ESTRO 36 Abstract Book

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S435 ESTRO 36
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4.97% for AXBDm and AXBDw, respectively. For these
organs at risk, differences up to -4.56% and to +3.37% were
found for the D2% for AXBDm and AXBDw, respectively.
Conclusion
The studied lung cases present small mean differences
among all calculation modalities; AXBDm and AXBDw
calculations are similar. The spine cases show strong
difference between AXBDm and AXBDw inside the PTV and
the spinal cord or the cauda equina. Acuros is known to
provide an accurate alternative to Monte Carlo
calculations for heterogeneity management [1] and
reporting dose to medium is the preferred choice [2].
Nevertheless, moving from AAA to AXBDm for SBRT
treatments, in particular for spine or for lung of low
density, has to be carefully evaluated.
[1] A. Fogliata et al. “Dosimetric evaluation of Acuros XB
Advanced Dose Calculation algorithm in heterogeneous
media.,” Radiat. Oncol., vol. 6, no. 1, p. 82, Jan. 2011.
[2] P. Andreo “Dose to ‘water-like’ media or dose to
tissue in MV photons radiotherapy treatment planning: still
a matter of debate.,” Phys. Med. Biol. , vol. 60, no. 1, pp.
309–37, Jan. 2015.
Poster: Physics track: Radiation protection, secondary
tumour induction and low dose (incl. imaging)
PO-0813 Cardiac Toxicity after Radiotherapy for
Hodgkin Lymphoma: Impact of Breath Hold and Proton
Therapy
L.A. Rechner1, M.V. Maraldo1, I.R. Vogelius1, P.M.
Petersen1, R.X. Zhu 2, B.S. Dabaja3, N.P. Brod in4, L.
Specht 1, M.C. Aznar5
1 The Finsen Center - Rigshospitalet, Department of
Oncology, Copenhagen, Denmark
2 MD Anderson Cancer Center, Radiation Physics,
Houston, USA
3 MD Anderson Cancer Center, Radiation Oncology,
Houston, USA
4 Albert Einstein College of Medicine, Institute for Onco-
Physics, Bronx, USA
5 University of Oxford, Nuffield Department of
Population Health, Oxford, United Kingdom
Purpose or Objective
We undertook this work to quantify the impact of deep
inspiration breath hold (DIBH) and proton therapy, alone
and in combination, relative to treatment in free
breathing (FB) with IMRT with respect to the estimated
risk of cardiac toxicity after radiotherapy for patients with
early-stage mediastinal Hodgkin lymphoma (HL).
Material and Methods
Treatment plans were generated for 22 patients in both
FB and DIBH to 30.6 Gy (Gy(RBE) for proton therapy) in 17
fractions. IMRT plans were created according to the
clinical procedure at the presenting author’s institution.
Proton plans were created with guidance from the authors
with clinical proton therapy expertise. Mean doses to the
heart, heart valves, and left anterior descending coronary
artery (LADCA) were exported and excess relative risks
(ERRs) of radiation-induced myocardial infarction, heart
failure, and valvular disease were estimated. Dose volume
histograms (DVHs) for the heart were extracted and mean
DVHs were created for each treatment technique. The
Friedman test was used to assess statistical significance,
and analysis was performed in Matlab (The MathWorks,
Inc).
Results
The use of both DIBH and proton therapy were found to
reduce the dose as well as the estimated risk to cardiac
structures (Table 1). Mean doses to the heart, valves, and
LADCA, and the ERRs of radiation induced myocardial
infarction, heart failure, and valvular disease were
statistically significantly reduced for all other treatment
technique combinations when compared with IMRT in FB,
and when proton therapy in DIBH was compared to proton
therapy in FB. Heart dose and the ERRs of myocardial
infarction and heart failure were significantly reduced
when proton therapy in DIBH was compared to IMRT in
DIBH. However, when proton therapy in FB was compared
to IMRT in DIBH no statistically significant differences
were seen for any doses or ERRs. To further analyze the
differences between proton therapy in FB and IMRT in
DIBH, the paired differences in heart dose from the
techniques were calculated (proton therapy in FB minus
IMRT in DIBH). The resulting median difference was 0.0 Gy
(range -4.3 to 3.5), revealing that the relative benefit of
these two techniques with respect to heart dose is
patient-specific. Furthermore, mean DVHs for the heart
show that, on average, the volume of the heart receiving
a dose above about 7 Gy is greater for proton therapy in
FB than it is for IMRT in DIBH (Figure 1).
Conclusion
DIBH and proton therapy both reduced the dose to cardiac
structures and the risk of cardiac toxicity, compared to
IMRT in FB, but no significant difference was found
between IMRT in DIBH and proton therapy in FB.
Therefore, with respect to cardiac toxicity, these data
suggest that given a choice in techniques, IMRT in DIBH
and/or proton therapy should be selected. However, the
difference between IMRT in DIBH and proton therapy in FB
is variable and should be evaluated on a patient-specific
basis.
PO-0814 The Influence of scans parameters on
effective dose of CBCT scans used for IGRT proce dures
Abuhaimed 1, C. J. Martin2, M. Sankaralingam3
1King Abdulaziz City for Science and Technology,
Department of Applied Physics, Riyadh, Saudi Arabia
2University of Glasgow, Department of Clinical Physics,
Glasgow, United Kingdom
3Beatson West of Scotland Cancer Centre, Department of
Radiotherapy Physics, Glasgow, United Kingdom
Purpose or Objective
A new software with a version of (V2.5) of On-Board
imager (OBI) system, which is utilized in the clinic for
image guided radiation therapy (IGRT) procedures, was