB (mean volume 63.4 ± 27 cc) was observed (p = 0.52). Conclusion: We found strong evidence that rectal/bladder preparation significantly decreased (HR < 0.6, b < −0.5) the probability of death from PCa, biochemical and clinical failures in pts treated with 3DCRT for PCa, presumably because pts with RBP are able to maintain a reproducible empty rectum and comfortable full bladder for all the treatment. http://dx.doi.org/10.1016/j.ejmp.2016.01.136
A.133 DOSIMETRIC COMPARISON OF EXTERNAL BEAM RADIOTHERAPY WITH 3DCRT, FORWARD-PLANNING IMRT AND VOLUMETRIC ARC THERAPY (VMAT) IN PANCREATIC CANCER A. Mameli *, E. Infusino, L. Bellesi, D. Gaudino, G. Stimato, C. Di Venanzio, M. Fiore, B. Floreno, P. Matteucci, A. Carnevale, S. Ramella, R.M. D’angelillo. Universita’ Campus Biomedico, Roma, Italy Purpose: To evaluate conformity, homogeneity and dose distribution to PTV and organ at risk (OAR) of three different types of radiotherapy techniques in pancreatic cancer. Materials and Methods: Three radiotherapy treatment plans, including 3DCRT, forward-planning IMRT and volumetric arc therapy (VMAT) were created for 18 consecutive patients with pancreatic cancer. Dose Volume Histogram (DVH) comparative analysis was performed for PTV and OAR. Paired t-test was used for statistical analysis. Results: All plans exhibited similar PTV coverage (V95%) and conformity (all p > 0.05). The Homogeneity Index (HI) was acceptable for all plans; in particular, it was higher in VMAT plans than in 3D-CRT and IMRT plans. The mean dose to the liver was 13.5 Gy for 3D, 12.1 Gy for IMRT, 10.9 Gy for VMAT (p < 0.001) to the benefit of VMAT. Volumes of kidneys irradiated to doses of 20 Gy (V20), 23 Gy (V23), 28 Gy (V28) by the VMAT plans were significantly less than those of the IMRT and 3D-CRT plans. The volume of kidneys irradiated to a dose of 12 Gy (V12) was not significantly different comparing the three techniques. Mean of the maximum point dose to spinal cord was better in VMAT plans (3D-CRT vs IMRT vs VMAT, 30.6 Gy, 34.1 Gy, 26.5 Gy, respectively; p < 0.001). Conclusions: VMAT can be a better option in treating pancreatic cancer as compared to IMRT and 3D-CRT. The VMAT plans resulted in equivalent or superior dose distribution with a reduction in the dose to organ at risk. http://dx.doi.org/10.1016/j.ejmp.2016.01.137
A.134 MULTICENTER EVALUATION OF THE DOSIMETRIC CHARACTERIZATION OF LINAC SMALL BEAMS USING A PLASTIC SCINTILLATOR DETECTOR P. Mancosu *,a, V. Ardu b, G. Benecchi c, C. Gasperri d, S. Linsalata e, G. Loi f, E. Menghi g, E. Mones f, R. Nigro h, F. Palleri c, M. Pasquino i, C. Pellegrini b, S. Riccardi h, L. Spiazzi j, M. Stasi i. a Radiotherapy Department, Humanitas, Milano, Italy; b Radiotherapy Department, Policlinico San Donato, San Donato M.se, Italy; c Medical Physics Department, AO Parma, Parma, Italy; d Radiotherapy Department, USL 8 Arezzo, Arezzo, Italy; e Medical Physics Department, USL Lucca, Lucca, Italy; f Medical Physics Department, AOU Maggiore delle Carità, Novara, Italy; g Medical Physics Department, I.R.S.T., Meldola, Italy; h Radiotherapy Department, O.G.P. S.Camillo de Lellis, Rieti, Italy; i AO Ordine Mauriziano Medical Physics Department, Torino, Italy; j Radiotherapy Department, AO Treviglio e Caravaggio, Treviglio, Italy
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Abstracts/Physica Medica 32 (2016) e1–e70
