Radiation Doses To Normal Tissues During Craniospinal Irradiations Biology Essay

Abstraction:

Craniospinal irradiation is considered an of import component of the multidesplinary attack in the intervention of medulloblastoma. It is a complex radiation therapy technique, patients who are treated successfully normally live long periods. Every attempt should be done to diminish the radiation therapy related side effects, particularly with the presently available 3D conformal radiation therapy planning system in our section.

This dosimetric survey is taking to describe the consequences of analysis of doses received by mark volumes and variety meats outside the mark volumes during intervention of medullblastoma patients. Besides taking at comparing the doses making to the eyes and the lens with the usage of different screening methods.

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Ten kids recent diagnosing of high hazard medulloblastoma ( big residuary & gt ; 1.5 centimeter, M0 ) were included in the survey after reexamining the pathology. All of them were subjected to MRI encephalon and spine together with CSF cytology three hebdomads after surgery. They were subjected to arrested development, conventional simulation, followed by CT simulation. The scans will be transferred to the intervention planning system. The encephalon, spinal canal, and different normal tissue will be outlined.

For the cranial Fieldss, parallel opposed Fieldss were used with the isocentre of the Fieldss in the mid-plan in the Centre of the encephalon, and behind the eyes. For the spinal field, the full length was opened to the desired place to handle the spinal column by asymmetric jaws. The inferior boundary line of the cranial field was matched to the superior boundary line of the spinal field utilizing collimator and couch rotary motion of the cranial field. Sensitive tissues near to the mark volume was shielded utilizing either MLCS or blocks.

The dosage prescribed was 36 Gy/20 fractions for cranial and spinal parts. The mention point was placed in the Centre of the cranial and spinal Fieldss. The upper limit, lower limit and intend dosage to each anatomic construction were computed utilizing dose volume histograms by summing the cranial and spinal intervention programs. All patients gave informed consent that we can analyze their program and do research on it

Introduction

Medulloblastoma constitutes 15-20 % of all childhood cardinal nervous system tumours. The average age at diagnosing is normally 6 old ages. The most common site of beginning is the vermis and the 4th ventricle. The presence of big residuary tumour & gt ; 1.5 centimeter or cerebro-spinal metastasis identifies high hazard patients ( 1 ) .

Reduced-dose ( 23.4 Gy ) craniospinal irradiation ( CSI ) in combination with hebdomadal Oncovin, followed by a boosting of the dosage to the buttocks fossa up to 55.8 Gy followed by accessory systemic chemotherapy in the signifier of Oncovin, CCNU, and cisplatin output a Progression-free endurance of 79 % at 5 old ages and is considered the province of art for standard hazard medulloblastoma patients. ( 2 )

Higher radiation therapy dosage to the CSI 36-39 Gy is normally considered for M0 instances ( & gt ; 1.5 centimeter residuary without cranio-spinal metastasis ) . ( 2 )

Craniospinal axis irradiation ( CSI ) is considered the corner rock in the intervention of medulloblastoma. It is a complex technique with really irregular clinical mark volume ( CTV ) . It is executed in two stages, the whole encephalon and neuraxis are treated in the initial stage. The site of the 1ry tumour is boosted in the 2nd stage ( 3 ) .

A figure of techniques are applied to better dose homogeneousness across the junction between the cranial and the spinal Fieldss ; including either direct abutment of the Fieldss or the debut of a spread with or without a traveling junction. Effort had been made to diminish the dosage to the lens, thyroid, bosom, GIT, and sex glands and to diminish the possible late effects of radiation therapy in those long life patients.

Several new modes and techniques are now available taking at more precise coverage of the mark volume ( spinal canal & A ; encephalon ) and more sparing of the variety meats at hazard, including the usage of CT simulators, better arrested development installations, the usage of conformal radiation therapy and IMRT. ( 4 )

Since the debut of our new additive gas pedal ( Elekta ) and intervention planning system ( Precise Elekta ) with many exposing and rating package tools 5 old ages ago in our section we became more able to give better radiation therapy to those patients.

