Effects of deep inspiration breath hold on prone photon or proton irradiation of breast and regional lymph nodes

Abstract

We report on a comparative dosimetrical study between deep inspiration breath hold (DIBH) and shallow breathing (SB) in prone crawl position for photon and proton radiotherapy of whole breast (WB) and locoregional lymph node regions, including the internal mammary chain (LN_MI). We investigate the dosimetrical effects of DIBH in prone crawl position on organs-at-risk for both photon and proton plans. For each modality, we further estimate the effects of lung and heart doses on the mortality risks of different risk profiles of patients. Thirty-one patients with invasive carcinoma of the left breast and pathologically confirmed positive lymph node status were included in this study. DIBH significantly decreased dose to heart for photon and proton radiotherapy. DIBH also decreased lung doses for photons, while increased lung doses were observed using protons because the retracting heart is displaced by low-density lung tissue. For other organs-at-risk, DIBH resulted in significant dose reductions using photons while minor differences in dose deposition between DIBH and SB were observed using protons. In patients with high risks for cardiac and lung cancer mortality, average thirty-year mortality rates from radiotherapy-related cardiac injury and lung cancer were estimated at 3.12% (photon DIBH), 4.03% (photon SB), 1.80% (proton DIBH) and 1.66% (proton SB). The radiation-related mortality risk could not outweigh the ~ 8% disease-specific survival benefit of WB + LN_MI radiotherapy in any of the assessed treatments.

Reproducibility of repeated breathhold and impact of breathhold failure in whole breast and regional nodal irradiation in prone crawl position

“…A recent meta-analysis by Lai et al even hinted that the combined use of prone positioning and breathholding seemed the most promising to decrease cardiopulmonary exposure, rather than breathholding or prone positioning on their own 15 . In our previous research, we showed a benefit of prone positioning over supine positioning in WB + RNI 9 , 12 , and in another paper that the addition of breathhold for WB + RNI in prone position was more beneficial than prone positioning alone in photon beam treatment 16 . But contrary to the breast itself in prone position 14 , nodal target volume locations may vary significantly between shallow breathing and breathhold, requiring strict breathhold monitoring to avoid missing the target.…”

“…The RBH manoeuvre was monitored using 2 Respisens magnetic sensors (Nomics, Angleur, Belgium) placed on the breast couch and thoracic wall 20 . Patient position and sensor placement is illustrated in a figure in the publication by Speleers et al 16 No IV-contrast was administered. This provided us with a set of 3 scans of distinct clinical situations for each patient, namely BH, RBH and free breathing, which for further purposes of this publication we will call failure to breathhold (FTBH).…”

“…Because we investigate BH robustness, a treatment plan was made for the BH scan for each patient using a previously described technique 9 , 12 , 16 . In short, treatment is designed using multiple short non-coplaner VMAT arcs.…”

Prone versus supine free-breathing for right-sided whole breast radiotherapy

“…A dosimetric study would be incomplete without a display of dose-volume histograms. Modern radiotherapy planning optimization processes deal with small dose differences, of the order of a few percentage points 41 . We strived to attain graphical integrity, visualizing small differences without undue distortion.…”

“…Early radiation pneumonitis is detectable on follow-up CT 1–3 months after breast cancer radiotherapy 45 . In a photon-proton collaborative study of patients at high risk of breast cancer recurrence, radiobiological modeling estimated the thirty-year mortality rates from radiotherapy-related cardiac injury and lung cancer at 1.66% to 4.03% 41 , although these rates did not outweigh the ~ 8% disease-specific survival benefit of radiotherapy. In a study estimating lung cancer and cardiovascular mortality among female breast cancer patients receiving radiotherapy, the risks were shown to increase with lung and heart dose, even in non-smokers without familial or cardiac history 46 .…”