Genitourinary Cancer

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SU_22_2223 - Partial Stereotactic Ablative Boost Radiation Therapy In Bulky Bladder/Urothelial Cancer

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Partial Stereotactic Ablative Boost Radiation Therapy In Bulky Bladder/Urothelial Cancer
Y. Bai, X. GAO, S. Qin, J. Chen, and M. Su; Department of Radiation Oncology, Peking University First Hospital, Beijing, China

Purpose/Objective(s): The present work aims to evaluate the safety and efficacy of partial stereotactic ablative boost radiotherapy (P-SABR) in bulky bladder and urothelial cancer and prove that P-SABR could optimize BED with equivalent toxicity.

Materials/Methods: From Jan 2013 through Aug 2017, 17 patients with bulky bladder and urothelial cancer treated with P-SABR technique were analyzed. The P-SABR plan consisted of one partial SABR plan (5-8 Gy/f, 3-5 fractions) to gross tumor boost (GTVb) followed by one conventional plan to the planning target volume (PTV). GTVb was the max volume receiving SABR to guarantee the PTV margin dose falloff to about 3 Gy/f. And the total dose of PTV margin was planned to about 55Gy. The simply CRT plans were created using the same planning parameters as the original plan, with the goal to achieve comparable organs-at-risks (OARs) doses and PTV margin dose to P-SABR plan. Dosimetric variables were acquired in both P-SABR and compared CRT plans. Toxicity, local control and survival were also evaluated.

Results: 9 patients (52.9%) were male, 8 patients (47.1%) was female. Median age at treatment was 66 years (46 to 84 years). 14( 82.3%) patients were pathologically diagnosed as urothelial cancer,1(5.9%) was SCC,and 2(11.8%) were other types. 2 patients (11.8%) had stage IV, 13 patients (76.5%)were recurrent after surgery and 2(11.8%) were metastases after surgery. Median volume of the tumor treated by P-SABR was 164.69cm3(54.776 to 409.608 cm3) with a median maximal diameter of 8.59cm (4.04 to 19.54 cm). Median follow up-was 11.9 months (range 2.7-39.8 months). No severe acute side effects >CTCAE Grade III were observed. 1-year overall survival was 84.4%. 2-year overall survival was 47.5%. 2 patients (11.8%) had CR, 5 patients (29.4%) had PR, 4 patients (23.5%) had SD and 6 patients (35.3%) had PD( All achieved local response but systemic progression). 2-year local control rate was 100%. P-SABR had significantly higher HI index (p<0.05), while the similar CI index (p>0.1). No differences were found in Dmin and D98 of PTV between P-SABR and the simply CRT plans (p>0.1). Compared to the conventional plan, P-SABR plans increased dose at the isocenter, BED at the isocenter, Dmean and Dmax by 18.9%, 27.1%, 11.9% and 18.1%, respectively(p<0.001). We define B80 as the ration of volume of BED>80Gy to the in-field tumor. B80, B90, B100, B110, V65, V70 and V75 were improved by 57.0%, 100%, 100%, 100%, 73.4%, 99.6% and 100% in P-SABR plan(p<0.05).

Conclusion: P-SABR is feasible and well tolerated in bulky bladder and urothelial cancer. Local control rate is encouraging, which may due to the ability of P-SABR to optimize BED with equivalent toxicity.

Author Disclosure: Y. Bai: None. J. Chen: None. M. Su: None.

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