Aim of this survey:

This dosimetric survey is taking at describing the consequences of analysis of doses received by mark volumes and variety meats at hazard ( OAR ) during intervention of high hazard medullblastoma patients. Besides we will compare the dose stretch to the lens with the usage of different screening methods.

Materials and methods:

Ten kids with recent diagnosing of high hazard medulloblastoma ( big residuary & gt ; 1.5 centimeter, M0 ) were included in the survey after reexamining the pathology. All of them were subjected to MRI encephalon and spine together with CSF cytology three hebdomads after surgery. All of these patients were planned to have whole craniospinal irradiation ( CSI ) accompaniment with hebdomadal vincristin get downing 4 hebdomads after surgery. All patients gave informed consent that their program will be studied and will be subjected to research.

All patients received craniospinal irradiation ( CSI ) with a sidelong analogue opposed Fieldss to the caput and a matched posterior spinal column field, with moving of the junction 1cm every 7 fractions ( The place of the lower cranial boundary line and upper spinal field were shifted ) .

The cranial Fieldss were treated iso-centrically while the spinal field was treated at fixed SSD.

An immobilisation mask was fabricated from thermoplastic stuff for each patient. The patients were simulated from the top of the caput to the mid-pelvis utilizing CT scan. During simulation, patients were placed in prone place with cervix extended so that a posteriorly oriented spine field could go out below the lower jaw.

CT spacing was 3mm for the encephalon and 5mm for the spinal column. Patients were marked with sagittal and sidelong optical maser lines during the confirmation, simulation and subsequent intervention.

The CT scans were so transferred to Precise Elekta intervention planning system where spinal canal and encephalon were contoured as the mark volumes. Variety meats at hazard and other normal tissues were besides contoured. They include lenses, eyes, ocular nervousnesss, bosom, lung, liver and kidneys. Care was taken to guarantee that the encephalon contour included the cribriform home base. Then the intervention Fieldss were designed for intervention.

The energies of the photon beams were 4MV & A ; 6MV for cranial and spinal Fieldss severally.

For the braincase, parallel opposed Fieldss were used with two isocenters for each patient one behind the oculus and the other in the Centre of the encephalon. The cranial Fieldss include whole encephalon and extended caudally every bit long as the shoulder permits with 1 centimeters above shoulder to let traveling junction. In order to bring forth the field aperture for the cranial Fieldss, the multi-leaf collimator was automatically positioned with the inside corner of the aperture 0.5cm from the contoured encephalon so MLC foliages were adjusted.

Because the inferior divergency of the cranial Fieldss may overlap into the spinal cord, a couch rotary motion of 6-80 was added to extinguish such divergency. Besides a collimator rotary motion of 8-100 on the sidelong cranial Fieldss was done to fit the divergency of the superior spinal field border.

So couch and collimator rotary motion in sidelong cranial Fieldss were applied to efficaciously hold all three field borders from both sidelong encephalon ports and the posterior spinal column port to run into at the cervical junction as a individual plane. So the dose homogeneousness at the craniospinal junction was achieved.

For the spinal field, a individual buttocks long thin spinal field was used. It should cover the whole spinal column. The posterior spinal column field was simulated ; the superior boundary line of the spinal field touches the inferior boundary line of the cranial field. The full length was opened to the desired place to handle the spinal column by asymmetric jaws. If the distance from 2nd cervical vertebra to the base of the spinal column ( 2nd sacral vertebra ) was more than 39cm so the intervention was carried out at drawn-out SSD. SSD was 100cm in 8 patients and 110cm and 120cm in two other patients.

For the cranial Fieldss, the averaged field size was 20x20cm. For the spinal field, the length ranged from 26cm -38cm. The breadth of the spinal field ranged from 4-8cm.

