1082 poster A dosimetric comparison of CT and traditional radiotherapy fields for stage one seminoma

S454

134 cm 3, PTV 30 cm3-194 cm 3. V20.1ungtoxicity 24.0% (6%38%).2°/ Upper lobes a)non-gating: GTV 28 cm3-112 cm 3, PTV 98 cm3-348 cm3. V20.1ungtoxicity 37.8% (21%-71%).b) gating: GTV 16 cm3-103 cm 3, PTV 48 cm3-238 m3. V20.1ungtoxicity 27.0% (14%-56%).( P-values <0.05) Results show substantial differences in volume of GTV and PTV and in V20 of normal lung tissue between gated and non-gated irradiation that are consistent, clinically important and significant. Because of the implementation of RPM gating, lung toxicity is reduced from 45.15% to 24% for patients irradiated with Tu in the lower parts of the lung, and from 37.8% to 27.0% for patients with Tu in the upper parts of the lung. The implementation of the technique seems most important for patients with visible Tu Iocalised in the lower parts of the lung. The approach ensures that the full target dose is applied and that unnecessary lung irradiation is avoided. The technique gives comfort to the patients because it allows patients to breath naturally. The technique is easily implemented in daily use. 1081 poster Gold marker based verification of proton treatment of prostate

S. Johansson ~, K. Nilsson ~ U. Isacsson 2, A. Montelius 2, S. Asplund ~, M. Bergqvist ~, E. Blomquist ~, I. Turesson ~, E. Grusell 2 ~Uppsala University Hospital, Oncology, Uppsala, Sweden 2Uppsala University Hospital, Radiophysics, Uppsala, Sweden Radiation therapy of adenocarcinoma of the prostate aims at treating the whole prostate volume to a high dose. The success of the treatment can depend on the dose delivered to the prostate and the precision of the delivery. With protons, the radiation dose can be increased without increasing treatment toxicity as each beam can closely be conformed to the target. The definition of margins around the prostate has to take in to account the daily reproducibility of position of the patient, organ motion and the maximum tolerable dose for organs at risk. With photon therapy, patient set-up variations are normally estimated by matching the bony structures in portal images. Organ motions relative to the bony structures can however be measured with small gold seeds, similar to those used in brachytherapy implanted to the prostate. Fifty-three patients with biopsy proven and localized adenocarcinoma of the prostate have been treated with a combined proton boost at the Svedberg Laboratory and a photon beam treatment at the Department of Oncology at the University Hospital of Uppsala, Sweden. Three to five gold seeds were implanted to the prostate through the perineum during local anesthesia with transrectal ultrasound guidance. The patients were immobilized for treatment planning using a specially designed fixation couch. All patients were initially treated with protons. A total dose of 20 Gy in four fractions was delivered to the prostate by a single proton beam through the perineum. The patients were positioned before each treatment using X-ray films showing the gold seeds relative to the proton beam and any misalignment was corrected before each treatment delivery. After the proton boost, an additional dose of 50 Gy was delivered to the prostate with conformal photon radiotherapy in 2 Gy fractions. The positioning accuracy of a hypofractionated proton treatment is very important, especially in a mobile organ such as the prostate. This study will present a combined computer and gold marker based verification model in proton beam treatment of the prostate. The factors affecting the accuracy of the treatment, such as marker visibility, marker migration,

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the time from imaging to treatment and also the prostate motion and deformation will be discussed. 1082 poster A dosimetric comparison of CT and radiotherapy fields for stage one seminoma

