Audit of radiographer led plan selection in imaged guided adaptive radiotherapy (IGART) for bladder cancer

Shaista Hafeez1,2, Helen McNair1,2, Karole Warren-Oseni1, Vibeke Hansen1,2, Robert Huddart1,2 The Royal Marsden NHS Foundation Trust1 The Institute of Cancer Research2, Sutton, Surrey, United Kingdom

Introduction Variation in bladder shape and position significantly compromises target coverage during standard radiotherapy despite use of large population based expansions [1].

Standard Plan selection was deemed appropriate if •  online radiographer plan selection used for treatment

matched off line plan selection by clinician. A >90% agreement was deemed acceptable [3]

•  target coverage of the bladder as assessed on cone

beam CT, CBCT (pre and post radiotherapy) was in accordance with ICRU-83 guidelines; achieving D98% >95% of prescribed dose [5]

Action plan Development of advanced competency-training workbook, illustrating consistent and inconsistent plan selection. Re-audit to ensure competencies maintained.

Method Patients receiving daily PoD bladder IMRT were assessed.

Conclusion Suitability trained radiographers deliver PoD for bladder cancer with good concordance with clinicians. Plan selection also adequately accounts for intra-fraction filling without compromise to target coverage.

We acknowledge NHS funding to the NIHR Biomedical Research Centre for Cancer and to Cancer Research UK (CRUK)

Results 125 CBCTs (63 pre; 62 post radiotherapy) were evaluated. Concordance of plan selection was 92% (58/63).

In accordance with NRAG recommendation to maximise use of a multi-skilled workforce, we have implemented radiographer led on-line verification and plan selection for those who have completed in-house training for bladder IGART [4]. This audit was performed to ensure that radiographers achieving initial competency maintained appropriate standards for treatment delivery.

Cone beam CT (CBCT) allows soft tissue visualisation and offers IGART planning solutions to compensate for this day-to-day variation with both improved target coverage and normal t issue sparing [2]. The plan of the day (PoD) strategy accesses a library of plans for treatment based on CBCT assessment immediately prior to each fraction [2,3].

Presumed empty bladder (patient asked to void on both occasions

Impact of rectal filling on bladder shape

variable margin used to create 3 PTV contours (small, medium, large) from which library of 3 plans created

Following automatic bone registration, PTV contours (small, medium, large) overlaid, assessment made to determine appropriate PTV contour covering bladder (with minimal normal tissue irradiation)

made. Treatment delivered with corresponding plan.

Planning CT

CBCT acquired prior to radiotherapy treatment delivery

Following treatment CBCT images were imported into the planning system (Pinnacle version 9.6). A clinical oncologist carried out off-line PoD selection for all pre-radiotherapy CBCTs. The bladder was contoured on each CBCT; the isodoses were overlaid to determine D98%. The time between pre and post radiotherapy CBCTs was used as a surrogate of plan selection and treatment delivery time.

Radiographer led plan selection for bladder IGART

Example of stepwise approach for plan selection

CBCT image acquisition and contrast adjustment registration to bone

Large PTV contour chosen, treatment delivered with corresponding plan (large)

Right to left shift made to determine if coverage of medium PTV could be optimized, however remains tight (arrow)

Assessment of PTV contours made by 2 trained radiographers; appropriate coverage of bladder

with minimal normal tissue selected, recommendation to include contour with 3mm

margin from bladder wall to account for bladder filling during treatment

References 1.Lalondrelle S, Huddart R: Improving radiotherapy for bladder cancer: an opportunity to integrate new technologies. Clin Oncol (R Coll Radiol) 2009, 21(5):380-384. 2.Lalondrelle S et al., Adaptive-predictive organ localization using cone-beam computed tomography for improved accuracy in external beam radiotherapy for bladder cancer. Int J Radiat Oncol Biol Phys 2011, 79(3):705-712. 3.McDonald F et al: Clinical implementation of adaptive hypofractionated bladder radiotherapy for improvement in normal tissue irradiation. Clin Oncol (R Coll Radiol) 2013, 25(9):549-556. 4.Radiotherapy: developing a world class service for England Report to Ministers from National Radiotherapy Advisory Group. 2007. 5. ICRU Report 83 Prescribing, Recording, and Reporting Intensity-Modulated Photon-Beam Therapy (IMRT). 2010.

32%

54%

14%

Radiographer plan selection

small medium large

34%

53%

13%

Clinician plan selection

small medium large

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Tim

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CBCT

Time between individual pre and post CBCT (surrogate for plan selection and treatment delivery time)

Mean time between pre and post CBCTs was 13 minutes (SD 2.1, range 9-18).

Mean intra-fraction filling was 14cm3 (SD 16.3, range 0.23-107.9). Mean D98% pre-RT CBCT was 99.1% (SD 1.09, range 95.5-100). Mean D98% post-RT CBCT was 98.7% (SD 1.78, range 89.9-100).

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D98% of individual paired CBCT (pre and post radiotherapy treatment) pre treatment CBCT post treatment CBCT