No date

Session Item

Sunday

November 29

14:15 - 15:30

Physics Stream 1

Radiobiological guidance for treatment planning

Overview: State-of-the-art radiotherapy optimization and plan evaluation is based on dose-volume indices rather than radiobiological metrics. Radiotherapy planning may potentially be improved by including tumor control probability (TCP) and normal tissue tolerance probability (NTCP) modelling, also by incorporating recent advances in functional imaging. In this symposium, a brief review of TCP and NTCP models will be given alongside optimization based on such models. Clinical experience with NTCP-guided treatment planning is discussed. For TCP modelling, how to account for spatial tumor heterogeneity and temporal dynamics will be presented together with employing patient-specific model parameters. Moreover, functional imaging for boost volume definition and dose painting will be highlighted. Here, the robustness of the image metrics and the use of functional imaging to monitor treatment response will be reported. Lastly, adaptation to functional changes will be elucidated. Examples from head and neck and lung cancer will be provided throughout the symposium.

Session Type: Symposium

Track: Physics

Journey:

11:10 - 11:20

Patient-Specific Heart Constraint lowers mean heart dose for patients receiving breast RT

Presentation Number: OC-0112

Abstract

Abstract Title:

Patient-Specific Heart Constraint lowers mean heart dose for patients receiving breast RT

Authors: West , Katrina(1,2)[katrina.west@health.nsw.gov.au];Ward , Rachel(1,2)*;Latty , Drew(2);Wang , Tim(1,3,4);Cross , Shamira(5);Gebski , Val(1,6);Stuart , Kirsty(1,3,4);

(1)Crown Princess Mary Cancer Centre, Westmead Hospital, Wentworthville, Australia;(2)Blacktown Cancer and Haematology Centre, Blacktown Hospital, Blacktown, Australia;(3)Westmead Breast Cancer Institute, Westmead Hospital, Wentworthville, Australia;(4)Sydney Medical School, University of Sydney, Sydney, Australia;(5)Nepean Cancer Care Centre, Nepean Hospital, Kingswood, Australia;(6)NHMRC Clinical Trials Centre, University of Sydney, Sydney, Australia;

Show Affiliations

Purpose or Objective

In 2014, our institution implemented a Patient-Specific Heart Constraint (PSHC) and a mean heart dose (MHD) constraint of 4Gy for patients receiving breast RT with a simultaneous boost (SIB). The PSHC uses a calculation method for determining MHD before optimising IMRT fields. The aim of this study was to determine whether the introduction of a PSHC would reduce MHD, whilst maintaining optimally-dosed treatment plans.

Material and Methods

Consecutive patients who received BCS and whole breast with SIB adjuvant RT were retrospectively identified and divided into two cohorts, pre- and post-implementation of the PSHC. Patients were simulated in the supine position. Prescribed dose to the breast PTV was 50Gy in 25 fractions; the SIB PTV was 57Gy in 25 fractions. Plans were generated using a hybrid IMRT technique, where 30Gy was delivered through a static tangential field arrangement, and the remaining 27Gy was delivered through IMRT fields. The calculation of the PSHC used the formula: MHD (open tangent fields) x 2. The following values were collected: D95% SIB PTV, RTOG conformity index (CI), homogeneity index (HI); MHD, V25Gy and V5Gy for heart, left anterior descending coronary artery (LAD) and ipsilateral lung mean doses.

Results

Data from 264 patients treated between June 2013 and July 2015 were collected. There were 138 patients in the pre-PSHC cohort and 126 patients post-PSHC. The plans showed no difference in the CI of the SIB PTV D95% (pre-PSHC mean 1.82 (±0.56), post-PSHC 1.79 (±0.45), p=0.634 (95% CI -0.09-0.15); HI was slightly worse post-PSHC but not clinically relevant (pre-PSHC 6.1 (±1.35), post-PSHC 6.46 (±1.5), p=0.04 (95% CI -0.7, -0.01). The SIB D95% coverage was reduced post-PSHC but was above the 54.15Gy limit (pre-PSHC 55.64Gy (±0.59) post-PSHC 55.31Gy (±0.48) p<0.001 (95% CI 0.19-0.45)). Organ at risk dose comparisons are displayed in Table 1. The PSHC benefit was enhanced further with DIBH for heart V5Gy (p=0.034; 95%CI 0.42-9.85), but not for other parameters. IMRT fields contributed less to MHD post-PSHC (Figure 1).

Table 1. Comparison of heart, left anterior descending coronary artery and ipsilateral lung doses pre- and post- implementation of a patient-specific heart constraint

Figure 1: Contribution to MHD from IMRT fields per patient in chronological order, for women receiving whole breast with SIB irradiation. This is based on the formula: Total MHD/(Open MHD x 1.67), where Total MHD is the sum of both the Open and IMRT components of heart dose received. The Open MHD component (representing MHD from the 30Gy delivered tangentially) is multiplied by 1.67 to predict MHD50 should 50Gy be delivered tangentially. The factor of 1.2 takes into account the boost contribution (57/50 = 1.14) with added buffer up to 60Gy (60/50 = 1.2)

Conclusion

Introduction of a PHSC has led to a decrease in MHD for patients receiving RT with SIB to the breast whilst maintaining optimally-dosed plans.