Image Guided Adaptive Radiation Therapy for Prostate Cancer: Toxicity Comparison for 3D Conformal Versus Intensity Modulated Beams

S398

International Journal of Radiation Oncology  Biology  Physics

Conclusions: The use of a hydrogel spacer does not affect the quality of life and may reduce the rectal toxicity. However, long term results are necessary before general use. Author Disclosure: E. Castellanos: None. K. Sjo¨din: None. M. Djordjevic: None. M. Gubanski: None.

Purpose/Objective(s): Accurate target definition and organ motion management are critical components of modern PPRT. Daily ERB use provides effective immobilization and rectal sparing in definitive prostate RT. Limited data exist regarding its role in PPRT. This study measures interfraction organ motion and associated dosimetric variation using weekly MRI in patients (pts) receiving PPRT with daily ERB. Materials/Methods: Twelve pts receiving PPRT to 70.2 Gy in 39 fractions at our institution were prospectively enrolled in this study, with 9 available for analysis. All pts underwent CT/MRI simulation. During PPRT course, pts underwent 6 additional pelvic MRI scans performed weekly in treatment position with ERB. Target volumes, and organs at risk were contoured on each MRI using T2 axial sequences. Two clinical target volumes (CTVs) were defined according to consensus guidelines from RTOG and EORTC. Each MRI scan was rigidly fused to the treatment planning CT to simulate image-guided bony alignment performed prior to daily treatment. Interfraction organ motion and dosimetric variation was analyzed. Fused images were then aligned to the ERB and volume displacement as well as dosimetric measurements were repeated. Statistical comparison was performed with the Wilcoxon Signed-Rank test. Results: We observed a consistent decline in relative mean bladder volume compared to simulation [87.6% (MRI 1) vs. 46.8% (MRI 6); p < 0.05] with primarily anterior bladder displacement (mean 10 mm, range 5.6-21.1 mm). This resulted in a mean 14% relative increase in bladder V65 by the final MRI compared to simulation. Variation of rectal volume was  5% throughout treatment with displacement  5 mm in all directions. Mean variation in rectal V60 was 1.8% for all patients. We found that CTVs defined according to RTOG guidelines were significantly less variable during the treatment course compared to EORTC CTVs (p < 0.05). In addition, alignment of patients to the ERB resulted in significantly reduced displacement of the RTOG CTV volumes compared to alignment based on bony anatomy (p < 0.05). Conclusions: To our knowledge, this is the first reported study using MRI to assess organ motion with daily ERB in PPRT. Rectal volumes remained stable throughout treatment, supporting ERB use in this setting. Alignment to the ERB reduced CTV displacement, suggesting an improved surrogate for patient positioning. Declining bladder volumes during the treatment course likely reflect treatment-related acute dysuria, and may also play a role in the observed increased variability of EORTC CTVs compared to RTOG CTVs, given differences in methodologies. These findings highlight the need for effective management strategies to minimize bladder filling variation, particularly when considering advanced PPRT techniques and dose escalation. Author Disclosure: S.D. Swisher-McClure: None. L. Yin: None. M. Rosen: None. V. Bui: None. M. Mehler: None. S. Both: None. N. Vapiwala: None.

