waiting times for radical radiotherapy in nsclc

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Results: For phase 1, the IMRT techniques reduced the mean dose to normal supratentorial and infratentorial brain (STB and ITB) by 2 and 4 Gy, respectively. Greater high-dose sparing of normal brain was achieved by increasing treatment complexity with 20% (8e25%) of STB-PTV1 and 34% (30e40%) of ITB-PTV1 spared at 20 Gy with IMRT plans. Mean conformity indices were 2.76 (PP), 2.13 (3F), 2.05 (4F), 1.58 (4FIMRT) and 1.38 (7FIMRT) for phase 1. Replacing WBRT by WVRT in phase 1 reduced the total mean dose to STB-PTV2 and ITB-PTV2 by 8 Gy but no significant reduction for the pituitary and parotid glands. Conclusions: Replacing WBRT with WVRT has a larger effect on reducing normal-brain dose than WVRT technique selection. 7FIMRT offered the best phase 1 high-dose sparing. However, whether this leads to a clinically meaningful reduction in late sequelae remains unverified. P68 Waiting Times for Radical Radiotherapy in NSCLC R. Muirhead, N. O’Rourke Beatson Oncology Centre, Glasgow, UK Introduction: In 2000, O’Rourke et al. presented a single-centre prospective audit of 29 NSCLC patients, investigating waiting times and tumour growth. It demonstrated that of patients who were deemed suitable for curative treatment, 21% became incurable while awaiting radical radiotherapy. In the past five years there has been substantial investment in UK radiotherapy resources and increasing political emphasis on cancer waiting times. Simulta- neously the evolution of MDT working has facilitated patient journeys through investigation to treatment. We repeated this audit to assess the improvement over five years in the light of these changes. Method: All NSCLC patients presenting to NOR within 2005, judged fit enough for radical radiotherapy treatment, were identified. Using the case notes, CT scans and planning CT scans, data were correlated. Results: 29 patients were found to be appropriate for radical oncological treatment. Twenty required immediate radical radio- therapy with either CHART, SOCCAR, or standard radical radio- therapy. The median wait from the first oncology appointment to commencing radiotherapy was 28.5 days (range 18e45 days). Four patients from this group progressed while on the waiting list, 20% of this group. Discussion: Although the time to radiotherapy has improved since 2000, the number of patients who progress while waiting for treatment remains at 20%. In spite of increased radiotherapy resources, waiting times for certain categories of patients remain critical. The proportion of NSCLC patients suitable for radical treatment is low, but it is this select group with a chance of long term survival whose outcome is most at risk on a waiting list. Cancer waiting time targets ignore the differing urgency in treating different tumour types and prioritise all equally. We contend that this approach can only have an adverse effect on the survival of those patients with rapidly growing tumours. Solutions to this continuing problem require a new approach to the prioritisation of radiotherapy waiting lists. P69 Use of Rectal DSHs to Compare Forward and Inverse IMRT Treatment Planning for Prostate Cancer O. F. Naismith*, D. P. Dearnaleyy, A. M. Bidmead* *Department of Physics, Royal Marsden NHS Foundation Trust, Fulham Road, London, UK; yDepartment of Academic Radiotherapy, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK Introduction: The doseesurface histogram (DSH) provides an alternative to the doseevolume histogram (DVH) for estimating dose to the rectal wall. This study compares rectal surface dose distributions for forward and inverse IMRT plans for treating prostate cancer in the CHHIP trial, and contrasts the results with a DVH evaluation. A model linking the DSH and DVH results is investigated. Method: Forward and inverse IMRT plans were created for targets of both prostate with seminal vesicles (SVs) and prostate-only for 10 patients. DSH analysis of the rectum was performed to compare the two planning methods. The trends identified were compared for the prostate-only and prostate+SV plans. Results: The inverse plans achieved superior dose conformality to the PTVs, reducing dose to the rectum. Rectal DSH curves for inverse plans were significantly lower than for forward plans for doses R 60 Gy. The DSH results followed similar trends to the DVH analysis. However, the mean differences between forward and inverse plans, evaluated using relative surface areas and relative volumes, differed. At 100% prescribed dose (74 Gy) the difference between forward and inverse plans in terms of rectal exposure was greater using DSHs than DVHs: the mean relative rectal surface area exposed to 74 Gy for the 10 forward-planned prostate+SV cases was 2.2%, whereas the mean relative volume exposed was 0.6%. Both were 0% for inverse plans. At doses from 60 to 70 Gy the differences between forward and inverse plans using relative rectal surface areas were lower than the relative volume differences. A theoretical model of DSHs and DVHs, treating the rectum as a cylinder, predicted lower rectal volumes than measured due to the irregularity of the rectum and the curvature of the isodoses within the rectum. Conclusion: Analysis of rectal dose distributions using DSHs and DVHs confirms that, for treatment of the prostate, inverse planning may reduce the risk of rectal complications for the same degree of local tumour control, in particular when treating prostate+SVs. P70 Redefining Rectal Volume d with Particular Reference to Prostate Cancer Radiotherapy H. E. O’Donnell, P. N. Plowman Department of Radiotherapy, St Bartholomew’s Hospital, West Smithfield, London, UK With the development of conformal radiotherapy, scrutiny of the dosimetry of normal structures abutting a target volume has intensified, particularly when new technology allows higher radiation doses to be delivered to tumours with improved cure results, for example prostate cancer. During prostate radiotherapy planning, the rectum is defined by its mural perimeter (axial plane) between the dentate line (caudally) and peritoneal reflection (rostrally). Such a definition in ‘avoidance’ planning presupposes that rectal tolerance depends on ‘whole organ’ radiation tolerance (as does, for example, lung or kidney tolerance). However, rectal morbidity with modern prostate radiotherapy is determined by anterior rectal wall tolerance d occurring between the rostral and caudal limits of the PTV that, we would argue, is not dependent on whole organ tolerance. Particularly in the IMRT era, a redefinition of the relevant rectal volume is recommended. Dose volume histograms presented demonstrate the improved usefulness of the new method appraising the anterior rectal wall dose. P71 The Simulator d Has it Had its Day? A Study of Radiotherapy Verification H. E. O’Donnell, M. S. Griffiths, V. A. Harris, M. E. B. Powell Department of Radiotherapy, St Bartholomew’s Hospital, West Smithfield, London, UK Aim: Accuracy and reproducibility are essential in radiotherapy. In our centre the verification process starts in the simulator and continues with electronic portal imaging (EPI) during the course of treatment. Alteration to the set up during treatment using EPI is protocol-defined and dependent on accepted tolerances for treatment site and method of immobilisation and not based on a single image. At initial simulation, however, change to the set up may be made on this single visit without using such protocols. This prospective study looked at all stages of verification for CT planned patients to see whether any set up alterations made at simulation were validated at subsequent verification. S41 CLINICAL ONCOLOGY

