In Reply to Mihaildis
1
In Reply to Mihaildis To the Editor: We appreciate the comments regarding our recent publication in this journal (1, 2). We will address some of the points brought forth in this response. First, we agree that the neutron contaminants are higher for passively scattered proton beam therapy (PBT). Of course, the magnitude of neutron contribution depends on many factors mentioned in the letter to the editor and, in addition, on the design of the passive scattering system. Our system was espe- cially designed to minimize neutron contaminants. It uses multiple range modulators (24) and scatterers (9) to modulate and to scatter protons just sufficiently to accommodate the volume to be treated. For our beams, the combination of the scattering system and the apertures dominate neutron production. Although our neutron contamination is less than has been reported for other systems, it is nevertheless substantial enough to cause some resets. There are virtually no neutrons in the incident scanning beams. However, neutrons are generated in the patient, as the letter to the editor states. Our estimation is that, for our system, neutrons produced in the patient are about the same order of magnitude as the external neutrons in our passively scattered system. The elimination of external neutrons should significantly reduce the probability of resets; however, clinical experience with scanning beams will be necessary to corroborate such a hypothesis. The letter to the editor suggests that patients receiving PBT can be managed in a manner similar to patients undergoing treatment with high-energy photons. We concur that the same principles of neutron contamination apply, although it has yet to be established whether PBT requires more rigid criteria with regard to patient selection because of differences in the magnitude of the effect. In general, we stress the ongoing need to balance the risk of device malfunctions with the benefit of PBT in select patients. We have designed our passive scattering system to significantly reduce the production of external neutrons. Although neutrons generated in patients cannot be avoided, the magnitude of neutron produc- tion is relatively small regardless of the proton delivery technique used (passive scattering or intensity modulated proton therapy). The best way to minimize risks in patients with cardiac devices with PBT may be to use a scanning beam for higher-risk patients, but not to entirely avoid the use of protons. Data collected from the treatment of larger numbers of patients will help to elucidate the optimal solution to this difficult issue. Thank you again for your feedback and insight. Daniel R. Gomez, MD Department of Radiation Therapy The University of Texas MD Anderson Cancer Center Houston, Texas Falk Poenisch, PhD Radhe Mohan, PhD Department of Radiation Physics The University of Texas MD Anderson Cancer Center Houston, Texas http://dx.doi.org/10.1016/j.ijrobp.2013.12.003 References 1. Gomez DR, Poenisch F, Pinnix CC, et al. Malfunctions of implantable cardiac devices in patients receiving proton beam therapy: Incidence and predictions. Int J Radiat Oncol Biol Phys 2013;87:570-575. 2. Mihailidis D. In regard to Gomez et al. Int J Radiat Oncol Biol Phys 2014;88:751. Proton Therapy for Breast Cancer After Mastectomy: Early Outcomes of a Prospective Clinical Trial In Regard to MacDonald et al To the Editor: I read with great interest the article by MacDonald et al (1) about proton therapy for breast cancer after mastectomy, where an interesting treatment planning comparison between proton and conventional photon approaches was presented. These conven- tional treatment planning approaches for the chest wall with the in- ternal mammary and supraclavicular nodal areas included were composed of electrons-photons and partially wide tangent fields (see Fig. 4 in Reference [1]). The authors concluded that the conventional planning approaches were suboptimal in target volume coverage compared to protons. In addition, protons provided a superior sparing of the cardiopulmonary structures for the cases they studied. One obvious question is why the authors chose to compare the protons with conventional photons and/or electrons-photons instead of comparing them with multiportal inverse-planned (intensity modu- lated radiation therapy [IMRT]) and volumetric arc therapy (VMAT) approaches that allow ways to optimize the dose delivery within the planning target volume and spare the critical structures. I feel that a comparison like that would provide the community with a greater appreciation for the potentially more beneficial modality