Efficacy of post-operative radiation in a prostatectomy cohort adjusted for clinical and genomic risk.

BACKGROUND: To date, there have been no published trials examining the impact of salvage radiation therapy (SRT) in the post-operative setting for prostate cancer (PCa). We conducted a retrospective, comparative study of post-operative radiation following radical prostatectomy (RP) for men with pT3 disease or positive margins (adverse pathological features, APF). METHODS: 422 PCa men treated at four institutions with RP and having APF were analyzed with a primary end point of metastasis. Adjuvant radiation treatment (ART, n=111), minimal residual disease (MRD) SRT (n=70) and SRT (n=83) were defined by PSA levels of <0.2, 0.2-0.49 and ⩾0.5 ng ml(-1), respectively, before radiation therapy (RT) initiation. Remaining 157 men who did not receive additional therapy before metastasis formed the no RT arm. Clinical-genomic risk was assessed by Cancer of the Prostate Risk Assessment Post-Surgical (CAPRA-S) and Decipher. Cox regression was used to evaluate the impact of treatment on outcome. RESULTS: During the study follow-up, 37 men developed metastasis with a median follow-up of 8 years. Both CAPRA-S and Decipher had independent predictive value on multivariable analysis for metastasis (P<0.05). Adjusting for clinical-genomic risk, SRT and no RT had hazard ratios of 4.31 (95% confidence interval, 1.20-15.47) and 5.42 (95% confidence interval, 1.59-18.44) for metastasis compared with ART, respectively. No significant difference was observed between MRD-SRT and ART (P=0.28). Men with low-to-intermediate CAPRA-S and low Decipher value have a low rate of metastatic events regardless of treatment selection. In contrast, men with high CAPRA-S and Decipher benefit from ART, however the cumulative incidence of metastasis remains high. CONCLUSIONS: The decision as to the timing and need for additional local therapy following RP is nuanced and requires providers and patients to balance risks of morbidity with improved oncological outcomes. Post-RP treatment can be safely avoided for men who are low risk by clinical-genomic risk, whereas those at high risk should favor enrollment in clinical trials.

The lag time in initiating clinical testing of new drugs in combination with radiation therapy, a significant barrier to progress?

BACKGROUND: The clinical development of new drugs with radiation appears to be limited. We hypothesised that phase I clinical trials with radiation therapy (RT) are initiated too late into a new drug's lifetime, impeding the ability to complete RT-drug development programmes before patent expiration. METHODS: We identified novel drug-radiation phase I combination trials performed between 1980 and 2012 within the PubMed and ClinicalTrials.gov databases. Data gathered for each drug included: date the initial phase I trial with/without RT was opened/published, date of the published positive phase III trials, and patent expiration dates. Lag time was defined as the interval between opening of the phase I trial without RT and the opening of the phase I with RT. Linear regression was used to model how the lag time has changed over time. RESULTS: The median lag time was 6 years. The initial phase I trial with RT was typically published 2 years after the first published positive phase III trial and 11 years before patent expiration. Using a best-fit linear model, lag time decreased from 10 years for phase I trials published in 1990 to 5 years in 2005 (slope significantly non-zero, P<0.001). CONCLUSIONS: Clinical drug development with RT commences late in the life cycle of anti-cancer agents. Taking into account the additional time required for late-phase clinical trials, the delay in initiating clinical testing of drug-RT combinations discourages drug companies from further pursuing RT-based development. Encouragingly, lag time appears to be decreasing. Further reduction in lag time may accelerate RT-based drug development, potentially improving patient outcomes.

Expanding the use of monoclonal antibody therapy of cancer by using ionising radiation to upregulate antibody targets.

