- Email: [email protected]
Innovative Practice Models in Radiation Therapy
Results: The population mean bladder volume (1Standard Deviation {SD}) was 371 ml (195 ml) at planning-CT, 307 ml (160 ml) at first CBCT and 238 ml (126 ml) at final CBCT. The mean bladder volume from the first day CBCT to CT was not statistically different (p¼ 0.07, mean¼ -64.33, SD¼ 210.53). The mean bladder volume from the last day CBCT to CT was statistically different (p<0.0001, mean¼ -132.83, SD¼ 156.48). The mean bladder volume from the last day CBCT to the first day CBCT was also statistically different (p¼ 0.008, mean¼ -68.50, SD¼ 148.71). Conclusion: A significant reduction in bladder volume during the course of radiotherapy treatment was observed when compared with the intended bladder volume for patients in this study.
PODIUM PRESENTATIONS Optimization of Eclipse Rapidarc’s Normal Tissue Objective to Determine a Standard Setting for Use in Post-Prostatectomy Radiotherapy Treatment Planning Presenting author: C. Wong Radiation Therapy student, Mohawk-McMaster University Medical Radiation Sciences Program, Juravinski Cancer Centre, Canada. E-mail: [email protected] Other authors: K.R. Diamond Purpose: To evaluate the influence of Eclipse RapidArc’s Normal Tissue Objective (NTO) when applied to a tissue-equivalent phantom pelvis, and to optimize the NTO parameter settings for use in dosimetric planning for radiation therapy to post-prostatectomy patients. Methods and Materials: This study was conducted in two phases. Phase I systematically assessed the individual parameters comprising the NTO setting on a water-equivalent cylindrical phantom: distance from target border, starting dose (%), ending dose (%), fall off, and priority. Four established NTO settings were also examined. Two novel NTO settings were formulated using the results of Phase I, CW1 and CW2, to be compared against three of the four established settings: JCC (in house), Jolly (literature), and Auto (Eclipse 10 automatic NTO setting). This comparison was performed in Phase II, where the five NTO settings were applied to five randomly selected post-prostatectomy treatment plans. Data from both phases were evaluated for target coverage, conformity, and volumes of low isodoses. Results: Of the five settings, only CW1, Auto, and Jolly yielded target coverage ranging from 94.8% to 95.2%. CW1 was best at reducing the dose to the surrounding tissues, with the 80% and 50% isodose volumes including 3.2% and 2.7% less tissue, respectively, than the setting with the best target coverage (Jolly). The best sparing was achieved using CW2 and JCC settings; however, target coverage was unacceptably low (w91%). Conclusions: The CW1 NTO parameter set achieved the most balanced outcome for delivering target coverage and maintaining dose conformity as defined by RTOG, while limiting the normal tissue dose beyond the boundary of the target volume for the patient treatment plans in Phase II. While key insights have been achieved by means of this study, it is recommended that further investigations be conducted to establish a more complete understanding of the NTO.
