, vol. 87, issue 2, pp. 746, 2013.
Purpose/Objective(s)
IMRT play an important role in the management of many pelvic tumors, and proved to have less toxicity on the intestine, bladder and rectum. Target volume delineation and optimization still can be done differently depending on the physician and the physicists. The aim of this method is a trial to facilitate and minimize variability in target volume delineation and optimization between the users.
Materials/Methods
Fifteen successive patients diagnosed with pelvic tumors (10 prostate cancer and 3 endometrial and one cervical cancer patients). All patients needed whole pelvis irradiation as part of their treatment. All patients were contoured by only one radiation oncologist using the RTOG target volume (TV) delineation guidelines. Step I: A 3-D plan is created using four-field box technique. The resulted isodose line of 95% (chosen to be the reference isodose line) was converted into a structure, which we called the 95% isodose structure. Step II: Using the planning system Boolean statistics option the delineated risk structures (rectum, bladder, bone marrow, intestine, femuri), were extracted from the Isodose line 95% to end up with a new target we called it “Boolean created structure,“ which includes all spaces in the pelvis, in certain areas included parts from risk structures as any PTV to allow for set-up errors, together with the target volume considered by the physician as a high risk region needs treatment. This “Boolean created Target structure” (BCTS) is similar to region treated with four field box technique (whole pelvis) but excluding risk structures. Optimization was done using seven-field plans, the target used for optimization was the BCTS. Optimization and plans results were compared to ordinary IMRT plans with the target volume used for optimization is the ordinary delineated PTV.
Results
Number of segments for both Boolean and IMRT methods was almost the same with a mean of 100 (range, 85-120) vs 110 (range, 90- 130) for Boolean and conventional IMRT respectively. Time for contouring and optimization for the Boolean method was much lower with a mean of 15 min (range, 12-20 min) vs 30 min (30-45 min) for the conventional method. Conformity index (RTOG definition) for the Boolean method was much better with a median of 1.2 (range, 0.8-1.5) vs a median of 1.4 (range, 0.7- 2) for the conventional method. The most striking feature for this method is the reproducibility and simplicity, minimum variability between plans.
Conclusions
Boolean method is a very practical method for target volume localization and optimization, will need further validation by measuring variability of results among different planning systems and different centers.
