ESTRO 37 Abstract book

Conclusion Although the total PTV volume is higher when applying an online correction strategy on the prostate due to the larger margins around the pelvic nodes, this strategy leads to the most optimal sparing of the relevant OARs (rectum, anal canal and bladder), at the cost of a slightly higher dose to the femoral heads and small bowel bag. This correction strategy (and the resulting CTV-PTV margins) is now used clinically in our hospital. EP-2361 What is the gain of breath hold for re- irradiation of recurrent left-sided breast cancer with VMAT? K.F. Crama 1 , J. Visser 1 , N. Bijker 1 , M.W. Kolff 1 , A. Bel 1 1 Academic Medical Center, Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective The use of a breath hold technique for left sided breast cancer is nowadays the standard to reduce high dose regions in the heart, especially when tangential fields are used. For most patients the heart moves away from the field borders when the patient is in breath hold, resulting in less overlap with the tangential fields than during free breathing. Re-irradiation of a recurrence of left sided breast cancer with in most cases a larger target volume, extending more to the medial side and posterior axillary line, often results in a higher heart dose compared with the primary treatment. At our clinic we use for treatment of these recurrences a Volume Metric Arc Therapy (VMAT) technique in free breathing, to get a more conformal plan. It is a completely different technique compared to tangential fields, because a VMAT technique gives a large region a low dose. The question is raised whether breath hold could also reduce the dose to the organs at risk further in this patient group, compared to free breathing [figure1].

In this study we investigated if there is a potential gain for heart and lung dose with a VMAT breath hold treatment for a local recurrence of left sided breast cancer in previously irradiated area. Material and Methods We retrospectively selected twenty patients who were treated at our clinic and had a free breathing and breath hold CT-scan. For the breath hold CT-scan we used the SpiroDynr’X system (Dyn'r Society) to receives a reproducible breath hold with visual feedback for the patient. For both scans the GTV, CTV and also heart and lungs were delineated. Using a CTV-PTV margin of 1cm, a dual arc VMAT, Elekta Agility, 6MV treatment plan, with a total dose of 46Gy in 23 fractions, was made for both CT-scans. For planning multi criterial optimization [MCO] within Raystation (Raysearch) was used. The mean dose to the heart was reduced as much as possible without compromising the target coverage. The V 43.7Gy (95% of prescribed dose) of the PTV; the D 2cc , D mean and V 43.7Gy of the heart; V 20Gy , V 10Gy and D mean of the lungs were compared using a paired sampled T-test. Results The average mean heart dose was reduced with 2.2Gy (10.3Gy vs. 8.1Gy) comparing breath hold with free breathing (P<0.01). However the difference per patient is widely spread ranging from -6.1Gy to 0.5Gy in favor of breath hold [table1]. Only 4 out of 20 patients had a difference less than 1Gy. The mean high dose(D 2cc ) in the heart is 4.2Gy lower for breath hold compared to the free breathing treatment plan (P<0.01). All patients had a lower D 2cc dose with a breath hold treatment plan. Only the mean dose to the lungs increased 0.4Gy with a breath hold technique (P=0.13).