128 A comprehensive genomic approach to the identification of predictive markers using dna and tissue repair gene polymorphisms in radiation induced late toxicity in prostate cancer patients treated with conformal radiotherapy

e15162 Background: The risk of secondary rectal malignancies (SRMs) is a significant concern following radiation therapy for prostate cancer patients. Modern prostate radiotherapy techniques include the use of intensity modulated radiation therapy (IMRT) and rectal balloons to decrease treatment related toxicity. These technologies may also lower the likelihood of radiation-induced SRMs. In this study, a novel biologically-based carcinogenesis model was used to quantify and to compare the predicted risks of SRMs in men treated with or without a rectal balloon in place using either standard 3-D conformal radiotherapy (3D-CRT) or IMRT radiotherapy. Methods: Treatment plans were developed for ten clinically localized prostate cancer patients using CT scans obtained both with and without a rectal balloon in place. Target and normal structures were contoured, and dose-volume histograms (DVHs) for these organs were determined with a planned 3D-CRT dose of 75.6 Gy or with a planned IMRT dose of 81 Gy. A biologically-based mathematical model of spontaneous and radiation-induced carcinogenesis was used to determine the excess absolute risk of SRMs for each plan. These risks were then compared to one another and to the baseline population. Results: Treatment with IMRT and a rectal balloon in place resulted in a significantly lower mean rectal wall dose in all patients compared with treatment with 3D-CRT without a rectal balloon. The average mean rectal wall dose with IMRT and a rectal balloon in place was 31.0 Gy versus 40.1 Gy with 3D-CRT without the rectal balloon (p < 0.001). A significantly higher risk of SRMs was predicted for patients treated with 3-D CRT without rectal balloons when compared with patients treated with IMRT with balloons in place (p < 0.001, relative risk 1.30; 95% confidence interval 1.16-1.44). Conclusions: For prostate cancer patients treated with definitive radiotherapy, the use of IMRT and rectal balloons during radiation, when compared to treatment with 3-D conformal radiotherapy, is associated with a significant reduction in the predicted risk of secondary rectal malignancies.

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Stereotactic hypofracionated radiotherapy for prostate cancer patients.

Journal of Clinical Oncology ◽

10.1200/jco.2013.31.15_suppl.e16097 ◽

2013 ◽

Vol 31 (15_suppl) ◽

pp. e16097-e16097

Author(s):

Monika Rucinska ◽

Marta Stefanczyk ◽

Joanna Minczewska ◽

Sergiusz Nawrocki

Keyword(s):

Prostate Cancer ◽

Cancer Patients ◽

Treatment Planning ◽

Stereotactic Radiotherapy ◽

Motion Tracking ◽

Specific Antigen ◽

Transrectal Ultrasound ◽

Late Toxicity ◽

Conformal Radiotherapy ◽

Genitourinary Toxicity

e16097 Background: 3D conformal radiotherapy (78Gy in 2Gy per fraction) is the standard treatment for prostate cancer patients. It is a very long treatment, not comfortable both for patients and radiotherapy departments. Stereotactic radiotherapy has recently been recognized as an alternative technique. Prostate cancer has probably a low α/β ratio (1.5Gy) and 33.5Gy in 5 fractions has the predicted efficacy of 78Gy in 39 fractions. The objective of the study was to investigate the effectiveness and safety of stereotactic radiotherapy for localized prostate cancer. Methods: This is a prospective one-center clinical study. The treatment was done with IMRT. PTV received 33.5Gy in 5 fractions twice a week. Three gold fiducial markers were placed in the prostate under transrectal ultrasound guidance for image-guided positioning and motion tracking. Treatment planning CT and MRI scans were performed. IMRT plans were done. Before each treatment MV Cone Beam CT and portal imagines for markers were performed. Results: In this analysis 32 patients were included (age 65-83 years, median 73 years) with localized low- and intermediate-risk (according to NCCN) adenocarcinoma of prostate T2-T3N0M0. Combined Gleason scores were 5 to 7, the prostate-specific antigen (PSA) was 4.7-20.0ng/ml (median 10.2ng/ml). The median prostate volume calculated during treatment planning (on CT and MR) was 40.5cc (15.8cc to 113.6cc). Acute genitourinary toxicity Grade 1–2 was observed in about 50% patients and only Grade 1 acute gastrointestinal toxicity in 25% patients. No Grade 3 or higher toxicity was reported. Only 3 patients reported rectal bleeding after radiotherapy (Grade 1 late toxicity). PSA level were systematically decreased to 1.08ng/ml 3 months, 0.91ng/ml 6 months and 0.56ng/ml 9 months after treatment end. Conclusions: Stereotactic hypofractionated radiotherapy for prostate cancer patients is an effective and safe treatment in short term analysis.

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