Program Information
Consequences of In-Correct Definition of Point A in CT Image Based Brachytherapy for Cervical Cancer
P Agarwal1*, J Swamidas2 , U Mahantshetty3 , S Chopra4 , D Deshpande5 , J Agarwal6 , (1) Tata Memorial Hospital, Mumbai, Maharashtra, (2) Tata Memorial Hospital, Navi Mumbai, Maharashtra, (3) Tata Memorial Hospital, Mumbai, Maharashtra, (4) Tata Memorial Hospital, Navi Mumbai, Maharashtra, (5) Tata Memorial Hospital, Mumbai, Maharashtra, (6) Tata Memorial Hospital, Mumbai, Maharashtra
Presentations
SU-I-GPD-T-49 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To quantify the consequences to the dose to OARs if incorrect definition of point A is done in CT image based brachytherapy for cervical cancer.
Methods: 12 patients diagnosed with cervical cancer, treated with Intracavitary brachytherapy in our institute during (three months) were analyzed. Tandem/ring applicator as with Tandem length 6cm and ring diameter 2.6 cm for all patients. Treatment planning (Oncentra Master plan v4.3) was done based on the standard institution protocol. The reference plan was made with definition of point A as per ABS/ICRU 89 recommendation. A dose of 7Gy was prescribed to point A, no optimization was carried out. To quantify the errors, deliberate shifting of the origin to define point A was introduced in the longitudinal direction (LD)along the uterine axis. This axis was chosen as it was the considered as the most error prone direction. The offset was done by 2mm, 4mm, 5mm superiorly and 2mm, 4mm inferiorly from the surface of ring. For each plan bladder, rectum and sigmoid doses were recorded for 2cc volume and Treatment time.
Results: For every 1mm error in the longitudinal direction in the definition of point A, the dose variation was 1% for all OARs. The mean (SD) percentage variation of D2cc for bladder for offsets of 5mm, 4mm, 2mm, -2mm and -4mm were 5.4±0.4, 4.3±0.26, 2.3±0.2, 2.9±0.5 and 6.2±0.6 respectively, similar values for rectum were 5.3±0.6, 4.4±0.4, 2.4±0.3, 2.9±0.4 and 6.2±0.6 and for sigmoid 5.4±0.4, 4.3±0.3, 2.3±0.2, 2.9±0.4 and 6.21±0.6. The percentage variation in Treatment time was found to be 2%, 3% and 6%, 5%, 4% respectively.
Conclusion: Quantification of dose variation for various OARs was quantified, when incorrect point A was defined by introducing error in the LD. It is estimated that similar values may be applicable to all other directions and rotation of ring.
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