Prostate cancer radiation dose response: results of the M. D. Anderson phase III randomized trial

Radical radiotherapy for prostate cancer

External beam radiotherapy is one of the curative treatment options for localised prostate cancer. This article will describe recent advances in prostate radiotherapy, focussing on the results of randomised trials which have addressed the role of radiation dose escalation and of adjuvant hormone therapy. Current controversies will then be considered, including the merits of radiotherapy in comparison with alternative approaches to early prostate cancer, and the possible role of adjuvant radiation following surgery. Finally, future developments will be described, including hypofractionation and dose individualisation, which have the potential to further improve the outcome of external beam radiotherapy for prostate cancer.

Mindless or mindful? Radiation oncologists' perspectives on the evolution of prostate cancer treatment

The evolution of radiation therapy treatment for prostate cancer has been striking over the last 10 years. Advances in brachytherapy (BT), external beam radiotherapy (EBRT), and the combination of EBRT + BT have led to improved biochemical and clinical results. This article describes these advances in the context of the treatment decision process. Key to this process is the assignment of patient risk, which is based on the results of conventional radiation dose and techniques. Using the 1992 AJCC palpation staging system, Gleason score, and pretreatment prostate-specific antigen, two different risk assessment algorithms were compared. Both gave comparable approximations of risk, although the single factor high-risk model was superior in differentiating those patients with the highest probability of failing treatment after radiotherapy. Such criteria are the foundation for treatment selection. Objective findings support BT alone or EBRT alone for low-risk patients, high-dose EBRT or EBRT + BT for intermediate-risk patients, and EBRT + androgen deprivation for high-risk patients. In summary, advances in radiation oncology have led to significant gains in prostate cancer control. Clinical prognostic factor-based patient selection is central to the optimization of outcome.

Prostate cancer update

Research has yielded important insights into the impact of radical prostatectomy in patients with localized prostate cancer. Other recent research has focused on the role of nutrition in prostate cancer development and progression, improved prognostication for patients with both early and advanced prostate cancer, efficacy of adjuvant and neoadjuvant hormonal therapy, and development of novel agents. In addition, the role of bisphosphonates in patients with bone metastasis was established.

What can we expect from dose escalation using proton beams?

It has been demonstrated without doubt in the literature, including elsewhere in this issue, that much better conformal dose distributions in radiation therapy can be obtained with proton beams than with photons (X-rays) or electrons. It is also clear that this remains entirely true--for the fundamental reason of particle range--even after the latest and projected developments in computer-generated IMRT (intensity-modulated radiation therapy) photon dose escalation are fully considered. We consider several examples of tumour dose-response curves that illustrate the quite large gains to be obtained when dose escalation can be achieved, if normal tissue complications can also be avoided. Two contrasting types of tumour are considered in detail, prostate tumours and non-small-cell lung carcinomas. There is a considerable way to go yet to achieve really high non-recurrence rates, especially in the lung tumours. Proton beams would make this progress much safer and more effective than any variants with photons.

Prostate biopsy status and PSA nadir level as early surrogates for treatment failure: analysis of a prostate cancer randomized radiation dose escalation trial

PURPOSE

A positive biopsy after external beam radiotherapy in patients free of any evidence of treatment failure is not synonymous with eventual recurrence. Although biopsy positivity is a predictor of outcome, the utility of biopsy status as a surrogate end point, the effect of radiation dose on biopsy status, and the interrelationships of these associations to prostate-specific antigen (PSA) nadir level are not well-defined. These issues were investigated in a cohort of men with Stage T1-T3 prostate cancer who were randomized to receive between 70 Gy and 78 Gy and were prospectively biopsied at about 2 years after the completion of radiotherapy (RT).

METHODS AND MATERIALS

Of the 301 assessable patients in the trial, 168 underwent planned sextant or greater prostate post-RT biopsies in the absence of biochemical or clinical failure; this group constituted the study cohort. Of the 168 patients, 87 were in the 70-Gy arm and 81 in the 78-Gy arm. Biopsies were classified into four groups: negative (no tumor), atypical/suspicious cells (not diagnostic of carcinoma), carcinoma with treatment effect (CaTxEffect), and carcinoma without treatment effect (CaNoTxEffect). Any diagnosis of carcinoma in the specimen was classified as biopsy positive. Freedom from failure (FFF) included biochemical failure and/or clinical failure. Kaplan-Meier curves were calculated from the completion of RT. For those alive in the study cohort, the median follow-up was 65 months.

RESULTS

The rate of biopsy without tumor was 42%; with atypical cells, it was 28%, with CaTxEffect 21%, and with CaNoTxEffect 9%. The overall biopsy positivity rate (CaTxEffect + CaNoTxEffect) was 30%; 28% in the 70-Gy group and 32% in the 78-Gy group (p = 0.52). The distribution of PSA nadir levels was 73% <or=0.5, 20% >0.5-1.0, 5% >1.0-2.0, and 1% >2.0 ng/mL. Significantly more patients randomized to 78 Gy had a PSA nadir of <or=0.5 ng/mL (80% vs. 67%; p = 0.02). No relationship was found between PSA nadir level and prostate biopsy status. The 5-year FFF rate for those classified as biopsy negative was 84% and for those biopsy positive was 60% (p = 0.0002). Radiation dose did not significantly alter FFF rates by prostate biopsy status. Nadir PSA level correlated with FFF, although this was dependent on the inclusion of the 2 patients with a PSA nadir >2.0 ng/mL.

CONCLUSION

For patients free of treatment failure at the time of prostate biopsy 2 years after RT, the prognosis of no tumor cells was the same as that of atypical/suspicious cells and CaTxEffect was the same as CaNoTxEffect. The biopsy positivity rate was not altered by dose, suggesting that most of the outcome differences between the 70-Gy and 78-Gy groups were due to events occurring before prostate biopsy at 2 years and/or were not entirely dependent on biopsy status. Biopsy status is a strong prognostic factor, but, as an early end point, it may be misleading. PSA nadir appears to have little clinical value in patients treated to doses of >/=70 Gy who are failure free 2 years after RT.