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Results: For phase 1, the IMRT techniques reduced the mean doseto normal supratentorial and infratentorial brain (STB and ITB) by 2and 4 Gy, respectively. Greater high-dose sparing of normal brainwas achieved by increasing treatment complexity with 20% (8e25%)of STB-PTV1 and 34% (30e40%) of ITB-PTV1 spared at 20 Gy withIMRT plans. Mean conformity indices were 2.76 (PP), 2.13 (3F), 2.05(4F), 1.58 (4FIMRT) and 1.38 (7FIMRT) for phase 1. Replacing WBRTby WVRT in phase 1 reduced the total mean dose to STB-PTV2 andITB-PTV2 by 8 Gy but no significant reduction for the pituitary andparotid glands.Conclusions: Replacing WBRT with WVRT has a larger effect onreducing normal-brain dose than WVRT technique selection.7FIMRT offered the best phase 1 high-dose sparing. However,whether this leads to a clinically meaningful reduction in latesequelae remains unverified.

P68 Waiting Times for Radical Radiotherapy in NSCLCR. Muirhead, N. O’RourkeBeatson Oncology Centre, Glasgow, UK

Introduction: In 2000, O’Rourke et al. presented a single-centreprospective audit of 29 NSCLC patients, investigating waiting timesand tumour growth. It demonstrated that of patients who weredeemed suitable for curative treatment, 21% became incurablewhile awaiting radical radiotherapy. In the past five years there hasbeen substantial investment in UK radiotherapy resources andincreasing political emphasis on cancer waiting times. Simulta-neously the evolutionofMDTworkinghas facilitated patient journeysthrough investigation to treatment. We repeated this audit to assessthe improvement over five years in the light of these changes.Method: All NSCLC patients presenting to NOR within 2005, judgedfit enough for radical radiotherapy treatment, were identified.Using the case notes, CT scans and planning CT scans, data werecorrelated.Results: 29 patients were found to be appropriate for radicaloncological treatment. Twenty required immediate radical radio-therapy with either CHART, SOCCAR, or standard radical radio-therapy. The median wait from the first oncology appointment tocommencing radiotherapy was 28.5 days (range 18e45 days). Fourpatients from this group progressed while on the waiting list, 20% ofthis group.Discussion: Although the time to radiotherapy has improved since2000, the number of patients who progress while waiting fortreatment remains at 20%. In spite of increased radiotherapyresources, waiting times for certain categories of patients remaincritical. The proportion of NSCLC patients suitable for radicaltreatment is low, but it is this select group with a chance of longterm survival whose outcome is most at risk on a waiting list.Cancer waiting time targets ignore the differing urgency in treatingdifferent tumour types and prioritise all equally. We contend thatthis approach can only have an adverse effect on the survival ofthose patients with rapidly growing tumours. Solutions to thiscontinuing problem require a new approach to the prioritisation ofradiotherapy waiting lists.

