2D vs. 3D EXTERNAL BEAM PLANNING IN CERVICAL CANCER

ANOMALIES IN TREATMENT VOLUME

ObjectiveTo estimate inadequacies in target volume coverage when using conventional planning based on bony landmarks.

EXTERNAL BEAM RADIOTHERAPY• (EBRT) plays an important role in the management of patients with

carcinoma cervix.• Whole pelvis is treated including clinically and radiologically apparent

tumour, uterine corpus, upper part of vagina, parametrium, and the draining lymph nodes.• The central disease can further be boosted by intracavitary

brachytherapy.

EBRT CONT’D• 2D planning is based on bony landmarks delivered by (AP-PA) parallel

opposed fields & opposed laterals (conventional four field planning).

• May provide good coverage to the target volume.

• Has few disadvantages.

3D CT BASED PLANNING• Preferred EBRT technique for cervical carcinomas.

• The conformal four field box technique with parallel opposed AP-PA fields and two lateral opposed fields (3D Planning).

• CTV and OAR are delineated prior to placement of beams.

2 Dimensional 3 Dimensional

METHODOLOGY• 30 patients of locally advanced uterine cervix cancer FIGO stage III A-

III B registered at Cancer Care Kenya were planned during the period January – August 2014.• Radical radiation of 50Gy delivered in 25 fractions over 5 weeks.• With concurrent chemotherapy.

• Central disease is boosted by intracavitary brachytherapy.

METHODOLOGY CONT’D• The clinically and the radiologically visualized primary tumour, was

included in the clinical target volume (CTV).

• CTV was delineated from the bifurcation of aorta.

• Bladder and Rectum (OAR) were delineated as per their extent.

METHODOLOGY CONT’D•Placement of beams on the Digitally Reconstructed

Radiograph (DRR).

• Two Parallel opposed and two Lateral opposed fields (Four Field Box Technique).

METHODOLOGY CONT’D• Conventional four field plan generated using the standard bony

landmarks.• AP-PA Sup:L4-L5 junction,Inf. Under ischial tuberosity• RL-LL Post: S2-S3 junction, Ant.:Include symphisis

• The target volume delineated previously was then projected onto the DRR.

• The volume of the target receiving at least 95% of the prescribed dose was calculated (V95). V95 for 2D was subtracted from the V95 for 3D .

RESULTSPATIENT

2D PLAN 3D PLAN

Bladder Rectum CTV V95 Bladder Rectum CTV V95(Gy) (Gy) (Gy) % (Gy) (Gy) (Gy) %

PATIENT A 49.662 46.087 49.135 93.8 50.151 42.306 50.073 98.8

PATIENT B 43.010 41.160 49.873 99.7 42.942 41,182 50.380 99.9

PATIENT C 29.215 31.943 34.965 91.7 28.018 31.983 36.074 100.0

PATIENT D 45.974 44.827 45.165 81.0 44.552 39.104 49.788 98.9

PATIENT E 49.393 41.193 49.575 98.9 46.676 42.628 49.899 99.3

PATIENT F 47.061 48.076 48.996 99.8 48.717 39.604 49.648 99.8

RESULTS CONT’D• Mean V95 for 2D plans 93.67 %

• Mean V95 for 3D plans 99.50 %

• In only 1 patient (3.33%) out of 30 was the whole of the target volume encompassed by the conventional four field marked on bony landmarks.

2D planning encompassed whole CTV Same for 3D

Doses to OAR for 2D and 3D• Mean dose to bladder and

rectum 44.053 Gy & 42.214Gy respectively.

• Median dose to bladder and rectum 49.975Gy & 47.810 Gy respectively.

• Mean dose to bladder and rectum 40.509 Gy & 39.468 Gy respectively.

• Median dose to bladder and rectum 45.885 Gy & 44.895 Gy respectively.

RESULTS CONT’D• The areas of miss were at the anterior and posterior border of the lateral

fields and the superior borders of the anterior-posterior fields.

• The median miss at the anterior and posterior borders was 3.135cm, and the maximum was 3.17cm

• The median miss at the superior borders was 1.365cm, and the maximum was 1.75cm

• The median V95 for conventional fields marked with bony landmarks was only 95.35% as compared to 99.55% for target delineation based on CT contouring.

Conclusion and Recommendation • Target volume miss in 29 out of 30 cases thus study shows

inadequate CTV coverage with conventional Four field technique. • Increase in dose to OAR with conventional planning.• 3D CT-based treatment planning for advanced cases of

uterine cervix carcinoma is recommended.