- Email: [email protected]
Reply to letter by A. Wambersie and B. J. Mijnheer
263 one requires a quantity which is simple to determine, relevant, and on which an agreement can easily be reached. (2) On the other hand, the radiotherapist, in a given hospital, is responsible for the prescription of the dose to be delivered to his patient. He should select the dose in the way he believes is the most appropriate taking into account RBE measurements performed in his own beam, RBE values reported from similar beams at others facilities, his previous experience, the experience reported from others centres as discussed more extensively elsewhere [9]. When prescribing the dose, the radiotherapist is of course allowed to use the “total effective dose” or a similar concept. However, this is a distinct problem from the need for uniformity in reporting. In conclusion, in our opinion, there is no need to modify a clinical practice which has generally been followed successfully over the last 10 years. No new data have appeared which would justify the reopening of the debate and to recommend a change in expression of dose in neutron therapy.
Andre Wambersie ’ and B. J. Mijnheer ‘Department
z
of Radiation Therapy
Neutron- and Curietherapy Catholic University of Louvain, University Clinics St.-Luc 1200 Brussels, Belgium and *The Netherlands
Cancer Institute (Antoni van Leeuwenhoek
Huis), 1066 CX Amsterdam The Netherlands
References
I Bewley, D. K. The Physics and Radiobiology
of Fast neutron Beams: Medical Science Series. Adam Hilger, Bristol and New York, 1989.
2 Bonnett, D. E. and Parnell, J. C. Effect of variation in the energy spectrum of a cyclotron produced fast neutron beam in a phantom relevant to its application in radiotherapy. Br. J. Radiol. 55: 48-55, 1982. 3 Catterall, M. C. and Bewley, D. K. Fast Neutrons in the Treatment of cancer. Academic Press, New York, 1979. 4 Field, S. B. and Joiner, M. C. Expression of dose in neutron therapy. Radiother. Oncol. 17: 73-79, 1990. 5 Hornsey, S., Myers, R., Parnell, C. J., Bonnett, D. E., Blake, S. W. and Bewley, D. K. Changes in relative biological effectiveness with depth ofthe Clatterbridge neutron therapy beam. Br. J. Radiol. 61: 1058-1065, 1988. 6 International Commission on Radiation Units and Measurements (ICRU). Clinical Neutron Dosimetry, Part I: Determination of Absorbed Dose in a Patient Treated by External Beams of Fast Neutrons. ICRU Report 45,791O Woodmont Avenue, Bethesda, MD, 20814-3095, U.S.A., 1989. 7 Kellerer, A. M. and Rassow, J. The correction for the gamma-ray component in neutron therapy. Med. Phys. 7: 503-506, 1980. 8 Mijnheer, B. J. Calculation of the variation in the relative biological effectiveness of collimated 14 MeV neutrons at different positions in a phantom. Proc. 8th Microdosimetry Svmposium. EUR 8395, 885-896, 1983. Mijnheer, B. J., Battermann J. J. and Wambersie, A. What degree ofaccuracy is required and can be delivered in photon and neutron therapy? Radiother. Oncol. 8: 237-252, 1987. Wambersie, A. Specific problems in neutron treatment planning in comparison with photon treatment planning. In: Treatment Planning for External Beam Therapy with Neutrons. Editors: G. Burger, A. Breit and J. J. Broerse. Urban and Schwarzenberg, Milnchen-Wien-Baltimore. Supplement to Strahlentherapie 77: 24-35, 1981. Wambersie, A. and Battermann, J. J. Practical problems related to RBE in neutrontherapy. In: Progress in Radio-Oncology, III, pp. 155-162. Editors: K. H. K%rcher, H. D. Kogelnik and T. Szepesi. ICRO (International Club for Radio-Oncology), Vienna, Austria, 1987. Zaider, M. and Rossi, H. H. The synergistic effects of different radiations. Radiat. Res. 83: 732-739, 1980.
