Ten-Year Results of Dose Escalation with 3-Dimensional Conformal Radiotherapy for Patients with Clinically Localized Prostate Cancer

English

Reviewer: John Wilson, MD
Abramson Cancer Center of the University of Pennsylvania
Ultima Vez Modificado: 20 de octubre del 2003

Presenter: Michael Zelefsky
Presenter's Affiliation: Memorial Sloan Kettering Cancer Center
Type of Session: Scientific

Background

Prostate cancer is the most commonly diagnosed cancer in men
External Beam Radiotherapy is a potentially curative treatment for patients with localized disease
There has been a trend of dose escalation in prostate cancer radiotherapy, which has been aided by the use of 3D conformal therapy (3D-CRT)

Materials and Methods

828 patients with clinical stage T1-3 prostate cancer were treated between 1988 and 1997 using 6-field 3D-CRT
Radiation was prescribed to include the prostate and seminal vesicles with a margin
Patients were treated to different dose levels as part of a phase II dose escalation study: 64.8 to <70.2 Gy (101 patients, 12%), 70.2 Gy (268 patients, 32.5%) and 75.6 Gy (459 patients, 55.5%)
The isocenter received a 5-7% higher dose than the prescribed dose
Patients were grouped into risk categories based on PSA levels, Gleason score, and clinical stage
283 patients (34%) received neo-adjuvant androgen deprivation therapy (ADT) to reduce target volume
PSA failure was defined by ASTRO criteria (3 consecutive rises in PSA)

Results

The ten year PSA relapse-free survival (PRFS) was 70%, 49%, and 35% for favorable, intermediate, and unfavorable risk patients, respectively (p<0.001)
The 10 year PRFS for favorable risk patients was 83% for those receiving 75.6 Gy compared to 57% for those treated to 70.2 Gy (p=0.003)
Intermediate risk patients had a 10 year PRFS of 50 and 42% after receiving 75.6 and 70.2 Gy, respectively (p=0.05)
Unfavorable risk patients had a 10 year PRFS of 42 and 24% after receiving 75.6 and 70.2 Gy, respectively (p=0.04)
Independent predictors of PSA control were: pre-treatment PSA < 10, radiation dose, T stage, Gleason score, and neo-adjuvant ADT.
Actuarial 10 year grade 3 or higher toxicity was 1.5% for GI and 2.5% for GU

Author's Conclusions

This study shows the importance dose escalation in localized prostate cancer
Doses of greater than 75.6 Gy may be needed for further improvement in long-term control
There has been minimal long term toxicity with doses up to 75.6 Gy using 3D-CRT

Clinical/Scientific Implications

This study supports the theory of dose escalation in prostate cancer. Long term results are still pending on higher doses, such as dose level V (78 Gy) in the RTOG 9406 study. Modalities such as intensity modulated radiotherapy and proton therapy may allow for even higher doses with better tumor control and acceptable toxicity. However, it is important to remember that those patients treated in the lower dose arms of this study have longer follow up then those treated at the higher doses. This could introduce bias and it is important to wait for longer follow up in the high dose arm to approach ten years before making definitive recommendations on dose escalation.

Oncolink's ASTRO Coverage made possible by an unrestricted Educational Grant from Siemens Medical Solutions.