PTV Margin Determination for Single-Fraction Stereotactic Body Radiation Therapy (SBRT) Boost for Intermediate-Risk Adenocarcinoma of the Prostate Presenting author: A. Nicolae Radiation Therapy student, University of Toronto/Michener Institute Medical Radiation Sciences Program, Odette Cancer Centre at Sunnybrook, Canada. E-mail: [email protected] Other authors: N. Venugopal, P. Cheung, A. Loblaw, W. Chu, M. Davidson, S. Jain and A. Ravi Purpose: This study aimed to determine an acceptable CTV-to-PTV margin that adequately covered the prostate displacement observed in a cohort of patients undergoing a single fraction SBRT boost to the prostate volume of either 10 Gy or 12.5 Gy, delivered using Volumetric-Modulated Arc Therapy (VMAT). Methods and Materials: 19 patients, with intermediate-risk adenocarcinoma confined to the prostate (T1-T2, Gleason Score (GS) 7, PSA 20 ng/mL or 158
T1-T2, GS 6, PSA 10-20 ng/mL), were implanted with gold fiducial markers under transrectal ultrasound guidance to serve as surrogates for prostate tracking. Pelvic immobilization was accomplished using a Kneefix 2(CIVCO) block. A water-filled endorectal balloon (ERB) was used with the intent of decreasing intrafractional prostatic motion. The urinary bladder was catheterized and filled with 200 cc of water to maintain a consistent volume. Patient specific expansions were generated using cine-MRI to account for intrafractional prostatic motion. Kilo-voltage Cone-beam Computed Tomography (CBCT) volumetric datasets were obtained for each patient directly before and immediately after treatment delivery for determining intrafraction prostate displacement during the elapsed treatment time. Cumulative histograms of the prostate displacement in the LR, SI, AP, and radial directions were then used to calculate an adequate CTV-to-PTV expansion to account for 95% of the displacements observed in the population. Results: An adequate CTV-PTV margin expansion to cover 95% of the observed displacements in the cohort was 3.0mm-3.2mm in LR, 2.2mm6.2mm in SI, and 2.8mm-8.0mm in AP. The isotropically-applied CTVPTV margin expansion was between 4.2mm-7.2mm. Conclusions: The current clinical protocol applies a 3.0mm-10.0mm (mean 5.0 1.4mm) isotropic CTV-to-PTV margin expansion that is adequate to cover the observed prostate displacements in the first cohort of patients studied. Evaluation of the next cohort of 10 patients will further refine the PTV margin that should be applied to patients being treated under the pHART5 protocol. Comparison between a Planned DVH and Calculated Daily DVH for Prostate Cancer Based on CBCT over a Course of EBRT – An Assessment of CTV, Bladder and Rectal Doses Presenting author: J. Wong Radiation Therapy student, British Columbia Institute of Technology Radiation Therapy Program, BC Cancer Agency, Canada. E-mail: [email protected] Other authors: N. McParland, I. Sigur and C. Stenger Purpose: To assess the accuracy of the initial CT plan dose-volume histograms (DVH’s) for prostate, rectum and bladder by comparison to DVH’s calculated from cone beam CT (CBCT) scans acquired during a course of EBRT. Materials and Methods: Five prostate patients treated with intensity modulated radiotherapy, and following daily bowel and bladder preparation protocol were studied. The prostate (CTV), rectum and bladder were contoured on daily CBCT scans and the approved treatment plan was applied to each dataset in order to calculate received doses. Bladder volumes receiving 50 Gy and 70 Gy, and rectal volumes receiving 45 Gy, 60 Gy, 70 Gy and 75 Gy were compared to the initial plan. The cumulative dose and volume changes found between the initial CT plan and contoured CBCT’s were tested for significance using the one sample t-test. An average DVH was constructed to identify all patients who failed rectal dose constraints based on DVH averages over the course of treatment. Prostate dose coverage was assessed by comparing % coverage of the 98% prescription dose to the CTV. Results: The 98% dose coverage of the CTV was found to be -1.8% to -4.7% of the predicted value. Three patients showed significant changes in bladder volumes and significantly higher bladder doses than expected (p < 0.001). Four patients showed significant changes in rectal volume and doses (p < 0.05). Based on the calculated average DVH, one patient failed rectal dose constraints over the entire course of treatment. Conclusions: Dose coverage of the prostate CTV was found to be lower than predicted. Calculated bladder and rectal doses were higher than predicted by the initial CT plan. The initial planning DVH does not accurately represent dose received during a course of EBRT. Innovative Practice Models in Radiation Therapy Presenting author: K. Brunskill Radiation Therapy student, Mohawk-McMaster University Medical Radiation Sciences Program, London Regional Cancer Centre/Juravinski Cancer Centre, Canada. E-mail: [email protected] Other authors: M. Smoke, T. Farrell and R. Singh Introduction/Purpose: Radiation Therapy is in an era of rapid technological advancement, increased entry-level education and growing specialization. The
Abstracts/Journal of Medical Imaging and Radiation Sciences 44 (2013) 157-162
question arises whether new staffing practice models in the Radiation Therapy departments should be implemented in order to manage and adapt to this change. A study was conducted to collect the opinions of Radiation Therapists at a large academic Canadian Cancer Centre on specialized versus generalized practice models of staffing. Understanding staff perceptions can indicate weaknesses and strengths of different practice models. This can lead to innovations in practice models for the Radiation Therapy departments for the better patient care and staff satisfaction. Methods and Materials: A literature review conducted summarized staffing model types used in major cancer centres. Concentrating the major themes of the literature review results, a survey was created and administered to analyze the perceptions of Radiation Therapists (N¼48) and Radiation Therapy students (N¼10) on a generalized versus specialized practice model of care in a Radiation Therapy department. Results: Staff wanted to work in areas with more advancing technology and displayed an interest to work in areas of the department that encouraged participation in inter-professional team dynamics. Job rotation within the department is consistently favoured by participants. Job satisfaction was another key theme arising from data analysis. Conclusion: Radiation therapy is dynamically evolving and pushing technological boundaries. Innovation in staffing practice models is paramount to the delivery of care. There is not one customary practice model that suits every agency the same. It is important to get a sense of the perceptions of the Radiation Therapy population from a larger, developed cancer centre. It will provide supportive information on preferred practice models that can be referred to by individuals in the future considering implementing a change within a department.
