The first real-world study on the role of carbon ion radiotherapy for oligo-metastatic, persistent, or recurrent (MPR) ovarian/fallopian tube cancer.

Introduction: In the multidisciplinary management of oligometastatic, persistent, or recurrent (MPR) ovarian cancer, radiotherapy (RT) is becoming a more and more worthwhile treatment to potentially improve the chronicity of the disease. Particle beam RT has proved to be effective in several gynecological malignancies, but so far no data are available for ovarian cancer.

Material And Methods: This is a real-world, retrospective, bi-institutional, single-arm study aimed to assess the effectiveness and the safety of carbon ion RT (CIRT) in this setting. The co-first endpoints are 1-year and 2-year actuarial local control (LC) rates and the objective response rate (ORR) defined on a "per lesion" basis. The secondary endpoint was toxicity. Actuarial outcomes were evaluated using the Kaplan-Meier method while potential predictors were explored using the Log-rank test. Bi-variable logistic regression was employed in the analysis of factors predicting the complete response on a per-lesion basis.

Results: 26 patients accounting for a total of 36 lesions underwent CIRT with a total median dose of 52.8 Gy[RBE] (range: 39-64 Gy[RBE]). Five patients received CIRT for re-irradiation. No concomitant systemic therapies were administered during CIRT. Within 12 months after the treatment, 17 lesions (47 %) achieved complete response while 18 (50 %) obtained a partial response with an ORR of 97 %. The achievement of a complete response is related to the dose per fraction (>4.2 Gy[RBE], p = 0.04) and total dose (>52,8 Gy[RBE], p = 0.05). The 1-year LC was 92 % and the 2-year LC was 83 %, according to the achievement of a CR (p = 0.007) and GTV ≤ 14 cm3 (p = 0.024). No grade > 3 toxicities were recorded both in naïve and re-irradiated patients. PARP-i and anti-VEGF seemed not to exacerbate the risk of severe toxicities.

Conclusions: CIRT was effective and safe in MPR ovarian cancers, even in the case of re-irradiation. Largest cohort studies and longer follow-up are needed to confirm these data.