Purpose: The standardization of small field dosimetry is fundamental to ensure that different institutions deliver comparable and consistent radiation doses. The current study presents a multicenter evaluation of MLCdefined small field Tissue Phantom Ratio (TPR), dose profiles FWHM and penumbra and output factors (OF), for the two major linear accelerator manufacturers. Materials and Methods: The project initially enrolled 31 Italian centers, 15 equipped with Elekta Linacs and 16 equipped with Varian Linacs. Each center performed TPR measurement, in-plane and cross-plane dose profile of 0.8 × 0.8 cm2 field and OFs measurements for field sizes ranging from 0.6 × 0.6 to 10 × 10 cm2 defined by both secondary jaws and MLC. Set-up conditions were 10 cm depth in water phantom at SSD 90 cm. Measurements were performed using the new Exradin W1 plastic scintillator detector. To take into account for the Cerenkov effect, a correction factor for each detector was measured and then applied before any measurement session. Results: The analysis of the measurements performed by 13 Varian and 13 Elekta centers was performed; 7 centers were excluded due to measurements inaccuracy, probably due to detector’s instability. TPR measurements showed standard deviations within 0.6%; penumbra values of dose profiles showed standard deviations within 0.5 mm, while FWHM measurements showed a greater variability. OF measurements showed standard deviations within 1.5% for field size greater than 2 × 2 cm2; for field size less than 2 × 2 cm2 measurements’ variability increases with decreasing field size. OF values show no dependence from the effective field size. Conclusions: Results show that there is a relatively high degree of consistency regarding TPR and penumbra values. FWHM and OF instead show greater variability, also for Linac with the same model of the head. Measurements confirm W1 PSD as a candidate for small field clinical radiation dosimetry in advanced radiation therapy techniques. http://dx.doi.org/10.1016/j.ejmp.2016.01.138 A.135 STUDY ON THE DOSIMETRY OF LASER ACCELERATED BEAMS FOR FUTURE CLINICAL APPLICATIONS R. Manna * ,a, G.A.P. Cirrone a, G. Cuttone a, F. Romano a, V. Scuderi a,b, A.G. Amico a,c , G. Candiano a , G. Larosa a , R. Leanza a,c , V. Marchese a , G. Milluzzo a,c, G. Petringa a,c, J. Pipek a, F. Schillaci a, N. Amato a, G. Gallo a, L. Allegra a. a Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare, Catania, Italy; b Department of Experimental Program at ELI-Beamlines, Institute of Physics of the ASCR, Prague, Czech Republic; c Dipartimento di Fisica e Astronomia, Università degli studi di Catania, Catania, Italy Introduction: Charged particle acceleration, based on the interaction of ultra-intense and ultra-short laser with a solid target, can represent a future alternative to conventional techniques, in many applications, from Nuclear Physics to Radiobiology. In this context, The ELIMED (MEDical and multidisciplinary applications at ELI-Beamlines) project aims to realise transport, diagnostics and dosimetric elements able to make suitable laser-driven ion beams for multidisciplinary applications, with particular interest in hadrontherapy. Materials and Methods: The detectors dedicated to dosimetry of laseraccelerated beams must offer a response independent of dose rate and they must be suitable to operate with a highly intense beam pulse and strong electromagnetic noise (EMP), in order to obtain a precise knowledge of the absolute dose delivered, which is mandatory for clinical applications. For the absolute dosimetry system, an innovative Faraday Cup, optimised for highly pulsed ion beams, has been developed within the ELIMED collaboration. The designed FC has a peculiar geometry, which has been inspired to similar detectors already developed for ion beam dosimetry; it contains a second bevelled electrode coaxial and internal to a traditional one that determines a special-shaped electric field. Results: Dosimetric tests, performed with conventional proton beam at CATANA facility (INFN-LNS), show that the innovative design of FC optimises the charge collection efficiency and reduces the uncertainties related to the charge collection in agreement with simulations performed using SIMION software. Furthermore, preliminary tests have been performed during experimental campaigns at laser facility; the preliminary results will be presented.
