Main Session
Sep 29
PQA 06 - Genitourinary Cancer, Gynecological Cancer, and Health Care Access and Engagement

3313 - Impact of Posterior PTV Margin on the Treatment Efficiency and Adverse Effects of Radical Radiotherapy for Prostate Cancer Patients

02:15pm - 03:30pm ET
Poster Hall - Exhibit Hall A
Screen: 13
POSTER

Presenter(s)

Lin Ma, MD - Peking University First Hospital, Beijing, Beijing

L. Ma1, J. Chen2, M. Ma2, and X. Gao2; 1Peking University First Hospital, Beijing, Beijing, China, 2Department of Radiation Oncology, Peking University First Hospital, Beijing, China

Purpose/Objective(s): Due to differences in radiotherapy technology and quality control levels, the margin of prerectal PTV is not consistent among centers. Based on a strict quality control plan, our center’s PTV margin on posterior prostate is 0mm. This study conducted a retrospective analysis on whether this precise and individualized prerectal PTV range can reduce rectal side effects without affecting the efficacy.

Materials/Methods: A total of 382 patients with localized prostate cancer who underwent radical radiotherapy between 2016 and 2020 were retrospectively included. An individualized PTV design was applied (5 mm margin expansion in other directions, 3 mm margin expansion on the rectal side with rectal exclusion). The median dose was 70 Gy/25 fractions. Daily Image-Guided Radiation Therapy (IGRT) was performed with registration focused on the anterior rectal wall. Acute (=3 months) and late (>3 months) genitourinary (GU) and gastrointestinal (GI) toxicities were evaluated using modified Radiation Therapy Oncology Group (RTOG) toxicity criteria. The 5-year overall survival (OS), biochemical progression-free survival (bPFS), imaging progression-free survival (PFS), event-free survival, and local recurrence rate were calculated. Baseline characteristics [age, Gleason score, PSA, T/N stage, pelvic irradiation status] and dosimetric parameters (PTV D95%, CTV V65, rectal/bladder Dmean, D0.03cc, etc.) were included in univariate and multivariate analyses for associations with toxicity incidence and efficacy endpoints. Actual cumulative dose verification was performed in 5 randomly selected patients using MIM software.

Results: The incidences of acute genitourinary (GU) and gastrointestinal (GI) toxicities were 53.7% and 52.8%, respectively, with = grade 2 toxicities at 7.6% and 7.2%. For late-phase toxicities, = grade 2 GU and GI toxicities were 19.9% and 11.1%, respectively, with rare = grade 3 severe toxicities (GI: 2.2%, GU: 0%). The 5-year OS, bPFS, and imaging PFS were 91.4%, 86.8%, and 92.3%, respectively, with a local recurrence rate of 0.52%. Dosimetric parameter analysis showed that rectal D0.03cc (P=0.022) and V65 (P=0.041) were key predictors of = grade 2 late GI toxicity. Univariate analysis identified PTV V65 as a protective factor for OS (HR=0.250, P=0.032). Actual cumulative dose verification in 5 randomly selected patients revealed a significant difference only in CTV D98%[69.30(68.17,70.18) vs. 71.00(69.51,72.06), P=0.043], with no significant differences observed between planned dosimetric parameters and actual doses for other target volumes, rectum, or bladder.

Conclusion: The PTV design with complete rectal exclusion combined with daily IGRT demonstrated low acute and chronic toxicities, reliable dose delivery, and favorable tumor control outcomes in radical radiation therapy for localized prostate cancer, providing a safe and effective clinical protocol for precision target volume optimization.