Service Evaluation Investigating The Potential Role Of External Beam Radiotherapy For A Solitary Pelvic Node Recurrence Following Adjuvant Vaginal Brachytherapy
(2014) Service Evaluation Investigating The Potential Role Of External Beam Radiotherapy For A Solitary Pelvic Node Recurrence Following Adjuvant Vaginal Brachytherapy, no. 93.
Aim: To establish whether a radical dose of external beam radiotherapy (EBRT) can be given to intermediate risk endometrial cancer patients with a solitary pelvic node recurrence, who have previously been treated with vaginal vault brachytherapy (VVB), without exceeding the dose tolerance of the pelvic organs at risk (OAR). Objectives: To calculate the total dose each OAR would be exposed to after VVB and EBRT and assess whether the OAR doses breach the departments dose tolerances; to determine whether the doses to OAR can be predicted by knowing the VVB OAR dose alone; to determine what factors influence the total dose given to OAR after VVB and EBRT is given. Methods: A retrospective service evaluation was carried out on previously treated VVB computed tomography (CT) datasets. A simple conformal radical dose EBRT plan, covering a solitary pelvic node recurrence, was created on each dataset and the total dose the OAR are exposed to was assess for OAR dose tolerance breach. The percentage of patients whose total OAR doses exceeded the OAR dose tolerances was then calculated. The percentage deviation between VVB OAR dose and the total OAR dose was worked out and assessed for a common trend. A Spearman's correlation coefficient score was used to determine a relationship between the volume of the OAR and the two treatment plan OAR doses. Results: 80 patient CT datasets were used in the service evaluation. 67 per cent (%) of patients were able to receive a radical dose simple oblique EBRT plan without exceeding the OAR dose tolerances. There was no consistent percentage deviation between VVB OAR doses and total OAR doses and, therefore, the total dose cannot be predicted. A strong positive relationship exists between the bladder volume and EBRT dose (0.516, p<0.001); the rectum volume and VVB dose (0.59, p<0.001) and EBRT dose (0.628, p<0.001); the small bowel volume and VVB dose (0.605, p< 0.001) and EBRT dose (0.702, p<0.001). Conclusion: The simple EBRT plan used shows it is possible for the majority of patients to undergo further irradiation to the pelvis without overdosing the OAR. The total dose to the OAR varies from patient to patient and is dependent on the position of the OAR within the pelvis and the volume of the OAR. Use of a more complex treatment planning technique and introduction of organ preparation would likely increase the number of patients able to receive EBRT without OAR dose tolerance breach. Further studies utilising these OAR dose reduction methods is warranted.