Conclusion: New technologies and innovative dosimeters must be developed and realised in order to achieve an accurate evaluation of the dose delivered for the future use of these non-conventional beams in medical applications. http://dx.doi.org/10.1016/j.ejmp.2016.01.139 A.136 EVALUATION OF SCATTERED RADIATION FROM ELECTRON APPLICATORS IN PATIENT WITH IMPLANTED ELECTRONIC DEVICES L. Mantovani *, M. Lamborizio, G. Daprati, R. Di Liberto. IRCCS Fondazione Policlinico San Matteo, Pavia, Italy Introduction: In this study, the out-of-field scattered dose from electron beams was measured in patient with implanted defibrillator Medtronic. Manufacturing company indicates 5 Gy as maximum dose to prevent damage or malfunction, but threshold dose may vary depending on the model. Materials and Methods: The PTV was the left parotid region irradiated with 9 MeV electron beam. The prescribed dose was 60 Gy (2 Gy per fraction), using 10 × 10cm2 applicator and 0.5 cm bolus. The inferior margin of PTV valuated with CT scan was about 8 cm from defibrillator in longitudinal direction; the depth of measurements was 1 mm simulating subcutaneous region. The total dose to defibrillator was considered as amount of scattered dose in body from direct beam and scattered dose in air from electron applicator. The Monte Carlo algorithm, with CT scan and water-equivalent slab phantom with a Markus chamber, were used to measure and evaluate the scattered dose in tissue and in air respectively. Two P-type silicon diode detectors have been used to monitor the dose delivered to defibrillator during treatment sessions. Results: The dose amount is mainly due to primary beam scattered from electron applicator. In the experimental setup (ionization chamber positioned at the side of applicator edge) the total measured dose for the complete treatment was 1.6 Gy. Dose typically increases with decreasing distance from the source and falls with depth. Dose measured in-vivo with semiconductor detectors confirms the expected results (0.05 Gy for single fraction) and drastic dose reduction is obtained applying a 2 cm water equivalent bolus on the top of defibrillator. Conclusions: The results show that it is very important to evaluate appropriate shielding for patient with electronic device to prevent malfunctions. The dose measured can be significant when the applicator is close to the electronic implanted device. The use of water equivalent bolus is a practical solution to reduce peripheral dose. http://dx.doi.org/10.1016/j.ejmp.2016.01.140 A.137 PROTOCOL IMPLEMENTATION OF TOTAL MARROW IRRADIATION (TMI) PLUS TOTAL LYMPHOID IRRADIATION (TLI) USING HELICAL TOMOTHERAPY (HT) M. Marcantonini *,a, V. Lancellotta b, G. Montesi b, L. Falcinelli a, C. Aristei b, R. Tarducci a. a Perugia General Hspital, Perugia, Italy; b University of Perugia and Perugia General Hospital, Perugia, Italy Introduction: TBI plays an important role in patients undergoing stemcell-transplant for a wide variety of hematological malignancies, but is associated with significant toxicities. TMI plus TLI delivered with HT may overcome this problem. The protocol implemented in our department is here described. Materials and Methods: Head and shoulders of patient are immobilized by means a thermoplastic mask, with arms along the sides. Buns, legs and feet are positioned in a vacuum cushion. Two CT scans 1 cm slice thickness are collected, with head first (part I) and with feet first (part II) supine orientation. The PTV (expansions 3–7 mm) consisted of whole body skeletal bone, spleen and major lymph node areas. The main OARs are lungs, heart, liver, kidneys, small intestine, eyes. The plan is prescribed to ensure 90% PTV dose coverage with the 90% of 13.5 Gy prescribed dose (1.5 Gy BID) and D50% = 13.5 Gy. Dose limit for lungs, heart, liver, kidneys, small intestine, eyes are maxD50% = 7.5 Gy, 8 Gy, 7.5 Gy, 7.5 Gy, 9 Gy, 6 Gy respectively. For each CT a treatment plan is elaborated, FW = 5.0 cm, Pitch = 0.430 and 0.287, MF = 2 and 2.5 for parts I and II. The junction region is divided into 3 parts A, B, C with D50% = 7.0 Gy, 3.5 Gy, 1.0 Gy in part I and D50% = 6.5 Gy,