2476 Early Toxicity Comparison of 3 Different Brachytherapy Boost Fractionation Schemes for Prostate Cancer J. Hannoun-Levi, H. Hijazi, M. Chand-Fouche, J. Gal, J. Feuillade, and C. Dejean; Antoine Lacassagne Cancer Center, Nice, France Purpose/Objective(s): To analyze the early toxicity of a high-dose rate brachytherapy (HDRB) boost for prostate cancer using 3 different fractionation schemes. Materials/Methods: From 02/09 to 01/12, after a first course of 3D external beam radiation therapy (EBRT - 46 Gy/23f), 118 patients (pts) underwent HDRB boost for low-risk (5 pts - 4%), intermediate-risk (20 pts - 17%) and high-risk (93 pts - 79%) prostate cancers. Pts underwent one insertion (under general anesthesia) then irradiated according to three different boost fractionation schemes. From 02/09 to 12/09, Group 1 Z 18 Gy/3f/2d (EQD2a/b3 32 Gy / 30 pts - 25%); from 01/10 to 04/11, Group 2 Z 18 Gy/2f/2d (EQD2a/ b3 43 Gy / 53 pts - 45%); and from 05/11 to 01/12 Group 3 Z 14 Gy/1f/1d (EQD2a/b3 48 Gy / 35 pts - 30%). Planning CT-scan was performed before each fraction. Organ at risk dose constraints for Group 1 and Group 2 were rV100 Z 0 (rectum volume receiving 100% of the prescribed dose - PD) and uV125 Z 0 (urethra volume receiving 125% of the PD), while for Group 3, rV90 Z 0 and uV115 Z 0. Genito-Urinary (GU) and Gastro-intestinal (GI) acute toxicities were assessed at 1 and 6 months after boost (CTCv3.0). Results: Median age was 71 years [50-82]. Median follow-up was 19 months [1-35]. Ninety-four pts (80%) received an anti-androgen therapy. Median CTV was 34 cc [11-77]. Median V100, V150 and V200 were 98% [82-100], 35% [16-81] and 12% [5-33] respectively. Median D10 and D30 (dose delivered to 10% and 30% of the urethral volume) were 119% [108-203] and 115% [70-183] respectively. The rate of GU toxicity  G2 was 6% and 0% at 1 and 6 months after the boost respectively. One patient developed G4 sepsis toxicity 2 days after HDRB and recovered without after-effects. The rate of GI toxicity  G2 was 0% and 1% at 1 and 6 months after boost respectively. GU and GI toxicities at 1 and 6 months after boost regarding different fractionation schemes applied are presented in the Table. Conclusions: During the study period, while a significant physical doseescalation was performed (33% and 10% between Group 1 vs Group 3 and Group 2 vs Group 3 respectively), no significant increase in GU and GI acute toxicities was observed. Poster Viewing Abstract 2476; Table Analysis of GU and GI complications observed at 1 and 6 months after HDRB boost regarding the complications Complications Grades 0 1 2 3 4 Fract. schemes G1 (18 Gy/3f/2d) G2 (18 Gy/2f/2d) G3 (14 Gy/1f/1d) p value

GU 1 month GU 6 months GI 1 month GI 6 months 61 33 5 0 1

69 31 0 0 0

74 26 0 0 0

77 22 0 0 0

22 51 27 0.41

33 63 4 0.49

23 30 47 0.07

45 50 5 0.34

Author Disclosure: J. Hannoun-Levi: None. H. Hijazi: None. M. ChandFouche: None. J. Gal: None. J. Feuillade: None. C. Dejean: None.

2477 MRI-based Evaluation of Interfraction Motion in Postprostatectomy Radiation Therapy (PPRT) With Daily Endorectal Balloon (ERB) S.D. Swisher-McClure, L. Yin, M. Rosen, V. Bui, M. Mehler, S. Both, and N. Vapiwala; University of Pennsylvania, Philadelphia, PA

2478 Image Guided Adaptive Radiation Therapy for Prostate Cancer: Toxicity Comparison for 3D Conformal Versus Intensity Modulated Beams N. Tonlaar, J.B. Wilkinson, D.S. Brabbins, J.T. Dilworth, H. Ye, M. Wallace, I. Grills, D. Yan, G. Gustafson, and D.J. Krauss; Oakland University William Beaumont School of Medicine, Royal Oak, MI Purpose: To report toxicity profiles for image-guided adaptive radiation therapy (IGART) for prostate cancer using three-dimensional conformal (3D-CRT) vs. intensity modulated (IMRT) beams. Methods and Materials: A total of 1,666 men with localized prostate cancer were treated from 1999 to 2011 with IGART (IMRT: 1027; 3DCRT: 639). GI and GU toxicity were assessed per CTCAE criteria (v. 3.0). Acute and chronic toxicities were compared by treatment technique. Patients were divided into low- (Group 1) or intermediate-high risk (Group 2) groups per NCCN criteria. Clinical target volume (CTV) was prostate only for Group 1 (target dose: 75.6 Gy) and prostate plus seminal vesicles for Group 2 (target dose: 79.2 Gy). Prescription doses were systematically reduced if anatomic factors resulted in normal tissue (rectum, bladder) dose constraints not being met. Results: Median follow up for all patients was 4.3 years (3D-CRT: 7.1 yrs / IMRT: 2.9 yrs.). Twenty-one percent of patients received androgen deprivation therapy (ADT) (18.8% 3D-CRT vs. 24% IMRT, p Z 0.01). Patients treated with ADT did not experience higher acute toxicities, and use of

