1 Introduction

The quantitative determination of energy deposition in a given medium by directly or indirectly ionizing radiation is called radiation dosimetry[1,2].Radiation dosimetry has a vital role in the medical field because the irradiation of patients is totally based upon the values determined by it[3].The International Atomic Energy Agency(IAEA)and several other international organizations have published their dosimetry protocols for calibration of photon and electron beams during the last several decades.With the passage of time,these protocols have been updated for improvement in the accuracy in dosimetry of high-energy photon and electron beams[4].In connection with these advances in dosimetry,the two latest dosimetry protocols,those of Task Group 51(TG-51)and TRS-398,have been implemented by the American Association of Medical Physicists(AAMP)and the IAEA,respectively[5,6].Both protocols are based on the calibration of an ionization chamber in terms of absorbed dose to water(NDw,Q0)in a standard reference quality beam,Q0,from which the dose to water in the user radiation beam is derived[7,8].In these protocols,different experimental approaches have been adopted,which results in variations in the patient dose.

绘制地籍图时，需把外业调查成果在对应的宗地和房屋上填写权属信息，通过地籍和房屋权属信息导出功能实现导出地籍图每宗地及其房屋的权属信息，直接在ArcGIS平台上挂接，不用一一手动填写，极大地提高了工作效率和准确性。

Huq et al.[7]have compared these two protocols by analyzing differences in the basic input data for photon and electron beam dosimetry.Experiments were performed using6,18,and25 MVclinicalphotonbeamenergiesand6,8,10,12,15,and18 MeVelectronbeamenergies[7].Inthis study,two Farmer-type chambers and three plane-parallel chambers,calibrated by a US accredited dosimetry calibrationlaboratory(K&SAssociates,Inc,Nashville,TN,USA),were used[7].It should be mentioned here that,in Pakistan,there is only one secondary standard dosimetry laboratory(SSDL)which provides calibration of radiation instruments on the national level[2,9].The SSDL follows the IAEA TRS-398dosimetryprotocolsforthecalibrationofradiation instruments,whereas physicists in some medical centers either follow AAPM TG-51 or IAEA TRS-398 for the radiation beam output measurement of different machines.

总之，在水权初始分配过程中，政府一方面需要为水权初始分配创设合理分配规则；另一方面需要根据不断变化的自然环境和社会条件调整合理分配规则。问题是，为什么不让市场作为合理分配规则的发现者呢？譬如，拍卖机制或许是判断何为合理用水的最佳选择，因为价格机制是偏好的最佳反映。但是，很少有国家将拍卖机制作为水权合理分配的机制。这或许源于一方面各国长期通过免费分配而非拍卖等价格机制来分配水资源；另一方面拍卖水资源可能会导致水资源垄断，因为出价较高者可能会垄断水资源。

3）污水在厌氧池内的滞留时间短，厌氧分解不充分及反硝化作用弱。进料直接被转水泵送到好氧池，厌氧池内微生物分解有机物时间不足，反硝化脱氮效果差，没有起到调节CNP（碳氮磷）比例的作用。

The clinical dosimetry was performed following the recommendations and reference conditions of the AAPM TG-51 and IAEA TRS-398 protocols[10,11].The depth dose curves were obtained experimentally with the help of a Blue Phantom scanner system loaded with the software Scanditronix-Wellho¨fer OmniPro-Accept for all photon and electron beams,as shown in Fig.1a,b[12–14].The relative measurements were evaluated with the software Scanditronix-Wellho¨fer OmniPro-Accept. The tissue phantom ratio (TPR20,10)and percentage depth dose(%dd（10）)were determined from the curves shown in Fig.1a,as these values are required for all of the photon beams under study,as per the requirements of the TRS-398 and TG-51 protocols.From the measured TPR20,10and%dd（10）,beam quality factors were determined.For each electron beam under study,the reference depth(Zref)and R50(i.e.,‘depth in water in a 10 × 10 cm2or larger beam of electrons at an SSD of 100 cm at which the absorbed dose falls to maximum and 50%of the dose maximum,respectively’[5])were calculated from the depth dose curves shown in Fig.1b as per the requirements of TRS-398&TG-51.Similarly,a polarity correction factor and an ion recombination correction factorwere calculated according to the guidelines provided in the TG-51 and TRS-398 protocols for each beam generated by the CLINAC DMX 2100C.Multiple measurements were performed in each session and were used as average values to minimize the error in the experimental values.Finally,the dose calculations were performed according to the recommendation of the AAPM TG-51 and IAEA TRS-398 protocols[5,6].

