关键词: 前列腺肿瘤, 锥束计算机体层摄影术, 放射疗法, 放射治疗剂量

Abstract:

Objective To investigate the feasibility and clinical value of establishing individualized target volumes for prostate cancer based on cone beam CT （CBCT） and implementing offline adaptive radiation therapy （ART）. Methods A retrospective collection was performed on the planning CT and CBCT images of 28 patients with localized prostate cancer who received radiotherapy at Ezhou Central Hospital of Hubei Province，between October 2022 and December 2025. An initial radiotherapy plan （Plan_p） was designed based on the planning target volume （PTV_p） delineated on the planning CT images. Based on the daily CBCT images acquired in the 1st and 4th weeks of treatment，the clinical target volume （CTV） was delineated and superimposed to generate the individualized internal target volume，which was then expanded by the corresponding weekly mean setup errors to sequentially generate the ART plan target volumes for the 1st week （PTV_a） and the 4th week （PTV_b）. ART plans Plan_a and Plan_b were subsequently designed based on PTV_a and PTV_b，respectively. All three plans （Plan_p，Plan_a，and Plan_b） were calculated using identical optimization parameters for dose computation. The three groups of radiotherapy plans were compared in terms of target volume，prescribed dose coverage，and dosimetric parameters for both targets and organs at risk （OARs）. Results The target volumes of PTV_p，PTV_a，and PTV_b were （281.6±52.8），（224.6±46.2），and （194.2±58.2） cm³，respectively，with a statistically significant difference （F=4.78，P=0.013）. Pairwise comparisons all showed statistically significant differences （all P<0.05）. The prescribed dose coverage rates for PTV_p，PTV_a，and PTV_b were （97.4±2.1）%，（97.8±2.4）%，and （98.3±2.0）%，respectively，showing no statistically significant difference （F=0.55，P=0.582）. Regarding target dose hotspots，the D_2% values for Plan_p，Plan_a，and Plan_b were （74.1±1.2），（73.9±1.2），and （73.6±1.3） Gy，respectively，with a statistically significant difference （F=3.88，P=0.027），and pairwise comparisons all reached statistical significance （all P<0.05）. No statistically significant differences were observed in D_50%，D_98%，or D_mean across the three plans （all P>0.05）. The homogeneity index values for the three plans were 0.051±0.019，0.046±0.021，and 0.042±0.018，respectively，with a statistically significant difference （F=4.28，P=0.019），and all pairwise comparisons were statistically significant （all P<0.05）. The conformity index （CI） values were 0.847±0.032，0.845±0.037，and 0.864±0.032，respectively，with a statistically significant difference （F=3.58，P=0.035）； pairwise comparisons showed a statistically significant difference only between Plan_a and Plan_b （P<0.05）. In terms of OARs dose，the V₅₀，V₆₀，and V₇₀ of the rectum and bladder all showed statistically significant differences among the three plans （all P<0.05），and all pairwise comparisons were also statistically significant （all P<0.05）. Pelvic bone V₃₀ showed a statistically significant difference （F=3.85，P=0.027），pairwise comparisons showed that both Plan_a and Plan_b differed significantly from Plan_p （both P<0.05）； however，pelvic bone D_mean showed no statistically significant difference （F=2.85，P=0.066）. No statistically significant differences were found in D_mean or V₃₀ for either the left or right femoral heads （all P>0.05）. Conclusions Offline CBCT-based ART for prostate cancer can significantly reduce target volume，decrease hotspots within the target，improve dose homogeneity，and effectively reduce radiation doses to the rectum and bladder，all while maintaining prescribed dose coverage of the target.

Key words: Prostatic neoplasms, Cone-beam computed tomography, Radiotherapy, Radiotherapy dosage