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Dosimetric Comparison of High-Dose-Rate Brachytherapy, Helical Tomotherapy and Linac-Based Intensity Modulated Radiaiton Therapy for Definitive Localized Prostate Cancer Treatment
S70
Abstracts / Brachytherapy 13 (2014) S15eS126
whole prostate cancer treatments. We believe that this is a meaningful way, based on clinical data, to create prescription guidelines for focal therapy. Materials and Methods: A software platform was built to create insilico prostate tumorlets, of specified morphology, volume and location. Actual knowledge of tumorlet location was replaced with statistical inference. In this first stage, we analyzed I-125 pre-implant plans for 35 patients, with prostate sizes ranging from 11.9 to 49.4 cm3. Biological growing of tumorlets in 9 volume categories from 0.1 to 10cm3 with 500 random tumorlets per category was simulated. No extra capsular tumor spread was considered. Each tumorlet was superimposed over the 3D dose distribution and positional, morphological, dosimetric and radiobiological quantities were computed. Two formalisms were used to integrate voxel level BED quantities: EUBED and gBEUD. A treatment reference (BEDo) was established using the BED EBRT equivalent of 78Gy regimen in 2Gy/ fx. ‘Probabilities of cure’ were calculated for each tumorlet, based on EUBED (and gBEUD) O BEDo. Results: The pre-plans studied had a mean D90 of 160.1 Gy (SD: 26.0 Gy) and mean V100 of 94.9% (SD: 11.6%). Treatment planning was performed using volume optimization followed by manual adjustment. The whole prostate EUBED was on average 88.7 Gy3 and range [49.6-137.5] Gy3, significantly lower than BED calculated based on D90, with an average of 161.8 Gy3 and range [96.2-211.8] Gy3 By comparison, BEDo for the EBRT regimen was ~130 Gy3. In all pre-implant plans studied the percentage of tumorlets receiving gBEUD and EUBED O BEDo shown a monotonic decrease with decreasing D90. When separated in ‘small’ (0.1-1cc) and ‘large’ (2-10cc) volumes, the small tumorlets showed less dramatic drops in ‘cure’ rates than large tumorlets (Figure 1). The slopes for EUBED and gBEUD-based ‘probabilities of cure’ were similar, at 0.55 vs. 0.52 for all tumorlet volumes, 0.40 vs. 0.35 for small volume tumorlets and 0.68 vs. 0.65 for large volume tumorlets. When each of the nine volume categories were analyzed, while the trend was similar, small volume tumorlets seem to show a much more linear ‘cure’ drop with decreasing D90, as evidenced by R2 of the linear fit. Conclusions: Smaller tumorlets, in the setting of prostate brachytherapy seed implants designed for whole prostate seem less sensitive to D90 decreases than large tumorlets. For all tumorlet volumes, there is a linear decreasing of EUBED with prostate D90. It has been reported in the literature, based on clinical outcome data that a BED greater than 200Gy seem to correlate with better outcome. These studies calculated BEDs based on D90, thus such BED O 200Gy would be the equivalent of D90 O 185Gy. Our model based on EUBED (or gBEUD) shows larger than 90% ‘cure’ rates for D90 greater than 185Gy, thus validating not only the model, but also the fact that constraints imposed on
tumorlets seem to be equivalent with constraints imposed on the whole prostate.
