ESTRO 36 Abstract Book

S753

ESTRO 36 2017

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approach uses moderated dose-fractionation schedules

and IMRT to meet tolerance constraints of critical normal

tissues (even at the cost of reduced coverage of PTV)

aiming to achieve disease control with an acceptable

safety profile.

Material and Methods

We analysed radiotherapy planning, clinical parameters

and outcomes for twelve consecutive patients treated at

our cancer centre. Nine patients received 60 Gy in 8

fractions delivered on alternate days, and three patients

received 45-50 Gy in 10 daily fractions. All treatments

were delivered as prescribed on a Varian Clinac iX using

daily online CBCT imaging. The most common primary

tumour types were colorectal (eight) or renal (two), and

mean patient age was 68 years (range 38-89). Eight

patients had previously undergone surgical resection (six)

and/or ablation (four) of lung metastases, on up to three

occasions.

Results

Median PTV size was 48.5 cc (range 10.7-111.4 cc) and one

patient underwent treatment of two separate lesions

(combined volume 42.3 cc). For eleven patients the PTV

overlapped with proximal bronchial tree (PBT, comprises

trachea and bronchi up to second division), and for the

other patient the PTV overlapped the heart and chest

wall. For the portion of PTV not overlapping organs-at-

risk (OARs), mean D95 was 85.0% of prescribed dose (range

69.6-99.0%), and minimum dose to this volume was

between 56.4-86.8% of prescribed dose (mean 67.7%). All

mandatory OAR dose constraints were met, however the

‘optimal’ constraint for PBT was not possible to meet for

any patient with overlap of PTV with PBT (Dmax 0.5cc <

32.0 Gy). After median follow-up of 218 days (range 14-

389 days) only one patient has had in-field progressive

disease; this patient subsequently died of metastatic

disease. Four further patients have had distant

progressive disease, including one who has died but for

whom local disease was controlled at six months. One

patient showed complete response on CT at 6 months, and

all others have shown partial response or stable

disease. No patients suffered acute toxicity affecting

delivery of radiotherapy. One patient developed Grade 2

pneumonitis which resolved with steroids.

Conclusion

Using moderated dose-fractionation schedules and IMRT to

meet tolerance constraints of normal tissues appears to

enable safe and effective delivery of SBRT to central chest

oligometastatic disease. Treatment resulted in very low

incidence of toxicity and excellent rates of local control,

though ongoing follow-up will be required to detect late

toxicity and record long-term survival outcomes.

EP-1426 A model for internal target volume definition

based on 4D-cone beam computed tomography.

M. Di Tommaso

, A. Allajbej

, L. Caravatta

, S.

Giancaterino

, G. Di Girolamo

, M.D. Falco

, D. Genovesi

Ospedale Clinicizzato S.S. Annunziata, Radiotherapy,

Chieti, Italy

Purpose or Objective

To describe the procedure to build up the internal target

volume (ITV) in stereotactic body radiotherapy using 4D

three-dimensional cone-beam CT (4D-CBCT) and Simmetry

Elekta X-Ray volume imaging system (XVI).

Material and Methods

It was employed a dynamic thoracic phantom (CIRS Inc), a

ball-shaped polystyrene phantom with a sphere of known

volume equipped of a motor-driven platform, simulating a

sinusoidal movement with changeable motion amplitude

and frequency. To simulate target motion during a normal

breathing to the sphere it was applied a movement of ± 5

mm in antero-posterior and lateral direction, ± 10 mm in

superior-inferior direction. The frequency of respiratory

cycles was set to 1 cycle/3 seconds. A planning CT of the

CIRS phantom was performed using a 3 mm slice thickness.

CT images were exported to the Oncentra Masterplan (OM)

version 4.3. Planning target volume (PTV) was obtained by

adding an isotropic expansion of 0.8 cm to sphere (gross

tumor volume, GTV) delineated on CT “lung” window and

without inclusion of blurring effect. A test VMAT

treatment plan with identification of the isocenter at the

center of the PTV was created. A verification of the target

sphere position by means of Symmetry TM was performed.

4D-CBCT was acquired and subsequently sent to the OM to

verify the correspondence between volumes planning CT-

based and volumes obtained on CBCT 4D and to obtain ITV-

4D. GTVs were delineated on all phases of 4D-CBCT to

define ITV.

Results

Simmetry XVI

software appeared able to follow organ

movements. It was found from this study that ITV4D-CBCT

and PTV4D-CBCT were overlapped. The margin applied to

obtain CTV was reliable.

Conclusion

The 4D-CBCT with Simmetry XVI was adequate in providing

imaging-guidance for treatment of lung cancer and other

tumors occurring in site influenced by organ motion.

Simmetry XVI is a valid instrument to perform a

respiratory-gated radiation therapy when 4D planning CT

is not available. Actually, in our department, the

applicability of this procedure on patients continues to

be under investigation.

EP-1427 Peer reviewed radiation treatment planning

process at a university hospital in a developing country

B.M. Qureshi

, A.N. Abbasi

, N. Ali

, A. Hafiz

, M.U.

Karim

, A. Mansha

Aga Khan University Hospital, Radiation Oncology

Section- Dept. of Oncology, Karachi, Pakistan

Purpose or Objective

The study aimed to evaluate if peer review in weekly

simulation review meeting impacts the radiation therapy

treatment planning process in a resource limited setting.

Material and Methods

The study was done at the Radiation Oncology facility of

Aga Khan University, Karachi Pakistan for a period of 2

months. Simulation review meeting (SRM) was held

weekly during the study to discuss all the patients being

planned for radiation therapy in the presence of

consultants and residents. Each patient's contour of organ

at risk and treatment volumes or fields, total dose, dose

per fraction, number of phases etc are discussed after

being planned by primary radiation oncologist.

In this study, data was recorded for patients being planned

for radiation in weekly SRM in the presence of at least 2

radiation oncologist. Intent was recorded as radical or

palliative and discussion for all the patients including 2-D,

3D-CRT and IMRT was noted. The study included patients

of primary malignancies of different anatomic regions,

treated with external beam radiation therapy at our

institute except those who were planned and treated on

the same day. Impact of peer reviewed SRM was recorded

as 'no change', 'minor change' or major change in contour,

dose, field size or intent of treatment. This data was

recorded after approval of institutional ethical review

committee.

Results

Data was collected for a total of 116 patients, out of which

96 we planned with radical intent and 20 for palliation.

61% patients were planned with 3D-CRT technique & 26%

with IMRT. Major primary sites included head and neck

(40%), thorax (26%), pelvis (51%) and brain (12%). At least

three radiation oncologists were present in two third

meetings and changes were mostly made in with gross

tumor volume or clinical target volume. It was observed

that minor changes were made in 13% patients and major

change was done in the plans of 9% of patients.

Conclusion