Characterization of the Accuracy of the Dose Delivery for Pelvic Adaptive Radiotherapy Using Cone-Beam CT for Post Planning Presenting author: D. Ribeiro Radiation Therapy student, Mohawk-McMaster University Medical Radiation Sciences Program, Juravinski Cancer Centre, Canada. E-mail: [email protected] Other author: J. Juhasz Purpose: Characterization of the feasibility of post-planning on Cone-Beam Computed Tomography (CBCT) images for pelvic adaptive radiotherapy. Methods and Materials: Previously, a commercially available phantom (CIRS 062) was modified to mimic the pelvis anatomy and to allow for full scatter conditions in a CBCT radiation field. Calibrated CBCT Hounsfield unit numbers were converted to electron density numbers. Afterwards, calibration curves were generated for dose calculation purposes to examine and compare dose distributions between treatment plans generated on CT-Simulator and CBCT images. In the Pinnacle Treatment Planning software, beams, points, and regions of interest (ROIs) were transferred from the original CT plan images to the CBCT images acquired on the treatment unit. Dose distributions were re-computed using the previous calibration curve and the new CBCT calibration curve specifically derived for this study. The generated treatment plans were cross-compared and analyzed. Results: Examination of Dose Volume Histograms (DVHs) and dose distribution analysis using an image processing software (Image J) confirmed the acceptable accuracy of the CBCT calibration curve. The results inferred that 3 of 4 patients received exceptional treatment accuracy using CBCT post-planning (within 3% difference). However, the comparison was based on image registration and not on the actual couch adjustment parameters before the treatment. Additional accuracy must be maintained, such as exact treatment setup parameters, and region of interest or contour adjustments on the CBCT images. Conclusions: The methodology established provides an insightful method in determining the accuracy in pelvic adaptive radiotherapy. Through the process of post-planning on CBCT scans, a valuable platform for pelvic adaptive therapy could possibly be made available and implemented in the treatment routine.
POSTER PRESENTATIONS An Evaluation of Two Approaches to Skin Bolus Design for Radiotherapy Planning of Head & Neck Cancers Presenting author: A. Luu Radiation Therapy student, Mohawk-McMaster University Medical Radiation Sciences Program, Juravinski Cancer Centre, Canada. E-mail: [email protected] Purpose: To compare our practice of placing bolus prior to CT simulation to an alternative where bolus is placed based on post-CT evaluation on the basis of target dose coverage and normal skin sparing. Methods and materials: Twelve previously planned head and neck patients requiring bolus were identified. The skin layers under the bolus but external to the CTV (normal skin) as well as the CTV layer within 5 mm of the bolus (superficial CTV) were delineated. The dose to these regions due to the original plan was compared to the dose resulting from the same plan, but with the original bolus region replaced (using density overrides) with a 1 cm thick custom bolus region overlaying the superficial CTV. The two configurations were compared on the basis of: bolus area and minimum dose to superficial CTV. Results: Out of 12 plans, 9 required a decrease in bolus area, while 3 required an increase. A Wilcoxon one-tail signed rank test at a 95% confidence interval determined that using the CT images to design bolus improves dose coverage compared to bolus made prior to the CT simulation. Post-CT designed bolus increased the minimum dose to superficial CTV by between 2.1% and 57.3%, roughly in proportion to the area under bolus. Similar statistical analysis indicated that the difference in bolus area between the two approaches was significant. Conclusion: Using the CT simulation image set to design bolus significantly improves dose coverage of the superficial CTV and significantly influences the area under bolus needed to ensure adequate target coverage and optimal sparing of normal skin.To determine if the minimum dose to a bolused CTV is affected when bolus is altered. Secondarily, this experiment attempts to determine if there is a noticeable difference in skin dose in the case of a difference in area of coverage from the pre-CT bolus to the treatment planning bolus.
