Main Session
Oct 01
QP 25 - Radiation and Cancer Physics 11: Advances in Dosimetry Optimization and Adaptive Planning

1147 - The Role of Skull Dosimetry in Minimizing Acute Hematologic Toxicities of Brain Metastasis Patients Receiving Radiotherapy and Immunotherapy

10:50am - 10:55am PT
Room 160

Presenter(s)

Jiachun Ma, MD, PhD - Shandong Cancer Hospital and Institute, Shandong First Medical University, Jinan, Shandong

J. Ma1, F. Wang2, J. Yu3, and D. Chen1; 1Department of Radiation Oncology and Shandong Provincial Key Laboratory of Precision Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China, 2Shandong Provincial Key Laboratory of Precision Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China, 3Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China

Purpose/Objective(s): Hematologic toxicities (HTs) are frequently observed in patients undergoing radiotherapy (RT) combined with immunotherapy. Preventing RT-induced HTs is critical, as they often lead to treatment interruption and subsequent lymphopenia, which may diminish the efficacy of immunotherapy. Given the significant role of skull bone marrow in hematopoiesis, this study aimed to investigate the relationship between skull RT dose and HTs in brain metastasis patients receiving concurrent RT and immunotherapy.

Materials/Methods: All radiation doses were standardized as 2-Gy equivalents (EQD2). Skull dosimetric parameters, including the mean dose (DmeanEQD2) and volume receiving 5–40 Gy (V5EQD2?V40EQD2), were analyzed. Logistic regression was used to assess associations between grade =3 HTs (HT3+) and dosimetric/clinical factors. Normal tissue complication probability (NTCP) models were developed via logistic regression to predict HT3+. Receiver operating characteristic (ROC) analysis identified optimal skull dosimetric thresholds. The post-RT absolute lymphocyte count (ALC) and immunotherapy responses were evaluated based on these thresholds.

Results: Among the 127 patients, 21 (16.5%) experienced HT3+. Multivariate analysis revealed significant associations between HT3+ and DmeanEQD2, V5EQD2, and V10EQD2 (as shown in the Table below, all P<0.05). NTCP models indicated a 50% probability of HT3+ at DmeanEQD2=36.7 Gy, V5EQD2=81.6%, and V10EQD2=70.2%. ROC analysis established optimal thresholds for HT3+ at DmeanEQD2=28.2 Gy, V5EQD2=63.7%, and V10EQD2=54.6%. Patients exceeding these thresholds had more than double the risk of HT3+, with significant reductions in post-RT ALC and poorer immunotherapy responses (all P<0.05).

Conclusion: Skull dosimetry is strongly correlated with HT3+ in brain metastasis patients treated with RT and immunotherapy. Implementing skull dose constraints may reduce the incidence of HT3+, preserve lymphocyte counts, and enhance immunotherapy outcomes. However, further prospective studies are needed to validate these findings.

Abstract 1147 - Table 1

Characteristic

 Univariate analysis

Multivariate analysis

OR (95% CI)

 P

OR (95% CI)

 P
BMI

 0.832 (0.708-0.960)

 0.015*

0.779 (0.625-0.970)

 0.032*
DmeanEQD2

 1.050 (1.013-1.088)

 0.010*

1.045 (1.006-1.085)

 0.028*
V5EQD2

 1.030 (1.008-1.049)

 0.010*

1.028 (1.006-1.053)

 0.021*
V10EQD2

 1.025 (1.008-1.042)

 0.006*

1.024 (1.006-1.043)

 0.013*
V20EQD2

 1.013 (0.998-1.028)

 0.130

V30EQD2

 1.063 (0.988-1.149)

 0.138

V40EQD2

 1.010 (0.991-1.032)

 0.455