International journal of radiation oncology, biology, physics
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Int. J. Radiat. Oncol. Biol. Phys. · Jun 2002
Dose escalation using conformal high-dose-rate brachytherapy improves outcome in unfavorable prostate cancer.
To overcome radioresistance for patients with unfavorable prostate cancer, a prospective trial of pelvic external beam irradiation (EBRT) interdigitated with dose-escalating conformal high-dose-rate (HDR) prostate brachytherapy was performed. ⋯ Pelvic EBRT interdigitated with transrectal ultrasound-guided real-time conformal HDR prostate brachytherapy boost is both a precise dose delivery system and a very effective treatment for unfavorable prostate cancer. We demonstrated an incremental beneficial effect on biochemical control and cause-specific survival with higher doses. These results, coupled with the low risk of complications, the advantage of not being radioactive after implantation, and the real-time interactive planning, define a new standard for treatment.
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Int. J. Radiat. Oncol. Biol. Phys. · Jun 2002
Biologically effective dose for permanent prostate brachytherapy taking into account postimplant edema.
To study the influence of radiobiologic and physical parameters and parameters related to edema on the biologically effective dose (BED) for permanent prostate implants and to determine the optimal timing of seed reconstruction for BED calculation. ⋯ The maximal BED depends strongly on the value of alpha, the potential tumor doubling time, and the choice of isotope. If prostate volume increase due to edema is not taken into account, the BED will be underestimated shortly after the implantation and overestimated if the calculations are based on images taken several months after implantation. The optimal timing of BED evaluation for 125I seed implants and typical prostate edema values is 25 days after implantation.
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Int. J. Radiat. Oncol. Biol. Phys. · Jun 2002
Practical application of biochemical failure definitions: what to do and when to do it.
The posttreatment prostate-specific antigen (PSA) profile can often be difficult to interpret after external beam radiotherapy for prostate cancer. We performed an extensive analysis of post-radiotherapy PSA measurements to determine the clinical significance of biochemical failure (BF) and the correlation of BF with clinical failure (CF) and cause-specific death (CSD). ⋯ Once the post-radiotherapy PSA profile reaches >or=3 ng/ml above the nadir, there is a high risk of clinical failure within a relatively short time period, for which treatment intervention may be considered, regardless of pretreatment characteristics. After a nadir >or=1.0 ng/ml or three consecutive rises, some patients (especially with low-risk pretreatment characteristics) may be considered for further PSA observation before treatment intervention.
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Int. J. Radiat. Oncol. Biol. Phys. · Jun 2002
Relative biological effectiveness (RBE) values for proton beam therapy.
Clinical proton beam therapy has been based on the use of a generic relative biological effectiveness (RBE) of 1.0 or 1.1, since the available evidence has been interpreted as indicating that the magnitude of RBE variation with treatment parameters is small relative to our abilities to determine RBEs. As substantial clinical experience and additional experimental determinations of RBE have accumulated and the number of proton radiation therapy centers is projected to increase, it is appropriate to reassess the rationale for the continued use of a generic RBE and for that RBE to be 1.0-1.1. ⋯ At present, there is too much uncertainty in the RBE value for any human tissue to propose RBE values specific for tissue, dose/fraction, proton energy, etc. The experimental in vivo and clinical data indicate that continued employment of a generic RBE value and for that value to be 1.1 is reasonable. However, there is a local "hot region" over the terminal few millimeters of the SOBP and an extension of the biologically effective range. This needs to be considered in treatment planning, particularly for single field plans or for an end of range in or close to a critical structure. There is a clear need for prospective assessments of normal tissue reactions in proton irradiated patients and determinations of RBE values for several late responding tissues in laboratory animal systems, especially as a function of dose/fraction in the range of 1-4 Gy.
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Int. J. Radiat. Oncol. Biol. Phys. · Jun 2002
Intrafraction prostate motion during IMRT for prostate cancer.
Although the interfraction motion of the prostate has been previously studied through the use of fiducial markers, CT scans, and ultrasound-based systems, intrafraction motion is not well documented. In this report, the B-mode, Acquisition, and Targeting (BAT) ultrasound system was used to measure intrafraction prostate motion during 200 intensity-modulated radiotherapy (IMRT) sessions for prostate cancer. ⋯ Using an ultrasound-based system, intrafraction prostate motion occurred predominantly in the anterior and superior directions, but was clinically insignificant. Intrafraction motion was much smaller than interfraction motion, and the two types of movement did not correlate.