as described in u . s . pat . nos . 6 , 868 , 289 and 7 , 016 , 725 each of which is incorporated herein by reference , and in u . s . patent application ser . no . 11 , 111 , 439 ( filed apr . 21 , 2005 ) and ser . no . 11 / 537 , 026 ( filed sep . 29 , 2006 ), each of which is incorporated herein by reference , intermediate frequency ( 100 - 300 khz ) alternating electric fields , termed ttfields , damage as well as inhibit the growth of numerous types of cancer cells in vitro and in vivo . the efficacy of the treatment is enhanced by sequentially applying fields of varying directions and by the use of special insulated electrodes . ttfields act by two mechanisms of action : first , they disrupt the normal polymerization - depolymerization process of the spindle microtubules during mitosis . secondly , they cause a physical disruption of cells towards the end of cytokinesis by producing a unidirectional force on all charge , polar and polarizable intracellular constituents , pushing them towards the narrow neck between the two daughter cells . see kirson , e . d ., et al ., disruption of cancer cell replication by alternating electric fields , cancer res ., 2004 . 64 ( 9 ): p . 3288 - 95 , which is incorporated herein by reference . the therapeutic efficacy of ttfields was found to be high and the therapeutic index extremely high ( no side effects ), however , treatment duration was relatively long and the required field intensities were relatively high . in order to improve the treatment efficacy , this invention is designed to enhance the treatment efficacy of ttfields by combining them with photodynamic treatment , pdt . pdt , or photodynamic therapy involves the use of light - activated dyes ( photosensitizers ) that preferably localize in target cells ( e . g . in tumors ) but not in normal , healthy cells . when illuminated by a source of appropriate light , the photosensitizers utilize energy from the illumination light to produce cytotoxic agents such as oxygen species which kill cancerous or diseased cells . in some preferred embodiments , leds are used to provide the illumination , and the leds are activated by the ttfields ( instead of using lead wires connected to a power supply ). a single led or multiple leds wired in parallel may be used to provide the illumination . fig1 depicts a schematic layout of a system that uses multiple leds 30 wired in parallel that are built into an assembly 26 that is implanted in the treated body 21 near a internal tumor 25 . as described in u . s . pat . nos . 6 , 868 , 289 & amp ; 7 , 089 , 054 , ttf treatment is preferably achieved using special insulated electrodes 23 placed on the body 21 surface . according to one exemplary embodiment , the apparatus for applying the electric field is an electronic apparatus that generates the desired electric signals in the shape of waveforms or trains of pulses . the electronic apparatus includes a generator that generates an alternating voltage waveform at frequencies in the range from about 50 khz to about 500 khz . the generator is operatively connected to conductive leads 24 which are connected at their other ends to insulated conductors / electrodes 23 ( also referred to as isolects ) that are activated by the generated waveforms . the insulated electrodes 23 consist of a conductor in contact with a dielectric ( insulating layer ) that is in contact with the conductive tissue , thus forming a capacitor . because the electrodes 23 act like capacitors , the ac electric fields are capacitively coupled into the target region . the insulation on the electrodes 23 preferably has an extremely high dielectric constant such that in the frequency range used , preferably 100 khz to 500 khz , the impedance of the insulation on the face of the electrodes 23 is significantly smaller than that of the tissues such that most of the potential drop is on the tissues . the preferred field intensities for ttf treatment are in the range of 1 - 10 v / cm . thus , if the leads 28 , 28 ′ and the corresponding exposed contact points 29 , 29 ′ of the led assembly 26 are positioned at a proper orientation relative to the electric field direction , and the distance d between them is such that the potential difference is about 2 - 5v ( as indicated by the equipotential lines 11 ), the leds 30 will light up when the ac field is applied . because the leds 30 light up when the ac field is applied , the illumination is provided simultaneously with treatment by the ttfields . thus , when a proper sensitizing agent is present in the tumor , one obtains the combined ttf plus pdt therapeutic effects simultaneously . the inset of fig1 depicts the details of the led assembly implanted in the tumor 25 . in this case the light beams have conical shape 31 , and are oriented to cover most of the tumor area . the number and positions of the individual leds 30 can be adjusted for the application at hand to cover the whole tumor area . fig2 is a schematic representation of experiments in which a single led 5 was implanted in a rabbit 13 and ttfields were applied to the rabbit by means of external insulated electrodes 23 . when the field was not applied , the led 5 remained off . when the field was applied , the implanted led 5 lit up , and a spot of illumination was visible through the rabbit &# 39 ; s intact skin . typical leds generate