PD54 Dosimetric Comparison of High-Dose-Rate Brachytherapy, Helical Tomotherapy and Linac-Based Intensity Modulated Radiaiton Therapy for Definitive Localized Prostate Cancer Treatment Thomas B. Skidmore, MD, Jessica Russell, RT (T), Josh Bryant, PhD, Steve Alder, PhD, John K. Hayes, MD, MPH. Radiation Oncology, Gammawest Cancer Services, Salt Lake City, UT. Purpose: A dosimetric analysis to compare the dose and volume of bladder, rectum and urethra using high-dose-rate brachytherapy (HDR-BT), Helical Tomotherapy (HT) and conventional linac based intensity-modulated radiation therapy (IMRT) in the treatment of prostate cancer. Materials and Methods: Ten successive patients with adenocarcinoma of the prostate treated with HDR-BT to a dose of 3900 cGy in six 650 cGy fractions were used for this study. An additional three theoretical plans for each patient were computed: (1) 7600cGy, in 200 cGy fractions, HT plan with no expansion from the HDR-BT PTV target, (2) 7600 cGy, in 200 cGy fractions, HT plan with 8mm circumferential expansion, except 5mm posteriorly and (3) 7600 cGy, in 200 cGy fractions, conventional linac 9 beam IMRT plan with similar expansions as above. Dose to the normal structures were calculated and Dose-volume histograms (DVH) were plotted for comparisons of all techniques. The V200, V150, V120, V100, V80, V60, V40, V20 and V10 were compared. Results: Data were compared across treatment approaches for each site and percent dose using Friedman tests. Data are reported in mean þ standard deviation in Table 1. Conclusions: HDR brachytherapy can provide better sparing of the rectum, bladder and urethra while delivering a higher dose to the prostate. This is especially true across low doses, ! 40%, which may be beneficial for long term side effects as there is less integral dose with HDR brachytherapy when compared to complex external beam delivery systems such at Helical Tomotherapy and linac based IMRT. Table 1 Volume with Percent Dose by Treatment Approach Tomotherapy Tomotherapy HDR Expanded No Brachytherapy PTV Expansion Pinnacle Bladder 20% 40% 60% 80% 100% Urethra 60% 80% 100% 120% Rectum 20% 40% 60% 80% 100%
p
64.3 26.0 10.4 3.2 0.4
26.6 14.7 6.2 2.9 0.7
89.5 57.1 37.4 23.5 9.9
31.6 25.0 18.2 10.9 4.6
56.3 28.3 14.3 5.5 0.1
23.4 13.5 6.7 2.7 0.1
59.2 36.0 21.6 10.8 0.3
16.9 0.002 11.2 !0.001 6.7 !0.001 2.7 0.001 0.5 0.279
2.5 2.2 1.6 0.0
0.6 0.6 0.6 0.0
2.8 2.8 2.5 0.0
0.6 0.6 0.6 0.0
2.6 2.3 1.9 0.0
0.7 0.7 0.7 0.0
2.8 2.6 1.2 0.0
0.6 !0.001 0.6 !0.001 0.4 0.033 0.0 0.995
47.6 16.9 4.7 0.6 0.0
14.3 7.6 3.0 0.6 0.0
50.1 30.6 14.4 5.9 1.1
19.9 15.3 9.4 3.3 1.2
29.1 10.3 3.7 1.0 0.0
13.0 5.5 2.8 1.3 0.1
44.7 27.5 14.0 5.4 0.1
15.3 9.4 4.6 2.4 0.1
0.001 0.002 0.003 0.003 0.100
PD55 Impact of Technology and Learning Curve on Migration and Seed Loss in Permanent Prostate Implants Sylviane Aubin, MSc1, William Foster, MD1, Andre-Guy Martin, MD1, Eric Vigneault, MD1, Luc Beaulieu, PhD1,2. 1Radiation Oncology, CHU de
Abstracts / Brachytherapy 13 (2014) S15eS126
whole prostate cancer treatments. We believe that this is a meaningful way, based on clinical data, to create prescription guidelines for focal therapy. Materials and Methods: A software platform was built to create insilico prostate tumorlets, of specified morphology, volume and location. Actual knowledge of tumorlet location was replaced with statistical inference. In this first stage, we analyzed I-125 pre-implant plans for 35 patients, with prostate sizes ranging from 11.9 to 49.4 cm3. Biological growing of tumorlets in 9 volume categories from 0.1 to 10cm3 with 500 random tumorlets per category was simulated. No extra capsular tumor spread was considered. Each tumorlet was superimposed over the 3D dose distribution and positional, morphological, dosimetric and radiobiological quantities were computed. Two formalisms were used to integrate voxel level BED quantities: EUBED and gBEUD. A treatment reference (BEDo) was established using the BED EBRT equivalent of 78Gy regimen in 2Gy/ fx. ‘Probabilities of cure’ were calculated for each tumorlet, based on EUBED (and gBEUD) O BEDo. Results: The pre-plans studied had a mean D90 of 160.1 Gy (SD: 26.0 Gy) and mean V100 of 94.9% (SD: 11.6%). Treatment planning was performed using volume optimization followed by manual adjustment. The whole prostate EUBED was on average 88.7 Gy3 and range [49.6-137.5] Gy3, significantly lower than BED calculated based on D90, with an average of 161.8 Gy3 and range [96.2-211.8] Gy3 By comparison, BEDo for the EBRT regimen was ~130 Gy3. In all pre-implant plans studied the percentage of tumorlets receiving gBEUD and EUBED O BEDo shown a monotonic decrease with decreasing D90. When separated in ‘small’ (0.1-1cc) and ‘large’ (2-10cc) volumes, the small tumorlets showed less dramatic drops in ‘cure’ rates than large tumorlets (Figure 1). The slopes for EUBED and gBEUD-based ‘probabilities of cure’ were similar, at 0.55 vs. 0.52 for all tumorlet volumes, 0.40 vs. 0.35 for small volume tumorlets and 0.68 vs. 0.65 for large volume tumorlets. When each of the nine volume categories were analyzed, while the trend was similar, small volume tumorlets seem to show a much more linear ‘cure’ drop with decreasing D90, as evidenced by R2 of the linear fit. Conclusions: Smaller tumorlets, in the setting of prostate brachytherapy seed implants designed for whole prostate seem less sensitive to D90 decreases than large tumorlets. For all tumorlet volumes, there is a linear decreasing of EUBED with prostate D90. It has been reported in the literature, based on clinical outcome data that a BED greater than 200Gy seem to correlate with better outcome. These studies calculated BEDs based on D90, thus such BED O 200Gy would be the equivalent of D90 O 185Gy. Our model based on EUBED (or gBEUD) shows larger than 90% ‘cure’ rates for D90 greater than 185Gy, thus validating not only the model, but also the fact that constraints imposed on
tumorlets seem to be equivalent with constraints imposed on the whole prostate.