REPLY TO LETTER BY A. WAMBERSIE AND B. J. MIJNHEER (Received 27 November 1989, accepted 27 December 1989)
Dear Sir, In their response to our paper [l], Wambersie and Mijnheer [2] point out that for reporting absorbed dose, a quantity is needed that is simple to determine, relevant and on which agreement can be reached easily. They conclude that the present practice in neutron therapy of reporting total dose has been followed successfully and that there is no need to change. We feel that of the above criteria, relevance is the most important. It is beyond question that the proportion of
gamma rays varies from beam to beam and with penetration into the body. The RBE and hence the biologically effective dose varies with the proportion of gamma rays. At the time, the decision was made to report total dose it was difficult to estimate the proportion of gamma rays with reasonable accuracy. This is no longer the case. The neutron and gamma components can now be measured separately with a reasonable degree of confidence and the use of the simple formula D, + 0.25 D, will give a more accurate and hence a more relevant measure of effect.
264 We took care in our paper to point out that the proportion of gamma rays was but one of several factors that can influence the RBE, for example, the change in spectrum with depth of penetration. But we were not addressing this problem. Also, we pointed out that use of the neutron and gamma component instead of the full ‘y spectrum was a pragmatic approach, since the means are not yet available in clinical practice to derive a biologically effective dose from a “y” or LET spectrum. But these arguments should not be used to deflect us from a basic principal of dosimetric physics which is that it should be as accurate and biologically representative as possible. Whether or not the present practice of reporting total dose is successful is highly questionable. With 8% gamma contamination the error from using total absorbed dose is greater than 6%. Regardless of other influencing factors this error can and should be avoided.
S. B. Field ’ and M. C. Joiner * ‘MRC Cyclotron Unit Hammersmith Hospital DuCane Rd. London WIZOHS, U.K. and *CRC Gray Laboratory Mount Vernon Hospital NorthwoodMiddelsex HA62JR. U.K.
References 1 Field, S. B. and Joiner, M. C. Expression of dose in neutron therapy. Radiother. Oncol. 17: 73-79, 1990. 2 Wambersie, A. and Mijnheer, B. J. Expression of dose in neutron therapy. Radiother. Oncol., this issue.
Editorial
SPECIFICATION OF DOSE IN NEUTRON THERAPY (Received and accepted 27 December 1989)
Dear Sir, The specification of dose in neutron therapy has been addressed recently in the paper by Field and Joiner [4], which provoked a letter by Wambersie and Mijnheer [13] and a reply by Field and Joiner [5]. This is an old acorn that has been debated by neutroneers for the best part of 20 years. There is no clear-cut answer as to the “correct” thing to do. No-one is right, and no-one is wrong; the various proponents are simply expressing different points of view on a cloudy issue; not only are both sides of the present debate perfectly reasonable, but there are also yet other views at variance with both sides that can equally well claim to represent the voice of reason. For example, if dose is really to be based on sound science there is the approach proposed by Booz and Poli [2] which uses microdosimetric spectra and calculates dose fractions for four components; 7, fast recoil protons, slow recoil protons and heavier recoil ions. The total mean quality factor is the sum of the Q of the four components weighted by the dose fractions and by dose mean LET. This method can employ specific relations between Y,, or L, and Q. Certainly the microdosimetric approach holds great promise for a more accurate specification of dose [3,12]. Whether it is a method practical enough to be adopted by radiotherapists is another question. Before addressing the central issue, some historical context is in order here. Radiotherapy treatments with X-rays are prescribed in terms of absorbed dose, since this quantity correlates well
with biological effect. Radiotherapy took a quantum leap forward when adequate methods were developed to measure dose accurately and repeatably. With the ability to measure dose, treatments could be standardized from one week to the next in a given institution and the outcome of treatment could be compared between different institutions. (There was always the complications oftime dose relationship, of course, but that’s another story.) Older members of the radiotherapy community will remember the chaos of the 1950s when the rad replaced the roentgen, and when it was found subsequently that the rad was “hotter” in some places than others. All this is long since a thing of the past - improvements in medical physics have standardized dosimetry for low LET radiations and we now take it for granted. Neutrons represent a whole new ball game, and a much more complicated problem. Any of the neutron beams used for radiation therapy inevitably include a proportion of gamma-rays, which may vary appreciably, and this is one confounding issue. Controlled clinical trials with neutrons were performed first at Hammersmith and it was their practice to specify neutron dose alone -the gamma-ray dose was noted but ignored in both specification and in prescription. The standard protocol of 1560 rads in 12 fractions implied that there was in addition a few hundred rads ofgamma-rays. When neutron therapy began in the U.S., several different cyclotrons were involved, each one with a different energy, and all different to Hammersmith! It was decided in the U.S.
