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Accuracy of postimplant seed reconstruction studied with a CT- and MRI-compatible prostate phantom
96
Abstracts / Brachytherapy 5 (2006) 78–117 PHYSICS
P-53 Accuracy of postimplant seed reconstruction studied with a CT- and MRI-compatible prostate phantom Marisol De Brabandere, M.Sc.,1 Christian Kirisits, Ph.D.,2 Frank-Andre Siebert, Ph.D.3 1Radiotherapy University Hospital Gasthusiberg, Leuven, Belgium; 2Radiotherapy and Radiobiology, Med. Univ. of Vienna, Vienna, Austria; 3Radiotherapy Clinic, University Hospital of Schleswig-Holstein, Kiel, Germany. Purpose: An important factor determining the reliability of seed implant postplanning in prostate is the precision of seed localization. However, few comparatitive data are available on the seed localization accuracy of CT- and MR-based reconstructions. This is mainly due to the lack of suitable phantoms. Therefore, the Braphyqs group (task group in ESTRO ESQUIRE) developed a) a solid phantom suitable for CT and X-ray based reconstruction checks and b) a gel-based phantom compatible for checks on CT and MRI. With these phantoms, we can assess the seed detection accuracy for several imaging modalities. The results obtained for the gelbased phantom are presented. Methods and Materials: The gel-based phantom consists of a PMMA container filled with agarose slabs. Besides similar density to tissue, agarose (4% in solution) possesses comparable T1- and T2-relaxation times to prostate tissue (T1 5 1,207 ms, T2 5 66 ms for agarose, T1 5 1,317 ms, T2 5 88 ms for prostate). This guarantees similar imaging characteristics as in prostate, regardless of the scan parameters. This is important as imaging characteristics may influence the seed visualization and hence the localization accuracy. The phantom has a coordinate system consisting of N-shaped tubes which allow absolute determination of seed positions with respect to an origion fixed to the phantom. 60 seeds were implanted in the agarose according to a clinical strand-like pattern, including tilted and shifted seeds. MRI (Philips and Siemens 1.5T) and CT (Siemens) scans were acquired with 3, 4 and 5 mm slice thickness using clinical sequences (for MR: T1-weighted gradient echo). Seeds were reconstructed in Variseed and their coordinates were compared with the exact coordinates. Results: The mean deviations between the reconstructed and exact positions were 0.9, 0.9, and 2.1 mm with CT, 2.1, 1.6, and 1.9 mm with the MR Philips and 2.3, 2.0, and 1.6 mm with the MR Siemens for 3, 4, and 5 mm, respectively. For all cases, the deviations within slices were negligible. The deviations were largest in longitudinal direction but still !2 mm, which is acceptable for clinical use. In general, reconstructions on MRI were slightly less accurate than with CT, especially in longitudinal direction. This was because artifacts of seeds projecting on multiple slices were more pronounced on MR than CT. Conclusions: The gel-based phantom is a useful QA tool to check the accuracy of the postimplant seed reconstruction procedure. The checks will be repeated in several European centres for different scanning sequences. The feasibility of using the phantom as a mailed QA tool will be evaluated. P-54 DVH analysis and quality assurance of high-dose-rate (HDR) brachytherapy for prostate cancer Murali Nair, Ph.D., Rufus Mark, M.D., Paul Anderson, M.D., Thomas Neumann, M.D., David White, C.M.D., Stephen Gurley, C.M.D. Radiation Oncology, Joe Arrington Cancer Research and Treatment Center, Lubbock, TX. Purpose: To analyze the dose volume histograms (DVH), for the planning target volume (PTV) enclosing prostate and seminal vesicle, urethra and rectum in order to evaluate the quality of interstitial implant brachytherapy. The treatment planning technique and the quality assurance method used for the treatment are explained. Methods and Materials: From July 2002 to December 2005, we have treated 115 patients with 230 implants at 2 sessions per patient. Our dose fractionation consisted of 7.5 Gy per fraction to PTV to deliver 22.5 Gy per session in 3 fractions, repeated after 30 days delivering
