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Extended radiotherapy may increase risk of biochemical failure in low risk patients

Posted Sep 29 2008 4:46pm

It appears that extending the amount of time over which radiotherapy (RT) is given to patients in treatment of localized prostate cancer may increase the risk for biochemical failure in a subset of those patients — the ones already at low risk for rapidly progressive disease. Patients at low risk for progressive prostate cancer who decide to undergo RT as first line therapy should be made aware of this risk. RT as first line therapy for early stage prostate cancer is normally given over 8 weeks on 5 days each week.

The protraction of external beam radiotherapy (RT) over extended periods of time is known to be detrimental in several disease sites. In prostate cancer, the overall treatment time can be considerable, as can the potential for treatment breaks. A recent study from Fox Chase Cancer Center in Philadelphia has evaluated the effect of elapsed treatment time on outcome after RT for early stage prostate cancer.

Between April 1989 and November 2004, 1,796 men with prostate cancer were treated with RT alone. The authors defined the number of non-treatment days divided by the total nukmber of elapsed days of RT as the “non-treatment days ratio (NTDR). This ratio was used to investigate the relationship between treatment duration and total RT dose. Men were divided into three groups with respect to their risk for progreszsive prostate cancer pre-gtreatment: low risk (n = 789), intermediate risk (n = 798), and high risk (n = 209), using a single-factor model.

The results of the analysis were as follows:

  • For all patients, the 10-year freedom from biochemical failure (FFBF) rate was 68 percent for an NTDR < 33 percent vs. 58 percent for an NTDR &ge; 33 percent. 
  • In the low-risk group, the 10-year FFBF rate was 82 percent for an NTDR < 33 percent vs. 57 percent for an NTDR &ge; 33 percent 
  • The NTDR was independently predictive for FFBF, in addition to T stage, and initial PSA level, including Gleason score and radiation dose.
  • The NTDR was not a significant predictor of FFBF when examined in the intermediate-risk group, high-risk group, or all risk groups combined.

The authors conclude that proportionally longer treatment duration is an adverse factor in low-risk patients. Treatment breaks resulting in a NTDR of &ge; 33% (e.g., four or more breaks during a 40-fraction treatment, 5 days per week) should be avoided.

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