PD54 Dosimetric Comparison of High-Dose-Rate Brachytherapy, Helical Tomotherapy and Linac-Based Intensity Modulated Radiaiton Therapy for Definitive Localized Prostate Cancer Treatment Thomas B. Skidmore, MD, Jessica Russell, RT (T), Josh Bryant, PhD, Steve Alder, PhD, John K. Hayes, MD, MPH. Radiation Oncology, Gammawest Cancer Services, Salt Lake City, UT. Purpose: A dosimetric analysis to compare the dose and volume of bladder, rectum and urethra using high-dose-rate brachytherapy (HDR-BT), Helical Tomotherapy (HT) and conventional linac based intensity-modulated radiation therapy (IMRT) in the treatment of prostate cancer. Materials and Methods: Ten successive patients with adenocarcinoma of the prostate treated with HDR-BT to a dose of 3900 cGy in six 650 cGy fractions were used for this study. An additional three theoretical plans for each patient were computed: (1) 7600cGy, in 200 cGy fractions, HT plan with no expansion from the HDR-BT PTV target, (2) 7600 cGy, in 200 cGy fractions, HT plan with 8mm circumferential expansion, except 5mm posteriorly and (3) 7600 cGy, in 200 cGy fractions, conventional linac 9 beam IMRT plan with similar expansions as above. Dose to the normal structures were calculated and Dose-volume histograms (DVH) were plotted for comparisons of all techniques. The V200, V150, V120, V100, V80, V60, V40, V20 and V10 were compared. Results: Data were compared across treatment approaches for each site and percent dose using Friedman tests. Data are reported in mean þ standard deviation in Table 1. Conclusions: HDR brachytherapy can provide better sparing of the rectum, bladder and urethra while delivering a higher dose to the prostate. This is especially true across low doses, ! 40%, which may be beneficial for long term side effects as there is less integral dose with HDR brachytherapy when compared to complex external beam delivery systems such at Helical Tomotherapy and linac based IMRT. Table 1 Volume with Percent Dose by Treatment Approach Tomotherapy Tomotherapy HDR Expanded No Brachytherapy PTV Expansion Pinnacle Bladder 20% 40% 60% 80% 100% Urethra 60% 80% 100% 120% Rectum 20% 40% 60% 80% 100%
p
64.3 26.0 10.4 3.2 0.4
26.6 14.7 6.2 2.9 0.7
89.5 57.1 37.4 23.5 9.9
31.6 25.0 18.2 10.9 4.6
56.3 28.3 14.3 5.5 0.1
23.4 13.5 6.7 2.7 0.1
59.2 36.0 21.6 10.8 0.3
16.9 0.002 11.2 !0.001 6.7 !0.001 2.7 0.001 0.5 0.279
2.5 2.2 1.6 0.0
0.6 0.6 0.6 0.0
2.8 2.8 2.5 0.0
0.6 0.6 0.6 0.0
2.6 2.3 1.9 0.0
0.7 0.7 0.7 0.0
2.8 2.6 1.2 0.0
0.6 !0.001 0.6 !0.001 0.4 0.033 0.0 0.995
47.6 16.9 4.7 0.6 0.0
14.3 7.6 3.0 0.6 0.0
50.1 30.6 14.4 5.9 1.1
19.9 15.3 9.4 3.3 1.2
29.1 10.3 3.7 1.0 0.0
13.0 5.5 2.8 1.3 0.1
44.7 27.5 14.0 5.4 0.1
15.3 9.4 4.6 2.4 0.1
0.001 0.002 0.003 0.003 0.100
PD55 Impact of Technology and Learning Curve on Migration and Seed Loss in Permanent Prostate Implants Sylviane Aubin, MSc1, William Foster, MD1, Andre-Guy Martin, MD1, Eric Vigneault, MD1, Luc Beaulieu, PhD1,2. 1Radiation Oncology, CHU de