Importance of Aortic Bifurcation for Pelvic Radiotherapy in Cervical Cancer Patients

Purpose: Radiotherapy is a major modality for treating cervical cancer patients. Conventionally, superior border of treatment portal in cervical cancer is kept at L4-L5 intervertebral spaces; however, newer concepts suggest that aortic bifurcation should be the determining factor for the superior border. This study aims to observe the level of aortic bifurcation in cervical cancer patients. Methods and materials: A retrospective observational study was conducted in cervical cancer patients undergoing radiotherapy between July 2019 and August 2020 in B.P. Koirala Memorial Cancer Hospital, Bharatpur. Histologically confirmed International Federation of Gynecology and Obstetrics (FIGO) stages II and III carcinoma cervix patients referred for radiation therapy were included in the study. Baseline variables including age group, FIGO stages were noted from the hospital record. Computed Tomography (CT) simulation images were reviewed from the treatment planning system to detect the levels of aortic bifurcations. Results: Total 281 patients of carcinoma cervix were registered for the study with age ranging from 29 years to 87 years and the commonest age group being 51-60. The maximum patients were of stage IIB (46.6%). The aortic bifurcations levels varied from mid L3 to L5-S1 intervertebral space and the commonest level observed was mid L4 vertebra in 70 (24.9%) patients. Conclusion: Anatomical variation in the level of aortic bifurcation, considered as the superior CTV border in pelvic radiotherapy in cervical cancer, demands the conventional superior border, L4-L5 intervertebral space, to be shifted more superior to include common iliac nodes in the treatment field.


Introduction:
Globally, cervical cancer accounts for over half a million of new cases annually. 1In Nepal, it is still the commonest cancers among females and over 2,000 new cases of cervical cancer are reported each year. 2 Radiotherapy, a combination of external beam radiotherapy and brachytherapy has been the standard of treatment for cervical cancer. 3though relentless advancements in external beam radiotherapy delivering techniques for carcinoma cervix in the form three dimensional-conformal radiotherapy, intensity-modulated radiotherapy, volumetricmodulated arc therapy, have been made, in the developing countries like ours where patient burden is high but health resourced are limited, two dimensional conventional treatment modalities are still in use for treating those patients.
The conventional Anterio-posterior (AP)posterio-anterior (PA) parallel-opposed fields or AP-PA fields with two additional lateral fields (four-field box techniques) are used for delivering pelvic radiotherapy. 3The aim of pelvic radiotherapy in such patients is to cover the main tumor bulk in cervix and its local extensions, and regional pelvic lymph nodes which include common iliac, external and internal iliac, obturator, and presacral nodes. 3The traditional superior border of the pelvic field lies at the level of L4-L5 intervertebral space.However, the newer consensus guidelines for conformal radiotherapy have come with the concept of aortic bifurcation being used as the superior clinical target volume (CTV) for pelvic radiotherapy in cervical cancer patients and it is also reported from the past studies that there is an individual variation in the level of aortic bifurcation. 4,5,6This study aims to observe the level of aortic bifurcation in c e r v i c a l c a n c e r p a t i e n t s r e c e i v i n g radiotherapy among Nepalese population.

A total of 281 patients of carcinoma cervix
were registered for the study.The age of the patients ranged from 29 years to 87 years with the commonest age group ranging between 51 years and 60 years.[Table 1] The maximum number of patients belonged to FIGO stage IIB (46.6%).[Table 1] The levels of aortic bifurcations varied from mid L3 to L 5 -S 1 i n t e r v e r t e b r a l s p a c e a n d t h e commonest level of aortic bifurcation was observed at mid L4 vertebra in 70 (24.9%)patients.[Table 2 and   where CT simulator is not available, the traditional superior border needs to be shifted more superior.

A
FIGO stages were retrieved from hospital record.Computed Tomography (CT) simulation axial sections of 3mm thickness extending from T12-L1 to mid-thigh which were utilized for conventional treatment planning were reviewed retrospectively from the treatment planning system.The vertebral levels of aortic bifurcations were then recorded separately for each case by determining the bifurcation in axial sections and then correlating the vertebral levels in sagittal sections.

Figure 1 ]
DiscussionThe present study was conducted to find out the vertebral level of aortic bifurcation among 281 patients receiving pelvic radiotherapy for cervical cancer.There was a great variation in the level of division of abdominal aorta into right and left common iliac branches and the most common being body of L4 vertebrae especially at the mid-level.Majority of the previous studies have demonstrated similar results that the abdominal aorta divides at the level of body of L4 vertebra in most of the patients; however, the upper, mid and lower level at the L4 vertebral body had differed.7,8,9,10

Table 2 :
Vertebral level of aortic bifurcation