Does conformal therapy improve dose distribution in comparison to old techniques in teleradiotherapy of cervical cancer patients?

Abstract

Background

The use of a combined modality approach – chemotherapy and radiation therapy – in the treatment of patients with cervical cancer is associated with significant toxicity, mainly haematological and gastrointestinal. Conformal radiotherapy has the potential to deliver an adequate dose to the target structures while sparing the normal tissue. Both the radiation dose to the small bowel and the volume are factors known to influence the risk of complications.

Aim

The aim of this study was to determine whether the implementation of conformal modality can reduce the volume of normal tissue included in the RT field.

Methods and Materials

14 cervical cancer patients (FIGO IIB and IIIB) treated with conformal radiotherapy concurrently with cisplatin (40 mg/m²) administration once a week were analyzed. According to ICRU 50 recommendations target volumes and the organs at risk were contoured on CT slices. For the gross tumour volume (GTV) the tumour of the uterus and cervix was traced. The clinical target volume (CTV) was defined as the vessels and lymph nodes from the obturator level to the aortic bifurcation, presacral region, and upper 1/3 of the vagina. The margin for planning target volume (PTV) was added. The normal tissue region included the small bowel, large bowel and bladder. Using a 3D system and multi-leaf collimator a four-field treatment plan was performed for each patient. All 14 patients were treated with radiotherapy using these conformal 3D plans. Additionally (just for study purposes) for each patient we prepared two simpler plans with (1) two-field: anterior-posterior (A-P) and posterior-anterior (P-A); and (2) four-field box techniques. Dose-volume histograms of target volumes and organs at risk were calculated for each three plans for every patient and compared. Analysis of variance was performed to compute the statistical significance.

Results

There is no statistical difference between doses received by target volumes – in each plan PTV is covered by the 95% isodose. Significantly different volumes of critical organs were included in the treatment field, depending on radiotherapy technique (conformal 3D method vs AP–PA two-field method): rectum 96.82% vs 38.23%, bowels 61.37% vs 30.79%.

Conclusion

These data suggest that implementation of conformal radiotherapy can reduce the irradiated volume in all the contoured critical organs, especially the bowels, compared to old techniques.