Techniques et innovations en radiothérapie pour le traitement conservateur des cancers infiltrants localisés de vessie

Assessment of Intrafraction Motion of the Urinary Bladder Using Magnetic Resonance Imaging (cineMRI)

AIM

To assess the intrafraction motion of the urinary bladder and delineate the appropriate margin size for radiotherapy planning, for both the full and empty bladder.

MATERIALS AND METHODS

This was a single-site, single-arm study of 20 patients planned to undergo radical cystectomy for histologically confirmed muscle-invasive bladder cancer. Patients underwent magnetic resonance imaging (cineMRI) of the entire pelvis using a 3-Tesla system, prior to cystectomy. Patients first underwent a cineMRI with a full bladder, then voided and underwent a second MRI with an empty bladder. All MRI sequences were acquired over 18 min. We assessed the differences in bladder filling and subsequent bladder wall displacement, between the empty and full bladder, during a time period consistent with radiotherapy treatment delivery.

RESULTS

Twenty patients underwent cineMRI of the entire pelvis. The maximum mean directional displacements of the bladder walls over the 18 min duration of the scan for the empty bladders were 9.8 mm superiorly, 1.1 mm inferiorly, 2.39 mm anteriorly, 3.73 mm posteriorly, 2.74 mm to the left and 2.48 mm to the right. The maximal mean displacements for the full bladders were 9.2 mm superiorly, 1.1 mm inferiorly, 2.28 mm anteriorly, 1.08 mm posteriorly, 1.85 mm to the left and 1.73 mm to the right. Statistically significant differences were seen in the posterior, left and right displacements but were quantitatively small.

CONCLUSIONS

Intrafractional motion secondary to bladder filling showed minimal variation between the full and empty bladder. Similar clinical target volume to planning target volume margins can be applied for the delivery of radiotherapy for a full and empty bladder.

Innovative image-guided CyberKnife stereotactic radiotherapy for bladder cancer

CyberKnife stereotactic body radiation therapy is used to treat extracranial tumour sites that move with respiration. It has also been employed for the successful treatment of prostate cancer, using the image-tracking CyberKnife system to compensate for intrafraction movements resulting from peristaltic motion and bladder filling. Large sporadic motions can be compensated for using an online target motion monitoring and cybernetic correction strategy. Radio-opaque gold markers can be implanted in the bladder during transurethral resection and used for online image-tracking during radiation to compensate for bladder filling and target movements. Transurethral bladder resection followed by chemoradiation and a stereotactic CyberKnife radiotherapy boost seems a promising approach for the treatment of invasive bladder cancer in heavily pre-treated patients or patients eligible for preservation strategies. In this case study of a patient with a previously irradiated pelvis, CyberKnife radiotherapy was feasible and well tolerated, with disease control and non-altered functional results two years after treatment completion. CyberKnife irradiation may also be considered for the conservative treatment of locally advanced T2-T4a N(0) M(0) bladder cancer with incomplete or uncertain transurethral resection.

[Perioperative strategies in patients with muscle invasive bladder cancer]

Radical cystectomy with bilateral pelvic lymph node dissection is the standard of care for patients with muscle-invasive bladder cancer, with 5-year survival rates not exceeding 60%. Consequently a multidisciplinary approach including perioperative chemotherapy and/or radiation therapy is required to improve these results. Data from clinical trials and meta-analyses with neoadjuvant chemotherapy have shown a significant benefit in overall survival, with a 5% absolute benefit at five years, provided cisplatin-based combination chemotherapy is used. Reported trials do not support the routine use of adjuvant chemotherapy. The current role of radiation therapy is limited to highly selected cases with a combination of external radiotherapy, partial cystectomy and interstitial brachytherapy.