Urinary Toxicity after Treatment of High Risk Prostate Cancer using HDR Brachytherapy Boost

CLINICAL ONCOLOGY Hills Road, Cambridge, UK; xUniversity of Cambridge Department of Oncology, Addenbrooke’s Hospital, Hills Road, Cambridge, UK Introduction: Patients with chordoma of the skull base present a complex radiotherapy planning problem, which may benefit from advanced techniques. Patients and methods: Between 1996 and 2005, 9 adult patients with skull base or cervical spine chordoma were treated with conformal photon radiotherapy (CRT) (including forward-planned IMRT), following surgery. Data for 8 cases were available. The patients were re-planned with inverse-planned IMRT solutions, and the dosimetry compared with the conventional results to see if there were any significant differences. The Equivalent Uniform Dose (EUD) for tumour and normal tissues was used to compare plans. Minimum and maximum doses, volume coverage by the 95% isodose, and doses to organs at risk were recorded. Results: The mean and median GTV were 30.9 and 23 cm3; the mean and median PTV were 120.8 and 114.1 cm3. In 5 cases, the PTV was greater than 100 cm3, and in 2 it reached approximately 200 cm3. The mean and median EUDs of the group were similar for the 2 planning methods means 92.5% and 93.6%; medians 97.9% and 94%, respectively. In 3 CRT cases the EUD fell below 90%, and in 2 IMRT significantly improved the dosimetry. In the 2 cases with very large PTVs, CRT provided worse coverage than IMRT. In 1 case, with the largest GTV, EUD with CRT was only 68%, improved to 94% with IMRT. In 5 cases, CRT provided excellent target volume coverage equivalent to an IMRT plan. For normal tissues, EUD values were similar for both planning methods, since the same constraints were used for both. Conclusions: In this group, for very large PTVs, IMRT would have conferred an important potential advantage. Where early efforts with CRT do not achieve good coverage, especially with a large PTV, switching to IMRT is worthwhile. EUD analysis can aid plan comparison in difficult cases. P24 On the Practicalities of Translational Radiobiology: Lessons from IORT (Intra-operative Radiotherapy) J. Gardner*, C. Y. Ackland*, A. M. Thompsony, S. J. Vaidyay, J. A. Dewar*, D. J. A. Adamson*, K. Armoogumz, C. D. Mackayz, A. J. Munro* *Department of Molecular Oncology, University of Dundee, UK; yDepartment of Surgery, University of Dundee, UK; zRadiotherapy Physics, University of Dundee, UK We have recently set up an IORT programme in Tayside to treat patients with solid tumours. The majority of patients with breast cancer who are treated with IORT are entered into a randomised trial (Target e website address insert here). The introduction of novel technologies into routine clinical practice presents both challenges and opportunities. We are exploiting the ability, provided by the IORT project, to obtain biopsies from normal tissues at and around the time of radiation treatment to provide a better understanding of the molecular response to radiation in normal tissues. Quality control is a key issue: we have to ensure that our sampling and processing procedures are rigorously controlled and reproducible on a day-today basis. This, in the context of a routine operating list, presents many practical difficulties. We will describe these problems, the protocols that we have devised to deal with them, and our experience so far in trying to bring translational research in radiobiology into the clinical environment. We gratefully acknowledge the Ninewells Cancer Campaign for supporting this research. P25 Urinary Toxicity after Treatment of High Risk Prostate Cancer using HDR Brachytherapy Boost S. A. Gayadeen, E. Armstrong, J. Solano, D. Souza, T. S. Sullivan, H. A. Payne University College Hospital London, UK Abstract not published

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P26 An Experimental Evaluation of Dosimetry for Targeted Radiotherapy J. Gear, E. Charles Edwards, M. Partridge, D. Flux Institute of Cancer Research In targeted radiotherapy, a radiolabelled cancer-targeting compound is delivered systemically. Despite the growing interest in these therapies calculation of absorbed dose to tumours and normal organs is not widely practised. There are currently a number of very different dosimetry techniques in use, and objective comparison between techniques is difficult. In addition, European directives and UK legislation now require dosimetry to be performed for all radiation therapies. There is therefore an urgent need for comparison, standardisation and validation of dosimetry methods. In this project we investigate the possible application of polymer gel dosimeters for radionuclide therapy. Such a method could provide an accurate, high-resolution and 3-dimensional method for independently validating existing dosimetry methods. Polymer gel dosimetry (developed for external beam radiotherapy) exploits radiation-induced polymerisation in the gel, the extent of which can be imaged and quantified using magnetic resonance imaging. For application to targeted radiotherapy, anatomical phantoms can be created and filled with gels containing the radioactive isotope of interest. We have investigated the potential of polymer gels for P32 and I-131 dosimetry. Different absorbed dose distributions within gel phantoms have been measured and compared using MRI and SPECT methods currently being employed at our centre. Compared to SPECT, MRI-based dosimetry is highly accurate, with the ability to measure absorbed dose to within 0.14 Gy. The poor spatial resolution of SPECT results in a misrepresentation of the absorbed dose distribution, including the loss of fine dose details and an apparent shift of the voxel containing the maximum absorbed dose. This situation is further amplified when high dose gradients are present. Using this method of polymer gel dosimetry we can begin to establish the limitations and accuracy in performing dosimetry calculations for targeted radiotherapy. In doing so, the validity of our dose calculations can be determined and used to establish a dose-response relationship for targeted radiotherapy.

P27 Audit of the Head and Neck Post Radiotherapy Allied Health Profession and Nurse Led Support Clinic J. Gemmill*, E. Rushbrook*, M. Pritchardy, S. West*, S. Jefferies*, R. Benson* *Cambridge University Hospitals NHS Foundation Trust Addenbrooke’s Hospital, Cambridge, UK; yNottingham City Hospital NHS Trust, Nottingham, UK Aim: Acute toxicity from head and neck irradiation is well documented. The head and neck post radiotherapy support clinic was set up in response to anecdotal, audit and focus group feedback, suggesting that a gap of 4e6 weeks after treatment cessation before the first follow up with medical staff is too long without review. Focus group patients mentioned depression, and that it would have been helpful to have seen someone during the 6 week interval after completing radiotherapy. The post radiotherapy clinic was audited in 2006 to evaluate efficiency of the clinic’s service delivery and patient satisfaction. Method: Patients were offered a multidisciplinary appointment to see a site specific specialist therapy radiographer and nurse, dietician and speech and language therapist. The clinic was audited retrospectively. 137 questionnaires were sent to head and neck patients reviewed from August 2004 to February 2006. 61% (84/137) anonymous replies were received. The clinical audit department analysed the responses and generated results. Results were measured against 13 standards. Results: Some questions were not answered by all patients in the questionnaires. 98%, 61 positive responses out of the 62 who answered the question, reported they found the clinic supportive. 81% (51/63) of patients found the post treatment phase easier to manage as a result of the appointment. 85% (40/47) felt their side