Cranio-Spinal Irradiation in low-middle income setting: A dosimetric comparison and literature review.

INTRODUCTION

Volumetric modulated arc therapy (VMAT) is a relatively new treatment technique in the middle-east and north African region. More so, is its application for cranio-spinal irradiation (CSI). We report the experience of this implementation in Tunisia, by comparing dosimetric outcomes between VMAT and Three-Dimensional Conformal Radiotherapy (3DCRT) and evaluating their efficiency in terms of treatment delivery time.

METHODS

We conducted an in-silico dosimetric study, on 29 patients treated with CSI. Patients treated with 3DCRT were replanned in VMAT and vice-versa. Doses to target volumes (TV) and organs at risk (OAR) were collected from the Treatment Planning System (TPS). Recorded treatment time was extracted from the TPS and beam-on-times were calculated.

RESULTS

VMAT provided higher TV coverage for CSI PTV (V95 % = 97.4 % vs 93.4 %, p < 0.001) and for boost PTV (96.3 % vs 93.4 %, p = 0.005). VMAT demonstrated better conformity (0.97 vs 0.93) and homogeneity (0.1 vs 0.26) indexes (p < 0.001). Both techniques met constraints for OAR, but neither achieved recommended limits for the skin, lens, or pituitary gland. VMAT showed lower maximum doses for the majority of OAR and achieved lower mean doses to the cochlea, parotids, heart, oesophagus, pancreas and bladder. However, it resulted in higher low doses to non-target tissue (V5Gy = 45.6 % vs 27.5 %, p < 0.001). Recorded treatment time was longer with VMAT compared to 3DCRT (1387 vs 683 s; p < 0.001), as well as the beam-on-time (453 and 162 s, p < 0.001).

CONCLUSION

VMAT offered improved TV coverage, conformity, and homogeneity. It protected some OAR better. This came at the expense of higher low-dose exposure to non-target tissue. Treatment times were longer with VMAT.

IMPLICATIONS FOR PRACTICE: Our study suggests the feasibility of implementing VMAT for CSI in low-middle-income countries. Follow-up is required to study the clinical translation of the dosimetric outcomes of VMAT.