Table 1 : Clinical Goals

Figure 1 : Example of I-IMRT Optimisation Objective List

Table 2 Numerical Plan Evaluation Summary of Different Planning Techniques.

References [1] Keyvan Jabbari et al. (2013). Optimizing of the Tangential Technique and Supraclavicular Fields in 3DCRT for Breast Cancer. J Med Signals Sens. 3(2). p107–116. [2] Barrett, A., Ash, D., Dobbs, J. and Morris, S. (2009). Practical Radiotherapy Planning. 4th ed. London: Hodder Arnold, pp.265-283. [3] Stefanovski, Zoran et al. (2013). Advantages of the technique with segmented fields for tangential breast irradiation. Conference on medical physics and biomedical engineering, Macedonia. (p. 80). [4] An-Cheng Shiau et al. (2014). “Left-Sided Whole Breast Irradiation with Hybrid-IMRT and Helical Tomotherapy Dosimetric Comparison,” BioMed Research International, vol. 2014, Article ID 741326, 7 pages. [5] Mondal D et al. (2016). External beam radiation techniques for breast cancer in the new millennium: New challenging perspectives. Journal of the Egyptian National Cancer Institute. 28(4). p211-218. [6] International Commission on Radiation Units and Measurements (ICRU). (2010). ICRU Report 83: Prescribing, Recording, and Reporting Photon-Beam Intensity-Modulated Radiation Therapy (IMRT). Journal of the ICRU. 10(1). p.1-106. [7] ICRU. (1999). Report 62: Prescribing, Recording, and Reporting Photon Beam Therapy (Supplement to ICRU Report 50). Maryland, USA:

Results & Analysis ctd.

Megara Srikaran (Supervised by Salam Souliman, Colin Mackay & Natalie Grieve), NHS Tayside.

Methods In Dundee, breast radiotherapy is currently planned using a three-dimensional conformal radiotherapy technique (3DCRT) on RayStation (RaySearch Laboratories, v5). Two tangential semi-opposed beams are positioned to cover the breast tissue, creating a field-based planning target volume (FBPTV). Wedges are then used to create a balanced dose distribution, with field-in-fields (FIF’s) added to reduce the hotspots or boost the dose coverage if required; this typically results in plans with greater than two fields. The superior border of the tangential fields is kept straight using the multi-leaf collimators (MLC’s) to allow matching of the fields for nodal treatments. Plan quality is assessed based on the clinical goals from the Fast Forward trial for both organs at risk (OAR’s) and FBPTV (Table 1). This method was compared with two intensity modulated radiotherapy (IMRT) planning techniques: (1) Forward-planned IMRT (F-IMRT), and (2) Inverse-planned IMRT (I-IMRT).

(1) F-IMRT: The same tangential beam arrangement as the 3DCRT method was used. However, a wedge-less approach was used to optimise the dose distribution; all optimisation was performed by manually creating segments within each field to produce the required coverage. These segments were then combined with the open field to create a single medial and lateral field.

Volume Clinical Goal

FBPTV D95% ≥ 38.0Gy

FBPTV D5% ≤ 42.0Gy

FBPTV D2% ≤ 42.8Gy

FBPTV D2cc ≤ 42.8Gy

Tumour Bed D100% ≥ 38.0Gy

Heart D30% ≤ 2.0Gy

Heart D5% ≤ 10.0Gy

Lung D15% ≤ 12Gy

Body Max Dose ≤ 44.0Gy

(2) I-IMRT: A hybrid technique was adapted, dividing the plan into open tangential beams and inverse-planned segments to deliver 80% and 20% of the prescription dose respectively (4). This hybrid approach attempts to overcome some of the limitations of full inverse IMRT methods, including requirements for patient-specific quality assurance (PSQA) and immobilisation difficulties (5). Fields were inversely optimised to provide the required coverage, using the dose from the tangential open field as a background or base dose. This optimisation process involves balancing the trade-off between the target coverage and organ sparing. An example of the types of objectives used are shown in Figure 1 below.

Results were analysed both quantitatively and qualitatively. The homogeneity index and conformity index were used to assess FBPTV coverage, as outlined in ICRU Report 83 & 62 (6 , 7). The method of prescription was also evaluated. The current prescription is 40Gy in 15#. For the 3DCRT and F-IMRT methods, a point dose approach was used. In accordance with ICRU Report 83 recommendations, a volume-based prescription was used for the I-IMRT method, with the dose prescribed to the FBPTV median dose, D50% (6). Results & Analysis

Figure 3: Example of isodose distribution for the central slice of Patient 3 for 3DCRT, F-IMRT,

and I-IMRT plans. Structures - FBPTV (pink), heart (purple), and lung (cyan)

Mean D95% FBPTV coverage improved for F-IMRT and I-IMRT plans compared with 3DCRT; 0.66% and 0.59% respectively.

Mean heart doses increased slightly for both F-IMRT (0.18Gy) and I-IMRT (0.35Gy) relative to 3DCRT. This was associated with the improved coverage.

Mean number of Monitor Unit (MU) required decreased for both IMRT methods, with large reductions in both planning and delivery times.

Changes incurred by different prescription methods (point dose vs. dose-volume approach) were considered clinically acceptable, within the ICRU recommended tolerance of D50% ± 3.5% (6).

Conclusions F-IMRT method is concluded as the favoured technique:

High quality plans with improved FBPTV D95% and tumour bed coverage, increased lung sparing, as well as reduced MU, planning and delivery times relative to 3DCRT plans.

Increased treatment delivery efficiency and patient throughput, with less impact on the workload of the radiotherapy service.

Produces fields with segment shapes similar to the currently used 3DCRT technique. The department does not PSQA breast patients with the current technique, therefore F-IMRT should not require PSQA.

Hybrid I-IMRT was not considered practical for implementation due to increase in plan checking time, and inability to match the tangential and nodal fields. It is recommended that training is provided for the F-IMRT technique with further investigation to assess reproducibility. PQSA should be performed for the first few patients to ensure the safety of the technique.

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Figure 2 : FBPTV D95% coverage of 12 patients planned using 3DCRT, F-IMRT and I-IMRT.

Challenges of I-IMRT Hybrid Planning Techniques Treated as two different plans in RayStation to separate the open fields and

inverse segments; requires two plans to be checked independently. Does not provide the straight edge at the superior border of the segment fields

to allow matching with nodal fields; does not produce plans in accordance with the current asymmetric half beam block technique.

Introduction Breast cancer (BC) is one of the most common malignancies, affecting 1 in every 9 women, with a high mortality rate (1). One of the current methods of treatment involves breast-conserving surgery followed by adjuvant radiotherapy (2). Radiotherapy of the breast is challenging due to the concave anatomy and variable shape of the breast, as well as proximity to low density lung and target motion due to breathing (3). As the number of breast cancer survivors increases, it is important to minimise treatment complications (2). The main aim of this project was to determine the optimum technique for breast radiotherapy at Tayside Cancer Centre in Dundee. A review of the current technique compared with alternative practices in the literature and practiced by other centres highlighted a number of possibilities for optimisation; the treatment planning technique was selected for further investigation. A systematic analysis of the current planning technique against a number of other methods was then performed for an anonymised set of patients. A recommendation on the optimum planning technique was then outlined.