P69 Use of Rectal DSHs to Compare Forward and Inverse IMRTTreatment Planning for Prostate Cancer

O. F. Naismith*, D. P. Dearnaleyy, A. M. Bidmead**Department of Physics, Royal Marsden NHS Foundation Trust,Fulham Road, London, UK; yDepartment of AcademicRadiotherapy, Institute of Cancer Research and Royal MarsdenNHS Foundation Trust, Sutton, Surrey, UK

Introduction: The doseesurface histogram (DSH) provides analternative to the doseevolume histogram (DVH) for estimatingdose to the rectal wall. This study compares rectal surface dosedistributions for forward and inverse IMRT plans for treatingprostate cancer in the CHHIP trial, and contrasts the results witha DVH evaluation. A model linking the DSH and DVH results isinvestigated.

Method: Forward and inverse IMRT plans were created for targetsof both prostate with seminal vesicles (SVs) and prostate-only for10 patients. DSH analysis of the rectum was performed to comparethe two planning methods. The trends identified were comparedfor the prostate-only and prostate+SV plans.Results: The inverse plans achieved superior dose conformality tothe PTVs, reducing dose to the rectum. Rectal DSH curves forinverse plans were significantly lower than for forward plans fordoses R 60 Gy.The DSH results followed similar trends to the DVH analysis.However, the mean differences between forward and inverseplans, evaluated using relative surface areas and relative volumes,differed. At 100% prescribed dose (74 Gy) the difference betweenforward and inverse plans in terms of rectal exposure was greaterusing DSHs than DVHs: the mean relative rectal surface areaexposed to 74 Gy for the 10 forward-planned prostate+SV cases was2.2%, whereas the mean relative volume exposed was 0.6%. Bothwere 0% for inverse plans. At doses from 60 to 70 Gy the differencesbetween forward and inverse plans using relative rectal surfaceareas were lower than the relative volume differences.A theoretical model of DSHs and DVHs, treating the rectum asa cylinder, predicted lower rectal volumes than measured due tothe irregularity of the rectum and the curvature of the isodoseswithin the rectum.Conclusion: Analysis of rectal dose distributions using DSHs andDVHs confirms that, for treatment of the prostate, inverse planningmay reduce the risk of rectal complications for the same degree oflocal tumour control, in particular when treating prostate+SVs.

P70 Redefining Rectal Volume d with Particular Reference toProstate Cancer Radiotherapy

H. E. O’Donnell, P. N. PlowmanDepartment of Radiotherapy, St Bartholomew’s Hospital,West Smithfield, London, UK

With the development of conformal radiotherapy, scrutiny of thedosimetry of normal structures abutting a target volume hasintensified, particularly when new technology allows higherradiation doses to be delivered to tumours with improved cureresults, for example prostate cancer. During prostate radiotherapyplanning, the rectum is defined by its mural perimeter (axial plane)between the dentate line (caudally) and peritoneal reflection(rostrally). Such a definition in ‘avoidance’ planning presupposesthat rectal tolerance depends on ‘whole organ’ radiation tolerance(as does, for example, lung or kidney tolerance). However, rectalmorbidity with modern prostate radiotherapy is determined byanterior rectal wall tolerance d occurring between the rostral andcaudal limits of the PTV that, we would argue, is not dependent onwhole organ tolerance. Particularly in the IMRT era, a redefinitionof the relevant rectal volume is recommended. Dose volumehistograms presented demonstrate the improved usefulness of thenew method appraising the anterior rectal wall dose.

P71 The Simulator d Has it Had its Day? A Study of RadiotherapyVerification

H. E. O’Donnell, M. S. Griffiths, V. A. Harris, M. E. B. PowellDepartment of Radiotherapy, St Bartholomew’s Hospital,West Smithfield, London, UK

Aim: Accuracy and reproducibility are essential in radiotherapy. Inour centre the verification process starts in the simulator andcontinues with electronic portal imaging (EPI) during the course oftreatment. Alteration to the set up during treatment using EPI isprotocol-defined and dependent on accepted tolerances fortreatment site and method of immobilisation and not based ona single image. At initial simulation, however, change to the set upmay be made on this single visit without using such protocols.This prospective study looked at all stages of verification for CTplanned patients to see whether any set up alterations made atsimulation were validated at subsequent verification.

S41CLINICAL ONCOLOGY