Conclusions: ART workflow, based on patients’ daily image and supported by hybrid algorithms, structures re-mapping and dose accumulation evaluations, could be integrated with novel predictive models to detect localized intra-organ displacements. Possible set-up errors could be localized during a specific treatment session. By using SIS epidemic model applied to RT, decision making process finalized to a re-planning strategy could be supported considering predicted PG variation and motion. http://dx.doi.org/10.1016/j.ejmp.2016.01.134 A.131 EVALUATION OF DOSE COMING FROM RADIOLOGICAL MONITOR IMAGES TO PACEMAKER IN PATIENT UNDERGOING CYBERKNIFE® TREATMENT S. Maffei *, L. Iadanza, V. Borzillo, L. D’Ambrosio, S. Imbimbo, M. Mormile, N. Villani, C. Zambella, V. Cerciello. Istituto Nazionale Tumori, Fondazione G. Pascale, Napoli, Italy Introduction: The aim of present work is showing a procedure to evaluate the radiological monitor dose to pacemaker of patient undergoing treatment with CyberKnife® (Accuray, Sunnyvale, CA). Radiological monitor dose is dose coming from radiological images that are generated by x-ray tubes to monitor patient positioning during radiotherapy dose delivering. The generation of such images gives patient total dose a contribution that is not accounted by treatment planning system (tps); tps in fact just takes into account radiotherapy dose and not even radiological monitor dose. In some situations this cannot be overlooked and it has to be accounted for; one of these may be a patient with a pacemaker. For this device manufacturer likely indicates a threshold dose value over witch functioning is compromised. Our patient to be treated with CyberKnife® has a pacemaker with a dose threshold value indicated by manufacturer as 2 Gy. Materials and Methods: To evaluate dose from radiological monitor images to the pacemaker we proceed with this tree step way: 1. measurement of dose in air in the same point pacemaker will be placed during patient treatment; 2. calculation in that same point of ratio between dose to pacemaker and dose in air; to do so we use Geant4 toolkit for the simulation of the passage of particles through matter; 3. evaluation of dose to pacemaker multiplying previous ratio by measurement of dose in air. Results: We get that dose in air is 0.650 mGy per image couple, and that the ratio between dose to pacemaker and dose in air is about 3.5; so multiplying 0.650 by 3.5 and by the total number of monitor image couples we obtain a estimation of dose to pacemaker. Conclusions: The sum of radiotherapy dose calculated by tps (1.4 Gy) and radiological monitor dose (0.4 Gy) is lower than threshold value of 2 Gy. The accuracy in evaluation of the dose to the pacemaker can be increased by knowing the real x-ray tubes emission spectra; we just used a rough estimation of it. http://dx.doi.org/10.1016/j.ejmp.2016.01.135 A.132 IS THE OUTCOME OF PROSTATE CANCER PATIENTS TREATED WITH 3D CONFORMAL RADIOTHERAPY INFLUENCED BY RECTAL/BLADDER PREPARATION? A. Maggio *,a, E. Garibaldi b, D. Gabriele c, S. Bresciani a, E. Delmastro b, A. Di Dia a, A. Miranti a, M. Poli a, P. Gabriele b, M. Stasi a. a Medical Physic Department, Candiolo Cancer Institute – FPO, IRCCS, Candiolo, Italy; b Radiotherapy Department, Candiolo Cancer Institute – FPO, IRCCS, Candiolo, Italy; c Neuroscience Department, Physiology Unit, University of Torino, Torino, Italy Purpose: To test the hypothesis that Cancer Specific Overall Survival (CSOS), Clinical Disease Free (CDFS) and Biochemical Disease free Survival (BDFS) are influenced by rectal/bladder preparation Material and Methods: From 1999 to 2012, 1080 prostate cancer patients (PCa) were treated with 3DCRT. 761 patients (pts) were treated with empty rectum and comfortable full bladder while for 319 pts no rectal/ bladder preparation (NRBP) protocol was adopted. The mean prescribed dose was 76 ± 2 Gy. The mean follow-up was 81 ± 39 months. Survival analysis was performed by Kaplan–Meier method. Comparison between groups