traditional

J. Martin ~, D. Lim Joon ~, N. Ng ~, D. Van Gelderen 2, M. Wada ~, M. Grace ~, M. Lawlor ~, M. Lim Joon ~, A. See ~, V.

K--E~oo

~Austin Health, Radiation Oncolegy Centre, Melbourne, Australia 2Austin Health, Diagnostic Imaging, Melbourne, Australia 3Christie Hospital, Academic Department of Radiation Oncology, Manchester, United Kingdom Introduction: Adjuvant radiotherapy is standard adjuvant treatment of Stage One Testicular Seminoma (SOS). CT based planning is becoming more accessible, and offers potential dosimetric advantages compared with traditional plans based on bony anatomy. Methods: Ten consecutive patients treated at the Austin Radiation Oncology Centre for SOS were simulated using fused intravenous contrast and non-contrast CT. All had two plans generated, one using traditional rectangular para-aortic fields, and one using conformal fields based on a threedimensional algorithm using the aorta and inferior vena cava to automatically define the target volume. The primary target volume compared was the dosimetric coverage of these vessels with a 15mm three dimensional margin. A diagnostic radiologist outlined visible lymph nodes at risk to generate a second set of target volumes (lymph node). Field size, patient separation and renal dosimetry were also recorded. Results: The CT based plan delivered improved Dosimetry to the vessel planning target volume compared with the traditional field (CT D95=24.7Gy, traditional D95=23.6Gy, p=0.002). Lymph node target volume Dosimetry was similar between the two plans, at least partly due to the symmetric algorithm used to generate the CT volumes not addressing disease laterality as well as the traditional plan. Mean Right kidney dose was higher for the CT plan (8.1Gy v 3.9Gy, p=0.002), but median dose was roughly equivalent between the two plans (2.0Gy v 1.7Gy, p=0.74), showing that the CT plan tended to irradiate small volumes of the kidneys to high doses. CT based plans were significantly larger than traditional plans (equivalent square CT=I 5.4cm, traditional=12.9cm, p=0.002), mainly because they were wider (CT=I 1.8cm, traditional=9cm, p=0.002),

IMimmum 4 7Gy

I

Vesse

PTV

23 7Gyi0 002 .........

iV23.75

................................ ................ ..... ..j ~93°/o 100% I0,002

!D95

123.6Gy

................

24.7Gy 0.002

,Mean 3.9Gy 8.1Gy 0.002 Right Kidney !i..............~.............................~ ...........o: V25 0% ~6% 0.008 Conclusion: CT based fields for SOS tend to be wider than traditional fields, and provide improved Dosimetry to vessels. An asymmetrically defined CT field is likely to give further dosimetric improvements. Given that traditional fields are

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$455

often delivering significantly less than the prescribed dose to the target volume, there is a suggestion that a lower dose more accurately delivered may be sufficient to achieve similar outcomes. 1083 poster Evaluating the accuracy of ultrasound Iocalisation for positioning prostate cancer patients for external beam radiotherapy

J. Coffev I, H.A. McNair 2, B. Shoulders 2, V.N. Hansen 3, S.A. ~4anga/, J. Staffurth ~, A.S.N. Jackson 1, S.A. Sohaib 4, D.P. Deamale/ ~Royal Marsden Hospital, Academic Urology Unit, Sutton, United Kingdom 2Royal Marsden Hospital, Radiotherapy Department, Sutton, United Kingdom 3Royal Marsden Hospital, Physics Department, Sutton, United Kingdom 4Royal Marsden Hospital, Radiology Department, Sutton, United Kingdom Purpose: To evaluate the accuracy of the ultrasound based (BAT®SXi, Nomos Corp.) system for Iocalisation of prostate position compared to CT Iocalisation. Materials and Methods: Prostate alignments using the BAT system were evaluated in the first nineteen of a projected twenty five patients. The BAT system was calibrated daily to the CT isocentre, thus if the BAT located the prostate in the same position as in the CT scan, the couch adjustment would be zero. Patients underwent an initial CT scan in the treatment position and the prostate, bladder and rectum were outlined. BAT ultrasound was then performed, capturing transverse and sagittat suprapubic ultrasound images, approximately 30 minutes later, whilst the patient remained in the same positin on the planning couch. The corresponding CT contours were imported into the BAT system and overlaid onto the ultrasound images and the necessary couch shifts were recorded to produce the alignment (US). In order to evaluate inter-user variability these measurements were taken by three different operators. To account for patient and prostate movement between the CT and the ultrasound, a second CT planning scan was taken approximately 30 seconds after the BAT ultrasound, again with the patient in the same position, and fused with the initial CT to determine any patient or prostate movement(CT2-CT I=CTM (. These measurements were deducted from the original BAT measurement to determine the accuracy of the BAT compared to CT (US-CTM (. Results: The BAT ultrasound system produced good quality images that were reproducible between different operators. Inter-observer variability was minimal. Table below shows the mean and SD displacements, in centimetres, in each direction.

