Assessment of concomitant testicular dose with radiochromic film

SCIENTIFIC PAPER

Assessment of concomitant testicular dose with radiochromic film

Katherine Fricker • Christine Thompson •

Juergen Meyer

Received: 3 April 2013 / Accepted: 17 June 2013

� Australasian College of Physical Scientists and Engineers in Medicine 2013

Abstract To assess the suitability of EBT2 and XRQA2

Gafchromic film for measuring low doses in the periphery

of treatment fields, and to measure the accumulative con-

comitant dose to the contralateral testis resulting from CT

imaging, pre-treatment imaging (CBCT) and seminoma

radiotherapy with and without gonadal shielding. Superfi-

cial peripheral dose measurements made using EBT2

Gafchromic film on the surface of water equivalent mate-

rial were compared to measurements made with an ioni-

sation chamber in a water phantom to evaluate the

suitability and accuracy of the film dosimeter for such

measurements. Similarly, XRQA2 was used to measure

surface doses within a kilovoltage beam and compared

with ionisation chamber measurements. Gafchromic film

was used to measure CT, CBCT and seminoma treatment

related testicular doses on an anthropomorphic phantom.

Doses were assessed for two clinical plans, both with and

without gonadal shielding. Testicular doses resulting from

the treatment of up to 0.83 ± 0.17 Gy were measured per

treatment. Additional doses of up to 0.49 ± 0.01 and

2.35 ± 0.05 cGy were measured per CBCT and CT image,

respectively. Reductions in the testicular dose in the order

of 10, 36 and 78 % were observed when gonadal shielding

was fitted for treatment, CT and CBCT imaging, respec-

tively. Gafchromic film was found to be suitable for

measuring dose in the periphery of treatment fields. The

dose to the testis should be limited to minimise the risk of

radiation related side effects. This can be achieved by using

appropriate gonadal shielding, irrespective of the treatment

fields employed.

Keywords Seminoma � Imaging dose � Peripheral dose �Gafchromic film

Introduction

Testicular cancer is rare, having a global prevalence of

0.8 % of male cancers, with a slightly increased incidence

in westernised countries (1.2 % in New Zealand) [1]. It is

the most common cancer in males of age 15–39 years in

New Zealand [1] but remains one on the most curable

cancers if treated in the early stages (5-year relapse-free

rate of 95–97 %) [2, 3].

Testicular seminoma has a predictable disease progres-

sion typically metastasising to the paraaortic (PA) lymph

nodes. For patients with a history of un-descended testes

and/or abnormal nodal drainage, there is also an increased

risk of disease spread to the pelvic and ipsilateral common

iliac lymph nodes [4]. Stage I seminoma is treated by

orchidectomy followed by one of the following: surveil-

lance, chemotherapy or radiotherapy to the PA lymph

nodes, including pelvic and iliac lymph nodes where

appropriate [4]. Lead shielding is routinely used to protect

This work was presented in part at Engineering and Physical Sciences

in Medicine (EPSM) Conference in the Gold Coast, Australia,

December 2012.

K. Fricker � J. Meyer

Department of Physics and Astronomy, University

of Canterbury, Private Bag 4800, Christchurch 8140,

New Zealand

K. Fricker (&) � C. Thompson

Cancer and Blood Services, Auckland City Hospital,

2 Park Road, Grafton, Auckland 1023, New Zealand

e-mail: [email protected]

J. Meyer

Department of Radiation Oncology, University of Washington,

1959 NE Pacific Street, Box 356043, Seattle, WA 98195, USA

123

Australas Phys Eng Sci Med

DOI 10.1007/s13246-013-0208-y

the remaining testis from radiation for patients undergoing

radiotherapy inclusive of the pelvic and ipsilateral common

iliac lymph nodes. Even though the testis is well removed

from the PA irradiation fields, scattered dose in the order of

1–6 % of the prescribed dose has been measured using

thermoluminescent detectors (TLDs) [5, 6]. The testicular

dose had been reported to be reduced to 0.4–3 % when

some form of gonadal shielding was fitted [5, 6].