for treat- ment delivery. Numerous reports over the last decade have outlined the superiority of IMRT for chest wall with regional nodes compared to conventional wide tangential fields or electron-photon mixed fields, and advanced inverse planning optimization approaches have been shown to greatly improve the quality of these complex plans and deliveries (2, 3). More recently, VMAT has also been compared with IMRT for the same locoregional breast radiation therapy (4, 5). It is reasonable to expect the same level of comparison with the newly proposed approach with protons. I am looking forward to the au- thors’ response and potential results of such comparisons. Dimitris N. Mihailidis, PhD Charleston Radiation Therapy Consultants, PLLC Charleston, West Virginia http://dx.doi.org/10.1016/j.ijrobp.2013.10.046 References 1. MacDonald SM, Patel SA, Hickey S, et al. Proton therapy for breast cancer after mastectomy: Early outcomes of a prospective clinical trial. Int J Radiat Oncol Biol Phys 2013;86:484-490. 2. Mihailidis DN, Plants B, Farinash L, et al. Superiority of equivalent uniform dose (EUD)-based optimization for breast and chest wall. Med Dosim 2010;35:67-76. 3. Rudat V, Alaradi AA, Mohamed A, et al. Tangential beam IMRT versus tangential beam 3D-CRT of the chest wall in postmastectomy breast cancer patients: A dosimetric comparison. Radiat Oncol 2011;6:26. 4. Popescu CC, Olivotto I, Beckham W, et al. Volumetric modulated arc therapy improves dosimetry and reduces treatment time compared to conventional intensity-modulated radiotherapy for locoregional radiotherapy of left-sided breast cancer and internal mammary nodes. Int J Radiat Oncol Biol Phys 2010;76:287-295. 5. Subramaniam S, Thirumalaiswamy S, Srinivas C, et al. Chest wall radio- therapy with volumetric modulated arcs and the potential role of flattening filter free photon beams. Stranhlenther Onkol 2012;188:484-491. COMMENTS International Journal of Radiation Oncology Biology Physics 754
Transcript of In Reply to Mihaildis
COMMENTS International Journal of Radiation Oncology � Biology � Physics754
In Reply to Mihaildis
To the Editor: We appreciate the comments regarding our recentpublication in this journal (1, 2). Wewill address some of the pointsbrought forth in this response. First, we agree that the neutroncontaminants are higher for passively scattered proton beam therapy(PBT). Of course, themagnitude of neutron contribution depends onmany factorsmentioned in the letter to the editor and, in addition, onthe design of the passive scattering system. Our system was espe-cially designed to minimize neutron contaminants. It uses multiplerange modulators (24) and scatterers (9) to modulate and to scatterprotons just sufficiently to accommodate the volume to be treated.For our beams, the combination of the scattering system and theapertures dominate neutron production. Although our neutroncontamination is less than has been reported for other systems, it isnevertheless substantial enough to cause some resets.
There are virtually no neutrons in the incident scanning beams.However, neutrons are generated in the patient, as the letter to theeditor states.Our estimation is that, for our system, neutrons producedin the patient are about the same order of magnitude as the externalneutrons in our passively scattered system. The elimination ofexternal neutrons should significantly reduce the probability of resets;however, clinical experience with scanning beams will be necessaryto corroborate such a hypothesis. The letter to the editor suggests thatpatients receivingPBTcanbemanaged in amanner similar topatientsundergoing treatment with high-energy photons. We concur that thesame principles of neutron contamination apply, although it has yet tobe establishedwhether PBTrequiresmore rigid criteriawith regard topatient selection because of differences in themagnitude of the effect.
In general, we stress the ongoing need to balance the risk ofdevice malfunctions with the benefit of PBT in select patients. Wehave designed our passive scattering system to significantly reducethe production of external neutrons. Although neutrons generatedin patients cannot be avoided, the magnitude of neutron produc-tion is relatively small regardless of the proton delivery techniqueused (passive scattering or intensity modulated proton therapy).The best way to minimize risks in patients with cardiac deviceswith PBT may be to use a scanning beam for higher-risk patients,but not to entirely avoid the use of protons. Data collected fromthe treatment of larger numbers of patients will help to elucidatethe optimal solution to this difficult issue.
