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Image Guided Radiotherapy to the Prostate after Implantation of Gold Fiducials: Is it Necessary to Wait 7 Days for Planning?
Proceedings of the 50th Annual ASTRO Meeting utilizing the ‘‘cine’’ mode. Volumes were contoured on standard single phase CT images as well as MIP images taking into account respiratory motion. Dosimetric consequences of intrafraction organ motion were assessed. Results: There were significant organ motion differences noted comparing prone vs. supine position (p \ 0.01). Prostate motion was more evident superiorly. Median AP motion for patients treated prone vs. supine were 3.9 mm (±1.4 mm) vs. 0.9 mm (±0.6 mm) at base, 3.2 mm (±1.2 mm) vs. 0 mm (±0.6 mm) at midgland, and 1.1 mm (±0.6 mm) vs. 0 mm (±0.3 mm) at apex (p \ 0.01). Sup-inf organ motion was also significant with a median of 2.1 mm (±1.5 mm) prone vs. 0mm (±0.6 mm) supine. Lateral organ motion was negligible in all patients. Rectal wall motion in an AP direction correlated with prostate organ motion with median of 4.1 mm, 2.5 mm, and 1.1 mm at levels of prostatic base, midgland, and apex, respectively, when prone and 1.1 mm, 0.5 mm, and 0 mm when supine. Bladder motion was also more evident in a prone vs. supine position with median values of 3.3 mm vs. 1.5 mm (p\0.01) measured at dome and 1.6mm vs. 0 mm (p\0.01) measured at bladder neck. Pubic symphysis motion and sacral motion were negligible when supine and measured a median of 1.4 and 1.8 mm prone, respectively. Dose coverage for prostate (D95) were reduced by a median value of 3.3% (1.6% - 4.2%), and doses of rectum and bladder changed by median values of 4.3% (0.2% to 7.6%) and 0.4% (-13.2% to +12.9%), respectively, in patients treated prone. Differences in organ motion were unaffected by bladder volume, prostate volume, BMI, or baseline AUA scores. Conclusions: 4D-CT simulation provides a useful method to assess respiratory organ motion. Intrafraction organ motion is more significant in a prone position and differs from base to apex. Dosimetrically, organ motion may lead to small but significant changes in target coverage. Using 4D-CT simulation, PTV margins can be selectively tightened in patients, which will have important implications for high dose hypo-fractionated regimens using IGRT. Author Disclosure: S. Sim, None; J. Li, None; M. Chan, None; K. Schupak, None; C. Burman, None; B. Mueller, None; D.M. Lovelock, None; M.J. Zelefsky, None.
2884
Image Guided Intermediate-stage Prostate Cancer IMRT: Minimum Margins and an Ideal Alignment Strategy
F. A. Lerma, S. Z. Liu, B. Liu, H. Li, B. Yi, P. Amin, C. X. Yu University of Maryland, Baltimore, MD Purpose/Objective(s): Previously, margins in Intermediate Stage Prostate Cancer IMRT planning have been inferred from motion and setup measurements from radiographic studies, and probabilistic simulations. We measure, target coverage of prostate, seminal vesicles (SV), and elective lymph node (LN) chains directly from serial CT imaging studies, comparing bony and soft tissue aligned Image-guided IMRT. Materials/Methods: Thirty CT scans of 5 prostate cancer patients are segmented manually; identifying the prostate, SV, and elective LN chains from the L5-S1 level to the obturator nodes. The LN are determined from expansions from the vascular bundles as seen from CT. A PTV is made from the union of a 5 mm margin expansions about the prostate and SV, and a 10 mm expansion about the vascular bundles, on each patient’s initial CT scan. The 10 mm margin on the vascular bundles accounts for the uncertainty in defining a CTV and geometrical variations leading to a PTV. The resultant PTV is used to create a unique IMRT plan, which is localized to the serial CT scans, by bony alignment and from the vector connecting the prostate centroid from the plan CT to the serial CT, simulating soft-tissue alignment. The coverage of the prostate, seminal vesicles; and of the vascular bundles, expanded by 0, 7, 9,and 10 mm, are evaluated on each serial CT. Results: Bony alignment delivers more than 95% of the target dose to 91-99% of the prostate and 83-97% of the SV, while prostate-soft-tissue alignment delivers more than 95% of the target dose to 95-99% of the prostate and 95-99% of the SV. 99, 98, 97, and 95% of targets resulting from 0, 7, 9, and 10 mm expansions of the vascular bundles are covered by 95% of the target dose after bony alignment. 