customized patient- related measurements - aapm...

Customized patientCustomized patient--related measurements: related measurements: no escape from nonno escape from non--standard standard

special proceduresspecial procedures

Charles Rhodes III, M.S.B.SCharles Rhodes III, M.S.B.SYiranYiran ZhengZheng Ph.D.Ph.D.David David MansurMansur M.D.M.D.

Min Min YaoYao M.D.M.D.ValdirValdir C. C. ColussiColussi, Ph.D., Ph.D.

University Hospitals of Cleveland University Hospitals of Cleveland SeidmanSeidman Cancer CenterCancer Center

OutlineOutline

►► Why focus on patient measurement?Why focus on patient measurement?►► NonNon--Standard Total Skin Electron casesStandard Total Skin Electron cases►► TSEITSEI

PrescriptionsPrescriptions DosimetryDosimetry/Calibration/Calibration Treatment DeliveryTreatment Delivery

►► Case 1Case 1 Film Film DosimetryDosimetry TLDTLD

►► Case 2 Case 2 Phantom Chamber MeasurementsPhantom Chamber Measurements TLDTLD

►► ConclusionConclusion

Why focus on Patient Measurements?Why focus on Patient Measurements?

►► With all the With all the technological advances technological advances in our field, why focus in our field, why focus on something so on something so basic?basic?

►► ““I learned that during I learned that during graduate school, I graduate school, I dondon’’t need to review t need to review it.it.””

Why focus on Patient Measurements?Why focus on Patient Measurements?

►►““Success is doing ordinary things Success is doing ordinary things extraordinarily wellextraordinarily well”” ––Jim Jim RohnRohn--

►►One of our job as physicists is to ensure One of our job as physicists is to ensure patients receive safe/prescribed levels of patients receive safe/prescribed levels of radiationradiation

►►We may not know our stuff as well as we We may not know our stuff as well as we thinkthink

Why Focus on Patient MeasurementsWhy Focus on Patient Measurements

►► A clear decrease can be seen between parts 2 and A clear decrease can be seen between parts 2 and 3 3 All Medical Physics specialtiesAll Medical Physics specialties-- Does not include conditional passDoes not include conditional pass

Percent of Physicists Passing ABR

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1 2 3

Exam Part

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2007 2008 2009 2010 2011 2012

NonNon--Standard TSEI casesStandard TSEI cases

►► In the course of 1 week, two patients were In the course of 1 week, two patients were prescribed TSEI treatmentprescribed TSEI treatment

►► Both cases had special considerationsBoth cases had special considerations Patient 1: Previous full skull electron Patient 1: Previous full skull electron

treatment. treatment. Disease near genital/Disease near genital/glutealgluteal regionregion

Patient 2: PacemakerPatient 2: Pacemaker►► How does a physicist ensure the patient How does a physicist ensure the patient

will receive appropriate dose?will receive appropriate dose?

Total Skin Electron IrradiationTotal Skin Electron Irradiation

►►One of the more common TSEI prescriptions One of the more common TSEI prescriptions is 36Gy in 2Gy fractions delivered to the is 36Gy in 2Gy fractions delivered to the entire skin surface at a depth of entire skin surface at a depth of ddmaxmax

At At SeidmanSeidman Cancer Center 3MeV and 6MeVCancer Center 3MeV and 6MeV

►►How do we deliver dose to the entire skin How do we deliver dose to the entire skin surface?surface?

TSEI DeliveryTSEI Delivery-- Stanford TechniqueStanford Technique

►► The six fields are The six fields are treated over the treated over the course of 2 days.course of 2 days.

►► All six fields equal 1 All six fields equal 1 fractionfractionDAY 1

Day 2

TSEI DeliveryTSEI Delivery-- Stanford TechniqueStanford Technique

►► Each field will have a Each field will have a top and bottom portiontop and bottom portion This increase field This increase field

uniformity and reduces uniformity and reduces XX--ray contaminationray contamination

SeidmanSeidman SetupSetup

►► The patient is set to an The patient is set to an SSD of 491cm using SSD of 491cm using the front portion of the the front portion of the apparatus displayed at apparatus displayed at the rightthe right

►► Patient positioning Patient positioning device developed by device developed by NogahNogah Engineering in Engineering in Cleveland OhioCleveland Ohio

Determining Dose Output for TSEIDetermining Dose Output for TSEI

►► Output is directly Output is directly measured at treatment measured at treatment distancedistance

►► A parallel plate A parallel plate chamber chamber can becan be used used if calibrated or cross if calibrated or cross calibratedcalibrated This is performed by This is performed by

following the TGfollowing the TG--51 51 protocolprotocol

Patient 1Patient 1-- Special Concerns:Special Concerns:Previous Skull TreatmentPrevious Skull Treatment

►► A A cerobandceroband block was poured block was poured large enough to cover the large enough to cover the patients head and suspended patients head and suspended from the treatment devicefrom the treatment device

►► Films were taken with the block in Films were taken with the block in field and out of field to determine field and out of field to determine effectivenesseffectiveness

►► Beam was delivered using the Beam was delivered using the lower treatment beam angle lower treatment beam angle Angled upAngled up

Film ResultsFilm ResultsDistance From Block vs Relative Dose

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-10.00 -5.00 0.00 5.00 10.00 15.00

Distance from Block (+ is toward head)

Rel

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ose

6 MeV 3 MeV

►► The The cerrobandcerroband block reduces dose by approx 90% for a block reduces dose by approx 90% for a single beam and 96% for a simulated treatment.single beam and 96% for a simulated treatment.