Radiation induced cancer to the contralateral testis and the

late side effects of infertility are potential risks for survivors of

testicular seminoma due to their long life expectancy [7–9].

A retrospective study assessing patients at least 3 years

after treatment for testicular cancer, which included

orchidectomy followed by surveillance, radiotherapy and/

or chemotherapy, found a 30 % decrease in fertility [9].

Radiotherapy was found to have the greatest detrimental

effect [9]. Additionally, following radiotherapy for testic-

ular seminoma, patients are more likely to develop (a

second) testicular cancer compared with the general pop-

ulation [10, 11].

Radiotherapy is not the only contributor to dose in the

periphery of the treatment field. Healthy tissue will receive

dose contributions from planning CT and pre-treatment

imaging in the order of mGy [12, 13]. Brenner et al. [14]

suggested that approximately 1.5–2.0 % of all cancers in

the United States may be related to the radiation dose from

CT studies. Similarly, Berrington de Gonzalez et al. [15]

estimated that approximately 2 % of the cancers diagnosed

every year in the United States could be CT related.

Contrary to this, Van Walraven et al. [16] concluded that

the excess risk of second cancers among testicular cancer

survivors is not associated with diagnostic imaging.

Despite the conflicting reports on the role of diagnostic

imaging in cancer induction, it is important to quantify and

interpret the peripheral doses delivered during seminoma

radiotherapy.

In this work the usefulness of clinically available EBT2

and XRQA2 Gafchromic film for measuring low peripheral

dose was assessed. Subsequently, the accumulative dose a

patient receives while undergoing radiation treatment for

testicular seminoma was measured. Dose contributions from

CT, CBCT and treatment scatter were considered. Both PA

lymph node and extended field treatments were assessed

with and without gonadal shielding fitted. Although treat-

ment and imaging related dose has been studied indepen-

dently [5, 6, 17, 18], the total concomitant treatment related

dose has yet to be investigated using Gafchromic film.

Methods and materials

In Gafchromic film calibration, the process of calibrating

Gafchromic film for measuring dose in the periphery of

18 MV seminoma treatment fields and related imaging

fields is presented. In Dosimeter comparison, the suitability

of Gafchromic film for measuring low doses in the

periphery of treatment fields was assessed. This is followed

by the measurements of seminoma treatment related dose

in Measurements.

Gafchromic film calibration

Gafchromic film (International Speciality Products (ISP),

Wayne, NJ) is a type of self-developing radiochromic film,

which since its introduction in 2004 is gaining popularity as a

suitable dosimeter in radiology [19–21] and radiation oncol-

ogy [22–24] applications. Two types of Gafchromic film were

used; EBT2 for measurements in a megavoltage (MV) beam

and XR-QA2 for measurement in kilovoltage (kV) beams.

EBT2 film calibration

EBT2 Gafchromic film was calibrated in a 6 and 18 MV

beam using a Varian iX linear accelerator (Varian Medical

Systems, Palo Alto, CA). The majority of calibration

measurements were made for doses less than 50 cGy to

ensure accuracy in the film calibration at low doses. Gaf-

chromic film was cut into 4 9 4 cm2 pieces and marked to

keep the orientation of the film consistent. A film piece was

placed in a 30 9 30 9 20 cm3 stack of Solid Water�

(Gammex RMI, Middleton, WI, USA) at a depth of 5 cm.