MLCS and or cerrobend screening blocks were used to screen eyes, lenses and other sensitive tissues near to the mark volume as kidneys and lungs. For each patient, four planes were created ; Plan 1, the isocenter of the cranial Fieldss was placed in the centre of the encephalon and MLCs were used to screen the eyes and lenses. In Plan 2 the isocenter was behind the eyes and MLCs were used to screen the eyes and lenses. In Plan 3 the isocenter was behind the eyes and screening block was used to screen the eyes and lenses. In Plan 4 the isocenter was in the centre of the encephalon and screening block was used to screen the eyes and lenses.

The dosage prescribed was 36 Gy/20 fractions for braincase and spinal column parts. For cranial dose prescription, the dosage was normalized to the Centre of the encephalon. For spinal cord dosage prescription the dosage was normalized to the Centre of the field at the anterior surface of the spinal cord to accomplish good coverage ( 95 % ) as the dosage is low at the anterior surface of the spinal cord. The delivered MU of the spinal Fieldss ranged from 190-300 and for the cranial field ranged from 95-108Mu.

For each plane of each patient the added dosage program map was used to look into the dose coverage of the combined cranial and spinal dosage programs. Then the four programs for each patient were compared utilizing ocular review of the dose distribution, dose volume histogram and dose volume histogram parametric quantities. These parametric quantities were listed and analyzed statistically utilizing excel sheet and SPSS ( version11 ) Wilcoxon signed Ranks trial

Consequences:

Radiation doses to aim volumes and variety meats at hazard during CSI ( Table 1 ) :

By reexamining the intervention planning and dose volume histograms of all 10 patients, the followerss were the consequences as respects the dose distribution of the mark volumes ( encephalon & A ; spinal canal ) and organs at hazard:

As respects the mark volumes ;

Brain was covered in all instances by 95 % of the dosage. The lower limit dosage received by any of the treated patients was 34.2 Gy while the maximal dose received was 40.3Gy ( still within the encephalon tolerance ) .

The spinal cord was covered in all instances by 95 % of the dosage. The lower limit dosage received by the spinal cord in any of the treated patients was 34.2 Gy, while the maximal dosage was 41.4Gy ( still within spinal cord tolerance ) .

As respects variety meats at hazard ( OARs ) :

The norm of the mean dosage received by the whole liver for all patients was 18 % of the prescribed dose i.e. 641 cGy, with a dose scope from 504-828cGy.

The norm of the mean dosage received by any of the kidneys was 8 % of the prescribed dose i.e. 280 cGy with a dose scope from 72-612 cGy.

The norm of the maximal dosage received by the bosom of the treated patients was 94.5 % of the prescribed dose i.e. 34Gy, with the dose scopes from 33-34.9 cGy

The norm of the dosage that 20 % of the lungs received is 10 % of the prescribed dose i.e. 360cGy with the dose scopes from 180cGy-540cGy.

The norm of the maximal dosage of ocular nervus was 98.5 % of the prescribed dose i.e. 36Gy, with the dose scopes from 34-37Gy. The maximal dosage is still below the maximal point dosage for the ocular nervus.

The norm of the organic structure maximal dosage was 118 % of the prescribed dose i.e 42Gy, with the dose scopes from 40 and 45 Gy ; this maximal point was in the back musculuss ( still within the tolerance of the musculus ) .

Table 1: Radiation doses in per centum for mark volumes and variety meats at hazard during CSI:

Patients

Brain min

Brain soap

Cord min

Cord soap

Liver intend

R. k. mean

L. k. mean

Heart soap

Heart mean

Lung D20 %

Ocular soap

Body soap.

1

96

107

95

115

16

5

5

97

51

10

99

124

2

95

109

96

113

18

5

10

92

54

10

99

115

3

96

106

97

115

17

8

7

95

50

8

101

117

4

95

110

96

111

14

9

7

95

55

8

101

117

5

95

111

95

110

20

4

4

92

39

15

100

113

6

95

112

95

113

16

3

5

95

49

8

95

119

7

95

112

95

115

22

14

2

93

51

5

95

125

8

95

109

95

110

23

11

13

95

54

12

104

112

9

95

106

98

113

17

14

17

97

56

15

97

119

10

95

110

96

109

15

8

8

94

50

9

97

118

min

95

106

95

109

14

3

2

92

39

5

95

112

soap

96

112

98

115

23

14

17

97

56

15

104

125

mean

95.2

109.2

95.8

112.4

17.8

8.1

7.8

94.5

50.9

10

98.8

117.9

Median

95.5

109.5

96.5

111

17.5

8

7.5

94

50.5

9.5

99.5

117.5

Average = mean of the agencies.

