OC-88 FIRST CLINICAL RESULTS OF THE GEC-ESTRO BREAST WG PHASE III MULTICENTRIC APBI TRIAL.

Abstract

were transformed to match the day 1 anatomy using MORPHEUS, a specialized soft tissue deformation algorithm. Finally, the accumulated HR-CTV D90, rectal wall D2cm 3 (RW) and bladder wall D2cm 3 (BW) were estimated (in equivalent 2 Gy fractions) assuming stable anatomy and dosimetry between scans. These were compared to the planned values. Median follow-up was 2.1 years. Rectal and bladder toxicity were recorded using CTAC 4.0. Results: There were no significant differences between the mean accumulated doses (AD) and mean planned doses (PD) for HR-CTV, RW or BW. However, there were large potentially significant differences in individual patients, particularly for BW and RW. For BW, the AD was greater than the PD in 30% of patients with the largest increase being 11.5 Gy. There was only 1 patient with late radiation cystitis (PD 86 Gy, AD 90 Gy). For RW, the AD was greater than PD in 52% of patients, with absolute differences ranging from -7.4 Gy to 9.3 Gy. Rectal bleeding occurred in 4 patients and 1 other developed a fistula. The RW PD was >75 Gy in only 1 of these patients (79 Gy) but the AD was >75 Gy in 4 of 5 patients (76 88 Gy). Among all patients with RW AD dose >75 Gy, 50% developed late rectal toxicity compared to only 5% with a lower RW AD. Conclusions: Accumulated deformation dose compared to planned dose can vary greatly from patient to patient. Accumulated deformation dose for RW D2cm 3 appeared to be of greatest consequence, with rectal toxicity occurring more frequently in patients with D2cm 3 greater than 75 Gy, which may not have been predicted from planned day 1 dosimetry. Further follow-up is required for outcomes in bladder toxicity and local tumor control.