Simple Figure of Merit to Assess Intraluminal Brachytherapy Plans Presenting author: T. Finnie Radiation Therapy student, Mohawk-McMaster University Medical Radiation Sciences Program, Juravinski Cancer Centre, Canada. E-mail: [email protected] Other authors: R. Hunter and T. Farrell Purpose: To design a simple figure of merit that can be used to assess the accuracy and optimization of intraluminal High Dose Rate (HDR) brachytherapy plans. Materials and Methods: Research was conducted in three phases, the first of which consisted of designing 15 multiline and 40 single line ’standard’ intraluminal HDR brachytherapy plans with visibly uniform and optimal dose distributions. The second phase involved the creation and assessment of 8 multiline plans and 10 single line plans that would be considered ‘‘unacceptable’’ for patient treatment based on their dose distributions. The final phase investigated plans that have been created and implemented as treatment for previous patients and have therefore already been considered ’acceptable’. The data collected from the standard plans assessed in phase I was graphed using various combinations of the three variables: irradiated volume (cm3), length of catheter (cm) and workload (curie seconds). Data collected in phases II and III were then compared with these graphs so see whether or not the unacceptable and acceptable plans would deviate from the expected standard graphs. Results: An algorithm designed from the data comparing the volume receiving 150% of the prescribed dose vs. the workload (curie seconds) identified the unacceptable single line plans with 100% accuracy and acceptable plans with 60% accuracy. There was no such algorithm that could be devised to effectively assess multi-line plans based on these three variables. Conclusion: More research is needed to design an accurate tool for the assessment of multi-line plans. Other factors are currently being implemented and
Abstracts/Journal of Medical Imaging and Radiation Sciences 44 (2013) 157-162
159
PODIUM PRESENTATIONS Optimization of Eclipse Rapidarc’s Normal Tissue Objective to Determine a Standard Setting for Use in Post-Prostatectomy Radiotherapy Treatment Planning Presenting author: C. Wong Radiation Therapy student, Mohawk-McMaster University Medical Radiation Sciences Program, Juravinski Cancer Centre, Canada. E-mail: [email protected] Other authors: K.R. Diamond Purpose: To evaluate the influence of Eclipse RapidArc’s Normal Tissue Objective (NTO) when applied to a tissue-equivalent phantom pelvis, and to optimize the NTO parameter settings for use in dosimetric planning for radiation therapy to post-prostatectomy patients. Methods and Materials: This study was conducted in two phases. Phase I systematically assessed the individual parameters comprising the NTO setting on a water-equivalent cylindrical phantom: distance from target border, starting dose (%), ending dose (%), fall off, and priority. Four established NTO settings were also examined. Two novel NTO settings were formulated using the results of Phase I, CW1 and CW2, to be compared against three of the four established settings: JCC (in house), Jolly (literature), and Auto (Eclipse 10 automatic NTO setting). This comparison was performed in Phase II, where the five NTO settings were applied to five randomly selected post-prostatectomy treatment plans. Data from both phases were evaluated for target coverage, conformity, and volumes of low isodoses. Results: Of the five settings, only CW1, Auto, and Jolly yielded target coverage ranging from 94.8% to 95.2%. CW1 was best at reducing the dose to the surrounding tissues, with the 80% and 50% isodose volumes including 3.2% and 2.7% less tissue, respectively, than the setting with the best target coverage (Jolly). The best sparing was achieved using CW2 and JCC settings; however, target coverage was unacceptably low (w91%). Conclusions: The CW1 NTO parameter set achieved the most balanced outcome for delivering target coverage and maintaining dose conformity as defined by RTOG, while limiting the normal tissue dose beyond the boundary of the target volume for the patient treatment plans in Phase II. While key insights have been achieved by means of this study, it is recommended that further investigations be conducted to establish a more complete understanding of the NTO.