The centre of the film was aligned with the central axis of

the beam along the crosswires. The linear accelerator dose

delivery is linear down to 3 Monitor Units (MU), where 1

MU is defined as 1 cGy to Dmax at a source to axis distance

(SAD) of 100 cm, in a 10 9 10 cm2 field. In order to

ensure linearity of the beam at low doses, the solid water

was placed at an extended SSD. The ratio of dose delivered

at isocentre in a water phantom (10 9 10 cm2 field, 95 cm

SSD) to that at the extended SSD in solid water (5 cm

depth, 5 9 5 cm2, 200 cm SSD) was used to correct for the

extended SSD setup. The correction factor, Cext, accounts

for the change in field size, SSD and any discrepancies

between measurements made in the water and solid water

phantoms. 12 pieces of film were irradiated with increasing

dose over the range 0–150 cGy. This was repeated three

times. The dose, D, to the films was calculated from the

delivered MU, with adjustments made for the deviation of

the machine output from calibration, Oc, which is the ratio

between the current machine output and that at calibration,

the placement of the film at depth and the extended SSD

setup and is given by

D ¼ MU � Oc � TMR� Cext ð1Þ

The tissue maximum ratio at a depth of 5 cm was 0.918

and 0.990 for 6 and 18 MV, respectively.


123

The film pieces were digitised one at a time using an

Epson Expression 10000XL scanner (Seiko Epson Corpo-

ration, Nagana, Japan) 24 ± 1 h post irradiation. Films

were placed at the centre of the scanner bed, in a consistent

landscape orientation, with the short edge of the original

film parallel to the scanning direction and the polyester

substrate layer facing the glass. The scanner was used in

professional mode, with software selections transmission

and positive film and with all filters and colour corrections

turned off. Images were acquired in 48-bit colour, using a

resolution of 72 dpi and saved in tagged image file format

(TIFF). The scanner was switched on 30 min prior to use

and a preview, followed by three scans to warm up the

scanner before film digitisation commenced [25, 26].

Additionally, a preview scan was performed prior to each

scan [26]. Gloves were worn at all times when handling the

film. The image files were imported into MATLAB�

(MATLAB R2011a, The MathWorks Inc., Natick, MA)

and the central 58 9 58 pixels (2 cm2) were extracted and

separated into red, blue and green channels. Care was taken

to exclude any film area within 0.5 cm from a cut film

edge. A correction recommended by the manufacturers was

applied to the red channel data to smooth out possible

inconsistencies in the thickness of the active layer [27].

The pixel values were converted to optical density as

follows:

OD ¼ � logðpixel value=65535Þ ð2Þ

For each film piece, the mean optical density of the cor-

rected red channel data was plotted against the applied dose

to establish the calibration curve. The mean of the three

calibration curves was used for film analysis. For all EBT2

dosimetry measurements, the above scanning protocol was

used and unless stated otherwise, the central 0.5 9 0.5 cm2

(14 9 14 pixels) was extracted for film analysis.

EBT2 Gafchromic film is designed for use in the energy

range 50 kiloelectron volt (keV) into MV and with sensi-

tivity down to 1 cGy. Although the treatment, CBCT and

CT beam energies were within the suitable range, the

expected dose from CBCT and CT was B1 cGy and

therefore the use of EBT2 was limited to MV photon

irradiations.

XR-QA2 film calibration

XR-QA2 Gafchromic film is radiochromic film designed

for dosimetric use in the energy range 20–200 kVp and

within the recommended dose range 0.1–20 cGy, making it

suitable for CBCT and CT applications.

XR-QA2 Gafchromic film was calibrated for mea-

suring surface dose from cone-beam CT and CT image

acquisition. Because of the strong energy dependence of

the film in the kV energy range, the beam qualities of

the X-ray sources were determined prior to calibration.

The X-ray beam qualities of an On-Board Imager�

(OBI) and cone-beam CT capable Varian Linear

Accelerator were measured for the default CBCT pro-

tocols (100, 110 and 125 kVp), which are used clini-

cally in the department. To assess the greatest range of

half value layers (HVLs) the full bowtie filter was fit-

ted. A Piranha multimeter (RTI, Sweden) was used to

evaluate the effects of the bowtie filter by measuring

HVLs on the central axis and at longitudinal displace-

ments up to 10 cm. The HVLs ranged 4.9–7.6 mm Al

(mean HVL = 6.3 mm Al) over all assessed positions.

The mean beam quality on the central axis from the 3

protocols was 5.5 mm Al. The HVL increased off axis

due to beam hardening.

According to manufacturer’s specifications, the Siemens

Somatom Sensation Open helical scanner (Siemens Medi-

cal Solutions, Erlangen, Germany) HVL was 9.1 mm Al

for a 120 kVp imaging protocol.