2 Materials and methods

The values of KT,Pfor both dosimetry protocols in the case of both 6 and 15 MV photon beams were same as the calibration for the dosimetry systems performed under the standard conditions of the IAEA TRS-398 protocol.Figure 2a,b shows a comparison of the Kionand Kqvalues for both protocols,whereas Fig.2c shows polarity correction factors for 6 and 15 MV photon beams for both protocols.As both the protocols follow the same approach for measurement of the polarity effect,contribution of polarity correction factor in the dosimetry is similar.

Calibration factors are provided under standard environmental conditions of temperature,pressure,and relative humidity according to the recommendations of followed dosimetry protocol.Inhospitals,measurementconditionsare normally different from the standard laboratory conditions recommended by each protocol.The difference in the environmental conditions affects the response of the ionization chamber.Therefore,correction factors must be applied for convertingthecavityairmasstothereferenceconditions.Our mainobjectiveinthepresentstudywasto findouttheeffectof environmental conditions on the patient dose.

Fig.1(Color online)a 6 and 15 MV photon depth dose curves,b electrons depth dose ionization curves of 6,9,12,and 15 MeV

Table 1 Comparison of Kq,Kion,Kpol,and absorbed doses at Zmax(DW(Zmax))values calculated based on the recommendations of AAPM TG-51 and IAEA TRS-398 protocols for 6,15 MV and Co-60 photon beams

*Depends upon the type of ionization chamber and beam energy.For 6 MV beam,%dd（10）X=%dd（10）,while for 15 MV,%dd（10）X=1.267%dd（10）-20.0 was used.Kqfor the ionization chamber was determined from the tabulated values of Kqand corresponds to%dd（10）Xfor the ionization chamber[5].The interpolation techniques were used while using these tabulated values**Depends upon the type of ionization chamber and beam energy.TPR20,10(=TPR20/TPR10;measured experimentally)was calculated first.Kq for the ionization chamber was determined from the tabulated values of Kqand corresponds to TPR20,10values for the ionization chamber[5].The interpolation techniques were used while using these tabulated values

Energy AAPM TG-51 IAEA TRS-398 KTP %dd(10)X Kq* Kion Kpol DW(Zmax) KTP TPR20,10 Kq** Kion Kpol DW(Zmax)6 MV 1.16055 66.7 0.991 1.00734 1.00054 0.9970 1.16055 0.668 0.992 1.00714 1.00054 0.9975 15 MV 1.16055 77.63 0.970 1.01135 1.00129 0.9967 1.16055 0.762 0.973 1.01109 1.00129 0.9995 Co-60 1.16055 NA 1.0 1.0 1.0 1.6489 1.16055 NA 1.0 1.0 1.0 1.6489

3 Results and discussion

3.1 Photon dosimetry

Table 1 shows beam quality speci fiers,namely TPR20,10 and%dd（10）X,for 6 and 15 MV photon beams which have been calculated from Fig.1a.With these values,a beam quality correction factor,Kq,for both photon energies(6 and 15 MV)was determined against the provided values of either TPR20,10or%dd（10）X[5,6],summarized in Table 1.In the case of TG-51,the Kqvalue is smaller than that of TRS-398.The percentage difference in Kqis-0.1 and-0.3%for 6 and 15 MV photon beams,respectively.

