1. Baseline Respiratory Parameters Documented
IMPACT OF BREATHING ON POSTMASTECTOMY RADIOTHERAPY: A DOSIMETRIC COMPARISON BETWEEN INTENSITY MODULATED RADIOTHERAPY AND 3D CONFORMAL (TANGENTIAL) RADIOTHERAPY A. Judith1, B. Sasidharan2, S. Ebenezer2, B. Thangakunam2, B. Antonisamy2, B. Selvamani2, 1CARITAS Cancer Institute, Kottayam, Kerala, India Christian Medical College, Vellore, Tamil Nadu, India
Introduction
Discussion
From literature we know that the mean amplitude of chest
wall movement with respiration is 8-10 mm. This was
confirmed by this study [4].
The effect of respiratory motion has been studied in whole
breast IMRT and great dose inhomogeneities within the
clinical target volume was found, with the minimal clinical
target volume dose being decreased by 6-9% with
respiration [5].
However effect of breathing on chest wall radiotherapy is
poorly understood.
This study found that :
There is significant reduction in target volume coverage in
different breathing phases with IMRT technique (Figure 1).
Greater dose inhomogeneity occurs within target volume.
The minimal clinical target volume is decreased by 20-25%
with respiration in IMRT technique and only 10-12% with
3D conformal tangents plan (Figure 2).
Lung dose increases with respiration in both IMRT and
3D conformal tangents technique. However, it does not cross
tolerance limits (Table 1).
Heart dose also increases with respiration in both
techniques. However, it crosses the tolerance dose (V25 >
10%) with respiration in 3D conformal tangent plan for patients
with left sided breast cancer (Table 2).
There was more than 5% under-coverage with different breathing phases in IMRT in comparison to 3D tangents technique for patients with tidal volume more than the median value of 0.67 litres (Figure 3).
Post-mastectomy radiotherapy (PMRT) is known to improve local control as well as overall survival in locally advanced cancers of breast[1-3].
Tangential beam radiotherapy is the standard technique used in PMRT.
It has long been assumed that respiratory motion does not significantly affect dose distribution within the target (chest wall) with standard tangential beam radiotherapy
However the impact of respiration on dose distribution within target (chest wall) while using newer techniques such as Intensity modulated radiotherapy is not clearly known.
Aim
To quantify the effect of breathing motion on post mastectomy radiotherapy with 3D conformal tangents and intensity modulated radiotherapy (IMRT)
Figure 2:Line diagrams showing the change in mean HOT SPOTS in terms of D2 (dose received by 2% of volume) and COLD SPOTS in terms of D98 (dose received by 98% of volume) with respiration in IMRT versus 3D conformal tangents. The prescribed dose was 50Gy.
Objectives
To determine the change in target coverage that can occur with respiratory motion when treated with IMRT and 3D CRT.
Assess whether the Lung & Heart doses are being under reported as compared to actual when plans are finalized on FB scan.
Dose to organs at risk
Table 1:Comparison of mean dose received by Ipsilateral lung and Combined lungs at different phases of breathing cycle for 3D conformal tangents technique and IMRT technique
Methods
IMRT and 3D conformal tangent plans generated on the FB scan
Prescription: 50 Gy in 25 fractions to CTV
Patients due for post mastectomy radiotherapy underwent spirometric evaluation to check breath hold time
Satisfactory
Patient Not Recruited
Baseline Respiratory Parameters Documented
Respiratory Rate at Rest  Tidal Volume (Liters)
Chest Wall Expansion with Normal Breathing (cm)
Patient Immobilised on Breast Board
Planning CT scan of thorax with RT markers in
Free Breathing (FB Scan)
2 more CT scans in the same position at
Normal Inspiration (NI Scan)
Normal Expiration (NE Scan)
CT scan images were transferred to Eclipse
Contouring was done on all 3 CT scans as per RTOG guideline
CTV- Chest wall
 Organs At Risk- lungs, heart
DVH of the 3 CT sets were compared (IMRT and 3D-CRT)
CTV - V95, D2, D98
Organs at risk
Lung – V20
Heart - V25
The IMRT and 3D conformal tangent plans finalized for FB scan were superimposed on the NI Scan and NE Scan without changing the beam parameters NO
Organs at risk
Technique
V20 (%) FB NI NE
Ipsilateral lung
3D Tangents
23.63
25.76
23.44
IMRT
18.36
24.98
22.63
Combined lungs
11.91
13.12
11.77
9.53
12.81
11.36
YES
Table 2: Comparison of mean dose received by Heart at different phases of breathing cycle for 3D conformal tangents technique and IMRT technique
Laterality of breast cancer
Technique
V25 (%) FB NI NE
Left sided
3D Tangents
9.82
11.5
10.4
IMRT
5.37
7.95
3.65
Right sided
0.03
0.63
1.21
1.15
Conclusions
Dosimetric coverage of target chest wall is sensitive to chest wall motion with respiration for IMRT technique when compared to 3D tangents technique.