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was performed by the log–rank test. Cox proportional hazards model was applied for univariate (UVA) and multivariate analysis (MVA) while Hazard Ratio (HR) allowed to measure how rapidly an event occurs. Results: Pts with rectal/bladder preparation (RBP) have significantly lower risk of dying of PCa, lower biochemical and clinical failures rates respect to NRBP pts (p < 0.0001). At 140 months for RBP and NRPB, the CSOS was 95% vs 85%, the CDFS was 81% vs 71%, the BDFS was 64% vs 48%, respectively. In MVA, for CSOS the Gleason Score (GS) and RBP predicted for death from PCa; for CDSF and BDFS the GS, D’Amico Risk, PSA, dose > 75 Gy, clinical stage and RBP predicted for clinical and biochemical failures. MVA indicates that RBP is an independent risk factor for biochemical failure (p = 0.003, HR = 0.6) while it is the strongest risk factor for clinical failures and PCa deaths (p < 0.0001, HR < 0.5). No statistical significant difference in rectal volume between RBP (mean volume 62.4 ± 24.5 cc) and NRPB (mean volume 63.4 ± 27 cc) was observed (p = 0.52). Conclusion: We found strong evidence that rectal/bladder preparation significantly decreased (HR < 0.6, b < −0.5) the probability of death from PCa, biochemical and clinical failures in pts treated with 3DCRT for PCa, presumably because pts with RBP are able to maintain a reproducible empty rectum and comfortable full bladder for all the treatment. http://dx.doi.org/10.1016/j.ejmp.2016.01.136
A.133 DOSIMETRIC COMPARISON OF EXTERNAL BEAM RADIOTHERAPY WITH 3DCRT, FORWARD-PLANNING IMRT AND VOLUMETRIC ARC THERAPY (VMAT) IN PANCREATIC CANCER A. Mameli *, E. Infusino, L. Bellesi, D. Gaudino, G. Stimato, C. Di Venanzio, M. Fiore, B. Floreno, P. Matteucci, A. Carnevale, S. Ramella, R.M. D’angelillo. Universita’ Campus Biomedico, Roma, Italy Purpose: To evaluate conformity, homogeneity and dose distribution to PTV and organ at risk (OAR) of three different types of radiotherapy techniques in pancreatic cancer. Materials and Methods: Three radiotherapy treatment plans, including 3DCRT, forward-planning IMRT and volumetric arc therapy (VMAT) were created for 18 consecutive patients with pancreatic cancer. Dose Volume Histogram (DVH) comparative analysis was performed for PTV and OAR. Paired t-test was used for statistical analysis. Results: All plans exhibited similar PTV coverage (V95%) and conformity (all p > 0.05). The Homogeneity Index (HI) was acceptable for all plans; in particular, it was higher in VMAT plans than in 3D-CRT and IMRT plans. The mean dose to the liver was 13.5 Gy for 3D, 12.1 Gy for IMRT, 10.9 Gy for VMAT (p < 0.001) to the benefit of VMAT. Volumes of kidneys irradiated to doses of 20 Gy (V20), 23 Gy (V23), 28 Gy (V28) by the VMAT plans were significantly less than those of the IMRT and 3D-CRT plans. The volume of kidneys irradiated to a dose of 12 Gy (V12) was not significantly different comparing the three techniques. Mean of the maximum point dose to spinal cord was better in VMAT plans (3D-CRT vs IMRT vs VMAT, 30.6 Gy, 34.1 Gy, 26.5 Gy, respectively; p < 0.001). Conclusions: VMAT can be a better option in treating pancreatic cancer as compared to IMRT and 3D-CRT. The VMAT plans resulted in equivalent or superior dose distribution with a reduction in the dose to organ at risk. http://dx.doi.org/10.1016/j.ejmp.2016.01.137
A.134 MULTICENTER EVALUATION OF THE DOSIMETRIC CHARACTERIZATION OF LINAC SMALL BEAMS USING A PLASTIC SCINTILLATOR DETECTOR P. Mancosu *,a, V. Ardu b, G. Benecchi c, C. Gasperri d, S. Linsalata e, G. Loi f, E. Menghi g, E. Mones f, R. Nigro h, F. Palleri c, M. Pasquino i, C. Pellegrini b, S. Riccardi h, L. Spiazzi j, M. Stasi i. a Radiotherapy Department, Humanitas, Milano, Italy; b Radiotherapy Department, Policlinico San Donato, San Donato M.se, Italy; c Medical Physics Department, AO Parma, Parma, Italy; d Radiotherapy Department, USL 8 Arezzo, Arezzo, Italy; e Medical Physics Department, USL Lucca, Lucca, Italy; f Medical Physics Department, AOU Maggiore delle Carità, Novara, Italy; g Medical Physics Department, I.R.S.T., Meldola, Italy; h Radiotherapy Department, O.G.P. S.Camillo de Lellis, Rieti, Italy; i AO Ordine Mauriziano Medical Physics Department, Torino, Italy; j Radiotherapy Department, AO Treviglio e Caravaggio, Treviglio, Italy
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Abstracts/Physica Medica 32 (2016) e1–e70