PTV Margin Determination for Single-Fraction Stereotactic Body Radiation Therapy (SBRT) Boost for Intermediate-Risk Adenocarcinoma of the Prostate Presenting author: A. Nicolae Radiation Therapy student, University of Toronto/Michener Institute Medical Radiation Sciences Program, Odette Cancer Centre at Sunnybrook, Canada. E-mail: [email protected] Other authors: N. Venugopal, P. Cheung, A. Loblaw, W. Chu, M. Davidson, S. Jain and A. Ravi Purpose: This study aimed to determine an acceptable CTV-to-PTV margin that adequately covered the prostate displacement observed in a cohort of patients undergoing a single fraction SBRT boost to the prostate volume of either 10 Gy or 12.5 Gy, delivered using Volumetric-Modulated Arc Therapy (VMAT). Methods and Materials: 19 patients, with intermediate-risk adenocarcinoma confined to the prostate (T1-T2, Gleason Score (GS) 7, PSA 20 ng/mL or 158
T1-T2, GS 6, PSA 10-20 ng/mL), were implanted with gold fiducial markers under transrectal ultrasound guidance to serve as surrogates for prostate tracking. Pelvic immobilization was accomplished using a Kneefix 2(CIVCO) block. A water-filled endorectal balloon (ERB) was used with the intent of decreasing intrafractional prostatic motion. The urinary bladder was catheterized and filled with 200 cc of water to maintain a consistent volume. Patient specific expansions were generated using cine-MRI to account for intrafractional prostatic motion. Kilo-voltage Cone-beam Computed Tomography (CBCT) volumetric datasets were obtained for each patient directly before and immediately after treatment delivery for determining intrafraction prostate displacement during the elapsed treatment time. Cumulative histograms of the prostate displacement in the LR, SI, AP, and radial directions were then used to calculate an adequate CTV-to-PTV expansion to account for 95% of the displacements observed in the population. Results: An adequate CTV-PTV margin expansion to cover 95% of the observed displacements in the cohort was 3.0mm-3.2mm in LR, 2.2mm6.2mm in SI, and 2.8mm-8.0mm in AP. The isotropically-applied CTVPTV margin expansion was between 4.2mm-7.2mm. Conclusions: The current clinical protocol applies a 3.0mm-10.0mm (mean 5.0 1.4mm) isotropic CTV-to-PTV margin expansion that is adequate to cover the observed prostate displacements in the first cohort of patients studied. Evaluation of the next cohort of 10 patients will further refine the PTV margin that should be applied to patients being treated under the pHART5 protocol. Comparison between a Planned DVH and Calculated Daily DVH for Prostate Cancer Based on CBCT over a Course of EBRT – An Assessment of CTV, Bladder and Rectal Doses Presenting author: J. Wong Radiation Therapy student, British Columbia Institute of Technology Radiation Therapy Program, BC Cancer Agency, Canada. E-mail: [email protected] Other authors: N. McParland, I. Sigur and C. Stenger Purpose: To assess the accuracy of the initial CT plan dose-volume histograms (DVH’s) for prostate, rectum and bladder by comparison to DVH’s calculated from cone beam CT (CBCT) scans acquired during a course of EBRT. Materials and Methods: Five prostate patients treated with intensity modulated radiotherapy, and following daily bowel and bladder preparation protocol were studied. The prostate (CTV), rectum and bladder were contoured on daily CBCT scans and the approved treatment plan was applied to each dataset in order to calculate received doses. Bladder volumes receiving 50 Gy and 70 Gy, and rectal volumes receiving 45 Gy, 60 Gy, 70 Gy and 75 Gy were compared to the initial plan. The cumulative dose and volume changes found between the initial CT plan and contoured CBCT’s were tested for significance using the one sample t-test. An average DVH was constructed to identify all patients who failed rectal dose constraints based on DVH averages over the course of treatment. Prostate dose coverage was assessed by comparing % coverage of the 98% prescription dose to the CTV. Results: The 98% dose coverage of the CTV was found to be -1.8% to -4.7% of the predicted value. Three patients showed significant changes in bladder volumes and significantly higher bladder doses than expected (p < 0.001). Four patients showed significant changes in rectal volume and doses (p < 0.05). Based on the calculated average DVH, one patient failed rectal dose constraints over the entire course of treatment. Conclusions: Dose coverage of the prostate CTV was found to be lower than predicted. Calculated bladder and rectal doses were higher than predicted by the initial CT plan. The initial planning DVH does not accurately represent dose received during a course of EBRT. Innovative Practice Models in Radiation Therapy Presenting author: K. Brunskill Radiation Therapy student, Mohawk-McMaster University Medical Radiation Sciences Program, London Regional Cancer Centre/Juravinski Cancer Centre, Canada. E-mail: [email protected] Other authors: M. Smoke, T. Farrell and R. Singh Introduction/Purpose: Radiation Therapy is in an era of rapid technological advancement, increased entry-level education and growing specialization. The
