ESTRO 36 Abstract Book

S633 ESTRO 36 _______________________________________________________________________________________________

EP-1164 Improved accuracy in IORT with electron beams by a new measuring system of mammary gland thickness P. Scalchi 1 , A. Marchesin 2 , G. Scalco 2 , S. Bacchiddu 3 , C. Mari 3 , L. Grandin 3 , P. Francescon 1 , F. De Marchi 2 , C. Baiocchi 3 1 Ospedale San Bortolo, MEDICAL PHYSICS, Vicenza, Italy 2 Ospedale San Bortolo, SURGERY, Vicenza, Italy 3 Ospedale San Bortolo, RADIOTHERAPY, Vicenza, Italy Purpose or Objective In IORT of the breast cancer using electron beams (IOERT), the beam energy should be properly chosen, as recommended by both ICRU 71 (2004) and AAPM TG72 (2006), to ensure that the entire PTV be covered by the 90% of the maximum dose (D max ) and the ICRU reference point be positioned as near as possible to D max . Due to the physical characteristics of these beams, the measurement of the mammary gland thickness can be critical. In fact, usually it is measured before docking using a needle and a ruler ('needle method”), or ultrasounds. Nevertheless the measured thickness can differ from the real one after docking completion, thus affecting the accuracy of the subsequent dose release. To allow accurate measurements of the gland thickness under treatment conditions, a new measurement system (MARK's) was developed at Vicenza Hospital. The aim of this work is to compare the needle method to MARK's in terms of surgeon- surgeon variability and dosimetry impact. Material and Methods A mobile IOERT-dedicated linac (LIAC,SIT) with four electron energies (4 to 10 MeV) is used at Vicenza Hospital. MARK’s is a sterilizable manual pointer with integrated ruler. After radioprotective disk positioning, the surgeon stitches the mammary gland to prepare the PTV. Then he inserts the terminal part of the applicator, after applying a thin patch layer underneath to prevent target herniation and, while keeping it pressed, he inserts the pointer inside the applicator allowing direct thickness measurements in treatment conditions.

would cause 11 erroneous energy choices and 5 treatments to be wrongly canceled.

N.

of

possible treatment cancelations following ICRU 71 and AAPM TG 72 (needle method)

N. of erroneous energy choices (needle method)

Surgeon- surgeon variability (needle method)

Surgeon- surgeon variability (MARK's)

Thickness difference between methods

0.0 ÷ 20.0 mm (5.4 mm on the average)

11

5

2 mm

1 mm

Conclusion A new system for measuring the mammary gland thickness prior to IOERT developed at Vicenza Hospital was compared to a traditional needle method. The former shows better reproducibility and accuracy, because it reproduces the same target thickness as it exists after the docking. Regarding both treatment decisions and dosimetric accuracy, the found differences are critical when the international recommendations are followed. EP-1165 Short and long term safety of a post- mastectomy conformal electron beam radiotherapy (PMERT) N. Grellier-Adedjouma 1 , M. Chevrier 2 , H. Xu 1 , N. Fournier-Bidoz 1 , F. Campana 1 , F. Berger 2 , A. Fourquet 1 , D. Peurien 1 , D. Lefeuvre 2 , Y.M. Kirova 1 1 Institut Curie, Radiation Oncology, Paris, France 2 Institut Curie, Statistics, Paris, France Purpose or Objective To evaluate short and long-term safety of a chest wall irradiation after mastectomy with our previously published PMERT technique, depending on patient characteristics and treatments received. Material and Methods We included all women irradiated after mastectomy for a non-metastatic breast cancer with PMERT between 2007 and 2011 in our Department of Radiation Oncology. Acute and late toxicities (CTCAE v3.0) were evaluated with a weekly clinical examination during irradiation and then with monitoring consultations at least every 6 months. We also conducted a dosimetric analysis of 100 consecutive patients irradiated on the chest wall and lymph nodes (LN) (50 right and 50 left), to assess the doses to organs at risk. Results Among the 796 women included, mean age was 53.2 years (22.1-90.8), 47.6% of them had at least one cardiovascular risk factor, regardless of age, 49% were post menopausal, 8.3% were obese (BMI ≥ 30) and 6.9% and 11.9% had cardiac and pulmonary comorbidities respectively. Internal mammary chain (IMC) was irradiated in 85.6% of cases, supra, infraclavicular LN and axilla in 88.3%, 77.9% and 14.9% of cases. Mean chest wall dose was 49.4Gy (39- 56) over 40 days (30-119). Energies of 6 and/or 9 MeV were used in 84.7% of cases. The maximum acute skin toxicity was grade 1 in 58.5% of patients, grade 2 in 35.9%, and grade 3 in 4.5% of them. There was no grade 4 toxicity. Concomitant chemotherapy was associated with an increased risk of grade 3 toxicity (p <0.001). With an median follow up of 64.1 months (5.6-101.5), 29.8% of patients had, temporarily or permanently, hyperpigmentation, fibrosis or telangiectasia (grade 1: 23.6%, grade 2: 5.2%, grade 3: 1%), which tended to be promoted by smoking (p = 0.06); 274 patients (34.4%) underwent breast reconstruction, on average 19.7 months after the end of irradiation (3.6-86.8), which was

14 patients were studied. The measurements were taken first by the needle method, and then by MARK's. Five measurements points were always taken, one at the center of the PTV and four marginal positions (cranio- caudal and lateral). The electron energies were chosen based on the resulting thickness. The two systems were compared in terms of both the choice of the electron energy, as resulting by following ICRU and AAPM recommendations, and the surgeon-surgeon variability. Results As shown in the following Table, the needle method systematically overestimates the PTV thickness and surgeon-surgeon reproducibility is better for MARK’s. Following ICRU71 and AAPM TG72 the needle method