- Email: [email protected]
A tool to check brachytherapy treatment time: A statistical approach
Abstracts/Physica Medica 32 (2016) e1–e70
Purpose: In this study, we investigated Ru-106/Rh-106 pediatric applicators (BEBIG, Germany) by utilizing two dosimetry equipments: a dedicated PTW Optidos dosimeter and a new synthetic diamond detector developed at the laboratories of Rome “Tor Vergata” University, commercialized by PTW as microDiamond (mD) and characterized for the present application by the National Institute of Ionizing Radiation Metrology – ENEAINMRI. The aim of this work was to compare depth-dose profiles with the ones provided by the manufacturer. Materials and methods: A BEBIG Ru-106 plaque type CCX was placed in a homemade water phantom on a dedicated PMMA support. Depth dose rate measurements were collected through a PTW-Optidos and two mD detectors. Measurements were performed along the central axis of the plaque. The results have been compared with the calibration data provided by the manufacturer. Results: The mD current integrated over 20 s resulted in charge measurements from about 0.5 to 15 pC in the depth range from 10 mm to 1.51 mm. In general, measurement repeatability was below 0.5% and reproducibility was within 2%, including detector positioning errors and differences between the results from two different mD detectors. Both PTW-Optidos and mD relative dose distributions showed a good agreement with the manufacturer’s data, with differences within 4% up to a distance of 8 mm from the plaque surface. Reference dose rate measured by mD at 2 mm depth was found about 19% lower than the manufacturer’s value, but still within the 95% confidence interval. A larger deviation (about −30%) was achieved using the PTW-Optidos dosimeter. Conclusions: The differences observed between measured and nominal dose rate values indicate that a verification of the manufacturer’s data should always precede the clinical use of Ru-106 eye-plaques. This work has also shown the suitability of microDiamond to perform accurate relative and absolute dosimetry of such eye-plaques. http://dx.doi.org/10.1016/j.ejmp.2016.01.093
A.90 ACTIVE BREATHING CONTROL (ABC) APPLIED TO LEFT BREAST CANCER (LBC): DOSIMETRIC RESULTS AFTER 50 PATIENTS AT SPEDALI CIVILI OF BRESCIA B. Ghedi *,a, L. Spiazzi a, R. Cavagnini b, N. Pasinetti b, L. Costa b, L. Pegurri b, R. Moretti a. a U.O. Fisica Sanitaria, A.O. Spedali Civili Di Brescia, Brescia, Italy; b Istituto Del Radio, A.O. Spedali Civili Di Brescia, Brescia, Italy Introduction: The toxic effect of radiation therapy (RT) for the heart has been extensively documented for LBC patients. Adjuvant chemotherapy regimens may exacerbate the problem, with the use of proven cardio-toxic drugs. We studied the impact of the implementation of ABC system, a medical device to reproducibly suspend the patients breathing at the moderate deep inspiration breath-hold, on the heart, left anterior descending artery (LAD) and ipsilateral lung dose. Methods and materials: 50 patients with stages 0–III LBC have been enrolled since May 2012. They underwent RT with ABC: the prescription dose was 50 Gy plus a boost in 88% and 2.75 Gy up to 44 Gy plus a boost in 22%. For each patient, a free breathing (FB) and a breath hold CT were taken. Two plans with tangent fields were elaborated. For each patient, the two DVHs were compared and analyzed using two SW: (1) A homemade Planning Reporting Orienteering (PRO)-DVH SW, which elaborates Bio-DVH (equivalent dose volume histograms for 25 fractions) that allows comparison regardless of the treatment schedule. (2) The Bioplan (Biological Evaluation of radiotherapy treatments PLANs) for NTCP calculations of cardiac mortality, according to the relative seriality model, using D50 = 52.3 Gy, γ = 1.28, s = 1 as parameters. PRO-DVH was used to compare the average Bio-DVH as well. Results: Analyzing the plans performed with FB and ABC, we obtain a comparable coverage of the PTV, while the cardiac mortality is significantly reduced in terms of NTCP with the use of ABC (p < 0.01 for a t-test, paired samples, two tailed). The same results for the reduction of mean, max and mean LAD dose. There is no significant difference in the ipsilateral lung dose. Conclusion: The clinical implementation of ABC gave encouraging dosimetric results and is now routinely adopted in our Institution for compliant LBC patients with significant LAD exposure in radiation fields. http://dx.doi.org/10.1016/j.ejmp.2016.01.094