BACKGROUND: Monoclonal antibody (mAb) therapy for the treatment of solid and haematologic malignancies has shown poor response rates as a monotherapy. Furthermore, its use is limited to tumours expressing certain molecular targets. It has been shown that single-dose radiation can induce immunogenic modulation that is characterised by cell-surface phenotypic changes leading to augmented tumour cell/cytotoxic T-cell interaction. METHODS: We examined radiation's ability to upregulate mAb therapy targets. We also used radiation to sensitise tumour cells to antibody-dependent cell-mediated cytotoxicity (ADCC). RESULTS: Radiation significantly increased cell-surface and total protein expression of mAb targets HER2, EGFR, and CD20. Focusing on HER2, targeted by trastuzumab, we observed significant upregulation of HER2 following radiation of 3 out of 3 breast cancer cell lines, one of which was triple negative, as well as in residential stem-cell populations. HER2 upregulation was sustained up to 96 h following radiation exposure and was largely dependent on intracellular reactive oxygen species. Improved ADCC and sensitisation to the antiproliferative effects of trastuzumab demonstrated the functional significance of radiation-induced HER2 upregulation. CONCLUSIONS: We show that single-dose radiation enhances mAb therapy. These findings highlight a mechanism for combining radiation with immunotherapy and expand the patient population that can be treated with targeted therapy.

Association between metabolic syndrome, diabetes mellitus and prostate cancer risk.

BACKGROUND: The worldwide incidence of diabetes mellitus is rapidly increasing. There is recent interest in the influence of glucose metabolism on oncogenesis. We investigated the role of diabetes mellitus and the metabolic syndrome (MS) on prostate cancer development. METHODS: This study consisted of 11 541 men with coronary heart disease screened to participate in a secondary cardiac prevention trial. MS was defined according to modified NCEP/ATP III criteria. Multivariable regression analysis accounting for competing risks was performed using a modified Cox proportional hazard model in order to assess the association between diabetes, the MS and the subsequent development of prostate cancer. RESULTS: At baseline, subjects were classified into one of the four groups: (1) 6119 (53%) with neither diabetic mellitus nor MS, (2) 3376 (29%) with the MS but without diabetes, (3) 560 (5%) with diabetes mellitus but without MS and (4) 1486 (13%) with both conditions. Median follow-up was 12.7 years (range 0-15.7 years). During follow-up, 459 new cases of prostate cancer were recorded. The age-adjusted hazard ratio (HR) for prostate cancer was reduced in diabetic patients compared with those without diabetes, 0.54 and 95% confidence interval of 0.40-0.73. No significant association was noted between the presence of MS and prostate cancer development. On multivariate analysis, diabetes mellitus continued to protect against the development of prostate cancer, this was more pronounced in the absence of MS (HR=0.43, P=0.01 for diabetes in the absence of MS; HR=0.64, P=0.08 in the presence of MS). CONCLUSIONS: The results of this study indicate an inverse association between type 2 diabetes mellitus and prostate cancer risk.

Implementation and experimental results of 4D tumor tracking using robotic couch.

PURPOSE: This study presents the implementation and experimental results of a novel technique for 4D tumor tracking using a commercially available and commonly used treatment couch and evaluates the tumor tracking accuracy in clinical settings. METHODS: Commercially available couch is capable of positioning the patient accurately; however, currently there is no provision for compensating physiological movement using the treatment couch in real-time. In this paper, a real-time couch tracking control technique is presented together with experimental results in tumor motion compensation in four dimensions (superior-inferior, lateral, anterior-posterior, and time). To implement real-time couch motion for tracking, a novel control system for the treatment couch was developed. The primary functional requirements for this novel technique were: (a) the treatment couch should maintain all previous∕normal features for patient setup and positioning, (b) the new control system should be used as a parallel system when tumor tracking would be deployed, and (c) tracking could be performed in a single direction and∕or concurrently in all three directions of the couch motion (longitudinal, lateral, and vertical). To the authors' best knowledge, the implementation of such technique to a regular treatment couch for tumor tracking has not been reported so far. To evaluate the performance of the tracking couch, we investigated the mechanical characteristics of the system such as system positioning resolution, repeatability, accuracy, and tracking performance. Performance of the tracking system was evaluated using dosimetric test as an endpoint. To investigate the accuracy of real-time tracking in the clinical setting, the existing clinical treatment couch was replaced with our experimental couch and the linear accelerator was used to deliver 3D conformal radiation therapy (3D-CRT) and intensity modulated radiation therapy (IMRT) treatment plans with and without tracking. The results of radiation dose distribution from these two sets of experiments were compared and presented here. RESULTS: The mechanical accuracies were 0.12, 0.14, and 0.18 mm in X, Y, and Z directions. The repeatability of the desired motion was within ±0.2 mm. The differences of central axis dose between the 3D-CRT stationary plan and two tracking plans with different motion trajectories were 0.21% and 1.19%. The absolute dose differences of both 3D tracking plans comparing to the stationary plan were 1.09% and 1.20%. Comparing the stationary IMRT plan with the tracking IMRT plan, it was observed that the central axis dose difference was -0.87% and the absolute difference of both IMRT plans was 0.55%. CONCLUSIONS: The experimental results revealed that the treatment couch could be successfully used for real-time tumor tracking with a high level of accuracy. It was demonstrated that 4D tumor tracking was feasible using existing couch with implementation of appropriate tracking methodology and with modifications in the control system.

