Protons are widely recognized to possess physical and biological properties superior to photons for conventional use [1, 3]. Protons are large, positively charged particles that penetrate tissues at different depths and deposit most of their energy in targeted tissues, known as the Bragg peak. . The physical properties of protons can maximize radiation focused on the tumor and minimize the effects on surrounding tissues. Moreover, the relative biological efficiency of protons reaches 1.1 or potentially more in the distal part of the spread Bragg peak . Despite theoretical concerns about damage to adjacent normal tissues associated with its greater biological effect, a large retrospective study rejected the higher risk of secondary malignancies in patients who underwent PBT than in those who underwent phototherapy. . Although its use in clinical applications remains challenging due to the equipment required and associated costs, PBT provides an ideal radiation regimen based on its physical and biological characteristics.
Since 1954, when the medical use of protons was first reported, PBT has been applied to various parts of the body, including the uvea, the base of the skull, and the spine. [1, 9, 10]. In the gynecological field, the clinical use and efficacy of PBT have been reported primarily for cervical cancer. [3,4,5]low-grade endometrial stromal sarcoma and solitary recurrent epithelial ovarian cancer . Only one case report of vaginal recurrence of endometrial carcinoma treated with PBT is available in the literature, which describes complete tumor regression; however, there was one complication of grade 1 cystitis. This case report indicated the potential efficacy of PBT for recurrent endometrial cancer . Unlike vaginal recurrence, curative radiation therapy is not widely recommended for endometrial cancer recurrence in the para-aortic lymph nodes. The number of patients with endometrial cancer has recently increased worldwide . Recurrence has been detected in about 20% of patients with endometrial cancer . Consequently, the number of patients with recurrent endometrial cancer also increased . Recurrent endometrial cancer often arises in the lymph nodes [14, 15]. Therefore, careful consideration of treatment strategies for recurrent endometrial cancer in para-aortic lymph nodes is essential to improve prognosis and quality of life for patients during treatment. In the present case, PBT effectively eradicated the isolated recurrence of endometrial cancer in the para-aortic lymph nodes adjacent to the left renal vein, the location of which precluded surgical interventions. Due to the limitations associated with conventional phototherapy, PBT was considered our patient’s preferred choice at the time.
No case report of gynecological cancer reported serious complications related to PBT. Previous studies reported only transient low-grade cystitis or fever as complications [6, 12]. A phase IIB randomized trial in esophageal cancer found that PBT was associated with fewer complications than intensity-modulated radiation therapy using conventional photons . A systematic review of esophageal cancer showed that PBT has the potential to not only improve patient outcomes, but also reduce complications . Because PBT maximizes targeted radiation to the tumor and minimizes effects on surrounding tissues, there are very few case reports of complications related to bone marrow suppression. . In the present case, there was no evidence of bone marrow suppression during or after PBT. Therefore, PBT is associated with fewer complications than conventional photon treatments, which is beneficial.
To our knowledge, this is the first case report describing the successful treatment of remote isolated recurrence of endometrial cancer by PBT, which can be considered as a potentially effective treatment modality for endometrial cancer. recurrent where the location of the tumor limits the application of surgery or conventional photon beam therapy. PBT is associated with fewer complications than conventional radiotherapy. Further accumulation of cases and further trials are needed to establish the effectiveness of PBT for recurrent endometrial cancer as well as cervical cancer.