►► Because of the beam angle, a gradient of approx 5cm can Because of the beam angle, a gradient of approx 5cm can be seen below the physical edge of the blockbe seen below the physical edge of the block

►► The block must be placed lower than expected to ensure The block must be placed lower than expected to ensure proper shielding.proper shielding.

Edge of physical block

Patient 1 Special Consideration:Patient 1 Special Consideration:Disease in the Disease in the glutealgluteal/genital region/genital region

►►This patient had patches of mycosis This patient had patches of mycosis fungoidesfungoides in the in the glutealgluteal/genital region/genital region

►►One of the drawbacks of TSEI is that One of the drawbacks of TSEI is that portions of the skin surface may be missedportions of the skin surface may be missed Soles of feet, Soles of feet, glutealgluteal cleft, perineum, top of cleft, perineum, top of

scalpscalp

►►The physician wished to measure dose to The physician wished to measure dose to this region to better treat the patientthis region to better treat the patient

SoSo……..How can we measure dose in How can we measure dose in

such a unique area?such a unique area?

ThermoluminescentThermoluminescent Dosimeters Dosimeters (TLD)(TLD)

►► The TLD is exposed to ionizing The TLD is exposed to ionizing radiation exciting an electron in radiation exciting an electron in the valence band.the valence band.

►► As the electron deAs the electron de--excites, it excites, it may become trapped in an may become trapped in an electron trap while maintaining electron trap while maintaining its excited state.its excited state.

►► When the TLD is heated, the When the TLD is heated, the trapped electron is removed trapped electron is removed from the trap.from the trap.

►► As the electron deAs the electron de--excites, it excites, it releases its excess energy as releases its excess energy as light.light.

TLD ResultsTLD Results

►► The average reading for The average reading for each of the 11 sites was each of the 11 sites was less than 4cGy per fractionless than 4cGy per fraction 11 TLD sets arranged on a 11 TLD sets arranged on a

tape straptape strap

►► The physician used these The physician used these results design a separate results design a separate boost field to treat the boost field to treat the visible disease visible disease

Patient 2Patient 2-- PacemakerPacemaker

►► A lead shield was designed to protect the pacemakerA lead shield was designed to protect the pacemaker

Determining Shield ThicknessDetermining Shield Thickness

►►A solid water was set up at treatment A solid water was set up at treatment distancedistance

►►An ion chamber was used to determine dose An ion chamber was used to determine dose to to ddmaxmax

6MeV= 1.2cm 3MeV = 3mm6MeV= 1.2cm 3MeV = 3mm

►►Lead sheets (approx 2mm thick) were Lead sheets (approx 2mm thick) were attached to the front of the phantom to attached to the front of the phantom to simulate the shield on the patient.simulate the shield on the patient.

Ion chamber setupIon chamber setup


►► It was determined that It was determined that 2mm of lead shielding 2mm of lead shielding blocked approximately blocked approximately 90% of incident 90% of incident radiationradiation

►► Additional thickness Additional thickness did not afford much did not afford much further protectionfurther protection

Dose behind Lead Shielding (Normalized)

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Pb Thickness (mm)Tr

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6MeV3MeV


►►These values (at extended SSD) are in These values (at extended SSD) are in agreement with Khanagreement with Khan’’s rule of thumb s rule of thumb (100SSD)(100SSD)

Thickness (mm)= Thickness (mm)= ½½ Incident Electron Energy Incident Electron Energy (MV)+1(MV)+1

3MeV=2mm 3MeV=2mm vsvs 2.5mm2.5mm 6MeV=26MeV=2--3mm 3mm vsvs 4mm4mm

ResultsResults-- Shielding EffectivenessShielding Effectiveness

►► TLDsTLDs were used to measure dose the patients were used to measure dose the patients pacemakerpacemaker

►► Dose reduced by 97% Dose reduced by 97% ►► Pacemaker received dose of approximately 80% of Pacemaker received dose of approximately 80% of

tolerancetolerance

ConclusionConclusion

►►No matter how far technology comes, there No matter how far technology comes, there will always need to return to the basics of will always need to return to the basics of our fieldour field

►►These cases served as a reminder to our These cases served as a reminder to our group that sometimes, unique solutions are group that sometimes, unique solutions are needed to address unique clinical situations. needed to address unique clinical situations.

►►Sometimes, a simple solution is the most Sometimes, a simple solution is the most usefuluseful

Thank YouThank YouQuestions?Questions?

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