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In Vivo Rectal Wall Dosimetry in Gynecological HDR Brachytherapy Using a Semi-Flexible Rectal Probe Provided with MOSkin Dosimeters
S30
Abstracts / Brachytherapy 15 (2016) S21eS204
Comparison between the BrachyVision calculated dose and dosimeter measurement was performed using CERR radiotherapy analysis software. Results: The dosimeter was reconstructed with 1 mm voxel spacing and a 3pixel median filter. Aside from the needle track itself, no fractures formed in the dosimeter from the insertion, resulting in a pristine readout free of major image artifacts. Line profiles show strong agreement between the calculated and measured doses across the entire distribution, with exceptionally high matching at the sharp gradients surrounding the site of insertion (Fig. 1). Gamma index calculation shows 99.9% of voxels passing at 3%/2mm criteria. Conclusions: This work introduces a new formulation of low-durometer, deformable Presage dosimeters, and demonstrates strong viability for their use in complete 3D validation of interstitial brachytherapy treatments. These dosimeters are able to address a growing need in brachytherapy dose planning, quality control, and likely treatment commissioning. Further work will test this dosimeter formulation with multiple needle insertions, anthropomorphically-correct anatomy, and varying deformation to closer represent real-life treatment scenarios.
PHSOR6 Presentation Time: 1:25 PM In Vivo Rectal Wall Dosimetry in Gynecological HDR Brachytherapy Using a Semi-Flexible Rectal Probe Provided with MOSkin Dosimeters Chiara Tenconi, MS1, Mauro Carrara, PhD1, Davide Mazzeo, MS2, Anna Romanyukha, MS3, Annamaria Cerrotta, MD1, Giulio Rossi, MS2, Marta Borroni, PhD1, Dean Cutajar, PhD3, Marco Petasecca, PhD3, Michael Learch, PhD3, Joseph Bucci, MD4, Carlo Fallai, MD1, Grazia Gambarini, PhD2, Emanuele Pignoli, PhD1, Anatoly Rosenfeld, PhD3. 1 Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy; 2 Universit a degli Studi and INFN, Milan, Italy; 3Centre for Medical Radiation Physics, Wollongong, Australia; 4St George Cancer Care Center, Kogarah, Australia. Purpose: To study if MOSkin dosimeters coupled to a semi-flexible rectal probe (RP) may be used for in vivo dosimetry (IVD) on the rectal wall surface during gynecological (gyn) HDR brachytherapy (BT) and to quantify discrepancies between planned and delivered doses. Moreover, to investigate possible correlations of these discrepancies with the position of the dosimeters on the probe and also with the time elapsed between imaging and treatment. Materials and Methods: MOSkin is a specific type of MOSFET dosimeter developed at the Centre for Medical Radiation Physics, optimized to measure dose in steep dose gradients. Its sensitive volume, defined by the volume of the gate oxide, is 4.8 x 10-6 mm3. In this study, 3 MOSkins were calibrated in phantom and then assembled over semi-flexible rectal probes (RPs) at known distances from a radiopaque marker, which was included on the tip of each RP to facilitate MOSkins localization on CT images. RP provided with the dosimeters was placed in the rectum at the same time of applicator insertion and then CT images were acquired. During treatment, RP was left inside the rectum and real time IVD measurements were performed. The doses calculated by means of the treatment planning system in the estimated dosimeters positions were compared to measured doses. Possible correlations of the obtained relative dose differences (relDD) with the position of the dosimeters on the RP and also with the time elapsed between imaging and treatment were investigated. RelDD was expressed as (meas. D - calc. D) / (calc. D) and its absolute value jrelDDj was also taken into account. After a preliminary validation of the RPs in a gel phantom, IVD was performed on five patients treated with HDR gyn BT between October and December 2015. Prescribed dose to the target was 700cGy. 4 patients treated with a Multichannel cylindrical applicator and 1 with a Fletcher applicator. Results: 17 treatment sessions for a total of 51 measurements were analyzed. Three different RPs were used to this aim, for a maximum of 6 sessions each. In one case, one MOSkin failed probably due to physical stress and provided an unreliable measurement. Two outliers with extremely high relDD were moreover detected (i.e. average relDD over
