Assessing Organ at Risk Doses and Dose Heterogeneity by Converting Isocenter Shifts to Absolute Couch Parameters in Craniospinal Irradiation

Abstract

Objective

To assess variation in organ at risk (OAR) doses and dose heterogeneity by converting isocenter shifts to absolute couch parameters in patients undergoing craniospinal irradiation (CSI).

Method

A total of 5 cases of standard risk medulloblastoma were selected from hospital database. Three additional treatment plans were generated for each case, with 3 consecutive shifts of 1 mm, 2 mm and 3 mm. A total dose of 2340 cGy was planned in 13 fractions at 180 cGy/fraction to craniospinal axis. Radiation technique, length of junction in cm, total number of junctions, reference and experimental doses to spinal cord and spinal canal along with maximum and minimum dose values relative to junction were recorded.

Results

Majority of patients (n=4, 80%) were between 6-20 years of age. Three patients (60%) were treated with Intensity Modulated Radiation Therapy (IMRT) and 2(40%) with Volumetric Modulated Arc Therapy (VMAT). Two (40%) patients had a junction at 10 cm, and the remaining patients (20%) at 3 cm, 4 cm, and 12 cm each. Three (60%) patients had 1 junction while 2(40%) had 2 junctions. Mean dose change in percentage for spinal cord was 0.98%(2.88), 1.46%(2.94) and 1.83%(2.99) for 1 mm, 2 mm and 3 mm shifts respectively. Mean dose change in percentage for spinal canal was 1.28%(2.3), 1.64%(2.7) and 1.82%(2.8) for 1mm, 2mm and 3mm shifts respectively. The maximum dose change relative to junction was 2.42%(3.6), 3.52%(6.1) and 3.96%(9) for 1mm, 2mm and 3mm shifts, respectively. The minimum dose change was 3.26%(6.3), 4.22%(8.2) and 7.08%(11.1) for 1mm, 2mm and 3mm shifts, respectively.

Conclusion

Our study explored the impact of various shifts in treatment planning for CSI, highlighting the importance of enhanced treatment delivery strategies to ensure optimal delivery of prescribed doses and reduce dose heterogeneity for patients undergoing CSI.