99, 97, 95, and 94% of targets resulting from 0, 7, 9, and 10 mm expansions of the vascular bundles are covered by 95% of the target dose after soft tissue alignment. Other margin expansions about the initial CTs prostate, seminals and vascular bundles are also examined. Conclusions: Margins less than 5 mm on the prostate and SV lead to significant underdosing in serial CTs, even after soft tissue localization. LN clinical targets are covered by 10 mm expansions from the vascular bundles in the initial CT, even after soft-tissue localization. We implement clinically 5 mm margins about the prostate and SV, and 10 mm margins on the vascular bundles, combined with soft-tissue guidance. Author Disclosure: F.A. Lerma, None; S.Z. Liu, None; B. Liu, None; H. Li, None; B. Yi, None; P. Amin, None; C.X. Yu, None.
2885
Image Guided Radiotherapy to the Prostate after Implantation of Gold Fiducials: Is it Necessary to Wait 7 Days for Planning?
A. Havnen, S. Liauw, C. Pelizzari, K. Yenice University of Chicago, Chicago, IL Purpose/Objective(s): Gold seeds are commonly used as fiducials for image-guided radiotherapy to verify the position of the prostate. Due to potential seed migration immediately following implantation, computed tomography (CT) imaging for treatment planning is often performed several days later. This study evaluates changes in fiducial positions between the day of implant and the day of CT simulation. Materials/Methods: 15 patients with prostate cancer were implanted using a transperineal technique, with 3 fiducials placed at the base, mid-gland, and apex of the prostate. CTs were acquired in all patients immediately after implantation (CT0) and at 7 to 9 days after implant for treatment planning (CTSim). The prostate and fiducials were contoured on each image set by the same person. Position coordinates of the prostate and each fiducial were determined from the center of mass (COM) of their contoured volumes. The COM of all three seeds (COMFids) was also calculated. Uncertainty in fiducial position due to partial volume effects from CT slice thickness was found to be less than 1 mm. The uncertainty in these positions resulted in a precision of 1 mm in the identification of COMFids.
S565
I. J. Radiation Oncology d Biology d Physics
S566
Volume 72, Number 1, Supplement, 2008
For each image set, the following distances were calculated: (1) fiducial to fiducial, (2) COMFids to each individual fiducial, and (3) COMFids to the prostate COM. The magnitudes of these distances in CT0 were compared to those in CTSim to evaluate migration. Results: Comparison of 45 inter-seed measurements (3 for each patient) from CT0 with those from CTSim demonstrated the absolute value of inter-seed migration averaged 0.9 mm with a standard deviation (SD) of 0.8 mm. The average accounting for both increases and decreases in inter-seed distances between CT0 and CTSim was near zero (0.1 mm with a SD of 1.3 mm), indicating no significant systematic increase or decrease during this period. Similarly, the absolute value of the change in distance between the COMFids and each individual seed averaged 1.2 mm with a SD of 0.9 mm, and the average of increases and decreases in this distance was 0.0 mm with SD of 1.5 mm. 95% of measured changes in the magnitude of inter-seed and COMFids-to-seed distances were less than 3 mm, and 90% were less than 2 mm. The absolute value of the change in distance between the COMFids and the prostate COM was on average 2.6 mm with a SD of 2.1 mm. This variation is reasonable considering the uncertainty in prostate localization. Conclusions: Inter-seed distances changed by less than 1 mm on average in the first week after implantation. The consistency of the distance between the COMFids and the prostate COM demonstrates the stability of the seeds within the prostate. CT simulation for treatment planning may occur on the day of fiducial implantation without concern for significant migration of the seeds. Author Disclosure: A. Havnen, None; S. Liauw, None; C. Pelizzari, None; K. Yenice, None.
