Radmtheral~ aad Oa ~ ca3 2 0992) 257-264 c 1992 Elsevier Science Publishers BV. All rights ~ s e ~ e d 016%8140,'92,'S05 0D 257 R~D]ON 00965 Accuracy of patient positioning in mantle field irradiation C. L. Creutzberg ~, A. G. Visser b, P. M. Z. R. De porte ~,*, J. H. Meerwaldt "**, V. G. M. Althof b and P. C. Levendag * Depa~ments of ~Radlat,~ Oncolo~ and hCltniial ploslcs, Dr Daniel den Hoed Can~r Cente,, Ronerdem, 771e~rethedands (Ke~ived 27 May 1991, revisioa ~ i v e d 14 October 1991, acoepted 3 January 1992) Summary A prospective stud}, of the accuracy of patient poshioning in mantle field i~adiation was carried om {n 13 lymphoma patients treated w/th eurafiw radintherapy. Padents were t~ated in the supine and p~ne position for anterior and posterior fields. ~specti~l). Individually shaped divergent shielding blocks were plaeed in a fixed position in a template which was poski~ed on a tra) above the patient. A total number of 94 megavolt age portal films (MV) wag analysed and e~pared to 26 sire eledon films (SIM), MV-SIM differ~ces were larger for posterlor fields th~ for ant~ior fields, Regarding the position &the lung shielding bl~k~, mean MV-SIM differences ranged from I.] to 4.4 mm and e~ors exceeding l cm were found in X2% ofe~es. Most dlserepaneles appeared to bc randomly d~str]but ed. A a-5 mm syst~atic cr~ial shier of patlents in the posteri~ treatment position was noted. Discrepancies ir the po~itlou of the Iaryngeel block, spinal cord shielding block and humerus blocks were small ~itb mean MV.SIM differences ranging from 0,3 to 2,7 ram. Differences betw~n simulation set-up and treatment ~t-up were modest as compared to error rates t~ported in the fiteraturQ. $ hiddlng of tumour-bearlng areas did :lot o~ur. It was concluded that the present standardised technique of patient positioning and the design of treatm~t fields results in accept able error rates, Attention should be directed towards increasing the stability of patients in the prone treatment position in ord~ to further reduce both syst~atlc and random error rates. Introduction Treatment of pmients with stage I and 1I supra- diaphragmatic Hodgkin's disease usuatly includes radiation therapy, resuking in high eu~ rates (80-90% relapse-f~e survival) [2]. Depending on the p~nee of prognostic ['actors such as B-symptoms, bulky disease, age, arid sex) treatment either consists of subtotal nodal irradiation or o[' a combination of chemotherapy ~d radiation therapy. The aim of'subtotal nodali~adiation is to treat in continuity the lymphatic chains that are involved or likely to be involved with Hodghin's disease. This is achieved by the combination o[` the so~afied mantle field and a subdiaphragmatie field including the spleen and para-aortie nodes. The mantle field ineludes nodes, axillary nodes, the medlastinum, and the hi[~ nodes. An important feature of the roande field technique is the indiniduMisatinn o1" radiation fields conformed to the patient's anatomy in the treatment posmon. The use of individually shaped blocks ensures adequate treat- ment of lymphoid tissue while sp~ing lung tissue, spinel cord. lmTn• heart and the humffus. Howe~r, the com- plex shape of these extended fields makes precision in radiotherapy s~t-up difficult to achieve [fi,12]. Dis- crepancies in daily t~atm~t positioning a~d differ- enees betw~n Ioealisatthn set-up and treatm~t set-up could result either in an underdosage in the field m~- gins, which might l~d to a clinically relevant g~ graphical miss. or in an ovffdosage to uo~al tissues. the cervical nodes, supraclavieu]ar and infraelavicular Underflosa~e in the field margins, due to either A ddreesfo, eorre,pondenee: C, L, Cmmzberg, M.D., D~par t ment of Radiation Oneolo~, O r. D~id den Hoed Caoe~ ~n ter, G~ene HiIled~jk 30]) 3075 EA Rot~rdam, The N*therlands, 9 presem addre~.. O.LV. Hospital, Anise, Bdglom, and **Mediseh Spect~m Twenm, Ensehede, The Netherlands