The absorbed doses(DW(Zmax))were calculated and normalized to Zmaxfor the Co-60 beam and 6 and 15 MV photon beams(Table 1)by using the%depth doses(%dd)that correspond to each beam quality.Figure 3 shows a comparison of the DW(Zmax)ratio(i.e.,DW(Zmax)TG-51/DW(Zmax)TRS-398)of Co-60 for the 6 and 15 MV photon beams for TG-51 and TRS-398 protocols.The same values of DW(Zmax)were observed for both protocols in the case of the Co-60 teletherapy unit,as there was no difference between the measured parameters.For the 6 and 15 MV photon beams,the percentage difference in absorbed dose was-0.05 and-0.3%,respectively.The TRS-398 gives relatively higher doses as compared to that of the TG-51 protocol.Moreover,the percentage difference in the calculated dose increased with an increase in the energy.

Fig.2 a Comparison of Kionof TG-51 and TRS-398 protocol,b comparison of Kqin both protocols,c calculated value of Kpol versus energy

Fig.3 Ratio of the absorbed doses at Zmax(i.e.,DW(Zmax)TG-51/DW(Zmax)TRS-398)for Co-60,for 6 and 15 MV photon beams,by comparing the two protocols(TG-51 and TRS-398)

In this study,dosimetry was performed for two therapeutic units,namely a Co-60 unit(THERATRON PHOENIX) and a high-energy Varian linear accelerator(CLINAC DMX 2100C),with 6 and 15 MV photon and 6,9,12,and 15 MeV electron beams.The dosimetry system consisted of a PTW stationary water phantom(T41014)with a cylindrical chamber(PTW-30001)connected to an electrometer(PTW UNIDOS E),which was used for the absolute dosimetry of the THERATRON PHOENIX.A Farmer-type ionization chamber(IBA-FC65-G)and a plane-parallel chamber(IBA PPC-05)were used for absolute dosimetry of the two photon and four electron beams that were generated by the CLINAC DMX 2100C,respectively.The chambers were connected to PTW UNIDOS E,attached to Blue water Phantom,and each chamber type combined with PTW UNIDOS E was calibrated in a Co-60 radiation beam with its reference point at a measuring depth of 5 cm in water at the SSDL at PINSTECH,Pakistan.The calibration was performed under the standard conditions of the IAEA TRS-398 protocol.

Following the recommendations and procedures adopted in both TG-51 and TRS-398 protocols,Kq,KT,P,Kpol,and Kionfor 6,9,12,and 15 MeV electron beams were measured.These values are summarized in Table 2.The values of KT,Pwere the same for both protocols,as explained earlier in the section on photon dosimetry.The calculated values of R50and the corresponding values of the reference depth,Zref,for electron energies of 6,9,12,and 15 MeV are also summarized in Table 2.According to the TRS-398 protocol,the Kqvalue is directly provided against R50,whereas,for TG-51 protocol,Kqwas calculated(Table 2)from R50for each electron energy[5].The calculated absorbed dose normalized to Zmaxfor the 6,9,12,and 15 MeV electron beams for the TG-51 and TRS-398 protocols is also listed in Table 2.

The beam quality,type of chamber,and some other measurement conditions,such as cable length and position,may affect the polarity for a particular ionization chamber.Therefore,a polarity correction factor,Kpol,must be applied for beams of different qualities.Furthermore,due to the lack of ion collection on the corresponding electrodes of the ion chamber,some of the ions produced may not contribute toward the actual signal.Therefore,recombination of ions(i.e.,ion recombination correction factor,Kion)has to be applied.Kiondepends upon the dose rate,the chamber geometry,and the applied polarizing voltage.Although the method(two-voltage method)for both protocolsunderstudy isthesame,theirmeasurement approaches are different.Similarly,the temperature and pressure correction factor,KT,P,also must be applied,as the clinical conditions are always different from the standard conditionsunder which the calibration ofthe dosimetry systems is performed.The KT,P,Kpol,and Kion were measured for both protocols according to the recommendations and procedures.These values are summarized in Table 1.

3.2 Electron dosimetry

By comparing the values of Kionand Kq,calculated based on recommendations of both protocols for corresponding beams,a measurable difference was observed for the studied photon beams(Fig.2a,b).In the case of the TG-51 protocol,the Kionhad a relatively greater value for both photon beams,as shown in Fig.2a,while Kqhad a relatively smaller value for both photon beams,as shown in Fig.2b.The results also showed that the polarity correction factor depends upon the photon beam energy.The polarity correction factor increases with an increase in the energy of the photon beam(Fig.2c).