The XR-QA2 Gafchromic film was calibrated on an

XStrahl 300 X-ray Therapy Unit (XStrahl Ltd., Surrey,

UK) using a 150 kVp beam with beam quality

HVL = 6.0 mm Al, similar to those expected during

CBCT acquisition. A 180 kVp beam with beam quality

HVL = 9.5 mm Al was used to calibrate the film for

measurements on CT.

Gafchromic XR-QA2 film was cut into 4 9 4 cm2 pie-

ces and marked with reference to the initial film orienta-

tion. The film was placed on the surface of a

30 9 30 9 13 cm3 Solid Water� phantom and a graphite

ionisation chamber was placed at a depth of 2 cm in the

solid water to record the dose at depth. The film was cal-

ibrated under the beam reference conditions (30 cm SSD,

8 cm circle applicator for 150 kVp and 50 cm SSD,

10 9 10 cm2 applicator for 180 kVp). 10 pieces of film

were irradiated with increasing dose over the range

0–20 cGy. This was repeated three times for each energy.

The delivered dose, D, to the film pieces was calculated

from the recorded ionisation chamber dose, Dion, with

corrections made for measuring at depth, percentage depth

dose (PDD), and in a Solid Water� phantom, Cp, and is

given by:

D ¼ Dion � Cp

PDDð3Þ

The PDD at 2 cm for the given beams was PDD150 kVp =

76.1 % and PDD180 kVp = 84.7 %. The difference between

ion chamber measurements made in water and Solid

Water� was 4.1 % (Cp = 1.041) and 3.7 % (Cp = 1.037)

for 150 and 180 kVp, respectively.

The same film digitisation and analysis process was

followed as with EBT2 except the films were digitised in

reflection mode with software selection photo.


123

Dosimeter comparison

The dose response of Gafchromic film was investigated to

determine the suitability of using this dosimeter in primary

kV and peripheral region of MV beams. Dose in the

peripheral regions of the MV treatment field is complex;

with dose contributions from scatter within the patient

(internal scatter), leakage from the head of the treatment

machine (head leakage) and collimator scatter. Internal

scatter is the major contributor of dose in the near

periphery of the treatment field, having spectra peaks near

500 keV, while head leakage dominates further a field [28].

The out-of-field dose is largely dependent on beam energy,

field size and distance from the field edge [28–30]. The

photon contribution decreases exponentially with distance

from the field and the neutron contribution, which is non-

negligible for beam energies [15 MV, is independent of

distance from the field but decreases with depth in tissue

[31]. All these factors influence the choice of appropriate

dosimeter to quantify peripheral dose.

MV beam

EBT2 Gafchromic film measurements were compared to

those made with an IBA CC13 Ionisation Chamber (SN

6690) which, due to low angular dependence and weak

energy dependence across a broad spectrum (100 kVp to 50

MV), is a suitable reference dosimeter for out of field

measurements [32]. The dosimeter comparison was per-

formed using a Varian iX 6 MV beam. The response to

higher energies was assumed to be similar since the energy

dependence of EBT2 is small in the MV energy range [33].

The response of the ionisation chamber and UNIDOS

electrometer system (PTW, Freiburg, Germany) was

established for the delivery of a range of doses

(1.9–186.2 cGy). A Scanditronix-Wellhofer water phantom

system (Scanditronix-Wellhofer, Uppsala, Sweden) was set

up with the ionisation chamber positioned at a depth of

5 cm in a 10 9 10 cm2 field, at 95 cm SSD. The mean of

two readings were recorded for each dose delivery.

Peripheral dose measurements were made at increasing

distances from the edge of a 10 9 10 cm2 irradiated field

using an ionisation chamber with the effective point posi-

tioned on the surface of the water, 1 cm from the edge of the

field. Two peripheral dose measurements were made for the

dose delivery on the central axis of 101.4 cGy to dmax.

