3286 - Is Early GU Radiation Toxicity in Prostate Cancer Patients Bladder-Related?

12:45pm - 02:00pm PT

Hall F

Screen: 18

POSTER

Presenter(s)

Wojciech Majewski, MD, PhD - Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice, Slaskie

W. Majewski¹, G. Matuszny², M. Gajek², P. Grzadziel³, and A. Napieralska²; ¹Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice, Slaskie, Poland, ²Radiotherapy Department, Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice, Poland, ³Department of Radiotherapy and Brachytherapy Planning, Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice, Poland

Purpose/Objective(s):

Radiation GU toxicity in prostate cancer patients is presumed to be associated with dose delivered to the bladder. However, it is also hypothesized that urethral reaction to radiation may be responsible for early urinary symptoms. To check that hypothesis we have undertaken the study on association of various bladder-related dosimetric parameters of radiotherapy with early GU toxicity.

Materials/Methods: We assumed that radiation effects and dose-volume relationships should be clearly notable in patients with predominantly large prostates. Therefore the study included patients treated with hypofractionated radiotherapy (HFRT) which is proposed in our center in case of contraindications to stereotactic radiotherapy (SBRT), mainly due to prostate volume reasons. The group of all consecutive patients treated with image-guided HFRT between 2022-2023 was analyzed. The CTV encompassed prostate gland and proximal 1 cm of seminal vesicles. A relation between CTV, PTV, bladder volume (BV), bladder dose-distribution parameters (V27-V68, D2, Dmax) and early GU radiation toxicity was evaluated. Early GU toxicity was evaluated with RTOG scale; the maximum toxicity score during RT and up to 3-months post-HFRT was reported. RTOG scale was modified by dividing Grade 2 toxicity into two distinct subgroups: G2a- indicating intermediate symptoms with sporadic/intermittent use of medications and G2b – indicating more enhanced symptoms requiring persistent, often combined medications for symptom control. That G2b grade was considered as more clinically relevant. A logistic regression was used to estimate the influence of selected parameters on the incidence of =G2b GU early toxicity and linear regression with Pearsons R coefficient for correlation between CTV, PTV and dose-distribution parameters.

Results:

During the study period there were 68 patients treated with HFRT (70 Gy in 28 fx). A median CTV was 85 cc (IQR 64-102) and median PTV was 176 cc (IQR 154-211). There was a statistically significant, correlation between CTV and all bladder dose-volume parameters (R=0.26 to 0.49) except for BV and Dmax. Slightly more pronounced relations were observed for PTV (R=0.33 to 0.52), also with exception of BV and Dmax. The incidence of early =G2 GU and =G2b toxicity was 46% and 21%, respectively. The positive association between CTV and =G2b GU toxicity was of borderline significance (p=0.054), which became significant for PTV (p=0.018). There was no significant relationship between any of bladder dose-distribution parameters and early =G2b GU toxicity.

Conclusion:

The lack of relationship between any bladder dose-volume parameters and early GU toxicity, but explicit association with CTV and PTV indirectly suggest that early GU toxicity is not bladder-related, but may originate in the urethral reaction to radiation. Therefore, dose constraints for bladder during prostate radiotherapy seem to be of limited reliability.