ESTRO 2022

Session Item

Monday

May 09

10:30 - 11:30

Room D4

Pelvic malignancies

Co-Chair: , Belgium;

Chair: Simon KB Spohn, Germany

Session Code: 3200

Session Type: Proffered Papers

Track: Clinical

11:00 - 11:10

Response of local disease at magnetic resonance after salvage radiotherapy for prostate cancer

Marta Bottero, Italy

Presentation Number: OC-0766

Abstract

Abstract Title:

Response of local disease at magnetic resonance after salvage radiotherapy for prostate cancer

Authors:

Marta Bottero¹, Adriana Faiella¹, Diana Giannarelli², Alessia Farneti³, Luca Bertini⁴, Valeria Landoni⁵, Patrizia Vici⁶, Giuseppe Sanguineti³

¹IRCCS, Regina Elena National Cancer Institute, Radiation Oncology, Rome, Italy; ²IRCCS, Regina Elena National Cancer Institute, Biostatistics, Rome, Italy; ³IRCCS Regina Elena National Cancer Institute, Radiation Oncology, Rome, Italy; ⁴IRCCS Regina Elena National Cancer Institute, Radiology, Rome, Italy; ⁵IRCCS Regina Elena National Cancer Institute, Physics, Rome, Italy; ⁶IRCCS Regina Elena National Cancer Institute, Medical Oncology, Rome, Italy

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Purpose or Objective

To assess the pattern of response on dynamic contrast enhancement magnetic resonance imaging (DCE-MRI) of presumed local lesions in the setting of salvage radiotherapy (sRT) after radical prostatectomy (RP).

Material and Methods

The present prospective study (NCT04703543) was conducted at a single Institution between August 2017 and June 2020. Eligibility criteria were: undetectable prostate specific antigen (PSA) after RP; biochemical recurrence (2 consecutive PSA rises to 0.2 ng/ml or greater); a presumed local failure at DCE-MRI (early/fast enhancing discrete lesion on DCE sequences); no distant metastases at choline-PET/CT; no previous history of androgen deprivation therapy and/or RT.

Accrued patients underwent sRT as it follows: 66-69 Gy/30 fractions to the prostatic bed, 73.5 Gy/30 fractions to the local failure at DCE-MRI, 54 Gy/30 fractions to the pelvic nodes (when treated).

All patients were offered DCE-MRI 3 months after sRT, and repeated at 3-month intervals until complete disappearance or a maximum of 4 scans. The endpoint of the study, complete response (CR), was defined as the complete disappearance of the target lesion at DCE-MRI. In case of misses before CR, the observation was considered as a persisting partial response (PR).

Results

62 patients with 72 nodules at DCE-MRI were accrued. All patients underwent the 1^st DCE-MRI at a median of 3.3 months (IQR: 3.1-4.1) after sRT, 33 patients (53.2%) presented a CR, 27 (43,5%) a PR, 2 (3.2%) no response. One patient, implanted with a cardiac device, did not undergo further MRI. Three more patients declined further testing after the 1^st (N=2) or the 2^nd (N=1) re-evaluation due to the COVID-19 pandemic. Twenty-eight patients underwent a 2^nd DCE-MRI after a median of 6.8 months (IQR: 6.5-7.6) from sRT, 20 had a CR, 8 had a PR. After a median time of 10.7 months (IQR: 10.6-12.6), 6 patients were scanned for a 3^nd DCE-MRI: 4 CR, 2 PR. The last patient reported a CR after 16.7 months.

The majority (94.3%, 95%CI: 88.0-100.0%) of lesions had completely disappeared by the 3^rd re-evaluation or a median time of 10.7 months from the end of sRT (Figure).

Independent predictors of CR at 1^st re-evaluation on multivariable analysis were: the volume of the lesion at pre-sRT DCE-MRI (OR 0.076, 95%CI 0.009-0.667; p=0.02), the time of re-evaluation from treatment (OR 3.39, 95%CI 1.156-9.993; p=0.026) and the PSA percent decrease at the 5^th week of sRT (OR 1.02, 95%CI 0.999-1.050; p= 0.058) (Table).

Receiver-operating characteristic curve (ROC) analysis identified the best cut-off on CR for baseline volume at 0.545 cc, AUC 0.683 (95%CI: 0.548-0.818, p=0.014). The probability of a CR for lesions larger than the cut-off identified at ROC analysis was only around 75% at 10.7 months.

Conclusion

The vast majority of local lesions disappears at DCE-MRI after sRT, though larger lesions may require more than 10 months from treatment end.