Table 2.Radiation doses in cGy for mark volumes and variety meats at hazard during CSI

Patients

Brain min

Brain soap

Cord min

Cord soap

Liver intend

R. k. mean

L. k. mean

Heart soap

Heart mean

Lung D20 %

Ocular soap

Body soap.

1

3456

3852

3420

4140

576

180

180

3492

1836

360

3564

4464

2

3420

3924

3456

4068

648

180

360

3312

1944

360

3564

4140

3

3456

3816

3492

4140

612

288

252

3420

1800

288

3636

4212

4

3420

3960

3456

3996

504

324

252

3420

1980

288

3636

4212

5

3420

3996

3420

3960

720

144

144

3312

1404

540

3600

4068

6

3420

4032

3420

4068

576

108

180

3420

1764

288

3420

4284

7

3420

4032

3420

4140

792

504

72

3348

1836

180

3420

4500

8

3420

3924

3420

3960

828

396

468

3420

1944

432

3744

4032

9

3420

3816

3528

4068

612

504

612

3492

2016

540

3492

4284

10

3420

3960

3456

3924

540

288

288

3384

1800

324

3492

4248

Minute

3420

3816

3420

3924

504

108

72

3312

1404

180

3420

4032

Soap

3456

4032

3528

4140

828

504

612

3492

2016

540

3744

4500

mean

3427

3931

3448.8

4046

640.8

291.6

280.8

3402

1832

360

3556.8

4244

Median

3438

3942

3474

3996

630

288

270

3384

1818

342

3582

4230

Average = mean of the agencies

As regard eyes & A ; lenses:

The dosage received by the eyes and lenses utilizing two different screening techniques and utilizing two different positioning for encephalon isocenters:

Four programs were carried out, they are

Plan 1 isocenter is in the centre of the encephalon with utilizing MLCs shielding.

Plan 2 isocenter is behind the eyes with utilizing MLCs screening

Plan 3 isocenter is behind the eyes with utilizing block shielding.

Plan 4 isocenter is in the centre of the encephalon with utilizing block shielding

The mean dosage received by the right and left eyes and the maximal dosage received by the right and left lens were listed and compared for the four programs. ( Tables 3-6 ) :

Plan 1 & A ; 2:

Plan 2 shows lower doses to eyes and lenses compared to be after 1

In program 2, the norm of the mean dosage of the right and left eyes was 46 % & A ; 45 % compared with 53 % & A ; 52 % in program 1 ( table 3 ) . In program 2 the norm of the maximal dosage of the right and left lens was 38 % & A ; 41 % compared with 44 % & A ; 48 % in plan1 ( table 5 ) . So utilizing MLCs to screen the eyes & A ; lenses with seting the isocenter behind the eyes shows lower doses than seting the isocenter in the centre of the encephalon.

Plan 3 & A ; 4: program 4 shows lower doses to eyes and lens compared to be after 3

In program 3, the norm of the mean dosage of the right and left eyes was 32 & A ; 31.5 % compared with 30.5 % & A ; 30 % in program 4 ( table 3 ) . The norm of the maximal dosage of the right and left lens was 15.5 % & A ; 11 % compared with 13 % & A ; 11 % in program 4 ( table 5 ) . So utilizing block to screen the eyes with seting isocenter behind the eyes or in the centre of the encephalon shows no important difference ( both show low doses to eyes and lenses )

Plan 2 & A ; 3: program 3 shows lower doses to eyes and lenses compared to be after 2

In program 2, the norm of the mean dosage of the right and left eyes was 46 % & A ; 45 % compared with 32 % & A ; 31.5 % in program 3 ( table3 ) . The norm of the maximal dosage of the right and left lens was 38 % & A ; 41 % compared with 15.5 % & A ; 11 % in program 3 ( table5 ) . So seting the isocenter behind the eyes with block screening shows low doses to eyes and lenses than seting the isocenter behind the eyes with utilizing MLCs shielding.

