Respiratory gating for proton beam scanning versus photon 3D-CRT for breast cancer radiotherapy

Abstract

Background Respiratory gating and proton therapy have both been proposed to reduce the cardiopulmonary burden in breast cancer radiotherapy. This study aims to investigate the additional benefit of proton radiotherapy for breast cancer with and without respiratory gating. Material and methods Twenty left-sided patients were planned on computed tomography (CT)-datasets acquired during enhanced inspiration gating (EIG) and free-breathing (FB), using photon three-dimensional conformal radiation therapy (3D-CRT) and scanned proton beams. Ten patients received treatment to the whole breast only (WBO) and 10 were treated to the breast and the regional lymph nodes (BRN). Dosimetric parameters characterizing the coverage of target volumes and the cardiopulmonary burden were compared using a paired, two-tailed Student's t-test. Results Protons ensured comparable or better target coverage than photons in all patients during both EIG and FB. The heterogeneity index decreased from 12% with photons to about 5% with protons. The mean dose to the ipsilateral lung was reduced in BRN patients from 12 Gy to 7 Gy (RBE) in EIG and from 14 Gy to 6-7 Gy (RBE) in FB, while for WBO patients all values were about 5-6 Gy (RBE). The mean dose to heart decreased by a factor of four in WBO patients [from 1.1 Gy to 0.3 Gy (RBE) in EIG and from 2.1 Gy to 0.5 Gy (RBE) in FB] and 10 in BRN patients [from 2.1 Gy to 0.2 Gy (RBE) in EIG and from 3.4 Gy to 0.3 Gy (RBE) in FB]. Similarly, the mean and the near maximum dose to the left anterior descending artery (LAD) were significantly lower (p < 0.05) with protons in comparison with photons. Conclusion Proton spot scanning has a high potential to reduce the irradiation of organs at risk and other normal tissues for most patients, beyond what could be achieved with EIG and photon therapy. The largest dose sparing has been seen for BRN patients, both in terms of cardiopulmonary burden and integral dose.

The influence of breathing motion and a variable relative biological effectiveness in proton therapy of left-sided breast cancer

“…However, by evaluating these scenarios, this study indicates that even when including the variable RBE and its uncertainties, the quality of the IMPT plans seems to be at least comparable to photon plans in most aspects. This happens even though the OAR doses for the photon plans in this study were substantially lower compared to other similar studies [9][10][11][12]. For example, the mean dose to the left lung and heart was reported as 3.1 and 0.8 Gy in this study (Table 1), respectively, whereas values around 5-8 Gy and 1-5 Gy have been seen in other similar studies [9][10][11][12].…”

“…Proton energies of 70-230 MeV were available and hence a range shifter with a water equivalent thickness of 4 cm was used for all fields to ensure superficial target coverage. This field arrangement is similar to other proton breast therapy studies [11,12]. Additionally to RBE ¼ 1.1, the RBE-weighted dose was also calculated using the variable RBE model by Wedenberg et al [17].…”

“…Additionally, the NTCP for Grade !2 radiation pneumonitis in the lungs [22] and the integral dose to the normal tissues were calculated for each patient. The integral dose was calculated from average doses and volumes of the delineated structures using volumetric mass densities of 0.26 g/cm 3 for the lungs and 1.06 g/cm 3 for other tissues [11]. The normal tissue doses were always tried to be kept to a minimum after ensuring fulfillment of the target goals, with clinical goals of D mean 2 Gy (RBE) for the heart, D mean 5 Gy (RBE) for the left lung and NTCP 1% for the lungs.…”

“…Although several proton and photon comparative planning studies have indicated the advantages of proton therapy for breast cancer treatment [9][10][11][12], no study has incorporated the variable RBE in the plan comparison to our knowledge. As breast cancer patients constitute a large patient group, which undoubtedly benefit from radiotherapy in terms of local control and overall survival [13], such inclusion might be of importance for the selection of breast patients for proton therapy.…”

Comparative treatment planning study for mediastinal Hodgkin’s lymphoma: impact on normal tissue dose using deep inspiration breath hold proton and photon therapy

“…The ID was calculated for the full CT scanned body volume excluding the PTV volume and was corrected for the lung density. Generic density values of 0.26 g/cm 3 for the lung and 1.06 g/cm 3 for all other tissues were used [25]. The plan conformity was evaluated using Paddick's conformity index (CI Paddick ) [26] (Equation (3)).…”