a total dose of 45 Gy to the PTV. The biological equivalent dose (BED) calculated for the two course of treatments was 258 Gy using a/b ratio of 1.5. the stainless needles were implanted into the prostate using transrectal ultrasound guidance. The treatment planning images were taken using the CT by keeping the patient in the treatment position. Radio-opaque catheter was inserted into the urethra and was helpful in outlining the urethral boundary. The needle position was readjusted in order to obtain optimum distribution of needles around prostate capsule. For quality assurance check, the length of the needle projecting from the template to the hub of the connector cable was recorded. The treatment plan was generated using Plato software. Using graphical optimization and inverse planning, we were able to achiever uniform coverage to PTV, 5 mm extending beyond the capsule lining. The maximum dose to urethra was restricted to 105% of the PTV dose. We have analyzed the DVH of PTV for uniform coverage, DVH of urethra and rectum for toxicity analysis based on the dose received by 1/3rd volume. The plan calculated Ci.s.cGy21 for the PTV was compared with the Paterson Parker table for volume implant and was used for plan verification. We have analyzed the data for 230 implants and the results are given below. Results: The PTV volume ranged from 35 to 196 cm3, mean of 85 G 29 cm3. The % dose coverage to PTV was in the range 0f 94.5 to 100%, with a mean of 98%. The 1.3rd rectal volume received a dose of 152 to 4.98 Gy, mean dose of 2.7 Gy. The maximum urethral dose at any point as a percentage of PTV dose ranged from 90 to 118%, mean of 108%. The Ci.s.cGy21 varied with the PTV volume linearly with a trend line equation Ci.s.cGy21 5 0.035) PTV 1 2.0347 Conclusions: The optimized dosimetry for HDR brachytherapy enabled in achieving uniform coverage to the PTV on the average of 108% dose to urethra and less than 70% to rectum. The data showed that HDR monotherapy is superior to conformal EBRT, in controlling rectal dose and urethral dose, while achieving 98% PTV coverage to the immobilized prostate. P-55 Clinical benefits of a class solution for inversely planned high-doserate prostate brachytherapy Etienne Lessard, Ph.D., I-Chow J Hsu, M.D., Jean Pouliot, Ph.D. Radiation Oncology, UCSF Comprehensive Cancer Center, San Francisco, CA. Purpose: To report the clinical benefits of a set of inverse planning parameters (Class Solution) for the treatment planning of prostate highdose-rate brachytherapy with ours in house inverse planning routine (IPSA). Methods and Materials: More than one thousand patients have been planned and treated with IPSA since 2000. IPSA is a treatment-planning tool that combines the flexibility of the inverse planning approach (IP) and the computational efficiency of a simulated annealing optimization engine (SA). IPSA takes into account dose constraints on multiple targets and multiple organs at risk. A class solution is a set of dose constraints relevant to one anatomical site that has been tuned to cover variations over a wide range of patients. Ours class solution was defined to maximize the prostate dose coverage while taking into account other clinical objectives such as the dose homogeneity and the organs at risk protection. To evaluate the efficiency of ours class solution for prostate high-dose-rate brachytherapy, the dose volume histograms of 30 consecutive prostate cancer patients were analyzed. Results: The prostate volume ranged from 17 to 107 cm3. The number of implanted catheters varied from 12 to 18. The class solution produced consistently excellent treatment plans independently of the gland size and shape. The prostate V100 average value was 96% with a standard deviation of 2%. The prostate V150 average value was 35% with a standard deviation of 7%, resulting in a homogeneity index (HI) average value of 61% with a standard deviation of 7%. The urethra V100 average value was 94% with a standard deviation of 3% and the urethra V150 was always zero. Conclusions: The class solution improved the procedure time while generating excellent treatment plans. The class solution can be used as a starting point for every patient, reducing the time needed to plan individual patient treatments. The advantage of such an approach is that