Cytidine deaminase single-nucleotide polymorphism is predictive of toxicity from gemcitabine in patients with pancreatic cancer: RTOG 9704.

The aim of this study is to validate the prognostic and predictive value of the non-synonymous cytidine deaminase (CDA) Lys²7Gln polymorphism for hematological toxicity and survival using a randomized phase III adjuvant trial (Radiation Therapy Oncology Group (RTOG) 9704) in pancreatic cancer in which one treatment arm received gemcitabine. CDA is involved in gemcitabine inactivation, and there is conflicting data on the role of the non-synonymous CDA Lys²7Gln polymorphism in predicting toxicity and survival in cancer patients treated with gemcitabine. RTOG 9704 randomized 538 patients after pancreatic resection to receive radiotherapy with either 5-fluorouracil (5-FU) or gemcitabine. CDA Lys²7Gln polymorphism genotype was analyzed. We tested an association between CDA single-nucleotide polymorphism genotype and the survival outcome by the Cox proportional hazard model adjusting for other covariates, as well as toxicity by the logistic regression model. There is statistically significant more severe hematological toxicity in patients treated with gemcitabine with either the homozygote wild-type genotype (Lys/Lys) alone (odds ratio (OR)=0.06, P=0.01), or in combination with the heterozygote (Lys/Gln; OR=0.14, P=0.03) when compared with homozygote variant genotype (Gln/Gln) when adjusted for other covariates. This was not seen in the non-gemcitabine treated arm. There are no genotype differences with respect to survival outcome. In conclusion, in this prospective randomized adjuvant study of patients with pancreatic cancer, the CDA Lys²7Gln polymorphism is validated as a predictive marker of gemcitabine hematological toxicity, but not with treatment response or survival.

Costs of early adjuvant radiation therapy after radical prostatectomy: a decision analysis.

BACKGROUND: This analysis was carried out to evaluate the cost-effectiveness of adjuvant radiation therapy (ART) versus observation, using a decision analysis model based primarily upon the published results of the Southwest Oncology Group prospective trial (SWOG 8794). PATIENTS AND METHODS: A decision analysis model was designed to compare ART versus observation over a 10-year time horizon. Probabilities of treatment success, utilization of salvage treatments, and rates of adverse events were taken from published results of SWOG 8794. Cost inputs were based on 2010 Medicare reimbursement rates. Primary outcome measure was incremental cost per prostate-specific antigen (PSA) success (i.e. serum PSA level <0.4 ng/ml). RESULTS: ART results in a higher PSA success rate than observation with probability of 0.43 versus 0.22. The mean incremental cost per patient for ART versus observation was $6023. The mean incremental cost-effectiveness ratio was $26,983 over the 10-year period. CONCLUSIONS: ART appears cost effective compared with observation based upon this decision analysis model. Future research should consider more costly radiation therapy (RT) approaches, such as intensity-modulated RT, and should evaluate the cost-effectiveness of ART versus early salvage RT.

Early toxicity predicts long-term survival in high-grade glioma.

