At UCSF, PTV margins to the prostate and seminal vesicles were 2â3mm ... Results: PTV dose coverage was not significantly different between NUH and UCSF, ...
I. J. Radiation Oncology d Biology d Physics
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Volume 69, Number 3, Supplement, 2007
Table 1: Toxicity following salvage RT to the prostatic bed
Acute $ Grade 2 GI $ Grade 2 GU Late $ Grade 2 GI $ Grade 2 GU $ Grade 2 GI or GU $ Grade 3 GI or GU
Overall (n = 73)
IMRT (n = 31)
Non-IMRT (n = 42)
p-value
20/72 (28%) 5/73 (7%)
13% 3%
38% 10%
0.0170 0.2719
5/69 (7%) 11/69 (16%) 15/69 (22%) 3/69 (4%)
10% 26% 32% 10%
5% 8% 13% 0%
0.4828 0.0417 0.0552 0.0258
Author Disclosure: S. Liauw, None; A.B. Jani, None; J. Fricano, None; C. Rash, None; C.A. Pelizzari, None; R.R. Weichselbaum, None.
2242
Does IGRT Improve the Toxicity Profile in Whole Pelvic-treated High-risk Prostate Cancer? A Comparison Between IGRT and Non-IGRT IMRT
L. W. Chan1, H. T. Chung2, P. Xia1, E. Park-Somers2, M. Roach1 1 Department of Radiation Oncology, University of California San Francisco, San Francisco, CA, 2Department of Radiation Oncology, The Cancer Institute, National University Hospital (NUH), Singapore, Singapore
Purpose/Objective(s): Using intraprostatic markers, studies have suggested that the prostate can exhibit significant inter- and intra-fraction motion. To address this, IGRT has been shown to enable the delivery of radiotherapy to an unprecedented degree of precision. However, the clinical impact of IGRT has not been studied. The objective of this study is to assess whether the use of IGRT translates to less toxicities in IMRT-treated prostate cancer. Materials/Methods: In 2006, a total of 25 consecutively treated patients (10 from NUH and 15 from UCSF) formed the study cohort. All had high-risk prostate cancer and received definitive IMRT to the whole-pelvis followed by a prostate boost. Similar IMRT contouring and planning techniques (e.g. beam number and angles, dose and dose-constraints) were used at both centers. Divided in 2 phases, the prescription doses to the pelvic nodes (LN) were 48.6 Gy, seminal vesicles (SV) 54 Gy and prostate 73.8 Gy. At UCSF, 3 intraprostatic fiducial markers were used for online corrections prior to each fraction delivery (IGRT), whereas at NUH no fiducial markers were used (non-IGRT). Portal images were taken 3 times during the first week, then weekly thereafter. At UCSF, PTV margins to the prostate and seminal vesicles were 2–3mm circumferentially, whereas at NUH, PTV margins were 1 cm circumferentially except 0.5 cm posteriorly. The acute rectal and bladder toxicities and dosimetric endpoints to the PTV and OAR were compared between the two centers. Toxicities were scored using CTC v3 and RTOG grading schemes. Results: PTV dose coverage was not significantly different between NUH and UCSF, respectively, for the prostate D100% (69.3 vs 70.4 Gy, p = 0.2) and D95% (75.0 vs 74.3 Gy, p = 0.4), SV D95% (54.6 vs 54.3 Gy, p = 0.7) and LN V48.6 Gy (95% vs 84%, p = 0.1). Rectum V40 (90.2% vs 42.4%), V60 (39.2% vs 7.4%), V70 Gy (19.2% vs 1.7%) and bladder V40 (75.2% vs 51.2%), V60 (24.8% vs 12.9%), V70 Gy (14.2% vs 3.7%) were all significantly less at UCSF than NUH (p \ 0.01). All patients completed the intended radiotherapy course. Acute grade 2 rectal toxicities were significantly less with IGRT using both the RTOG (80% vs 13%, p = 0.004) and CTC (50% vs 6.7%, p = 0.033) grading systems. Acute grade 2 bladder toxicities were also significantly less with IGRT for both RTOG (60% vs 13%, p = 0.014) and CTC (40% vs 6.7%, p = 0.013). No grade 3–5 toxicities were observed. Conclusions: IGRT, via daily image-guided target localization and alignment using electronic portal imaging of intraprostatic markers, permits the use of smaller margins and correspondingly lower doses to OAR such as the rectum and bladder. These tangible gains appear to translate into clinically significant lower rectal and bladder toxicities. Author Disclosure: L.W. Chan, None; H.T. Chung, None; P. Xia, None; E. Park-Somers, None; M. Roach, None.