Abstracts / Brachytherapy 5 (2006) 78–117 PHYSICS
P-53 Accuracy of postimplant seed reconstruction studied with a CT- and MRI-compatible prostate phantom Marisol De Brabandere, M.Sc.,1 Christian Kirisits, Ph.D.,2 Frank-Andre Siebert, Ph.D.3 1Radiotherapy University Hospital Gasthusiberg, Leuven, Belgium; 2Radiotherapy and Radiobiology, Med. Univ. of Vienna, Vienna, Austria; 3Radiotherapy Clinic, University Hospital of Schleswig-Holstein, Kiel, Germany. Purpose: An important factor determining the reliability of seed implant postplanning in prostate is the precision of seed localization. However, few comparatitive data are available on the seed localization accuracy of CT- and MR-based reconstructions. This is mainly due to the lack of suitable phantoms. Therefore, the Braphyqs group (task group in ESTRO ESQUIRE) developed a) a solid phantom suitable for CT and X-ray based reconstruction checks and b) a gel-based phantom compatible for checks on CT and MRI. With these phantoms, we can assess the seed detection accuracy for several imaging modalities. The results obtained for the gelbased phantom are presented. Methods and Materials: The gel-based phantom consists of a PMMA container filled with agarose slabs. Besides similar density to tissue, agarose (4% in solution) possesses comparable T1- and T2-relaxation times to prostate tissue (T1 5 1,207 ms, T2 5 66 ms for agarose, T1 5 1,317 ms, T2 5 88 ms for prostate). This guarantees similar imaging characteristics as in prostate, regardless of the scan parameters. This is important as imaging characteristics may influence the seed visualization and hence the localization accuracy. The phantom has a coordinate system consisting of N-shaped tubes which allow absolute determination of seed positions with respect to an origion fixed to the phantom. 60 seeds were implanted in the agarose according to a clinical strand-like pattern, including tilted and shifted seeds. MRI (Philips and Siemens 1.5T) and CT (Siemens) scans were acquired with 3, 4 and 5 mm slice thickness using clinical sequences (for MR: T1-weighted gradient echo). Seeds were reconstructed in Variseed and their coordinates were compared with the exact coordinates. Results: The mean deviations between the reconstructed and exact positions were 0.9, 0.9, and 2.1 mm with CT, 2.1, 1.6, and 1.9 mm with the MR Philips and 2.3, 2.0, and 1.6 mm with the MR Siemens for 3, 4, and 5 mm, respectively. For all cases, the deviations within slices were negligible. The deviations were largest in longitudinal direction but still !2 mm, which is acceptable for clinical use. In general, reconstructions on MRI were slightly less accurate than with CT, especially in longitudinal direction. This was because artifacts of seeds projecting on multiple slices were more pronounced on MR than CT. Conclusions: The gel-based phantom is a useful QA tool to check the accuracy of the postimplant seed reconstruction procedure. The checks will be repeated in several European centres for different scanning sequences. The feasibility of using the phantom as a mailed QA tool will be evaluated. P-54 DVH analysis and quality assurance of high-dose-rate (HDR) brachytherapy for prostate cancer Murali Nair, Ph.D., Rufus Mark, M.D., Paul Anderson, M.D., Thomas Neumann, M.D., David White, C.M.D., Stephen Gurley, C.M.D. Radiation Oncology, Joe Arrington Cancer Research and Treatment Center, Lubbock, TX. Purpose: To analyze the dose volume histograms (DVH), for the planning target volume (PTV) enclosing prostate and seminal vesicle, urethra and rectum in order to evaluate the quality of interstitial implant brachytherapy. The treatment planning technique and the quality assurance method used for the treatment are explained. Methods and Materials: From July 2002 to December 2005, we have treated 115 patients with 230 implants at 2 sessions per patient. Our dose fractionation consisted of 7.5 Gy per fraction to PTV to deliver 22.5 Gy per session in 3 fractions, repeated after 30 days delivering