Thank you again for your feedback and insight.
Daniel R. Gomez, MDDepartment of Radiation Therapy
The University of Texas MD Anderson Cancer CenterHouston, Texas
Falk Poenisch, PhDRadhe Mohan, PhD
Department of Radiation PhysicsThe University of Texas MD Anderson Cancer Center
Houston, Texas
http://dx.doi.org/10.1016/j.ijrobp.2013.12.003
References
1. Gomez DR, Poenisch F, Pinnix CC, et al. Malfunctions of implantable
cardiac devices in patients receiving proton beam therapy: Incidence
and predictions. Int J Radiat Oncol Biol Phys 2013;87:570-575.
2. Mihailidis D. In regard to Gomez et al. Int J Radiat Oncol Biol Phys
2014;88:751.
Proton Therapy for Breast Cancer AfterMastectomy: Early Outcomes of a ProspectiveClinical Trial
In Regard to MacDonald et al
To the Editor: I read with great interest the article by MacDonaldet al (1) about proton therapy for breast cancer after mastectomy,where an interesting treatment planning comparison between protonand conventional photon approaches was presented. These conven-tional treatment planning approaches for the chest wall with the in-ternal mammary and supraclavicular nodal areas included werecomposed of electrons-photons and partially wide tangent fields (seeFig. 4 in Reference [1]). The authors concluded that the conventionalplanning approaches were suboptimal in target volume coveragecompared to protons. In addition, protons provided a superior sparingof the cardiopulmonary structures for the cases they studied. Oneobvious question is why the authors chose to compare the protonswith conventional photons and/or electrons-photons instead ofcomparing them with multiportal inverse-planned (intensity modu-lated radiation therapy [IMRT]) and volumetric arc therapy (VMAT)approaches that allow ways to optimize the dose delivery within theplanning target volume and spare the critical structures. I feel that acomparison like that would provide the community with a greaterappreciation for the potentially more beneficial modality for treat-ment delivery. Numerous reports over the last decade have outlinedthe superiority of IMRT for chest wall with regional nodes comparedto conventional wide tangential fields or electron-photon mixedfields, and advanced inverse planning optimization approaches havebeen shown to greatly improve the quality of these complex plansand deliveries (2, 3). More recently, VMAT has also been comparedwith IMRT for the same locoregional breast radiation therapy (4, 5).It is reasonable to expect the same level of comparisonwith thenewlyproposed approach with protons. I am looking forward to the au-thors’ response and potential results of such comparisons.
Dimitris N. Mihailidis, PhDCharleston Radiation Therapy Consultants, PLLC
Charleston, West Virginia
http://dx.doi.org/10.1016/j.ijrobp.2013.10.046
References
1. MacDonald SM, Patel SA, Hickey S, et al. Proton therapy for breast
cancer after mastectomy: Early outcomes of a prospective clinical
trial. Int J Radiat Oncol Biol Phys 2013;86:484-490.
2. Mihailidis DN, Plants B, Farinash L, et al. Superiority of equivalent
uniform dose (EUD)-based optimization for breast and chest wall.
Med Dosim 2010;35:67-76.
3. Rudat V, Alaradi AA, Mohamed A, et al. Tangential beam IMRT versus
tangential beam 3D-CRT of the chest wall in postmastectomy breast
cancer patients: A dosimetric comparison. Radiat Oncol 2011;6:26.
4. Popescu CC, Olivotto I, Beckham W, et al. Volumetric modulated arc
therapy improves dosimetry and reduces treatment time compared to
conventional intensity-modulated radiotherapy for locoregional
radiotherapy of left-sided breast cancer and internal mammary nodes.
Int J Radiat Oncol Biol Phys 2010;76:287-295.
5. Subramaniam S, Thirumalaiswamy S, Srinivas C, et al. Chest wall radio-
therapy with volumetric modulated arcs and the potential role of flattening
filter free photon beams. Stranhlenther Onkol 2012;188:484-491.
