ESTRO 2024 - Abstract Book

S1543

Clinical - Lower GI

ESTRO 2024

From September 2009 to March 2023, 152 patients (pts) were treated. Toxicity. Seventeen pts (11%) experienced G3 gastrointestinal toxicity: diarrhoea 10 (6.5%), proctitis 6 (4%), rectal bleeding 1 (0.5%), nausea/vomiting 1(0.5%). Five pts had G3 skin toxicity (3%), 1 pt (0.5%) genitourinary toxicity. Two thirds of pts experienced toxicity before the adaptive phase and the third cycle of oxaliplatin, when prescribed. Feasibility. One hundred fourty-nine pts completed RT with full Radiotherapy dose. Three cycles of Oxaliplatin were prescribed in 90 pts (59%), < 2 cycles in 62 pts (41%). Eighty-five percent of pts received > 80% of capecitabine dose. Efficacy. All 152 pts underwent surgery, 5 pts (3%) abdominal-perineal resection, 147 (97%) pts conservative resection. Overall, 39 pts (26%) achieved pathological complete response, 26 pts (17%) TGR 1-5%, 22 pts (14%) TRG 6-10%. Considering pts who received 3 cycles of oxaliplatin, 26 out of 90 (29%) achieved pCR against 13/62 (21%) pts who received 1-2 cycles (not statistically significant). Ninety pts (60%) received adjuvant chemotherapy. Outcome. With a median FU of 50,3 months (5,9-149), relapse occurred in 45 pts (30%), locoregional in 5 pts (3%), distant in 43 pts (28%). Thirty two pts (21%) died. Median DFS and OS were 105 and 133 months, respectively.

Conclusion:

Adaptive RT is feasible and can be administered with an acceptable toxicity rate: outcome data are consistent with literature data. Our approach achieves a promising pCR rate and locoregional control providing a good base for further improvement probably obtainable with more chemotherapy (total neoadjuvant therapy) and/or increasing RT dose on residual tumor, likely modulating the intensity of the boosting according to their response as measured by early regression, as previously shown [2]. This could be important in considering tailored wait and see strategies. The previously reported impact of skipping the last oxaliplatin cycle [3] was only in part confirmed, as the found difference of pCR between the two groups (2 vs 3 oxaliplatin cycles) was not found to be significant.

Keywords: Adaptive radiotherapy, Preoperative, rectal cancer

References:

[1] Passoni et al. Int J Radiat Oncol Biol Phys 87:67-72, 2013

[2] Fiorino et al Radiother Oncol 128:564-568, 2018

[3] Broggi et al Radiother Oncol 149: 174-180, 2020