High-dose 3DCRT well tolerated by prostate cancer patients
MedWire News: A long-term follow-up study of prostate cancer patients in the Radiation Therapy Oncology Group (RTOG) 9406 study found that tolerance to high-dose 3DCRT remained excellent for up to 12 years.
Patients treated with three-dimensional conformal radiation therapy (3DCRT) at up to 79.2 Gy at 1.8 Gy/fraction and up to 74 Gy at 2 Gy/fraction suffered significantly less grade 2 or greater toxicity than patients treated with a dose of 78 Gy at 2 Gy/fraction.
A team led by Jeff Michalski, from the Washington University Medical School in St Louis, Missouri, USA, reported rates of long-term toxicity in 1055 patients with early-stage prostate cancer who were treated with five dose levels of 3DCRT of up to 78 Gy.
The patients were divided into three groups: Group 1 patients had clinical Stage T1 disease with minimal risk of seminal vesicle invasion, while Group 2 patients had a risk of seminal vesicle invasion exceeding 15. 3DCRT was delivered to the prostate only in men in Group 1 and to the prostate and seminal vesicles with a prostate boost in men in Group 2.
The dose of 3DCRT delivered was 68.4 Gy for level I; 73.8 Gy for level II; 79.2 Gy for level III; 74 Gy for level IV; and 78 Gy for level V. Levels I to III were given at 1.8 Gy/fraction, and levels IV to V at 2.0 Gy/fraction.
The median follow-up period for surviving patients was 6.1 years (level V) to 12.1 years (level I).
Overall, the incidence of Radiation Therapy Oncology Group (RTOG) Grade 3 or less gastrointestinal (GI) or genitourinary (GU) toxicity in patients in group 1 was 3%, 4%, 6%, 7%, and 9% at dose levels of I, II, III, IV, and V, respectively. The corresponding incidence for patients in group 2 was 6%, 2%, 6%, 9%, and 12%.
“Because of the low rates of grade 3 toxicity, we also examined rates of grade 2 or greater toxicity,” the researchers note in the International Journal of Radiation Oncology Biology Physics. “While these toxicity rates are not considered serious, they are of sufficient severity that they may have an impact on a patient’s quality of life.”
The researchers found that, in group 1, level V patients had a higher probability of experiencing grade 2 or greater late GI or GU toxicity than those in levels I, II, and III, at hazard ratios (HRs) of 1.93, 2.29, and 2.52, respectively. In group 2, dose level V patients also had a higher probability of grade 2 or greater late GI or GU toxicity than those in dose levels II, III, and IV, at HRs of 2.61, 2.22, and 1.60, respectively.
Writing in the, the researchers conclude: “Dose escalation to 79.2 Gy in 44 fractions of 1.8 Gy/day is well tolerated by men with early-stage prostate cancer and can be delivered safely in the context of a multi-institutional clinical trial.”
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By Joel Levy