3374 - Preliminary Results of a Prospective Cohort Study on the Protective Effect of Bone Marrow Protection Against Lymphocytopenia during Radiotherapy in Prostate Cancer

Purpose/Objective(s):

Pelvic radiation therapy for prostate cancer damages the hematopoietic active bone marrow, resulting in a significant reduction of lymphocytes during radiotherapy. Only retrospective studies have shown that optimizing cerebrospinal dose (such as limiting the volume of lumbosacral vertebra receiving 24 Gy (V24) to =307 cc) can alleviate myelotoxicity, but there is a lack of prospective research data. The objective of this study was to explore whether bone marrow protective radiotherapy can reduce the incidence of lymphocytopenia in prostate cancer patients undergoing pelvic radiotherapy.

Materials/Methods:

This is a prospective, two-cohort study of prostate cancer patients scheduled for prostate and pelvic radiation therapy. The intervention was bone marrow protection, and the standard was lumbosacral vertebra V24=307 cc. Radiation regimens: Definitive RT: Prostate/seminal vesicles 70 Gy/25 fx, pelvic lymphatic drainage (PLD: aortic bifurcation to obturator nodes) 47.5 Gy/25 fx. Postoperative RT: Prostatic bed 62.75 Gy/25 fx, PLD 47.5 Gy/25 fx. The primary outcome was the incidence of G2+ lymphocytopenia during radiotherapy. The secondary endpoint was the incidence of G2+ diarrhea. Fisher's accurate test and continuity test were used for statistical analysis.

Results:

From January 2024 to September 2024, a total of 40 patients were enrolled, including 17 patients in the bone marrow protected group and 23 patients in the bone marrow unprotected group. Baseline characteristics, including median age, distribution of definitive versus postoperative radiotherapy, and proportion of patients receiving androgen deprivation therapy (ADT), were well-balanced between the two groups, with no statistically significant differences observed (all p>0.05). There was no significant difference in the incidence of G2+ or G3+ lymphocytopenia between bone marrow protected and unprotected groups (94% vs 100%, p=0.425),(65% vs. 43%, p=0.313). Similarly, there was no significant difference in G2+ diarrhea rate between the two groups (23.5% vs. 34.7%,p=0.675). However, it is worth noting that V24 values in the lumbosacral vertebrae were significantly lower in the bone marrow protected group (median 265.39 cc vs. 361.98 cc, p<0.001), while target coverage was not affected in all cases in the PTV group.

Conclusion:

Although participants in the bone marrow protection group achieved their predetermined dose limitation target (V24 =307 cc), this did not lead to a statistically significant reduction in G2+ lymphopenia incidence compared to those without such limitations. These findings suggest that limiting radiation exposure to the lumbosacral vertebrae alone may not be sufficient to effectively prevent lymphocytopenia in patients receiving standard pelvic irradiation. Reducing the pelvic irradiated field may be a more viable way to protect lymphocytes, but the risk of lymph node metastasis must be weighed.