Volume 84  Number 3S  Supplement 2012 hormones did not influence acute or chronic toxicity rates between radiation treatment groups. Chronic grade 3 urinary retention was higher, however, in patients treated with ADT (2.6% vs. 0.7%, p Z 0.03). Mean dose in 3D-CRT and IMRT groups was 75.1 Gy and 76.3 Gy, respectively (p < 0.001), while mean dose for Group 1 was 75.2 Gy vs. 76.4 Gy for Group 2 (p < 0.001). In the IMRT group, the mean dose for Group 1 was lower than Group 2 (75.5 Gy vs. 76.8 Gy, p < 0.001). This was not true for 3D-CRT cases. Dysuria and frequency were the most common acute grade 2 GU toxicities (3.0% and 8.4%), which decreased after six months (1.4% and 4.7%). Urinary incontinence, however, increased over time (0.6% acute, 1.7% chronic) as did grade 2 rectal bleeding/proctitis (0%/0.2% acute vs. 3.4%/2.2% chronic). We found less acute grade 1 rectal bleeding with IMRT vs. 3D-CRT (9.5% vs. 1.3%, p Z 0.04). Chronic toxicities were largely similar between techniques except for grade 1 rectal bleeding again being lower for IMRT (11.2% vs. 6.8%, p < 0.02). Within the IMRT cohort, Group 2 patients (with larger CTVs) had higher rates of grade 2 rectal bleeding (5.2% vs. 1.4%, p Z 0.01), while all other toxicities were not statistically different. Conclusion: For prostate cancer patients receiving IGART, a higher mean radiation therapy dose may be achieved using IMRT with equal or lower rates of GI and GU toxicity. Additional study to decrease side effects for higher-risk patients with larger target volumes is warranted. Author Disclosure: N. Tonlaar: None. J.B. Wilkinson: None. D.S. Brabbins: None. J.T. Dilworth: None. H. Ye: None. M. Wallace: None. I. Grills: None. D. Yan: None. G. Gustafson: None. D.J. Krauss: None.

2479 Stereotactic Body Radiotherapy (SBRT) for Low Risk Prostate Cancer: Plan comparison With Real Time Tracking By Beacons and Helical Tomotherapy A. Sen, D. Lollar, W. Falwell, H. Sakhalkar, P. Sourivong, W.C. Goad, M.S. Payne, O. Taylor, and J.P. Flynn; Cancer Treatment Centers of America, Tulsa, OK Purpose/Objective(s): Hypofractionated treatment of low risk prostate cancer by external beam are planned and delivered using rotational arc (RA) treatment planning on a conventional linac. Treatment plans are generated retrospectively on helical Tomotherapy (HT) for comparison. Materials/Methods: Eight low risk prostate patients were implanted each with three commercial beacons. RA plans were generated on an Eclipse planning system and delivered using CBCT image guidance for localization and real time tracking of beacons. Dose fractionation was 7.25 Gy/fx for 5 fractions to a total dose of 36.25 Gy. Planning goals were set for 95% of the planning target volume (PTV) to receive at least the prescription dose. Treatment plans were also generated on a HT planning system using the same fractionation and dose-volume constraints. Margins for the PTV were set at 5 mm in all directions except 3 mm posteriorly. Treatment plans were evaluated based on the target coverage measured by minimum, mean and maximum dose to the target volumes in the dose-volume-histogram (DVH) analysis and the conformity index (CI).The heterogeneity of the dose distribution in the PTV was measured by a dose heterogeneity index as DHI. The volumes covering 5, 10, 20, 50 and 70% of the prescription dose (V5, V10, V20, V50 and V70) for two OARs were determined. Results: The mean age of the patients was 61 y (range 53-79) and the mean prostate volume was 49.1 cm3 (range 30.3-77.4 cm3). The mean PSA value was 7.0 ng/mL (range 3.8-8.91). All patients were staged at T1cN0M0 except for one at T1bN0M0. For the RA plans the average values of monitor units (MU), actual beam delivery time, CI and DHI are 3193, 328.6 s, 1.194 and 2.88, respectively. The equivalent biological dose at 2 Gy/fx (EQD2) for the SBRT treatment was 90.63 Gy with an a/b ratio of 1.5 for prostate. For HT plans, the average values of the monitor units, treatment beam-on time, CI and DHI are 14330, 984.9 s, 1.307 and 3.22, respectively. Conclusions: Analysis of the DVH data shows that, on average, the minimum dose coverage of the PTV for RA plans is 4% higher than the HT plans. The averages of the maximum and mean dose coverage of the PTV for the two planning systems are almost same. The average monitor unit and beam-on time for HT plans are 4.5 and 3 times, respectively, higher than the RA plans. Thus the RA treatment is more efficient. The CI