Purpose: The standardization of small field dosimetry is fundamental to ensure that different institutions deliver comparable and consistent radiation doses. The current study presents a multicenter evaluation of MLCdefined small field Tissue Phantom Ratio (TPR), dose profiles FWHM and penumbra and output factors (OF), for the two major linear accelerator manufacturers. Materials and Methods: The project initially enrolled 31 Italian centers, 15 equipped with Elekta Linacs and 16 equipped with Varian Linacs. Each center performed TPR measurement, in-plane and cross-plane dose profile of 0.8 × 0.8 cm2 field and OFs measurements for field sizes ranging from 0.6 × 0.6 to 10 × 10 cm2 defined by both secondary jaws and MLC. Set-up conditions were 10 cm depth in water phantom at SSD 90 cm. Measurements were performed using the new Exradin W1 plastic scintillator detector. To take into account for the Cerenkov effect, a correction factor for each detector was measured and then applied before any measurement session. Results: The analysis of the measurements performed by 13 Varian and 13 Elekta centers was performed; 7 centers were excluded due to measurements inaccuracy, probably due to detector’s instability. TPR measurements showed standard deviations within 0.6%; penumbra values of dose profiles showed standard deviations within 0.5 mm, while FWHM measurements showed a greater variability. OF measurements showed standard deviations within 1.5% for field size greater than 2 × 2 cm2; for field size less than 2 × 2 cm2 measurements’ variability increases with decreasing field size. OF values show no dependence from the effective field size. Conclusions: Results show that there is a relatively high degree of consistency regarding TPR and penumbra values. FWHM and OF instead show greater variability, also for Linac with the same model of the head. Measurements confirm W1 PSD as a candidate for small field clinical radiation dosimetry in advanced radiation therapy techniques. http://dx.doi.org/10.1016/j.ejmp.2016.01.138 A.135 STUDY ON THE DOSIMETRY OF LASER ACCELERATED BEAMS FOR FUTURE CLINICAL APPLICATIONS R. Manna * ,a, G.A.P. Cirrone a, G. Cuttone a, F. Romano a, V. Scuderi a,b, A.G. Amico a,c , G. Candiano a , G. Larosa a , R. Leanza a,c , V. Marchese a , G. Milluzzo a,c, G. Petringa a,c, J. Pipek a, F. Schillaci a, N. Amato a, G. Gallo a, L. Allegra a. a Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare, Catania, Italy; b Department of Experimental Program at ELI-Beamlines, Institute of Physics of the ASCR, Prague, Czech Republic; c Dipartimento di Fisica e Astronomia, Università degli studi di Catania, Catania, Italy Introduction: Charged particle acceleration, based on the interaction of ultra-intense and ultra-short laser with a solid target, can represent a future alternative to conventional techniques, in many applications, from Nuclear Physics to Radiobiology. In this context, The ELIMED (MEDical and multidisciplinary applications at ELI-Beamlines) project aims to realise transport, diagnostics and dosimetric elements able to make suitable laser-driven ion beams for multidisciplinary applications, with particular interest in hadrontherapy. Materials and Methods: The detectors dedicated to dosimetry of laseraccelerated beams must offer a response independent of dose rate and they must be suitable to operate with a highly intense beam pulse and strong electromagnetic noise (EMP), in order to obtain a precise knowledge of the absolute dose delivered, which is mandatory for clinical applications. For the absolute dosimetry system, an innovative Faraday Cup, optimised for highly pulsed ion beams, has been developed within the ELIMED collaboration. The designed FC has a peculiar geometry, which has been inspired to similar detectors already developed for ion beam dosimetry; it contains a second bevelled electrode coaxial and internal to a traditional one that determines a special-shaped electric field. Results: Dosimetric tests, performed with conventional proton beam at CATANA facility (INFN-LNS), show that the innovative design of FC optimises the charge collection efficiency and reduces the uncertainties related to the charge collection in agreement with simulations performed using SIMION software. Furthermore, preliminary tests have been performed during experimental campaigns at laser facility; the preliminary results will be presented.