Abstracts/Journal of Medical Imaging and Radiation Sciences 44 (2013) 157-162
question arises whether new staffing practice models in the Radiation Therapy departments should be implemented in order to manage and adapt to this change. A study was conducted to collect the opinions of Radiation Therapists at a large academic Canadian Cancer Centre on specialized versus generalized practice models of staffing. Understanding staff perceptions can indicate weaknesses and strengths of different practice models. This can lead to innovations in practice models for the Radiation Therapy departments for the better patient care and staff satisfaction. Methods and Materials: A literature review conducted summarized staffing model types used in major cancer centres. Concentrating the major themes of the literature review results, a survey was created and administered to analyze the perceptions of Radiation Therapists (N¼48) and Radiation Therapy students (N¼10) on a generalized versus specialized practice model of care in a Radiation Therapy department. Results: Staff wanted to work in areas with more advancing technology and displayed an interest to work in areas of the department that encouraged participation in inter-professional team dynamics. Job rotation within the department is consistently favoured by participants. Job satisfaction was another key theme arising from data analysis. Conclusion: Radiation therapy is dynamically evolving and pushing technological boundaries. Innovation in staffing practice models is paramount to the delivery of care. There is not one customary practice model that suits every agency the same. It is important to get a sense of the perceptions of the Radiation Therapy population from a larger, developed cancer centre. It will provide supportive information on preferred practice models that can be referred to by individuals in the future considering implementing a change within a department.
Characterization of the Accuracy of the Dose Delivery for Pelvic Adaptive Radiotherapy Using Cone-Beam CT for Post Planning Presenting author: D. Ribeiro Radiation Therapy student, Mohawk-McMaster University Medical Radiation Sciences Program, Juravinski Cancer Centre, Canada. E-mail: [email protected] Other author: J. Juhasz Purpose: Characterization of the feasibility of post-planning on Cone-Beam Computed Tomography (CBCT) images for pelvic adaptive radiotherapy. Methods and Materials: Previously, a commercially available phantom (CIRS 062) was modified to mimic the pelvis anatomy and to allow for full scatter conditions in a CBCT radiation field. Calibrated CBCT Hounsfield unit numbers were converted to electron density numbers. Afterwards, calibration curves were generated for dose calculation purposes to examine and compare dose distributions between treatment plans generated on CT-Simulator and CBCT images. In the Pinnacle Treatment Planning software, beams, points, and regions of interest (ROIs) were transferred from the original CT plan images to the CBCT images acquired on the treatment unit. Dose distributions were re-computed using the previous calibration curve and the new CBCT calibration curve specifically derived for this study. The generated treatment plans were cross-compared and analyzed. Results: Examination of Dose Volume Histograms (DVHs) and dose distribution analysis using an image processing software (Image J) confirmed the acceptable accuracy of the CBCT calibration curve. The results inferred that 3 of 4 patients received exceptional treatment accuracy using CBCT post-planning (within 3% difference). However, the comparison was based on image registration and not on the actual couch adjustment parameters before the treatment. Additional accuracy must be maintained, such as exact treatment setup parameters, and region of interest or contour adjustments on the CBCT images. Conclusions: The methodology established provides an insightful method in determining the accuracy in pelvic adaptive radiotherapy. Through the process of post-planning on CBCT scans, a valuable platform for pelvic adaptive therapy could possibly be made available and implemented in the treatment routine.
