[Benefit of a pretreatment planning library-based adaptive radiotherapy for cervix carcinoma?]

In case of intensity-modulated radiotherapy (IMRT) for locally advanced cervix carcinoma, the objectives were to quantify the difference between the planned and the delivered doses by a standard irradiation, and to estimate the dosimetric benefit of a pretreatment planning library-based adaptive radiotherapy.

Ten patients with locally advanced cervix carcinoma had three planning CTs corresponding to three bladder volumes: empty, intermediate (vi) and full. On each CT, two IMRT plans were generated to deliver 45 Gy to the planning target volume (PTV), with two different margins: clinical target volume (CTV)+10mm and CTV+15 mm. Using bi-weekly CBCTs, three scenarios of treatment have been simulated and compared: standard IMRT (one vi planning) with 10 and 15 mm margins and adaptive radiotherapy with 10mm margin. The cumulated dose in the organs at risk was estimated by elastic registration.

In case of standard IMRT, the cumulated dose was significantly different than the planning dose, with an under-dose of the CTV and the bladder, and an over-dose of the rectum and the peritoneal cavity. For 54% of the fractions, the adaptive radiotherapy planning was not based on vi. Considering the cumulated dose and compared to IMRT with 10-mm margin, adaptive radiotherapy increased the dose to the CTV (1.4 Gy for D98%) and decreased slightly the dose to the rectum and the peritoneal cavity. Compared to a standard IMRT with 15 mm margin, adaptive radiotherapy decreased significantly the dose to the rectum (20% for V40), the bladder (13% for V40) and the peritoneal cavity (2% for V35).

A pretreatment planning library-based adaptive radiotherapy in cervix carcinoma decreases the dose to the organs at risk and increases the dose to the CTV.