2886
Analysis of Dose Volume Histogram Differences between High Dose Rate Brachytherapy and Intensity Modulated Radiotherapy for Prostate Treatment
J. Hermesse1, S. Biver1, B. Thissen1, B. Warlimont1, N. Jansen1, P. Coucke1, P. Nickers2 1
CHU Liege, Liege, Belgium, 2Oscar Lambret, Lille, France
Purpose/Objective(s): We aimed at comparing the dose distribution of HDR brachytherapy and IMRT in prostate cancer. Materials/Methods: The tomodensitometric data of ten successive patients treated with HDR brachytherapy for prostate cancer were recovered for the dosimetric intercomparison. The Nomos-Corvus treatment planning system (TPS) was used for IMRT planning while dose distribution for HDR brachytherapy was calculated with the Brachyvision TPS. A theoretical dose of 10 Gy applied by 2 Gy per fraction (EQD2) was prescribed on the PTV in the IMRT approach. We selected an a/b ratio of 1.5 Gy to calculate a biological equivalent unique dose for HDR brachytherapy (5.22 Gy). The dose was normalized in order to allow 95% coverage of the PTV. The dose-volume histograms were calculated for PTV and organs at risk (OARs). For these, doses were converted to EQD2, considering an a/b ratio of 3 Gy. Differences between the obtained dose-distributions were compared with a two-sided Student’s t test. Results: Dose heterogeneity is more pronounced with HDR brachytherapy with a mean dose to the PTV of 23.8 Gy as compared to 10.5 Gy with IMRT. Cold spots are similar with both methods: 7.93 Gy and 8.17 Gy, respectively, with IMRT and HDR brachytherapy (p = 0.6). The rectal dose is reduced by HDR brachytherapy as 0.5 cc of the rectum received 5.9 Gy as compared to 10.2 Gy with IMRT (p \ 0.0001). 8.08 Gy was delivered to 20% of the rectal volume with IMRT as compared to 2.74 Gy with HDR brachytherapy (p \ 0.0001). The same observation favoring HDR brachytherapy is made for the bladder: 20% of the organ received 7.11 Gy with IMRT but 1.76 Gy with HDR brachytherapy (p \ 0.0001). The maximal dose delivered to the urethra is increased by HDR brachytherapy to 13.4 Gy as compared to 11.1 Gy with IMRT but mean dose and minimal dose on the urethra are significantly lower with HDR brachytherapy (p \ 0.0025). The volume of normal tissues receiving 1 Gy was reduced by a factor 8 with HDR brachytherapy (p \ 0.0001). Conclusions: HDR brachytherapy allows high hyperdosage sleeves inside the PTV while sparing dramatically the OARs as compared to IMRT. The lower number of expected secondary cancers will thus favor brachytherapy use in exclusive or boosting radiation programs, particularly for younger patients. Author Disclosure: J. Hermesse, None; S. Biver, None; B. Thissen, None; B. Warlimont, None; N. Jansen, None; P. Coucke, None; P. Nickers, None.
