Dosimetric comparison of sequential planning (SP) versus bias dose planning (BDP) in volumetric modulated arc therapy
Thirumal Mani1, Palanivelu Duraikannu2, Chandramouli Ramalingam1
1Department of Radiations Oncology, All India Institute of Medical Sciences (AIIMS), Bibinagar, Hyderabad, Telangana, India.
Aim/Purpose:
This study aims to evaluate and compare the dosimetric parameters of breast cancer radiotherapy plans using Volumetric Modulated Arc Therapy (VMAT), specifically contrasting the use of the bias dose planning (BDP) feature with sequential planning (SP) without bias in the Monaco Treatment Planning System (TPS).
Materials And Methods:
A total of twenty left breast carcinoma patients were randomly selected for this study, which followed a two-phase treatment regimen. In Phase 1, a dose of 40 Gy was delivered using the Elekta Versa HD, and the treatment plans were generated with 6 MV beams in the Monaco TPS using the VMAT technique. Phase 2 involved a sequential boost, delivering an additional 12.5 Gy, also using VMAT. For each patient, two treatment plans were created for Phase 2: one utilizing the BDP feature and the other SP, allowing for a direct dosimetric comparison of target volume, Organ at risk (OAR), normal tissue exposures, conformity index (CI) and Homogeneity index (HI).
Results:
Both the BDP and SP achieved comparable target volume coverage, with similar conformity and homogeneity indices. However, BDP demonstrated better sparing of OARs. Specifically, BDP significantly reduced the mean doses to the left lung (1496.4 ± 47.9 cGy vs. 1594 ± 189.3 cGy), right lung (465.9 ± 109.1 cGy vs. 591.6 ± 251.4 cGy), and heart (770.1 ± 232.0 cGy vs. 970.2 ± 65.5 cGy) compared to SP (all p < 0.05). Additionally, volume-based metrics, including V20 and V5Gy, consistently favored BDP. There was no substantial difference in the absolute volumes (cc) of the Body-PTV structure receiving 10% to 90% of the prescription dose between the BDP and SP plans, and the differences were not statistically significant (P ≥ 0.05). These findings underscore the dosimetric advantage of BDP in minimizing radiation exposure to critical structures without compromising target coverage.
Conclusion:
The integration of the bias dose feature in VMAT-based breast cancer radiotherapy planning offers dosimetric advantages by improving sparing of critical organs without compromising target coverage or plan quality. This study highlights the importance of incorporating bias dose planning (BDP) in multiphase breast radiotherapy, especially when sequential boosts are required and supports its suitability for adoption in routine clinical practice.