Plan 1 & A ; 3: Plan 3 shows lower doses to eyes and lenses compared to be after 1

In program 1, the norm of the mean dosage of the right and left eyes was 53 % & A ; 52 % compared with 32 % & A ; 31.5 % in program 3 ( table 3 ) . In program 1, the norm of the maximal dosage of the right and left lens was 44 % & A ; 48 % compared with 15.5 % & A ; 11 % in program 3 ( table5 ) . so seting the isocenter behind the eyes with block shielding shows lower doses than seting the isocenter in the centre of the encephalon with utilizing MLCs screening

Plan 1 & A ; 4: program 4 shows lower doses to eyes and lenses compared to be after 1

In program 1, the norm of the mean dosage of the right and left eyes was 53 % & A ; 52 % compared with 30.5 % & A ; 30 % in program 4 ( table 3 ) . The norm of the maximal dosage of the right and left lens was 44 % & A ; 48 % compared with 13 % & A ; 11 % in program 4 ( table 5 ) . So seting the isocenter in the centre of the encephalon with utilizing block shielding shows lower doses than seting the isocenter in the centre of the encephalon with utilizing MLCs shielding.

The mean dosage to both eyes and the maximal point dosage to both lenses for these programs were assessed and analyzed statistically utilizing Wilcoxon signed rank trial. We found that there is a important difference in saving the eyes and the lenses between program 1 & A ; 2, between program 2 & A ; 3, between plan1 & A ; 3 and between program 4 & A ; 1 ( P values & lt ; 0.05 for all ) . On the other manus, there is no important difference between program 3 & A ; 4. Both show low doses to eyes and lenses ( P values & gt ; 0.05 ) .

Table 3, The mean dosage received by the oculus in % for four different planes utilizing two different encephalon isocenters and different shielding methods

Rt oculus

mean dosage

Lt oculus

mean dosage

patients

program 1

plan2

plan3

plan4

program 1

plan2

plan3

plan4

1

31

31

12

12

33

23

12

13

2

70

56

36

32

57

41

21

19

3

77

68

46

48

60

55

32

35

4

46

41

30

24

50

42

36

30

5

65

64

50

49

51

47

34

30

6

33

32

17

18

24

26

15

11

7

38

20

18

11

37

27

19

13

8

62

57

46

49

75

72

59

60

9

43

38

29

25

61

52

37

40

10

65

55

37

37

74

61

50

47

min %

31

20

12

11

24

23

12

11

max %

77

68

50

49

75

72

59

60

mean

53

46.2

32.1

30.5

52.2

44.6

31.5

29.8

Median

46

41

30

25

54

44.5

33

32.5

Average = mean of the agencies

Table 4, The mean dosage received by the oculus in cGy for four different planes utilizing two different encephalon isocenters and different shielding methods

Rt oculus

mean dosage

Lt oculus

mean dosage

patients

program 1

plan2

plan3

plan4

program 1

plan2

plan3

plan4

1

1116

1116

432

432

1188

828

432

468

2

2520

2016

1296

1152

2052

1476

756

684

3

2772

2448

1656

1728

2160

1980

1152

1260

4

1656

1476

1080

864

1800

1512

1296

1080

5

2340

2304

1800

1764

1836

1692

1224

1080

6

1188

1152

612

648

864

936

540

396

7

1368

720

648

396

1332

972

684

468

8

2232

2052

1656

1764

2700

2592

2124

2160

9

1548

1368

1044

900

2196

1872

1332

1440

10

2340

1980

1332

1332

2664

2196

1800

1692

min

1116

720

432

396

864

828

432

396

soap

2772

2448

1800

1764

2700

2592

2124

2160

mean

1908

1663.2

1155.6

1098

1879.2

1605.6

1134

1072.8

Median

1656

1476

1080

900

1944

1602

1188

1170

Average = mean of the agencies.

