Strategies for improving the outcome of patients with poor prognosis prostate cancers

Importance of implant dosimetry for patients undergoing prostate brachytherapy

OBJECTIVES

To evaluate the disease and treatment-related factors for predicting biochemical freedom from recurrence (BFR) in patients with clinically localized prostate cancer undergoing permanent prostate brachytherapy.

METHODS

Between November 1992 and June 1998, 883 consecutive patients with T1-T2 prostate cancer underwent permanent prostate brachytherapy. Computed tomography-based dosimetry was performed, and the minimal dose to 90% of the prostate volume relative to the prescribed dose (D(90)) was calculated. BFR was defined as three prostate-specific antigen (PSA) rises from nadir, with patients having one or two PSA rises censored early. Follow-up was calculated by censored events. Kaplan-Meier actuarial outcome was determined, and multivariate Cox regression analysis was performed to assess the significance of the D(90), initial PSA value, Gleason score, addition of external beam radiotherapy, addition of hormonal therapy, and isotope selection.

RESULTS

The mean follow-up was 55 months (range 3 to 125). The 10-year BFR rate was 79.1%. Cox proportional analysis identified D(90) as a predictor of BFR (P <0.0001), along with Gleason score, initial PSA level, and clinical stage (P = 0.001, P = 0.001, and P = 0.011, respectively). The addition of external beam radiotherapy, hormonal therapy, and isotope selection did not have an impact on BFR (P = 0.128, P = 0.399, and P = 0.224, respectively).

CONCLUSIONS

The quality of permanent prostate brachytherapy as measured by the D(90) was the most significant predictor for BFR in this study cohort at 10 years. Furthermore, adding external beam radiotherapy and/or hormonal therapy as adjuvant therapies did not independently predict for BFR. Overall, the reported 10-year BFR rates in this study were favorable. Strategies for ensuring the best quality implant should be used and, when reporting brachytherapy outcomes, the implant quality should be noted.

Permanent Prostate Brachytherapy in Men with Clinically Localised Prostate Cancer

Permanent prostate brachytherapy techniques are associated with excellent biochemical control for patients with localised prostate cancer. Ten-year data show that permanent prostate brachytherapy is compatible with external beam irradiation or radical prostatectomy. However, treatment protocols and techniques for prostate brachytherapy vary between centres and there is little conformity of treatment protocols. The selection of patients for monotherapy or combined external beam irradiation and brachytherapy is controversial. The role of neoadjuvant androgen deprivation also remains unanswered in patients with localised prostate cancer. In addition, post-implant dosimetry may in fact be more significant for predicting outcome than the addition of adjuvant therapies, and should be a requirement when performing prostate brachytherapy. Data now seem to support specific computed tomography (CT)-based criteria to evaluate implant quality and delivered dose to the prostate. Unfortunately, prostate oedema and poor imaging techniques are limiting factors for evaluating implant dosimetry. Treatment planning techniques that use new treatment planning computers may assist in improving the implant procedure and dosimetry and are now available.

Dose selection for prostate cancer patients based on dose comparison and dose response studies

PURPOSE

To better define the appropriate dose for individual prostate cancer patients treated with three-dimensional conformal radiation therapy (3D CRT).

METHODS AND MATERIALS

Six hundred eighteen patients treated with 3D CRT between 4/89 and 4/97 with a median follow-up of 53 months are the subject of this study. The bNED outcomes were assessed by the American Society for Therapeutic Radiology and Oncology (ASTRO) definition. The patients were grouped into three groups by prostate-specific antigen (PSA) level (<10 ng/ml, 10-19.9 ng/ml, and 20+ ng/ml) and further subgrouped into six subgroups by favorable (T1, 2A and Gleason score < or =6 and no perineural invasion) and unfavorable characteristics (one or more of T2B, T3, Gleason 7-10, perineural invasion). Dose comparisons for bNED studies were made for each of the six subgroups by dividing patients at 76 Gy for all subgroups except the favorable <10 ng/ml subgroup, which was divided at 72.5 Gy. Five-year bNED rates were compared for the median dose of each dose comparison subgroup. Dose response functions were plotted based on 5-year bNED rates for the six patient groupings, with the data from each of the six subgroups divided into three dose groups. The 5-year bNED rate was also estimated using the dose response function and compares 73 Gy with 78 Gy.

RESULTS

Dose comparisons show a significant difference in 5-year bNED rates for three of the six subgroups but not for the favorable <10 ng/ml, the favorable 10-19.9 ng/ml, or the unfavorable > or =20 ng/ml subgroups. The significant differences ranged from 22% to 40% improvement in 5-year bNED with higher dose. Dose response functions show significant differences in 5-year bNED rates comparing 73 Gy and 78 Gy for four of the six subgroups. Again, no difference was observed for the favorable <10 ng/ml group or the unfavorable > or =20 ng/ml group. The significant differences observed in 5-year bNED ranged from 15% to 43%.

CONCLUSIONS

Dose response varies by patient subgroup, and appropriate dose can be estimated for up to six subdivisions of prostate cancer patients. The appropriate use of high dose with 3D CRT results in 5-year cure rates that equal or exceed other treatments. The national practice must be upgraded to allow the safe administration of 75-80 Gy with 3D CRT.

Conformal radiotherapy for prostate cancer

This review presents the contribution conformal treatment has made to the external beam treatment of prostate cancer drawing on 10 years of experience with three-dimensional conformal radiation treatment in 1500 patients with prostate cancer at our institution. Major contributions from other institutions and the Radiation Therapy Oncology Group (RTOG) clinical trials group are also noted. Patient immobilization, computed tomography (CT) scan identification of the target in three dimensions and beams-eye-view conformal treatment portals are critical to the process. Higher doses of radiation are associated with a marked increase in cure rates as the dose-response curve is extremely steep. The advantage given by the high dose depending on prognostic group ranges from 14% to 35% in 5-year cures. Conformal techniques protect normal tissues so that late complications are rare and in fact fewer than those observed with standard radiation technique at standard radiation doses. Educational efforts are underway in the USA to assist practising radiation oncologists to deliver the required radiation doses of 75-80 Gy safely. Conformal therapy cures more prostate cancers causing fewer complications than standard treatment technique and standard dose. It must therefore be disseminated into the practice of radiation oncology worldwide.

Progress in 3D conformal radiation treatment of prostate cancer

The development of 3D conformal radiation is reviewed and the proof given of three key hypotheses that result in improved patient results. The Fox Chase outcomes from 3D CRT show 7- and 8-year biochemical freedom of disease rates of 72% for all patients, 84% for PSA < 10 ng/ml, 73% for PSA 10-19.9 ng/ml and 37% for PSA > 20 ng/ml. Dose responses by pretreatment PSA level grouping show steep slopes for patients with PSA> 10 ng/ml. Dose response is also demonstrated for 'favorable' and 'unfavorable' prognostic subgroupings of the classic three pretreatment PSA groups. A matched pair analysis of high-dose 3D CRT versus low-dose 3D CRT shows on multivariate analysis a significant advantage in freedom from distant metastasis. A similar matched comparison of high-dose 3D CRT with low-dose 3D CRT patients and low-dose conventional technique patients shows a significant advantage in distant metastasis, cause-specific survival and overall survival for the high-dose group. Future studies including those using biochemical endpoints to direct differential dose distributions are discussed.