International journal of radiation oncology, biology, physics
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Int. J. Radiat. Oncol. Biol. Phys. · Nov 2001
ReviewThe rush to judgment: Does the evidence support the enthusiasm over three-dimensional conformal radiation therapy and dose escalation in the treatment of prostate cancer?.
To discuss the assumptions behind and current clinical evidence on three-dimensional conformal radiation therapy (3D-CRT) and dose escalation in the treatment of prostate cancer. ⋯ Although 3D-CRT is a promising technology that many radiation oncologists and clinics are quickly adopting to treat such tumors as prostate cancer, the long-term evidence on the benefits and limitations of this technology is still lacking. Until we have solid long-term evidence on the true clinical potential of this new technology, let us not rush to judgment, but exercise caution, diligence, and thoughtfulness in using this new technology to treat our patients.
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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.
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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
Implant volume as a prognostic variable in brachytherapy decision-making for malignant gliomas stratified by the RTOG recursive partitioning analysis.
When an initial retrospective review of malignant glioma patients (MG) undergoing brachytherapy was carried out using the Radiation Therapy Oncology Group (RTOG) recursive partitioning analysis (RPA) criteria, it revealed that glioblastoma multiforme (GBM) cases benefit the most from implant. In the present study, we focused exclusively on these GBM patients stratified by RPA survival class and looked at the relationship between survival and implanted target volume, to distinguish the prognostic value of volume in general and for a given GBM class. ⋯ For all GBM patients, an inverse relationship between implanted TV size and median survival is suggested by this study. However, when GBM patients are stratified using the RTOG's RPA criteria, the prognostic effect of implant volume disappears within each RPA survival class. At the critical volume of 25 cc, which approximates an implant of 5-cm diameter (upper implantation limit of many CNS brachytherapy protocols), the "poorest" prognosis GBM patients stratified by RPA still demonstrate a survival benefit with implant. We suggest that any GBM patient meeting brachytherapy recognized size criteria be considered for I-125 implant.