Measurements were repeated at 2, 3, 4, 5, 6, 8 and 10 cm

from the field edge and again at 3, 4, 5, 6, 8 and 10 cm for the

delivery on the central axis of 202.9 cGy to dmax.

3 9 3 cm2 pieces of EBT2 film were positioned on the

surface of a 30 9 30 9 20 cm3 stack of Solid Water�

(95 cm SSD), at distances 1, 2, 3, 4, 5, 6, 8 and 10 cm from

the edge of a 10 9 10 cm2 field. Individual sets of film

pieces were exposed to peripheral dose from dose deliv-

eries on the central axis to dmax of 101.6 and 203.3 cGy,

respectively. These measurements were repeated three

times and the film was digitised 24 h later. The uncertainty

in the ion chamber measurements was 1 % as specified by

the manufacturers.

kV beam

In order to accurately measure dose within CBCT and CT

fields, the suitability of XR-QA2 Gafchromic film for

measuring dose within kV beams was determined. All

measurements were performed using the XStrahl 300 X-ray

Therapy Unit.

3 9 3 cm2 pieces of XR-QA2 Gafchromic film were

fixed centrally using tape on a stack of solid water, at least

10 cm high to ensure sufficient backscatter. A NE2571

graphite cylindrical ionisation chamber was placed at a

depth of 2 cm on the central axis. Measurements were

made under reference conditions for deliveries of 1.1, 3.2,

5.2 and 10.3 cGy. The film was digitised 46 h after

irradiation.

Measurements

Treatment planning

A Rando Phantom (Alderson Research Laboratories, Long

Island City, New York), fitted with a wax scrotum (den-

sity = 0.9 g/cm3) which was moulded in the department

workshop, was positioned on the CT couch. Three surface

measurement points were identified and marked with tape;

one on the anterior scrotal surface, one on the posterior

scrotal surface and one on the abdomen, 5 cm superior to

the superior edge of the wax mould. These can be seen in

Fig. 1. In addition to identifying the measurement points,

the tape markings protected the Gafchromic film from wax

residue. Lead gonadal clam-like shielding is used at treat-

ment to protect the remaining testis, however, this results in

image artefacts if fitted at CT imaging. To accommodate

this, a replicate constructed from PVC, which is used

clinically, was fitted. Both the pseudo and lead clam

gonadal shielding were crafted in the department work-

shop. The phantom was scanned on a Siemens Somatom

Sensation Open helical scanner (Siemens Medical Solu-

tions, Erlangen, Germany) following departmental protocol

for pelvis CT scans (120 kV, 148 mA, 3 mm slice thick-

ness). The scan extended from the T7/T8 joint to mid

femur.

Two treatment plans consisting of anterior/posterior

parallel opposed beams were created using 18 MV pho-

tons in Pinnacle3 (Philips Medical Systems, Milpitas


123

CA). The PA plan consisted of a rectangular field 20 cm

long and 8 cm wide in the abdominal region to include

the PA lymph nodes with a prescribed dose of 20 Gy in

10 fractions. The kidneys were shielded by multileaf

collimators (MLCs). This treatment was prescribed to

100 % of the dose at the isocentre, which corresponds

to the zero slice in the data set. The posterior beam

(Gantry = 180�) was a mirror of the anterior beam

(Gantry = 0�). The anterior beam digitally reconstructed

radiograph (DRR) in Fig. 2 shows the treatment field and

kidney shielding. The second treatment plan, commonly

referred to as a dogleg (DL), was an extension of the PA

to include the ipsilateral pelvic and common iliac lymph

nodes while avoiding the remaining testis, with a pre-

scribed dose of 30 Gy in 18 fractions. The prescription

isocentre was positioned more inferiorly than in the PA

treatment plan and MLCs were used to shield the kidneys

and the remaining testis (Fig. 3). Again, the posterior

beam was a mirror of the anterior treatment beam. The

isodose distributions from the respective plans are shown

in Figs. 2 and 3.

CT

The Rando anthropomorphic phantom was positioned on

the CT scanner bed and aligned with the lasers.