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A.91 A TOOL TO CHECK BRACHYTHERAPY TREATMENT TIME: A STATISTICAL APPROACH M. Giacometti *, L. Tesei, L. Vicenzi, S. Costantini, M. Cardinali, S. Maggi. Azienda Ospedaliera Universitaria Ospedali Riuniti, Ancona, Italy Introduction: Verification of treatment time accuracy is one of the specific activities of medical physicist. In external beam planning this issue has been faced for both 3DCRT and now for IMRT. Instead brachytherapy has not received the same attention, given the simplicity of the technique and the reduced diffusion. The aim of this work is to evaluate a possible approach for the verification of the correctness of BRT treatment times. Materials and methods: Our department is equipped with a microSelectron therapy unit and Oncentra v.4.1SP2 TPS, both by Nucletron Elekta. In this work we considered gynecological treatments, 195 with cylindrical applicator and 69 with Fletcher applicator, performed from 2011 until today. For each plan we recorded: source Air kerma strength (mGy m2/h), volume of the PTV enclosed within 90% isodose of prescription (V90, cc), prescription dose (cGy) and treatment time (s); following, we calculated the parameter F obtained as treatment time multiplied by activity and divided by prescription dose. Results: Data relating to the two types of treatment were analyzed separately. We applied a linear fit to the F parameter as a function of V90; the R2 values of 0.9593 and 0.9503 relate to fit for, respectively, treatments with cylindrical and Fletcher applicator. Following, we analyzed the distribution of per cent difference between time calculated by TPS and time obtained from the linear fit. In both cases we got a Gaussian distribution with mean and standard deviation (−0.1%, 4.2%) and (−0.3%, 4.2%) for cylindrical and Fletcher applicator, respectively. Conclusion: This work shows that, assuming the same criteria for volume contouring, it is possible to obtain a parameter F statistically correlated to V90. The per cent difference between the time calculated by TPS and the one estimated using the linear fit shows a Gaussian distribution with a standard deviation of 4%, thus suggesting a tool to evaluate BRT treatment time’s accuracy. http://dx.doi.org/10.1016/j.ejmp.2016.01.095
A.92 EPID-BASED IN-VIVO DOSIMETRY FOR PROSTATE CANCER TREATED BY VOLUMETRIC ARC THERAPY: PRELIMINARY CLINICAL RESULTS S. Giancaterino *,a, A. De Nicola a, N. Adorante a, P. Bagalà a, F. Perrotti a, S. Menna b , A. Fidanzio b , A. Piermattei b , D. Genovesi a , M.D. Falco a . a Department of Radiation Oncology, SS Annunziata Hospital, Chieti, Italy; b Istituto di Fisica e Unità Operativa di Fisica, Sanitaria Università Cattolica del S. Cuore, Roma, Italy Purpose: The purpose of this study is to report the in-vivo dosimetry (IVD) results obtained using the SOFTDISO software (Best Medical Italy) during VMAT prostate cancer treatments. Materials and methods: The SOFTDISO software reconstructs the dose at the isocenter (Diso) in the patient from the transit signal acquired by the EPID and allows the comparison between EPID images obtained during the therapy fractions. In particular for each beam and fraction, the ratios, R, between the dose reconstructed at the isocenter point Diso in single-arc VMAT plans and the dose calculated by the treatment planning system Diso,TPS (generally about 2 Gy for fraction) obtained by Oncentra Masterplan were computed. The acceptance criteria were: 0.95 < R < 1.05. Moreover the γ-analysis (2%-2 mm) between portal images was reported. 15 patients with prostate cancer were treated with 6 MV photon beam delivered by an Elekta Synergy Agility. Our protocol required, for each patient, 5 consecutive IVDs in the first 5 treatment sessions after a cone beam CT (CBCT) based setup correction and the IVD test once weekly afterward for the rest of the treatment course when the CBCT scan was not acquired. Results: The IVD procedure supplied 110 tests and the average R was equal to 1.004 ± 0.024 (1 SD), in a range between 0.948 and 1.059. The global R value for each single patient was well within the 5% tolerance level. The γ-analysis between EPID images yielded P(γ < 1) > 97% in 80% of the tests. The remaining 20% of the tests gave P(γ < 1) > 93%; they were mainly related to the sessions where the CBCT scans were not performed indicating that small set-up variations occurred.