BACKGROUND: Patients with high-grade gliomas are treated with surgery followed by chemoradiation. The risk factors and implications of neurological side effects are not known. METHODS: Acute and late ≥ grade 3 neurological toxicities (NTs) were analysed among 2761 patients from 14 RTOG trials accrued from 1983 to 2003. The association between acute and late toxicity was analysed using a stepwise logistic regression model. The association between the occurrence of acute NT and survival was analysed as an independent variable. RESULTS: There were 2610 analysable patients (86% glioblastoma, 10% anaplastic astrocytoma). All received a systemic agent during radiation (83% chemotherapy, 17% biological agents). Median radiation dose was 60 Gy. There were 182 acute and 83 late NT events. On univariate analysis, older age, poor performance status, aggressive surgery, pre-existing neurological dysfunction, poor mental status and twice-daily radiation were associated with increased acute NT. In a stepwise logistic regression model the occurrence of acute NT was significantly associated with late NT (OR=2.40; 95% CI=1.2-4.8; P=0.014). The occurrence of acute NT predicted poorer overall survival, independent of recursive partitioning analysis class (median 7.8 vs 11.8 months). INTERPRETATION: Acute NT is significantly associated with both late NT and overall survival.

Zebrafish: an emerging model system for human disease and drug discovery.

In vivo studies represent an essential step in drug development and currently rely largely on mice, yet limitations of mammalian models motivated the search for complementary vertebrate model systems. This review focuses on zebrafish, Danio rerio, as a facile model system to study human disease and drug responses. Zebrafish are particularly suited for this purpose because they represent a vertebrate species, their genome is sequenced, and a large number of synchronously developing, transparent embryos can be produced. Zebrafish embryos are permeable to drugs and can easily be manipulated using well-established genetic and molecular approaches. Here, we summarize recent work on drug discovery and toxicity in zebrafish embryos. In addition, we provide a synopsis of current efforts to establish disease models in zebrafish focusing on neoplasia. The results of these studies highlight the potential of zebrafish as a viable addition to established animal models by offering medium and, potentially, high throughput capabilities.

E-mail and oncology: a survey of radiation oncology patients and their attitudes to a new generation of health communication.

Electronic mail (e-mail) is a powerful tool that can greatly enhance communication and has numerous potential applications within the medical profession. Physician-patient e-mail communication volume is increasing, but little research has addressed patient interests and concerns about this now commonplace technology. The goals of this study were to review the available literature regarding physician-patient e-mail practices, evaluate patient interest, assess patient perspectives about how e-mail communication might facilitate medical treatment and advice, and determine areas of patient concern regarding e-mail communication with their physicians. To this end, a population of cancer patients was sent a written survey designed to assess their access to e-mail and attitudes about physician-patient e-mail communication. We found that patients favored e-mail for increased convenience, efficiency, and timeliness about general health problems, while it was not favored for urgent matters.

Effects of androgen suppression and radiation on prostate cancer suggest a role for angiogenesis blockade.

Antiandrogen therapy is an important modality in the treatment of prostate cancer. Recent research into the role of angiogenesis in tumour growth and metastasis has uncovered links between antiandrogen therapy, radiation therapy and angiogenesis, which have exciting implications for the treatment of prostate cancer. Angiogenic cytokines such as vascular endothelial growth factor (VEGF) have been identified in prostate cancer cells and tumours, and androgens appear to stimulate VEGF. This article assesses the antiangiogenic effects of hormonal therapy and assesses the role that angiogenesis may play in the observed cooperation between hormonal and radiation therapies for prostate cancer.

Assessment of angiogenesis: implications for ultrasound imaging.

In this paper, the fundamentals of tumor angiogenesis and the implications for ultrasound imaging will be described. Twenty-eight athymic nude mice were implanted with the human melanoma cell lines DB-1 or MW-9 (14 mice/group). Ultrasound contrast agents were injected in the tail veins. Power Doppler and pulse inversion harmonic imaging (PI-HI) was performed (in real time and intermittently). Ultrasound results were compared to immunohistochemical stains for endothelial cells (CD31), vascular endothelial growth factor (VEGF), and cyclooxygenase-2 (COX-2). Linear regression analysis indicated statistically significant correlations between percent area stained with COX-2 and with VEGF relative to power Doppler (p<0.05) and intermittent PI-HI (p<0.05) measures of tumor neovascularity in the MW-9 and the DB-1 mice, respectively. Preliminary results from a human trial of the anti-angiogenic drug Angiostatin (Entremed, Rockville, MD) showed tumor volumes increased in two patients, while the vascularity remained virtually unchanged. Conversely, in three patients with diminished tumor volumes vascularity increased by 38%. In conclusion, contrast enhanced ultrasound imaging of tumor neovascularity may provide noninvasive markers of angiogenesis and may become a useful tool for monitoring anti-angiogenic therapies in vivo.

