Daryl Lim Joon MBBS, Presenter: Nothing to Disclose

Nicole Ng, Abstract Co-Author: Nothing to Disclose

Jahrad Martin, Abstract Co-Author: Nothing to Disclose

David Van Gelderen, Abstract Co-Author: Nothing to Disclose

Vincent Khoo MD, Abstract Co-Author: Nothing to Disclose

Michael Lim Joon, Abstract Co-Author: Nothing to Disclose

Mori Wada, Abstract Co-Author: Nothing to Disclose

George Quong MD, Abstract Co-Author: Nothing to Disclose

Malcolm Feigen MD, Abstract Co-Author: Nothing to Disclose

Andrew See, Abstract Co-Author: Nothing to Disclose

Michael Grace, Abstract Co-Author: Nothing to Disclose

Marita Lawlor, Abstract Co-Author: Nothing to Disclose

Aldo Rolfo, Abstract Co-Author: Nothing to Disclose

Kym Rykers, Abstract Co-Author: Nothing to Disclose

Carmel Mantle, Abstract Co-Author: Nothing to Disclose

Angela Stella, Abstract Co-Author: Nothing to Disclose

et al, Abstract Co-Author: Nothing to Disclose

Purpose/Objective: The purpose of this study is to analyse the 3D CT dosimetry of treatment fields using traditional planning techniques. Materials/Methods: 15 consecutive stage one seminoma patients that underwent CT planning were identified. CT study-sets (contrast and non-contrast) of each patient was obtained using a slice thickness of 5 mm. The two studysets were then co-registered. The para-aortic lymph nodes relevant to the lymph node drainage of the testes were contoured for each patient by a radiologists and this formed the basis of the clinical target volume (CTV). The adjacent aorta and inferior vena cava were also contoured as targets as they are central to the lymphatic drainage and thus the CTV. Planning target volumes (PTV) were assigned by using a 1 cm 3D expansion of the CTV to account for motion due to respiration, vessel pulsation and set-up uncertainty. Conventional para-aortic treatment fields were created on the digitally reconstructed radiograph associated with the CT datasets. These treatment plans were transferred to a CMS Focus planning system for dosimetric calculation based on delivering 25 Gy in 20 fractions over 4 weeks. Dosimetric parameters including maximum, minimum and average doses were calculated for each patients volumes. Dose volume contraint parameters were also calculated for kidneys. Results: The contoured para-aortic lymph nodes received doses ranging from 16.4 to 25.7 Gy on with an mean dose of 24.4 Gy. The aorta and IVC received doses that ranged from 21.6 Gy to 25.9 Gy with an average of 25.0 Gy. When uncertainties were taken into account the PTV doses ranged from 3 Gy to 26 Gy with an average of 24.4 Gy. Analysis of the field borders showed that some lymph nodes and even the aorta and IVC could lie close to the periphery of the fields. In some patients the PTV contours were situated outside the field borders. The average doses delivered to the kidneys ranged from 0.45 Gy to 24.7 Gy with a mean of 3.7 Gy. The dose volume values were well within tolerance with the average V>23Gy being 3.78%. Conclusions: In general the prescribed dose was delivered to the defined volume while appropriately limiting the dose to kidneys. However in some patients the defined targets are situated at lateral edge of the traditional fields. If uncertainties are taken into account it is possible that these targets may fall outside these fields. The morbidity and mortality associated with para-aortic radiotherapy (albeit small) necessitates the better understanding of the anatomical targets and dose that is required. Adjuvant radiotherapy in stage 1 seminoma is very effective but the present study is hypothesis generating in terms of whether the volume and/or dose can be reduced so as to decrease late toxicity.

Lim Joon, D, Ng, N, Martin, J, Van Gelderen, D, Khoo, V, Lim Joon, M, Wada, M, Quong, G, Feigen, M, See, A, Grace, M, Lawlor, M, Rolfo, A, Rykers, K, Mantle, C, Stella, A, et al, , 3D CT Dosimetric Analysis of Conventional Para-Aortic Radiotherapy Fields for Stage 1 Seminoma.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4418057.html