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Abstract
BACKGROUND:
We performed a prospective phase II study to compare acute toxicity among five different hypofractionated schedules using proton therapy. This study was an exploratory analysis to investigate the secondary end-point of biochemical failure-free survival (BCFFS) of patients with long-term follow-up.

METHODS:
Eighty-two patients with T1-3bN0M0 prostate cancer who had not received androgen-deprivation therapy were randomized to one of five arms: Arm 1, 60 cobalt gray equivalent (CGE)/20 fractions/5 weeks; Arm 2, 54 CGE/15 fractions/5 weeks; Arm 3, 47 CGE/10 fractions/5 weeks; Arm 4, 35 CGE/5 fractions/2.5 weeks; and Arm 5, 35 CGE/5 fractions/4 weeks. In the current exploratory analysis, these ardms were categorized into the moderate hypofractionated (MHF) group (52 patients in Arms 1-3) and the extreme hypofractionated (EHF) group (30 patients in Arms 4-5).

RESULTS:
At a median follow-up of 7.5 years (range, 1.3-9.6 years), 7-year BCFFS was 76.2% for the MHF group and 46.2% for the EHF group (p = 0.005). The 7-year BCFFS of the MHF and EHF groups were 90.5 and 57.1% in the low-risk group (p = 0.154); 83.5 and 42.9% in the intermediate risk group (p = 0.018); and 41.7 and 40.0% in the high risk group (p = 0.786), respectively. Biochemical failure tended to be a late event with a median time to occurrence of 5 years. Acute GU toxicities were more common in the MHF than the EHF group (85 vs. 57%, p = 0.009), but late GI and GU toxicities did not differ between groups.

CONCLUSIONS:
Our results suggest that the efficacy of EHF is potentially inferior to that of MHF and that further studies are warranted, therefore, to confirm these findings.

TRIAL REGISTRATION:
This study is registered at ClinicalTrials.gov, no. NCT01709253 ; registered October 18, 2012; retrospectively registered).

Author information

Ha B1,2, Cho KH3, Lee KH4, Joung JY4, Kim YJ1, Lee SU1, Kim H1, Suh YG1, Moon SH1, Lim YK1, Jeong JH1, Kim H1, Park WS4, Kim SH4.
1
Proton Therapy Center, National Cancer Center, 323 Ilsan-ro, Ilsandong-gu, Goyang-si, Gyeonggi-do, 10408, Republic of Korea.
2
Department of Radiation Oncology, Hallym University Dongtan Sacred Heart Hospital, Seoku-dong, Hwaseong-si, Gyeonggi-do, 18450, Republic of Korea.
3
Proton Therapy Center, National Cancer Center, 323 Ilsan-ro, Ilsandong-gu, Goyang-si, Gyeonggi-do, 10408, Republic of Korea. kwancho@ncc.re.kr.
4
Center for Prostate Cancer, National Cancer Center, 323 Ilsan-ro, Ilsandong-gu, Goyang-si, Gyeonggi-do, 10408, Republic of Korea.