Table 5 ; The upper limit dosage received by the lenses in % for 4 different planes utilizing two different isocenters and different screening methods:

Rt lens

soap dosage

Lt lens

soap dosage

patients

program 1

plan2

plan3

plan4

program 1

plan2

plan3

plan4

1

24

29

12

12

41

33

12

13

2

69

59

10

11

37

23

10

11

3

93

80

53

28

75

54

12

12

4

23

17

23

20

77

60

10

10

5

53

56

12

12

60

45

12

11

6

18

19

6

7

38

46

10

10

7

17

17

7

10

9

12

7

9

8

34

29

11

11

62

68

23

17

9

36

30

11

11

20

19

9

7

10

70

46

10

8

60

49

9

8

min %

17

17

6

7

9

12

7

7

max %

93

80

53

28

77

68

23

17

mean

43.7

38.2

15.5

13

47.9

40.9

11.4

10.8

Median

35

38

11

11

41

45.5

10

10.5

Average = mean of the agencies.

Table 6 ; the upper limit dosage received by the lenses in cGy for 4 different planes utilizing two different isocenters and different shielding methods

Rt lens

Max. dose

Lt lens

Max dosage

patients

program 1

plan2

plan3

plan4

program 1

plan2

plan3

plan4

1

864

1044

432

432

1476

1188

432

468

2

2484

2124

360

396

1332

828

360

396

3

3348

2880

1908

1008

2700

1944

432

432

4

828

612

828

720

2772

2160

360

360

5

1908

2016

432

432

2160

1620

432

396

6

648

684

216

252

1368

1656

360

360

7

612

612

252

360

324

432

252

324

8

1224

1044

396

396

2232

2448

828

612

9

1296

1080

396

396

720

684

324

252

10

2520

1656

360

288

2160

1764

324

288

min

612

612

216

252

324

432

252

252

soap

3348

2880

1908

1008

2772

2448

828

612

mean

1573.2

1375.2

558

468

1724.4

1472.4

410.4

388.8

Median

1260

1368

396

396

1476

1638

360

378

Discussion:

This dosimetric survey was conducted to describe the consequences of analysis of doses received by mark volumes and variety meats at hazard during intervention of 10 kids with high hazard medullblastoma treated with craniospinal irradiation accompaniment with chemotherapy at our section. Besides we compared the dosage making to the eyes and the lens with the usage of two different screening methods and two different places for encephalon isocenter.

As respects the mark volume ; the lower limit dosage received by the encephalon in any of the treated patients was 34.2Gy and the maximal dose received was 40.3Gy. The median of the maximal dosage received by the encephalon was 39.4 Gy while the median of the lower limit dosage received by the encephalon was 34.38 Gy.

The lower limit dosage received by the spinal cord by any of the treated patients was 34Gy, and the maximal dosage was 41.4Gy, The median of the maximal dosage received by the cord was 39.96 Gy while the median of the lower limit dosage received by the encephalon was 34.74 Gy.

These consequences are closely related to the consequences published by Darunee Tongwan in his dosimetric analysis of craniospinal irradiation in the supine place comparing four different techniques, where the average dosage received by the encephalon was 36.91Gy and the average dosage received by the spinal column was 38.12 Gy. ( 5 )

As respects variety meats at hazard, get downing with the liver, the average dosage received by the whole liver for all patients was 17.5 % of the prescribed dose i.e. 630 cGy, with a dose scopes between 504-828cGy. This was similar to darunee ‘s survey in which the dosage to the liver ranged from 533-698 cGy with a average dosage of 576 cGy.

Sing the kidneys, the average dosage received by the right and left kidneys were 8 and 7.5 % of the prescribed dose i.e. 288 and 270 cGy to the right and left kidney severally with a dose scope between 72-612 cGy, which is about indistinguishable to the average dosage received by the kidneys in darunee ‘s survey.

