ESTRO 36 Abstract Book

S994

ESTRO 36 2017

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The goal of the study was to compare two different

respiratory gating techniques to treat left-sided breast

cancer with Deep Inspiration Breath Hold (DIBH): infrared

tracking

camera

with a reflective marker (RPM, Varian)

and the optical surface monitoring system (OSMS, Varian)

and to improve our daily radiation therapy workflow.

Material and Methods

9 breast cancer patients, undergoing DIBH were treated in

our clinic using 3D tangential fields. They were positioned

supine, on the C-QualTM Breastboard (CIVCO Medical

Solutions). Before the first treatment the patient

reference breathing curve was imported to a linac

treatment workstation together with calculated

thresholds. Additionally, the reference surface from the

CT scan in free-breathing (FB) as well as in DIBH were

imported to the OSMS and the region of interest was

selected. Patients were leveled according to the CT

reference marks and then positioned with OSMS using FB

surface from CT (5 patients) or acquired FB surface on the

first day of treatment (4 patients). After aligning the

patient, MV imaging in DIBH based on RPM was done and

bone match on the chest wall was used to correct for

positioning error. OSMS deltas using the DIBH surface,

acquired before performing the couch shifts, were

assessed against MV imaging results in the breath hold for

every patient to compare the two methods.

Results

Positioning based on OSMS was in good agreement with the

positioning based on RPM and MV imaging. The mean 3D

deviation between the two techniques was within 5mm

accuracy. The FB reference surface from CT was found less

reliable than the one obtained on the first day of the

treatment. For 2 patients, the CT reference DIBH surface

shown more than 5mm discrepancy compared to MV

imaging with RPM and a new one was taken on the first

day of the treatment and used for consecutive treatments.

OSMS detected patient pitch of up to 10 degrees.

Conclusion

According to our preliminary data, DIBH patient

positioning based on OSMS is feasible and reproducible.

More data will be collected to confirm these findings and

shifts of patients based on the DIBH reference surface,

before performing MV imaging, will be implemented into

the

workflow.

EP-1843 An audit evaluating the frequency of patient

re-preparation after CBCT analysis in prostate IMRT

K. Crowther

Cancer Centre- Belfast City Hospital, Radiotherapy,

Belfast, United Kingdom

Purpose or Objective

As imaging techniques have advanced and kV-CBCT is now

routinely used to verify prostate radiotherapy (RT),

changes in bladder and rectal volume affecting the

position of the prostate can be seen. The consequences of

this can potentially lead to a reduction in PTV

coverage, an increase in treatment toxicity, and even

biochemical failure. Patients should be treated with a

‘comfortably full’ bladder and an empty rectum with the

aims of reducing rectal distension and minimising prostate

movement

Material and Methods

All kV-CBCT images for patients receiving prostate IMRT

on a treatment unit were examined over a one month

period. All patients followed the departmental

Bladder/Bowel preparation pathway- patients' self-

administer daily micro-enemas and follow a simple

bladder filling protocol (500 mls of water, 45 mins prior to

treatment). The departmental prostate CBCT protocol

was used (minimum day 1-3 and weekly). A record of

patients requiring re-prep after analysis of CBCT was kept

with details of the action taken. The data recorded was

reviewed to identify any trends and to quantify the impact

on daily workflow.

Results

In total 137 scan sets were acquired during this time

period. In the majority of cases (89.78%) treatment was

delivered as planned after analysis of initial CBCT.

In 14 cases (10.22%) after acquiring the CBCT the

patient was taken off the treatment couch. Three were

due to the patient experiencing urinary urgency

and needing to void.

The

remaining 11 cases after analysis of the CBCT variation in

rectal distension and/or bladder filling was observed and

the radiographers did not continue to treatment

delivery (Figure 1).

A summary of the results is shown in Table 1.The mean

delay caused on the treatment unit was 15 minutes (mins)

(range 0-20), this equates to on average 210 mins per

month or 21 treatment slots. The time taken from image

acquisition to decision to take the patient off the

treatment couch mean was 3.21 mins (range 1-6).

Scheduled appointment time to time of CBCT acquisition

mean was 7.6 mins (range 1-18). A variety of instructions

were given to patients with inconsistencies observed with

regards to bladder filling.

Conclusion

This is a small sample but it has highlighted important

issues seen within this patient population. Patient

compliance with preparation and the instructions given to

patients who require re-prep are important. Guidance and

training should be available to ensure consistency in

patient instructions. With the introduction of more

advanced prostate RT, the demand for IGRT will continue

to increase; this will have an impact on the daily workflow

with the potential to increase patient waiting times if

issues such as patient compliance with preparation

instructions are not addressed.

Electronic Poster: RTT track: Motion management and

adaptive strategies

EP-1844 Clinical introduction of simple adaptive

radiotherapy for transitional cell bladder carcinoma

N.J.W. Willems

, P.S. Kroon

, J.C.J. De Boer

, G.J.

Meijer

, J.R.N. Van der Voort van Zyp

, J.L. Noteboom

UMC Utrecht, radiotherapy, Utrecht, The Netherlands

Purpose or Objective