| Part I:Evaluation on variable factors influencing determination for the target volumes of the intact breast in intensity-modulated radiotherapy for breast cancerPurpose:To determine the factors influencing the delineation of clinical target volume(CTV) and the set-up errors during tangential irradiation and the impact of free breathing on target volume motion of intact breast in order to perform intensity-modulated radiotherapy(IMRT) for breast cancer.Methods and materials:From Jan, 2003 to Dec, 2003, selected patients with early-stage breast cancer after breast conserving surgery, were eligible for the study. All patients were immobilized in treatment position by breast board of Med-Tec 250 type, and underwent virtual simulation using Marconi CT simulator. The palpable glandular breast tissue was marked with a radio-opaque wire in some patients before CT scanning. The motion of the breast treatment volume was observed on fluoroscopy in different directions under free breathing in 16 patients. The set-up errors in different dimensions during irradiation were evaluated by weekly portal films(PF) in comparison with digital reconstructed radiograph(DRR) or simulating film(SF) in 11 patients. Using delineation tool in planning system of ADAC-pinnacle3-6.2b, the CTVs of intact breast of 6 patients were delineated in CT slices by four radiation oncologists and one radiologist individually, and reference CTV was determined by group consensus. The extent of variation in CTV delineation was quantified by the ratio between the common volumes of all CTVs(the common volume, Vco) and the smallest volume encompassing all CTVs(the maximum volume, Vmax). The deviation in the CTVs' extent from the reference CTV's extent was quantified in each orthogonal direction for each patient to find the origins of variations. In addition, all central lung distances(CLD) in tangential fields, which were designed based on CTVs, were measured and the mean CLD was also calculated in all patients.Results:Observed from fluoroscopy, the CLD variation during free breathing was greatest with the extent of 2.1±1.2mm, while all less than 1mm in other directions, including cranial, caudal, medial and posterior-lateral directions. From the measurement by PFs and DRRs or SFs, the systemic error, random error and overall error in the posterior, anterior and cranial-caudal dimensions were 1.9mm, 1.6mm, 2.5mm, and 2.4mm, 1.7mm, 3.1mm, and 2.6mm, 2.3mm, 3.5mm, respectively. In addition, the time trend analysis revealed that the discrepancy of the treatment position in cranial-caudal direction and breast volume was most obvious at the beginning 2 weeks with the peak of breast volume at the second week. The set-up errors decreased gradually during the following 3 weeks. The variation in CTVs delineation varied in different extent. The ratio between Vco and Vmax was lowest(0.660 and 0.651, respectively) in two patients with low glandular density. Among the other 4 patients with high glandular density, the ratio in 2 patients with radio-opaque marks was relatively higher than the other 2 patients with no marks(0.799, 0.769 vs. 0.735, 0.752, respectively). Compared to the reference CTV, the patient-averaged deviations of CTVs' extent in orthogonal directions were greater in the posterior (-1.2±3.4mm), cranial (-1.5±2.1mm), caudal(-0.7±4.1mm), and medial (-0.6±3.3mm) than in the anterior (0 mm) and lateral directions(-0.8±0.8mm). The most obvious variations were observed in the area of breast axillary part and primary tumor bed after surgery. The mean CLD in 66.7% patients(4/6) exceeded over the conventional limitation of 2cm.Conclusions:Our study suggests that the influence of free breathing on the motion of the breast treatment volume is insignificant. The set-up errors during irradiation is greatest in cranial-caudal direction, which suggests that the fixing precision of the breast board could be improved further in cranial-caudal direction especially. The set-up errors during irradiation is most obvious at the beginning 2 weeks with the...
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