the 3 MOSkins were of -33.5% and -50.1%) and excluded from the subsequent analysis. This high discrepancy was most probably due to a significant shift of the RP towards the anus that occurred after imaging. The remaining 44 measurements ranged between 139cGy and 518cGy. Average measured dose and average relDD were 32696cGy and 1.87.0% (k51), respectively. In three cases, relDD was higher than 10%, indicating a significant underestimation of the delivered dose to the rectal wall, whereas in 2 cases it resulted lower than -10%. Average jrelDDj was 5.84.3%, subdivided in 7.99.6%, 5.56.0% and 3.84.4% for the three different MOSkins positions, starting from the most cranial to the most caudal one, respectively. Both average jrelDDjs and standard deviations are therefore higher for deeper MOSkins. This is probably due to the fact that a possible change of the rectum position (and/or of the RP within the rectum) is more probable for higher distances of the rectum/RP from the anal canal. When grouping jrelDDj according to the time elapsed between imaging and treatment (i.e. group 1: #90min; group 2: O90min), average jrelDDj for group 1 and 2 were significantly different (p50.03), resulting in 3.83.5% and 6.54.3%, respectively. Planning time should be therefore kept as low as possible to reduce both uncertainties in measured and possibly also in calculated doses to the rectal wall, because of a resulting lowered probability of a rectum/RP shift between imaging and treatment. Conclusions: MOSkin dosimeters coupled to a semi-flexible RP may be used for IVD on the rectal wall surface during HDR gyn BT. Results are very promising, however further studies are still necessary to better immobilize the RP within the rectum and to reduce uncertainties related to its position.
PHSOR7 Presentation Time: 1:30 PM Building a Culture of Safety in Brachytherapy Using an Incident Learning System, Quantitative Analysis of 8 Years of Data Christopher L. Deufel, PhD, Keith M. Furutani, PhD, Luke B. McLemore, MS, Luis Fong de los Santos, PhD, Kelly L. Classic, MS. Radiation Oncology, Mayo Clinic, Rocheter, MN, USA. Purpose: Incident learning systems (ILS) helps to identify modes of failure that were unimagined or thought to be insignificant. It has been suggested that almost half of reported incidents may not be predicted by typical failure mode and effects analysis (FMEA)(1). We performed a quantitative analysis of results from an electronic incident learning system that was developed exclusively for brachytherapy starting in January 2007. An analysis was undertaken to determine what impact the incident learning system had on practice quality and safety culture. Materials and Methods: The brachytherapy incident learning system encouraged reporting of all deviations from standard operating procedure including incidents with very limited potential clinical impact. In order to promote a culture of safety, and not a culture of blame and train, patient information and staff involved in the incident were not included in the report. Additionally, regular meetings were held to determine a risk priority number (RPN) score for every report entered in the ILS and identify opportunities for practice improvements. The analysis of the incident results was shared with physicians, physicists, and support staff to reduce the likelihood of future incidents. Moreover, specific changes were implemented as a result of the incident learning reports, including changes to procedure checklists and written directive format. Incident rate, RPN, and dose risk were analyzed as a function of time. Results: 1879 incidents were reported between January 2007 and January 2015. The average reported incident rate during that time period was approximately 0.4 incidents per treatment. The incident, averaged in one month bins, ranged from 0 to 1.5 incidents per treatment. Incident rate was lower in treatments with greater fractionation (e.g. HDR vs. LDR). The incident submission rate is consistent with greater use of the system over time, increasing from and average of !0.1 incidents per patient treatment to approximately 0.5 incidents per patient treatment. The average risk of dosimetric error, scored on a scale from 1 (zero possible dose error) to 5 (possible harm to patient) decreased, during the eight
