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Dose Escalation of Intensity-Modulated Radiotherapy or Brachytherapy Benefits Patients With Intermediate-Risk Prostate Cancer: Presented at ASCO-GU

By Deborah Brauser

ORLANDO, Fla -- March 1, 2009 -- Patients with intermediate-risk prostate cancer achieve higher rates of biochemical control with dose escalation of intensity-modulated radiotherapy (IMRT) or permanent transperineal brachytherapy (BRT) -- alone or combined with a conventional-dose 3-dimensional conformal radiotherapy (3D-CRT) -- compared with patients treated with 3D-CRT alone, according to results from a retrospective comparison study.

The research was presented here at the American Society of Clinical Oncology 2009 Genitourinary Cancers Symposium (ASCO-GU), cosponsored by the American Society for Therapeutic Radiology and Oncology and the Society of Urologic Oncology.

Researcher William Wong, MD, Radiation Oncology Department, Scottsdale, Arizona, reported the results here in a poster session on February 26.

In this study, Dr. Wong and colleagues evaluated the effects of dose escalation in 270 patients who received treatment with 3D-CRT, 314 who received high-dose IMRT, 225 who received BRT, and 44 who received external-beam radiation plus a BRT boost (EB+BRT).

The median pretreatment prostate-specific antigen (PSA) level was 7 ng/mL. The median radiation dose for 3D-CRT was 68.4 Gy, with 75.6 Gy for IMRT. BRT-treated patients received a prescribed dose of 144 Gy with iodine-125 (I-125) or 120 Gy with palladium-103 (Pd-103). Patients in the EB+BRT group received 45 Gy of EB plus either a 110-Gy dose of I-125 or 90 Gy of Pd-103.

There were 343 low-risk patients, 400 with intermediate risk, and 110 in the high-risk group. Low-risk was categorized by T1-T2, PSA <=10 ng/mL, and Gleason score <=6; intermediate-risk was defined as an increase in the value of 1 of the factors; and high-risk was defined as an increase in value of at least 2 factors.

Univariate analysis was performed using the log-rank test and multivariate analysis used the Cox proportional hazards model. Adverse effects of each treatment modality were compared using the Pearson Chi Square test.

At a median follow-up of 58 months, the biochemical control rate for 3D-CRT was significantly lower than for the higher-dose modalities at 74% versus 87% for IMRT, 94% for BRT alone, and 94% for EB+BRT (P < .0001).

Local control rates were 93%, 99%, 100%, and 100%, respectively. Distant control rates were measured at 96%, 97%, 99%, and 97%, respectively.

For the intermediate-risk and high-risk groups, high-dose IMRT or BRT with or without EB achieved significantly better rates of biochemical control than 3D-CRT (88% vs 94% vs 74% for intermediate risk; 74% vs 72% vs 49% for high risk, P < .0001). No improvement was seen in the low-risk group (P = .22).

On univariate analysis, factors found to be significantly associated with biochemical control were treatment modality, clinical T-stage, PSA level, Gleason score, perineural invasion, and risk group. Multivariate analysis showed that these same factors (except for risk group) were significantly associated with treatment outcome.

There was no increase in gastrointestinal (GI) toxicity from high-dose IMRT compared with conventional-dose 3D-CRT. However, high-dose IMRT did have more grade 2 genitourinary (GU) toxicity. BRT caused more GU toxicity but less GI toxicity than IMRT or 3D-CRT.

Said Dr. Wong. "Basically, our data show that for patients who have prostate cancer treatment with radiation, those in the intermediate-risk group would benefit from dose escalation in the form of IMRT or brachytherapy when compared to 3D conformal therapy."

"In the high-risk group, there's a trend that shows that the higher dose with IMRT or [BRT or EB+BRT] appears to be better. But the total number of patients in that group is relatively small -- too small to say for sure," he added. "And for the low-risk group, we really don't show any improvement in biochemical control. They will probably get as much benefit from the radiation that we're doing now."

In summary, Dr. Wong said, "The most important finding is in the intermediate-risk group. We can draw a pretty firm conclusion there: dose escalation improved the treatment outcome."

[Presentation title: Radiation Dose Escalation for Localized Prostate Cancer: Intensity Modulated Radiation Therapy Compared With Permanent Transperineal Brachytherapy. Abstract 118]

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