Can extraprostatic extension be treated by prostate brachytherapy? An analysis based on postimplant dosimetry.

PURPOSE: To determine whether extraprostatic extension (EPE) can be treated by Pd-103 prostate implants. METHODS AND MATERIALS: The postimplant dosimetry of 22 consecutive Pd-103 prostate implants was analyzed to determine whether potential EPE was adequately treated. The implants were peripherally loaded and planned with a 3-5-mm dose margin at midgland. Seeds were not implanted outside of the capsule except at the base and apex. The postimplant dosimetry was based on a CT scan obtained 32 +/- 8 days postimplant. The radial distance between the prostate edge and the prescription isodose line was measured at the left lateral, left posterolateral, posterior, right posterolateral, and right lateral positions on each prostate contour. Similar measurements were made of the preplan dose margins. RESULTS: The mean postimplant dose margin was > or =4.5 mm at the midgland and apex of the prostate in agreement with the preplan. However, at the base, the mean margins at the five measurement locations were less than planned, typically ranging from 2.5 to 3.5 mm. The postimplant margin at the base was smaller than expected due to source placement errors, a correctable problem. CONCLUSIONS: Peripherally loaded Pd-103 prostate implants can deliver the prescription dose 3-5 mm outside the capsule, which is believed to be sufficient to treat 95-100% of EPE in favorable risk patients. However, dose coverage of EPE, like dose coverage of the prostate, is operator-dependent.

Targeting angiogenic processes by combination rofecoxib and ionizing radiation.

Tumor growth and angiogenesis are interdependent. Cyclooxygenase (COX) catalyzes the synthesis of prostaglandins from arachidonic acid. Nonsteroidal antiinflammatory drugs (NSAIDs) inhibit COX-mediated synthesis of prostaglandins. COX-1 is constitutively expressed in a wide range of tissues, whereas COX-2 is cytokine inducible. Enhanced COX-2 expression has been attributed a key role in the development of inflammation and related processes observed in pathologically altered disease states. Two specific COX-2 inhibitors, namely rofecoxib (Vioxx) and celecoxib (Celebrex), both oral agents and U.S. Food and Drug Administration approved, have been shown preclinically and clinically to have efficacy comparable to that of NSAIDs for relief of pain and inflammation in osteoarthritis, with decreased risk of gastrointestinal damage. Little is known about how angiogenesis is affected by the combination of rofecoxib and radiation. We have evaluated the combination of rofecoxib, at various concentrations, and radiation on cytokine-induced angiogenesis in vitro. We have found that rofecoxib inhibited endothelial cell proliferation, migration, and tube formation (differentiation) at clinically relevant doses. In combination with radiation, inhibition of endothelial cell function further increased twofold. The combination of rofecoxib and radiation suggests a complementary strategy with clinical ramifications to target angiogenesis-dependent malignancies.

Elevated COX-2 expression in cervical carcinoma: reduced cause-specific survival and pelvic control.

The purpose of this study was to correlate the level of cyclooxygenase-2 (COX-2) expression in carcinoma of the cervix with the clinical endpoints: local control, cause-specific survival, and patterns of failure in patients treated with radiotherapy. Formalin-fixed, paraffin-embedded tumor biopsies were stained for COX-2. Clinical factors such as stage, grade, tumor size, pre- and posttreatment hemoglobin level, and radiotherapy dose were also evaluated. Actuarial local control rates and cause-specific survival were determined according to the Kaplan-Meier method. COX-2 distribution staining was the only prognostic factor that was associated with local control and cause-specific survival. High COX-2 distribution staining was associated with decreased local control and decreased cause-specific survival by log rank comparison of Kaplan-Meier survival curves. The 5-year cause-specific survival rates for tumors with low versus high COX-2 distribution values were 90% and 22%, respectively (p = 0.0003). Actuarial pelvic control at 5 years was superior in patients with low COX-2 distribution staining (92%) compared with high staining (42%, p = 0.005). COX-2 staining intensity was found to correlate positively with tumor size (p = 0.02). These findings indicate that increased expression of COX-2 yields reduced pelvic control and cause-specific survival in patients with invasive carcinoma of the cervix treated with radiotherapy. Previously, inhibition of COX-2 has been demonstrated to sensitize tumors to radiation without effect on normal tissue. Taken together, these data may support a novel therapeutic application of COX-2 inhibitors in the treatment of carcinoma of the cervix.