In the present survey, the upper limit dosage received by the bosom in any of the treated patients was 34.9Gy, with the mean dosage ranged between 14.04 Gy and 20.16 Gy. This is in agree with, the dosage received by the bosom in darunee ‘s survey, which ranged from 14,00-19,00 Gy.

In darunee ‘s survey, the lungs received a dose runing from 413-565 cGy with a average dosage of 476 cGy. This is about the same in our survey where the dosage received by 20 % of the lungs ranged from 180-540 cGy with a average dosage of 342 cGy.

In this survey, the norm of the mean dosage received by the right and left eyes was 53 % and 52 % of the prescribed dose when utilizing program 1 ( MLC and isocenter in the centre of the encephalon ) , this was improved to 46 % and 45 % for both right and left eyes when the isodose was moved to merely behind the eyes and maintaining utilizing of MLCs for screening ( program 2 ) . On the other manus, utilizing blocks for shielding was associated with dramatic betterment in the mean dosage making the eyes i.e. 32 % , 31.5 % to right and left eyes severally when utilizing ( program 3 ) & A ; 30.5 % , 30 % severally when utilizing ( program 4 ) .

So, by utilizing blocks for screening alternatively of MLCs there was a dramatic lessening in the dosage making the eyes. The mean dosage to the eyes was reduced by up to 42 %

In the present survey, the norm of the maximal dosage received by the right and left lens was 44 % and 48 % of the prescribed dose when utilizing program 1 ( MLC used and the isocenter is in the centre of the encephalon ) , this was improved to 38 % and 41 % for both right and left lens when the isocentre was moved to merely behind the eyes and maintaining utilizing of MLCs for screening ( program 2 ) . On the other manus, utilizing blocks for shielding was associated with dramatic betterment in the maximal dose making the lens i.e. 15.5 % , 11 % to right and left lenses severally when utilizing ( program 3 ) & A ; 13 % , 11 % severally when utilizing ( program 4 ) . The soap. dose to the lens was reduced by 70 % & A ; 77 % for the right & A ; left lens severally.

Our consequences were similar to the consequences obtained by Kalapurakal et Al in his survey measuring the inauspicious consequence of the usage of multileaf collimator on the dosage received by the lens in kids with leukaemia having cranial irradiation where the dosage to the lens was increased by approximately 64 % and 72 % when utilizing MLC without screening blocks ( 6 ) .

The fact that the usage of MLCs was associated with addition the dosage to the lens was besides recognized by vijay et Al ( 7 ) measuring shielding of the whole encephalon by three different methods in 10 kids having whole encephalon irradiation and making the decision that the usage of conformal planning and screening utilizing MLCs will take to better coverage of the PTV by the 95 % isodose curves but higher dosage to the eyes and lenses

The dosage to the lens was besides evaluated in the survey done by Cochran et Al ( 8 ) measuring the dosage to the lens during craniospinal irradiation utilizing protons and demoing that angling the cranial proton beam 15-20 grade posteriorly will take to significant lessening in the dosage received by the lens by about 50 % .

But still our consequences were off from the consequences shown by pakisch et Al ( 9 ) who showed that the dosage to the lens was reduced to 4 % merely from the described midplan dose with usage of combination of angulation of the sofa, arrangement of extra oculus blocks near to the surface, and angulation of the gauntry during contraceptive cranial irradiation and with the usage of 8 MV photon beams.

Decision:

From the above motioned survey we can reason that, the dosage of radiation received by the mark volume and the variety meats at hazard during craniospinal irradiation of kids with high hazard medulloblastoma with the usage of our new additive gas pedal and intervention planning system Elekta & A ; Precise Elekta is about indistinguishable to other surveies and is making its mark ( OARs are within normal tissue tolerance ) .

As respects the dosage to the lenses, utilizing block shielding shows lower doses to eyes and lenses irrespective to the place of isocenter, on the other manus, with the usage of MLCs for screening, the isocenter should be behind the oculus non in the centre of the encephalon as this shows lower doses to eyes and lenses. If we use the isocenter in the encephalon so we should utilize block.

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