a total dose of 45 Gy to the PTV. The biological equivalent dose (BED) calculated for the two course of treatments was 258 Gy using a/b ratio of 1.5. the stainless needles were implanted into the prostate using transrectal ultrasound guidance. The treatment planning images were taken using the CT by keeping the patient in the treatment position. Radio-opaque catheter was inserted into the urethra and was helpful in outlining the urethral boundary. The needle position was readjusted in order to obtain optimum distribution of needles around prostate capsule. For quality assurance check, the length of the needle projecting from the template to the hub of the connector cable was recorded. The treatment plan was generated using Plato software. Using graphical optimization and inverse planning, we were able to achiever uniform coverage to PTV, 5 mm extending beyond the capsule lining. The maximum dose to urethra was restricted to 105% of the PTV dose. We have analyzed the DVH of PTV for uniform coverage, DVH of urethra and rectum for toxicity analysis based on the dose received by 1/3rd volume. The plan calculated Ci.s.cGy21 for the PTV was compared with the Paterson Parker table for volume implant and was used for plan verification. We have analyzed the data for 230 implants and the results are given below. Results: The PTV volume ranged from 35 to 196 cm3, mean of 85 G 29 cm3. The % dose coverage to PTV was in the range 0f 94.5 to 100%, with a mean of 98%. The 1.3rd rectal volume received a dose of 152 to 4.98 Gy, mean dose of 2.7 Gy. The maximum urethral dose at any point as a percentage of PTV dose ranged from 90 to 118%, mean of 108%. The Ci.s.cGy21 varied with the PTV volume linearly with a trend line equation Ci.s.cGy21 5 0.035) PTV 1 2.0347 Conclusions: The optimized dosimetry for HDR brachytherapy enabled in achieving uniform coverage to the PTV on the average of 108% dose to urethra and less than 70% to rectum. The data showed that HDR monotherapy is superior to conformal EBRT, in controlling rectal dose and urethral dose, while achieving 98% PTV coverage to the immobilized prostate. P-55 Clinical benefits of a class solution for inversely planned high-doserate prostate brachytherapy Etienne Lessard, Ph.D., I-Chow J Hsu, M.D., Jean Pouliot, Ph.D. Radiation Oncology, UCSF Comprehensive Cancer Center, San Francisco, CA. Purpose: To report the clinical benefits of a set of inverse planning parameters (Class Solution) for the treatment planning of prostate highdose-rate brachytherapy with ours in house inverse planning routine (IPSA). Methods and Materials: More than one thousand patients have been planned and treated with IPSA since 2000. IPSA is a treatment-planning tool that combines the flexibility of the inverse planning approach (IP) and the computational efficiency of a simulated annealing optimization engine (SA). IPSA takes into account dose constraints on multiple targets and multiple organs at risk. A class solution is a set of dose constraints relevant to one anatomical site that has been tuned to cover variations over a wide range of patients. Ours class solution was defined to maximize the prostate dose coverage while taking into account other clinical objectives such as the dose homogeneity and the organs at risk protection. To evaluate the efficiency of ours class solution for prostate high-dose-rate brachytherapy, the dose volume histograms of 30 consecutive prostate cancer patients were analyzed. Results: The prostate volume ranged from 17 to 107 cm3. The number of implanted catheters varied from 12 to 18. The class solution produced consistently excellent treatment plans independently of the gland size and shape. The prostate V100 average value was 96% with a standard deviation of 2%. The prostate V150 average value was 35% with a standard deviation of 7%, resulting in a homogeneity index (HI) average value of 61% with a standard deviation of 7%. The urethra V100 average value was 94% with a standard deviation of 3% and the urethra V150 was always zero. Conclusions: The class solution improved the procedure time while generating excellent treatment plans. The class solution can be used as a starting point for every patient, reducing the time needed to plan individual patient treatments. The advantage of such an approach is that