1.5 9 3 cm2 XR-QA2 Gafchromic film strips were secured

with tape at the anterior and posterior scrotal positions and

a 3 9 3 cm2 piece of film was placed at the abdominal

position, ensuring the tape extended no further than 0.5 cm

over the film edge. These film piece dimensions were used

for all measurements unless stated otherwise. The scan was

carried out as per departmental protocol (see ‘‘Treatment

planning’’). The measurements were repeated three times

with and three times without the clam shielding fitted. An

unexposed film piece was used for each scan. In keeping

with calibration, the film was digitised 46 h post irradiation

and analysed as previously described.

CBCT

Rando was positioned on the treatment couch with the XR-

QA2 film and lead shielding in place and aligned with the

.tnemecalpmlifcimorhcfaG(b).dettifgnidleihsdaellluF(a)

Fig. 1 a Rando set up on the

treatment couch with XR-QA2

film positioned at the

measurement points. The

treatment gantry angle is not

shown. b Half the clam

shielding is removed showing

the placement of the film

dosimeter. (The posterior scrotal

measurement point is not seen.)

(a) A digitally reconstructed radiograph of the (b) A coronal view of the isodose distribution at the.tniopecnereferTC.maebtnemtaertroiretna

Fig. 2 The paraaortic treatment

plan. a The centre of the beam is

aligned with the isocentre (red

wireframe sphere). b The pink

and red isodose lines represent

the 95 and 100 % dose

coverage, respectively


123

lasers to the CT reference point. The half bow tie was fitted

and a pelvis CBCT image, using the standard imaging

protocol (125 kVp, 706 mA s, 360�), was taken for pre-

treatment image matching. The CBCT field was 16 cm

wide, inclusive of the abdominal measurement point;

however, the scrotum lay out of the imaging field. Three

CBCT images were performed with and three without the

shielding fitted.

Treatment

EBT2 Gafchromic film was cut to size and secured in place

using tape. Rando was set up on the treatment couch, with

the gonadal shielding fitted, using localisation lasers to

match the position at CT. One fraction of the PA treatment

was delivered. A total of three measurements with shield-

ing and three without shielding were performed. Mea-

surements were carried out in the same manner for the DL

treatment plan delivery.

Results

A. Dosimeter comparison

MV beam

The mean (95 % CI) of the measurements was normalised

to the ionisation chamber water surface dose measurements

at the respective distances. These values are compared in

Fig. 4.

Overall, EBT2 tended to overestimate the dose. In one

instance, the EBT2 measurement was 40 % greater than the

ionisation chamber. This translates to an overestimation

of 0.69 cGy. The maximum variation from the CC13

ionisation chamber measurements across the range of dose

deliveries was 1.3 cGy.

kV beam

The mean (95 % CI) of the measurements was calculated

and the numerical values were normalised to the applied

dose. The ratios are represented graphically in Fig. 5.

XR-QA2 measures within 5 % of the ionisation cham-

ber measurements for doses above 3 cGy but overestimates

the dose by approximately 25 % for a dose delivery of

1.1 cGy. This dose is approaching the limit of the recom-

mended dose range 0.1–20 cGy. XR-QA2 film has excel-

lent precision across the delivered dose range. Overall, XR-

QA2 is in good agreement with the ionisation chamber for

doses above 3 cGy.

(a) A digitally reconstructed radiograph of the (b) A coronal view of the isodose distribution.tniopecnereferTCehtta.maebtnemtaertroiretna

Fig. 3 The Dogleg treatment

plan. a The MLCs shielding the

kidneys and testis can be seen in

the DRR. b The turquoise, red

and pink isodose lines represent

the 102, 100 and 95 % dose

coverage, respectively

Fig. 4 EBT2 Gafchromic film measurements made in the periphery

of a 10 9 10 cm2 6 MV beam, for a delivery of 101 and 203 cGy to

dmax on the central axis, were normalised to those measured with a

CC13 ionisation chamber


123

B. Measurements

CT and CBCT imaging

The mean (95 % CI) of the measurements recorded while

acquiring images is given in Table 1. For CBCT imaging

using XR-QA2, a dose reduction to the testis of more than

60 % is seen when the lead shielding is fitted. With the

pseudo shielding fitted, the dose to the testis from CT

acquisition is reduced by approximately 36 %.