Abstracts / Brachytherapy 15 (2016) S21eS204
Comparison between the BrachyVision calculated dose and dosimeter measurement was performed using CERR radiotherapy analysis software. Results: The dosimeter was reconstructed with 1 mm voxel spacing and a 3pixel median filter. Aside from the needle track itself, no fractures formed in the dosimeter from the insertion, resulting in a pristine readout free of major image artifacts. Line profiles show strong agreement between the calculated and measured doses across the entire distribution, with exceptionally high matching at the sharp gradients surrounding the site of insertion (Fig. 1). Gamma index calculation shows 99.9% of voxels passing at 3%/2mm criteria. Conclusions: This work introduces a new formulation of low-durometer, deformable Presage dosimeters, and demonstrates strong viability for their use in complete 3D validation of interstitial brachytherapy treatments. These dosimeters are able to address a growing need in brachytherapy dose planning, quality control, and likely treatment commissioning. Further work will test this dosimeter formulation with multiple needle insertions, anthropomorphically-correct anatomy, and varying deformation to closer represent real-life treatment scenarios.
PHSOR6 Presentation Time: 1:25 PM In Vivo Rectal Wall Dosimetry in Gynecological HDR Brachytherapy Using a Semi-Flexible Rectal Probe Provided with MOSkin Dosimeters Chiara Tenconi, MS1, Mauro Carrara, PhD1, Davide Mazzeo, MS2, Anna Romanyukha, MS3, Annamaria Cerrotta, MD1, Giulio Rossi, MS2, Marta Borroni, PhD1, Dean Cutajar, PhD3, Marco Petasecca, PhD3, Michael Learch, PhD3, Joseph Bucci, MD4, Carlo Fallai, MD1, Grazia Gambarini, PhD2, Emanuele Pignoli, PhD1, Anatoly Rosenfeld, PhD3. 1 Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy; 2 Universit a degli Studi and INFN, Milan, Italy; 3Centre for Medical Radiation Physics, Wollongong, Australia; 4St George Cancer Care Center, Kogarah, Australia. Purpose: To study if MOSkin dosimeters coupled to a semi-flexible rectal probe (RP) may be used for in vivo dosimetry (IVD) on the rectal wall surface during gynecological (gyn) HDR brachytherapy (BT) and to quantify discrepancies between planned and delivered doses. Moreover, to investigate possible correlations of these discrepancies with the position of the dosimeters on the probe and also with the time elapsed between imaging and treatment. Materials and Methods: MOSkin is a specific type of MOSFET dosimeter developed at the Centre for Medical Radiation Physics, optimized to measure dose in steep dose gradients. Its sensitive volume, defined by the volume of the gate oxide, is 4.8 x 10-6 mm3. In this study, 3 MOSkins were calibrated in phantom and then assembled over semi-flexible rectal probes (RPs) at known distances from a radiopaque marker, which was included on the tip of each RP to facilitate MOSkins localization on CT images. RP provided with the dosimeters was placed in the rectum at the same time of applicator insertion and then CT images were acquired. During treatment, RP was left inside the rectum and real time IVD measurements were performed. The doses calculated by means of the treatment planning system in the estimated dosimeters positions were compared to measured doses. Possible correlations of the obtained relative dose differences (relDD) with the position of the dosimeters on the RP and also with the time elapsed between imaging and treatment were investigated. RelDD was expressed as (meas. D - calc. D) / (calc. D) and its absolute value jrelDDj was also taken into account. After a preliminary validation of the RPs in a gel phantom, IVD was performed on five patients treated with HDR gyn BT between October and December 2015. Prescribed dose to the target was 700cGy. 4 patients treated with a Multichannel cylindrical applicator and 1 with a Fletcher applicator. Results: 17 treatment sessions for a total of 51 measurements were analyzed. Three different RPs were used to this aim, for a maximum of 6 sessions each. In one case, one MOSkin failed probably due to physical stress and provided an unreliable measurement. Two outliers with extremely high relDD were moreover detected (i.e. average relDD over
