Purpose: Identify an MU-efficient treatment planning methodology that maintains the dosimetric quality of the treatment plan.
Methods: Seventeen hypofractionated (7-18Gy/fx) and twenty-five conventional fractionated (1.8-3Gy/fx) volumetric modulated arc therapy (VMAT) treatment plans were selected utilizing the Varian Eclipse™ version AcurosXB_15.6. The treatment sites included H&N, lung, liver, and prostate. A base plan was created without utilizing the MU objective tool. Then, an MU-efficient plan was created by utilizing the MU objective tool with a strength setting of 70, a lower objective of zero, and an upper objective (MaxMU) of different values. Dosimetric quality and MU-efficient metrics were used to compare the base plan and the MU-efficient plan. The MaxMU parameter was identified for each treatment site that best reduced the total MU, but at the same time gave a similar to or better plan than the base plan by as determined by fulfilment of the dose constraint metrics.
Results: For the hypofractionated lung and liver plans, a MaxMU of 1.25 times the prescription dose per fraction (1.25x) resulted in the total MU reduction by 24% and 25% respectively. For the hypo-fractionated prostate, a MaxMU of 2x resulted in the total MU reduction by 13%. For the conventional fractionated bilateral H&N and prostate with lymph nodes plans, a MaxMU of 600MU resulted in the total MU reduction by 19% and 15% respectively. For the conventional fractionated unilateral H&N and prostate minus lymph nodes plans, a MaxMU of 400MU resulted in the total MU reduction by 13% and 18% respectively. MU-efficient plans with the above-mentioned MaxMUs resulted in similar plans compared to the base plans, and in some cases, gave better dosimetric results for OARs.
Conclusion: The MaxMU for four studied sites were identified that led to the optimum MU reduction without sacrificing target coverage or any other studied plan quality metrics.
Treatment Planning, Treatment Techniques
TH- External Beam- Photons: treatment planning/virtual clinical studies