Conclusion: New technologies and innovative dosimeters must be developed and realised in order to achieve an accurate evaluation of the dose delivered for the future use of these non-conventional beams in medical applications. http://dx.doi.org/10.1016/j.ejmp.2016.01.139 A.136 EVALUATION OF SCATTERED RADIATION FROM ELECTRON APPLICATORS IN PATIENT WITH IMPLANTED ELECTRONIC DEVICES L. Mantovani *, M. Lamborizio, G. Daprati, R. Di Liberto. IRCCS Fondazione Policlinico San Matteo, Pavia, Italy Introduction: In this study, the out-of-field scattered dose from electron beams was measured in patient with implanted defibrillator Medtronic. Manufacturing company indicates 5 Gy as maximum dose to prevent damage or malfunction, but threshold dose may vary depending on the model. Materials and Methods: The PTV was the left parotid region irradiated with 9 MeV electron beam. The prescribed dose was 60 Gy (2 Gy per fraction), using 10 × 10cm2 applicator and 0.5 cm bolus. The inferior margin of PTV valuated with CT scan was about 8 cm from defibrillator in longitudinal direction; the depth of measurements was 1 mm simulating subcutaneous region. The total dose to defibrillator was considered as amount of scattered dose in body from direct beam and scattered dose in air from electron applicator. The Monte Carlo algorithm, with CT scan and water-equivalent slab phantom with a Markus chamber, were used to measure and evaluate the scattered dose in tissue and in air respectively. Two P-type silicon diode detectors have been used to monitor the dose delivered to defibrillator during treatment sessions. Results: The dose amount is mainly due to primary beam scattered from electron applicator. In the experimental setup (ionization chamber positioned at the side of applicator edge) the total measured dose for the complete treatment was 1.6 Gy. Dose typically increases with decreasing distance from the source and falls with depth. Dose measured in-vivo with semiconductor detectors confirms the expected results (0.05 Gy for single fraction) and drastic dose reduction is obtained applying a 2 cm water equivalent bolus on the top of defibrillator. Conclusions: The results show that it is very important to evaluate appropriate shielding for patient with electronic device to prevent malfunctions. The dose measured can be significant when the applicator is close to the electronic implanted device. The use of water equivalent bolus is a practical solution to reduce peripheral dose. http://dx.doi.org/10.1016/j.ejmp.2016.01.140 A.137 PROTOCOL IMPLEMENTATION OF TOTAL MARROW IRRADIATION (TMI) PLUS TOTAL LYMPHOID IRRADIATION (TLI) USING HELICAL TOMOTHERAPY (HT) M. Marcantonini *,a, V. Lancellotta b, G. Montesi b, L. Falcinelli a, C. Aristei b, R. Tarducci a. a Perugia General Hspital, Perugia, Italy; b University of Perugia and Perugia General Hospital, Perugia, Italy Introduction: TBI plays an important role in patients undergoing stemcell-transplant for a wide variety of hematological malignancies, but is associated with significant toxicities. TMI plus TLI delivered with HT may overcome this problem. The protocol implemented in our department is here described. Materials and Methods: Head and shoulders of patient are immobilized by means a thermoplastic mask, with arms along the sides. Buns, legs and feet are positioned in a vacuum cushion. Two CT scans 1 cm slice thickness are collected, with head first (part I) and with feet first (part II) supine orientation. The PTV (expansions 3–7 mm) consisted of whole body skeletal bone, spleen and major lymph node areas. The main OARs are lungs, heart, liver, kidneys, small intestine, eyes. The plan is prescribed to ensure 90% PTV dose coverage with the 90% of 13.5 Gy prescribed dose (1.5 Gy BID) and D50% = 13.5 Gy. Dose limit for lungs, heart, liver, kidneys, small intestine, eyes are maxD50% = 7.5 Gy, 8 Gy, 7.5 Gy, 7.5 Gy, 9 Gy, 6 Gy respectively. For each CT a treatment plan is elaborated, FW = 5.0 cm, Pitch = 0.430 and 0.287, MF = 2 and 2.5 for parts I and II. The junction region is divided into 3 parts A, B, C with D50% = 7.0 Gy, 3.5 Gy, 1.0 Gy in part I and D50% = 6.5 Gy,