Purpose: In this study, we investigated Ru-106/Rh-106 pediatric applicators (BEBIG, Germany) by utilizing two dosimetry equipments: a dedicated PTW Optidos dosimeter and a new synthetic diamond detector developed at the laboratories of Rome “Tor Vergata” University, commercialized by PTW as microDiamond (mD) and characterized for the present application by the National Institute of Ionizing Radiation Metrology – ENEAINMRI. The aim of this work was to compare depth-dose profiles with the ones provided by the manufacturer. Materials and methods: A BEBIG Ru-106 plaque type CCX was placed in a homemade water phantom on a dedicated PMMA support. Depth dose rate measurements were collected through a PTW-Optidos and two mD detectors. Measurements were performed along the central axis of the plaque. The results have been compared with the calibration data provided by the manufacturer. Results: The mD current integrated over 20 s resulted in charge measurements from about 0.5 to 15 pC in the depth range from 10 mm to 1.51 mm. In general, measurement repeatability was below 0.5% and reproducibility was within 2%, including detector positioning errors and differences between the results from two different mD detectors. Both PTW-Optidos and mD relative dose distributions showed a good agreement with the manufacturer’s data, with differences within 4% up to a distance of 8 mm from the plaque surface. Reference dose rate measured by mD at 2 mm depth was found about 19% lower than the manufacturer’s value, but still within the 95% confidence interval. A larger deviation (about −30%) was achieved using the PTW-Optidos dosimeter. Conclusions: The differences observed between measured and nominal dose rate values indicate that a verification of the manufacturer’s data should always precede the clinical use of Ru-106 eye-plaques. This work has also shown the suitability of microDiamond to perform accurate relative and absolute dosimetry of such eye-plaques. http://dx.doi.org/10.1016/j.ejmp.2016.01.093
A.90 ACTIVE BREATHING CONTROL (ABC) APPLIED TO LEFT BREAST CANCER (LBC): DOSIMETRIC RESULTS AFTER 50 PATIENTS AT SPEDALI CIVILI OF BRESCIA B. Ghedi *,a, L. Spiazzi a, R. Cavagnini b, N. Pasinetti b, L. Costa b, L. Pegurri b, R. Moretti a. a U.O. Fisica Sanitaria, A.O. Spedali Civili Di Brescia, Brescia, Italy; b Istituto Del Radio, A.O. Spedali Civili Di Brescia, Brescia, Italy Introduction: The toxic effect of radiation therapy (RT) for the heart has been extensively documented for LBC patients. Adjuvant chemotherapy regimens may exacerbate the problem, with the use of proven cardio-toxic drugs. We studied the impact of the implementation of ABC system, a medical device to reproducibly suspend the patients breathing at the moderate deep inspiration breath-hold, on the heart, left anterior descending artery (LAD) and ipsilateral lung dose. Methods and materials: 50 patients with stages 0–III LBC have been enrolled since May 2012. They underwent RT with ABC: the prescription dose was 50 Gy plus a boost in 88% and 2.75 Gy up to 44 Gy plus a boost in 22%. For each patient, a free breathing (FB) and a breath hold CT were taken. Two plans with tangent fields were elaborated. For each patient, the two DVHs were compared and analyzed using two SW: (1) A homemade Planning Reporting Orienteering (PRO)-DVH SW, which elaborates Bio-DVH (equivalent dose volume histograms for 25 fractions) that allows comparison regardless of the treatment schedule. (2) The Bioplan (Biological Evaluation of radiotherapy treatments PLANs) for NTCP calculations of cardiac mortality, according to the relative seriality model, using D50 = 52.3 Gy, γ = 1.28, s = 1 as parameters. PRO-DVH was used to compare the average Bio-DVH as well. Results: Analyzing the plans performed with FB and ABC, we obtain a comparable coverage of the PTV, while the cardiac mortality is significantly reduced in terms of NTCP with the use of ABC (p < 0.01 for a t-test, paired samples, two tailed). The same results for the reduction of mean, max and mean LAD dose. There is no significant difference in the ipsilateral lung dose. Conclusion: The clinical implementation of ABC gave encouraging dosimetric results and is now routinely adopted in our Institution for compliant LBC patients with significant LAD exposure in radiation fields. http://dx.doi.org/10.1016/j.ejmp.2016.01.094
e27
