Computed Tomography Scan Planning in Radiation Oncology: Prospective Evaluation of the "Mini-CT Scan" Procedure Prior to a Routine Immediate Planning Computed Tomography Scan Practice. Results of the OPTIMAL Study.

PURPOSE

To determine the benefit/risk in terms of radioprotection of performing a mini-computed tomography (CT) scan prior to the planning CT scan in patients requiring pelvic irradiation. The study population included patients who received curative intent external beam radiation therapy for pelvic malignancies. The results are applicable to all supine pelvic external beam radiation therapy patients.

METHODS AND MATERIALS

Between April 9, 2021, and October 5, 2021, 53 patients were included in the study. A mini-CT scan was performed for each patient to determine whether they were properly prepared with a full bladder and empty rectum for the planning CT scan. Depending on the result, it was decided to either perform the planning CT scan or repeat a mini scan after rectal enema and drinking to better empty the rectum and fill the bladder. Up to 3 mini scans could be performed, after which a new CT appointment was scheduled if the patient was considered not sufficiently prepared.

RESULTS

Among the 53 patients included in the study, 64 wide CT scans were performed (average, 1.2 scans per patient). A total of 47, 3, 2, and 1 patients were treated for prostate, rectal, bladder, and anal canal cancers, respectively. The median age was 75 years (range, 57-94), with 51 men and 2 women. For 29 patients, a single mini-CT scan was performed prior to the wide CT scan, corresponding to an additional mean effective dose of 2.3 mSv to the mini-CT scan. For 25 patients, multiple wide CT scans and mini-CT scans were performed. For these patients, the mini-CT scan allowed us to decrease patient exposure by reducing the average effective dose by 22.1 mSv per patient. The systematic use of a mini-CT scan in the whole cohort allowed reducing the mean effective dose by 9.44 mSv based on a paired test ( < .0001).

CONCLUSIONS

We demonstrated that the effective dose delivered to the patient was significantly lower if we carried out 1 or more mini-CT scans to avoid doing iterative planning CT scans that deliver a higher dose to the patient.