3194 - Long-Term Outcomes of Image-Guided Proton Therapy with Gold Fiducial Marker for Localized Prostate Cancer

H. Iwata¹, Y. Hattori¹, K. Nakajima¹, K. Nomura¹, Y. Tsuzuki¹, S. Sudo Sr¹, K. Hayashi², T. Toshito³, M. Oguri⁴, S. Hashimoto⁵, Y. Umemoto⁶, A. Hiwatashi⁴, and H. Ogino¹; ¹Department of Radiation Oncology, Nagoya Proton Therapy Center, Nagoya City University West Medical Center, Nagoya, Japan, ²Department of Proton Therapy Technology, Nagoya Proton Therapy Center, Nagoya City University West Medical Center, Nagoya, Japan, ³Department of Proton Therapy Physics, Nagoya Proton Therapy Center, Nagoya City University West Medical Center, Nagoya, Japan, ⁴Department of Radiology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan, ⁵Department of Radiation Oncology, Aichi Cancer Center Hospital, Nagoya, Japan, ⁶Department of Nephro-Urology, Nagoya City University West Medical Center, Nagoya, Japan

Purpose/Objective(s): Proton therapy (PT) remains much controversy about its routine use in localized prostate cancer treatment. Particularly, comprehensive data on the efficacy and safety of gold fiducial marker matching in PT is less abundant compared to bone matching. We have previously reported on acute toxicity and quality of life changes of image-guided PT (IGPT) for localized prostate cancer. The aim of this study was to evaluate long-term efficacy and safety of IGPT for localized prostate cancer. Materials/

Methods: We sequentially started prospective studies for normofractionated PT (NFPT: 74-78 GyRBE/37-39 Fr) in February 2013, and moderately hypofractionated PT (MHPT: 60-63 GyRBE/20-21 Fr) in October 2014. After the start of MHPT, patients could choose either NFPT or MHPT. Main eligibility criteria included: (1) histologically confirmed primary prostate cancer; (2) T1-T3bN0M0 staged by UICC; (3) age = 20 years; (4) no serious underlying disease or other cancers, and (5) written informed consent. Patients with castration-resistant prostate cancer or enrolled in other clinical trials were excluded from the analysis. The NCCN classification was used. The biochemical relapse free survival (bRFS) was based on the Phoenix definition (nadir + 2.0 ng/mL). The rates of bRFS, overall survival (OS) and incidence of late gastrointestinal (GI) and genitourinary (GU) toxicities were estimated using the Kaplan-Meier methods. Toxicities were evaluated with the CTCAE version 5.0. The dose constraints were partially changed in August 2014, and hydrogel spacer was introduced in May 2018. In principle, low-risk patients received no androgen-deprivation therapy (ADT), intermediate-risk patients received 6-month neoadjuvant ADT, and high- or very-high-risk patients received two-year neoadjuvant and adjuvant ADT. Patients registered until March 2021, before the transition to the new fractionation protocol, were analyzed.
Results: The total number of prostate cancer patients who received PT at our institution until March 2021 was 1,643. A total of 327 patients treated using NFPT and 1243 patients treated using MHPT were analyzed (Total 1570). The number of patients in the low-risk, intermediate-risk, and high- or very-high-risk groups were 228, 715, and 627, respectively. The median follow-up period of surviving patients was 68.0 months (range: 20-130). The 5-year rates of bRFS and OS in the low-risk, intermediate-risk, and high- or very-high-risk patients were 95.7%, 96.5%, 91.8% for bRFS, and 97.1%, 97.5%, 97.7% for OS, respectively. Of the 76 patients who died, 71 of them were due to other disease. Biochemical relapse was observed in 62 patients, 31 of whom showed clinical relapse. Local recurrence was noted in 4 patients. The incidence of grade 2 and 3 late GI and GU toxicities were 4.4%, 0.8% and 2.9%, 0.1%, retrospectively.
Conclusion: IGPT with gold fiducial marker for localized prostate cancer is favorable and well tolerated. Further hypofractionated IGPT with hydrogel spacer is expected.