International journal of radiation oncology, biology, physics
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Int. J. Radiat. Oncol. Biol. Phys. · Dec 2001
The position and volume of the small bowel during adjuvant radiation therapy for rectal cancer.
The rate of small bowel toxicity from adjuvant pelvic radiation therapy (RT) for rectal cancer has been reported to be lower for patients treated preoperatively (Preop). This was probably due to a lesser volume of irradiated small bowel; however, studies of postoperative treatment reported that patients with an abdominoperineal resection (APR), who likely have the largest volume of small bowel in the pelvis, had less acute and chronic toxicity than those with a low anterior resection (LAR). In this study, three-dimensional treatment planning techniques were used to characterize the position and volume of small bowel in the pelvis and compare these to repeat studies obtained during the typical 5-week course of treatment to attempt to explain the above observations. ⋯ Because treatment planning CT scans can detect small bowel that does not contain contrast, they may be more accurate than the traditional small bowel series. The Preop patients had significantly less pelvic small bowel supporting the clinical observation of better tolerance to therapy. The higher small bowel toxicity reported for LAR vs. APR patients may be explained by the greater variability of both the position and volume of the small bowel in the posterior pelvis for LAR patients. This finding suggests that a single planning study may not be accurate for the block design used for boost treatment of LAR patients. Bladder-filling techniques were useful for Preop and LAR but not APR patients, and decreased in benefit over time. This study suggested that treatment planning CT scans were more useful than a small bowel series and that more than one treatment planning CT may be obtained in any patient receiving > 45 Gy for rectal cancer. However, further research will be necessary to determine the optimal timing and total number of repeat studies.
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Int. J. Radiat. Oncol. Biol. Phys. · Nov 2001
Lack of prostate cancer radiosensitization by androgen deprivation.
The majority of clinical trials have shown that high-grade prostate cancer patients treated with androgen deprivation (AD) plus radiation (RT) have a survival advantage over those treated with RT alone. One possible mechanism for such a favorable interaction is that AD sensitizes cells to radiation. Animal model studies have provided suggestive evidence that AD sensitizes cells to radiation, but this mechanism is difficult to confirm conclusively in vivo. This question was investigated in LNCaP cells grown in vitro. ⋯ The results show that in LNCaP prostate tumor cells supra-additive apoptosis does not translate into radiosensitization by clonogenic survival. Because clonogenic survival is a measure of overall cell death, either the level of apoptosis is too small a component of overall cell death or the increases in apoptosis occurred in a subpopulation that would have been killed by other mechanisms. Although the findings indicate that AD does not act by sensitizing prostate cancer cells to RT, the additive cell death and growth inhibitory effects of AD + RT are clinically meaningful.
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Int. J. Radiat. Oncol. Biol. Phys. · Nov 2001
Observer variation in contouring gross tumor volume in patients with poorly defined non-small-cell lung tumors on CT: the impact of 18FDG-hybrid PET fusion.
To quantify interobserver variation in gross tumor volume (GTV) localization using CT images for patients with non-small-cell lung carcinoma and poorly defined tumors on CT and to determine whether variability would be reduced if coregistered 2-[18F]fluoro-2-deoxy-d-glucose (FDG)-hybrid positron emission tomography (PET) with CT images were used. ⋯ High observer variability in CT-based definition of the GTV can occur. A more consistent definition of the GTV can often be obtained if coregistered FDG-hybrid PET images are used.
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Int. J. Radiat. Oncol. Biol. Phys. · Nov 2001
Clinical TrialFitting tumor control probability models to biopsy outcome after three-dimensional conformal radiation therapy of prostate cancer: pitfalls in deducing radiobiologic parameters for tumors from clinical data.
The goal of tumor control probability (TCP) models is to predict local control for inhomogeneous dose distributions. All existing fits of TCP models to clinical data have utilized summaries of dose distributions (e.g., prescription dose). Ideally, model fits should be based on dose distributions in the tumor, but usually only dose-volume histograms (DVH) of the planning target volume (PTV) are available. We fit TCP models to biopsy outcome after three-dimensional conformal radiation therapy of prostate cancer using either a dose distribution summary or the full DVH in the PTV. We discuss differences in the radiobiologic parameters and dose-response curves and demonstrate pitfalls in interpreting the results. ⋯ For our data, TCP parameters derived from DVHs likely do not reflect true radiobiologic parameters in the tumor, but are a consequence of the reduced importance of low-dose regions at the periphery of the PTV. Deriving radiobiologic parameters from TCP(Dmean(calc)) fits is not possible unless one parameter is already known. TCP predictions using TCP(DVH(calc)) and TCP(Dmean(calc)) parameters may differ substantially, requiring consistency in the derivation and application of model parameters. The proper derivation of radiobiologic parameters from clinical data requires both substantial dose inhomogeneities and understanding of how these coincide with tumor location.
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Int. J. Radiat. Oncol. Biol. Phys. · Nov 2001
Long-term follow-up of RTOG 92-10: cervical cancer with positive para-aortic lymph nodes.
The purpose of this study was to evaluate the late toxicity and efficacy of twice-daily external irradiation to the pelvis and lumbar para-aortic region with brachytherapy and concurrent chemotherapy for carcinoma of the cervix with positive para-aortic lymph nodes. ⋯ The results suggest that twice-daily external irradiation to the pelvis and lumbar para-aortic region with brachytherapy and concurrent chemotherapy resulted in an unacceptably high rate (17%, 5 of 29) of Grade 4 late toxicity. One patient died of acute complications of therapy. The survival estimates seem no better than standard fractionation irradiation without chemotherapy.