No abstract

The purpose of this investigation was to evaluate the dose on megavoltage CT (MVCT) images required for tomotherapy. As imaging possibilities are often used before each treatment and usually used several times before the session, we tried to evaluate the dose delivered during the procedure. For each scanning mode (fine, normal, and coarse), we first established the relative variation of these doses according to different technical parameters (explored length, patient setup). These dose variations measured with the TomoPhant, also known as Cheese phantom, showed the expected variations (due to the variation of scattered radiation) of 15% according to the explored length and ±5% according to the phantom setup (due to the variation of the point of measurement in the bore). In order to estimate patient doses, an anthropomorphic phantom was used for thermoluminescent and film dosimetry. The degree of agreement between the two methods was very satisfactory (the differences correspond to 5 mGy per imaging session) for the three sites studied (head & neck, thorax, and abdomen). These measurements allowed us to estimate the delivered dose of between 1 cGy and 4 cGy according to the site and imaging mode. Finally, we attempted to investigate a way to calculate this delivered dose in our patients from the study conducted on a cylindrical phantom and by taking into account data from the initial kV‐CT scan. The results we obtained were close to our measurements, with discrepancies below 5 mGy per MVCT.PACS numbers: 87.53.Bn, 87.55.km, 87.55.Qr

Introuction: The six worldwilde ongoing APBI phase III trials are characterized by a significant heterogeneity regarding inclusion criteria and stratifications. One non-inferiority trial (SHARE) is currently ongoing in France. SHARE Trial design: SHARE will randomize 2800 patients in 3 arms: standard (Arm A; 6.5 weeks) versus hypofractionated (Arm B; 3 weeks) versus APBI (Arm C; 1 week) using only 3D conformal radiotherapy (3D CRT). In this trial high quality and homogeneous criteria in surgery, pathology and RT for the 3 arms is planed. Primary objective: To estimate and compare the rates of local recurrences between the experimental and control arms. Inclusion criteria Post menopausal women aged ≥ 50y (stratification: < 70 yrs vs ≥ 70 yrs) Menopausal status confirmed since ≥ 12 months (Clinically and/or biologically) No previous ipsilateral breast and/or mediastinal irradiation Pathologic confirmation of invasive carcinoma (all types of invasive carcinomas) Unifocal tumor confirmed on the pathologic specimen Pathologic tumor size of the carcinoma ≤ 2cm (including the in situ component) All pathologic grades (stratification: HER2/triple negative vs others) Clear lateral margins confirmed on the final pathology report. The minimal size from the invasive and in situ disease should be 2 mm (≥ 2mm) pN0 (i+/−) (stratification: pN0 vs pN(i+)) Chemotherapy and trastuzumab are not allowed - RT should be started ≥ 4weeks and ≤ 12 weeks after surgery (including the date of second excision for close or involved margins) Clips in the tumor bed placed during surgery (4 to 5 clips) Treatment Arm A 3D CRT should be started within 12 weeks after the last surgery. A total of 50 Gy is delivered in 25 fractions, one fraction of 2 Gy per day, 5 days a week. In this arm, the boost of 10 to 16 Gy is delivered in 5 to 8 fractions. Dose prescription (arm B) The main point is that in both schedules the total dose is delivered in 3 weeks: – The Canadian schedule described by Whelan et al. delivers 42.5 Gy in 16 fractions (2.65Gy/fraction, 5 fractions/week).– The UK schedule, reported in START B trial delivers 40 Gy in 15 fractions (2.66 Gy/ fraction, 5 fractions/week). Nodal and boost RT is not allowed. Arm C 3D CRT should be started within 12 weeks after the last surgery. Intensity modulated RT (IMRT) and brachytherpayare not allowed. A total dose of 40 Gy in 10 fractions over 1 week (4Gy per fraction twice a day with minimal delay of 6h). Conclusion: In summary, the French trial will allow: – Selected patients according to age and low risk of local recurrence parameters.– To evaluate in a subgroup of patients (4 to 5 centers), the impact of magnetic resonance imaging (MRI) for patient selection and the rate of occult disease (multifocality) not detected by standard imaging evaluation which is considered as an exclusion criteria.– To determine APBI parameters adapted to the surgical procedure in the tumor bed remodeling setting.– To determine homogeneous criteria for the surgical procedure, minimal requirements and optimal criteria that have to be mentioned in the final pathology report in all 3 arms of the study.– To test hypofractionation using 3 weeks-schedules as compared to APBI Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr OT1-2-02.