ABSTRACT
PURPOSE: To compare measured and calculated doses using Pencil Beam (PB) and Monte Carlo (MC) algorithm on a CIRS thorax phantom for SBRT lung treatments. METHODS: A 6MV photon beam generated by a Primus linac with an Optifocus MLC (Siemens) was used. Dose calculation was done using iPlan v4.1.2 TPS (BrainLAB) by PB and MC (dose to water and dose to medium) algorithms. The commissioning of both algorithms was done reproducing experimental measurements in water. A CIRS thorax phantom was used to compare doses using a Farmer type ion chamber (PTW) and EDR2 radiographic films (KODAK). The ionization chamber, into a tissue equivalent insert, was placed in two position of lung tissue and was irradiated using three treatments plans. Axial dose distributions were measured for four treatments plans using conformal and IMRT technique. Dose distribution comparisons were done by dose profiles and gamma index (3%/3mm). RESULTS: For the studied beam configurations, ion chamber measurements shows that PB overestimate the dose up to 8.5%, whereas MC has a maximum variation of 1.6%. Dosimetric analysis using dose profiles shows that PB overestimates the dose in the region corresponding to the lung up to 16%. For axial dose distribution comparison the percentage of pixels with gamma index bigger than one for MC and PB was, plan 1: 95.6% versus 87.4%, plan 2: 91.2% versus 77.6%, plan 3: 99.7% versus 93.1% and for plan 4: 98.8% versus 91.7%. It was confirmed that the lower dosimetric errors calculated applying MC algorithm appears when the spatial resolution and variance decrease at the expense of increased computation time. CONCLUSIONS: The agreement between measured and calculated doses, in a phantom with lung heterogeneities, is better with MC algorithm. PB algorithm overestimates the doses in lung tissue, which could have a clinical impact in SBRT lung treatments.
ABSTRACT
PURPOSE: Prospective monocentric study of the skin and heart tolerance of a concurrent administration of trastuzumab (T) and radiotherapy (RT) for breast cancer (BC). PATIENTS AND METHODS: From February 2004 to January 2007, 57 patients (pts), were treated by a concomitant administration of T and normo-fractionated RT of either whole breast (+/-boost) or chest. The perfusion of T started either with or after chemotherapy (CT). Left ventricular ejection fractions (LEVF), assessed at baseline, before start of RT, after completion of RT and then every four to six months with either echocardiography or multiple gated acquisition scanning, were considered normal if greater or equal to 50% or stated so by the cardiologist. Inclusion criteria included a normal LVEF at baseline. Skin toxicity was evaluated using CTCAEV3. Median age was 49 years (25-80). CT with anthracycline was administered in 84% (total dose 300 mg/m(2)). All but one patient (treated weekly) received T every three weeks (8 mg/kg followed by 6 mg/kg) for a median duration of 12 months (6-33). The internal mammary chain was irradiated in 88% of cases. Median follow-up for LVEF assessment was 13 months (2-33). RESULTS: LVEF at pre-RT were normal in 54 pts (100%, three Missing Data [MD]), at post-RT in 56 pts (98%, no MD) and at last follow-up in 53 pts (95%, one MD). There were two grade 0, 44 grade I and 11 grade II skin reactions. For the 27 patients with a skin toxicity assessment after six months, late skin toxicity was grade 0 in 22 pts, grade 1 in four, grade 2 in one. CONCLUSION: Provided that the technique is adapted, the acute skin and heart toxicities of the concomitant administration of T-RT appeared satisfactory. More patients and longer follow-up are still mandatory.