Does hormonal therapy influence sexual function in men receiving 3D conformal radiation therapy for prostate cancer?

PURPOSE: We evaluated the effect of three-dimensional conformal radiation therapy (3D-CRT) with or without hormonal therapy (HT) on sexual function (SF) in prostate cancer patients whose SF was known before all treatment. METHODS AND MATERIALS: Between March 1996 and March 1999, 144 patients received 3D-CRT (median dose = 70.2 Gy, range 66.6-79.2 Gy) for prostate cancer and had pre- and post-therapy SF data. All SF data were obtained with the O'Leary Brief SF Inventory, a self-administered, multidimensional, validated instrument. We defined total sexual potency as erections firm enough for penetration during intercourse. Mean follow-up time was 21 months (SD +/- 11 months). The Wilcoxon signed-rank test was used to test for significance of the change from baseline. RESULTS: Before 3D-CRT, 87 (60%) of 144 men were totally potent as compared to only 47 (47%) of 101 at 1-year follow-up. Of the 60 men totally potent at baseline and followed for at least 1 year, 35 (58%) remained totally potent. These changes corresponded to a significant reduction in SF (p < 0.05). Patients who had 3D-CRT alone were more likely to be totally potent at 1 year than those receiving 3D-CRT with HT (56% vs. 31%, p = 0.012); however, they were also more likely to be potent at baseline (71% vs. 44%, p = 0.001). Although these two groups had a significant reduction in SF from baseline, their change was not significantly different from each other. CONCLUSION: These data indicate that 3D-CRT causes a significant reduction in total sexual potency as compared to pretreatment baseline. The addition of HT does not appear to increase the risk of sexual dysfunction.

Increased hypoxia correlates with increased expression of the angiogenesis marker vascular endothelial growth factor in human prostate cancer.

OBJECTIVES: To test the hypothesis that increasing levels of hypoxia are associated with increased expression of vascular endothelial growth factor (VEGF) in prostate cancer by correlating the level of median tissue oxygenation in human prostate tumors with the immunohistochemically determined level of VEGF expression. METHODS: Custom-made Eppendorf oxygen microelectrodes were used to quantitate the pO(2) levels in prostate tumors of 13 men undergoing radical prostatectomy. All pO(2) measurements were performed under fluorine-based general anesthesia. Paraffin-embedded tumor tissue from these men was analyzed to measure the level of VEGF expression by immunohistochemical staining. The significance of the associations between the pO(2) levels and VEGF staining were determined by the Pearson correlations. RESULTS: The range of the median pO(2) levels (based on between 97 and 129 individual measurements) among 13 prostate tumors was 0.5 to 44.9 mm Hg. The blinded comparison of pO(2) levels and VEGF staining intensity demonstrated a significant correlation between increasing hypoxia and the percentage of cells staining positive for VEGF (r = -0.721, P = 0.005). This correlation was also significant when pO(2) levels were compared with the overall immunoreactive score, which takes into account staining intensity (r = -0.642, P = 0.018). CONCLUSIONS: To our knowledge, this is the first study demonstrating a significant association between increasing levels of hypoxia and increased expression of the angiogenesis marker VEGF in human prostate carcinoma. The results of our study further support the exploration of antiangiogenesis strategies for the treatment of human prostate cancer.

Defining a future role for radiogenic therapy.

The goal of cancer therapy is to eliminate the cancer and/or to arrest further growth while decreasing normal tissue toxicity, i.e. to increase the therapeutic ratio. This review focuses on a group of therapeutics that are either (1) directly stimulated by radiation to produce either directly or indirectly cytotoxic agents (i.e. genes under the control of a radiation inducible promoter that produce a cytotoxic protein or an enzyme that converts a prodrug to an active form, respectively); (2) auger-electron emitting radiolabelled oligonucleotides, antibodies, nucleotide analogues, or other small molecules that are internalized; (3) radiation inducible genes that produce a ligand or transporter (or the like) which then can be targeted by cytotoxic agents (e.g. radiolabelled substance). We have termed this group of therapeutics radiogenic therapy.