2887
Fractional Integral Target Dose Comparison for I-125, Pd-103 and Cs-131 in Prostate Seed Implants
T. Li, L. Fountain, E. Duffy Tuomey Healthcare System, Sumter, SC Purpose/Objective(s): To use fractional integral target dose to obtain the fraction of energy absorbed by the prostate from integral dose, which is an indication of ‘‘radiation delivery efficiency’’ in brachytherapy. Also to introduce a parameter that shows the fraction of excess energy absorbed in the prostate. Those parameters can be used to aid the clinical choice of isotopes. Materials/Methods: A total of 15 boost therapy implant cases (5 for each isotope) are utilized for this comparison. The TRUS images are obtained intra-operatively using B&K Ultrasound unit in 5 mm steps. The planning parameters are defined according to RTOG 0232 guidelines. The prescription doses are: 85 Gy for Cs-131, 108 Gy for I-125 and 100 Gy for Pd-103. The seed strengths employed are: 1.8 U (Cs-131), 1.42 U (Pd-103) and 0.279-0.356 U (I-125). The prostate volume ranges from 25 to 50 cc. Planning goals are: V100 95%, D90100%, and prostatic urethra D10 150%. Dose calculations are performed using Variseed (ver7.1, VMS, Palo Alto, CA) planning system using AAPM TG-43 formalism. All plans are evaluated to insure the planning goals are met. Uniformity (V200), D90 for urethra, and D30 for rectum are also evaluated. Integral target dose are obtained by multiplying the prostate volume V with mean dose Dmean. Total integral dose is obtained by adopting the point source model from AAPM TG43. The integral dose E delivered by a single source with unit activity is the integration of 4Pi r2 D(r)/r2 dr times 1.44T1/2. Let A be the total activity implanted, the total integral dose will be AE. The fractional integral target dose the prostate receives is defined as DmeanV/AE. We also define a parameter (Dmean-mPD)V/AE that indicates the fraction of excess energy absorbed in the prostate. This parameter shows the amount of energy that is more than needed to achieve the minimum peripheral dose (mPD).
2884
Image Guided Intermediate-stage Prostate Cancer IMRT: Minimum Margins and an Ideal Alignment Strategy
F. A. Lerma, S. Z. Liu, B. Liu, H. Li, B. Yi, P. Amin, C. X. Yu University of Maryland, Baltimore, MD Purpose/Objective(s): Previously, margins in Intermediate Stage Prostate Cancer IMRT planning have been inferred from motion and setup measurements from radiographic studies, and probabilistic simulations. We measure, target coverage of prostate, seminal vesicles (SV), and elective lymph node (LN) chains directly from serial CT imaging studies, comparing bony and soft tissue aligned Image-guided IMRT. Materials/Methods: Thirty CT scans of 5 prostate cancer patients are segmented manually; identifying the prostate, SV, and elective LN chains from the L5-S1 level to the obturator nodes. The LN are determined from expansions from the vascular bundles as seen from CT. A PTV is made from the union of a 5 mm margin expansions about the prostate and SV, and a 10 mm expansion about the vascular bundles, on each patient’s initial CT scan. The 10 mm margin on the vascular bundles accounts for the uncertainty in defining a CTV and geometrical variations leading to a PTV. The resultant PTV is used to create a unique IMRT plan, which is localized to the serial CT scans, by bony alignment and from the vector connecting the prostate centroid from the plan CT to the serial CT, simulating soft-tissue alignment. The coverage of the prostate, seminal vesicles; and of the vascular bundles, expanded by 0, 7, 9,and 10 mm, are evaluated on each serial CT. Results: Bony alignment delivers more than 95% of the target dose to 91-99% of the prostate and 83-97% of the SV, while prostate-soft-tissue alignment delivers more than 95% of the target dose to 95-99% of the prostate and 95-99% of the SV. 99, 98, 97, and 95% of targets resulting from 0, 7, 9, and 10 mm expansions of the vascular bundles are covered by 95% of the target dose after bony alignment. 99, 97, 95, and 94% of targets resulting from 0, 7, 9, and 10 mm expansions of the vascular bundles are covered by 95% of the target dose after soft tissue alignment. Other margin expansions about the initial CTs prostate, seminals and vascular bundles are also examined. Conclusions: Margins less than 5 mm on the prostate and SV lead to significant underdosing in serial CTs, even after soft tissue localization. LN clinical targets are covered by 10 mm expansions from the vascular bundles in the initial CT, even after soft-tissue localization. We implement clinically 5 mm margins about the prostate and SV, and 10 mm margins on the vascular bundles, combined with soft-tissue guidance. Author Disclosure: F.A. Lerma, None; S.Z. Liu, None; B. Liu, None; H. Li, None; B. Yi, None; P. Amin, None; C.X. Yu, None.