POSTER PRESENTATIONS An Evaluation of Two Approaches to Skin Bolus Design for Radiotherapy Planning of Head & Neck Cancers Presenting author: A. Luu Radiation Therapy student, Mohawk-McMaster University Medical Radiation Sciences Program, Juravinski Cancer Centre, Canada. E-mail: [email protected] Purpose: To compare our practice of placing bolus prior to CT simulation to an alternative where bolus is placed based on post-CT evaluation on the basis of target dose coverage and normal skin sparing. Methods and materials: Twelve previously planned head and neck patients requiring bolus were identified. The skin layers under the bolus but external to the CTV (normal skin) as well as the CTV layer within 5 mm of the bolus (superficial CTV) were delineated. The dose to these regions due to the original plan was compared to the dose resulting from the same plan, but with the original bolus region replaced (using density overrides) with a 1 cm thick custom bolus region overlaying the superficial CTV. The two configurations were compared on the basis of: bolus area and minimum dose to superficial CTV. Results: Out of 12 plans, 9 required a decrease in bolus area, while 3 required an increase. A Wilcoxon one-tail signed rank test at a 95% confidence interval determined that using the CT images to design bolus improves dose coverage compared to bolus made prior to the CT simulation. Post-CT designed bolus increased the minimum dose to superficial CTV by between 2.1% and 57.3%, roughly in proportion to the area under bolus. Similar statistical analysis indicated that the difference in bolus area between the two approaches was significant. Conclusion: Using the CT simulation image set to design bolus significantly improves dose coverage of the superficial CTV and significantly influences the area under bolus needed to ensure adequate target coverage and optimal sparing of normal skin.To determine if the minimum dose to a bolused CTV is affected when bolus is altered. Secondarily, this experiment attempts to determine if there is a noticeable difference in skin dose in the case of a difference in area of coverage from the pre-CT bolus to the treatment planning bolus.
Simple Figure of Merit to Assess Intraluminal Brachytherapy Plans Presenting author: T. Finnie Radiation Therapy student, Mohawk-McMaster University Medical Radiation Sciences Program, Juravinski Cancer Centre, Canada. E-mail: [email protected] Other authors: R. Hunter and T. Farrell Purpose: To design a simple figure of merit that can be used to assess the accuracy and optimization of intraluminal High Dose Rate (HDR) brachytherapy plans. Materials and Methods: Research was conducted in three phases, the first of which consisted of designing 15 multiline and 40 single line ’standard’ intraluminal HDR brachytherapy plans with visibly uniform and optimal dose distributions. The second phase involved the creation and assessment of 8 multiline plans and 10 single line plans that would be considered ‘‘unacceptable’’ for patient treatment based on their dose distributions. The final phase investigated plans that have been created and implemented as treatment for previous patients and have therefore already been considered ’acceptable’. The data collected from the standard plans assessed in phase I was graphed using various combinations of the three variables: irradiated volume (cm3), length of catheter (cm) and workload (curie seconds). Data collected in phases II and III were then compared with these graphs so see whether or not the unacceptable and acceptable plans would deviate from the expected standard graphs. Results: An algorithm designed from the data comparing the volume receiving 150% of the prescribed dose vs. the workload (curie seconds) identified the unacceptable single line plans with 100% accuracy and acceptable plans with 60% accuracy. There was no such algorithm that could be devised to effectively assess multi-line plans based on these three variables. Conclusion: More research is needed to design an accurate tool for the assessment of multi-line plans. Other factors are currently being implemented and
Abstracts/Journal of Medical Imaging and Radiation Sciences 44 (2013) 157-162
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