Dosimetric analysis of urinary morbidity following prostate brachytherapy (125I vs. 103Pd) combined with external beam radiation therapy.

The purpose of this analysis was to correlate isotope selection with the urinary symptoms of patients who received a combination of external beam radiotherapy (EBRT) and a transperineal interstitial permanent prostate brachytherapy (TIPPB) boost with either a (103)palladium ((103)Pd) or a (125)iodine ((125)I) radioisotope. Postimplant dosimetry was performed to evaluate both urethral dose and implant quality. The American Urologic Association (AUA) scores in both the (125)I and (103)Pd groups were similar initially. However, at 1, 3, 6, and 12 months of follow-up, the mean AUA scores for the (125)I and (103)Pd patients were 18 +/- 6 vs. 11 +/- 9, 17 +/- 7 vs. 11 +/- 7, 10 +/- 3 vs. 9 +/- 4, and 14 +/- 8 vs. 7 +/- 5, respectively (P < 0.01). The only significant difference between the postimplant dose-volume histogram (DVH) of the (125)I and (103)Pd implants was the minimum dose that 90% of the urethra received (D(90)). The increased AUA score of the (125)I group was weakly correlated (R(2) = 0.20) with the D(90) dose but that of the (103)Pd patients was not (R(2) = 0.00). This suggests that the higher AUA score of the (125)I patients was not necessarily the result of the higher D(90) dose. Thus, patients who received (103)Pd experienced less urinary morbidity than those implanted with (125)I. We recommend further validating these findings in prospective studies in which the quality of the (125)I and (103)Pd implants can be evaluated.

Isotope selection for permanent prostate implants? An evaluation of 103Pd versus 125I based on radiobiological effectiveness and dosimetry.

Transperineal interstitial permanent prostate brachytherapy (TIPPB) has become an increasingly popular treatment for early-stage/favorable-risk adenocarcinoma of prostate. Within TIPPB, permanent implants often use either (103)Pd (T(1/2) = 17 days) or (125)I (T(1/2) = 60 days). This review compares the radiobiological and treatment planning effectiveness of (103)Pd and (125)I implants by using the linear-quadratic model with recently published data regarding: prostate tumor cell doubling times, T(pot), alpha and alpha/beta, ratio. The tumor potential doubling times (T(pot)) were determined based on recently published proliferation constants (K(p)). The initial slope of the cell radiation dose survival curve, alpha, the terminal slope beta and the alpha/beta ratio were taken from recent published clinical and cellular results. The total dose delivered from each isotope was the dose used clinically, that is, 120 Gy for (103)Pd and 145 Gy for (125)I. Dale's modified linear-quadratic equation was used to estimate the biological effective dose, the cell-surviving fraction, the effective treatment time, and the wasted radiation dose for different values of T(pot). Treatment plans for peripherally loaded implants were compared. The T(pot) reported for organ-confined prostate carcinomas varied from 16 to 67 days. At short T(pot) both isotopes were less effective, but (103)Pd had much less dependence on T(pot) than (125)I. However, at long T(pot) both isotopes produced similar effects. The minimum surviving fraction for exposure to (103)Pd decreased from 1.40 x 10(-4) to 1.31 x 10(-5) as the T(pot) increased from 16 to 67 days. By contrast for exposure to (125)I, the minimum surviving fraction decreased from 3.98 x 10(-3) to 1.98 x 10(-5) over the same range of T(pot). A comparison of treatment plans revealed that (103)Pd plans required more needles and seeds; however, this was a function of seed strength. Both isotopes had similar dose-volume histograms for prostate, urethra, and rectum. The theoretical prediction of effectiveness using the linear quadratic equation for the common clinically prescribed total radiation doses indicated that (103)Pd should be more effective than (125)I because it had less dependence on T(pot). The greatest benefit of (103)Pd was shown to be with tumors with a short T(pot). Although the regrowth delay would be longer with (125)I, the benefit was inconsequential compared with the very slow doubling times of localized prostate cancer. Treatment planning with either isotope revealed no significant differences. These findings may explain why clinically there seemed to be no clear difference in treatment outcome with either isotope. Based on these predictions, we recommend a clinical trial to compare the efficacy of the two isotopes.