the 3 MOSkins were of -33.5% and -50.1%) and excluded from the subsequent analysis. This high discrepancy was most probably due to a significant shift of the RP towards the anus that occurred after imaging. The remaining 44 measurements ranged between 139cGy and 518cGy. Average measured dose and average relDD were 32696cGy and 1.87.0% (k51), respectively. In three cases, relDD was higher than 10%, indicating a significant underestimation of the delivered dose to the rectal wall, whereas in 2 cases it resulted lower than -10%. Average jrelDDj was 5.84.3%, subdivided in 7.99.6%, 5.56.0% and 3.84.4% for the three different MOSkins positions, starting from the most cranial to the most caudal one, respectively. Both average jrelDDjs and standard deviations are therefore higher for deeper MOSkins. This is probably due to the fact that a possible change of the rectum position (and/or of the RP within the rectum) is more probable for higher distances of the rectum/RP from the anal canal. When grouping jrelDDj according to the time elapsed between imaging and treatment (i.e. group 1: #90min; group 2: O90min), average jrelDDj for group 1 and 2 were significantly different (p50.03), resulting in 3.83.5% and 6.54.3%, respectively. Planning time should be therefore kept as low as possible to reduce both uncertainties in measured and possibly also in calculated doses to the rectal wall, because of a resulting lowered probability of a rectum/RP shift between imaging and treatment. Conclusions: MOSkin dosimeters coupled to a semi-flexible RP may be used for IVD on the rectal wall surface during HDR gyn BT. Results are very promising, however further studies are still necessary to better immobilize the RP within the rectum and to reduce uncertainties related to its position.
PHSOR7 Presentation Time: 1:30 PM Building a Culture of Safety in Brachytherapy Using an Incident Learning System, Quantitative Analysis of 8 Years of Data Christopher L. Deufel, PhD, Keith M. Furutani, PhD, Luke B. McLemore, MS, Luis Fong de los Santos, PhD, Kelly L. Classic, MS. Radiation Oncology, Mayo Clinic, Rocheter, MN, USA. Purpose: Incident learning systems (ILS) helps to identify modes of failure that were unimagined or thought to be insignificant. It has been suggested that almost half of reported incidents may not be predicted by typical failure mode and effects analysis (FMEA)(1). We performed a quantitative analysis of results from an electronic incident learning system that was developed exclusively for brachytherapy starting in January 2007. An analysis was undertaken to determine what impact the incident learning system had on practice quality and safety culture. Materials and Methods: The brachytherapy incident learning system encouraged reporting of all deviations from standard operating procedure including incidents with very limited potential clinical impact. In order to promote a culture of safety, and not a culture of blame and train, patient information and staff involved in the incident were not included in the report. Additionally, regular meetings were held to determine a risk priority number (RPN) score for every report entered in the ILS and identify opportunities for practice improvements. The analysis of the incident results was shared with physicians, physicists, and support staff to reduce the likelihood of future incidents. Moreover, specific changes were implemented as a result of the incident learning reports, including changes to procedure checklists and written directive format. Incident rate, RPN, and dose risk were analyzed as a function of time. Results: 1879 incidents were reported between January 2007 and January 2015. The average reported incident rate during that time period was approximately 0.4 incidents per treatment. The incident, averaged in one month bins, ranged from 0 to 1.5 incidents per treatment. Incident rate was lower in treatments with greater fractionation (e.g. HDR vs. LDR). The incident submission rate is consistent with greater use of the system over time, increasing from and average of !0.1 incidents per patient treatment to approximately 0.5 incidents per patient treatment. The average risk of dosimetric error, scored on a scale from 1 (zero possible dose error) to 5 (possible harm to patient) decreased, during the eight