2243
Dose-volume Comparison of Proton Therapy and Intensity Modulated Radiation Therapy in the Treatment of Prostate Cancer
C. E. Vargas, A. Fryer, C. Mahajan, D. Indelicato, D. Horne, A. Chellini, C. McKenzie, P. Lawlor, Z. Li, S. Keole, et al. Proton Therapy Institute, Jacksonville, FL Purpose/Objective(s): The contrast in dose distribution between proton radiation therapy and intensity modulated radiation therapy (IMRT) is unclear, particularly in regard to critical structures such as the rectum or bladder. More studies are necessary to define the potential benefits of these two distinct technologies. Materials/Methods: Between August and November of 2006, the first 10 consecutive patients treated in our phase II low-risk prostate proton protocol (UFPTI 0001) were reviewed. The double-scatter proton beam plans used in treatment were analyzed for various dosimetric endpoints. For all plans, each beam dose distribution, angle, smearing, and aperture margin was optimized. Back-up IMRT plans were created for all cases and simultaneously analyzed. IMRT plans were optimized through multiple volume objectives, beam weighting, and individual leaf movement. The patients were treated to 78 Gray-Equivalent (GE) in 2 GE fractions with a BED of 1.1. Statistical analysis was performed for all 20 plans. Results: Prostate and PTV coverage for both treatment modalities was excellent with 100% and $95% of the volumes respectively covered by 100% of the dose. However, target homogeneity was better for the proton plan with an average of 1.9% (SD 4.7%) of the PTV receiving 105% of the dose compared to 19.2% (SD 17.9%) for the IMRT plan (p = 0.01). All rectal and rectal wall volumes treated to 10 GE–80 GE (V10–V80) were significantly lower with proton therapy (p \ 0.05). Rectum V50 was reduced from 31.3% ± 4.1% with IMRT to 14.6% ± 3.0% with proton therapy for a relative improvement of 53.4% and an absolute benefit of
Proceedings of the 49th Annual ASTRO Meeting 16.7% (p\0.001). Mean rectal dose decreased 59% with proton therapy (p\0.001). For both the bladder and bladder wall, proton therapy produced significantly volumes treated to doses between 10 GE to 35 GE (p\0.05) with a non-significant advantage demonstrated for the volume receiving up to 60 GE. Bladder V30 was reduced from 42.8 ± 15.1% with IMRT to 27.7 ± 11.1% with proton therapy for a relative improvement of 35.3% and an absolute benefit of 15.1% (p = 0.02). Mean bladder dose decreased 35% with proton therapy (p = 0.002) (Figure). Conclusions: Compared to IMRT, proton therapy at our institution improved target homogeneity and significantly reduced the dose to traditional dose-limiting normal structures while maintaining excellent PTV coverage.
Author Disclosure: C.E. Vargas, None; A. Fryer, None; C. Mahajan, None; D. Indelicato, None; D. Horne, None; A. Chellini, None; C. McKenzie, None; P. Lawlor, None; Z. Li, None; S. Keole, None.
2244
Hypofractionated Conformal Radiotherapy for Good Prognosis Carcinoma of the Prostate: Seven Year Outcome Analysis
R. A. Cowan1, D. M. Mitchell1, I. C. Bottomley2, J. P. Wylie1, J. E. Livsey1, T. Elliott1, J. P. Logue1 Christie Hospital Trust, Manchester, United Kingdom, 2University of Manchester, Christie Hospital Trust, Manchester, United Kingdom 1
Purpose/Objective(s): The optimal external beam radiotherapy dose and fractionation in the radical treatment of localised prostate cancer continues to be investigated. This includes not only dose escalation using conventional fractionation, but also the exploration of hypo-fractionated regimes for prostate cancer given its suggested low a/b ratio. We report the long term efficacy of radiotherapy using a hypo-fractionated 50 Gy in 16 fractions (3.13 Gy per fraction) in men with localised prostate cancer. Materials/Methods: A retrospective review of men with localised prostate cancer treated consecutively with conformal radiotherapy at a single institution between January 1995 and May 2001 was performed. Only patient’s in the good prognostic group (PSA #10 ng/ml and Gleason score #6 and clinical stage T1/2) were included in the study. A conformal external beam radiotherapy dose of 50 Gy in 16 fractions over 22 days was delivered using a 4 field arrangement on a linear accelerator with energy $6 MV. The planning target volume (PTV) was defined as GTV (Prostate ± base of seminal vesicles) + 1 cm in all directions except posteriorly where 7 mm was used. Patients treated with neo-adjuvant, concurrent or adjuvant hormonal therapies were excluded. Biochemical failure was defined using both the American Society for Therapeutic Radiology and Oncology consensus definition and Phoenix definition. Results: One hundred and ninety nine men were identified. 73 with clinical T1 and 126 with clinical T2 disease at presentation. The median age at presentation was 67.9 years (49.9–81.65 years) and median initial PSA was 5.9 ng/ml (0.1–10 ng/ml). Histological review demonstrated that 78, 49 and 72 patients had Gleason scores of #4, 5 and 6 respectively. At a median follow-up of 84 months (4.6–134.9 months), the 7 year actuarial overall survival was 83.2% and the biochemical failure free survival was 55% and 76.8% as defined by the ASTRO consensus and Phoenix definition respectively. Conclusions: This data demonstrates the efficacy of a hypo-fractionated regime for good prognosis patients. It provides similar levels of biochemical control when compared with other reported long term outcomes using conventionally fractionated radiotherapy (2 Gy per fraction). Author Disclosure: R.A. Cowan, None; D.M. Mitchell, None; I.C. Bottomley, None; J.P. Wylie, None; J.E. Livsey, None; T. Elliott, None; J.P. Logue, None.
2245
Valproic Acid as an Established Histone Deacetylase Inhibitor for Radiosensitizing Androgen-independent Prostate Cancer Cells
R. R. Rajendran, M. L. Dowling, S. Chandrasekaran, K. A. Cengel, N. Vapiwala, G. D. Kao Hospital of the University of Pennsylvania, Philadelphia, PA Purpose/Objective(s): Over 40,000 deaths each year in the U.S. are caused by prostate cancer, the most commonly diagnosed cancer in men. There is an urgent need for treatment strategies effective in androgen-independent prostate cancer (AIPC), the
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