Table 2 Comparison of Kq,Kion,Kpol,and absorbed doses at Zmax(DW(Zmax))values calculated on the basis of the recommendations of the AAPM TG-51 and IAEA TRS-398 protocols for 6,9,12,and 15 MeV electron beams

*Zreffor electron beams is the depth in water in a 10×10 cm2or larger beam of electrons at an SSD of 100 cm at which the absorbed dose falls to 50%of its maximum[5].It is determined from Fig.1b **R50=1.029I50-0.06(cm) （for2≤I50≤10cm）[5],I50is the depth at which the ionization falls to 50%of its maximum value.I50is determined from Fig.1b ***R50=1.029R50，ion-0.06(g/cm2）（forR50，ion ≤ 10g/cm2）orR50=1.059R50，ion-0.37(g/cm2）（forR50，ion ＞ 10g/cm2）[5],R50,ionis the depth in water(in g/cm2)at which the ionization current is 50%of its maximum value.R50,ionis determined from Fig.1b

Energy(MeV)IAEA TRS-398 KTP Zref*(cm) R50**(cm) Kq Kion Kpol DW(Zmax) KTP Zmax(cm) R50***(cm) Kq Kion Kpol DW(Zmax)6 1.17 1.19 2.15 0.94 1.023 1.013 1.026 1.17 1.08 2.15 0.92 1.023 1.013 1.013 9 1.17 1.98 3.46 0.92 1.010 1.005 1.006 1.17 1.99 3.42 0.91 1.005 1.010 0.996 12 1.17 2.85 4.91 0.91 1.013 1.008 1.006 1.17 2.44 4.83 0.91 1.013 1.008 1.003 15 1.17 3.64 6.24 0.90 1.014 1.007 0.910 1.17 2.80 6.12 0.90 1.013 1.007 0.998 AAPM TG-51

Fig.4 a Comparison of the Kionof TG-51 and TRS-398 protocols,b comparison of the beam quality factor,Kq,for both protocols,c calculated Kpolversus energy

Fig.5 Ratio of the absorbed doses at Zmax(i.e.,DW(Zmax)TG-51/DW(Zmax)TRS-398)for 6,9,12,and 15 MeV electron beams by use of two protocols(TG-51 and TRS-398)

Figure 4a,b shows a comparison of the Kionand Kq values for both protocols,and Fig.4c shows Kpolfor 6,9,12,and 15 MeV electron beams.There was no regular pattern recorded in the variation in Kionwith a change in the energy of the beam.Both the dosimetry protocols followed the same irregular pattern of variation in Kion(Fig.4a).By inter-comparison of both protocols for the values of Kq(i.e.,by keeping the energy of the beam constant),higher values of Kqfor the TG-51 protocol as compared to the TRS-398 protocol were observed for all the studied electron beams as shown in Fig.4b.Furthermore,variation in Kqdecreases as the electron beam energy increases.The percentage difference between the Kqvalues for 6,9,12,and 15 MeV electron beams was 1.5,0.9,0.3,and 0.0%,respectively,for both protocols.Figure 4c shows a variation in Kpolwith a change in the energy of the electron beam.Kpoldecreases with an increase in the energy of the electron beam.

对照组:开展日常护理,包括严格隔离制度,密切监测患者意识和生命体征,持续开展心电监护,测量中心静脉压,血氧饱和度,体温等;观察咳嗽的性质,痰液的颜色和数量,确保患者水,电解质和酸碱平衡;对温度超过38℃的患者进行降温治疗,根据医生的指示来使用解热镇痛药等[3]。

The ratio of the absorbed doses at Zmaxcorresponding to TG-51 and TRS-398 is illustrated in Fig.5.The percentage differences in the measured dose for both protocols for 6,9,12,and 15 MeV electron beams were 1.3,0.9,0.3,and 0.1%,respectively.In this case,the TG-51 gives relatively high doses as compared to the TRS-398 protocol,and it showed an inverse relationship with energy of the electron beams.