Poster Viewing Abstracts S399 of the RA plans is slightly better than the HT plans e the average being about 10% lower for the RA plans. Also, the dose heterogeneity of the PTV in the RA plans is around 12% lower than the HT plans. Comparison of the averages of the minimum, maximum and mean doses for the rectum and bladder shows no statistical difference between the two planning systems.

2480 Decreasing Utilization of Brachytherapy for the Treatment of Prostate Cancer: A National Pattern of Care Analysis Using NCCN Risk Categorization U. Mahmood,1 M. Koshy,2 T. Pugh,1 K. Hoffman,1 D. Kuban,1 and A. Lee1; 1M.D. Anderson Cancer Center, Houston, TX, 2University of Chicago, Chicago, IL Purpose/Objective(s): External beam radiation therapy and brachytherapy are sometimes competing treatment modalities for localized prostate cancer. Previous patterns of care analyses had shown increasing utilization of brachytherapy relative to external beam radiation therapy during the 1990’s. Our aim was to analyze more recent trends in the utilization of these two radiation treatment modalities using a large, population-based US database. Materials/Methods: Using the Surveillance, Epidemiology, and End Results (SEER) database, information was obtained for all patients diagnosed with localized adenocarcinoma of the prostate between 2004 and 2008. Patients were classified as low (T1-2a, GS  6, and PSA < 10), intermediate (T2b-c, GS 7, or PSA 10-20), or high (T3a-4, GS 8, or PSA > 20) risk according to the NCCN risk categories. Trends in the utilization of external beam radiation therapy (EBRT), brachytherapy (BT), or combination therapy (BT + EBRT) were analyzed by year of diagnosis using regression analysis. For the purposes of this analysis, brachytherapy included both LDR and HDR techniques. Results: A total of 57,968 patients were identified. Median age for the entire cohort was 68 years old. A total of 22,108 (38%) were classified as low risk, 24,250 (42%) were classified as intermediate risk, and 11,610 (20%) were classified as high risk. When analyzing all patients, EBRT use increased from 57% in 2004 to 62% in 2008 whereas BT use correspondingly decreased from 31% in 2004 to 26% in 2008 (p < 0.0001). BT + EBRT use, on the other hand, remained at 12% between 2004 and 2008. When analyzed by NCCN risk categories, the increasing utilization of EBRT was most pronounced among low risk patients (9% increase) versus intermediate (3% increase) and high (0% change) risk patients. Correspondingly, the decreasing utilization of BT was most pronounced among low risk patients (7% decrease) versus intermediate (3% decrease) and high (2% decrease) risk patients. The utilization of BT + EBRT remained relatively stable among low (1% decrease), intermediate (0% change), and high (2% increase) risk patients. Conclusions: This patterns of care analysis reveals decreasing utilization of brachytherapy relative to external beam radiation therapy, which is most pronounced among lower risk patients. Although our analysis did not address the cause of this trend, we hypothesize that it may be the result of changing patient/physician preference, lack of emphasis on brachytherapy during radiation oncology training, and/or physician reimbursement/selfreferral. Author Disclosure: U. Mahmood: None. M. Koshy: None. T. Pugh: None. K. Hoffman: None. D. Kuban: None. A. Lee: None.

2481 Intraprostatic Boost Using High-dose-rate Brachytherapy (HDR-BT) According to Gross Tumor Volume (GTV) Location for Prostate Cancer: A Dosimetric Feasibility Study J. Helou,1 R. Verstraet,2 P. Blanchard,1 A. Rodriguez,2 J. Bourhis,1 D. Lefkopoulos,2 L. Calmels,2 F. Azoury,1 and A. Bossi1; 1Institut Gustave Roussy, Radiation Oncology department, Villejuif, France, 2Institut Gustave Roussy, Medical Physics department, Villejuif, France