A.91 A TOOL TO CHECK BRACHYTHERAPY TREATMENT TIME: A STATISTICAL APPROACH M. Giacometti *, L. Tesei, L. Vicenzi, S. Costantini, M. Cardinali, S. Maggi. Azienda Ospedaliera Universitaria Ospedali Riuniti, Ancona, Italy Introduction: Verification of treatment time accuracy is one of the specific activities of medical physicist. In external beam planning this issue has been faced for both 3DCRT and now for IMRT. Instead brachytherapy has not received the same attention, given the simplicity of the technique and the reduced diffusion. The aim of this work is to evaluate a possible approach for the verification of the correctness of BRT treatment times. Materials and methods: Our department is equipped with a microSelectron therapy unit and Oncentra v.4.1SP2 TPS, both by Nucletron Elekta. In this work we considered gynecological treatments, 195 with cylindrical applicator and 69 with Fletcher applicator, performed from 2011 until today. For each plan we recorded: source Air kerma strength (mGy m2/h), volume of the PTV enclosed within 90% isodose of prescription (V90, cc), prescription dose (cGy) and treatment time (s); following, we calculated the parameter F obtained as treatment time multiplied by activity and divided by prescription dose. Results: Data relating to the two types of treatment were analyzed separately. We applied a linear fit to the F parameter as a function of V90; the R2 values of 0.9593 and 0.9503 relate to fit for, respectively, treatments with cylindrical and Fletcher applicator. Following, we analyzed the distribution of per cent difference between time calculated by TPS and time obtained from the linear fit. In both cases we got a Gaussian distribution with mean and standard deviation (−0.1%, 4.2%) and (−0.3%, 4.2%) for cylindrical and Fletcher applicator, respectively. Conclusion: This work shows that, assuming the same criteria for volume contouring, it is possible to obtain a parameter F statistically correlated to V90. The per cent difference between the time calculated by TPS and the one estimated using the linear fit shows a Gaussian distribution with a standard deviation of 4%, thus suggesting a tool to evaluate BRT treatment time’s accuracy. http://dx.doi.org/10.1016/j.ejmp.2016.01.095
A.92 EPID-BASED IN-VIVO DOSIMETRY FOR PROSTATE CANCER TREATED BY VOLUMETRIC ARC THERAPY: PRELIMINARY CLINICAL RESULTS S. Giancaterino *,a, A. De Nicola a, N. Adorante a, P. Bagalà a, F. Perrotti a, S. Menna b , A. Fidanzio b , A. Piermattei b , D. Genovesi a , M.D. Falco a . a Department of Radiation Oncology, SS Annunziata Hospital, Chieti, Italy; b Istituto di Fisica e Unità Operativa di Fisica, Sanitaria Università Cattolica del S. Cuore, Roma, Italy Purpose: The purpose of this study is to report the in-vivo dosimetry (IVD) results obtained using the SOFTDISO software (Best Medical Italy) during VMAT prostate cancer treatments. Materials and methods: The SOFTDISO software reconstructs the dose at the isocenter (Diso) in the patient from the transit signal acquired by the EPID and allows the comparison between EPID images obtained during the therapy fractions. In particular for each beam and fraction, the ratios, R, between the dose reconstructed at the isocenter point Diso in single-arc VMAT plans and the dose calculated by the treatment planning system Diso,TPS (generally about 2 Gy for fraction) obtained by Oncentra Masterplan were computed. The acceptance criteria were: 0.95 < R < 1.05. Moreover the γ-analysis (2%-2 mm) between portal images was reported. 15 patients with prostate cancer were treated with 6 MV photon beam delivered by an Elekta Synergy Agility. Our protocol required, for each patient, 5 consecutive IVDs in the first 5 treatment sessions after a cone beam CT (CBCT) based setup correction and the IVD test once weekly afterward for the rest of the treatment course when the CBCT scan was not acquired. Results: The IVD procedure supplied 110 tests and the average R was equal to 1.004 ± 0.024 (1 SD), in a range between 0.948 and 1.059. The global R value for each single patient was well within the 5% tolerance level. The γ-analysis between EPID images yielded P(γ < 1) > 97% in 80% of the tests. The remaining 20% of the tests gave P(γ < 1) > 93%; they were mainly related to the sessions where the CBCT scans were not performed indicating that small set-up variations occurred.