Treatment delivery

The mean (95 % CI) of the doses measured for DL and PA

treatment deliveries, averaged over the duration of treat-

ment, are given in Table 2. For a total prescription of

20.0 Gy to the PA region, the mean measured dose to the

contralateral testis was 0.30 ± 0.08 and 0.31 ± 0.04 Gy

with and without lead shielding, respectively. For the PA

region, including the pelvic and ipsilateral common iliac

lymph nodes, and with a prescribed dose of 30.0 Gy, the

mean testicular dose was 0.61 ± 0.11 and 0.68 ± 0.39 Gy

with and without shielding, respectively. In general, less

dose was recorded for the PA treatment. This was expected

as the DL fields were closer to the measurement points. At

the anterior scrotum, a dose reduction of approximately 1/4

was seen with the gonadal shielding fitted. Contrary to this,

marginal change was recorded at the posterior scrotal

position when the shielding was fitted.

Discussion

The use of clinically available XR-QA2 and EBT2 Gaf-

chromic film was assessed for measuring dose in imaging

fields and the periphery of treatment fields, respectively.

XR-QA2 was found to agree within 5 % for applied doses

greater than 3 cGy. For an applied dose of 1.1 cGy, the

measured dose was overestimated by approximately 25 %.

This dose is approaching the minimal usable range of the

film.

For distances up to 5 cm from the edge of the field,

EBT2 overestimated the peripheral dose by as much as

25 % relative to the ionisation chamber. At a distance of

10 cm, the dose was overestimated by approximately

40 %. This equates to a dose overestimation of 0.69 cGy,

which in absolute terms is relatively small.

There are limitations in the current approach. The ion

chamber produces an over response in signal at the surface

due to the large chamber volume [34] and although the

dose at the surface was determined relative to the signal

response at depth, perturbation errors are introduced by the

placement of the chamber proud of the water surface. On

the other hand, surface dose measurements comparing

EBT2 with an Attix parallel plate chamber [35] and Monte

Carlo simulations [36] are in good agreement. A more

detailed analysis is beyond the scope of the paper but

further work is required to fully understand the use of ion

chambers and EBT2 for out of field surface dose

measurements.

Fig. 5 XR-QA2 Gafchromic film surface dose measurements within

150 and 180 kVp orthovoltage beams. The measured doses were

normalised to the applied doses, which were measured using a

NE2571 graphite cylindrical ionisation chamber

Table 1 Dose measured using XR-QA2 film for a single scan of each

imaging technique

Imaging dose (cGy)

Technique Shielding Regions of interest

Abdomen ANT POST

CBCT Y 3.25 ± 0.03 0.19 ± 0.01 0.02 ± 0.01

N* 3.26 ± 0.02 0.49 ± 0.01 0.46 ± \ 0.01

CT Y 2.63 ± 0.12 1.70 ± 0.04 1.26 ± 0.05

N 2.56 ± 0.18 2.28 ± 0.17 2.35 ± 0.05

Measurements were made with and without gonadal shielding present

* The mean of two measurement sets. The third set was discarded due

to visible anomalies

Table 2 Dose recorded using EBT2 film, with and without lead

shielding fitted, for paraaortic and dogleg treatment techniques

Seminoma treatment dose (Gy)

Technique Shielding Regions of interest

Abdomen ANT POST

Dogleg Y 1.72 ± 0.06 0.63 ± 0.02 0.59 ± 0.10

N 1.77 ± 0.02 0.83 ± 0.17 0.53 ± 0.28

PA Y 0.70 ± 0.07 0.32 ± 0.04 0.27 ± 0.06

N 0.68 ± 0.11 0.43 ± 0.02 0.19 ± 0.02


123

Overall, Gafchromic film was found to be suitable for

measuring imaging dose and dose in the periphery of

treatment fields, but is subject to the above findings.

