SIMPLE IMPLEMENTATION OF A DIBH TANGENTIAL IMRT TECHNIQUE FOR LEFT-SIDED BREAST CANCER

Transcription

1 SIMPLE IMPLEMENTATION OF A DIBH TANGENTIAL IMRT TECHNIQUE FOR LEFT-SIDED BREAST CANCER Dominique Mathieu MD MSc, Nicolas Côté MSc, Andrée-Anne Bernard MD, Noémie Lahaie RTT, Stéphane Bedwani PhD, Jean-François Aubry PhD, David Roberge MD, Sophie Lavertu MD, Pierre Rousseau MD, Toni Vu MD Centre hospitalier de l Université de Montréal September 14, 2017

2 None Conflicts of interest

3 Introduction Free breathing (FB) left breast tangential irradiation carries a long-term risk of cardiac toxicity. The probability of major coronary events increases linearly with the mean dose to the heart, with no minimal threshold for risk. Cardiac avoidance can be achieved with deep inspiration breath-holding (DIBH).

4 Deep inspiration breath holding: Creates a separation between the heart and chest wall. Introduction Moves cardiac silhouette inferiorly and posteriorly. Can result in significant mean heart dose reduction. Fig Heart position comparison between FB and DIBH.

5 Clinical assessment DIBH candidate selection: Side of irradiation Age, cardiac comorbidity Pulmonary function Comprehension/cooperation Introduction Clinical workflow at CHUM Treatment planning DIBH device set-up and coaching FB CT acquisition Expected gain in DIBH? 2 DIBH CT acquisitions Treatment Daily DIBH device set-up Specialized technologist or medical physicist Dosimetry Plans generated from FB and DIBH CT scan Quantitative gain in DIBH? 10 cc in-field heart volume during FB? Significant heart dose reduction during DIBH?

6 Purpose To evaluate the effectiveness of the Abches system in the irradiation of left-sided breast cancer in DIBH. To measure DIBH heart dosimetric benefits compared to FB radiotherapy.

7 Abches Simple device allowing to self-control the respiratory motion of the chest and abdomen. (a) Indicator unit (b) Arms with chest and abdominal contacts

8 Method Thirty-two early-stage left-sided breast cancer patients were included. Patients had breast-conserving surgery followed by whole breast hypofractionated radiotherapy. Doses of 42,5 Gy in 16 fx was delivered by tangential irradiation in DIBH. DIBH was performed with Abches device for treatment planning and radiation delivery.

9 Method FB and DIBH treatment tangential plans were retrospectively analyzed. Plans were optimized to obtain equivalent planning target volume (PTV) coverage. Plans were compared in terms of Field specific measures (heart depth and infield heart volume). Dose volume histograms to left lung, heart and left anterior descending artery (LAD).

10 Method Fig Schematics of field specific measures assessing efficacy of DIBH. HD (a) Heart depth (HD) (b) In-field heart volume

11 Results Mean (±SD) field specific measures on FB scans were 1,4 ± 0,5 cm for heart depth of penetration. 24 ± 17 cc for in-field heart volume. A correlation between in field-heart volume and mean heart dose was found trough linear analysis (R 2 = 0,836). No field specific measures on FB scan were predictor of dose reduction during DIBH.

12 Results Fig: Correlation between irradiated heart volume and mean heart dose.

13 Results Analysis of DIBH scan showed Mean in-field heart volume of 2 ± 5 cc. 15/32 (47%) with complete cardiac exclusion from tangential field. (a) FB field (b) DIBH field

14 Results DIBH resulted in statistically significant cardiac doses reduction 65% of mean heart dose. 75% of mean LAD dose. Doses FB DIBH *p-value Mean heart 2,6 Gy 0,9 Gy p< Max heart 42,9 Gy 29,9 Gy p< Mean LAD 20,2 Gy 4,9 Gy p=0.01 Max LAD 39,7 Gy 16,3 Gy p< *Paired Student's t-test

15 Results Maximum mean heart dose reduction obtained with DIBH was 3,3 Gy (a) FB dose colorwash V tang = 35 cc D moy = 4 Gy (b) BH dose colorwash V tang = 0 cc D moy = 0,7 Gy

16 Results DIBH resulted in statistically significant increasement in total lung volume of 60%. Although the absolute left lung volume was increased with DIBH, proportionately less of the left lung was irradiated. Doses FB DIBH *p-value Mean total lung volume 2581 cc 4083 cc p< Mean left lung dose 6,2 Gy 5,8 Gy p=0.01 Mean left lung V cc 203 cc p< Mean left lung V20 12,2% 10,9% p=0.01 *Paired Student's t-test

17 Strengths Discussion - Abches No electrical parts used. Independent from LINAC or CT station. Sensitive to chest and abdominal movement. Easy-to-understand device. Limitations X Constant monitoring from treatment station. X Ressource intensive.

18 Conclusion Abches is a simple way to implement DIBH tangential IMRT for left-sided breast radiotherapy. DIBH is effective in reducing cardiac and main artery doses.

19 Acknowledgment Medical Physicists - Nicolas Côté - Stéphane Bedwani - Jean-Francois Aubry Resident Radiation oncologists - Toni Vu - Sophie Lavertu - Pierre Rousseau - David Roberge - Andrée-Anne Bernard Dosimetrist - Noémie Lahaie