Andre Wambersie ’ and B. J. Mijnheer ‘Department
z
of Radiation Therapy
Neutron- and Curietherapy Catholic University of Louvain, University Clinics St.-Luc 1200 Brussels, Belgium and *The Netherlands
Cancer Institute (Antoni van Leeuwenhoek
Huis), 1066 CX Amsterdam The Netherlands
References
I Bewley, D. K. The Physics and Radiobiology
of Fast neutron Beams: Medical Science Series. Adam Hilger, Bristol and New York, 1989.
2 Bonnett, D. E. and Parnell, J. C. Effect of variation in the energy spectrum of a cyclotron produced fast neutron beam in a phantom relevant to its application in radiotherapy. Br. J. Radiol. 55: 48-55, 1982. 3 Catterall, M. C. and Bewley, D. K. Fast Neutrons in the Treatment of cancer. Academic Press, New York, 1979. 4 Field, S. B. and Joiner, M. C. Expression of dose in neutron therapy. Radiother. Oncol. 17: 73-79, 1990. 5 Hornsey, S., Myers, R., Parnell, C. J., Bonnett, D. E., Blake, S. W. and Bewley, D. K. Changes in relative biological effectiveness with depth ofthe Clatterbridge neutron therapy beam. Br. J. Radiol. 61: 1058-1065, 1988. 6 International Commission on Radiation Units and Measurements (ICRU). Clinical Neutron Dosimetry, Part I: Determination of Absorbed Dose in a Patient Treated by External Beams of Fast Neutrons. ICRU Report 45,791O Woodmont Avenue, Bethesda, MD, 20814-3095, U.S.A., 1989. 7 Kellerer, A. M. and Rassow, J. The correction for the gamma-ray component in neutron therapy. Med. Phys. 7: 503-506, 1980. 8 Mijnheer, B. J. Calculation of the variation in the relative biological effectiveness of collimated 14 MeV neutrons at different positions in a phantom. Proc. 8th Microdosimetry Svmposium. EUR 8395, 885-896, 1983. Mijnheer, B. J., Battermann J. J. and Wambersie, A. What degree ofaccuracy is required and can be delivered in photon and neutron therapy? Radiother. Oncol. 8: 237-252, 1987. Wambersie, A. Specific problems in neutron treatment planning in comparison with photon treatment planning. In: Treatment Planning for External Beam Therapy with Neutrons. Editors: G. Burger, A. Breit and J. J. Broerse. Urban and Schwarzenberg, Milnchen-Wien-Baltimore. Supplement to Strahlentherapie 77: 24-35, 1981. Wambersie, A. and Battermann, J. J. Practical problems related to RBE in neutrontherapy. In: Progress in Radio-Oncology, III, pp. 155-162. Editors: K. H. K%rcher, H. D. Kogelnik and T. Szepesi. ICRO (International Club for Radio-Oncology), Vienna, Austria, 1987. Zaider, M. and Rossi, H. H. The synergistic effects of different radiations. Radiat. Res. 83: 732-739, 1980.
REPLY TO LETTER BY A. WAMBERSIE AND B. J. MIJNHEER (Received 27 November 1989, accepted 27 December 1989)
Dear Sir, In their response to our paper [l], Wambersie and Mijnheer [2] point out that for reporting absorbed dose, a quantity is needed that is simple to determine, relevant and on which agreement can be reached easily. They conclude that the present practice in neutron therapy of reporting total dose has been followed successfully and that there is no need to change. We feel that of the above criteria, relevance is the most important. It is beyond question that the proportion of
gamma rays varies from beam to beam and with penetration into the body. The RBE and hence the biologically effective dose varies with the proportion of gamma rays. At the time, the decision was made to report total dose it was difficult to estimate the proportion of gamma rays with reasonable accuracy. This is no longer the case. The neutron and gamma components can now be measured separately with a reasonable degree of confidence and the use of the simple formula D, + 0.25 D, will give a more accurate and hence a more relevant measure of effect.