For a total prescription of 20.0 Gy to the PA region, the

mean measured dose to the contralateral testis was

0.30 ± 0.08 and 0.31 ± 0.04 Gy with and without lead

shielding, respectively. The DL field treatment, with a

prescribed dose of 30.0 Gy, resulted in a mean testicular

dose of 0.61 ± 0.11 and 0.68 ± 0.39 Gy with and without

shielding, respectively. For the Seminoma treatment, dose

reductions up to 10 % were observed with shielding fitted.

This increased to approximately 25 % when considering

the anterior scrotal dose alone.

The testicular doses measured were approximately two

times the doses previously reported. Bieri et al. [5] mea-

sured mean doses, using TLDs, of 0.09 Gy (±0.05 SD) and

0.26 Gy (±0.12 SD) with and without gonadal shielding,

respectively, for a prescribed dose of 25.2 Gy to the PA

region. For the same dose prescribed, only with DL treat-

ment fields, mean doses of 0.55 Gy (±0.20 SD) and

0.21 Gy (±0.07 SD) were measured, without and with

shielding, respectively. Similarly, Jacobsen et al. [37]

reported a mean dose of 0.32 Gy (±0.08 SD) to the

shielded testis for a delivered dose of 30.0 Gy with DL

fields. The contralateral testicle was shielded using a 5 mm

lead belt and a 5 cm thick lead block. The disparity

between the doses in this work and those reported may be

due to differences in shielding techniques used and varia-

tions in the type and placement of dosimeters.

Kinsella et al. [38] reported a temporary reduction in

sperm count for testicular doses of 0.2–0.7 Gy, returning to

normal within 12–24 months, while Centola et al. [39]

reported doses above 1.2 Gy indicate permanent testicular

damage. Following this, the doses recorded in this work are

within a range in which no permanent testicular damage

should occur.

A mean testicular dose of 2.32 cGy was measured per

CT scan without the use of gonadal shielding. This was

0.48 cGy per CBCT image. Dose reductions to the

remaining testis of up to 36 and 78 % were recorded with

gonadal shielding fitted at CT and CBCT acquisition,

respectively.

The reported role of diagnostic imaging in cancer

induction is conflicted in the literature. A population-based

study observed the incidence of second malignancies in

2,569 men who were either monitored via active surveil-

lance or treated with chemotherapy for testicular cancer

and received 10 CT scans in 5 years after diagnosis. With a

median follow-up was 11.2 years, Van Walraven et al. [16]

concluded that the excess risk of second cancers among

testicular cancer survivors is not associated with diagnostic

imaging. In contrast, a model based study report a lifetime

cancer risk ranging from 1 in 39 to 1 in 85 for a similar

surveillance protocol [40]. Nevertheless, the majority of

diagnostic imaging in this work was CBCT imaging, which

based on this work delivered doses approximately 1/5 of

those reported at CT acquisition.

In summary, the concomitant dose to the remaining

testis while undergoing radiotherapy for seminoma cancer

is small. Still, gonadal shielding should be fitted to ensure

the dose to the testis is as low as reasonably achievable

(ALARA) [41] regardless of the treatment fields.

Conclusions

Mean testicular doses of 0.30 ± 0.08 and 0.31 ± 0.04 Gy

with and without lead shielding, respectively, were mea-

sured with film for a prescription of 20 Gy to the PA

region. Seminoma radiotherapy via DL fields resulted in

respective mean doses of 0.61 ± 0.11 and 0.68 ± 0.39 Gy,

with and without shielding. Additional doses of up to

0.49 ± 0.01 and 2.35 ± 0.05 cGy were measured per

CBCT and CT image, respectively. The dose to the

remaining testis was reduced when shielding was employed

at treatment (10 %), planning CT imaging (36 %) and pre-

treatment CBCT imaging (78 %).

The dose to the testis should be limited to minimise the

risk of radiation related side effects. This can be achieved

by using appropriate gonadal shielding, irrespective of the

treatment fields employed.

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Assessment of concomitant testicular dose with radiochromic film