2885
Image Guided Radiotherapy to the Prostate after Implantation of Gold Fiducials: Is it Necessary to Wait 7 Days for Planning?
A. Havnen, S. Liauw, C. Pelizzari, K. Yenice University of Chicago, Chicago, IL Purpose/Objective(s): Gold seeds are commonly used as fiducials for image-guided radiotherapy to verify the position of the prostate. Due to potential seed migration immediately following implantation, computed tomography (CT) imaging for treatment planning is often performed several days later. This study evaluates changes in fiducial positions between the day of implant and the day of CT simulation. Materials/Methods: 15 patients with prostate cancer were implanted using a transperineal technique, with 3 fiducials placed at the base, mid-gland, and apex of the prostate. CTs were acquired in all patients immediately after implantation (CT0) and at 7 to 9 days after implant for treatment planning (CTSim). The prostate and fiducials were contoured on each image set by the same person. Position coordinates of the prostate and each fiducial were determined from the center of mass (COM) of their contoured volumes. The COM of all three seeds (COMFids) was also calculated. Uncertainty in fiducial position due to partial volume effects from CT slice thickness was found to be less than 1 mm. The uncertainty in these positions resulted in a precision of 1 mm in the identification of COMFids.
S565
I. J. Radiation Oncology d Biology d Physics
S566
Volume 72, Number 1, Supplement, 2008
For each image set, the following distances were calculated: (1) fiducial to fiducial, (2) COMFids to each individual fiducial, and (3) COMFids to the prostate COM. The magnitudes of these distances in CT0 were compared to those in CTSim to evaluate migration. Results: Comparison of 45 inter-seed measurements (3 for each patient) from CT0 with those from CTSim demonstrated the absolute value of inter-seed migration averaged 0.9 mm with a standard deviation (SD) of 0.8 mm. The average accounting for both increases and decreases in inter-seed distances between CT0 and CTSim was near zero (0.1 mm with a SD of 1.3 mm), indicating no significant systematic increase or decrease during this period. Similarly, the absolute value of the change in distance between the COMFids and each individual seed averaged 1.2 mm with a SD of 0.9 mm, and the average of increases and decreases in this distance was 0.0 mm with SD of 1.5 mm. 95% of measured changes in the magnitude of inter-seed and COMFids-to-seed distances were less than 3 mm, and 90% were less than 2 mm. The absolute value of the change in distance between the COMFids and the prostate COM was on average 2.6 mm with a SD of 2.1 mm. This variation is reasonable considering the uncertainty in prostate localization. Conclusions: Inter-seed distances changed by less than 1 mm on average in the first week after implantation. The consistency of the distance between the COMFids and the prostate COM demonstrates the stability of the seeds within the prostate. CT simulation for treatment planning may occur on the day of fiducial implantation without concern for significant migration of the seeds. Author Disclosure: A. Havnen, None; S. Liauw, None; C. Pelizzari, None; K. Yenice, None.