264 We took care in our paper to point out that the proportion of gamma rays was but one of several factors that can influence the RBE, for example, the change in spectrum with depth of penetration. But we were not addressing this problem. Also, we pointed out that use of the neutron and gamma component instead of the full ‘y spectrum was a pragmatic approach, since the means are not yet available in clinical practice to derive a biologically effective dose from a “y” or LET spectrum. But these arguments should not be used to deflect us from a basic principal of dosimetric physics which is that it should be as accurate and biologically representative as possible. Whether or not the present practice of reporting total dose is successful is highly questionable. With 8% gamma contamination the error from using total absorbed dose is greater than 6%. Regardless of other influencing factors this error can and should be avoided.
S. B. Field ’ and M. C. Joiner * ‘MRC Cyclotron Unit Hammersmith Hospital DuCane Rd. London WIZOHS, U.K. and *CRC Gray Laboratory Mount Vernon Hospital NorthwoodMiddelsex HA62JR. U.K.
References 1 Field, S. B. and Joiner, M. C. Expression of dose in neutron therapy. Radiother. Oncol. 17: 73-79, 1990. 2 Wambersie, A. and Mijnheer, B. J. Expression of dose in neutron therapy. Radiother. Oncol., this issue.
Editorial
SPECIFICATION OF DOSE IN NEUTRON THERAPY (Received and accepted 27 December 1989)
Dear Sir, The specification of dose in neutron therapy has been addressed recently in the paper by Field and Joiner [4], which provoked a letter by Wambersie and Mijnheer [13] and a reply by Field and Joiner [5]. This is an old acorn that has been debated by neutroneers for the best part of 20 years. There is no clear-cut answer as to the “correct” thing to do. No-one is right, and no-one is wrong; the various proponents are simply expressing different points of view on a cloudy issue; not only are both sides of the present debate perfectly reasonable, but there are also yet other views at variance with both sides that can equally well claim to represent the voice of reason. For example, if dose is really to be based on sound science there is the approach proposed by Booz and Poli [2] which uses microdosimetric spectra and calculates dose fractions for four components; 7, fast recoil protons, slow recoil protons and heavier recoil ions. The total mean quality factor is the sum of the Q of the four components weighted by the dose fractions and by dose mean LET. This method can employ specific relations between Y,, or L, and Q. Certainly the microdosimetric approach holds great promise for a more accurate specification of dose [3,12]. Whether it is a method practical enough to be adopted by radiotherapists is another question. Before addressing the central issue, some historical context is in order here. Radiotherapy treatments with X-rays are prescribed in terms of absorbed dose, since this quantity correlates well
with biological effect. Radiotherapy took a quantum leap forward when adequate methods were developed to measure dose accurately and repeatably. With the ability to measure dose, treatments could be standardized from one week to the next in a given institution and the outcome of treatment could be compared between different institutions. (There was always the complications oftime dose relationship, of course, but that’s another story.) Older members of the radiotherapy community will remember the chaos of the 1950s when the rad replaced the roentgen, and when it was found subsequently that the rad was “hotter” in some places than others. All this is long since a thing of the past - improvements in medical physics have standardized dosimetry for low LET radiations and we now take it for granted. Neutrons represent a whole new ball game, and a much more complicated problem. Any of the neutron beams used for radiation therapy inevitably include a proportion of gamma-rays, which may vary appreciably, and this is one confounding issue. Controlled clinical trials with neutrons were performed first at Hammersmith and it was their practice to specify neutron dose alone -the gamma-ray dose was noted but ignored in both specification and in prescription. The standard protocol of 1560 rads in 12 fractions implied that there was in addition a few hundred rads ofgamma-rays. When neutron therapy began in the U.S., several different cyclotrons were involved, each one with a different energy, and all different to Hammersmith! It was decided in the U.S.