There is definitely a trend favouring 3D CRT technique for chest wall in patients with large tidal volume or chest wall expansion. However, it needs to be tested in a larger sample.
However, in patients with left sided breast cancer there might be a benefit with IMRT technique.
Correlating respiratory parameters and target coverage
It was found that there was more than 5% under-coverage with different breathing phases in IMRT when compared to 3D tangents technique for patients with tidal volume more than the median value of 0.67 litres.
However no correlation with chest wall expansion and chest wall coverage was noticed.
Acknowledgements
We gratefully thank all our colleagues for their contribution towards this study as well as all the participants who willingly consented.
Results B A
A total of 10 patients were recruited.
The mean respiratory rate was 20.3 breaths/ minute ranging from 15 to 30.
The mean tidal volume was 0.66 litres ranging from 0.44 to 0.85 litres. Median tidal
volume was 0.67 litres.
Mean chest expansion was 0.67 cm ranging from 0.5 to 1.2 cm.
CTV coverage
References
Danish Breast Cancer Cooperative Group, Nielsen HM, Overgaard M, Grau C, Jensen AR, Overgaard J. Study of failure pattern among high-risk breast cancer patients with or without postmastectomy radiotherapy in addition to adjuvant systemic therapy: long-term results from the Danish Breast Cancer Cooperative Group DBCG 82 b and c randomized studies. J Clin Oncol Off J Am Soc Clin Oncol May 20;24(15):2268–75.
Overgaard M, Jensen M-B, Overgaard J, Hansen PS, Rose C, Andersson M, et al. Postoperative radiotherapy in high-risk postmenopausal breast- cancer patients given adjuvant tamoxifen: Danish Breast Cancer Cooperative Group DBCG 82c randomised trial. The Lancet May 15;353(9165):1641–8.
Overgaard M, Hansen PS, Overgaard J, Rose C, Andersson M, Bach F, et al. Postoperative Radiotherapy in High-Risk Premenopausal Women with Breast Cancer Who Receive Adjuvant Chemotherapy. N Engl J Med ;337(14):949–55.
Saliou MG, Giraud P, Simon L, Fournier-Bidoz N, Fourquet A, Dendale R, et al. [Radiotherapy for breast cancer: respiratory and set-up uncertainties]. Cancer Radiothérapie J Société Fr Radiothérapie Oncol Nov;9(6- 7):414–21.
Frazier RC, Vicini FA, Sharpe MB, Yan D, Fayad J, Baglan KL, et al. Impact of breathing motion on whole breast radiotherapy: a dosimetric analysis using active breathing control. Int J Radiat Oncol Biol Phys ;58(4):1041–7.
Figure 3: Shows the 95% isodose colour wash in axial and sagittal sections at the level of carina and head of humerus respectively on FB scan (A) and NI scan (B) with IMRT plan in a patient with tidal volume more than 0.67 litres. The target under coverage in NI scan can be clearly visualised.
FB- Free Breathing Scan, NI- Normal Inspiration Scan, NE- Normal Expiration scan
Figure 1:Line diagram showing the change in mean target coverage in terms of V95 (volume receiving 95% of dose) with respiration in IMRT versus 3D conformal tangents.