Improvement of matching fields using coplanar field border method in postmastectomy radiotherapy

Aim: To propose a new matching method for the supraclavicular (SC) and tangential fields on three-dimensional radiotherapy (3DRT) for postmastectomy radiotherapy (PMRT). Methods: A method of matching coplanar field borders (CFB) between the tangential and SC fields was created in 3DRT. The collimator angle of the medial tangential field was calculated to coplanar the SC field. The proposed method performance was ultimately benchmarked using the half beam block (HBB) and traditional three-field monoisocenter (TTM) methods by dosimetric comparison. The decision score was then employed to clarify the performance among these methods. Results: The results show that the TTM method exhibited not only low doses on the organs at risk (OAR) but also on the matching fields. The CFB and HBB produced comparable results, but the ipsilateral lung yielded lesser amounts than the HBB. The decision score indicated a low performance level when using the TTM method, whereas the CBF method exhibited a slightly higher performance score than the HBB. Findings: The CFB exhibited good performance in terms of the dose on OARs and at the matching fields. This method offers a comparable level of performance to the HBB. Thus, the CFB offers an alternative method of significant interest in PMRT.

Dosimetric study on the use of Eclipse beam angle optimiser for conformal planning

Aim: The aim of this study was to evaluate the use of Eclipse’s beam angle optimiser (BAO) for three-dimensional conformal radiotherapy planning. Materials and methods: Eleven 3D conformal lung plans, with varied tumour volumes, were retrospectively studied. For each clinical plan, a BAO plan was produced and then optimised by an experienced planner. Plan quality was assessed using International Commission on Radiation Units and Measurements (ICRU)-83 and Radiation Therapy Oncology Group (RTOG) recommended dose reporting metrics for dose volume prescribing and reporting. Results: Differences in dose volume histograms for both methods showed no clinical significance. Planning target volume Dmax for both plans was comparable and within ICRU guidelines. Reported spinal cord Dmax and the doses to 33% and 67% volume of the heart were within the RTOG recommended limits. Mean lung V20 values for BAO and non-BAO plans were 20 and 16%, respectively. The average monitor units for the BAO plans were about 11% lower. The conformity and homogeneity indices were within the acceptable range for both cases. On average, it took 23 minutes to plan using the BAO compared to 68 minutes for the non-BAO plans. Conclusion: Eclipse BAO shows the potential to produce good quality conformal plans and reduce planning time. This process could be further refined with multi-leaf collimator and optimal collimator angle options.

Estimation of Out-of-Field Dose Variation using Markus Ionization Chamber Detector

Objective: The aim of This work to provide evaluation for the out-of-field dose with different plan parameters as field size and depth using Markus ionization chamber detector in the measurement that are frequently used in electron and superficial dosimetery, in radiotherapy. Methods: This is carried out through the application of these detector in estimation of the out-of-field dose with important dosimetric parameters such as field size (from 5×5 to 30×30 cm2) and depth (from 1.5 to 30 cm) at energy 6 MV and collimator angle 0° at SSD 100 cm. Results: Results show that, the Markus detector reported an increase in out-of-field dose with field size, depth in almost all measurements. For 6 MV and 0° collimator angle, the out-of-field dose at field size of 5×5 cm2 (depth of 1.5 cm) is 1.1% and at field size of 30×30 cm2 (depth of 1.5 cm) is 4.4% . The out-of-field dose for a depth of 1.5 cm (field size of 10×10 cm2) is 2.3% and for a depth of 30 cm (field size of 10×10 cm) is 5.5%. the measured out-of-field dose by Markus detector overestimated in the calculated at different field sizes (2.7% instead of 2.3% at field size of 10×10 cm2 and 5.2% instead of 4.4% at field size of 30×30 cm2) and different depths (2.7% instead of 1.1% at depth of 1.5 cm and 4.1% instead of 3.4% at depth of 30 cm). Analysis: The result reported an increase in mean out-of-field dose with field size, depth, energy and SSD. Markus ionization chamber detector show overestimation of the measured out-of-field dose in the calculated values at all field sizes and depths, this may be attributed to the poor detection of out-of-field dose by TPS.

Radiobiological assessment of nasopharyngeal cancer IMRT using various collimator angles and non-coplanar fields

Aim: The aim of this study was to evaluate clinical efficacy and radiobiological outcome of intensity-modulated radiation therapy (IMRT) modalities using various collimator angles and non-coplanar fields for nasopharyngeal cancer (NPC). Materials and methods: A 70-Gy planning target volume dose was administered for 30 NPC patients referred for IMRT. Standard IMRT plans were constructed based on the target and organs at risk (OARs) volume; and dose constraints recommended by Radiation Therapy Oncology Group (RTOG). Using various collimator angles and non-coplanar fields, 11 different additional IMRT protocols were investigated. Homogeneity indexes (HIs) and conformation numbers (CNs) were calculated. Poisson and relative seriality models were utilised for estimating tumour control probability (TCP) and normal tissue complication probabilities (NTCPs), respectively. Results: Various collimator angles and non-coplanar fields had no significant effect on HI, CN and TCP, while significant effects were noted for some OARs, with a maximum mean dose (Dmax). No significant differences were observed among the calculated NTCPs of all the IMRT protocols. However, the protocol with 10° collimator angle (for five fields out of seven) and 8° couch angle had the lowest NTCP. Furthermore, the standard and some of non-coplanar IMRT protocols led to the reduction in OARs Dmax. Conclusions: Using appropriate standard/non-coplanar IMRT protocols for NPC treatment could potentially reduce the dose to the OARs and the probability of inducing secondary cancer in patients.