2886
Analysis of Dose Volume Histogram Differences between High Dose Rate Brachytherapy and Intensity Modulated Radiotherapy for Prostate Treatment
J. Hermesse1, S. Biver1, B. Thissen1, B. Warlimont1, N. Jansen1, P. Coucke1, P. Nickers2 1
CHU Liege, Liege, Belgium, 2Oscar Lambret, Lille, France
Purpose/Objective(s): We aimed at comparing the dose distribution of HDR brachytherapy and IMRT in prostate cancer. Materials/Methods: The tomodensitometric data of ten successive patients treated with HDR brachytherapy for prostate cancer were recovered for the dosimetric intercomparison. The Nomos-Corvus treatment planning system (TPS) was used for IMRT planning while dose distribution for HDR brachytherapy was calculated with the Brachyvision TPS. A theoretical dose of 10 Gy applied by 2 Gy per fraction (EQD2) was prescribed on the PTV in the IMRT approach. We selected an a/b ratio of 1.5 Gy to calculate a biological equivalent unique dose for HDR brachytherapy (5.22 Gy). The dose was normalized in order to allow 95% coverage of the PTV. The dose-volume histograms were calculated for PTV and organs at risk (OARs). For these, doses were converted to EQD2, considering an a/b ratio of 3 Gy. Differences between the obtained dose-distributions were compared with a two-sided Student’s t test. Results: Dose heterogeneity is more pronounced with HDR brachytherapy with a mean dose to the PTV of 23.8 Gy as compared to 10.5 Gy with IMRT. Cold spots are similar with both methods: 7.93 Gy and 8.17 Gy, respectively, with IMRT and HDR brachytherapy (p = 0.6). The rectal dose is reduced by HDR brachytherapy as 0.5 cc of the rectum received 5.9 Gy as compared to 10.2 Gy with IMRT (p \ 0.0001). 8.08 Gy was delivered to 20% of the rectal volume with IMRT as compared to 2.74 Gy with HDR brachytherapy (p \ 0.0001). The same observation favoring HDR brachytherapy is made for the bladder: 20% of the organ received 7.11 Gy with IMRT but 1.76 Gy with HDR brachytherapy (p \ 0.0001). The maximal dose delivered to the urethra is increased by HDR brachytherapy to 13.4 Gy as compared to 11.1 Gy with IMRT but mean dose and minimal dose on the urethra are significantly lower with HDR brachytherapy (p \ 0.0025). The volume of normal tissues receiving 1 Gy was reduced by a factor 8 with HDR brachytherapy (p \ 0.0001). Conclusions: HDR brachytherapy allows high hyperdosage sleeves inside the PTV while sparing dramatically the OARs as compared to IMRT. The lower number of expected secondary cancers will thus favor brachytherapy use in exclusive or boosting radiation programs, particularly for younger patients. Author Disclosure: J. Hermesse, None; S. Biver, None; B. Thissen, None; B. Warlimont, None; N. Jansen, None; P. Coucke, None; P. Nickers, None.
2887
Fractional Integral Target Dose Comparison for I-125, Pd-103 and Cs-131 in Prostate Seed Implants
T. Li, L. Fountain, E. Duffy Tuomey Healthcare System, Sumter, SC Purpose/Objective(s): To use fractional integral target dose to obtain the fraction of energy absorbed by the prostate from integral dose, which is an indication of ‘‘radiation delivery efficiency’’ in brachytherapy. Also to introduce a parameter that shows the fraction of excess energy absorbed in the prostate. Those parameters can be used to aid the clinical choice of isotopes. Materials/Methods: A total of 15 boost therapy implant cases (5 for each isotope) are utilized for this comparison. The TRUS images are obtained intra-operatively using B&K Ultrasound unit in 5 mm steps. The planning parameters are defined according to RTOG 0232 guidelines. The prescription doses are: 85 Gy for Cs-131, 108 Gy for I-125 and 100 Gy for Pd-103. The seed strengths employed are: 1.8 U (Cs-131), 1.42 U (Pd-103) and 0.279-0.356 U (I-125). The prostate volume ranges from 25 to 50 cc. Planning goals are: V100 95%, D90100%, and prostatic urethra D10 150%. Dose calculations are performed using Variseed (ver7.1, VMS, Palo Alto, CA) planning system using AAPM TG-43 formalism. All plans are evaluated to insure the planning goals are met. Uniformity (V200), D90 for urethra, and D30 for rectum are also evaluated. Integral target dose are obtained by multiplying the prostate volume V with mean dose Dmean. Total integral dose is obtained by adopting the point source model from AAPM TG43. The integral dose E delivered by a single source with unit activity is the integration of 4Pi r2 D(r)/r2 dr times 1.44T1/2. Let A be the total activity implanted, the total integral dose will be AE. The fractional integral target dose the prostate receives is defined as DmeanV/AE. We also define a parameter (Dmean-mPD)V/AE that indicates the fraction of excess energy absorbed in the prostate. This parameter shows the amount of energy that is more than needed to achieve the minimum peripheral dose (mPD).