4 Conclusion

To conclude,small differences in the absorbed doses to water at the Zmaxratio were found for the two protocols.The TRS-398 protocol gave higher doses as compared to the TG-51 protocol.The percentage difference in the measured absorbed dose increased as the energy increased in the case of the photon beams;however,for the electron beams,TG-51 gave relatively higher doses as compared to the TRS-398 protocol.Unlike photon beams,the percentage difference in the measured absorbed dose decreased with an increase in the energy.To reduce uncertainty in the patient dose,the clinically followed dosimetry protocol and dosimetry protocol followed for the calibration of a dosimetry system should be the same.

References

1.J.Seuntjens,W.Strydom,K.Shortt,in Radiation Oncology Physics:A Handbook for Teachers and Students,Vol.ed.(International Atomic Energy Agency(IAEA),Vienna,Austria,2005),p.45

2.W.Muhammad,A.Ullah,K.Mahmood et al.,Assessment of national dosimetry quality audits results for teletherapy machines from 1989 to 2015.J.Appl.Clin.Med.Phys.17,145–152(2016).https://doi.org/10.1120/jacmp.v17i2.5984

3.W.Muhammad,H.Sang,A.Khan et al.,Dose non-linearity of the dosimetry system and possible monitor unit errors on medical linear accelerators used in conventional and intensity-modulated radiation therapy.Nucl.Technol.Radiat.27,368–373(2012).https://doi.org/10.2298/NTRP1204368M

4.P.Andreo,M.S.Huq,M.Westermark et al.,Protocols for the dosimetry of high-energy photon and electron beams:a comparison of the IAEA TRS-398 and previous international Codes of Practice.Phys.Med.Biol.47,3033(2002).https://doi.org/10.1088/0031-9155/47/17/301

5.P.R.Almond,P.J.Biggs,B.Coursey et al.,AAPM’s TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams.Med.Phys.26,1847(1999).https://doi.org/10.1118/1.598691

6.P.Andreo,D.Burns,K.Hohlfeld et al.,Absorbed Dose Determination in External Beam Radiotherapy:An International Code of Practice for Dosimetry Based on Standards of Absorbed Dose to Water.Technical Reports Series No.398(2000)

7.M.S.Huq,P.Andreo,H.Song,Comparison of the IAEA TRS-398 and AAPM TG-51 absorbed dose to water protocols in the dosimetry of high-energy photon and electron beams.Phys.Med.Biol.46,2985(2001).https://doi.org/10.1088/0031-9155/46/11/315

8.S.Saju,S.Jamema,D.Kumar et al.,Comparison Of IREA TRS 398,TRS 381 And AAPM TG 51 protocols For high energy electron beams.J.Med.Phys.29,9–16(2004)

9.W.Muhammad,A.Ullah,A.Hussain,EP-1502:effects on dosimetric measurements due to difference in calibration and dosimetry protocols followed.Radiother.Oncol.119(Supplement 1),S694(2016).https://doi.org/10.1016/S0167-8140(16)32752-9

10.M.Affonseca,P.Andreo,M.Arib et al.,in Implementation of the international code of practice on dosimetry in radiotherapy(TRS 398):review of testing results,vol.9201050054(International atomic energy agency(IAEA),Vienna,Austria,2005)

11.M.S.Huq,Everything you wanted to know about the Practical Implementation of TG-51 protocol in the clinic.Phys.Med.30(6),1378(2003)

12.M.Ahmad,A.Hussain,W.Muhammad et al.,Studying wedge factors and beam pro files for physical and enhanced dynamic wedges.J.Med.Phys.35,33–41(2010).https://doi.org/10.4103/0971-6203.57116

13.W.Muhammad,M.Maqbool,M.Shahid et al.,Accuracy checks of physical beam modi fier factors algorithm used in computerized treatment planning system for a 15 MV photon beam.Rep.Pract.Oncol.Radiother.14,214–220(2009).https://doi.org/10.1016/j.rpor.2009.12.002

14.W.Muhammad,M.Maqbool,M.Shahid et al.,Assessment of computerized treatment planning system accuracy in calculating wedge factors of physical wedged fields for 6 MV photon beams.Phys.Medica 27,135–143(2011).https://doi.org/10.1016/j.ejmp.2010.06.003