significant light output at current of about 2 - 10 ma , with a voltage drop across the led in the range of about 2 - 5 v . that means that its forward resistance is about 1 kω . ( the reverse resistance is obviously much higher .) if the contact area between each of the metal contacts , which are connected to the two led leads , is about 1 mm 2 or more , the contact resistance will only be a few ohms . typical tissue ( e . g ., muscle ) has a specific resistance of 100 ω - cm . thus , if one uses fields of 1 v / cm or more , when the trajectory of the distance d between the contact points along the lines if the field is in the order of 2 cm or more , the potential drop between the contact points will be 2 v or more , which is sufficient to light up the led . in fig1 , 3 , and 4 , similar numbering is used to represent corresponding items . fig3 depicts an equivalent circuit for a single led 5 with leads 7 terminating in contact points 1 . note that resistances 2 , 6 indicated in this figure are not actual resistors — rather , they are the resistances of an equivalent circuit , where resistance 6 represents the forward resistance of the led , and resistance 2 represents the resistance of the tissue in which the led is implanted , which is in parallel with the led . since the led &# 39 ; s forward resistance 6 is significantly larger that the resistance 2 of the tissue ( on the order of 1000ω for the led vs . 100ω for the tissue ) and is also significantly larger that the resistance of the contacts , the forward resistance 6 of the led does not affect the potential drop to a significant level , so the led current will be the required 2 ma when the led sits in a 1 v / cm field with its contacts spaced apart by a distance of 2 cm . distances for the contact spacing between 0 . 5 and 5 cm are preferred . for fat tissue or brain , where the specific resistance may be 500 ω - cm , the field intensity or distance between contacts should be increased to compensate . fig4 illustrates the impact of the orientation of the led with respect to the field . the led 5 must be oriented so that the potential difference between the two contact points 1 , 1 ′ is adequate to get the led 5 to turn on . in a homogeneous field the parallel orientation ( orientation a in fig5 ) is optimal , and this is the orientation that was used in the rabbit experiment depicted in fig2 . if the led is oriented at a different angle with respect to the field , the resulting potential difference is a function of the cosine of the angle between the line connecting the contact points and the field direction ( angle a in fig4 ). note that the distance between the contacts may be set to a particular value in anticipation of the field intensities that will be generated in the tissue . when the led axis is oriented parallel to the field generating electrodes ( orientation b in fig4 ), the orientation of the contact points is normal to the lines of force 10 , i . e . parallel to the equipotential lines 11 , and no voltage is induced across the led , so it will not illuminate . this characteristic , taken together with the led turn - on threshold voltage can be used to turn the illumination on or off as required . for example , when only ttfields treatment is required with no pdt , the field orientation or intensity can be adjusted such that the potential difference between the led contacts will remain below the led turn - on threshold . optionally , a resistor or an active circuit can be added to adjust the potential drop to an optimal level . optionally , a suitable current limiting and voltage limiting circuit may be used to prevent the led from burning out , the design of which will be apparent to persons skilled in the relevant arts . for example , a resistor may be added in series with the led , with a zener diode wired in parallel with the series combination of the resistor and the led . two zener diodes of opposite polarity may be used to take care of both forward and reverse voltages . practically any standard led can be used , but the spectral emission of the led should preferably be matched to the optimal absorption or activation spectrum of the molecule sensitized by the light . in cases where the absorption spectra can not be matched by an led , white light emitting leds can be used . examples of suitable leds include the hlmp - cw24 - sv0 from agilant technologies , the nspw300bs from nichia , and the tlhb440 , tlhg440 , tlho440 , tlhp440 , tlhr440 , tlhy440 series of leds from vishay . an advantage of this combination is the dual therapeutic effect and the fact that both effects can be obtained in internal organs without the need to use wire leads that penetrate the body surface ( skin or other types of lining ). in alternative embodiments the leds may be replaced by other light sources . these may include : low voltage incandescent lamps , fluorescent light source , halogen light source , etc . also voltage sensitive dyes , as part of the implant , or as chromophores added to the photosensitizers or as part of molecules injected to the patient together with the photosensitizers so as to bind to similar cells . the voltage sensitive dyes , bound to molecules or other entities that bind to the relevant cells for long periods of time , can also be used systemically or locally . since ttfields show no systemic toxicities , the fields can be used in conjunction with other anti - cancer treatments with a synergistic effect due to the different mechanisms of action by which the various treatments act . examples of other anti - cancer treatments that can be combined with ttfields include , but are not limited to , five general categories : the first categories is surgery , including but not limited to open surgery , laparoscopic surgery , minimal resection surgery , debulking surgery , complete resection surgery , etc . the second category is local ablation techniques including but not limited to radio - surgery , rf ablation , and focused ultrasound . the third category is ionizing radiation using various dosing and focusing regimen including but not limited to whole organ radiation ( e . g . brain ), regional radiation ( e . g . y shaped ), focal radiation , single dose radiation , fractionated dose radiation , and hyper - fractionated dose radiation . the fourth category is chemotherapy , including but not limited to { a } alkylating agents that act mainly by forming covalent bonds between dna bases , including but not limited to nitrogen mustards ( e . g ., cyclophosphamide ), aziridines and epoxides ( e . g ., thiopeta ), alkyl sulfonates ( e . g . busulfan ), nitrosureas ( e . g ., bcnu and ccnu ), hydrazine and triazine derivatives ( e . g ., procarbazine and temozolomide ); { b } cisplatin and its analogs that act by forming dna adducts which lead to intra - strand and inter - strand linking leading to the formation of dna filaments , including but not limited to carboplatin , cisplatin , and oxaliplatin ; { c } antimetabolites including but not limited to folate metabolism inhibitors ( e . g ., methotrexate , trimetrexate , tomudex ), 5 - fluoropyrimidines ( e . g ., 5 - fu ), oral fluoropyramidines ( e . g ., tegafur , uracil , capecitabine ), necleoside analogs ( e . g ., cytarabine ), gemcitabine , and 6 - thiopurines ( e . g ., 6 - mp and 6 - tg ); { d } topoisomerase interactive agents that affect the topologic states of dna by interfering or modulating dna cleavage , strand passage and religation , including but not limited to epipodophyllotoxins ( e . g ., etoposide and teniposide ), camptothecin analogs , anthracyclines ( e . g ., doxorubicin , daunorubicin , epirubicin , idarubicin ), mitoxantrone and losoxantrone , and dactinomycin ; { e } antimicrotubule agents , which interfere with the proper polymerization / depolymerization of microtubules , including but not limited to vinca alkaloids ( e . g ., vincristine , vinorelbine and vinblastine ), taxanes ( e . g ., paclitaxel , docetaxel ), and estramustine phosphate ; and { f } numerous miscellaneous agents exist which cannot be classified into any of the above groups , including but not limited to suramin , bleomycin , l - asparaginase , and amifostine . the fifth category is biological therapies , including but not limited to { a } inteferons ; { b } interleukin - 2 ; { c } hormonal therapies including but not limited to tamoxifen , toremifene , raloxifene , medroxyprogesterone and megestrol , aromatase inhibitors , gnrh analogues , antiandrogens , diethylstilbesterol and estradiol , and octreotide ; { d } differentiation agents that catalyze the differentiation of cancerous cells into their mature ( differentiated ) forms and then to programmed cell death , including but not limited to retinoids ( e . g ., all - trans - retinoic acid ), arsenic trioxide , histone deacetylase inhibitors , vitamin d , and cytokines ; { e } therapeutic monoclonal antibodies ; and { f } antiangiogenesis agents ( e . g ., vegf inhibitors ). since ttfields show no systemic toxicities , it appears that ttfields can be applied to patients before , during and / or after any other anti - cancer treatment to attack the cancer using two different modalities . in addition , it may be possible to lower the toxicity of current anti - cancer treatments by using lower doses of these agents together with ttfields , and still maintain the existing efficacy profile . the dosages , strengths , and timing of the various treatments may be changed to optimize the results that are desired . note that the most beneficial combination regimen may differ considerably depending on the type of cancer treated , the exact stage of the disease and the type of anticancer treatment used , it should be relatively simple to determine the best combination regimen experimentally . ttfields can also be applied together with more than one of the other anti - cancer approaches ( e . g ., with pdt plus another therapy ). note that above - described embodiments are merely preferred implementations of the invention , and numerous alternative embodiments and variations will be apparent to persons skilled in the relevant arts , and are included within the scope of the invention .
a light generating circuit is implanted in a subject &# 39 ; s body and aimed at a target region such as a tumor . a photosensitizer is introduced into the target region , and an ac electric field is induced in the region . the field causes the light generating circuit to generate light , which activates the photosensitizer ; and at certain field strengths and frequencies , the field itself has a beneficial effect . the beneficial effects of the field and the activated photosensitizer are thereby obtained simultaneously .