CT,-uslnitial couch shifts:

!0.3 (0.9){0.4; (0.4) 0.2 (0.3)

Organ and patient movement ^ ,_ _, 0 (0.3) u (u.4) 0 (0.b) CTz.CTI=CTM Accuracy of BAT system: U S -CTM

0.3 (0.6) 0.3 (0.4) 0.2 (0.3)

Conclusions The BAT ultrasound system proved to be mobile, non invasive and quick to use. The ultrasound images gained were reproducible by all users and showed little inter-observer variability. The mean displacement of the

BAT compared to the CT scan was <0.3cm in all directions. However, there was a larger SD in the S/I than in the A/P and PJL direction. This may have arisen from the difficulty in determining the inferior aspect of the prostate on the sagittal ultrasound views. 1084 poster 3D postoperative chemoradiation in gastric carcinoma: acute toxicity and treatment feasibility

F. Cellini 1, E. D'Angelo 1, G. C. Mattiuccf , A. Caiazza ~, G. ~ , L. Di Lullo 3, F. Deodato 2, P. Murino 2, D. D'Ugo 4, V. Valentini ~ I Universit~ Cattolica S. Cuore, Radioterapia, Roma, Italy 2Universit& Cattolica S. Cuore, Radioterapia, Campobasso, Italy 30spedale Civile, U.O. Oncologia, Isernia, Italy 4Universita Cattolica S. Cuore, U.O. Chirurgia, Campobasso, Italy Introduction: The results of U.S.Intergroup 0116 demonstrated that concomitant chemoradiation improves local control and overall survival in resected gastric carcinoma. However postoperative chemoradiation was associated with major probability of severe toxicity. Therefore only 64% of the patients completed the prescribed combined modality treatment. Material and methods: 27 patients (median age:60 ys; M/F:16/11) were treated with postoperative chemoradiation after surgical resection. Pathological stage (UICC 2002) was as follow: la:l;Ib:l; 11:4; Illa:12; IIIb:3; IV:6. Tumor site was: Upper Third:7 (25.9 %); Middle Third:8 (29.6 %); Lower Third: 12 (44.5%). 19 (70.4%) patients received 45 Gy (1.8Gy/fract.) over five weeks plus adjuvant and concurrent 5-Fu according to Intergroup 0116 study. 8 (29.6%) patients with major risk factors received a 9 Gy boost to the tumor bed; in these patients 5-Fu was delivered by continuous i.v. infusion (225 mg/day) during the entire treatment. Radiotherapy was delivered by CT based 3D-conformal technique. The dose was prescribed according to ICRU 62. Results: 25/27 (92.5%) patients completed the entire combined modality treatment. One patient definitively interrupted the radiation therapy after 27 Gy delivered due to a GI Grade 3 toxicity, and severe PS worsening. Another patient definitively interrupted the concurrent chemotherapy due to GI Grade 4 toxicity. Two (7.4%) patients had a temporarily treatment interruption due to toxicity. Overall 2/27 (7.4%) patients had a GI Grade 3 toxicity, 1/27 (3.7%) had a GI Grade 4 toxicity, 1/27 (3.7%) patient had a grade 3 thrombocytopenia. Conclusions: In spite of the relatively low number of patients, this analysis seems to suggest that 3D conformal therapy improves tolerance and feasibility of postoperative concurrent chemoradiation in gastric cancer. 1085 poster Correlation between the movement of the chest wall and the movement of the target volume in 3D-radiotherapy of the oesophagus cancer using the gating technique

J. Dumas 1, F. Lorchef, C. Gaffard 2, C. Poirot 2, A. No~i 3-4, J. Bosset ~, P. Alettf -4, D. Wolf 4 ~University Hospital, Radiotherapy, Besan~on, France 2Postgraduate Institute of Ingineers of Franche-Comte , Besan~on, France 3Centre Alexis Vautrin , Radiotherapy, Nancy, France 4Polytechnic National Institute of Lorraine, CRAN CNRS UMR 7039, Nancy, France