Résumé
ObjectiveTo discuss dosimetric characteristics of an intensity-modulated radiotherapy (IMRT) technique for treating the chest wall and regional nodes as an integrated volume after modified radical mastectomy ( MRM ),and observe acute side-effects following irradiation.Methods From June 2009 to August 2010,75 patients were randomly enrolled.Of these,41 had left-sided breast cancer.Each eligible patient had a planning CT in treatment position,on which the chest wall,supraclavicular,and infraclavicular nodes,+/-internal mammary region,were contoured as an integrated volume.A muhi-beam IMRT plan was designed with the target either as a whole or two segments divided at below the clavicle head.A dose of 50 Gy in 25 fractions was prescribed to cover at least 90％ of the PTV.Internal mammary region was included in 31 cases.Dose volume histograms were used to evaluate the IMRT plans.The acute side effects were followed up regularly during and after irradiation.The independent two-sample t-test was used to compare the dosimetric parameters between integrated and segmented plans.ResultsPlanning design was completed for all patients,including 55 integrated and 20 segmented plans,with median number of beams of 8.The conformity index and homogeneity index was 1.43 ± 0.15 and 0.14 ± 0.02,respectively.Patients with internal mammary region included in PTV had higher homogeneity index PT.The percent volume of PTV receiving ＞ 110％ prescription dose was ＜ 5％.None of the dose constraints to normal structures was violated.There were statistically significant differences in the means of dosimetric parameters of PTV,such as Dmax,DmeanV107％,and V110％,between integrated and segmented plans (t=2.19 -2.53,P=0.013-0.031 ).≥ grade 2 radiation dermatitis was identified in 3 2 patients ( grade 2 in 2 2 patients,grade 3 in 10 patients ),mostly occurred within 1 - 2 weeks after treatment.The sites of moist desquamation were anterior axillary fold (27/37) and chest wall (10/37).Only 2 patients developed grade 2 radiation pneumonitis.Conclusions The IMRT technique applied after MRM with integrated locoregional target volume is dosimetrically feasible,and the treatment was proved to be well-tolerated by most patients.
Résumé
Objective To determine the change of tumor bed volume during whole breast irradiation by repeated computed tomography scanning and to analyze the dosimetric impact of boost-planning on different CT images. Methods From July 2008 to Jan 2009, sixteen patients with early-stage breast cancer underwent breast conservative surgery (BCS) were enrolled in the study. All patients received whole breast irradiation and tumor bed boost, no adjuvant chemotherapy was given. Two additional CT scans were acquired in addition to the planning CT ( CT1 ), one in the course of radiotherapy ( CT2 ) and the other before the boost (CT3). Tumor beds were contoured in all CT images. Three-dimensional conformal radiotherapy planning for tumor bed boost was done on CT1 and CT3 respectively. Results The mean tumor bed volume on CT1, CT2 and CT3 were 49.5 cm3, 25.6 cm3 and 22. 2 cm3 ( F = 5. 63, P = 0. 007 ),respectively. Further analysis found statistically significant difference between CT1 and CT2 ( q = 0. 03, P =0. 010), CT1 and CT3 ( q = 0. 01, P = 0. 004), but not between CT2 and CT3 ( q = 1.00, P = 0. 333 ). The average reduction of tumor bed volume from CT1 to CT3 was 43.4%. A reduction of 20% or above was found in 88% of the patients ( n = 14), 50% or above in 38% of the patients (n = 6). In the boost-planning, the volume of the ipsilateral breast receiving 100% prescribed dose (V100%) on CT1 and CT3 was 183.5 cm3 and 144. 5 cm3, respectively ( t = 3.06, P = 0. 008 ). Conclusions Volume of tumor bed is dynamically reduced in the course of whole breast irradiation after BCS, with more important reduction in the early weeks after the beginning of irradiation. A second CT scan before tumor bed boost is warranted.
Résumé
Objective To assess set-up errors measured with kilovoltage cone-beam CT (KV-CBCT), and the impact of online corrections on margins required to account for set-up variability during IMRT for patients with prostate cancer. Methods Seven patients with prostate cancer undergoing IMRT were enrolled onto the study. The KV-CBCT scans were acquired at least twice weekly. After initial set-up using the skin marks, a CBCT scan was acquired and registered with the planning CT to determine the setup errors using an auto grey-scale registration software. Corrections would be made by moving the table if the setup errors were considered clinically significant ( i. e. , ＞ 2 mm). A second CBCT scan was acquired immediately after the corrections to evaluate the residual error. PTV margins were derived to account for the measured set-up errors and residual errors determined for this group of patients. Results 197 KV-CBCT images in total were acquired. The random and systematic positioning errors and calculated PTV margins without correction in mm were:a) Lateral 3. 1,2. 1,9. 3;b) Longitudinal 1.5, 1.8, 5. 1 ;c) Vertical 4. 2,3.7, 13.0. The random and systematic positioning errors and calculated PTV margin with correction in mm were:a) Lateral 1.1,0. 9, 3.4;b) Longitudinal 0. 7, 1.1, 2. 5;c) Vertical 1.1, 1.3, 3.7. Conclusions With the guidance of online KV-CBCT, set-up errors could be reduced significantly for patients with prostate cancer receiving IMRT. The margin required after online CBCT correction for the patients enrolled in the study would be appoximatively 3-4 mm.